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• Effects of different pH control treatments on WAS fermentation were studied. • The purity of VFAs were enhanced by initial pH 10 fermentation (RIA). • P removal efficiency and fermented sludge dewaterability was also improved in RIA. • VFAs via RIA was a better way to applied as carbon resource into the WWTP. Volatile fatty acids (VFAs) from waste activated sludge (WAS) via alkaline fermentation have been shown to provide an effective alternative carbon source for biological nutrient removal in wastewater treatment plants (WWTPs) that promotes the subsequent release of phosphorus (P) and refractory dissolved organic matter. The dewatering ability of fermented sludge is known to decrease during alkaline fermentation. Here, a novel strategy of initiating fermentation at a pH of 10 was developed to improve VFA purity, P removal efficiency, and fermented sludge dewaterability during WAS fermentation. Although VFAs concentration was lower (1.69 ± 0.09 g COD/L) when the pH was only initially adjusted to pH 10 (R IA) relative to when the pH was maintained at 10 on a daily basis (R DC), the purity of VFAs in the fermented liquid was improved (58.48%). Furthermore, the release of total phosphorous (TP) in R IA was 5.90 times lower than that in R DC (139.37 mg/L). The normalized capillary suction time and specific resistance to filtration in R IA decreased to 42.23% and 40.70%, respectively, suggesting that the dewaterability of fermented sludge also improved. The amount of alkali needed was 17.44 kg for each ton of total solid (TS) in R IA , which was 5.49 times lower than that in R DC. Thus, approximately 45.44 USD was saved in operational costs for each ton of TS processed in R IA. These results indicated that VFAs production via initial pH 10 fermentation was a robust and cost-efficient way for providing carbon resources in WWTPs. [ABSTRACT FROM AUTHOR]

Aluminum-based chemically enhanced primary sedimentation has seen increasing use in wastewater treatment plants. However, the derived sludge (Al-sludge) has low biodegradability due to the inhibition of Al-coagulants on organic hydrolysis, which increases the difficulty of sludge treatment and limits the potential for resource recovery. In this study, the effects of pH adjustment on the pretreatment and fermentation of Al-sludge was investigated, with a focus on sludge hydrolysis and production of volatile fatty acids (VFAs). The effects of abiotic and biotic hydrolysis on sludge disintegration, organics solubilization, and hydrolytic enzyme activity were also evaluated. The results show that adjustment of the pH to between 8.0 and 10.0 was more effective than adjustment to between 2.0 and 6.0 for sludge hydrolysis and subsequent VFA production. The enzymatic activities of protease and α -glucosidase showed a positive correlation with the pH values, leading to the highest VFA yield (275 mg-COD/g-VS) for the initial pH 10.0 condition, with 46% improvement over the control reactor (without pH adjustment). Semi-continuous fermentation was found to be more effective than batch fermentation for the biotic hydrolysis rate, k H . Little phosphorus (<0.1 mg/L) was released from the Al-sludge into the fermented sludge liquor, so P removal was not necessary before the VFAs were used. The wastewater treatment process with Al-based chemically enhanced primary sedimentation and pH adjustment for enhanced sludge fermentation can recover 24% of organic carbon from domestic wastewater. [ABSTRACT FROM AUTHOR]

Iron-based chemically enhanced primary sedimentation (CEPS) is increasingly adopted for wastewater treatment in mega cities, producing a large amount of sludge (Fe-sludge) with a high content of organics for potential organic resource recovery. In this experimental study, acidogenic fermentation was applied treat FeCl 3 -based CEPS sludge for production of volatile fatty acids (VFAs) at different pHs. Batch fermentation tests on the Fe-sludge with an organic content of 10 g-COD/L showed that the maximum VFAs production reached 2782.2 mg-COD/L in the reactor without pH control, and it reached 688.4, 3095.3, and 2603.7 mg-COD/L in reactors with pHs kept at 5.0, 6.0 and 8.0, respectively. Analysis of the acidogenesis kinetics and enzymatic activity indicated that the alkaline pH could accelerate the rate of organic hydrolysis but inhibited the further organic conversion to VFAs. In semi-continuous sludge fermentation tests, the VFAs yield in the pH6 reactor was 20% higher than that in the control reactor without pH regulation, while the VFAs yield in the pH8 reactor was 10% lower than the control. Illumina MiSeq sequencing revealed that key functional microorganisms known for effective sludge fermentation, including Bacteroidia and Erysipelotrichi , were enriched in the pH6 reactor with an enhanced VFAs production, while Clostridia became more abundant in the pH8 reactor to stand the unfavorable pH condition. The research presented acidogenic fermentation as an effective process for CEPS sludge treatment and organic resource recovery and provided the first insight into the related microbial community dynamics. [ABSTRACT FROM AUTHOR]

In this work, a mathematical model was developed to describe the dynamics of fermentation products in sludge alkaline fermentation systems for the first time. In this model, the impacts of alkaline fermentation on sludge disintegration, hydrolysis, acidogenesis, acetogenesis, and methanogenesis processes are specifically considered for describing the high-level formation of fermentation products. The model proposed successfully reproduced the experimental data obtained from five independent sludge alkaline fermentation studies. The modeling results showed that alkaline fermentation largely facilitated the disintegration, acidogenesis, and acetogenesis processes and severely inhibited methanogenesis process. With the pH increase from 7.0 to 10.0, the disintegration, acidogenesis, and acetogenesis processes respectively increased by 53%, 1030%, and 30% while methane production decreased by 3800%. However, no substantial effect on hydrolysis process was found. The model also indicated that the pathway of acetoclastic methanogenesis was more severely inhibited by alkaline condition than that of hydrogentrophic methanogenesis. [ABSTRACT FROM AUTHOR]

Long-term effect of pH (4, 10, and uncontrolled) on short-chain fatty acid (SCFA) accumulation, microbial community and sludge reduction were investigated in waste activated sludge (WAS) fermentors for over 90 days. The average SCFAs accumulation was 1721.4 (at pH 10), 114.2 (at pH 4), and 58.1 (at uncontrolled pH) mg chemical oxygen demand (COD)/L. About 31.65 mg COD/L was produced at pH 10, accounting for 20% of the influent COD. Illumina MiSeq sequencing revealed that Alcaligenes (hydrolic bacteria) and Erysipelothrix (acidogenic bacteria) were enriched at pH 10, while less acidogenic bacteria existed at pH 4 than pH 10, and no acidogenic bacteria were detected at the uncontrolled pH. The ratios of archaea to bacteria were 1:41, 1:16, and 1:9 at the pH of 10, 4, and uncontrolled. This study elucidated the effects of pH on WAS fermentation, and established the correlation of microbial structure with SCFAs accumulations and sludge reduction. [ABSTRACT FROM AUTHOR]

Pretreatment technologies for improving the anaerobic digestion of waste activated sludge have been studied extensively; however, studies on the improvement of pretreatment technology for primary sludge (PS) fermentation and anaerobic digestion are scarce. In this study, a novel mechanical cutting pretreatment (MCP) method was proposed to enhance the performance of PS fermentation and anaerobic digestion. PS was disintegrated by MCP, the average particle size of PS reduced from 45.7 µm to 7.0 µm, and soluble COD (SCOD) increased by 1206 mg/L with pretreatment for 8 min. The hydrolysis and acidification of PS was promoted significantly by MCP. Compared with the control group, the production of SCOD and volatile fatty acids (VFAs) in the pretreatment group during sludge fermentation increased by 167% and 115.3%, respectively. The performance of PS anaerobic digestion was remarkably improved by MCP. The maximum cumulative biogas production in the pretreatment group was 3153 mL, which was 6.33 times that in the control group (498.5 mL). Sludge disintegration by mechanical pretreatment resulted in the enrichment of bacteria, especially Firmicutes , in the sludge fermentation system, and the quantity of bacteria in the pretreatment group was 1.95 times that in the control group. However, MCP had little effect on archaea in the anaerobic digestion of PS, and the methanogens in the control and pretreatment reactors were 1.493 × 109 and 1.519 × 109 copies/g, respectively. [Display omitted] • Primary sludge was crushed by mechanical cutting and particle size reduced by 84.7%. • VFAs yield in sludge fermentation increased by 115.3% after mechanical pretreatment. • Biogas yield in anaerobic digestion increased by 5.33 times by cutting pretreatment. • Primary sludge disintegration resulted in Firmicutes enrichment. [ABSTRACT FROM AUTHOR]

Abstract: New wastewater treatment processes resulting in considerably reduced sludge production and more effective treatment are needed. This is due to the more stringent legislations controlling discharges of wastewater treatment plants (WWTPs) and existing problems such as high sludge production. In this study, the feasibility of implementing biological hydrolysis and acidification process on different types of municipal sludge was investigated by batch and semi-continuous experiments. The municipal sludge originated from six major treatment plants located in Denmark were used. The results showed that fermentation of primary sludge produced the highest amount of volatile fatty acids (VFAs) and generated significantly higher COD- and VFA-yields compared to the other sludge types regardless of which WWTP the sludge originated from. Fermentation of activated and primary sludge resulted in 1.9–5.6% and 8.1–12.6% COD-yields, soluble COD (SCOD)/total COD (TCOD), in batch experiments, respectively. The COD-yields for primary, activated and mixed sludge were 19.1%, 6.5% and 21.37%, respectively, in semi-continuous experiments operated at solids retention time (SRT) of 5d and temperature of 37°C. The benefit of fermentation for full-scale application was roughly estimated based on the experiments performed in semi-continuous reactors. The results revealed that even though the VFA production of primary sludge was higher compared to activated sludge, substantial amounts of VFA could be produced by fermentation of activated sludge due to the substantially higher production of activated sludge in WWTPs. [Copyright &y& Elsevier]

• Butyrate could be utilized to maintain good EBPR performance at 30 °C. • Butyrate had a negative impact on GAOs. • Glycogen turnover was limited with the addition of butyrate. • Accumulibacter and other Rhodocyclaceae PAOs adapted better to butyrate. • Butyrate can support PAOs but not GAOs in tropical climates. Glycogen accumulating organisms (GAOs) are thought to compete with polyphosphate accumulating organisms (PAOs) for the often-limiting carbon sources available in wastewater, deteriorating enhanced biological phosphorus removal (EBPR) performance at high temperatures. Fermentation liquids are often used to provide an additional carbon source supply in EBPR processes, where butyrate is known to be an important volatile fatty acid (VFA) produced in sludge fermentation. Nevertheless, the impact of butyrate on the PAO-GAO competition is not well understood especially at high temperature. The results of this study demonstrate that butyrate, as a supplemental or sole carbon source, could be promising for EBPR in tropical climates. When the carbon source was gradually changed from acetate to butyrate, a substantial PAO population was found under both conditions, despite a substantial shift in the abundance of Candidatus Accumulibacter phosphatis (decreased from 37.4% to 13.9%) to Rhodocyclaceae (increased from 2.0% to 14.5%), where both organisms likely played an important role in P-removal. Thus, a relatively stable P removal performance was realized throughout the whole operation period. Nevertheless, butyrate had a negative impact on GAOs. The biomass concentration and microbial diversity continually decreased in the GAO reactor, and Candidatus Competibacter phosphatis reduced from 27.3% to 6.2%, where the dominant population was replaced by Zoogloea. With the addition of butyrate as carbon source, the total amount of synthesized PHAs reduced in both PAO and GAO cultures and the composition of PHA was greatly changed. The presence of a novel PHA fraction (PHH) may disturb the microbial activity in the aerobic phase, where the GAO culture was more severely affected. Glycogen cycling also seemed to be limited in both reactors. This could reduce the GAO metabolism in both cultures and favor PAOs and P removal. Furthermore, the biomass growth rate of the PAO culture was higher than that of GAO when fed with butyrate, which also provides PAO a competitive advantage. All the above results indicate that butyrate could not be well metabolized by GAOs, but could provide PAOs a competitive advantage. Thus, mixed VFAs (i.e. acetate, propionate and butyrate) are likely to favor PAOs over GAOs in EBPR processes operated in warm climates, where the impact of substantial butyrate fractions represents an advantage towards successful process operation. Image, graphical abstract [ABSTRACT FROM AUTHOR]