Application of Rice-Straw Biochar and Microorganisms in Nonylphenol Remediation: Adsorption-Biodegradation Coupling Relationship and Mechanism

Unveiling the long-term dynamic effects: Biochar mediates bacterial communities to modulate the petroleum hydrocarbon degradation in oil-contaminated sediments

Sediment, as the destination of marine pollutants, often bears much more serious petroleum pollution than water. Biochar is increasingly utilized for remediating organic pollutant-laden sediments, yet its long-term impacts on oil-contaminated sediment remain poorly understood. In this study, simulation experiments adding 2.5 wt% biochars (corn straw and wood chips biochar at different pyrolysis temperatures) were conducted. The effects on petroleum hydrocarbon attenuation, enzyme activities, and microbial community structure were systematically investigated. Results showed enhanced degradation of long-chain alkanes in certain biochar-treated groups. Biochar species and PAH characteristics together lead to the PAHs' attenuation, with low-temperature corn straw biochar facilitating the degradation of phenanthrene, fluorene, and chrysene. Initially, biochars reduced polyphenol oxidase activity but increased urease and dehydrogenase activities. However, there was a noticeable rise in polyphenol oxidase activity for a long time. Biochars influenced bacterial community succession and abundance, likely due to nutrient release stimulating microbial activity. The structural equations model (SEM) reveals that DON affected the enzyme activity by changing the microbial community and thus regulated the degradation of PAHs. These findings shed light on biochar's role in bacterial communities and petroleum hydrocarbon degradation over extended periods, potentially enhancing biochar-based remediation for petroleum-contaminated sediments.

The sorption of Tebuconazole and Linuron from an Aqueous Environment with a Modified Sludge-Based Biochar: Effect, Mechanisms, and Its Persistent Free Radicals Study

In this study, the sludge-based biochar was prepared and utilized as an adsorbent for the removal of two commonly used pesticides in agriculture, namely tebuconazole (Teb) and linuron (Lin) in an aqueous solution. The main contributing factors such as biochar preparation conditions, persistent free radicals as well as contact time, agitation speed, biochar dose, temperature, and pH were investigated. The physicochemical properties were characterized by SEM + EDS, FTIR, BET, EPR, etc. The results showed that the maximum adsorption capacities based on the Langmuir model was 7.8650 mg g−1 for tebuconazole and that based on Freundlich model was 9.0645 mg·g-1 for linuron at 25°C. The pseudo-second-order kinetic equations were all fitted well to the kinetic process of the adsorption of the two pesticides with all R2 ≥ 0.915. The maximum values of tebuconazole adsorption capacity occur at pH = 3. Meanwhile, linuron was not affected by pH. Both Cr6+ (r = −0.793∗∗/ −0.943∗∗) and humic acid (r = −0.798∗∗/ −0.947∗∗) significantly inhibited the adsorption amount of tebuconazole and linuron onto the biochar. Electron spin resonance signals (ESR) indicated that environmentally persistent radicals (EPFRs) are preferentially formed at lower pyrolysis temperatures and lower transition metal concentrations. The g-factors for BC400, BC600, BCF400, and BCF600 were 2.0036, 2.0035, 2.0034, and 2.0033, respectively, indicating that the EPFRs mainly have a carbon-centered structure with adjacent oxygen atoms. In addition, to close to the actual situation, natural water (from YanTai) was collected to simulate pesticide contamination. This study demonstrates that sludge-based biochar can achieve efficient removal of tebuconazole and linuron in aqueous environment in a short period of time with no secondary environmental risk especially on the waste activated sludge.

Study on the Removal Efficiency and Mechanism of Tetracycline in Water Using Biochar and Magnetic Biochar

In this study, a new type of sludge-derived biochar material with high tetracycline removal efficiency, named magnetic Fe3O4 biochar, was accomplished by KOH activated and loaded with magnetic Fe3O4. The particles with spherical pellets observed by SEM, as well as the XRD patterns, indicated that magnetic Fe3O4 nanoparticles were successfully loaded onto the biochar. We studied the adsorption effects and mechanisms of the following three different adsorption materials for tetracycline: biochar (BC), magnetic Fe3O4, and magnetic biochar (MBC), and the loading conditions and reusability of the materials were also considered. The adsorption effects were as follows: Fe3O4 (94.3%) > MBC (88.3%) > BC (65.7%), and the ratio of biochar to ferric salt was 0.2:1; the removal effect reached the best result. Under an acidic condition, the adsorption capacity of all the materials reached the maximum, and the adsorption of tetracycline in water, by three adsorbents, involves chemical adsorption as the leading process and physical adsorption as the auxiliary process. Various characterizations indicated the removal of tetracycline, including pore filling, electrostatic interaction, hydrogen bond action, and cationic-π action. Complex bridging is a unique adsorption mechanism of magnetic Fe3O4 and magnetic biochar. In addition, the magnetic biochar also possesses π–π bond interaction. The magnetic materials can still maintain a certain amount of adsorption capacity on tetracycline after five cycles. This study proved that the magnetic sludge-based biochar are ideal adsorbents for the removal of tetracycline from water, as well as an effective route for the reclamation of waste sludge.

The dominant effect of black carbon on the chemical degradability of PCB1: Sequestration or/and catalysis

Black carbon (BC) plays a crucial role in the migration, transformation, and remediation of hydrophobic organics (HOCs) in soil/sediment. Previous studies mainly focus on the sorption characteristic of BC, while the chemical degradability of HOCs, which is affected by sequestration and catalytic effects of BC, has not yet been systematically studied. In this study, the dechlorination process of 2-chlorobiphenyl (PCB1), adsorbed on BC prepared at different pyrolysis temperatures, by bimetal modified nano zero-valent iron (nZVI/Pd) was investigated. The results showed that, on the one hand, adsorption limited the dechlorination process. PCB1 in the resistant desorption state exhibited lower degradation efficiency than that in other adsorption state. On the other hand, the catalysis of high-temperature BC reduced the inhibition of adsorption on dechlorination to some extent. As the pyrolysis temperature rose from 400 °C to 900 °C, the degradation efficiency of adsorbed PCB1 within 48 h improved from 53.5% to 95.3%, and the rate constant (k_obs) increased from 0.104 h^-1 to 0.197 h^-1. High-temperature BC promoted the electrons release of Fe⁰ and the generation of [H], and its conductivity improved the electron utilization efficiency so that the dechlorination reaction could proceed both on the surface of nZVI/Pd particles and BC, thereby promoting the dechlorination of PCB1. Therefore, adsorption effect dominated degradability of PCB1 sequestrated by low-temperature BC, while for high-temperature BC, synergistic catalytic effect played a dominant role. These findings indicate that reductive efficiency of nZVI should be systematically evaluated according to different types of BC in soil/sediment.

Effect of the structure and micropore of activated and oxidized black carbon on the sorption and desorption of nonylphenol

Activated, oxidized, and solvent-extracted black carbon samples (BCs) were produced from a shale kerogen at temperatures ranging from 250 to 500 °C by chemical activation regents (KOH, ZnCl₂), oxidative regents (H₂O₂, NaClO), and organic solvents, respectively. Extracted organic matter (EOM) and polycyclic aromatic hydrocarbons (PAHs) were quantified in BCs, and they increased and then decreased with increasing temperature. Sorption and desorption isotherms of nonylphenol (NP) on BCs were compared with those previously reported for phenanthrene (Phen). The desorption hysteresis coefficients of NP were greater than those of Phen, while the adsorption capacities of NP were different from those of Phen. The micropore volume and micropore size were critical factors for the micropore filling mechanism of NP in BCs. The ZnCl₂ activation and oxidation treatments were observed to effectively enhance the adsorption of NP and to remove native PAHs from the investigated BCs. But the KOH activation and oxidation treatments were not as efficient as expected. Moreover, the NP desorption hysteresis suggested that a hydrogen bonding and micropore deformation mechanism occurred on the extracted activated BCs. This finding improves our understanding of the sorption and desorption mechanisms of NP from the perspective of the modified BCs and their applications.

Application of biochar for the remediation of polluted sediments

Polluted sediments pose potential threats to environmental and human health and challenges to water management. Biochar is a carbon-rich material produced through pyrolysis of biomass waste, which performs well in soil amendment, climate improvement, and water treatment. Unlike soil and aqueous solutions, sediments are both the sink and source of water pollutants. Regarding in-situ sediment remediation, biochar also shows unique advantages in removing or immobilizing inorganic and organic pollutants (OPs). This paper provides a comprehensive review of the current methods of in-situ biochar amendments specific to polluted sediments. Physicochemical properties (pore structure, surface functional groups, pH and surface charge, mineral components) were influenced by the pyrolysis conditions, feedstock types, and modification of biochar. Furthermore, the remediation mechanisms and efficiency of pollutants (heavy metals [HMs] and OPs) vary with the biochar properties. Biochar influences microbial compositions and benthic organisms in sediments. Depending on the location or flow rate of polluted sediments, potential utilization methods of biochar alone or coupled with other materials are discussed. Finally, future practical challenges of biochar as a sediment amendment are addressed. This review provides an overview and outlook for sediment remediation using biochar, which will be valuable for further scientific research and engineering applications.

Efficient biodegradation of DEHP by CM9 consortium and shifts in the bacterial community structure during bioremediation of contaminated soil

Di(2-ethylhexyl) phthalate (DEHP), the most extensively used plasticizer in plastic formulations, is categorized as a priority environmental contaminant with carcinogenic, teratogenic, and mutagenic toxicities. Many isolated microorganisms exhibit outstanding performance as pure cultures in the laboratory but are unable to cope with harsh environmental conditions in the field. In the present study, a microbial consortium (CM9) with efficient functionality was isolated from contaminated farmland soil. CM9 could consistently degrade 94.85% and 100.00% of DEHP (1000 mg/L) within 24 h and 72 h, respectively, a higher efficiency than those of other reported pure and mixed microorganism cultures. The degradation efficiencies of DEHP and di-n-butyl phthalate were significantly higher than those of dimethyl phthalate and diethyl phthalate (p < 0.05). The primary members of the CM9 consortium were identified as Rhodococcus, Niabella, Sphingopyxis, Achromobacter, Tahibacter, and Xenophilus. The degradation pathway was hypothesized to include both de-esterification and β-oxidation. In contaminated soil, bioaugmentation with CM9 and biochar markedly enhanced the DEHP removal rate to 87.53% within 42 d, compared to that observed by the indigenous microbes (49.31%) (p < 0.05). During simulated bioaugmentation, the dominant genera in the CM9 consortium changed significantly over time, indicating their high adaptability to soil conditions and contribution to DEHP degradation. Rhodococcus, Pigmentiphaga and Sphingopyxis sharply decreased, whereas Tahibacter, Terrimonas, Niabella, Unclassified_f_Caulobacteraceae, and Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium showed considerable increases. These results provide a theoretical framework for the development of in situ bioremediation of phthalate (PAE)-contaminated soil by composite microbial inocula.

Dynamic processes in conjunction with microbial response to disclose the biochar effect on pentachlorophenol degradation under both aerobic and anaerobic conditions

Organochlorines are critical soil contaminants and the use of biochar has recently shown potential to improve soil remediation. However, little is known about biochar-microbe interactions nor the impact on environmental processes such as the immobilization and biodegradation of organochlorine compounds. In this study, we performed microcosm experiments to elucidate how biochar affected the biodegradation and sequestration of pentachlorophenol (PCP). Our results showed that the amendment of biochar markedly inhibited PCP biodegradation due to a strong sorption affinity for PCP under both aerobic and anaerobic conditions. Notably, the inhibitory effect was relatively weaker under anaerobic conditions than under aerobic conditions. The addition of biochar can dramatically shift the bacterial community diversity in the PCP-spiked soils. Under aerobic conditions, biochar significantly stimulated the growth of PCP-degrading bacteria Bacillus and Sphingomonas, but reduced the opportunities for microbes to contact with PCP directly. Under anaerobic conditions, the non-strict organohalide-respiring bacteria Desulfovibrio, Anaeromyxobacter, Geobacter and Desulfomonile were the main drivers of PCP transformation. Our results imply that the use of biochar as a soil remediation strategy for organochlorine compounds should be cautious.

Adsorption and degradation in the removal of nonylphenol from water by cells immobilized on biochar

To investigate the role of adsorption by biochar and biodegradation by bacteria in the wastewater treatment system of microorganisms immobilized on biochar, Nonylphenol (NP) removal (adsorption + degradation) rates and degradation rates from water by NP degrading bacteria immobilized on bamboo charcoal (BC) and wood charcoal (WC) were examined in a short-term and long-term. Results showed that cells immobilized on different biochar had different NP removal effects, and cells immobilized on bamboo charcoal (I-BC) was better. After eight rounds of long-term reuse, the cumulative removal rate and the degradation rate of NP in water by I-BC were 93.95% and 41.86%, respectively, significantly higher than those of cells immobilized on wood charcoal (69.60%, 22.78%) and free cells (64.79%, 19.49%) (P < 0.01). The rise in the ratio of the degradation rate to the removal rate indicated that the long-term NP removal effect is more dependent on biodegradation. The amount of residual NP in I-BC still accounted for about 50%, indicating that the secondary pollution in the disposal of carrier could not be ignored. In addition, promotion effect of biochar on microorganisms were observed by SEM, quantitative PCR and 16S rRNA. Pseudomonas, Achromobacter, Ochrobactrum and Stenotrophomonas were predominant bacteria for NP degradation. The addition of biochar (especially bamboo charcoal) also effectively delayed the transformation of their community structure.

Role of biochar and plant growth promoting rhizobacteria to enhance soil carbon sequestration-a review

Global climate is undergoing significant changes due to extensive release of greenhouse gases (GHGs) such as CO₂ and methane in the atmosphere. These gases are produced and released as a result of anthropogenic activities and fossil fuel burnings which also result in depletion of soil carbon resources. Biochar has various distinctive properties, which contribute to make it an effective, economical, and eco-friendly approach for soil carbon sequestration. The versatility in physicochemical properties of biochar provides an opportunity to optimize its efficacy to obtain desired benefits. A critical review of the literature indicates that biochar and plant growth-promoting microbes have the potential to improve soil organic carbon (SOC). Recent studies have depicted a significant role of the combined application of plant growth-promoting microbes and biochar on SOC dynamics. In future, these areas need to be explored as these have the potential to improve SOC dynamics and it could be a better strategy to sustain natural resources and ultimately mitigation of the climate change.

Biochar accelerates microbial reductive debromination of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) in anaerobic mangrove sediments

A common congener of polybrominated diphenyl ethers, 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), is a prevalent, persistent and toxic pollutant. It could be removed by reduction debromination by microorganisms but the rate is often slow. The study hypothesized that spent mushroom substrate derived biochar amendment could accelerate the microbial reductive debromination of BDE-47 in anaerobic mangrove sediment slurries and evaluated the mechanisms behind. At the end of 20-week experiment, percentages of residual BDE-47 in slurries amended with biochar were significantly lower but debromination products were higher than those without biochar. Such stimulatory effect on debromination was dosage-dependent, and debromination was coupled with iron (Fe) reduction. Biochar amendment significantly enhanced the Fe(II):Fe(III) ratio, Fe(III) reduction rate and the abundance of iron-reducing bacteria in genus Geobacter, thus promoting bacterial iron-reducing process. The abundances of dehalogenating bacteria in genera Dehalobacter, Dehalococcoides, Dehalogenimonas and Desulfitobacterium were also stimulated by biochar. Biochar as an electron shuttle might increase electron transfer from iron-reducing and dehalogenating bacteria to PBDEs for their reductive debromination. More, biochar shifted microbial community composition in sediment, particularly the enrichment of potential PBDE-degrading bacteria including organohalide-respiring and sulfate-reducing bacteria, which in turn facilitated the reductive debromination of BDE-47 in anaerobic mangrove sediment slurries.

Environmental application of biochar: Current status and perspectives

In recent years, there has been a significant interest on biochar for various environmental applications, e.g., pollutants removal, carbon sequestration, and soil amelioration. Biochar has several unique properties, which makes it an efficient, cost-effective and environmentally-friendly material for diverse contaminants removal. The variability in physicochemical properties (e.g., surface area, microporosity, and pH) provides an avenue for biochar to maximize its efficacy to targeted applications. This review aims to highlight the vital role of surface architecture of biochar in different environmental applications. Particularly, it provides a critical review of current research updates related to the pollutants interaction with surface functional groups of biochars and the effect of the parameters variability on biochar attributes pertinent to specific pollutants removal, involved mechanisms, and competence for these removals. Moreover, future research directions of biochar research are also discussed.

Effect of rice-straw biochar on selective biodegradation of nonylphenols in isomer specificity

In a previous study, we found that rice-straw biochar degraded and removed hydrophobic organic contaminants (HOCs) through coupled adsorption-biodegradation. However, few studies have determined whether biochar affects HOC isomer degradation and isomer-selective biodegradation or whether biochar can alter HOC isomer features, resulting in changes to HOC isomer residues in water environments. In this study, the effects of biochar at two dosages (0.001 and 0.01 g) on the biodegradation of ten isomers of a typical xenoestrogen of nonylphenol (NP) were evaluated. The results revealed that there were no effects of biochar on the adsorption of NP isomers. However, biochar addition affected the biodegradation of a specific isomer without altering the features of the NP isomers. The treatment of NP isomers with Pseudoxanthomonas sp. yielded degradation ratios ranging from 60.7 to 100%. At 0.001 g biochar treatment, the degradation of eight NP isomers was enhanced (except for NP₁₉₄ and NP_193a+b) due to their bulky structures. The degradation of the ten NP isomers was inhibited when 0.01 g biochar was added. These findings characterized the effects of biochar on NP isomer contaminants and provided basic information for the application of biochar for the remediation of NP isomer contaminants.

Enhancement of As(v) adsorption from aqueous solution by a magnetic chitosan/biochar composite

In this study, a magnetic chitosan/biochar composite (MCB) was prepared successfully, and characterized by SEM, TEM, VSM, XRD, FTIR, XPS, and zeta-potential to obtain its physical and chemical properties.