Robust biochar-assisted alleviation of membrane fouling in MBRs by indirect mechanism

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.

Advances from conventional to biochar enhanced biotreatment of dyeing wastewater: A critical review

DW (Dyeing wastewater) contains a large amount of dye organic compounds. A considerable proportion of dye itself or its intermediate products generated during wastewater treatment process exhibits CMR (Carcinogenic/Mutagenic/Toxic to Reproduction) toxicity. Compared with physicochemical methods, biological treatment is advantageous in terms of operating costs and greenhouse gas emissions, and has become the indispensable mainstream technology for DW treatment. This article reviews the adsorption and degradation mechanisms of dye organic compounds in wastewater and analyzed different biological processes, ranging from traditional methods to processes enhanced by biochar (BC). For traditional biological processes, microbial characteristics and communities were discussed, as well as the removal efficiency of different bioreactors. BC has adsorption and redox electron mediated effects, and coupling with biological treatment can further enhance the process of biosorption and degradation. Although BC coupled biological treatment shows promising dye removal, further research is still needed to optimize the treatment process, especially in terms of technical and economic competitiveness.

Aggregation of biochar nanoparticles and the impact on bisphenol A sorption: Experiments and molecular dynamics simulations

The unique properties and environmental implications of biochar nanoparticles (BNPs) have attracted increasing attention. The abundant functional groups and aromatic structures in BNPs may promote the aggregation of BNPs, but the mechanism and implications of this aggregation process remain unclear. Thus, this study investigated the aggregation of BNPs and the sorption of bisphenol A (BPA) on BNPs by combining experimental investigations with molecular dynamics simulations. As the concentration of BNP increased from 100 mg/L to 500 mg/L, the particle size increased from approximately 200 nm to 500 nm, and the exposed surface area ratio in the aqueous phase decreased from 0.46 to 0.05, which confirmed the aggregation of BNPs. The sorption of BPA on BNPs decreased with increasing BNP concentration in both the experiments and molecular dynamics simulations because of BNP aggregation. According to a detailed analysis of the BPA molecules adsorbed on BNP aggregates, the sorption mechanisms were hydrogen bonding, hydrophobic effect, and π-π interactions, which were driven by aromatic rings and O- and N-containing functional groups. The aggregation of BNPs embedded some functional groups in the aggregates and thus inhibited sorption. Interestingly, the steady configuration of the BNP aggregates in the molecular dynamics simulations (2000 ps relaxation) also determined the apparent BPA sorption. BPA molecules were adsorbed in the V-shaped interlayers of the BNP aggregates that acted as semi-closed pores, but could not be adsorbed in the parallel interlayers because of their small layer spacing. This study can provide theoretical guidance for the application of BNPs in pollution control and remediation.

Effects of biochar addition towards the treatment of blackwater in anaerobic dynamic membrane bioreactor (AnDMBR): Comparison among room temperature, mesophilic and thermophilic conditions

Effects of biochar addition on the performance of anaerobic dynamic membrane bioreactor (AnDMBR) under different temperatures for blackwater treatment was investigated. When the organic load ratios (OLR) was 1.0 g COD/L·d, the specific methane yield for the three biochar-amended reactors were 125.7, 148.0 and 182.3 mLCH₄/g COD_removed, respectively. Compare to those digesters without biochar participation, the methane production in the thermophilic reactor with biochar increased by 12% while the other two digesters increased by 6-10%. An analysis of membrane filtration resistance showed a reduction in total resistance (R_t) of 6.2 × 10¹¹-7.3 × 10¹¹ m^-1 when biochar was added to the three reactors. The thermophilic reactors with biochar increased the relative abundance of Methanothermobacter and promoted gene expression of metabolic pathways related to hydrolysis, acid production and methane production. Overall, biochar showed great potential as an inexpensive conductive material to increase methane production with reduced membrane fouling in AnDMBR systems.

Biochar Addition in Membrane Bioreactor Enables Membrane Fouling Alleviation and Nitrogen Removal Improvement for Low C/N Municipal Wastewater Treatment

Membrane bioreactors (MBRs) are frequently used to treat municipal wastewater, but membrane fouling is still the main weakness of this technology. Additionally, the low carbon-nitrogen (C/N) ratio influent has been shown to not only increase the membrane fouling, but also introduce challenges to meet the effluent discharge standard for nitrogen removal. Herein, the authors addressed the challenges by adding cost-effective biochar. The results suggested that the biochar addition can enable membrane fouling alleviation and nitrogen removal improvement. The reduced membrane fouling can be ascribed to the biochar adsorption capacity, which facilitates to form bigger flocs with carbon skeleton in biochar as a core. As a result, the biochar addition significantly altered the mixed liquor suspension with soluble microbial product (SMP) concentration reduction of approximately 14%, lower SMP protein/polysaccharide ratio from 0.28 ± 0.02 to 0.22 ± 0.03, smaller SMP molecular weight and bigger sludge particle size from 67.68 ± 6.9 μm to 113.47 ± 4.8 μm. The nitrogen removal is also dramatically improved after biochar addition, which can be due to the initial carbon source release from biochar, and formation of aerobic-anaerobic microstructures. Microbial diversity analysis results suggested more accumulation of denitrification microbes including norank_f__JG30-KF-CM45 and Plasticicumulans. Less relative abundance of Aeromonas after biochar addition suggested less extracellular polymer substance (EPS) secretion and lower membrane fouling rate.

Biochar addition supports high digestion performance and low membrane fouling rate in an anaerobic membrane bioreactor under low temperatures

The enhancement effects of biochar to an anaerobic membrane bioreactor (AnMBR) treating sewage at low temperatures was investigated in this study through analyzing organics removal, digestion performance, mixed liquor properties, membrane resistance, and foulant compositions. The chemical oxygen demand (COD) removal efficiency and the COD converted to methane rate increased by more than 12.5% at 10 °C, mainly because of the promotion of biochar to volatile fatty acids degradation. Although biochar caused higher dissolved organic matter (DOM) concentration in the AnMBR, it improved the filtration property of the bulk sludge and absorbed the hydrophobic DOM. The decreased filtration resistance assisted by biochar leads to a prolonged membrane operation duration over 200%. Surface foulants, especially cake foulants, were largely mitigated by the enhanced scouring intensity of mixed liquor at the membrane surface, and hence, decreasing the cake/gel foulants ratio.

Performance of anaerobic membrane bioreactor treating landfill leachate

BACKGROUND

Landfill leachate has been known as non-biodegradable/hardly-biodegradable wastewater, which contains significant amount of soluble organic and inorganic compounds. However, membrane bioreactor (MBR) technology have become a more viable treatment option for complex and recalcitrant compounds compared to activated sludge systems.

METHODS

This study aims at evaluating the performance of anaerobic membrane bioreactor (AnMBR) for the treatment of middle/old-aged landfill leachate (LFL).AnMBR was operated at different hydraulic retention times (HRTs) (48-12 h) and relaxation and backwashing (30 min-5 min, 5 min-0.5 min) periods. Additionally, Air stripping (pH 8, 24 g lime/L, 1.4 L/s air flow rate) as a pretreatment was evaluated prior to AnMBR.

RESULTS

Air stripping removed about 90%, 25%, and 64% NH₄ ⁺, COD (Chemical Oxygen Demand) and color (RES₆₂₀), respectively. The best results were obtained in combined air stripping-AnMBR operation corresponding to 95%, and 83% overall removals of color, and COD removals, respectively. Maximum methane yield and COD removal rate in AnMBR were 0.35 L methane/g COD _removed and 5 gCOD removed /L.d, respectively.

CONCLUSION

Pretreatment provided higher AnMBR flux that reached to 5.5LMH but increased fouling frequency due to the calcium precipitates in AnMBR which was verified with SEM-EDX analysis. Additionally, DEHP and DINP were not detected in permeate indicating AnMBR was successful for removing these micropollutants. This study showed that pretreatment clearly increased methane yield and COD removal rate.

A review on facilitating bio-wastes degradation and energy recovery efficiencies in anaerobic digestion systems with biochar amendment

In this review, progress in the potential mechanisms of biochar amendment for AD performance promotion was summarized. As adsorbents, biochar was beneficial for alleviating microbial toxicity, accelerating refractory substances degradation, and upgrading biogas quality. The buffering capacity of biochar balanced pH decreasing caused by volatile fatty acids accumulation. Moreover, biochar regulated microbial metabolism by boosting activities, mediating electron transfer between syntrophic partners, and enriching functional microbes. Recent studies also suggested biochar as potential useful additives for membrane fouling alleviation in anaerobic membrane bioreactors (AnMBR). By analyzing the reported performances based on different operation models or substrate types, debatable issues and associated research gaps of understanding the real role of biochar in AD were critically discussed. Accordingly, Future perspectives of developing biochar-amended AD technology for real-world applications were elucidated. Lastly, with biochar-amended AD as a core process, a novel integrated scheme was proposed towards high-efficient energy-resource recovery from various bio-wastes.

Enhanced treatment performance of phenol wastewater and membrane antifouling by biochar-assisted EMBR

Biochar-assisted EMBR (BC-assisted EMBR) was built to enhance treatment performance of phenol wastewater and membrane antifouling. BC-assisted EMBR significantly increased phenol degradation efficiency, owing to combined effects of biodegradation, adsorption and electro-catalytic degradation. Meanwhile, BC-assisted EMBR obviously mitigated membrane fouling. The coupling effect of BC and voltage led to the lower N-acyl-homoserine lactones (AHLs) and bound extracellular polymeric substances (bound EPS) contents around and on membrane surface. Protein (PN)/polysaccharide (PS) in bound EPS was decreased, led to the increase of negative charge and decrease of hydrophobicity of sludge, which abated bound EPS adsorption on membrane surface. Microbial community analyses revealed that the coupling effect of BC and voltage could enrich phenol-degraders (e.g., Comamonas), electron transfer genus (Phaselicystis), and biopolymer-degraders (Phaselicystis and Tepidisphaera) in BC-assisted EMBR and on its membrane surface, while decrease biofilm-former (e.g., Acinetobacter) and bound EPS-producer (Devosia), which was beneficial to promote phenol treatment and mitigate membrane fouling.

Biological performance and fouling mitigation in the biochar-amended anaerobic membrane bioreactor (AnMBR) treating pharmaceutical wastewater

Anaerobic membrane bioreactor (AnMBR) is an advanced technology in treating pharmaceutical wastewater, but the membrane fouling limits its development. In this study, the biochar with adsorption capacity of biopolymers was added in AnMBR to investigate its potential in treating pharmaceutical wastewater and alleviating membrane fouling. In the biochar-amended AnMBR, adsorbable organic halogen (AOX) was removed effectively, and more COD was biotransformed into CH₄. Membrane fouling mitigation was achieved in the third stage with a 56% decrease of average transmembrane pressure difference (TMP) rising rate. The predominant culprit, proteins of extracellular polymeric substance (EPS-proteins) in sludge mixture and cake layer, was reduced significantly. Particularly, the proportion of micromolecular (0.1-0.15 kDa) EPS-proteins in cake layer was 1.5-folds that of the control group. The important bio-foulant genus Arcobacter aggregating on the membrane had less and almost half the relative abundance (16.5%) than that of the control group (30.7%).

Recent advances in mitigating membrane biofouling using carbon-based materials

Biofouling is the Achilles Heel of membrane processes. The accumulation of organic foulants and growth of microorganisms on the membrane surface reduce the permeability, shorten the membrane life, and increase the energy consumption. Advancements in novel carbon-based materials (CBMs) present significant opportunities in mitigating biofouling of membrane processes. This article provides a comprehensive review of the recent progress in the application of CBMs in antibiofouling membrane. It starts with a detailed summary of the different antibiofouling mechanisms of CBM-containing membrane systems. Next, developments in membrane modification using CBMs, especially carbon nanotubes and graphene family materials, are critically reviewed. Further, the antibiofouling potential of next-generation carbon-based membranes is surveyed. Finally, the current problems and future opportunities of applying CBMs for antibiofouling membranes are discussed.

Response of microbes to biochar strengthen nitrogen removal in subsurface flow constructed wetlands: Microbial community structure and metabolite characteristics

Four subsurface flow constructed wetlands (SFCWs) were constructed on the basis of the volume ratio of biochar in common gravel (0%, 10%, 20%, and 30%) for the evaluation of microbe and metabolite characteristics response to biochar addition. The results showed that the biochar added SFCWs provided higher removal efficiencies for ammonium (49.69%-63.51%) and total nitrogen (81.83%-86.36%), compared with pure gravel packed SFCWs for ammonium (47.40%) and total nitrogen (80.75%), respectively. Illumina MiSeq sequencing results revealed that the dominant phyla were Proteobacteria, Bacteroidetes, and Firmicutes. Biochar addition can improve the removal of nitrogen by altering microbial community and increasing the relative abundance of Thauera, Candidatus Competibacter, Dechloromonas, Desulfobulbus, Chlorobium, and Thiobacillus. Protein and humic substances were the primary components of extracellular polymeric substance (EPS) in SFCWs. The amount of total EPS considerably decreased with biochar addition, which caused a shift in the EPS functional groups including carbonyl of protein, amide, and hydroxyl groups. Moreover, biochar could enhance the high molecular weight compounds metabolized into low molecular compounds. The results can provide new insights into the use of biochar in the enhancement of nitrogen removal by microbial community and metabolic product characteristics.

Extracellular polymeric substances (EPS) modulate adsorption isotherms between biochar and 2,2',4,4'-tetrabromodiphenyl ether

Extracellular polymeric substances (EPS), chars and persistent organic pollutants (POPs) frequently coexist in the environment. However, a knowledge gap exists regarding their interactions. Therefore, we applied 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) as a model POP to investigate the influence of bovine serum albumin (BSA) and sodium alginate (SA) - representing protein and polysaccharide components of EPS - on POP adsorption to biochars. Surface activities of tested biochars were characterised using nuclear magnetic resonance, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The adsorption capacities of BDE-47 on biochars were significantly improved by both EPS analogues: BSA at concentrations of only 5 mg L^-1 and SA at 80 mg L^-1 at c_e = 1 S_w BDE-47 concentration. However, 80 mg L^-1 BSA decreased the BDE-47 adsorption capacities on biochars at the tested BDE-47 concentrations. Chemisorption and pore filling mechanisms appeared to dominate the adsorption process of BDE-47 on maize straw and wheat straw biochars. After adding BSA (or SA), a hydrophobic partition effect was found to best explain the adsorption process and linearity of adsorption was enhanced. These results progress our understanding of bioavailability and migration of POPs: especially relevant to the water industry and biochar/EPS facilitated removal of these contaminants.