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Graphical abstract Highlights • 95% of phosphorus from wastewater was concentrated into Fe-sludge at 25 mg/L FeCl 3. • Phosphorus release and recovery from alkaline Fe-sludge fermentation was studied. • 69.35% of phosphorus was released at pH 11 with 20.57 mg/L. • 90% of the released phosphorus in the fermented liquid can be precipitated as MAP. Abstract Phosphorus release and recovery from Fe-based chemically enhanced primary sedimentation (CEPS) sludge via alkaline fermentation was investigated. The coagulation results showed that 78% of organic matter and 95% of phosphorus were concentrated from sewage into sludge with the optimum dosages of 25 mg/L FeCl 3. The batch fermentation results revealed that 69.35% of the phosphorus in the Fe-sludge can be released and the maximum phosphorus concentration was 20.57 mg/L at pH 11. In the recovery stage, 90% of the P released in the fermented sludge supernatant was precipitated at a 2:1 ratio of magnesium to phosphorus and pH 11. The result of X-ray diffraction indicated that magnesium ammonium phosphate (MAP) was the major component of the precipitated solids. Thus, the present study provides an alternative option for phosphorus release and recovery as MAP from CEPS sludge via alkaline fermentation. [ABSTRACT FROM AUTHOR]

In this study, a thermophilic (65 °C) single-stage wasted activated sludge (WAS) digester was established and the effects of solid retention time (SRT) on the reactor performance were investigated. The result showed that the optimum SRT was 6 days with methane yield of 186.16 mL/g VS. It was found that SRT had little effect on the hydrolysis and volatile solids (VS) destruction, and the high temperature employed seemed sufficient to achieve maximum hydrolysis and VS destruction performance. Longer SRT, however, promoted the release of recalcitrant compounds and impaired acidification, leading to the low methane yield. The microbial community analysis revealed that the dominant pathway for methane production was through syntrophic activity of acetate oxidizing bacteria and hydrogenotrophic methanogens while acetoclastic methanogens were absent in the system. [ABSTRACT FROM AUTHOR]

This study aimed to develop an in-situ sludge pretreatment method by increasing the temperature from thermophilic to extreme thermophilic condition in a single-stage anaerobic digester. The results revealed that a stable performance was obtained within the temperature range of 55–65 °C, and the maximum methane yield of 208.51 ± 13.66 mL/g VS was obtained at 65 °C. Moreover, the maximum extent of hydrolysis (33%) and acidification (27.1%) was also observed at 65 °C. However, further increase of temperature to 70 °C did not improve the organic conversion efficiency. Microbial community analysis revealed that Coprothermobacter , highly related to acetate oxidisers, appeared to be the abundant bacterial group at higher temperature. A progressive shift in methanogenic members from Methanosarcina to Methanothermobacter was observed upon increasing the temperature. This work demonstrated single-stage sludge digestion system can be successfully established at high temperature (65 °C) with stable performance, which can eliminate the need of conventional thermophilic pretreatment step. [ABSTRACT FROM AUTHOR]

High-purity propionate production from glycerol in mixed culture fermentation (MCF) induced by high ammonium concentration was investigated. Fed-batch experiments revealed that higher ammonium concentration (>2.9 g/L) had simultaneous negative effects on acetate and propionate degradation. Propionate production and yield was up to 22.6 g/L and 0.45 g COD/g COD glycerol, respectively, with a purity of 96%. Sequential batch experiments demonstrated that the yields of propionate were 0.3 ± 0.05, 0.32 ± 0.01, and 0.34 ± 0.03 g COD/g COD at a glycerol concentration of 2.78, 4.38, and 5.56 g/L, respectively, and the purity of propionate was 91–100%. Microbial community analysis showed that the phylum Firmicutes dominated the bacterial community at different glycerol concentrations. However, the Methanosaeta population decreased from 46% to 6% when glycerol concentration increased from 2.78 to 5.56 g/L, resulting in lower acetate degradation rate. Thus, the present study might provide an alternative option for the production of propionate from glycerol via MCF. [ABSTRACT FROM AUTHOR]

Acetate is an important industrial chemical and its production from wastes via mixed culture fermentation (MCF) is economic. In this work, the effect of hydraulic retention time (HRT) on acetate production from tofu processing wastewater (TPW) in extreme-thermophilic (70 °C) MCF was first investigated. It was found that long HRT (>3 days) could lead to less acetate production while stable acetate production was achieved at short HRT (3 days) with the yield of 0.57 g-COD/g-COD TPW . The microbial community analysis showed that hydrogenotrophic methanogens (mainly Methanothermobacter ) occupied up to 90% of archaea at both HRTs of 3 and 5 days. However, Coprothermobacter , the main acetate-degraders, decreased from 35.74% to 10.58% of bacteria when HRT decreased from 5 to 3 days, supporting the aggravation of syntrophic acetate oxidation in long HRT. This work demonstrated that HRT was a crucial factor to maintain stable acetate production from TPW in extreme-thermophilic MCF. [ABSTRACT FROM AUTHOR]

A coupling of low-temperature sulfuric acid-assisted carbonization and H 3 PO 4 activation was employed to convert NaOH-pretreated rice husks into activated carbons with extremely high surface area (2028 m 2 g −1 ) and integrated characteristics. The influences of the activation temperature and impregnation ratio on the surface area, pore volume of activated carbons were thoroughly investigated. The morphology and surface chemistry of activated carbons were characterized using N 2 sorption, FTIR, XPS, SEM, TEM, etc. The adsorption capacity of resulting carbons obtained under optimum preparation conditions was systematically evaluated using methylene blue under various simulated conditions. The adsorption process can be well described by both Langmuir isotherm model and the pseudo-second order kinetics models; and the maximum monolayer capacity of methylene blue was ca. 578 mg g −1 . [ABSTRACT FROM AUTHOR]

• Anaerobic acidic and alkaline fermentation in WAS was comprehensively compared. • VFAs yield from alkaline fermentation was 2.7 times higher than acidic fermentation. • Better sludge dewaterability was achieved at acidic fermentation. • Acidic fermentation produced less organics (PN, PS), nutrients (P, N) and metals. • VFAs via acidic fermentation may be a suitable way as carbon source for BNR process. This study conducted a comprehensive comparison of acidic (R 5.0) and alkaline (R 10.0) anaerobic fermentations of waste activated sludge (WAS). The results showed that alkaline fermentation was able to increase biopolymer release and benefitted the production of volatile fatty acids (VFAs). However, large amounts of the released organic matter in the R 10.0 fermented liquid had low biodegradability unsuitable for the biological nutrient removal (BNR) process, resulting in increased C, nitrogen, and phosphorus loads in BNR effluent. Further, Al was more readily released than other metals and its maximum concentration reached 134.52 mg/L in R 10.0 , 2.99 times higher than in R 5.0. The fermented sludge filterability was severely deteriorated at R 10.0 , as indicated by the normalized capillary suction time and specific resistance to filtration. Considering these findings, VFAs from WAS via acidic fermentation may represent a suitable carbon source for direct use in the BNR process. [ABSTRACT FROM AUTHOR]

• VFAs and P production via Al-WAS fermentation with stepwise pH increase was studied. • The maximum yield of VFAs was 358.03 mg-COD/g VS at pH 11. • VFAs yield was enhanced from Al-WAS with step-wise pH operation. • P was also released and the maximum concentration was 186 mg/L at pH 11. • IP release at pH 11 fermentation was originated from NAIP dissolution. In this study, the performance of volatile fatty acids (VFAs) production and phosphorus (P) release during Al-waste activated sludge (Al-WAS) anaerobic fermentation with stepwise pH increases from 8 to 11 was investigated via a long-term acclimation strategy. As results, VFAs concentration increased with increasing pH and the maximum yield of VFAs was 358.03 mg-COD/g VS at pH 11, which was much higher than at pH 8. P was also released during the process, and the P concentration increased gradually from 26 mg/L at pH 8 to 186 mg/L at pH 11, accounting for 35.8% of the total P in the Al-WAS. The P distribution results demonstrated the dissolution of non-apatite inorganic phosphorus (NAIP) and organic P in the sludge contributed to release P into the liquid at pH 8, 9, and 10, while inorganic P release originated from the dissolution of NAIP at pH 11. [ABSTRACT FROM AUTHOR]

• Organics and P recovery from PACl-sludge via alkaline fermentation was studied. • 43.3% of organics and 36.49% of P can be released to fermentation liquid at pH 11. • 24.9% of organics and 27.9% of P from wastewater can be formed to valuable product. • Alkaline fermentation promotes organics and phosphorus recovery from PACl sludge. In this study, alkaline fermentation was applied to promote organics and P recovery from polyaluminum chloride (PACl)-enhanced primary sedimentation sludge. Coagulant results demonstrated that the optimum PACl dosage of 100 mg/L resulted in the effective concentration of 73% of organic matter and 90% of P from wastewater into sludge. Batch fermentation results highlighted the ability of alkaline fermentation in improving the biodegradability of PACl sludge. More specifically, at pH 11, 43.3% of soluble organics and 36.49% of P were released to the fermentation supernatant. Furthermore, P fractionation fermented sludge results revealed that partial Al-P dissolution and organic phosphorus hydrolysis were the main drivers of the released P. Finally, at pH 11, 85% of P was recovered as magnesium ammonium phosphate from the fermentation supernatant at the 2:1 Mg/P molar ratio. In conclusion, 24.9% of organics and 27.9% of P from raw wastewater were converted to valuable products via alkaline fermentation. [ABSTRACT FROM AUTHOR]

• Multiple uses of MgCl 2 addition in WAS alkaline fermentation was investigated. • Higher MgCl 2 concentration inhibited acidogenesis, while it improved the VFAs purity. • Phosphorus removal efficiency was higher than 80% with MgCl 2 addition. • Sludge dewaterability was enhanced with increased MgCl 2 addition. Multiple uses of magnesium chloride during waste activated sludge (WAS) alkaline fermentation was investigated. The results revealed that a higher MgCl 2 concentration inhibited acidogenesis, while the purity of volatile fatty acids (VFAs) improved and the maximum percentage of VFAs accounted for 52.92% (w/w) of soluble chemical oxygen demand (SCOD) at 120 mmol/L Mg2+. A phosphate removal efficiency of 81.22% was obtained at 15 mmol/L MgCl 2 concentration, while only a 14.77% increase was observed when further MgCl 2 was added (120 mmol/L MgCl 2). Capillary suction time (CST) values decreased sharply from 4410.20 s to 207.30 s with the increase of MgCl 2. A similar trend was observed in bound water and the minimum value was 85.56 ± 0.06%. The distribution of extracellular polymeric substances (EPS) and rheological profiles of the fermented sludge were also analyzed and the results confirmed that a high MgCl 2 concentration had a positive effect on sludge dewatering. [ABSTRACT FROM AUTHOR]

[Display omitted] • MCFAs were generated from mixed sludge and THP treated sludge without external EDs. • Self-generated ethanol could serve as the actual ED to elongate SCFAs. • Caproiciproducens predominated the CE populations in the bioreactors. • External ethanol could enhance the reverse β-oxidation pathway. In this study, medium-chain fatty acid (MCFA) generation from mixed sludge (including primary sludge and waste activated sludge) was investigated without additional electron donors (EDs). 0.5 g COD/L of MCFAs was produced and the in situ generated ethanol could serve as the EDs during the anaerobic fermentation of mixed sludge without thermal hydrolysis process (THP) pretreatment. THP increased the MCFA production by approximately 128% in the anaerobic fermentation. During 102 days of operation, the fermentation of THP pre-treated mixed sludge stably generated 2.9 g COD/L MCFAs. The self-generated EDs could not maximize MCFA production, and external addition of ethanol improved MCFA yield. Caproiciproducens was the dominant chain-elongating bacteria. PICRUST2 revealed that both fatty acid biosynthesis and reverse β-oxidation pathways could participate in MCFA synthesis, and ethanol addition could enhance the contribution of the reverse β-oxidation pathway. Future studies should focus on the improvement of MCFA production from THP-assisted sludge fermentation. [ABSTRACT FROM AUTHOR]

[Display omitted] • P release from Al-WAS via wet chemical treatment with reaction time was studied. • P can be effectively released from Al-WAS in both acidic and alkali treatment. • Alkali treatment saved half of reaction time to obtain similar P release efficiency. • Chemical cost in acidic condition was 8.49 times higher than in alkali condition. • Short reaction time coupled with alkalization could improve P release from Al-WAS. In this study, the performance and mechanism of P release from Al-waste activated sludge (WAS) via wet-chemical treatment at different reaction times were investigated. The maximum P release (46% of TP) was achieved at 20 min when the pH was maintained at 2 during acidic treatment. During alkali treatment, the maximum P concentration (363.96 mg/L, 46.07%) was achieved at 10 min when pH was initially adjusted to 12. Acidic treatment took twice as long to achieve the same efficiency of released P as the alkali treatment. Furthermore, P release mainly originated from Al-P and Ca-P during acidic treatment and Al-P dissolution during alkali treatment. The cost of chemical consumption was 483.96 USD/ton TS sludge with acidic treatment, which was 8.49 times higher than that of alkali treatment without pH control. Thus, short reaction times (ca. 10 min) coupled with alkalization provide an effective approach for improving P release from Al-WAS. [ABSTRACT FROM AUTHOR]

• >85% of methane was generated via SAO rather than AM pathway at 50–150 mM acetate. • Almost 100% of methane was produced via SAO pathway at 200 mM acetate. • SWCNT accelerated the methane production from SAO pathway. • Enriched Thermacetogenium and potential DIET contributed to methane acceleration. The effect of single walled carbon nanotubes (SWCNT) on methane production under high acetate concentration and thermophilic condition was evaluated. An isotope labeling experiment verified that >85% of methane was generated from syntrophic acetate oxidation (SAO) at 50, 100 and 150 mM acetate and almost 100% at 200 mM. SWCNT addition had little effect on the methanogenesis pathway, whereas it accelerated methane production via decreasing lag phase times and increasing maximum methane production rates. Electrochemical impedance spectroscopy (EIS) results revealed the electrical resistivity of sludge in groups of SWCNT was distinctly smaller than CK groups, indicating higher sludge conductivity was achieved. Further, the results of communities described that Coprothermobacter and Thermacetogenium played the most important role in SAO under all conditions. Meanwhile, the enriched Thermacetogenium and direct interspecies electron transfer (DIET) pathway in SAO consortia contributed to the acceleration of methane production via SWCNT addition. [ABSTRACT FROM AUTHOR]

The inhibition of acetate under acidic pH is an ideal way to reduce methanogenesis in mesophilic mixed culture fermentation (MCF). However, the effects of acetate concentration and acidic pH on methanogenesis remain unclear. Besides, although hydrogenotrophic methanogens can be suitable targets in MCF, they are generally ignored. Therefore, we intentionally enriched hydrogenotrophic methanogens and found that free acetic acid (FAA, x) concentration and specific methanogenic activity (SMA, y) were correlated according to the equation: y = 0.86 × 0.31/(0.31 + x) (R 2  = 0.909). The SMA was decreased by 50% and 90% at the FAA concentrations of 0.31 and 2.36 g/L, respectively. The coenzyme M concentration and relative electron transport activity agreed well with the FAA concentration. Moreover, the methanogenic activity could not be recovered when the FAA concentration exceeded 0.81 g/L. These findings indicated that neither acetate nor acidic pH, but FAA was the key factor to inhibit methanogenesis in MCF. [ABSTRACT FROM AUTHOR]

The major obstacle for thermophilic anaerobic digestion (TAD) is the inhibited microorganism activity and process instability during the start-up period. This study proposed a strategy to accelerate and stabilize the thermophilic reactors start-up via adding conductive materials. The results show that methane production rate in conductive materials supplemented (CMS) reactors was almost two times higher than the control reactors. Caloramator sp., a candidate of electroactive bacteria, was significantly enriched in the carbon nano-tube (CNT) supplemented groups (12.89%) as compared to control groups (1.26% only). Together with the doubled abundance of Methanosaeta and Methanosarcina methanogens in CMS groups, it is highly possible Caloramator sp. and Methanosaeta / Methanosarcina have established syntrophic direct interspecies electron transfer (DIET), via adopting conductive materials as electron conduit. Microbial community analysis indicates DIET was likely to be an unstable condition triggered syntrophic process. This study demonstrated that conductive materials could promote microbial activity and shorten start-up period for thermophilic anaerobic system. [ABSTRACT FROM AUTHOR]

• N and P were efficiently removed at various NLR in UAFB. • Numerous micron-sized crystals attached on the biofilm were identified as HAP. • Anammox-driven HAP formation was the main mechanism of P recovery. A strategy that integrates the anammox and hydroxyapatite crystallization in an up-flow anaerobic fixed-bed reactor (UAFB) was investigated to simultaneously remove nitrogen and recover phosphorus. During the 430 days of operation, 73.1 ± 6.6% of influent phosphorus was removed with an efficient nitrogen removal efficiency of 87.8 ± 1.7%. After long-term operation, numerous acicular and micron-sized crystals were observed on the matured biofilm, of which the phosphorus content was around 10.21% (wt%) and hydroxyapatite was the main form of crystals through SEM-EDS, FT-IR and XRD analysis. The variation of substrates along the axial length of UAFB showed that phosphate removal was positively correlated with anammox and pH. Moreover, three anammox bacteria including Candidatus Brocadia (19.73%), Candidatus Jettenia (0.49%) and Candidatus Kuenenia (0.85%) were detected at the bottom of UAFB, while Candidatus Jettenia (4.67%) was dominant at the top. Hence, the anammox-based biofilm system could be alternative for the recovery of phosphorus from nutrient-rich wastewater. [ABSTRACT FROM AUTHOR]

• N and P were efficiently removed at various NLR in UAFB. • Numerous micron-sized crystals attached on the biofilm were identified as HAP. • Anammox-driven HAP formation was the main mechanism of P recovery. A strategy that integrates the anammox and hydroxyapatite crystallization in an up-flow anaerobic fixed-bed reactor (UAFB) was investigated to simultaneously remove nitrogen and recover phosphorus. During the 430 days of operation, 73.1 ± 6.6% of influent phosphorus was removed with an efficient nitrogen removal efficiency of 87.8 ± 1.7%. After long-term operation, numerous acicular and micron-sized crystals were observed on the matured biofilm, of which the phosphorus content was around 10.21% (wt%) and hydroxyapatite was the main form of crystals through SEM-EDS, FT-IR and XRD analysis. The variation of substrates along the axial length of UAFB showed that phosphate removal was positively correlated with anammox and pH. Moreover, three anammox bacteria including Candidatus Brocadia (19.73%), Candidatus Jettenia (0.49%) and Candidatus Kuenenia (0.85%) were detected at the bottom of UAFB, while Candidatus Jettenia (4.67%) was dominant at the top. Hence, the anammox-based biofilm system could be alternative for the recovery of phosphorus from nutrient-rich wastewater. [ABSTRACT FROM AUTHOR]