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Aiming to strengthen the performance of waste activated sludge digestion, pretreatment is a prerequisite for keeping operations within an industrially acceptable time- frame. In this study, the performance of microaeration coupled with thermophilic (MT) pretreatment on waste activated sludge solubilization and acidification was investigated. The results showed that the maximum soluble organics concentrations, including soluble proteins and carbohydrates, reached 2290 mg COD/L in 24 h when the ventilation rate and temperature were 0.05 vvm and 70 °C. SDS-polyacrylamide gel electrophoresis (SDS-PAGE) test on pure-culture (E.coli) and scanning electron microscopy analysis indicated that MT pretreatment effectively destroyed microbial cell wall and resulted in an increase in soluble proteins. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis revealed that MT pretreatment reduced the diversity of the bacterial community during pretreatment. Along with the dissolution of a large quantity of organic matter, microbial species such as Lactococcus and Methyloversatilis bloomed at the end of acidification period, which contributed to SCFAs production. This study revealed that MT pretreatment facilitated the WAS hydrolysis efficiency and enhanced SCFAs (3149 mg COD/L with fermentation for 96 h) production, especially for acetic acid (50%) accumulation, which provides a new perspective for the application and recovery of sludge resources.

To break the bottlenecks of slow hydrolysis and low acid production efficiency of waste-activated sludge (WAS) in the traditional anaerobic fermentation process, this study investigated the employment of ferrous-iron (Fe(II))-activated sulfite to produce hydroxyl, sulfate, and other highly oxidizing radicals on WAS floc cracking and short-chain fatty acid (SCFAs) production during anaerobic fermentation. The effect of the dosage ratio of Fe(II)/S(IV) was also studied. Results showed that the combined pretreatment of Fe(II)-activated sulfite significantly promoted the exfoliation of extracellular polymers and the subsequent SCFAs production. The highest concentration of SCFAs reached 7326.5 mg COD/L under the optimal dosage of 1:2 for Fe(II)/S(IV), which was 1.1~2.1 times higher than that of other research groups. Meanwhile, the analysis by 3D fluorescence spectroscopy and EPR (electron paramagnetic resonance) showed that Fe(II)-activated sulfite had a synergistic effect on the rupture of sludge cells and the stripping of extracellular polymers, with SO4− and OH as the key radicals generated and being much stronger in the 1:1 and 1:2 groups. High-throughput sequencing showed that the Fe(II)-activated sulfite system significantly changed the functional microbial diversity. The anaerobic fermentation bacteria and sulfate-reducing bacteria were significantly enriched. The underlying mechanism of Fe(II)-activated sulfite oxidation and molecular ecological network of key microbiomes were unveiled. [ABSTRACT FROM AUTHOR]

Persulfate oxidation (PS) is widely employed as a promising alternative for waste activated sludge pretreatment due to the capability of generating free radicals. The product differences and microbiological mechanisms by which PS activation triggers WAS digestion through multiple modes need to be further investigated. This study comprehensively investigated the effects of persulfate oxidation activated through multiple modes, i.e., ferrous, zero-valent iron (ZVI), ultraviolet (UV) and heat, on the performance of sludge digestion. Results showed that PS_ZVI significantly accelerated the methane production rate to 12.02 mL/g VSS. By contrast, PS_Heat promoted the sludge acidification and gained the maximum short-chain fatty acids (SCFAs) yield (277.11 ± 7.81 mg COD/g VSS), which was 3.41-fold compared to that in PS_ZVI. Moreover, ferrous and ZVI activated PS achieved the oriented conversion of acetate, the proportions of which took 73% and 78%, respectively. MiSeq sequencing results revealed that PS_Heat and PS_UV evidently enriched anaerobic fermentation bacteria (AFB) (i.e., Macellibacteroides and Clostridium XlVa). However, PS_Ferrous and PS_ZVI facilitated the enrichment of Woesearchaeota and methanogens. Furthermore, molecular ecological network and mantel test revealed the intrinsic interactions among the multiple functional microbes and environmental variables. The homo-acetogens and sulfate-reducing bacterial had potential cooperative and symbiotic relationships with AFB, while the nitrate-reducing bacteria displayed distinguishing ecological niches. Suitable activation modes for PS pretreatments resulted in an upregulation of genes expression responsible for digestion. This study established a scientific foundation for the application of sulfate radical-based oxidation on energy or high value-added chemicals recovery from waste residues. [Display omitted] • Effect of multiple activated persulfate oxidation on sludge digestion was studied. • Heat and UV activated persulfate effectively promoted the accumulation of SCFAs. • ZVI and Ferrous activated persulfate were beneficial for methane production. • Microbial community structures were altered by multiple persulfate activation modes. • Suitable activation modes for persulfate upregulated the critical genes expression. [ABSTRACT FROM AUTHOR]

Boosting acetate production from waste activated sludge (WAS) fermentation is often hindered by the inefficient solubilization in the hydrolysis step and the high hydrogen pressure ( p H 2) during the acidogenesis of C3–C5 short-chain fatty acid (SCFAs), i.e., propionate (HPr), butyrate (HBu) and valerate (HVa). Therefore, this study employed persulfate (PS) oxidation and C3–C5 incomplete-oxidative sulfate reducing bacteria (io-SRB) metabolizers to tailor SCFAs conversion from WAS fermentation. The decomposition efficiency, performance of SCFAs production was investigated. Results showed that the PS significantly promoted WAS decomposition, with a dissolution rate of 39.4%, which is 26.0% higher than the un-treated test. Furthermore, SCFAs yields were increased to 462.7 ± 42 mg COD/g VSS in PS-HBu-SRB, which was 7.4 and 2.2 times higher than that of un-treated and sole PS tests, respectively. In particular, the sum of acetate and HPr reached the peak value of 85%, indicating that HBu-SRB mediation promoted the biotransformation of HBu and macromolecular organics by reducing the p H 2 restriction. Meanwhile, sulfate radical (SO 4 ∙-)-based oxidation (SR-AOPs) was effective in the decomposition of WAS, the oxidative product, i.e., sulfate served the necessary electron acceptor for the metabolism of io-SRB. Further analysis of Mantel test revealed the cluster of the functional genus and their interaction with environmental variables. Additionally, molecular ecological network analysis explored the potential synergistic and competitive relationships between critical genera. Additionally, the potential synergistic and competitive relationships between critical genera was explored by molecular ecological network analysis. This study provides new insights into the integration of SR-AOPs with microbial mediation in accelerating SCFAs production from WAS fermentation. [Display omitted] • Integration of SR-AOPs and io-SRB mediation tailored SCFAs conversion from WAS. • SR-AOPs efficiently promoted WAS decomposition with hydrolysis rate increased by 26%. • HBu-SRB promoted C2–C3 SCFAs conversion by reducing the p H 2 restriction. • Synergetic relationship among io-SRB and fermentative genera was revealed. • Thermodynamic mechanism of acetate-oriented conversion by io-SRB was explored. [ABSTRACT FROM AUTHOR]

• Advanced pretreatment strategies to promote the release and conversion of inner carbon sources in sludge are reviewed. • The biochemical principles, types and challenges for SCFAs bio-production from waste-activated sludge are comprehensively reviewed. • The principles and progress of fermentation liquid recovery and in situ use for denitrification are reviewed and challenges are summarized. • LCA strategies for the production of SCFAs from sludge and in situ use in WWTPs are reviewed and refined. The increasing waste-activated sludge (WAS) and shortage of carbon source (CSs) production for biological nitrogen removal (BNR) have limited sewage treatment development. However, WAS is CS-rich and contains nutrients and extracellular polymeric substances (EPS), which can be carbon banks for BNR but are difficult to attain and have low bioavailability. Thus, inner CS recycling and in situ use in wastewater treatment plants (WWTPs) are crucial. Pretreatment and bioconversion strategies have been adopted to enhance carbon release and production of bioavailable carbon products, especially short-chain fatty acids (SCFAs). Here, this work reviewed (i) advanced pretreatment methods designed to enhance the release of CSs, including proteins, polysaccharides, lipids, and DNA, by cracking EPS, disintegrating sludge flocs, and cracking cell walls; (ii) WAS-based SCFAs bioproduction to improve SCFAs yield and quality by improving the properties of the fermentation substrate and controlling environmental factors; (iii) fermentation process and recovery of CS and in situ use by removing impurities, recovering CS by dehydration, and replenishing the BNR. Furthermore, life cycle assessment (LCA) of this strategy was reviewed and refined. This review guides optimization of the design of inner CS recycling in WWTP and provides development directions. [Display omitted] [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]

• Coupling SO 4 ∙‾ oxidation with io-SRB mediation enhanced acetogenesis from WAS. • SO 4 ∙‾ and ∙OH were the key radicals responsible for coupled Fe(VI)/S(IV) oxidation. • io-SRB mediation promoted the organics transformation on the basis of SO 4 ∙‾ oxidation. • SO 4 ∙‾/io-SRB altered the structure of WAS fermentative acidogenic microbiome. • Synergistic relationships among io-SRB, hydrolyzing bacteria and acidogens were revealed. Acetate (HAc) production via acetogenesis is a promising biorefinery approach for waste activated sludge (WAS); however, it is hampered by the thermodynamic constraints of the bioconversion of 3–5 carbon atom short-chain fatty acids (SCFAs). Sulfate radical (SO 4 ∙‾)-based advanced oxidation is regarded as an appropriate candidate for accelerating WAS fermentation. In this study, we enriched an incomplete-oxidative sulfate reducing bacteria (io-SRB), combined with SO 4 ∙‾ oxidation (generated by potassium ferrate (PF) and sodium sulfite (Na 2 SO 3)), to boost WAS acetogenesis. Generated sulfate during SO 4 ∙‾ oxidation served as the necessary substrates for io-SRB metabolism. A proof-of-concept based on experimental data for the whole process is presented. Results confirmed that the PF + Na 2 SO 3 + SRB test achieved the maximum SCFAs generation (4261 ± 210 mg COD/L with 60.9 ± 0.5% HAc) over the PF + Na 2 SO 3 test without io-SRB mediation (2521 ± 109 mg COD/L with 50.6 ± 0.3% HAc). Particle size analysis and fluorescence spectroscopy indicated that PF + Na 2 SO 3 oxidation had positive effects on accelerating soluble organics release. SO 4 ∙‾ was the key radical, playing the most important role, as indicated by electron paramagnetic resonance and radical scavenging analysis. X-ray photoelectron spectroscopy revealed that io-SRB mediation further promoted the transformation of polysaccharides and proteins into carboxylic acids, based on SO 4 ∙‾ oxidation. Moreover, 79% Fe(VI) was reduced to Fe(III), and most S(IV) was converted to SO 4 2−, approximately 40% of which was metabolized by io-SRB consortium. Clearly, SO 4 ∙‾ oxidation and io-SRB stimulation significantly altered the composition of the key microbiome, with fermentative acidogenic bacteria predominating. The possible synergistic relationships among io-SRB, hydrolyzing bacteria and acidogens were revealed by molecular ecological network analysis. This study provides new insights into the improvement of value-added bio-metabolite recovery from SO 4 ∙−-based WAS fermentation. [ABSTRACT FROM AUTHOR]

Maximizing the internal carbon sources in raw wastewater was found to be an alternative option to alleviate the financial burden in external carbon sources (ECS) addition to the biological nutrient removal (BNR) process. Based on previous studies on particulate recovery via fine-sieving technologies, alkali pretreatment was used to improve the short-chain fatty acid (SCFA) production from the fine-sieving fractions (FSF). Hydrolysis performance and methane production were monitored to evaluate the reasons for the SCFA boost. Besides, the microbial community structure was evaluated by high-throughput sequencing. Furthermore, mass balance and financial benefits were preliminarily estimated. The results showed that alkali pretreatment effectively promoted the generation of SCFAs with 234 mg/g volatile suspended solids (VSS), almost double that of the control test. This was partially attributed to the efficient hydrolysis, with soluble polysaccharides and protein increased by 2.1 and 1.2 times compared to that of the control, respectively. Inhibition of methanogens was also devoted to the accumulation of SCFAs, with no methane production until 150 h at high pH value. Finally, a preliminary evaluation revealed that 44.51 kg/d SCFAs could be supplied as the electron donor for denitrification, significantly reducing the cost in ECS addition for most wastewater treatment plants (WWTPs) with carbon insufficiency. [ABSTRACT FROM AUTHOR]

Extraction of short-chain fatty acids (SCFAs) from fermentation liquid of waste activated sludge (WAS) is the key bottleneck hindering its application as electron donor in denitrification. This study explores the feasibility of polyether-type polyurethane (PU)-modified layered double hydroxides (LDHs, prepared using eggshell waste as calcium source) in SCFAs adsorbing from WAS fermentation liquid (SFL). The adsorption parameters were first optimized by adsorption tests using artificial fermentation liquid (AFL). Then, adsorption kinetics, thermodynamic and isotherms were explored to further understand the adsorption mechanism. It revealed that SCFAs absorption by PU-LDHs from SFL was an endothermic and spontaneous process with positive enthalphy (ΔH◦) values and negative Gibbs free energy (ΔG◦) values. In addition, the maximum adsorption capacity of 208.0 mg SCFAs/g PU-LDHs was obtained from the Langmuir isotherm. Noting that both soluble carbohydrates and soluble proteins were simultaneously extracted, with efficiencies of 30.9%, 6.2%, respectively, compared with 62.9% SCFAs. The reuse tests confirmed that the prepared PU-LDHs can be used at least three times with high adsorptive capacity. With PU-LDHs-loaded SFL as external carbon source in the biodenitrification process, a denitrification rate of 0.014 mg NO 3 −-N/mg mixed liquid suspended solids (MLSS)·d was recorded. This study provided a sound basis for the preparation of cost-effective biodenitrification carbon source from SFL by a novel adsorbent. Image 1 • A waste-to-resource concept was established for eggshell waste and WAS treatment. • PU-LDHs can be repeatedly used as the carrier of SCFAs with high adsorption capacity. • PU-LDHs retained SFL showed good performance as electron donor in denitrification. • Recycle test confirmed PU-LDHs can be reused multiple times for biodenitrification. [ABSTRACT FROM AUTHOR]

Anaerobic fermentation (AF) could achieve simultaneous recovery of short-chain fatty acids (SCFAs) and phosphorus (P) when waste activated sludge (WAS) and meat processing waste (MPW) act as co-substrate. However, long-chain fatty acids, the degradation intermediates of lipids, always inhibit anaerobic microbial activity. Therefore, sodium hydroxide (NaOH) conditioning was applied to improve the lipid-rich AF performance in this study. The results demonstrated that 96% WAS (v/v) with NaOH addition that remaining at pH 7.5 could achieve the maximum SCFAs yield (1180.05 mg/g VS fed) at 12 d, and ortho-P content in the AF liquor (AFL) was much more than that of without NaOH addition. Anaerovibrio and Aminobacterium , one kind of lipolytic and proteolytic bacteria, respectively, became the major genus in the lipid-rich AF system. 86% of P in the AFL from 96% WAS + pH 7.5 reactor was recovered through vivianite crystallization method, with 91% of SCFAs remaining in the post-AFL. Meanwhile, analysis results verified vivianite formation in the P precipitate products. Overall, this study provided a new idea to achieve SCFAs and P simultaneous recovery from WAS and MPW through AF with NaOH conditioning and vivianite crystallization. [Display omitted] • Meat processing waste and activated sludge were treated by anaerobic fermentation. • NaOH conditioning enhanced SCFAs yield and P release from lipid-rich AF. • Maximal SCFAs yield (1180.05 mg/g VS fed) occurred at pH 7.5 with NaOH addition. • Anaerovibrio , one kind of lipolytic bacteria, was stimulated during lipid-rich AF. • Ortho-P release from the fermentation system was favorable for vivianite recovery. [ABSTRACT FROM AUTHOR]

• 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]

Abstract: The short-chain fatty acids (SCFAs) accumulated in waste activated sludge (WAS) fermentation was adopted as an alternative extra carbon source for biohydrogen production in microbial electrolysis cells (MECs). WAS was pretreated by bi-frequency ultrasonic and the highest SCFAs were accumulated at 3rd day. Three groups of tests were conducted in single chamber MECs for H2 production under different SCOD concentrations. SCOD removals were up to 60% at diluted influent, but reduced to 50% at original concentration. Highest H2 yield was 1.2 mL H2/mg COD at 2-fold dilution with 155% energy efficiency. Results showed that >90% of acetate and ∼90% of propionate were effectively converted to hydrogen, and next were n-butyrate and n-valerate (at dilutions), but <20% of iso-butyrate and iso-valerate were converted. The overall biohydrogen recovery in this study was 120 ml H2/g VSS/d. This work shows a possibility of cascade utilization of WAS fermentation liquid and H2 generation in MEC. [Copyright &y& Elsevier]

[Display omitted] • Fe anode achieved 101–743% higher of hydrogen productivity than other iron sources. • Fe anode led complete removal of phosphate within 2 d (vs. 0–39.4% in other groups). • More crystalline vivianite particles were observed in EF system assisted by Fe anode. • Homo-acetogens (78.0%), EAB (8.0%) and DIRB (2.3%) were enriched in Fe anode group. • Correlation and syntrophy between functional microbes and metabolites were explored. Electro-fermentation (EF) is a promising technology for extracting valuable metabolites from waste biomass, while its effectiveness for phosphorus recovery has received little attention. In this study, we investigated the impact of different iron sources, i.e., FeCl 3 , FeOOH, Fe 2 O 3 , zero-valent iron (ZVI), a built-in Fe anode, and stainless-steel mesh (SSM), on concurrent biohydrogen and vivianite (Fe 3 (PO 4) 2 ·8H 2 O) recovery from sludge fermentation liquid (SFL) in an EF system. Results indicated that the Fe anode group achieved the highest hydrogen productivity of 17.7 mmol/g COD at 5 d, which was 101–743% higher than that of other iron sources. The utilization efficiency of short-chain fatty acids (SCFAs) peaked at 79.1% within 5 d, which was 1.2 folds higher than that of Control (without iron addition). Moreover, the phosphate removal efficiency reached 100% within 2 d and 5 d in Fe anode and SSM group, respectively, while the other groups achieved only 0–39.4% removal. SEM and XRD analyses demonstrated the existence of vivianite particles in the recovered products in the groups of FeCl 3 , FeOOH and Fe anode. Electrochemically active bacteria (EAB), e.g., Geobacter , Comamonas , and Desulfovibrio , accounted for 3.6–60.2% of all groups. Geobacter , Azospira , Comamonas , and Desulfovibrio , which are also considered dissimilatory iron reducing bacteria (DIRB), were enriched to 0.1–40.7% in all groups. Acetoanbacterium and Acetoaerobium , typical homo-acetogens, were enriched to 78.0% in the Fe anode group, while was only 9.0–29.3% in other groups. Correlation and molecular ecological network (MEN) analyses of the functional microbial consortia further indicated the intertrophic interaction. This study provides a theoretical basis for synchronous hydrogen and phosphorus recovery from WAS in the further industrial implementation. [ABSTRACT FROM AUTHOR]