Surface-modified biochar in a bioretention system for Escherichia coli removal from stormwater

Magnetic composite photocatalyst NiFe₂O₄/ZnIn₂S₄/biochar for efficient removal of antibiotics in water under visible light: Performance, mechanism and pathway

The widespread presence of antibiotics in aquatic environments, resulting from excessive use and accumulation, has raised significant concerns. A NiFe₂O₄/ZnIn₂S₄/Biochar (NFO/ZIS/BC) magnetic nanocomposite was successfully synthesized, demonstrating significantly enhanced electron-hole separation properties. Comprehensive investigations were conducted to evaluate the impact of various parameters, including catalyst mass, pH, and the presence of co-existing ions on the composite's performance. The nanoparticles of NiFe₂O₄ (NFO) and ZnIn₂S₄ (ZIS) were found to improve the surface stability and sulfamethoxazole removal capabilities of porous biochar, while also demonstrating high total organic carbon removal efficiencies. •O₂⁻ and h⁺ were identified as the predominant reactive oxygen species (ROS) in NFO/ZIS/BC-4 during the degradation process. The degradation outcomes of sulfamethoxazole under natural sunlight and water conditions were consistent with laboratory findings, affirming the robust applicative potential of NFO/ZIS/BC. Density functional theory (DFT) calculations were performed to elucidate the photocatalytic mechanism and identify potential intermediate products. Additionally, the types of heterojunctions present in the system were characterized and discussed. After multiple iterations, NFO/ZIS/BC-4 maintained effective photodegradation capabilities through five cycles. This study presents an effective method for the treatment of antibiotics in aquatic environments, offering significant potential for environmental applications.

Urban wastewater disinfection by FeCl3-activated biochar/peroxymonosulfate system: Escherichia coli inactivation and microplastics interference

Biochar coupled with peroxymonosulfate (PMS) to produce sulfate radicals and its application to urban wastewater disinfection has been rarely investigated and no information is available about microplastics (MPs) interference on the disinfection process. In this study, FeCl3-activated biochar (Fe-BC) was coupled to PMS to evaluate the inactivation of Escherichia coli (E. coli) in real secondary treated urban wastewater. Surface morphology of Fe-BC sample, characterized by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS), showed a rough texture with uniform distribution of iron particles over the entire surface area. E. coli inactivation improved (∼3.8 log units, detection limit = 1 CFU/100 mL) as Fe-BC concentration was decreased (from 1.0 g/L to 0.5 g/L), at a constant PMS dose (300 mg/L). Besides, removal efficiency of E. coli was negatively affected by the presence of small (30-50 μm) polyethylene MPs (PE MPs) (200 mg/L), which could be attributed to the adsorption of MPs on Fe-BC surface, according to SEM images of post-treated Fe-BC. The low disinfection efficiency of Fe-BC/PMS system in presence MPs could be due to blocking of Fe-BC sites for PMS activation and/or radicals scavenging during treatment. These results allowed to unveil the mechanisms of MPs interference on E. coli inactivation by Fe-BC/PMS, as well as the potential of this process to make the effluent in compliance with the stringent limit for agricultural reuse.

The impact of recycling polyaluminium chloride and anionic polyacrylamide water treatment residuals on heavy metal adsorption in soils: implications for stormwater bioretention systems

Despite the high adsorption capacity of polyaluminum chloride and anionic polyacrylamide water treatment residuals (PAC-APAM WTRs) for Pb2+, Cd2+, Cu2+, and Zn2+, their influence on the adsorption behavior of heavy metals in traditional bioretention soil media remains unclear. This study investigated the impact of PAC-APAM WTRs at a 20% weight ratio on the adsorption removal of Pb2+, Cd2+, Cu2+, and Zn2+ in three types of soils. The results demonstrated improved heavy metal adsorption in the presence of PAC-APAM WTRs, with enhanced removal observed at higher pH levels and temperatures. The addition of PAC-APAM WTRs augmented the maximum adsorption capacity for Pb2+ (from 0.98 to 3.98%), Cd2+ (from 0.52 to 10.99%), Cu2+ (from 3.69 to 36.79%), and Zn2+ (from 2.63 to 13.46%). The Langmuir model better described the data in soils with and without PAC-APAM WTRs. The pseudo-second-order model more accurately described the adsorption process, revealing an irreversible chemical process, although qe demonstrated improvement with the addition of PAC-APAM WTRs. This study affirms the potential of PAC-APAM WTRs as an amendment for mitigating heavy metal pollution in stormwater bioretention systems. Further exploration of the engineering application of PAC-APAM WTRs, particularly in field conditions for the removal of dissolved heavy metals, is recommended.

Adsorption of acetochlor-contaminated water systems using novel P-doped biochar: Effects, application, and mechanism

Given the serious threat of acetochlor (ACT) to the aquatic ecological environment, designing wastewater treatment-oriented adsorbents for the sustainable remediation of actual ACT-contaminated water is a promising yet challenging strategy. Herein, a novel P-doped biochar (PBC-800) with a high adsorption capacity (51.34 mg g-1) and a rapid reaction rate (47.35 mg g-1 h-1) for ACT was prepared through pyrolyzing of rice straw biomass pre-impregnated with potassium dihydrogen phosphate (KH2PO4). Additionally, P-doped biochars synthesized at different pyrolysis temperatures exhibited significant variations in ACT adsorption performance, which was mainly ascribed to the distinction between hydrophilicity and sp2 conjugate C (ID/IG = 0.84-1.08). The adsorption behavior of ACT on PBC-800 followed the Elovich kinetics and Freundlich adsorption isotherm models. Thermodynamic calculations indicated that the adsorption of ACT by PBC-800 was a spontaneously disordered decreasing exothermic process. Besides, PBC-800 exhibited a powerful anti-interference for ACT adsorption within complex water matrices, highlighting its potential for various of practical applications. Through characterization analysis and further experiments, it was proved that the excellent adsorption performance of PBC-800 on ACT was ascribed to a combination of physical and chemical adsorption mechanisms, including 57.5% pore filling, 23.4% hydrophobic interaction, 12.7% π-π interaction, and 6.4% hydrogen bonding. Moreover, PBC-800 exerted a prominent adhesion impact upon Gram-positive and negative bacteria at 3 h. This study offers a new idea for the utilization of agricultural residues and provides insights into the mechanism of ACT adsorption through its derived biochar.

Structural and functional perspectives of carbon filter media in constructed wetlands for pollutants abatement from wastewater

Constructed wetlands (CWs) represent the most viable artificial wastewater treatment system that works on the principles of natural wetlands. Filter media are integrally linked to CWs and have substantial impacts on their performance for pollutant removal. Carbon-derived substrates have been in the spotlight for decades due to their abundance, sustainability, reusability, and potential to treat complex contaminants. However, the efficiency and feasibility of carbon substrates have not been fully explored, and there are only a few studies that have rigorously analyzed their performance for wastewater treatment. This critical synthesis of the literature review offers comprehensive insights into the utilization of carbon-derived substrates in the context of pollutant removal, intending to enhance the efficiency and sustainability of CWs. It also compares several carbon-based substrates with non-carbon substrates with respect to physiochemical properties, pollutant removal efficiency, and cost-benefit analysis. Furthermore, it addresses the concerns and possible remedies about carbon filtration materials such as configuration, clogging minimization, modification, and reusability to improve the efficacy of substrates and CWs. Recommendations made to address these challenges include pretreatment of wastewater, use of a substrate with smaller pore size, incorporation of multiple filter media, the introduction of earthworms, and cultivation of plants. A current scientific scenario has been presented for identifying the research gaps to investigate the functional mechanisms of modified carbon substrates and their interaction with other CW components.

Enhanced Escherichia coli removal from stormwater with bermudagrass-derived activated biochar filtration systems

Stormwater treatment and reuse can alleviate water pollution and scarcity while current sand filtration systems showed low treatment performance for stormwater. For enhancing E. coli removal in stormwater, this study applied the bermudagrass-derived activated biochars (BCs) in the BC-sand filtration systems for E. coli removal. Compared with the pristine BC (without activation), the FeCl3 and NaOH activations increased the BC carbon content from 68.02% to 71.60% and 81.22% while E. coli removal efficiency increased from 77.60% to 81.16% and 98.68%, respectively. In all BCs, the BC carbon content showed a highly positive correlation with E. coli removal efficiency. The FeCl3 and NaOH activations also led to the enhancement of roughness of BC surface for enhancing E. coli removal by straining (physical entrapment). The main mechanisms for E. coli removal by BC-amended sand column were found to be hydrophobic attraction and straining. Additionally, under 105-107 CFU/mL of E. coli, final E. coli concentration in NaOH activated BC (NaOH-BC) column was one order of magnitude lower than those in pristine BC and FeCl3 activated BC (Fe-BC) columns. The presence of humic acid remarkably lowered the E. coli removal efficiency from 77.60% to 45.38% in pristine BC-amended sand column while slightly lowering the E. coli removal efficiencies from 81.16% and 98.68% to 68.65% and 92.57% in Fe-BC and NaOH-BC-amended sand columns, respectively. Moreover, compared to pristine BC, the activated BCs (Fe-BC and NaOH-BC) also resulted in the lower antibiotics (tetracycline and sulfamethoxazole) concentrations in the effluents from the BC-amended sand columns. Therefore, for the first time, this study indicated NaOH-BC showed high potential for effective treatment of E. coli from stormwater by the BC-amended sand filtration system compared with pristine BC and Fe-BC.

Effects of different modifying agents on the preparation and properties of coagulants derived from excess sludge

The contents and kinds of oxygen-containing functional groups are very significant when preparing cationic hydrochar coagulants via graft copolymerization. Herein, the hydrothermal conditions to produce sludge-based hydrochar (SBC) precursors were optimized by introducing different kinds and amounts of modifying agents (i.e., HCOOH, citric acid (CA), H2SO4, and H2O2), then the surface properties and flocculation performance of derived cationic coagulants (SBC-g-DMC) were studied. Results showed that the utilization of four modifiers raised the acidic groups on the SBC surface; thereinto, the presence of CA could evidently increase the content of phenolic hydroxyl groups. After DMC monomer grafting, the formed coagulants possess positive zeta potentials over a wide pH range (i.e., 3.0 ~ 11.0), showing a typical cationic property. The grafting ratio and efficiency, as well as the cationic degree of coagulants prepared with different SBC precursors follow a descending order of SBCCA-g-DMC > [Formula: see text]-g-DMC > SBCHCOOH-g-DMC > [Formula: see text]-g-DMC; thus, SBCCA-g-DMC coagulant with the best grafting result shows a superior flocculation performance. When a dosage of 4 mg/L was adopted, the average turbidity removal rate of SBCCA-g-DMC could reach up to 94.44%. Meanwhile, due to the possible and robust oxidation with the initiator, H2O2 seems not a perfect modifier for SBC preparation. This study could provide an essential reference for the optimal synthesis of SBC and its based coagulants for organic matter recovery and pollutant removal.

Application of conventional and emerging low-cost adsorbents as sustainable materials for removal of contaminants from water

The impact of water pollution has led to the search for cost-effective and environmentally friendly treatment processes to alleviate the associated environmental hazards. Adsorption is identified as an advanced treatment technology that offers simplicity and cheap alternatives to water treatment technologies when low-cost adsorbents such as industrial by-products, waste, and agricultural waste are utilized. The utilization of these materials as low-cost adsorbents for the treatment of drinking water will bring them some value. Several practices have been done to improve the removal efficiencies of the low-cost adsorbents in order to achieve WHO standards of drinking water quality. The paper highlights some of the synthesis routes employed for the modification of low-cost adsorbents. This updated review provides information on the different applications of low-cost adsorbents in removing pollutants and their adsorption capacities in an attempt to deploy the recent sustainable low-cost adsorbents with high removal efficiencies for water treatment. Future research should focus on the fabrication of hybrid low-cost adsorbents with multifunctional and antimicrobial properties. In addition, life cycle assessment (LCA) should be conducted to reveal the environmental burdens associated with the modification of the low-cost adsorbent to improve their removal efficiencies.

Distribution and biodegradation potential of polycyclic aromatic hydrocarbons (PAHs) accumulated in media of a stormwater bioretention

Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds that can be captured and accumulate in the bioretention cell media, which may lead to secondary pollution and ecological risks. This research aimed to understand the spatial distribution of 16 priority PAHs in bioretention media, identify their sources, evaluate their ecological impact, and assess the potential for their aerobic biodegradation. The highest total PAH concentration (25.5 ± 1.7 μg/g) was observed 1.83 m from the inlet and 10-15 cm deep. The individual PAHs with the highest concentrations were benzo [g,h,i]perylene in February (1.8 ± 0.8 μg/g) and pyrene in June (1.8 ± 0.8 μg/g). Data indicated that primary sources of PAHs were fossil fuel combustion and petroleum. The ecological impact and toxicity of the media were assessed by probable effect concentrations (PECs) and benzo [a]pyrene total toxicity equivalent (BaP-TEQ). The results showed that the concentrations of pyrene and chrysene exceeded the PECs, and the average BaP-TEQ was 1.64 μg/g, primarily caused by benzo [a]pyrene. The functional gene (C12O) of PAH-ring cleaving dioxygenases (PAH-RCD) was present in the surface media, which indicated that aerobic biodegradation of PAHs was possible. Overall, this study revealed the PAHs accumulated most at medium distance and depth, where biodegradation may be limited. Thus, the accumulation of PAHs below the surface of the bioretention cell may need to be considered during long-term operation and maintenance.

Escherichia coli inactivation in water by sulfate radical-based oxidation process using FeCl3-activated biochar/persulfate system

Pathogenic microbes in water present great risks to environments, water resources, and human health. In the present study, for the first time, a FeCl₃-activated bermudagrass-derived biochar (FA-BC) was applied to activate persulfate (PS) for E. coli inactivation. The PS activation was ascribed to the presence of Fe⁰ and Fe₃O₄ on the surface of FA-BC, and SO₄^·- radicals were proved to be the main role for E. coli inactivation using FA-BC activated PS system (FA-BC/PS). Decreasing the pH (5-9) and increasing the PS concentration (50-300 mg/L), reaction temperature (20-50 °C), and FA-BC dosage (100-500 mg/L) resulted in the enhancement of disinfection efficiency of E. coli using FA-BC/PS. 6.21 log reductions of E. coli were achieved within 20 min under the optimal conditions (500 mg/L FA-BC, 200 mg/L PS, pH 7, and 20 °C with 10⁷ CFU/mL E. coli in DI water). The FA-BC/PS effectively eliminated various initial concentrations of E. coli (10⁵-10⁸ CFU/mL). The E. coli inactivation rate decreased from 0.1426 min^-1 to 0.0883, 0.1268 min^-1, and 0.1093 min^-1 with the presence of 10 mg/L humic acid, 100 mg/L Cl^-, and 100 mg/L HCO₃^-, respectively. In addition, after three cycles of disinfection tests using FA-BC/PS, the E. coli inactivation rate only slightly decreased from 0.1426 to 0.1288 min^-1. The FA-BC/PS also effectively removed the E. coli in real stormwater with a 99.2 % inactivation efficiency within 180 min. The FA-BC/PS in fixed-bed column tests revealed the continuous and high inactivation of E. coli in water. Increasing the FA-BC amount (1.5 %-5 %) and PS concentration (50-200 mg/L) and decreasing the flow rate (2-4 mL/min) caused the lower E. coli concentration in effluent. Therefore, the FA-BC/PS can be considered as a promising and efficient technique for water disinfection.

Biochar and fungi as bioretention amendments for bacteria and PAH removal from stormwater

Bioretention has been widely used to mitigate hydrologic impacts of stormwater runoff and is increasingly being relied upon to treat chemical and biological pollutants transported by stormwater. Despite this reliance, we still lack an understanding of treatment performance for certain organic and biological contaminants which may interact with biotic and abiotic components of bioretention systems. We evaluated the treatment of fecal indicator bacteria (FIB) and polycyclic aromatic hydrocarbons (PAHs) in stormwater runoff by bioretention. We compared treatment performance by Washington's standard bioretention mix of 60% sand: 40% compost (by volume), and by three other mixtures amended with biochar, fungi (Stropharia rugosoannulata), or both. All bioretention columns were conditioned with clean water and then dosed with collected roadway runoff at a rate equivalent to a 6 month, 24 h storm in this region during 8 events over a 14-month period. Effluents for each column were analyzed for 23 PAHs, Escherichia coli, fecal coliform, dissolved organic carbon (DOC), and total suspended solids (TSS). The fate and transport of PAHs within the bioretention columns was tracked by measuring soil PAHs in media cores taken from the columns. ΣPAH were almost completely removed by all treatments across all storms, with removal rates ranging from 97 to 100% for 94 out of 96 samples. Compost appeared to be a source of PAHs in bioretention media, as biochar-amended media initially contained half the ΣPAHs as treatments with the standard 60:40 sand:compost mixture. We observed a net loss of ΣPAHs (19-73%) in bioretention media across the study, which could not be explained by PAHs in the effluent, suggesting that bioremediation by microbes and/or plants attenuated media PAHs. E. coli and fecal coliform were exported in the first dosing event, but all columns achieved some treatment in subsequent dosing events. Overall, these findings suggest that PAHs in stormwater can be remediated with bioretention, are unlikely to accumulate in bioretention media, and that biochar amendments can improve the treatment of E. coli.

Green, zero-waste pathway to fabricate supported nanocatalysts and anti-kinetoplastid agents from sugarcane bagasse

The conversion processes of sugarcane into direct-consumption sugar and juice are generating a tremendous amount of waste, the so-called sugarcane bagasse (SCB). Biochar preparation is among the practical solutions aiming to manage and valorize SCB into high added-value functional material (FM). Herein, we propose a novel zero-waste pathway to fabricate two FMs from one biomass. The SCB was first macerated and ultrasonicated to obtain the natural extract that served as bio-reducing medium. Then, the H₂O/EtOH-extracted SCB was in-situ impregnated with a bimetallic solution of copper and silver nitrates. The process produced an intermediate composite (FM₀), Ag/Cu-Ag⁺/Cu²⁺-loaded SCB which was carbonized to elaborate Ag/Cu-Biochar (FM₁), free Ag/Cu nanoparticles (FM₂) were obtained by microwaving the residual liquid waste. FM₁ exhibited high catalytic activity for the total Fenton-like degradation of methylene blue. The experimental data followed the pseudo-first and the pseudo-second order rate laws with apparent degradation rate constants K₁ 45 10^-3 min^-1 and K₂ 0.115 g.mg^-1.min^-1, respectively. FM₀, FM₁ and FM₂ were tested as new anti-kinetoplastid materials against two flagellated protozoans namely the Leishmania spp and the Trypanosoma cruzi. Notably, Ag/Cu (FM₂) showed exceptional leishmanicidal and trypanocidal effects with IC₅₀ values of 2.909 ± 0.051, 3.580 ± 0.016 and 3.020 ± 0.372 ppm for L.donovani, L. amazonensis and Trypanosoma cruzi, respectively. In this way, we combine green chemistry and agrowaste valorization in a full zero-waste process, to address the 3rd (indicator 3.3.5) and 6th (indicator 6.3.1) United Nations sustainable development goals, ″Good Health and Well-Being″ and ″Clean Water and Sanitation″.

Potential application of spent mushroom compost (SMC) biochar as low-cost filtration media in heavy metal removal from abandoned mining water: a review

Overpopulation and rapid development have put an increasing burden on the environment, leading to various water crisis. Importing water from abandoned mines as an alternative raw water source could be the next answer to alleviate water scarcity problems globally. However, due to its high heavy metals content, there is a need to find an economical and effective method to remove heavy metals before reusing it as potable water source. Biochar, a low-cost and carbon-rich biosorbent, has received increasing attention on its application as a remediating agent to remove heavy metals from water. Previous studies have revealed the potential properties of biochar as a heavy metal removal agent including high cation exchange capacity, high surface area, active surface functional groups, as well as efficient adsorption. Apparently, the most important factor influencing the sorption mechanism is the type of feedstock materials. Spent mushroom compost (SMC), a waste product from mushroom cultivation, has been found as an excellent biosorbent. SMC has received global attention as it is low cost and eco-friendly. It also has been proved as an efficient heavy metals remover from water. Nevertheless, its application as biochar is still scarce. Therefore, this review focuses on the potential of transforming SMC into modified biochar to remove heavy metals, especially from abandoned mining water. The present review emphasizes the current trends in adsorption methods for heavy metal removal from water, assembles data from previous studies on the feedstock of biosorbents to biochars, and discusses the potentials of SMC as a biochar for water treatment.

Considerations for evaluating innovative stormwater treatment media for removal of dissolved contaminants of concern with focus on biochar

Stormwater from complex land uses is an important contributor of contaminants of concern (COCs) such as polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), Copper, and Zinc to receiving water bodies. A large portion of these COCs bind to particulate matter in stormwater, which can be removed through filtration by traditional media. However, the remaining dissolved COCs can be significant and require special attention such as engineered treatment measures and media. Biochar is a porous sorbent produced from a variety of organic materials. In the last decade biochar has been gaining attention as a stormwater treatment medium due to low cost compared to activated carbon. However, biochar is not a uniform product and selection of an appropriate biochar for the removal of specific contaminants can be a complex process. Biochars are synthesized from various feedstocks and using different manufacturing approaches, including pyrolysis temperature, impact the biochar properties thus affecting ability to remove stormwater contaminants. The local availability of specific biochar products is another important consideration. An evaluation of proposed stormwater control measure (SCM) media needs to consider the dynamic conditions associated with stormwater and its management, but the passive requirements of the SCM. The media should be able to mitigate flood risks, remove targeted COCs under high flow SCM conditions, and address practical considerations like cost, sourcing, and construction and maintenance. This paper outlines a process for selecting promising candidates for SCM media and evaluating their performance through laboratory tests and field deployment with special attention to unique stormwater considerations.

Application of biochar as an innovative soil ameliorant in bioretention system for stormwater treatment: A review of performance and its influencing factors

As an emerging environment functional material, biochar has become a research hotspot in environmental fields because of its excellent ecological and environmental benefits. Recently, biochar has been used as an innovative soil ameliorant in bioretention systems (BRS) to effectively enhance pollutant removal efficiency for BRS. This paper summarizes and evaluates the performance and involved mechanisms of biochar amendment in BRS with respect to the removal of nutrients (TN (34-47.55%) and PO₄^3--P (47-99.8%)), heavy metals (25-100%), pathogenic microorganisms (Escherichia coli (30-98%)), and organic contaminants (77.2-100%). For biochar adsorption, the pseudo-second-order and Langmuir models are the most suitable kinetic and isothermal adsorption models, respectively. Furthermore, we analyzed and elucidated some factors that influence the pollutant removal performance of biochar-amended BRS, such as the types of biochar, the preparation process and physicochemical properties of biochar, the aging of biochar, the chemical modification of biochar, and the hydraulic loading, inflow concentration and drying-rewetting alternation of biochar-amended BRS. The high potential for recycling spent biochar in BRS as a soil ameliorant is proposed. Collectively, biochar can be used as an improved medium in BRS. This review provides a foundation for biochar selection in biochar-amended BRS. Future research and practical applications of biochar-amended BRS should focus on the long-term stability of treatment performances under field conditions, chemical modification with co-impregnated nanomaterials in biochar surface, and the durability, aging, and possible negative effects of biochar.

Remediation of Chromium (VI) from Groundwater by Metal-Based Biochar under Anaerobic Conditions

Iron salt-modified biochar has been widely used to remove Cr(VI) pollution due to the combination of the generated iron oxides and biochar, which can bring positive charge and rich redox activity. However, there are few comprehensive studies on the methods of modifying biochar with different iron salts. In this study, two iron salt (FeCl3 and Fe(NO3)3) modification methods were used to prepare two Fe-modified biochar materials for removing Cr(VI) in simulated groundwater environment. It was revealed by systematic characterization that FeCl3@BC prepared via the FeCl3 modification method, has larger pore size, higher zeta potential and iron oxide content, and has higher Cr(VI) adsorption-reduction performance efficiency as compared to Fe(NO3)3@BC prepared via Fe(NO3)3 modification method. Combined with XRD and XPS analyses, Fe3O4 is the key active component for the reduction of Cr(VI) to Cr(III). The experimental results have shown that acidic conditions promoted Cr(VI) removal, while competing ions (SO42− and PO43−) inhibited Cr(VI) removal by FeCl3@BC. The Elovich model and intra-particle diffusion model of FeCl3@BC can describe the adsorption behavior of Cr(VI) well, indicating that both the high activation energy adsorption process and intra-particle diffusion control the removal process of Cr(VI). The Freundlich model (R2 > 0.999) indicated that there were unevenly distributed chemisorptions centers on the FeCl3@BC surface. Stability experiments exposed that FeCl3@BC was stable under neutral, acidic, and alkaline conditions. Furthermore, the main mechanisms of FeCl3@BC removal of Cr(VI) include electrostatic adsorption, chemical reduction, ion exchange, and co-precipitation. In conclusion, our findings provide a new insight for the selection of iron salt-modified biochar methods, and will also be beneficial for the preparation of more efficient Fe-modified biochars in the future.

A reduced graphene oxide-Fe3O4 composite functionalized with cetyltrimethylammonium bromide for efficient adsorption of SARS-CoV-2 spike pseudovirus and human enteric viruses

The latent dangers of waterborne viral transmission have become a major public health concern. In this study, reduced graphene oxide (rGO)-Fe₃O₄ nanoparticles were decorated with cetyltrimethylammonium bromide (CTAB) to adsorb severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike pseudovirus and three human enteric viruses (HuNoV, HRV, and HAdV). The successful combination of CTAB with rGO-Fe₃O₄ was confirmed by transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, zeta potential, Brunner-Emmet-Teller, and vibrating sample magnetometer measurements. The adsorption of HuNoV and HAdV followed pseudo-first-order kinetics, while that of HRV conformed to the pseudo-second-order model. CTAB-functionalized rGO-Fe₃O₄ exhibited exceptionally high adsorption of HuNoV, HRV, HAdV and SARS-CoV-2 spike pseudovirus, with maximum adsorption capacities of 3.55 × 10⁷, 7.01 × 10⁷, 2.21 × 10⁷ and 6.92 × 10⁶ genome copies mg^-1, respectively. Moreover, the composite could effectively adsorb the four types of virus particles from coastal, tap, and river water. In addition, concentrating the virions using CTAB functionalized rGO-Fe₃O₄ composites before qPCR analysis significantly improved the detection limit. The results indicate that viruses are captured on the surface of CTAB functionalized rGO-Fe₃O₄ composites through electrostatic interactions and the intrinsic adsorption ability of rGO. Overall, CTAB-functionalized rGO-Fe₃O₄ composites are promising materials for the adsorption and detection of human enteric viruses as well as SARS-CoV-2 from complex aqueous environments.

Biochar application in biofiltration systems to remove nutrients, pathogens, and pharmaceutical and personal care products from wastewater

Although conventional on-site wastewater treatment systems (OWTSs) provide only primary treatment of domestic wastewater, removal of a limited level of nutrients (N, P), pathogens, and pharmaceuticals and personal care products (PPCPs) could be achieved by such a treatment process. Biochar has the capacity to remove various contaminants and has been widely used as an ideal soil amendment in agriculture due to its persistence, superior nutrient-retention properties, low cost, and ready availability. However, few applications on the use of biochar in onsite wastewater treatment have been explored. In this review, we systematically reviewed the applications of biochar in filtration-based OWTSs for nutrient (N, P) removal and recovery as well as pathogen and PPCP removal. Although adsorption was the main mechanism for P, pathogen, and PPCP removal, biochar can also serve as the growth media for enhanced biological degradation, improves available alkalinity, and increases water holding capacity in the OWTSs. The biochar source, surface modification methods, and preparation procedures (e.g., pyrolysis temperature change) have significant effects on contaminant removal performance in biochar-amended OWTSs. Specifically, contradictory results have been reported on the effect of pyrolysis temperature change on biochar removal performance (i.e., increased, decreased, or no change) of N, P, and PPCPs. Wastewater composition and environmental pH also play important roles in the removal of nutrients, pathogens, and PPCPs. Overall, biochar holds great potential to serve as an alternative filtration material or to be amended to the current OWTS to improve system performance in removing a variety of contaminants at low cost.

Sustainable remediation of hazardous environmental pollutants using biochar-based nanohybrid materials

Biochar is a well-known carbon material with diversified functionalities and excellent physicochemical characteristics with high wastewater treatment potential. This review aims to summarize recent advancements in the development of biochar and biochar-based nanohybrid materials as a potential tool for the removal of harmful organic compounds such as synthetic dyes/effluents. The formation of biochar using pyrolysis of renewable feedstocks and their applications in various industries are explained hereafter. The characteristics and construction of biochar-based hybrid materials are explained in detail. Diversity of feedstocks, including municipal wastes, industrial byproducts, agricultural, and forestry residues, endows different biochar types with a wide structural variety. The production of cost-effective biochar drives the interest in manipulating biochars and induces desire functionality using nanoscale reinforcements. Various types of biochars, such as magnetic biochar, layered nanomaterial coated biochar, nanometallic oxide composites, chemically and physically functionalized biochar, have been produced. With the aid of nanomaterial, hybrid biochar exhibits a high potential to remove toxic contaminants. Depending upon biochar type, dyes/effluents can be removed via different mechanisms, including the Fenton process, photocatalytic degradation, π-π interaction, electrostatic interaction, and physical adsorption. In conclusion, desired physicochemical features, and tunable surface properties of biochar present high potential material in removing organic dyes and other effluents. The blended biochar with different materials/nanomaterials endows broader development and multi-functional opportunities for treating dyes/effluents.

Impacts of different activation processes on the carbon stability of biochar for oxidation resistance

Biochar modification is widely used to improve its capability for environmental application, while its impact on carbon sequestration potential is unknown. Herein, the oxidation-resistance stability of biochar with different activation processes was first evaluated, which is crucial for sustainable production of engineered biochar. Thermal activation enhanced the thermal stability of biochar with a higher R₅₀ as 61.5-62.7%, whereas a higher carbon loss of 15.2-17.2% was revealed after chemical oxidation. Physical activation of biochar had marginal effect on thermal stability, but it still weakened its chemical stability. By contrast, chemical activation with H₂SO₄ improved the stability in terms of chemical-oxidation (6.7% carbon loss) and thermal-oxidation (R₅₀ as 66.2%). Further analysis revealed that the thermal stability of engineered biochar was controlled by aromaticity, while the surface area was a vital factor correlating to the chemical stability. Our findings serve as an important reference to understand trade-off between biochar stability and broader application.

Bioretention systems for stormwater management: Recent advances and future prospects

Bioretention is a popular stormwater management strategy that is often utilized in urban environments to combat water quality and hydrological impacts of stormwater. This goal is achieved by selective designing of a system, which consists of suitable vegetation at the top planted on an engineered media with drainage system and possible underdrain at the bottom. Bibliometric analysis on bioretention studies indicates that most of the original research contributions are derived from a few countries and selected research groups. Hence, most of the bioretention systems installed in diverse geographical locations are based on guidelines from climatically different countries, which often lead to operational failures. The current review critically analyzes recent research findings from the bioretention literature, provides the authors' perspectives on the current state of knowledge, highlights the key knowledge gaps in bioretention research, and points out future research directions to make further advances in the field. Specifically, the role and desired features of bioretention components, the importance of fundamental investigations in laboratory, field-based studies and modeling efforts, the real-time process control of bioretention cells, bioretention system design considerations, and life cycle assessment of full-scale bioretention systems are discussed. The importance of local conditions in guiding bioretention designs in difference climates is emphasized. At the end of the review, current technical challenges are identified and recommendations to overcome them are provided. This comprehensive review not only offers fundamental insights into bioretention technology, but also provides novel ideas to combat issues related to urban runoff and achieve sustainable stormwater management.

Food waste and sewage sludge co-digestion amended with different biochars: VFA kinetics, methane yield and digestate quality assessment

This work investigated the impact of the addition of different biochar types on mitigation of volatile fatty acid (VFA) accumulation, methane recovery and digestate quality in mesophilic food waste-sludge co-digestion. Four biochars derived from agricultural and sludge residues under different pyrolysis temperatures were compared. Specific biochar properties such as pH, surface area, chemical properties and presence of surface functional groups likely influenced biochar reactions during digestion, thereby resulting in a varying performance of different biochars. Miscanthus straw biochar addition led to the highest specific methane yield of 307 ± 0.3 mL CH₄/g VS_added versus 241.87 ± 5.9 mL CH₄/g VS_added from control with no biochar addition over 30 days of the co-digestion period. Biochar supplementation led to enhanced process stability which likely resulted from improved syntrophic VFA oxidation facilitated by specific biochar properties. Overall, a 21.4% increase in the overall methane production was obtained with biochar addition as compared to control. The resulting digestate quality was also investigated. Biochar-amended digester generated a digestate rich in macro- and micro-nutrients including K, Mg, Ca, Fe making biochar-amended digestate a potential replacement of agricultural lime fertilizer. This work demonstrated that the addition of specific biochars with desirable properties alleviated VFA accumulation and facilitated enhanced methane recovery, thereby providing a means to achieve process stability even under high organic loading conditions in co-digestions. Moreover, the availability of biochar-enriched digestate with superior characteristics than biochar-free digestate adds further merit to this process.

Application of Biochar in Stormwater Treatment: Experimental and Modeling Investigation

This research investigated the removal of heavy metal ions (Cd, Cu, Pb, and Zn) and metalloid (As) common to stormwater runoff onto biochar-based media arranged in multiple configurations. Laboratory scale column experiments were conducted to quantify heavy metal removal efficiencies using sand, biochar, and nZVI-modified biochar (BC-nZVI) in four media configurations: a homogeneous mixture of sand and biochar (BCM); biochar layered in sand (BCL); BC-nZVI layered in sand (BCZ); and sand as a control. An inverse modeling approach was implemented to measured moisture and experimental data to determine media hydraulic parameters (θr, θs, α, n and Ks) and adsorption coefficients. The experiment was conducted using laboratory synthesized stormwater over 200 days at a rate of 5 cm/day. BCZ exhibited an excellent removal (99%) of As due to the high attachment to nZVI, via surface complexations. Biochar with abundant surface oxygen functional groups exhibited a great (99%) removal of Cd and Zn in both BCL and BCM columns. Water contents were observed 66.0, 44.3, 41.4, and 7.2% for BCL, BCM, BCZ, and sand, respectively. The attachment coefficients varied from 21.5 to 44.9, 16.1 to 19.3, 18.8 to 26.0, and 9.6 to 19.9 L/kg for BCL, BCM, BCZ, and sand, respectively. This study’s output provides useful information for stormwater management practices.

Hydrology and rainfall runoff pollutant removal performance of biochar-amended bioretention facilities based on field-scale experiments in lateritic red soil regions

Bioretention has been found to lower the effluent loads of various pollutants from rainfall runoff. However, it is still a challenge to effectively use bioretention for rainfall runoff control in lateritic red soil regions where have high rainfall intensity and low soil infiltration capacity. Hence, in this study, the hydrologic performance and rainfall runoff pollutant removal capacity of field-scale biochar-amended bioretention facilities were tested with four rainfall recurrence periods under different biochar distributions, internal water storage (IWS) zone heights, and exfiltration conditions. The results confirmed that incorporation of biochar into planting soil would improve its water content raising capacity (WCRC), especially when the biochar was uniformly mixed with the lateritic red soils. Besides, more infiltrating from the planting soil layer and higher IWS zone heights effectively enhanced WCRC of the stone chip packing layer. For runoff volume control, adding biochar and increasing the IWS zone height could effectively improve runoff volume control capacity. Besides, the unlined bioretention had a higher runoff volume control capacity than lined bioretention. Considering runoff pollutant removal performance, biochar could contribute to significantly improving the runoff pollutant event mean concentration removal rate (R_c) of nutrient pollutants (TN, NO₃-N, NH₃-N, and TP). The average runoff pollutant load removal rate (R_l) of different biochar distributions decreased as follows: biochar was uniformly mixed with the lateritic red soils > biochar was stratified with the lateritic red soils > biochar was excluded in the planting soil layer. The average R_c and average R_l of all pollutants except COD under different IWS zone heights decreased as follows: 40 cm > 20 cm > 0 cm. Meanwhile, the average R_l of the lined bioretention with an IWS zone height of 0 cm was lower than that of the unlined bioretention. Overall, higher rainfall recurrence periods would reduce the treatment capacity of bioretention facilities.

Co-existing TiO2 nanoparticles influencing adsorption/ desorption of tetracycline on magnetically modified kaolin

Interaction of coexisting nanoparticles (NPs) and other pollutants may affect their behavior in the environment. In this study, we investigated the effects of TiO₂ NPs on the adsorption and desorption of tetracycline (TC) by magnetized kaolin (MK). The interactions among TC, TiO₂ NPs, and MK were then discussed through their morphology and characteristics by using scanning electron microscopy, X-ray energy dispersive spectrometry, Transmission electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy analyses. Results showed that TiO₂ NPs increased TC adsorption on MK by 2.02% and increased TC desorption by 45.26%, TC increased the maximum adsorption of TiO₂ on MK from 31.32 to 49.42 mg g^-1 and decreased the amount of stable adsorption state TiO₂ NPs on MK from 17.92 to 12.71 mg g^-1. The characterization results demonstrated that TC molecules combined on MK though hydrogen bonding, π-π bonding and hydrophobic interaction. The adsorption of TiO₂ NPs on MK can provide additional hydrogen-bonding sites for TC adsorption by increasing the number of hydroxyl groups. However, TC can decrease the electrostatic attraction sites for TiO₂ NPs adsorption on the MK surface. The complexation of TC and TiO₂ NPs weakened the electrical attraction between MK and TiO₂ NPs and decreased the amount of stable adsorption state TiO₂ NPs.

Size-dependent biochar breaking under compaction: Implications on clogging and pathogen removal in biofilters

Breaking of biochar during compaction of amended soil in roadside biofilters or landfill cover can affect infiltration and pollutant removal capacity. It is unknown how the initial biochar size affects the biochar breaking, clogging potential, and contaminant removal capacity of the biochar-amended soil. We compacted a mixture of coarse sand and biochar with sizes smaller than, similar to, or larger than the sand in columns and applied stormwater contaminated with E. coli. Packing columns with biochar pre-coated with a dye and analyzing the dye concentration in the broken biochar particles eluted from the columns, we proved that biochar predominantly breaks under compaction by disintegration or splitting, not by abrasion. Increases in biochar size decrease the likelihood of biochar breaking. We attribute this result to the effective dissipation of compaction energy through a greater number of contact points between a large biochar particle and the adjacent particles. Most of the broken biochar particles are deposited in the pore spaces of the background geomedia, resulting in an exponential decrease in hydraulic conductivity of amended sand with an increase in suspended sediment loading. The clogging rate was higher in the columns with small biochar. The columns with small biochar also exhibited high E. coli removal capacity, partly because of an increase in bacterial straining at reduced pore size after compaction. These results are useful in selecting appropriate biochar size for its application in soils and roadside biofilters for stormwater treatment.

Engineered Biochar Production and Its Potential Benefits in a Closed-Loop Water-Reuse Agriculture System

Biochar’s potential to remove various contaminants from aqueous solutions has been widely discussed. The rapid development of engineered biochar produced using different feedstock materials via various methods for wastewater treatment in recent years urges an up-to-date review on this topic. This article centers on summarizing state-of-the-art methods for engineered biochar production and discussing the multidimensional benefits of applying biochar for water reuse and soil amendment in a closed-loop agriculture system. Based on numerous recent articles (<5 years) published in journals indexed in the Web of Science, engineered biochar’s production methods, modification techniques, physicochemical properties, and performance in removing inorganic, organic, and emerging contaminants from wastewater are reviewed in this study. It is concluded that biochar-based technologies have great potential to be used for treating both point-source and diffuse-source wastewater in agricultural systems, thus decreasing water demand while improving crop yields. As biochar can be produced using crop residues and other biomass wastes, its on-farm production and subsequent applications in a closed-loop agriculture system will not only eliminate expensive transportation costs, but also create a circular flow of materials and energy that promotes additional environmental and economic benefits.

Compaction conditions affect the capacity of biochar-amended sand filters to treat road runoff

Amending roadside soil with adsorbents such as biochar can help remove pollutants from road runoff. To maintain soil stability, the roadside soil requires compaction. However, it is unknown how compaction conditions affect the capacity of biochar-augmented roadside biofilters to infiltrate stormwater and remove pollutants. This work examines the effect of compaction conditions on the release of biochar particles disintegrated during compaction, and the change in their capacity to infiltrate stormwater and remove E. coli. The net loss of biochar particles by mobilization with stormwater was insignificant compared to the biochar remained in the filters. The initial release of biochar particles in wet-compacted biochar columns was greater than that in dry-compacted biochar. The results revealed that compaction can affect the release of biochar particles in a series of three-step processes: generation of particles by disintegration of large biochar under compaction, diffusion of particles deposited near grain walls to bulk pore water, and transport and retention of particles in constricted pore paths based on pore water connectivity. Under similar conditions, compost columns released more particles than biochar columns, suggesting biochar is more stable than compost under compaction. E. coli removal in wet-compacted columns was greater than removal in dry-compacted columns, owing to greater pore path connectivity in wet-compacted columns. These results indicate that addition of moisture during compaction can increase contaminant removal, initial particle release, and infiltration capacity of biochar-augmented sand filters for road runoff treatment. The results would help develop design guidelines for roadside stormwater treatment systems that require compaction of filter media.

Biochar technology in wastewater treatment: A critical review

Biochar is a promising agent for wastewater treatment, soil remediation, and gas storage and separation. This review summarizes recent research development on biochar production and applications with a focus on the application of biochar technology in wastewater treatment. Different technologies for biochar production, with an emphasis on pre-treatment of feedstock and post treatment, are succinctly summarized. Biochar has been extensively used as an adsorbent to remove toxic metals, organic pollutants, and nutrients from wastewater. Compared to pristine biochar, engineered/designer biochar generally has larger surface area, stronger adsorption capacity, or more abundant surface functional groups (SFG), which represents a new type of carbon material with great application prospects in various wastewater treatments. As the first of its kind, this critical review emphasizes the promising prospects of biochar technology in the treatment of various wastewater including industrial wastewater (dye, battery manufacture, and dairy wastewater), municipal wastewater, agricultural wastewater, and stormwater. Future research on engineered/designer biochar production and its field-scale application is discussed. Based on the review, it can be concluded that biochar technology represents a new, cost effective, and environmentally-friendly solution for the treatment of wastewater.

Biocidal Activity of Fast Pyrolysis Biochar against Escherichia coli O157:H7 in Soil Varies Based on Production Temperature or Age of Biochar

ABSTRACT

Soils in which fresh produce is grown can become contaminated with foodborne pathogens and are sometimes then abandoned or removed from production. The application of biochar has been proposed as a method of bioremediating such pathogen-contaminated soils. The objectives of the present study were to evaluate three fast-pyrolysis-generated biochars (FPBC; pyrolyzed in house at 450, 500, and 600°C in a newly designed pyrolysis reactor) and 10 United Kingdom Biochar Research Center (UKBRC) standard slow-pyrolysis biochars to determine their effects on the viability of four surrogate strains of Escherichia coli O157:H7 in soil. A previously validated biocidal FPBC that was aged for 2 years was also tested with E. coli to determine changes in antibacterial efficacy over time. Although neither the UKBRC slow-pyrolysis biochars or the 450 and 500°C FPBC from the new reactor were antimicrobial, the 600°C biochar was biocidal (P < 0.05); E. coli populations were significantly reduced at 3 and 3.5% biochar concentrations (reductions of 5.34 and 5.84 log CFU/g, respectively) compared with 0.0 to 2.0% biochar concentrations. The aged 500°C FPBC from the older reactor, which was previously validated as antimicrobial, lost efficacy after aging for 2 years. These results indicate that the biocidal activity of FPBC varies based on production temperature and/or age.

HIGHLIGHTS

Biochar for Wastewater Treatment—Conversion Technologies and Applications

Biochar as a stable carbon-rich material shows incredible potential to handle water/wastewater contaminants. Its application is gaining increasing interest due to the availability of feedstock, the simplicity of the preparation methods, and their enhanced physico-chemical properties. The efficacy of biochar to remove organic and inorganic pollutants depends on its surface area, pore size distribution, surface functional groups, and the size of the molecules to be removed, while the physical architecture and surface properties of biochar depend on the nature of feedstock and the preparation method/conditions. For instance, pyrolysis at high temperatures generally produces hydrophobic biochars with higher surface area and micropore volume, allowing it to be more suitable for organic contaminants sorption, whereas biochars produced at low temperatures own smaller pore size, lower surface area, and higher oxygen-containing functional groups and are more suitable to remove inorganic contaminants. In the field of water/wastewater treatment, biochar can have extensive application prospects. Biochar have been widely used as an additive/support media during anaerobic digestion and as filter media for the removal of suspended matter, heavy metals and pathogens. Biochar was also tested for its efficiency as a support-based catalyst for the degradation of dyes and recalcitrant contaminants. The current review discusses on the different methods for biochar production and provides an overview of current applications of biochar in wastewater treatment.

Mineralogical evidence of unfavorable geochemical interactions between urban runoff pollutants and filter materials in low-impact systems

We report on the geochemical interactions between a synthetic urban runoff (SUR) and the minerals of materials used in a multi-layered column filter (soil, sand, gravel, and tezontle) at the laboratory scale, which mimicked an unvegetated low-impact development (LID) system. After five 8 h infiltration cycles using the SUR, the average concentrations of Pb and Mn decreased slightly at the column outlet, as did HCO₃^-, SO₄^2-, and Na⁺, whereas Mg increased and Cl^-, Ca²⁺, and K⁺ were only detected at the outlet. The filter materials were comprised of silicates, Mn-bearing oxides (hausmannite and manganite), carbonates (calcite), chlorides (sylvite), and sulfates (anglesite, lanarkite, barite, and epsomite). PHREEQC modeling allowed the identification of the geochemical processes that occurred in the filter. The results showed the removal capacity of the filter materials through the formation of secondary minerals such as rhodochrosite (MnCO₃) and the over-saturation of anglesite (PbSO₄), and also showed that they may mobilize ions from the upper to the interior layers (as Mg²⁺ from epsomite, MgSO₄·7H₂O, and Ba²⁺ from barite, BaSO₄). We highlight the importance of knowing the geological nature of filter materials used in LID systems because they may lead to the geogenic mobilization of toxic contaminants to the environment.

Water treatment residual: A critical review of its applications on pollutant removal from stormwater runoff and future perspectives

In recent years, many studies have been conducted on using different filter media in bioretention systems for stormwater runoff treatment. This critical review paper provides a comprehensive review on the current state of water treatment residual (WTR), a recycled material that can be used as bioretention filter media for removals of key stormwater runoff pollutants (especially phosphorus) and future perspectives with innovative modification on WTR applied for pathogen removal from stormwater runoff. This review paper comprised (i) a brief summary of the reported WTR characteristics, (ii) a thorough evaluation of WTR performance on major pollutants removal from stormwater runoff (iii) a discussion on phosphorus removal mechanisms by WTR applied in the stormwater runoff treatment, and (iv) a review of the future perspectives of WTR for pathogen removal and other potential practical application in the field of stormwater treatment. As outlined in this review, WTR in stormwater runoff treatment has yet to be fully explored. The possible enhancements, especially metal surface modification on WTR are reviewed to bring about the widespread use of WTR in stormwater reuse practices.

Removal of E. coli from stormwater by bioretention system: parameter optimization and mechanism

Four bioretention simulation columns were used to study the removal effects and influencing factors of Escherichia coli (E. coli) in stormwater. The mechanism of E. coli removal in the bioretention system was also analyzed. The results show that the removal effects of the four new composite filters are better than that of the conventional filter. The specific surface area and porosity of the filter may be the key factors affecting the removal effect; the increase of the filter depth is beneficial to the removal of E. coli; the area is conducive to the removal of E. coli. Excessive depth of the submerged zone will reduce the E. coli removal effect; drying will reduce the E. coli removal effect, but it can be restored by rewetting.

Waste-derived compost and biochar amendments for stormwater treatment in bioretention column: Co-transport of metals and colloids

Bioretention systems, as one of the most practical management operations for low impact development of water recovery, utilize different soil amendments to remove contaminants from stormwater. For the sake of urban sustainability, the utilization of amendments derived from waste materials has a potential to reduce waste disposal at landfill while improving the quality of stormwater discharge. This study investigated the efficiency of food waste compost and wood waste biochar for metal removal from synthetic stormwater runoff under intermittent flow and co-presence of colloids. Throughout intermittent infiltration of 84 pore volumes of stormwater, columns amended with compost and biochar removed more than 50-70% of influent metals, whereas iron-oxide coated sand was much less effective. Only a small portion of metals adsorbed on the compost (< 0.74%) was reactivated during the drainage of urban pipelines that do not flow frequently, owing to abundant oxygen-containing functional groups in compost. In comparison, co-existing kaolinite enhanced metal removal by biochar owing to the abundance of active sites, whereas co-existing humic acid facilitated mobilization via metal-humate complexation. The results suggest that both waste-derived compost and biochar show promising potential for stormwater harvesting, while biochar is expected to be more recalcitrant and desirable in field-scale bioretention systems.

Facile hydrothermal synthesis of novel Fe-Cu layered double hydroxide/biochar nanocomposite with enhanced sonocatalytic activity for degradation of cefazolin sodium

This study reports the successful synthesis of Fe-Cu layered double hydroxide (Fe-Cu-LDH) /biochar (BC) nanocomposite by a hydrothermal method. The sonocatalytic performance of Fe-Cu-LDH/BC nanocomposite was investigated for the degradation of cefazolin sodium (CFZ), as a model emerging contaminant, from the solution. The physico-chemical properties of the synthesized samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX), Brunauer-Emmett-Teller (BET), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR), and UV-Vis diffuse reflectance spectroscopy (DRS) analyses. The best sonocatalytic efficiency of 97.6% was achieved by using 1.0 g/L sonocatalyst, 0.1 mM CFZ, and an ultrasonic power of 300 W at pH = 6.5 (natural) within 80 min. Additionally, the effects of the addition of various oxidants, dissolved gases, and organic and inorganic scavengers on the degradation of CFZ were studied. Moreover, the possible sonocatalytic mechanism of the sonochemical degradation of CFZ in the presence of Fe-Cu-LDH/BC sonocatalyst was proposed based on the results of GC-MS analysis. The mineralization of CFZ solution was evaluated using COD and IC analyses. Finally, the reusability test of Fe-Cu-LDH/BC nanocomposite in the CFZ degradation revealed that almost 9% drop occurred after five successive cycles.

Use of Bacillus-siamensis-inoculated biochar to decrease uptake of dibutyl phthalate in leafy vegetables

Dibutyl phthalate (DBP) is a frequently detected farmland contaminant that is harmful to the environment and human health. In this study, a DBP-degrading endophytic Bacillus siamensis strain T7 was immobilized in rice husk-derived biochar for bioremediation of DBP-polluted agricultural soils. The effects of this microbe-biochar composite on the soil prokaryotic community and the mechanism by which it regulates DBP degradation, were also investigated. A supplement of T7-biochar composite not only significantly boosted DBP biodegradation in soil by raising the DBP degradation rate constant and half-life from 0.1979 d^-1 and 2.3131 d to 0.2434 d^-1 and 2.1062 d, respectively, but also impeded DBP uptake by leafy vegetables. The general bioremediation effect of T7-biochar alliance excelled pure T7 suspensions and biochar, by trapping more DBP and boosting its complete degradation in soil. Besides, the combination of strain T7 and biochar can increase the proportion of some beneficial bacteria and boost the functional diversity of soil prokaryotic community, then to a certain extent may reverse the negative effect of DBP pollution on the agricultural soils. These results indicate that the rice-husk-derived biochar is a proper media when utilizing functional microbes into environmental treatment. Overall, T7-biochar composite is a promising soil modifier for soil bioremediation and the production of DBP-free crops.

Comparative toxicity of organic mixture attached to road deposited sediments: Inadequacy of conventionally using individual pollutants to assess comprehensive hazard effects

Organic pollutants attached on road deposited sediments (RDS) during dry days can be washed-off into stormwater runoff during rainfall events, undermining stormwater reuse safety. Previous research studies commonly utilized individual pollutant groups and their quantity to evaluate the hazard effect of pollutants attached to RDS in terms of stormwater reuse. Since many types of organic pollutants are present together rather than individually, conventional approaches might not permit a comprehensive understanding of how appropriately the RDS polluted stormwater can be reused. This study undertook a toxicity test of organic pollutants attached to RDS using Chinese hamster ovary cells (CHO), testing a hypothesis that solely focusing on individual pollutant groups are not adequate to represent hazard effects of resulting stormwater and hence their adequacy for reuse. It is noted that comparative toxicity of RDS is not strongly related to total solids (commonly seen as the key carrier of pollutants) and chemical oxygen demand (COD, representing organic matters). Additionally, the comparison results of spatial distributions of toxicity (in this study) and individual pollutants in previous studies did not show a similar trend. These results imply that toxicity should be also used to indicate how stormwater can be safely reused while solely investigating individual pollutants can not adequately show a comprehensive hazard effect in terms of ensuring stormwater reuse safety. Based on study outcomes, a new assessment approach considering both pollutant and toxicity were proposed. This will assist on effective stormwater reuse and ensuring their reuse safety.

Fecal indicator bacteria and virus removal in stormwater biofilters: Effects of biochar, media saturation, and field conditioning

Stormwater biofilters are used to attenuate the flow and volume of runoff and reduce pollutant loading to aquatic systems. However, the capacity of biofilters to remove microbial contaminants remains inadequate. While biochar has demonstrated promise as an amendment to improve microbial removal in laboratory-scale biofilters, it is uncertain if the results are generalizable to the field. To assess biochar performance in a simulated field setting, sand and biochar-amended sand biofilters were periodically dosed with natural stormwater over a 61-week conditioning phase. Impact of media saturation was assessed by maintaining biofilters with and without a saturated zone. Biochar-amended biofilters demonstrated improved Escherichia coli removal over sand biofilters during the first 31 weeks of conditioning though media type did not impact E. coli removal during the last 30 weeks of conditioning. Presence of a saturated zone was not a significant factor influencing E. coli removal across the entire conditioning phase. Following conditioning, biofilters underwent challenge tests using stormwater spiked with wastewater to assess their capacity to remove wastewater-derived E. coli, enterococci, and male-specific (F+) coliphage. In challenge tests, biochar-amended biofilters demonstrated enhanced removal of all fecal indicators relative to sand biofilters. Additionally, saturated biofilters demonstrated greater removal of fecal indicators than unsaturated biofilters for both media types. Discrepant conclusions from the conditioning phase and challenge tests may be due to variable influent chemistry, dissimilar transport of E. coli indigenous to stormwater and those indigenous to wastewater, and differences in E. coli removal mechanisms between tests. Mobilization tests conducted following challenge tests showed minimal (<2.5%) observable mobilization of fecal indicators, regardless of media type and presence of a saturated zone. While our results emphasize the challenge of translating biochar’s performance from the laboratory to the field, findings of this study inform biofilter design to remove microbial contaminants from urban stormwater.

Role of metal modified water treatment residual on removal of Escherichia coli from stormwater runoff

Extensive studies have been conducted on bioretention filter media applied in best management practices for stormwater runoff treatment. To date, more reported studies are focused on pollutants elimination such as suspended solids and nutrients. There has been limited research on pathogen removal from stormwater runoff. More focused studies on pathogen removal are therefore required if the intended stormwater is harvested for indirect potable use. In this study, water treatment residuals (WTR), a recycled biofilter media was surface-modified with metals to assess its potential for E. coli removal from stormwater runoff. To achieve this goal, four types of modified WTRs, prepared using iron, copper, platinum, and silver as antibacterial agents, were tested in parallel batch tests. After the cost-effectiveness evaluation among the four modified WTRs for bacterial removal, Fe₂O₃- and CuO-WTRs were shortlisted for further mechanism and stability studies. Stable antibacterial performances (E. coli log removal of 0.58 ± 0.04 and 0.90 ± 0.04, respectively) were achieved using the Fe₂O₃- and CuO-WTRs under intermittent synthetic and natural stormwater runoff conditions. No significant metal leaching was observed over prolonged continuous treatment. The experimental results showed the bio-adsorption onto the surface modified Fe₂O₃- and CuO-WTR was a key mechanism for E. coli removal followed by E. coli inactivation at solid-liquid interface caused by the antibacterial effect of metal coatings (where CuO was reported to have higher biotoxicity than Fe₂O₃). These findings clearly suggested the potential of CuO-modified WTR for pathogen removal in stormwater treatment practices.

Diversity and metabolism effects of microorganisms in bioretention systems with sand, soil and fly ash

Recently, both sand and fly ash have been used for nutrient removal in bioretention systems. However, the improvement in nutrient removal was hampered by a lack of data about of microbial diversity and metabolism effects in the mentioned materials based bioretention systems. Therefore, a mixture with sand, soil and fly ash (1:1:1) was selected as the base in bioretention systems. The investigation of microbial diversity implied that 11 dominant microflora were found, which changed weakly at phylum level but significantly at genus level. The analysis for both urease and extracellular polymer (EPS) showed that urease levels increased with the increase of submerged zone height, which was in line with nitrogen removal, while EPS had the opposite situation. Overall evaluation of microbial role suggested that the enhancement of dominant microflora in the used bioretention systems, like Chloroflexi and Nitrospirae, could strengthen nitrogen removal.

Engineered multifunctional sand for enhanced removal of stormwater runoff contaminants in fixed-bed column systems

The degradation of surface water quality in the US is mostly contributed by nonpoint-source pollution, in which stormwater runoff plays a major role. Stormwater runoff pollution is difficult to control due to its diffuse and stochastic loading. In this study, multifunctional AlMg/GO engineered sand synthesized via a simple method was used to address four major categories of runoff contaminants, namely nutrient (phosphate), metal (zinc), organic contaminant (caffeine), and pathogen (E. coli), simultaneously. For chemical contaminants (phosphate, zinc, and caffeine), Freundlich and Thomas models can successfully describe the batch isotherms and breakthrough curves of column flow-through experiments, respectively. Better E. coli retention capacity and antibacterial activity of the engineered sand than that of the raw sand was demonstrated in E. coli retention and revitalization experiments. The engineered sand also showed good performance in actual surface runoff. Based on the results of the column flow-through experiments and the literature-reported typical field conditions and design criteria (e.g. 50 m³ engineered sand for 5000 m² catchment; dissolved concentrations in the runoff: phosphate 0.2 mg/L, zinc 0.3 mg/L, and caffeine 0.0002 mg/L), a preliminary operational lifetime estimation was conducted, which indicated that the engineered sand can maintain its effectiveness for 90% removal of the dissolved phosphate, zinc, and caffeine from stormwater runoff for 81, 15, and >100 years, respectively. The engineered multifunctional sand proved to be a promising solution to future stormwater runoff management.

A simple method to improve the adsorption properties of drinking water treatment residue by lanthanum modification

The loading of La can substantially enhance the adsorption capability of drinking water treatment residue (DWTR) for better recycling. Normally, the modification was based on incubation of DWTR and La solution at a certain ratio, following by solid-liquid separation and drying processes. This study attempted to simplify La loading procedures by adopting high ratio of DWTR and La solution to eliminate the solid-liquid separation, aiming to promote the potential actual production. According to the results of the short- (2 d) and long-term (30 d) P adsorption tests, the N₂ gas sorption and desorption analysis, the X-ray photoelectron spectroscopy analysis, and the metal fractionation, the substantial enhanced adsorption capability of the modified DWTR was maintained and the La loading mechanisms to DWTR changed little after eliminating solid-liquid separation processes during modification; typically, La loading increased the initial P adsorption rates from 1.00 (raw DWTR) to 6.08 and 6.03 mg g^-1 d^-1 for the modified DWTR with and without the separation processes. Furthermore, the DWTR before and after modification had little unfavorable effect on the survival of snail Bellamya aeruginosa, while eliminating the separation processes tended to reduce the bioavailability of Al, Fe, and La in the modified DWTR. These results demonstrated that solid-liquid separation was not the key step for DWTR modification and that the developed simple modification method was feasible for La loading to DWTR, promoting the beneficial recycling in environmental remediation.

Multifunctional iron-biochar composites for the removal of potentially toxic elements, inherent cations, and hetero-chloride from hydraulic fracturing wastewater

This paper evaluates a novel sorbent for the removal of potentially toxic elements, inherent cations, and hetero-chloride from hydraulic fracturing wastewater (FWW). A series of iron-biochar (Fe-BC) composites with different Fe/BC impregnation mass ratios (0.5:1, 1:1, and 2:1) were prepared by mixing forestry wood waste-derived BC powder with an aqueous FeCl₃ solution and subsequently pyrolyzing them at 1000 °C in a N₂-purged tubular furnace. The porosity, surface morphology, crystalline structure, and interfacial chemical behavior of the Fe-BC composites were characterized, revealing that Fe chelated with CO bonds as COFe moieties on the BC surface, which were subsequently reduced to a CC bond and nanoscale zerovalent Fe (nZVI) during pyrolysis. The performance of the Fe-BC composites was evaluated for simultaneous removal of potentially toxic elements (Cu(II), Cr(VI), Zn(II), and As(V)), inherent cations (K, Na, Ca, Mg, Ba, and Sr), hetero-chloride (1,1,2-trichlorethane (1,1,2-TCA)), and total organic carbon (TOC) from high-salinity (233 g L^-1 total dissolved solids (TDS)) model FWW. By elucidating the removal mechanisms of different contaminants, we demonstrated that Fe-BC (1:1) had an optimal reducing/charge-transfer reactivity owing to the homogenous distribution of nZVI with the highest Fe⁰/Fe²⁺ ratio. A lower Fe content in Fe-BC (0.5:1) resulted in a rapid exhaustion of Fe⁰, while a higher Fe content in Fe-BC (2:1) caused severe aggregation and oxidization of Fe⁰, contributing to its complexation/(co-)precipitation with Fe²⁺/Fe³⁺. All of the synthesized Fe-BC composites exhibited a high removal capacity for inherent cations (3.2-7.2 g g^-1) in FWW through bridging with the CO bonds and cation-π interactions. Overall, this study illustrated the potential efficacy and mechanistic roles of Fe-BC composites for (pre-)treatment of high-salinity and complex FWW.

Chemical activation of biochar for energy and environmental applications: a comprehensive review

Biochar (BC) generated from thermal and hydrothermal cracking of biomass is a carbon-rich product with the microporous structure. The graphene-like structure of BC contains different chemical functional groups (e.g. phenolic, carboxylic, carbonylic, etc.), making it a very attractive tool for wastewater treatment, CO2 capture, toxic gas adsorption, soil amendment, supercapacitors, catalytic applications, etc. However, the carbonaceous and mineral structure of BC has a potential to accept more favorable functional groups and discard undesirable groups through different chemical processes. The current review aims at providing a comprehensive overview on different chemical modification mechanisms and exploring their effects on BC physicochemical properties, functionalities, and applications. To reach these objectives, the processes of oxidation (using either acidic or alkaline oxidizing agents), amination, sulfonation, metal oxide impregnation, and magnetization are investigated and compared. The nature of precursor materials, modification preparatory/conditions, and post-modification processes as the key factors which influence the final product properties are considered in detail; however, the focus is dedicated to the most common methods and those with technological importance.

Phosphoric acid pretreatment enhances the specific surface areas of biochars by generation of micropores

Biochars are being increasingly applied in soil for carbon sequestration, fertility improvement, as well as contamination remediation. Phosphoric acid (H₃PO₄) pretreatment is a method for biochar modification, but the mechanism is not yet fully understood. In this work, biochars and the raw biomass were treated by H₃PO₄ prior to pyrolysis. Due to an acid catalysis and crosslink, the micropores of the pretreated particles were much more than those without H₃PO₄ pretreatment, resulting in the dramatical enhancement of specific surface areas of the pretreated particles. Crystalline cellulose (CL) exhibited a greater advantage in the formation of micropores than of amorphous lignin (LG) with H₃PO₄ modification. The formation mechanisms of micropores were: (a) H⁺ from H₃PO₄ contributes to micropores generation via H⁺ catalysis process; (b) the organic phosphate bridge protected the carbon skeleton from micropore collapse via the crosslinking of phosphate radical. The sorption capacities to carbamazepine (CBZ) and bisphenol A (BPA) increased after H₃PO₄ modification, which is ascribed to the large hydrophobic surface areas and more abundant micropores. Overall, H₃PO₄ pretreatment produced biochars with large surface area and high abundance of porous structures. Furthermore, the H₃PO₄ modified biochars can be applied as high adsorbing material as well as P-rich fertilizer.

Modeling the effects of parameter optimization on three bioretention tanks using the HYDRUS-1D model

The operation effects of bioretention on different tanks were investigated through tests and simulations. Three layered bioretention tanks, namely, #1, #2, and #3, were selected for intermittent operation tests. The artificial filler layers of the tanks consisted of mixed fillers of fly ash and sand, blast furnace slag, and planting soil. Models were established by using HYDRUS-1D software based on test results. The sensitivity of model parameters was analyzed through Morris screening method. Results showed that return period, thickness of media layer, and solute concentration in the liquid phase were the parameters that significantly influenced the operation effects. The Nash-Sutcliffe efficiency coefficients of the models were greater than 0.85. The simulation results showed that the reduction effects at different inflow loads were better under low loads than under high loads. The comprehensive reduction rate of pollutant load was 5.22% less under high concentrations than under low concentrations. The comprehensive reduction rates of water and pollutant loads were 35.97% and 20.68% greater, correspondingly, in the 1 year return period than in the 10 year return period. The artificial fillers comprising a mixture of fly ash and sand also showed the optimal reduction effects, with comprehensive reduction rates of 69.33% and 83.08% for water and pollutant load, respectively. The reduction effects of water and pollutants for the #1 tank presented an upward trend, whereas those for the #2 tank showed a downward trend given an increase in planting soil thickness. An increase in media thickness enhanced the reduction effects. The media with 60 cm thickness demonstrated the optimal effect.

Plenty of room for carbon on the ground: Potential applications of biochar for stormwater treatment

Low impact development (LID) systems are increasingly used to manage stormwater, but they have limited capacity to treat stormwater-a resource to supplement existing water supply in water-stressed urban areas. To enhance their pollutant removal capacity, infiltration-based LID systems can be augmented with natural or engineered geomedia that meet the following criteria: they should be economical, readily available, and have capacity to remove a wide range of stormwater pollutants in conditions expected during intermittent infiltration of stormwater. Biochar, a carbonaceous porous co-product of waste biomass pyrolysis/gasification, meets all these criteria. Biochar can adsorb pollutants, improve water-retention capacity of soil, retain and slowly release nutrients for plant uptake, and help sustain microbiota in soil and plants atop; all these attributes could help improve removal of contaminants in stormwater treatment systems. This article discusses contaminant removal mechanisms by biochar, summarizes specific biochar properties that enhance targeted contaminants removal from stormwater, and identifies challenges and opportunities to retrofit biochar in LID to optimize stormwater treatment.

Continuous leaching modifies the surface properties and metal(loid) sorption of sludge-derived biochar

After the application of sludge derived biochar (SDBC) for soil stabilization, it is subjected to continuous leaching that may change its surface properties and metal(loid) immobilization performance. This study simulated the continuous leaching through the fresh SDBC sample in columns with unsaturated and saturated zones under flushing with 0.01M NaNO₃ solution (pH5.5) and acidic solution (pH adjusted to 3.2 by HNO₃:H₂SO₄=1:2), respectively. The resultant changes were assessed in terms of the SDBC surface characteristics and metal(loid) sorption capacities. Continuous leaching was found to gradually decrease the density of basic functional groups and increase the density of carboxyl groups as well as cation exchange capacity on the SDBC surface. It was attributed to the surface acidification and oxidation process by the leaching process, yet it occurred to a lesser extent than the atmospheric exposure. Continuous leaching increased Pb(II), Cr(VI), and As(III) sorption capacity of the SDBC, probably because the increase in carboxyl groups promoted inner-sphere complexation and Fe oxidation as revealed by spectroscopic analysis. It was noteworthy that the SDBC in the unsaturated and saturated zones under continuous leaching displayed distinctive effects on metal(loid) sorption capacity than the atmospheric exposure. Future investigations are needed for understanding the fate and interactions of the SDBC under varying redox conditions and intermittent leaching process.

Experimental study and simulation of phosphorus purification effects of bioretention systems on urban surface runoff

Excessive phosphorus (P) contributes to eutrophication by degrading water quality and limiting human use of water resources. Identifying economic and convenient methods to control soluble reactive phosphorus (SRP) pollution in urban runoff is the key point of rainwater management strategies. Through three series of different tests involving influencing factors, continuous operation and intermittent operation, this study explored the purification effects of bioretention tanks under different experimental conditions, it included nine intermittent tests, single field continuous test with three groups of different fillers (Fly ash mixed with sand, Blast furnace slag, and Soil), and eight intermittent tests with single filler (Blast furnace slag mixed with sand). Among the three filler combinations studied, the filler with fly ash mixed with sand achieved the best pollution reduction efficiency. The setting of the submerged zone exerted minimal influence on the P removal of the three filler combinations. An extension of the dry period slightly promoted the P purification effect. The combination of fly ash mixed with sand demonstrated a positive purification effect on SRP during short- or long-term simulated rainfall duration. Blast furnace slag also presented a positive purification effect in the short term, although its continuous purification effect on SRP was poor in the long term. The purification abilities of soil in the short and long terms were weak. Under intermittent operations across different seasons, SRP removal was unstable, and effluent concentration processes were different. The purification effect of the bioretention system on SRP was predicted through partial least squares regression (PLS) modeling analysis. The event mean concentration removal of SRP was positively related to the adsorption capacity of filler and rainfall interval time and negatively related to submerged zones, influent concentration and volume.