Side-Stream Enhanced Biological Phosphorus Removal (S2EBPR) enables effective phosphorus removal in a pilot-scale A-B stage shortcut nitrogen removal system for mainstream municipal wastewater treatment

While the adsorption/bio-oxidation (A/B) process has been widely studied for carbon capture and shortcut nitrogen (N) removal, its integration with enhanced biological phosphorus (P) removal (EBPR) has been considered challenging and thus unexplored. Here, full-scale pilot testing with an integrated system combining A-stage high-rate activated sludge with B-stage partial (de)nitrification/anammox and side-stream EBPR (HRAS-P(D)N/A-S2EBPR) was conducted treating real municipal wastewater. The results demonstrated that, despite the relatively low influent carbon load, the B-stage P(D)N-S2EBPR system could achieve effective P removal performance, with the carbon supplement and redirection of the A-stage sludge fermentate to the S2EBPR. The novel process configuration design enabled a system shift in carbon flux and distribution for efficient EBPR, and provided unique selective factors for ecological niche partitioning among different key functionally relevant microorganisms including polyphosphate accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs). The combined nitrite from B-stage to S2EBPR and aerobic-anoxic conditions in our HRAS-P(D)N/A-S2EBPR system promoted DPAOs for simultaneous internal carbon-driven denitrification via nitrite and P removal. 16S rRNA gene-based oligotyping analysis revealed high phylogenetic microdiversity within the Accumulibacter population and discovered coexistence of certain oligotypes of Accumulibacter and Competibacter correlated with efficient P removal. Single-cell Raman micro-spectroscopy-based phenotypic profiling showed high phenotypic microdiversity in the active PAO community and the involvement of unidentified PAOs and internal carbon-accumulating organisms that potentially played an important role in system performance. This is the first pilot study to demonstrate that the P(D)N-S2EBPR system could achieve shortcut N removal and influent carbon-independent EBPR simultaneously, and the results provided insights into the effects of incorporating S2EBPR into A/B process on metabolic activities, microbial ecology, and resulted system performance.

Effect of different types of volatile fatty acids on the performance and bacterial population in a batch reactor performing biological nutrient removal

Different ratios of four volatile fatty acids (VFAs) were used as the primary feed to a laboratory scale biological nutrient reactor during four operational stages. The reactor performed efficiently over 500 days of operation with over 90% dissolved phosphorus and over 98% ammonium-nitrogen (NH4+-N) removal. Through in the first experimental phase, acetate and propionate were present in a significant proportion as carbon sources, the relative abundance of Candidatus Accumulibacter, a potential polyphosphate accumulating organism, increased from 10% to 57% and the Defluviicoccus genus, a known glycogen accumulating organism (GAO), decreased from 41% to 5%. Further tests indicated the presence of denitrifying phosphorus accumulating organisms (DPAO) belonging to Clade IIC, that could use nitrite as the electron acceptor during P-uptake. In general, VFAs favored the increase of the genus Defluviicoccus and Candidatus Accumulibacter. High relative abundance of Defluviicoccus did not affect the stability and the performance of the BNR process.

Comprehensive understanding of DOM reactivity in anaerobic fermentation of persulfate-pretreated sewage sludge via FT-ICR mass spectrometry and reactomics analysis

Understanding the composition and reactivity of dissolved organic matter (DOM) at molecular level is vital for deciphering potential regulators or indicators relating to anaerobic process performance, though it was hardly achieved by traditional analyses. Here, the DOM composition, molecular reactivity and transformation in the enhanced sludge fermentation process were comprehensively elucidated using high-resolution mass spectrometry measurement, and data mining with machine learning and paired mass distance (PMD)-based reactomics. In the fermentation process for dewatered sludge, persulfate (PDS) pretreatment presented its highest performance in improving volatile fatty acids (VFAs) production with the increase from 2,711 mg/L to 3,869 mg/L, whereas its activation in the presence of Fe (as well as the hybrid of Fe and activated carbon) led to the decreased VFAs production performance. In addition to the conventional view of improved decomposition and solubilization of N-containing structures from sludge under the sole PDS pretreatment, the improved VFAs production was associated with the alternation of DOM molecular compositions such as humification generating molecules with high O/C, N/C, S/C and aromatic index (AI_mod). Machine learning was capable of predicting the DOM reactivity classes with 74-76 % accuracy and found that these molecular parameters in addition to nominal oxidation state of carbon (NOSC) were among the most important variables determining the generation or disappearance of bio-resistant molecules in the PDS pretreatment. The constructed PMD-based network suggested that highly connected molecular network with long path length and high diameter was in favor of VFAs production. Especially, -NH related transformation was found to be active under the enhanced fermentation process. Moreover, network topology analysis revealed that CHONS compounds (e.g., C₁₃H₂₇O₈N₁S₁) can be the keystone molecules, suggesting that the presence of sulfur related molecules (e.g., cysteine-like compounds) should be paid more attention as potential regulators or indicators for controlling sludge fermentation performance. This study also proposed the non-targeted DOM molecular analysis and downstream data mining for extending our understanding of DOM transformation at molecular level.

Realization of partial nitrification and in-situ anammox in continuous-flow anaerobic/aerobic/anoxic process with side-stream sludge fermentation for real sewage

A continuous-flow anaerobic/aerobic/anoxic reactor with complete suspended activated sludge using sludge alkaline fermentation products as carbon source was utilized to strengthen nitrogen removal performance for low C/N ratio (<4) wastewater. Long-time performance indicated that the nitrite accumulation rate reached 60.40%, which strengthened the contribution of anammox. The average total inorganic nitrogen removal efficiency improved 19.40%. The abundance of ammonia oxidizing bacteria has not changed, but the abundance of nitrite oxidizing bacteria reduced from 5.79% to 0.69%. Quantitative PCR results demonstrated that the abundance of anammox bacteria has raised by 80.5 times. These results indicated that side-stream sludge alkaline fermentation promoted the mainstream partial nitrification, consequently accelerating the in-situ enrichment of anammox bacteria. No external carbon source dosing and short oxic hydraulic retention time (5.3 h) save energy and reduce consumption significantly in this system.

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.

A novel strategy for improving volatile fatty acid purity, phosphorus removal efficiency, and fermented sludge dewaterability during waste activated sludge fermentation

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.

An integrated membrane bioreactor system with iron-dosing and side-stream co-fermentation for enhanced nutrient removal and recovery: System performance and microbial community analysis

An integrated membrane bioreactor (MBR) system was developed for enhanced nutrient (N and P) removal and effective P recovery in wastewater treatment. The system consisted of an iron-dosing MBR and side-stream fermentation for P removal and recovery and side-stream denitrification for N removal. Around 98.1% of the total phosphorus (TP) in wastewater was removed by ferric iron-induced precipitation and membrane filtration in the aerobic MBR, and nearly 53.4% of the TP could be recovered via anaerobic fermentation from the MBR sludge. In addition, the fermenter that allowed acidogenic co-fermentation with food waste provided sufficient soluble organics for biological denitrification, and an overall 91.8% total N removal was achieved through the side-stream denitrification. High-throughput sequencing was applied to analyse the microbial communities in the integrated system, and important functional bacteria were identified for nitrification, denitrification, acidogenic fermentation and dissimilatory iron reduction through the different components of the system.

Use of solid phosphorus fractionation data to evaluate phosphorus release from waste activated sludge

Waste activated sludge (WAS) can become an important source of phosphorus (P). P speciation was examined under anaerobic conditions, with different pH (4, 6 and 8) and temperatures (10, 20 and 35 °C). Aqueous P was measured and an extraction protocol was used to find three solid phosphorus fractions. A pH of 4 and a temperature of 35 °C gave a maximum of 51% of total P solubilized in 22 days with 50% of total P solubilized in 7 days. Batch tests indicate that little pH depression is needed to release non-apatite inorganic P (including microbial polyphosphate), while a pH of 4 rather than 6 will release more apatite inorganic P, and that organic P is relatively more difficult to release from WAS. Fractionation analysis of P in WAS can aid in design of more efficient methods for P recovery from WAS.

Acidogenic fermentation of iron-enhanced primary sedimentation sludge under different pH conditions for production of volatile fatty acids

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 FeCl₃-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.

Approach of describing dynamic production of volatile fatty acids from sludge alkaline fermentation

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.

Long-term effect of pH on short-chain fatty acids accumulation and microbial community in sludge fermentation systems

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 90days. 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 31.65mgCOD/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.

The effect of pH on solubilization of organic matter and microbial community structures in sludge fermentation

Sludge fermentation between pH 4 and 11 was investigated to generate volatile fatty acids (VFA). Despite the highest sludge solubilization of 25.9% at pH 11, VFA accumulation was optimized at pH 8 (12.5% out of 13.1% sludge solubilization). 454 pyrosequencing identified wide diversity of acidogens in bioreactors operated at the various pHs, with Tissierella, Petrimonas, Proteiniphilum, Levilinea, Proteiniborus and Sedimentibacter enriched and contributing to the enhanced fermentation at pH 8. Hydrolytic enzymatic assays determined abiotic effect to be the leading cause for improved solubilization under high alkaline condition but the environmental stress at pH 9 and above might lead to disrupt biological activities and eventually VFA production. Furthermore, molecular weight (MW) characterization of the soluble fractions found large MW aromatic substances at pH 9 and above, that is normally associated with poor biodegradability, making them disadvantageous for subsequent bioprocesses. The findings provided information to better understand and control sludge fermentation.

Integrated production of polyhydroxyalkanoates (PHAs) with municipal wastewater and sludge treatment at pilot scale

A pilot-scale process was operated over 22 months at the Brussels North Wastewater Treatment Plant (WWTP) in order to evaluate polyhydroxyalkanoate (PHA) production integration with services of municipal wastewater and sludge management. Activated sludge was produced with PHA accumulation potential (PAP) by applying feast-famine selection while treating the readily biodegradable COD from influent wastewater (average removals of 70% COD, 60% CODsol, 24% nitrogen, and 46% phosphorus). The biomass PAP was evaluated to be in excess of 0.4gPHA/gVSS. Batch fermentation of full-scale WWTP sludge at selected temperatures (35, 42 and 55 °C) produced centrate (6-9.4 gCODVFA/L) of consistent VFA composition, with optimal fermentation performance at 42 °C. Centrate was used to accumulate PHA up to 0.39 gPHA/gVSS. The centrate nutrients are a challenge to the accumulation process but producing a biomass with 0.5 gPHA/gVSS is considered to be realistically achievable within the typically available carbon flows at municipal waste management facilities.