Deciphering the role of extracellular polymeric substances in the adsorption and biotransformation of organic micropollutants during anaerobic wastewater treatment.

Extracellular polymeric substances (EPS) participate in the removal of organic micropollutants (OMPs), but the primary pathways of removal and detailed mechanisms remain elusive. We evaluated the effect of EPS on removal for 16 distinct chemical classes of OMPs during anaerobic digestion (AD). The results showed that hydrophobic OMPs (HBOMPs) could not be removed by EPS, while hydrophilic OMPs (HLOMPs) were amenable to removal via adsorption and biotransformation of EPS. The adsorption and biotransformation of HLOMPs by EPS accounted up to 19.4 ± 0.9 % and 6.0 ± 0.8 % of total removal, respectively. Further investigations into the adsorption and biotransformation mechanisms of HLOMPs by EPS were conducted utilizing spectral, molecular dynamics simulation, and electrochemical analysis. The results suggested that EPS provided abundant binding sites for the adsorption of HLOMPs. The binding of HLOMPs to tryptophan-like proteins in EPS formed nonfluorescent complexes. Hydrogen bonds, hydrophobic interactions and water bridges were key to the binding processes and helped stabilize the complexes. The biotransformation of HLOMPs by EPS may be attributed to the presence of extracellular redox active components (c-type cytochromes (c-Cyts), c-Cyts-bound flavins). This study enhanced the comprehension for the role of EPS on the OMPs removal in anaerobic wastewater treatment.

Deciphering the behavior and potential mechanism of biochar at different pyrolysis temperatures to alleviate membrane biofouling.

Biofouling limits applications of membrane technology in wastewater treatment, but dosing additives to membrane tanks is an effective method to alleviate biofouling. In this study, biochar derived from corncob and pyrolyzed at 300, 500, and 700°C was dosed to determine the underlying anti-biofouling mechanism. The effects of the biochar on the membrane properties and foulant behavior were systematically investigated. The results showed that biochar delayed the occurrence of the fouling transition (0.5-3.0 h), and decreased the flux decline rate, thus achieving a higher water flux (3.1-3.7 times of the control group). Biochar altered membrane surface properties, and increased the membrane surface charge, roughness, and hydrophilicity, which all contributed to higher membrane permeability. Moreover, adding biochar reduced the number of foulants in the fouling layer, particularly protein substances. The flux model fit and the XDLVO theory further revealed the mitigating effect of biochar on membrane biofouling. At the initial intermediate-blocking stage, the effect of biochar on membrane fouling was determined by its properties, and adsorption capacity to the foulants, BC500 presented the best mitigation performance. At the later cake-filtration stage, the role of biochar in membrane fouling was strongly associated with protein content in the fouling layer, and the minimum rate of flux decline occurred in BC300. This study promotes the understanding and development of biochar to alleviate membrane biofouling.

Quantitative structure-biotransformation relationships of organic micropollutants in aerobic and anaerobic wastewater treatments.

Biotransformation is one of the dominant processes to remove organic micropollutants (OMPs) in wastewater treatment. However, studies on the role of molecular structure in determining the biotransformation rates of OMPs are limited. We evaluated the biotransformation of 14 OMPs belonging to different chemical classes under aerobic and anaerobic conditions, and then explored the quantitative structure-biotransformation relationships (QSBRs) of the OMPs based on biotransformation rates using valid molecular structure descriptors (electrical and physicochemical parameters). Pseudo-first-order kinetic modeling was used to fit the biotransformation rate, and only 2 of the 14 OMPs showed that the biotransformation rate constant (kbio) values were higher under anaerobic conditions than aerobic conditions, indicating that aerobic conditions were more favorable for biotransformation of most OMPs. QSBRs infer that the electrophilicity index (ω) is a reliable predictor for OMPs biotransformation under aerobic conditions. ω corresponds to the interaction between OMPs and microbial enzyme active sites, this process is the rate-limiting step of biotransformation. However, under anaerobic conditions the QSBR based on ω was not significant, indicating that specific functional groups may be more critical than electrophilicity. In conclusion, QSBRs can serve as alternative tools for the prediction of the biotransformation of OMPs and provide further insights into the factors that influence biotransformation.

Biochar enhances the biotransformation of organic micropollutants (OMPs) in an anaerobic membrane bioreactor treating sewage.

The removal of emerging organic micropollutants (OMPs) in anaerobic membrane bioreactors (AnMBRs) has garnered considerable attention owing to the rapid development of AnMBR technology and the increased environmental risk caused by OMP discharge. We investigated the removal efficiency of 22 typical OMPs from sewage being treated in an AnMBR, and implemented and evaluated an upgrading strategy by adding biochar. The average removal efficiency of OMPs was only 76.8% due to hydrophilic OMPs containing electron-withdrawing groups (ketoprofen, ibuprofen, diclofenac, and carbamazepine) being poorly removed. Biochar addition (5.0 g/L) promoted the removal of recalcitrant OMPs by 45%, leading to an enhanced removal efficiency of 88.7%. Although biochar has a high adsorption capacity to different OMPs, the biotransformation rather than sorption removal efficiency of 13 of the 22 OMPs was largely enhanced, suggesting that adsorption-biotransformation was the main approach by which biochar enhances the OMP removal. Biotransformation test and microbial analysis revealed that the enrichment of species (Flavobacterium, Massilia, Acinetobacter, and Cloacibacterium) involved in OMP biotransformation on biochar contributed largely to the enhanced biotransformation removal efficiency of OMPs. In this way, the enhanced electron transfer activity and syntrophic metabolism between hydrogenotrophic methanogens and species that oxidize acetate to H2/CO2 on biochar jointly contributed to the stable CH4 production and OMP biotransformation. This study provides a promising strategy to enhance the OMP removal in AnMBRs and improves our understanding of the underlying mechanism of biochar-amended OMP removal in anaerobic treatment systems.

Partial-nitritation of low-strength anaerobic effluent: A moderate-high dissolved oxygen concentration facilitates ammonia-oxidizing bacteria disinhibition and nitrite-oxidizing bacteria suppression.

Integrating anaerobic treatment with partial nitritation (PN)/anammox is a promising technology to achieve energy-efficient wastewater treatment, while partial nitritation of the mainstream anaerobic effluent (Aneff) was rarely reported. A PN reactor fed with low-strength Aneff was employed in this study to investigate the performance and technology bottleneck of this process. When operated at low dissolved oxygen (DO) concentration (0.30-0.43 mg/L), gene coding hydroxylamine oxidation (hao) was severely suppressed by bio-refractory organics, which results in a decreased ammonia-oxidizing bacteria activity and nitrite accumulation rate. The ammonium conversion and nitrite accumulation were recovered by increasing the DO concentration to a moderate-high level (1.10 ± 0.20 mg/L) and achieved long-term stable operation. At this condition, hao showed a dramatic increase while gene encoding nitrite oxidoreductase was appropriately suppressed; the effluent NO2-/NH4+ ratio reached 1.17, and a low NO3-/NOx- ratio of 0.38 was achieved simultaneously. The findings in this study revealed the adverse effects of Aneff on PN and supported a practical operating strategy for efficient PN of Aneff.

Insight into using up-flow anaerobic sludge blanket-anammox to remove nitrogen from an anaerobic membrane reactor during mainstream wastewater treatment.

A partial nitritation/anammox system treating the effluent of an anaerobic membrane bioreactor was investigated in this study with emphases on the nitrogen conversion and microbial dynamics along the up-flow anaerobic sludge blanket. An average total nitrogen concentration of 12.3 mg/L was achieved in effluent, which resulted in a total nitrogen removal efficiency of 75.9% ± 0.6%, in which the contribution of anammox was over 98%, and mainly occurred at the bottom of the up-flow anaerobic sludge blanket. Furthermore, external nitrite produced from nitrate reduction enhanced the nitrogen removal efficiency. Ca. Brocadia was the dominant anammox bacteria and was enriched at the bottom; Dokdonella and Thermomonas were identified as the denitrifiers for nitrite production and existed in the whole reactor. Findings of this study can be used in a practical model for the future development of integrating anaerobic digestion with partial nitritation/anammox in mainstream wastewater treatment.

Preparation and catalytic performance of alginate-based Schiff Base.

As a biomass polymer, alginate-based material has drawn considerable attention and been applied in many fields. However, the research on alginate-based Schiff Base metal complex is scarce. Herein, a novel alginate-based Schiff Base Cu (II) complex was prepared via oxidation and imidization of alginate by periodate and organic amine, respectively. In additon, their catalytic performance in phenol hydroxylation reaction was investgated. Results illustrated that degree of oxidation had significant influence on metal loaded content. Compared with alginate, the alginate-based Schiff Base has more reactive groups, and can stablize more Cu cations which endowed their better catalytic activities.

Graphene oxide enhanced polyacrylamide-alginate aerogels catalysts.

Biomass aerogel is a promising catalyst and has attracted extensive attention. However, most of the biomass aerogels are fragile, which limits their practical application. Herein, we significantly enhance the mechanical property of biomass aerogel catalysts by 30 times through incorporating graphene oxide into polyacrylamide and Cu-cross-linked alginate formed supper-strong double network aerogels. In addition to enhance the mechanical property, the graphene oxide also significantly increases the catalytic activity. Graphene oxide enhancement for biomass aerogel catalyst provides a new method to develop next generation supper catalysts.