A new activated primary tank developed for recovering carbon source and its application

The effect of Fenton sludge on anaerobic digestion of papermaking wastewater in an upflow anaerobic sludge blanket reactor

An upflow anaerobic sludge blanket (UASB) reactor was used to investigate the effect of adding Fenton sludge (FS) on the anaerobic digestion of actual papermaking wastewater. The results showed that a one-time addition of 10 g/L FS could sustainably promote the performance of UASB for more than 40 days. The organic matter removal efficiency increased by 15.56%, and the biogas production increased by 24.52%. The proportion of methane in biogas increased by 12.87%. Adding FS increased the capacitance values of sludge extracellular polymeric substances and the electron transfer system activity in reactor increased by 1.76 times. The dehydrogenase activity and coenzyme F420 of the sludge increased by 1.54 and 2.11 times, respectively. Adding FS enriched the iron-reducing bacteria (Thermodesulfobacteriota) and hydrolytic acid-producing bacteria (Chloroflexota and Synergistota), thereby promoting the hydrolysis and acidification process. Adding FS was beneficial to the enrichment of methanogen, especially Methanosaeta, significantly increasing the methane production.

Key function of Kouleothrix in stable formation of filamentous aerobic granular sludge at low superficial gas velocity with polymeric substrates

Forming and maintaining stable aerobic granular sludge (AGS) at a low superficial gas velocity (SGV) is challenging, particularly with polymeric substrates. This study cultivated filamentous aerobic granular sludge (FAGS) with filamentous Kouleothrix (Type 1851) at low SGV (0.15 cm/s) utilizing mixed acetate-soluble starch. Within approximately 260 days, notable increases in the relative abundance of Kouleothrix (from 4 % to 10 %) and Ca. Competibacter (from 1 % to 26 %) were observed through 16S rRNA gene analysis. Metagenomic analysis revealed increased expression of functional genes involved in volatile fatty acid (VFA) production (e.g., ackA and pta) and polyhydroxyalkanoate synthesis (e.g., phbB and phbC). Kouleothrix acted as a skeleton for bacterial attachment and was the key fermenting bacteria promoting granulation and maintaining granule stability. This study provides insight into the formation of FAGS with low-energy and non-VFA substrates.

Enhanced volatile fatty acid production from waste activated sludge by urea hydrogen peroxide: performance and mechanisms

Anaerobic acidogenesis of waste activated sludge (WAS) presents significant potential for resource recovery and waste treatment. However, the slow hydrolysis of WAS limits the efficiency of this approach. In this study, we applied urea hydrogen peroxide (UHP) pretreatment to enhance WAS hydrolysis and investigated the effects of operating parameters on volatile fatty acid (VFA) production and the associated mechanisms. Results demonstrated that UHP significantly improved WAS hydrolysis and VFA production, with a three-fold increase in soluble chemical oxygen demand (SCOD) compared to the control group. UHP dosage emerged as the most critical factor for VFA production, with the maximum VFA concentration increasing from 1127.6 to 8800.9 mg COD per L as UHP dosage ranged from 0 to 6 mmol g-1 VSS (Volatile suspended solids). At an optimal UHP dosage of 4 mmol g-1 VSS, both the unit oxidant promotion efficiency (ΔVFAs/ΔUHP) and the maximum VFA concentration reached relatively high levels, at 35.3 mg COD per mmol and 7527.3 mg COD per L, respectively. UHP pretreatment generated alkaline conditions, H2O2, ·OH and free ammonia, which collectively disrupted the extracellular polymeric substances (EPS) structure, transforming unextractable EPS into extractable forms and promoting the release of organic matter during both the pretreatment and fermentation stages. Excitation-emission matrix (EEM) analysis revealed that UHP increased the concentration of easily utilizable organic matter, providing more substrates for acidogenic bacteria and enhancing VFA production. Furthermore, weak alkaline conditions and high free ammonia concentrations in the UHP group facilitated VFA accumulation by preventing rapid acidification and suppressing methanogen activity. This study offers valuable insights into the potential of UHP pretreatment for enhancing WAS hydrolysis and VFA production, with promising applications in wastewater treatment and resource recovery.

Systematic review: External carbon source for biological denitrification for wastewater

Nitrogen mitigation is serious environmental issue around the globe. Several methods for wastewater treatment have been introduced, but biological denitrification has been recommended, particularly with addition of the best external carbon source. The key sites of denitrification are wetlands; it can be carried out with different methods. To highlight the aforementioned technology, this paper deals to review the literature to evaluate biological denitrification and to demonstrate cost effective external carbon sources. The results of systematic review disclose the denitrification process and addition of different external carbon sources. The online literature exploration was accomplished using the most well-known databases, that is, science direct and the web of science database, resulting 625 review articles and 3084 research articles, published in peer-reviewed journals between 2015 and 2021 were identified in first process. After doing an in-depth literature survey and exclusion criteria, we started to shape the review from selected review and research articles. A number of studies confirmed that both nitrification and denitrification are significant for biological treatment of wastewater. The studies proved that the carbon source is the main contributor and is a booster for the denitrification. Based on the literature reviewed it is concluded that biological denitrification with addition of external carbon source is cost effective and best option in nitrogen mitigation in a changing world. Our study recommends textile waste for recovery of carbon source.

A comprehensive assessment of upgrading technologies of wastewater treatment plants in Taihu Lake Basin

To meet the increasingly stringent discharge standards of wastewater treatment plants (WWTPs) in the Taihu Lake Basin, the Chinese government successively established the National Special Water Project Program to develop new technologies to retrofit and upgrade existing wastewater treatment processes during the 11th, 12th, and 13th Five-Year Plans. However, there is a lack of systematic sorting of the existing research outcomes, and thus hinders the application and promotion of the upgrade technologies. Based on the outcomes of the National Special Water Project and a field survey, this research analyzed the current status of wastewater treatment in the Taihu Lake Basin and systematically integrated the retrofitting measures of WWTPs in terms of achieving the Grade IA of the national standard and local stricter discharge standards (DB 32/1072-2018 and DB 33/2169-2018). In particular, the boundary conditions, design parameters, specific recommendations of the technologies, and some typical engineering cases were provided accordingly. Finally, this study discussed the future development directions of WWTPs during the upgrade process from the perspective of carbon neutrality and digitalization. The present work will hopefully assist in retrofitting and constructing WWTPs to achieve the stricter effluent discharge criteria and help optimize the design and construction of WWTPs in the best way.

Effects of pH Adjustment on the Release of Carbon Source of Particulate Organic Matter (POM) in Domestic Sewage

The use of anaerobic hydrolytic fermentation to develop more available carbon sources from domestic sewage influent particulate organic matter (POM) has received increasing attention. However, the slow hydrolysis rate of POM limits the application of this technology. This study aimed to improve the carbon source release efficiency of POM by pH adjustment and to reveal the hydrolysis mechanism. Results showed that adjusting the initial pH of POM to 3, 9, and 11 enhanced carbon source release in the anaerobic hydrolysis fermentation process of POM. The pretreatment under pH value of 11 contributed to the highest yield and productivity of carbon source, reaching the soluble chemical oxygen demand (SCOD) of 2782 mg/L at the 4th day. The pH 3 pretreatment was more beneficial for phosphorus resource recovery, which contributed to the highest release concentration of PO43−-P, reaching 48.2 mg/L at the 3rd day, accounting for 90% of TP. Microbial community structure analysis indicated that pH 11 preconditioning promoted the enrichment of proteolytic bacteria (Proteocatella and Proteiniclasticum) and polysaccharide hydrolytic bacteria (Trichococcus and Acinetobacter) and inhibited the growth of acetate-consuming methanogenic archaea, which contributed to the highest carbon release of POM in domestic sewage.

Characteristics of flow regime adjustment enhancing carbon source recovery in activated primary sedimentation tank

In this study, different numbers of baffles were arranged in settling zone of an activated primary sedimentation tank (APST) to adjust the flow regime of sewage, and the characteristics of flow regime adjustment enhancing carbon source recovery in the APST were explored. The results showed that, compared with the APST without baffles, setting one baffle at the front end of settling zone led to the lowest sedimentation loss of soluble chemical oxygen in the settling zone, and the SCOD and volatile fatty acid concentrations in the effluent increased by 52 mg/L and 4.49 mg/L, respectively, furthermore, the SCOD/total nitrogen (TN), and SCOD/total phosphorus (TP) in the effluent also increased by 22.47%, and 11.95%, respectively. To evaluate the mechanism of setting baffles for carbon source recovery, the numerical simulation of flow regime adjustment was utilized. The results showed that, under the condition of setting one baffle, three large recirculation zones were formed which increased the probability of collision and friction between particulates to avoid the dissolved carbon that had been desorbed in the mechanical agitation zone from being re-adsorbed and settling in the settling zone. Moreover, the baffle changed the streamlines of sewage, thereby resuspending more small carbon sources that had already settled and increasing the carbon source content of effluent. Thus, this study provided a new method of adjusting sewage flow regime in APST for enhancing the efficiency of carbon source recovery which could help improving biological nitrogen and phosphorus removal in wastewater treatment plants.

Effect of mechanical elutriation on carbon source recovery from primary sludge in a novel activated primary tank

A novel activated primary tank (APT) with an elutriation unit was developed for recovering carbon by the fermentation and elutriation of primary sludge, and the mechanical elutriation mechanism was analysed by conducting a batch fermentation experiment to improve carbon source recovery. The results indicated that a high stirring velocity gradient could cause sludge disintegration, which could not only shorten the fermentation time, but also increase the production of soluble chemical oxygen demand (SCOD) and volatile fatty acids (VFAs) by 8.3% and 9.5%, respectively. Moreover, mechanical elutriation could also promote the release of SCOD from sludge to water, resulting in an increase in the yield of SCOD by 9.2%, it was observed that elutriation intensity plays a more important role than the elutriation time. The microbial community structure of the fermentation system was influenced by the stirring intensity. The relative abundance of fermentative bacteria in the reactor with a stirring intensity (G) of 160 s^-1 was 13.8%, which was significantly higher than that in the reactor with G = 31 s^-1 (8.037%), so the accumulation of VFAs and SCOD in the reactor with G = 160 s^-1 was improved.

Treatment of low C/N ratio wastewater and biomass production using co-culture of Chlorella vulgaris and activated sludge in a batch photobioreactor

The aim of this work was to study the performance of pollutants removal and biomass production by co-culture of Chlorella vulgaris and activated sludge in a batch photobioreactor (PBR), compared with their single system to treat a low C/N ratio (COD/N = 4.3) wastewater. The co-culture system surpassed activated sludge system in terms of nutrients removal and outperformed microalgae alone system in regard to COD removal. Biomass productivity of the co-culture system was 343.3 mg L^-1 d^-1, and the harvested biomass could be developed as biofuels, animal feeds or soil conditioners due to the improved calorific value and cellular composition compared with activated sludge. The low C/N ratio wastewater enabled bacteria to maintain a relatively low level, hence in favor of microalgae enrichment and nutrient recovery.