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• 150 mgN/L of nitrate photolysis improved SCFAs production from WAS. • Nitrate increase (150∼375 mgN/L) has no significant promotion on SCFAs in photolysis. • ROS contributed more than RNS on WAS solubilization, hydrolysis and acidification. • Both AFB and NRB enriched for the high SCFAs production and complete denitrification. • Genes related to glycolysis, amino acid, acetate and nitrogen metabolism were enhanced. Nitrate photolysis has become an efficient, low-cost and promising technology for emerging contaminants removal, while its performance and mechanism for waste activated sludge (WAS) treatment is still unknown. This study innovatively introduced nitrate photolysis for WAS disintegration, and investigated the effect of nitrate addition (150–375 mg N/L) for short-chain fatty acids (SCFAs) production during anaerobic fermentation (AF). The results showed that nitrate photolysis significantly promoted the SCFAs production from WAS, and peaked at 280.7 mg/g VSS with 7-d fermentation with 150 mg N/L addition (150N-UV), which increased by 8.8–35.0 % and 10.7–23.3 % compared with other photolysis groups and sole nitrate groups. Effective release of the soluble organics was observed in the nitrate photolysis groups during AF, especially soluble proteins, reaching 1505.4 mg COD/L at 9 d in 150N-UV group, promoted by 7.0∼15.7 % than nitrate/nitrate photolysis groups. The model compounds simulation experiment further demonstrated the positive effect of nitrate photolysis on organics hydrolysis and SCFAs accumulation. The result of the radical capture and quenching verified the reactive oxygen species contributed more compared with reactive nitrogen species. Functional group analysis confirmed the effective bioconversion of the macromolecular organics during the fermentation. Moreover, the nitrate photolysis enhanced the enrichment of the functional consortia, including anaerobic fermentation bacteria (AFB), e.g., Fnoticella, Romboutsia, Gracilibacter and Sedimentibacter , and nitrate reducing bacteria (NRB), e.g., Acinerobacter and Ahniella. The macrogenetic analysis further revealed that glycolysis, amino acid metabolism, acetate metabolism and nitrogen metabolism were the dominating metabolic pathways during fermentation, and the abundance of the relevant genes were enhanced in 150N-UV group. [Display omitted] [ABSTRACT FROM AUTHOR]

Electro-fermentation (EF) has been extensively studied for recovering hydrogen and phosphorus from waste activated sludge (WAS), while was limited for the further application due to the low hydrogen yield and phosphorus recovery efficiency. This study proposed an efficient strategy for hydrogen and vivianite recovery from the simulated sludge fermentation liquid by sacrificial iron anode in EF. The optimum hydrogen productivity and the utilization efficiency of short chain fatty acids (SCFAs) reached 45.2 mmol/g COD and 77.6% at 5 d in pH 8. Phosphate removal efficiency achieved at 90.8% at 2 d and the high crystallinity and weight percentage of vivianite (84.8%) was obtained. The functional microbes, i.e., anaerobic fermentative bacteria, electrochemical active bacteria, homo-acetogens and iron-reducing bacteria were highly enriched and the inherent interaction between the microbial consortia and environmental variables was thoroughly explored. This work may provide a theoretical basis for energy/resource recovery from WAS in the further implementation. [Display omitted] • Enhanced hydrogen and vivianite recovery were realized in pH 8 via Fe mediated EF. • Appropriate iron release led to the higher crystallinity of vivianite in pH 8 group. • EAB, AFB and homo-acetogens preferred to enrich in pH 8 than other pH conditions. • The mutual symbiosis of microbes and environmental factors was the main mechanism in EF. [ABSTRACT FROM AUTHOR]

Waste activated sludge (WAS) is a promising phosphorus (P) source for fertilizer production; however, it is mainly enmeshed inside microbial cells or extracellular polymeric matrixes. Thus, efficient P release is a key goal. This study provided an effective route to simultaneously release organic P (OP) and harvest hydrogen from WAS via bio-electrolysis assisted with prefermentation system (AD_MEC). The clarification of P fractions in both solid and liquid phases and the underlying mechanism in this cascading system were explored. Free nitrous acid (FNA) was employed to enhance WAS hydrolysis. The results showed that hydrogen generation was effectively accelerated: 0.54 mL per gram sludge (in volatile suspended solids (VSS)) was produced from raw WAS (AD_MEC_RWAS), which increased to 1.27 mL/g VSS from FNA-pretreated WAS (AD_MEC_FWAS). The limited OP release by prefermentation was enhanced via MECs; additionally, it was further promoted by FNA, and the treatment time was also shortened. The maximum OP release efficiency reached 54.6% at 112 h (AD_MEC_FWAS). Additionally, non-apatite and inorganic apatite P may regenerate in MECs due to the localized decrease in pH caused by hydrogen generation. This work may provide a scientific basis to enhance P and hydrogen co-recovery from WAS in forthcoming implementation. Image 1 • H 2 recovery and P release from WAS was achieved in cascading conversion system. • The limited OP release in prefermentation was accelerated via bio-electrolysis. • FNA played a positive effect on H 2 recovery and OP release from WAS. • Underlying mechanism of cascading conversion system for P release was explored. [ABSTRACT FROM AUTHOR]

Current studies have employed various chemicals for disintegrating and hydrolyzing microbial cells in waste activated sludge (WAS). However, a comprehensive process assessment over the whole anaerobic digestion process has seldom been proposed. Besides, the characterization of microbial community responses to these chemicals is not well understood. In this study, the effects of five typical chemicals: solubilizer (β-cyclodextrin, CD), alkaline (NaOH), peroxide (peracetic-acid, PA), biological (rhamnolipid, RL) and chemical (sodium dodecylsulphate, SDS) surfactants on WAS digestion were examined. Higher efficiencies of WAS solubilization, hydrolysis and acidification were achieved by CD treatment, followed by RL and SDS. Methanogenesis was also strongly chemicals-dependent. Shifts in microbial community structure were observed in all chemical-pretreated WAS. The community in RL, CD and PA was dominated by microorganisms that anaerobically hydrolyze organics to acids, while that in NaOH and SDS was mainly associated to biogas production. This study proved that the overall performance of WAS digestion was substantially depended on the initial chemical pretreatments, which in turn influenced and was related to the microbial community structures. Although the economic advantage might not be clear yet, the findings obtained in this work may provide a scientific basis for the potential implementation of chemicals for WAS treatment. [ABSTRACT FROM AUTHOR]

The effects of chemosynthetic and biological surfactants on accelerating hydrogen generation from waste activated sludge (WAS) is investigated in a short-cut fermentation-bioelectrochemical system. The specific experiments are conducted in a series of completely stirred tank reactors (CSTRs) and single-chamber microbial electrolysis cells (MECs). Results shows that rhamnolipid (RL) lead to a VFAs yield 1.16-fold and 3.63-fold higher over with sodium dodecylsulphate (SDS) and sodium dodecyl benzene sulfonate (SDBS) treatments in CSTRs on 72 h. By contrast, the corresponding conversion efficiency of methanogenesis is inhibited (0.18 ± 0.03% versus 1.89 ± 0.15% (SDS) and 6.63 ± 0.77% (SDBS)), which is beneficial for subsequent hydrogen production in MECs. The distribution of the acidogenesis metabolites is also affected by the types of surfactants, reflected on cascade changing of hydrogen production. Highest hydrogen yield is 12.90 mg H 2 g −1 VSS in RL-MECs, which is larger than all values that have been reported for fermentation and single-chamber MECs. Current and electrochemical impedance spectroscopy clearly demonstrate the important role of RL treatment in electron/proton transfer and the internal resistance decrease. This study demonstrate the sustainability and attractiveness of WAS short-cut fermentation-elelctrohydrogenesis, providing a sound basis for sludge stabilization and bioenergy recovery. [ABSTRACT FROM AUTHOR]

The effects of three widely-used surfactants on waste activated sludge (WAS) fermentation and microbial community structures were investigated. Rhamnolipid bio-surfactants (RL) showed more positive effects on WAS hydrolysis and acidification compared to chemosynthetic surfactants, such as sodium dodecylsulphate (SDS) and sodium dodecyl benzene sulfonate (SDBS). The highest SCOD and VFAs concentrations obtained with RL were 1.15-fold and 1.16-fold that of SDS, and up to 1.73 and 3.63 times higher than those obtained with SDBS. Pyrosequencing analysis showed that an evident reduction in bacterial diversity in surfactant-treated WAS. Moreover, acid-producing bacteria (such as Megasphaera and Oscillibacter ), detected with RL, were (6.8% and 6.4% in proportion) more abundant than with SDS, and were rarely found in SDBS and the control. The results also revealed that RL allowed efficient hydrolysis enhancement and was favorable to functional microorganisms for further acidification during WAS fermentation. [ABSTRACT FROM AUTHOR]

To improve anaerobic digestibility of waste activated sludge (WAS), a novel treatment was explored by a plant-derived biosurfactant (saponin biosurfactant (SB)). SB showed positive effects on WAS hydrolysis and acidogenesis with increasing concentration, but was insignificant at dosage >0.20 g SB/g total suspended solids (TSS). Soluble protein and carbohydrate concentrations reached 2029 ± 28 and 343 ± 52 mg chemical oxygen demand (COD)/L (0.20 g SB/g TSS, 48 h), which were 4.77-fold and 5.87-fold higher than that without treatment. Volatile fatty acids (VFAs) bioproduction showed a 3.51-fold increase in 72 h. Moreover, acetic acid increased already after 2 h with SB treatment, but after 8 h in the control, indicating that SB accelerated syntrophic acetogenesis from butyric acid degradation to acetic acid. Additionally, methane production was enhanced at lower dosage (<0.05 g SB/g TSS) and inhibited at higher dosage (>0.10 g SB/g TSS), with 63.0 and 20.3 mL/g volatile suspended solids (VSS), respectively, while it was 46.5 mL/g VSS in the control. The results obtained are in good agreement with previous ones obtained with chemosynthetic surfactants. Moreover, SB has advantages of easy production and sustainability of supply, which should promote the implementation for WAS treatment. [ABSTRACT FROM AUTHOR]

Antibiotics in waste activated sludge (WAS) has drawn increasing attention because of their persistent and bioaccumulation characteristics. Most study illustrated the role of antibiotics in anaerobic fermentation from WAS, but lacking the analysis at microbial level as well as the possible interaction between them. This study investigated the effect of three sulfonamide antibiotics (sulfamethoxazole (SMX), sulfaquinoxaline (SQX), and sulfadiazine (SD)) on WAS fermentation and explored its microbiological mechanism. Results indicated that the production of short-chain fatty acids (SCFAs) was significantly improved by 1.9 folds with a peak value at 4626.1 mg COD L−1 in the existence of SD. This was attributed to the promoted release of soluble proteins and polysaccharides with the existence of sulfonamide antibiotics (SAs) as revealed by the excitation-emission matrix (EEM) spectrum. Analysis of microbial community structure showed that the total abundance of the fermenters in groups with SAs was1.2–1.6 times of that in Control. Specifically, the acid-forming genus Tissierella in SMX and SQX increased by 12.1%–15.0% compared with the Control, while the proteolytic genus Proteinivorax dominated in SD with 39.5%. Molecular ecological networks (MENs) analysis further revealed the potential cooperative relationships among different fermenters. This study was anticipated to provide some valuable information for the behavior of antibiotics in WAS fermentation. [Display omitted] • The existence of SMX, SQX and SD facilitated SCFAs production from WAS anaerobic fermentation. • The presence of SMX, SQX and SD enhanced the solubility and biodegradability of proteins and polysaccharides. • The abundance of fermenters was increased in fermentation systems containing SMX, SQX and SD. • The potential cooperative relationships were established among the key microbial community. [ABSTRACT FROM AUTHOR]

Free nitrous acid (FNA) has been recently reported to be an effective and eco-friendly inactivator for waste activated sludge (WAS), while the limited decomposition of the extracellular polymeric substance (EPS) matrix hampers resource recovery from WAS. This work employed peracetic acid (PAA) to assist FNA and explored the contribution of co-pretreatment to hydrogen recovery in a prefermentation-bioelectrolysis cascading system. The results showed that co-pretreatment led to approximately 8.8% and 20.4% increases in the exfoliation of particulate proteins and carbohydrates, respectively, from tightly bound EPS (TB-EPS) over that of sole FNA pretreatment. Electron paramagnetic resonance analysis verified that the synergistic effect of FNA, PAA and various generated free radicals was the essential process. This effect further promoted the accumulation of volatile fatty acids (VFAs) after 96 h of prefermentation, and the peak concentration in co-pretreated WAS (AD-FPWAS) was approximately 2.5-fold that in sole FNA-pretreated WAS (AD-FWAS). Subsequently, the cascading utilization of organics in the bioelectrolysis step contributed to efficient hydrogen generation. A total of 10.8 ± 0.3 mg H 2 /g VSS was harvested in microbial electrolysis cells (MECs) fed with AD-FPWAS, while 6.2 ± 0.1 mg H 2 /g VSS was obtained from AD-FWAS. X-ray photoelectron spectroscopy (XPS) revealed the effective decomposition of the phospholipid bilayer in the cytomembrane and the transformation of macromolecular organics into VFAs and hydrogen in the cascading system. Further microbial community analysis demonstrated that co-pretreatment enhanced the accumulation of functional consortia, including anaerobic fermentative bacteria (AFB, 28.1%), e.g., Macellibacteroides (6.3%) and Sedimentibacter (6.9%), and electrochemically active bacteria (EAB, 57.0%), e.g., Geobacter (39.0%) and Pseudomonas (13.6%), in the prefermentation and MEC steps, respectively. The possible synergetic and competitive relationships among AFB, EAB, homo-acetogens, nitrate-reducing bacteria and methanogens were explored by molecular ecological network analysis. From an environmental and economic perspective, this promising FNA and PAA co-pretreatment approach provides new insight for energy recovery from WAS biorefineries. Image 1 • PAA, FNA and their intermediates led to effective EPS decomposition. • PAA + FNA pretreatment boosted 2.5-fold VFAs and 1.7-fold H 2 recovery versus sole FNA. • XPS confirmed the destruction of phospholipid bilayer and organics transformation. • 28% AFB in prefermentation and 57% EAB in bioelectrolysis were enriched. • Synergetic relationships of AFB, EAB, homoacetogen, NRB and methanogen were explored. [ABSTRACT FROM AUTHOR]