Potential of biochar filters for onsite wastewater treatment: Effects of active and inactive biofilms on adsorption of per- and polyfluoroalkyl substances in laboratory column experiments

Efficient adsorption of short-chain perfluoroalkyl substances by pristine and Fe/Cu-loaded reed straw biochars

As the substitutes of legacy long-chain per-/polyfluoroalkyl substances (PFASs), short-chain PFASs have been widely detected in the environment. Compared to long-chain PFASs, short-chain PFASs have smaller molecules and are more hydrophilic. Therefore, they are more likely to experience long-distance transport and pose lasting environmental impacts. In this study, Fe-doped (R-Fe) and Cu-doped biochars (R-Cu) were prepared using reed straw biochar (R). The results showed that the PFBA and PFPeA sorption capacities of R-Fe were 25.81 and 43.59 mg g-1, 1.65 and 1.55 times higher than those of R, respectively. The PFBA and PFPeA sorption capacities of R-Cu were 19.34 and 33.69 mg g-1, 1.24 and 1.20 times higher than those of R, respectively. In addition, R, R-Fe, and R-Cu exhibited higher PFBA and PFPeA sorption capacities than the biochars previously reported. The excellent PFAS sorption performances of the biochars were attributed to the highly porous structure of R, which provided rich adsorption sites. Ion-pair sorption, pore filling, electrostatic interaction between the Fe/Cu and cationic groups on biochar and the anionic groups of PFASs, and hydrophobic interaction between the hydrophobic surface of biochar and the fluorinated tails of PFASs were the underlying sorption mechanisms. The biochars presented high removal rates (>86 %) of multiple PFASs (∑PFAS: 350 μg L-1) from synthetic wastewaters, including legacy and emerging PFASs of different chain lengths and with different functional groups. The biochars reported in this study are promising candidate adsorbents for treating waters contaminated with short-chain PFASs.

A critical review of biochar for the remediation of PFAS-contaminated soil and water

Per- and polyfluoroalkyl substances (PFAS) present significant environmental and health hazards due to their inherent persistence, ubiquitous presence in the environment, and propensity for bioaccumulation. Consequently, the development of efficacious remediation strategies for soil and water contaminated with PFAS is imperative. Biochar, with its unique properties, has emerged as a cost-effective adsorbent for PFAS. Despite this, a comprehensive review of the factors influencing PFAS adsorption and immobilization by biochar is lacking. This narrative review examines recent findings indicating that the application of biochar can effectively immobilize PFAS, thereby mitigating their environmental transport and subsequent ecological impact. In addition, this paper reviewed the sorption mechanisms of biochar and the factors affecting its sorption efficiency. The high effectiveness of biochars in PFAS remediation has been attributed to their high porosity in the right pore size range (>1.5 nm) that can accommodate the relatively large PFAS molecules (>1.02-2.20 nm), leading to physical entrapment. Effective sorption requires attraction or bonding to the biochar framework. Binding is stronger for long-chain PFAS than for short-chain PFAS, as attractive forces between long hydrophobic CF2-tails more easily overcome the repulsion of the often-anionic head groups by net negatively charged biochars. This review summarizes case studies and field applications highlighting the effectiveness of biochar across various matrices, showcasing its strong binding with PFAS. We suggest that research should focus on improving the adsorption performance of biochar for short-chain PFAS compounds. Establishing the significance of biochar surface electrical charge in the adsorption process of PFAS is necessary, as well as quantifying the respective contributions of electrostatic forces and hydrophobic van der Waals forces to the adsorption of both short- and long-chain PFAS. There is an urgent need for validation of the effectiveness of the biochar effect in actual environmental conditions through prolonged outdoor testing.

Per- and poly-fluoroalkyl substances in agricultural contexts and mitigation of their impacts using biochar: A review

Growing concern over the presence of per- and polyfluoroalkyl substances (PFAS) in agricultural compartments (e.g., soil, water, plants, soil fauna) has led to an increased interest in scalable and economically feasible remediation technologies. Biochar is the product of pyrolyzing organic materials (crop waste, wood waste, manures, grasses) and has been used as a low-cost adsorbent to remove contaminants including PFAS. This review frames biochar as a strategy for mitigating the detrimental impacts of PFAS in agricultural systems and discusses the benefits of this strategy within the framework of the needs and challenges of contaminant remediation in agriculture. To gauge the optimal physicochemical characteristics of biochar in terms of PFAS adsorption, principal component analysis using >100 data points from the available literature was performed. The main biochar-based PFAS treatment strategies (water filtration, soil application, mixing with biosolids) were also reviewed to highlight the benefits and complications of each. Life cycle analyses on the use of biochar for contaminant removal were summarized, and data from selected studies were used to calculate (for the first time) the global warming potential and net energy demand of various agriculturally important biochar classes (crop wastes, wood wastes, manures) in relation to their PFAS adsorption performance. This review serves to identify key gaps in our knowledge of (i) PFAS adsorption by biochars in agricultural remediation applications and (ii) environmental costs/benefits of biochars in relation to their adsorptive properties toward PFAS. The concepts introduced in this review may assist in developing large-scale biochar-based PFAS remediation strategies to help protect the agricultural food production environment.

Biochar-enhanced anaerobic mixed culture for biodegradation of 1,2-dichloroethane: Microbial community, mechanisms, and techno-economics

While anaerobic digestion (AD) has been employed for the degradation of chlorinated aliphatic hydrocarbons, the associated digester performance might suffer from volatile fatty acids accumulation, insufficient substrate-microbes interaction, and lower biogas yields. To overcome these limitations, this study is the first to augment the hydrocarbon-degrading microbial capacities by adding agricultural waste-based biochar to the digestion medium. 1,2-dichloroethane (1,2-DCA) was selected as the target pollutant because it is discharged in large quantities from oil refining, petrochemical, and chemical industries, causing serious environmental and human health concerns. A multi-chamber anaerobic reactor (MAR) was operated at a 1,2-DCA loading rate of 1.13 g/L/d, glucose dosage (as an electron donor) range of 200-700 mg/L, and hydraulic retention time of 11.2 h, giving dechlorination = 32.2 ± 6.9% and biogas yield = 210 ± 30 mL/g CODremoved. These values increased after biochar supplementation (100 mg/g volatile solids, VS, as an inoculum carrier) up to 60.2 ± 11.5% and 290 ± 40 mL/g CODremoved, respectively, owing to the enhancement of dehydrogenase enzyme activities. Burkholderiales (15.3%), Clostridiales (2.3%), Bacteroidales (3.5%), Xanthomonadales (3.3%), and Rhodobacterales (6.1%) involved in 1,2-DCA degradation were dominant in the reactor supplemented with biochar. It's suggested that biochar played a major role in facilitating the direct interspecies electron transfer (DIET) between syntrophic bacteria and methanogens, where chloride, ethylene glycol, and acetate derived from 1,2-DCA dechlorination could be further used to promote methanogenesis and methane production. The synergetic effect of adsorption and dechlorination towards 1,2-DCA removal was validated at various biochar dosages (50-120 mg/g) and 1,2-DCA concentrations (50-1000 mg/L). The techno-economic results showed that the cost of treating 1,2-DCA-laden discharge (100 m3/d) by the MAR module could be 0.83 USD/m3 with a payback period of 6.24 years (NPV = 2840 USD and IRR = 10%), retrieving profits from pollution reduction (9542 USD/yr), biogas selling (10418 USD/yr), and carbon credit (10294 USD/yr).

PFAS remediation in soil: An evaluation of carbon-based materials for contaminant sequestration

The presence of per- and poly-fluoroalkyl substances (PFAS) in soils is a global concern as these emerging contaminants are highly resistant to degradation and cause adverse effects on human and environmental health at very low concentrations. Sequestering PFAS in soils using carbon-based materials is a low-cost and effective strategy to minimize pollutant bioavailability and exposure, and may offer potential long-term remediation of PFAS in the environment. This paper provides a comprehensive evaluation of current insights on sequestration of PFAS in soil using carbon-based sorbents. Hydrophobic effects originating from fluorinated carbon (C-F) backbone "tail" and electrostatic interactions deriving from functional groups on the molecules' "head" are the two driving forces governing PFAS sorption. Consequently, varying C-F chain lengths and polar functional groups significantly alter PFAS availability and leachability. Furthermore, matrix parameters such as soil organic matter, inorganic minerals, and pH significantly impact PFAS sequestration by sorbent amendments. Materials such as activated carbon, biochar, carbon nanotubes, and their composites are the primary C-based materials used for PFAS adsorption. Importantly, modifying the carbon structural and surface chemistry is essential for increasing the active sorption sites and for strengthening interactions with PFAS. This review evaluates current literature, identifies knowledge gaps in current remediation technologies and addresses future strategies on the sequestration of PFAS in contaminated soil using sustainable novel C-based sorbents.

Suitable biochar application practices simultaneously alleviate N2O and NH3 emissions from arable soils: A meta-analysis study

Nitrogen (N) fertilization profoundly improves crop agronomic yield but triggers reactive N (Nr) loss into the environment. Nitrous (N2O) and ammonia (NH3) emissions are the main Nr species that affect climate change and eco-environmental health. Biochar is considered a promising soil amendment, and its efficacy on individual Nr gas emission reduction has been widely reported. However, the interactions and trade-offs between these two Nr species after biochar addition have not been comprehensively analysed. The influencing factors, such as biochar characteristics, environmental conditions, and management measures, remain uncertain. Therefore, 35 publications (145 paired observations) were selected for a meta-analysis to explore the simultaneous mitigation potential of biochar on N2O and NH3 emissions after its application on arable soil. The results showed that biochar application significantly reduced N2O emission by 7.09% while having no significant effect on NH3 volatilisation. Using biochar with a low pH, moderate BET, or pyrolyzed under moderate temperatures could jointly mitigate N2O and NH3 emissions. Additionally, applying biochar to soils with moderate soil organic carbon, high soil total nitrogen, or low cation exchange capacity showed similar responses. The machine-learning model suggested that biochar pH is a dominating moderator of its efficacy in mitigating N2O and NH3 emissions simultaneously. The findings of this study have major implications for biochar application management and aid the further realisation of the multifunctionality of biochar application in agriculture, which could boost agronomic production while lowering environmental costs.

Interactions between biofilms and PFASs in aquatic ecosystems: Literature exploration

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) have been detected in most aquatic environments worldwide and are referred to as "forever chemicals" because of their extreme chemical and thermal stability. Biofilms, as basic aquatic bioresources, can colonize various substratum surfaces. Biofilms in the aquatic environment have to interact with the ubiquitous PFASs and have significant implications for both their behavior and destiny, which are still poorly understood. Here, we have a preliminary literature exploration of the interaction between PFASs and biofilms in the various aquatic environments and expect to provide some thoughts on further study. In this review, the biosorption properties of biofilms on PFASs and possible mechanisms are presented. The complex impact of PFASs on biofilm systems was further discussed in terms of the composition and electrical charges of extracellular polymeric substances, intracellular microbial communities, and overall contaminant purification functions. Correspondingly, the effects of biofilms on the redistribution of PFASs in the aqueous environment were analyzed. Finally, we propose that biofilm after adsorption of PFASs is a unique ecological niche that not only reflects the contamination level of PFASs in the aquatic environment but also offers a possible "microbial pool" for PFASs biodegradation. We outline existing knowledge gaps and potential future efforts for investigating how PFASs interact with biofilms in aquatic ecosystems.

A review of PFAS adsorption from aqueous solutions: Current approaches, engineering applications, challenges, and opportunities

Per- and polyfluoroalkyl substances (PFAS) have drawn great attention due to their wide distribution in water bodies and toxicity to human beings. Adsorption is considered as an efficient treatment technique for meeting the increasingly stringent environmental and health standards for PFAS. This paper systematically reviewed the current approaches of PFAS adsorption using different adsorbents from drinking water as well as synthetic and real wastewater. Adsorbents with large mesopores and high specific surface area adsorb PFAS faster, their adsorption capacities are higher, and the adsorption process are usually more effective under low pH conditions. PFAS adsorption mechanisms mainly include electrostatic attraction, hydrophobic interaction, anion exchange, and ligand exchange. Various adsorbents show promising performances but challenges such as requirements of organic solvents in regeneration, low adsorption selectivity, and complicated adsorbent preparations should be addressed before large scale implementation. Moreover, the aid of decision-making tools including response surface methodology (RSM), techno-economic assessment (TEA), life cycle assessment (LCA), and multi criteria decision analysis (MCDA) were discussed for engineering applications. The use of these tools is highly recommended prior to scale-up to determine if the specific adsorption process is economically feasible and sustainable. This critical review presented insights into the most fundamental aspects of PFAS adsorption that would be helpful to the development of effective adsorbents for the removal of PFAS in future studies and provide opportunities for large-scale engineering applications.

Impact of biological activated carbon filtration and backwashing on the behaviour of PFASs in drinking water treatment plants

PFASs are present in surface water, tap water and even commercial drinking water and pose a risk to human health. In this study, the treatment efficiency of 14 PFASs was studied in a large drinking water treatment plant (DWTP) using Taihu Lake as the source, and it was found that the ozone/biological activated carbon (O₃-BAC) process was the most effective process for the removal of PFASs in DWTPs. For the O₃-BAC process, there were differences in the removal of PFASs by BACs (1,4,7,13 years) of different ages. The sterilization experiments revealed that for GAC, its physical adsorption capacity reached saturation after one year, while for BAC with mature biofilms, biosorption was the main mechanism for the removal of PFASs. The abundance of Alphaproteobacteria and Gammaproteobacteria in biofilms was positively correlated with the age of the BAC. The microbial community with higher abundance is beneficial to the biodegradation of organic matter and thus provides more active sites for the adsorption of PFASs. PFASs can leak in the early stage of filtration after backwashing, so it is necessary to pay close attention to the influent and effluent concentrations of PFASs during biofilm maturation after backwashing.

Changing bioavailability of per- and polyfluoroalkyl substances (PFAS) to plant in biosolids amended soil through stabilization or mobilization

Biosolids containing per- and polyfluoroalkyl substances (PFAS) could contaminate the receiving environments once they are land applied. In this study, we evaluated the feasibility of controlling the bioavailability of PFAS in biosolids to timothy-grass through stabilization or mobilization approaches. Stabilization was accomplished by adding a sorbent (i.e. granular activated carbon (GAC), RemBind, biochar) to biosolids, while mobilization was achieved by adding a surfactant, sodium dodecyl sulphate (SDS), to biosolids. The results showed that the ΣPFAS concentration in grass shoots grown in biosolids amended soil treated by GAC or RemBind at 2% was only 2.77% and 3.35% of the ΣPFAS concentration detected in shoots grown in biosolids amended soil without a sorbent, respectively, indicating the effectiveness of GAC and RemBind for stabilizing PFAS and reduce their bioavailability. On the other hand, mobilization by adding SDS to biosolids at a dose range of 10-100 mg/kg significantly increased the plant uptake of ΣPFAS by 15.48%-108.57%. Thus, mobilization by adding SDS could be a valuable approach for enhancing the PFAS removal if phytoremediation is applied. Moreover, higher rate of PFAS uptake took place after grass cutting was observed in this study. Thus, proper mowing and regrowth of timothy-grass could lead to efficient and cost-effective removal of PFAS from biosolids amended soil through phytoremediation and leave the site clean to be used for other purposes.

A Polyhydroxybutyrate (PHB)-Biochar Reactor for the Adsorption and Biodegradation of Trichloroethylene: Design and Startup Phase

In this work, polyhydroxy butyrate (PHB) and biochar from pine wood (PWB) are used in a mini-pilot scale biological reactor (11.3 L of geometric volume) for trichloroethylene (TCE) removal (80 mgTCE/day and 6 L/day of flow rate). The PHB-biochar reactor was realized with two sequential reactive areas to simulate a multi-reactive permeable barrier. The PHB acts as an electron donor source in the first “fermentative” area. First, the thermogravimetric (TGA) and differential scanning calorimetry (DSC) analyses were performed. The PHB-powder and pellets have different purity (96% and 93% w/w) and thermal properties. These characteristics may affect the biodegradability of the biopolymer. In the second reactive zone, the PWB works as a Dehalococcoides support and adsorption material since its affinity for chlorinated compounds and the positive effect of the “coupled adsorption and biodegradation” process has been already verified. A specific dechlorinating enriched culture has been inoculated in the PWB zone to realize a coupled adsorption and biodegradation process. Organic acids were revealed since the beginning of the test, and during the monitoring period the reductive dichlorination anaerobic pathway was observed in the first zone; no chlorinated compounds were detected in the effluent thanks to the PWB adsorption capacity.

Coupled Adsorption and Biodegradation of Trichloroethylene on Biochar from Pine Wood Wastes: A Combined Approach for a Sustainable Bioremediation Strategy

Towards chlorinated solvents, the effectiveness of the remediation strategy can be improved by combining a biological approach (e.g., anaerobic reductive dechlorination) with chemical/physical treatments (e.g., adsorption). A coupled adsorption and biodegradation (CAB) process for trichloroethylene (TCE) removal is proposed in a biofilm-biochar reactor (BBR) to assess whether biochar from pine wood (PWB) can support a dechlorinating biofilm by combining the TCE (100 µM) adsorption. The BBR operated for eight months in parallel with a biofilm reactor (BR)-no PWB (biological process alone), and with an abiotic biochar reactor (ABR)-no dechlorinating biofilm (only an adsorption mechanism). Two flow rates were investigated. Compared to the BR, which resulted in a TCE removal of 86.9 ± 11.9% and 78.73 ± 19.79%, the BBR demonstrated that PWB effectively adsorbs TCE and slows down the release of its intermediates. The elimination of TCE was quantitative, with 99.61 ± 0.79% and 99.87 ± 0.51% TCE removal. Interestingly, the biomarker of the reductive dechlorination process, Dehalococcoides mccartyi, was found in the BRR (9.2 × 10⁵ 16S rRNA gene copies/g), together with the specific genes tceA, bvcA, and vcrA (8.16 × 10⁶, 1.28 × 10⁵, and 8.01 × 10³ gene copies/g, respectively). This study suggests the feasibility of biochar to support the reductive dechlorination of D. mccartyi, opening new frontiers for field-scale applications.

Biochar sorption of perfluoroalkyl substances (PFASs) in aqueous film-forming foams-impacted groundwater: Effects of PFASs properties and groundwater chemistry

The widespread use of per- and polyfluoroalkyl substances (PFASs)-related products such as aqueous film-forming foams (AFFF) has led to increasing contamination of groundwater systems. The concentration of PFASs in AFFF-impacted groundwater can be several orders of magnitude higher than the drinking water standard. There is a need for a sustainable and effective sorbent to remove PFASs from groundwater. This work aims to investigate the sorption of PFASs in groundwater by biochar column. The specific objectives are to understand the influences of PFASs properties and groundwater chemistry to PFASs sorption by biochar. The PFASs-spiked Milli-Q water (including 19 PFASs) and four aqueous film-forming foams (AFFF)-impacted groundwater were used. The partitioning coefficients (log K_d) of long chain PFASs ranged from 0.77 to 4.63 while for short chain PFASs they remained below 0.68. For long chain PFASs (C ≥ 7), log K_d increased by 0.5 and 0.8 for each CF₂ moiety of PFCAs and PFSAs, respectively. Dissolved organic matter (DOM) was the most influential factor in PFASs sorption over pH, salinity, and specific ultraviolet absorbance (SUVA). DOM contained hydrophobic compounds and metal ions which can form DOM-PFASs complexes to provide more sorption sites for PFASs. The finding is useful for executing PFASs remediation by biochar filtration column, especially legacy long chain PFASs, for groundwater remediation.

Efficient adsorptive removal of short-chain perfluoroalkyl acids using reed straw-derived biochar (RESCA)

Drinking water and groundwater treatment of perfluoroalkyl acids (PFAAs) heavily relies on adsorption-based approaches using carbonaceous materials, such as granular activated carbon (GAC). Application of GAC is restricted by its inefficiency to remove short-chain PFAAs that have prevalently emerged as substitutes and/or metabolites of long-chain polyfluoroalkyl and perfluoroalkyl substances (PFAS). Here, we synthesized reed straw-derived biochar (RESCA) exhibiting exceptional removal efficiencies (>92%) toward short-chain PFAAs at environment-relevant concentrations (e.g., 1 μg/L). Pseudo-second-order kinetic constants of RESCA were 1.13 and 1.23 L/(mg h) for perfluorobutanoic acid (PFBA) and perfluorobutanesulfonic acid (PFBS), respectively, over six times greater than GAC. SEM imaging and BET analysis revealed the combination of highly hydrophobic surface and scattered distribution of mesopores (2-10 nm in diameter) was associated with the rapid adsorption of short-chain PFAAs. RESCA-packed filters demonstrated effective removal of the mixture of three short-chain and three long-chain PFAAs in the influent with the flow rate up to 45 mL/min. In contrast, GAC-packed filters were significantly less efficient in the removal of short-chain PFAAs, which were also negatively affected by the increase of the flow rate. Efficacy of RESCA-packed filters was also validated in four PFAA-spiked groundwater samples from different sites. Dissolved organic matter (DOC) of >8 mg/L can negatively affect the removal of short-chain PFAAs by RESCA. Feasibility of scaling up the RESCA adsorption system was investigated using breakthrough simulation. Overall, RESCA represents a green adsorbent alternative for the feasible and scalable treatment of a wide spectrum of PFAAs of different chain lengths and functional moieties.

New directions and challenges in engineering biologically-enhanced biochar for biological water treatment

Cost-effective, efficient, and sustainable water treatment solutions utilising existing materials and technology will make it easier for low and middle-income countries to adopt them, improving public health. The ability of biochar to mediate and support microbial degradation of contaminants, combined with its carbon-sequestration potential, has attracted attention in recent years. Biochar is a possible candidate for use in cost-effective and sustainable biological water treatment, especially in agrarian economies with easy access to abundant biomass in the form of crop residues and organic wastes. This review evaluates the scope, potential benefits (economic and environmental) and challenges of sustainable biological water treatment using 'Biologically-Enhanced Biochar' or BEB. We discuss the various processes occurring in BEB systems and demonstrate the urgent need to investigate microbial degradation mechanisms. We highlight the need to correlate biochar properties to biofilm development, which can eventually determine process efficiency. We also demonstrate the various opportunities in adopting BEB as a cheaper and more viable alternative in Low and Middle Income Countries and compare it to the current benchmark, 'Biological Activated Carbon'. We focus on the recent advances in the areas of data science, mathematical modelling and molecular biology to systematically and sustainably design BEB filters, unlike the largely empirical design approaches seen in water treatment. 'Sequential biochar systems' are introduced as specially designed end-of-life techniques to lower the environmental impact of BEB filters and examples of their integration into biological water treatment that can fulfil zero waste criteria for BEBs are given.

Release of soil colloids during flow interruption increases the pore-water PFAS concentration in saturated soil

Groundwater flow through aquifer soils or packed bed systems can fluctuate for various reasons, which could affect the concentration of natural colloids and per- and polyfluoroalkyl substances (PFAS) in the pore water. In such cases, PFAS concentration could either decrease due to matrix diffusion of PFAS or increase by the detachment of colloids carrying PFAS. Yet, the effect of flow fluctuation on PFAS transport or release in porous media has not been examined. To examine the relative importance of either process, we interrupted the flow during an injection of groundwater spiked with perfluorobutanoic acid (PFBA), perfluorooctanoic acid (PFOA), and bromide as conservative tracer through clay-rich soil, so that diffusive transport would be prominent during flow interruption. After flow interruption, the PFAS concentration did not decrease indicating an insignificant contribution of matrix diffusion. The concentration increased, potentially due to enhanced release of colloid-associated PFAS. Analysis of samples before and after flow interruption by particle size analysis and SEM confirmed an increase in soil colloid concentration after the flow interruption. XRD analysis of soil and the colloids proved that PFAS were associated with specific sites of the colloids. Due to a higher affinity of PFOA to soil colloids, the total PFOA concentration in the effluent samples increased more than PFBA after the flow interruption process. The results indicate that colloids may have a disproportionally higher role in the transport of PFAS in conditions that release colloids from porous media. Thus, fluctuations in groundwater flow can increase this colloid facilitated mobility of PFAS.

Biofilms Enhance the Adsorption of Toxic Contaminants on Plastic Microfibers under Environmentally Relevant Conditions

Microplastics (MPs) exposed to the natural environment provide an ideal surface for biofilm formation, which potentially acts as a reactive phase facilitating the sorption of hazardous contaminants. Until now, changes in the contaminant sorption capacity of MPs due to biofilm formation have not been quantified. This is the first study that compared the capacity of naturally aged, biofilm-covered microplastic fibers (BMFs) to adsorb perfluorooctane sulfonate (PFOS) and lead (Pb) at environmentally relevant concentrations. Changes in the surface properties and morphology of aged microplastic fibers (MF) were studied by surface area analysis, infrared spectroscopy, and scanning electron microscopy. Results revealed that aged MFs exhibited higher surface areas because of biomass accumulation compared to virgin samples and followed the order polypropylene>polyethylene>nylon>polyester. The concentrations of adsorbed Pb and PFOS were 4-25% and 20-85% higher in aged MFs and varied among the polymer types. The increased contaminant adsorption was linked with the altered surface area and the hydrophobic/hydrophilic characteristics of the samples. Overall, the present study demonstrates that biofilms play a decisive role in contaminant-plastic interactions and significantly enhance the vector potential of MFs for toxic environmental contaminants. We anticipate that knowledge generated from this study will help refine the planetary risk assessment of MPs.

A review of the occurrence, transformation, and removal of poly- and perfluoroalkyl substances (PFAS) in wastewater treatment plants

Poly- and perfluoroalkyl substances (PFAS) comprise more than 4,000 anthropogenically manufactured compounds with widescale consumer and industrial applications. This critical review compiles the latest information on the worldwide distribution of PFAS and evaluates their fate in wastewater treatment plants (WWTPs). A large proportion (>30%) of monitoring studies in WWTPs were conducted in China, followed by Europe (30%) and North America (16%), whereas information is generally lacking for other parts of the world, including most of the developing countries. Short and long-chain perfluoroalkyl acids (PFAAs) were widely detected in both the influents (up to 1,000 ng/L) and effluents (15 to >1,500 ng/L) of WWTPs. To date, limited data is available regarding levels of PFAS precursors and ultra-short chain PFAS in WWTPs. Most WWTPs exhibited low removal efficiencies for PFAS, and many studies reported an increase in the levels of PFAAs after wastewater treatment. The analysis of the fate of various classes of PFAS at different wastewater treatment stages (aerobic and/aerobic biodegradation, photodegradation, and chemical degradation) revealed biodegradation as the primary mechanism responsible for the transformation of PFAS precursors to PFAAs in WWTPs. Remediation studies at full scale and laboratory scale suggest advanced processes such as adsorption using ion exchange resins, electrochemical degradation, and nanofiltration are more effective in removing PFAS (~95-100%) than conventional processes. However, the applicability of such treatments for real-world WWTPs faces significant challenges due to the scaling-up requirements, mass-transfer limitations, and management of treatment by-products and wastes. Combining more than one technique for effective removal of PFAS, while addressing limitations of the individual treatments, could be beneficial. Considering environmental concentrations of PFAS, cost-effectiveness, and ease of operation, nanofiltration followed by adsorption using wood-derived biochar and/or activated carbons could be a viable option if introduced to conventional treatment systems. However, the large-scale applicability of the same needs to be further verified.

Field study on the transportation characteristics of PFASs from water source to tap water

Perfluoroalkyl substances (PFASs) can occur in water sources, pass through drinking water treatment plants (DWTPs), drinking water distribution systems (DWDSs), to the consumer taps. This investigation was carried out to present the transportation behaviors of 17 PFASs, involving seven DWTPs with different water sources, raw water transportation modes, treatment processes, and DWDS structures in eastern and northern China. The results showed that the long-distance raw water transportation pipelines removed a certain extent of PFASs from raw water, probably due to the accumulation of loose deposits. The long-distance, open-channel South-to-North water diversion increased PFAS contamination risk. In the DWTPs, granular activated carbon (GAC) adsorption and ultraviolet radiation removed less than 25% of PFASs, but ozonation-biological activated carbon (O₃-BAC) was superior to GAC alone in removing PFASs. Loose deposits couldsignificantly influence PFAS accumulation and release within branch-structured DWDSs. In loop-structured DWDSs, finished water with different PFAS characteristics could mix along the pipeline, with the corresponding DWTP as the center, ultimately forming a relatively uniform distribution in the entire DWDS.

Pharmaceutical compound removal efficiency by a small constructed wetland located in south Brazil

The fate of pharmaceuticals during the treatment of effluents is of major concern since they are not completely degraded and because of their persistence and mobility in environment. Indeed, even at low concentrations, they represent a risk to aquatic life and human health. In this work, fourteen pharmaceuticals were monitored in a constructed wetland wastewater treatment plants (WWTP) assessed in both influent and effluent samples. The basic water quality parameters were evaluated, and the removal efficiency of pharmaceutical, potential for bioaccumulation, and the impact of WWTP were assessed using Polar Organic Chemical Integrative Sampler (POCIS) and biofilms. The pharmaceutical compounds were quantified by High Performance Liquid chromatography coupled to mass spectrometry. The sampling campaign was carried out during winter (July/2018) and summer (January/2019). The WWTP performed well regarding the removal of TSS, COD, and BOD₅ and succeeded to eliminate a significant part of the organic and inorganic pollution present in domestic wastewater but has low efficiency regarding the removal of pharmaceutical compounds. Biofilms were shown to interact with pharmaceuticals and were reported to play a role in their capture from water. The antibiotics were reported to display a high risk for aquatic organisms.

Biochar Water Treatment for Control of Organic Micropollutants with UVA Surrogate Monitoring

Biochar adsorbent can be produced in low-resource settings using local materials and simple pyrolysis technology, and it has shown promise for uptake of micropollutants (MPs) such as pesticides, pharmaceuticals, industrial compounds, and chemicals released from consumer goods present in water at ng/L to μg/L levels. Accordingly, the use of biochar in water treatment applications where granular activated carbon (GAC) is economically or logistically infeasible is gaining interest. Monitoring treatment systems for individual MPs require laboratory analytical techniques that are typically cost-prohibitive and impractical for low-resource settings. Therefore, identification of surrogate parameters(s) for adsorbent bed life that can be measured inexpensively and in the field is a high priority. Background dissolved organic matter (DOM) is ubiquitous in natural and anthropogenic waters at concentrations typically 1,000 to 100,000 that of MPs. Some constituents of DOM foul the adsorbent and reduce bed life for removal of target contaminants. Aromatic DOM foulants absorb ultraviolet light at a wavelength of 254 nm (UVA₂₅₄). Because DOM fouling directly affects MP adsorption capacity and DOM is a bulk water parameter that can be quantified using relatively inexpensive and portable instruments, it could be exploited as a surrogate for monitoring biochar adsorber bed life under field conditions. The objective of this study was to quantify removal of MPs from waters containing different types and concentrations of background DOM (surface water, wastewater, dump leachate) and thus exhibiting different UVA₂₅₄ breakthrough profiles in bench-scale column experiments. Breakthrough profiles of weakly to moderately adsorbing MPs, including herbicides, pharmaceuticals and personal care products, and perfluoroalkyl acids, were collected using biochars generated under different pyrolysis conditions and a commercial GAC as a performance benchmark. Optimal conditions for biochar water treatment include using biochar produced from wood at ≥850°C under slightly aerobic conditions, empty bed contact times of ≥30 min, and upstream treatment processes to reduce DOM. Relative UVA₂₅₄ breakthrough (C/C ₀) up to 0.6-0.9 corresponded to ≥90% MP removal for most MP-water combinations studied.

Effect of biofertilizer and wheat straw biochar application on nitrous oxide emission and ammonia volatilization from paddy soil

Biofertilizer can improve soil quality, especially the microbiome composition, which potentially affect soil nitrogen (N) cycling. However, little is known about the responses of nitrous oxide (N₂O) emission and ammonia (NH₃) volatilization from biochar-amended paddy soil to the biofertilizer application. Therefore, we conducted a soil column experiment using four 240 kg N ha^-1 (equivalent to 1.7 g N pot^-1) treatments consisting of biofertilizer (3 t ha^-1, equivalent to 21.2 g pot^-1), biochar (7.5 t ha^-1, equivalent to 63.6 g pot^-1), and a mixture of biofertilizer and biochar at the same rate and a control (CK). The results showed that the N₂O emissions and NH₃ volatilizations were equivalent to 0.15-0.28% and 18.0-31.5% of rice seasonal N applied to the four treatments, respectively. Two treatments with biofertilizer and biochar individual amendment significantly increased (P < 0.05) the N₂O emissions to same degree by 30.2%, while co-application of biochar and biofertilizer further increased the N₂O emission by 74.4% compared to the control. The higher N₂O emission was likely attributed to the increased gene copies of AOA, nirK, and nirS. Applying biofertilizer significantly increased (P < 0.05) NH₃ volatilization by 24.7% relative to the control, while applying biochar had no influence on NH₃ volatilization. Co-application of biofertilizer and biochar significantly decreased (P < 0.05) NH₃ volatilization by 12.3% compared to the control. Overall, the net global warming potential based on NH₃ and N₂O in current study increased by 13.0-26.0% in both the individual- and co-application of biofertilizer and biochar. Interestingly, both individual- and co-applications of biofertilizer and biochar increased the rice grain yield by 16.5-38.3%. Therefore, applications of biofertilizer and biochar did not increase the GHGI. Particularly, the co-applying of them significantly lowered (P < 0.05) the GHGI by 15.2%. In conclusion, biofertilizer and biochar should be co-applied to achieve the goals of environment protection and food security.

Biochar from Pine Wood, Rice Husks and Iron-Eupatorium Shrubs for Remediation Applications: Surface Characterization and Experimental Tests for Trichloroethylene Removal

Nowadays porous materials from organic waste, i.e., Biochar (BC), are receiving increased attention for environmental applications. This study adds information on three BCs that have undergone a number of studies in recent years. A Biochar from pine wood, one from rice husk and one from Eupatorium shrubs enriched with Iron, labelled as PWBC, RHBC and EuFeBC respectively, are evaluated for Trichloroethylene (TCE) removal from aqueous solution. Physical-chemical description is performed by SEM-EDS and BET analysis. The decrease of TCE over time follows a pseudo-second order kinetics with increased removal by the PWBC. Freundlich and Langmuir models well fit equilibrium test data. The optimized values of the maximum adsorbed amount, q_max (mg g⁻¹), follows this order 109.41 PWBC > 30.35 EuFeBC > 21.00 RHBC. Fixed-bed columns are also carried out. Best performance is again achieved by PWBC, which operates for a higher number of pore volume, followed by EuFeBC and RHBC. Continuous testing confirms batch studies and makes it possible to evaluate the workability of materials in configurations closer to reality. Results are promising for potential environmental application. In particular, the characterization of several classes of contaminants opens the doors to possible uses in mixed contamination cases.

Kinetic modelling of the uranium biosorption by Deinococcus radiodurans biofilm

Increasing number of reports on uranium contamination in groundwater bodies is a growing concern. Deinococcus radiodurans biofilm-based U(VI) bioremediation has great potential to provide solution. This study focuses on the kinetic modelling of uranium biosorption by D. radiodurans biofilm biomass and identification of the functional groups involved in the sequestration process. The effect of temperature, pH and amount of biofilm dry mass were studied using two uranyl ion concentrations (100 and 1000 mg/L). D. radiodurans dry biomass showed good affinity for uranyl ion adsorption. The kinetic experiments revealed that the biosorption process was spontaneous and exothermic in nature. The modelling of kinetic adsorption data revealed that U(VI) sorption by D. radiodurans biofilm biomass follows a pseudo-second-order reaction. Mechanism of U(VI) sorption was suggested to follow an intra-particle diffusion model, which includes covalent bonding between U(VI) and functional groups present on the surface of biofilm biomass, and diffusional barrier acts as a rate limiting step. External mass transfer was the rate-limiting step as evident from Boyd and Elovich plot. Chemical modifications in surface functional groups of biofilm biomass, confirmed the involvement of carboxyl, phosphate, and hydroxyl groups in uranium binding as a significant loss in U(VI) sorption capacity was recorded in these chemically modified biomasses. XRD data indicated the formation of metal deposits, predominantly as uranyl phosphates.

Physico-chemical processes

By summarizing 187 relevant research articles published in 2019, the review is focused on the research progress of physicochemical processes for wastewater treatment. This review divides into two sections, physical processes and chemical processes. The physical processes section includes three sub-sections, that is, adsorption, granular filtration, and dissolved air flotation, whereas the chemical processes section has five sub-sections, that is, coagulation/flocculation, advanced oxidation processes, electrochemical, capacitive deionization, and ion exchange. PRACTITIONER POINTS: Totally 187 research articles on wastewater treatment have been reviewed and discussed. The review has two major sections with eight sub-topics.

Combined Vertical-Horizontal Flow Biochar Filter for Onsite Wastewater Treatment—Removal of Organic Matter, Nitrogen and Pathogens

This study investigated the performance of a combined vertical-horizontal flow biochar filter (VFF-HFF) system in terms of organic matter, total nitrogen (Tot-N), Escherichia coli and Salmonella removal and explored the effects of hydraulic loading rate (HLR) on pollutant removal. The combined VFF-HFF system used biochar as the filter medium and comprised two stacked sections: (i) an aerobic vertical flow filter (VFF) in which the wastewater percolated through the biochar medium in unsaturated mode and (ii) a horizontal flow filter (HFF), in which the biochar was saturated with water and had limited access to air, to enable anaerobic conditions and enhance the denitrification process. The system was tested over 126 weeks using real wastewater applied at different HLR (23, 31, 39 L m−2 day−1). The results showed that long-term removal of organic matter in the entire system was 93 ± 3%, with most (87 ± 5%) occurring in the VFF. For Tot-N, the long-term removal was 71 ± 12%, with increasing trends for nitrification in the VFF and denitrification in the HFF. Mean long-term nitrification efficiency in the VFF was 65 ± 15% and mean long-term denitrification efficiency in the HFF 49 ± 14%. Increasing HLR from 23 to 31 L m−2 day−1 increased the nitrification efficiency from 42 to 61%. Increasing the HLR further to 39 L m−2 day−1 decreased the denitrification efficiency from 45 to 25%. HLR had no significant effects on VFF and HFF performance in terms of E. coli and Salmonella removal, although the VFF achieved a 1.09–2.1 log10 unit reduction and the HFF achieved a 2.48–3.39 log10 unit reduction. Thus, long-term performance, i.e., removal of pollutants measured during the last 52 weeks of the experiment, was satisfactory in terms of organic matter and nitrogen removal, with no signs of clogging, indicating good robustness of the combined VFF-HFF biochar filter system.