Sludge Reduction Efficiency Research Articles

Carbon footprint analysis of wastewater treatment processes coupled with sludge in situ reduction

The goal of this study was to assess the impacts or benefits of sludge in situ reduction (SIR) within wastewater treatment processes with relation to global warming potential in wastewater treatment plants, with a comprehensive consideration of wastewater and sludge treatment. The anaerobic side-stream reactor (ASSR) and the sludge process reduction activated sludge (SPRAS), two typical SIR technologies, were used to compare the carbon footprint analysis results with the conventional anaerobic - anoxic - oxic (AAO) process. Compared to the AAO, the ASSR with a typical sludge reduction efficiency (SRE) of 30 % increased greenhouse gas (GHG) emissions by 1.1 - 1.7 %, while the SPRAS with a SRE of 74 % reduced GHG emissions by 12.3 - 17.6 %. Electricity consumption (0.025 - 0.027 kg CO2-eq/m3), CO2 emissions (0.016 - 0.059 kg CO2-eq/m3), and N2O emissions (0.009 - 0.023 kg CO2-eq/m3) for the removal of secondary substrates released from sludge decay in the SIR processes were the major contributor to the increased GHG emissions from the wastewater treatment system. By lowering sludge production and the organic matter content in the sludge, the SIR processes significantly decreased the carbon footprints associated with sludge treatment and disposal. The threshold SREs of the ASSR for GHG reduction were 27.7 % and 34.6 % for the advanced dewatering - sanitary landfill and conventional dewatering - drying-incinerating routes, respectively. Overall, the SPRAS process could be considered as a cost-effective and sustainable low-carbon SIR technology for wastewater treatment.

Comprehensive study on pilot nitrification-sludge fermentation coupled denitrification system with extended sludge retention time

The sludge fermentation-coupled denitrification process, utilized for sludge reduction and nitrogen removal from wastewater, is frequently hindered by its hydrolysis step’s efficacy. This study addresses this limitation by extending the sludge retention time (SRT) to 120 days. As a result, the nitrate removal efficiency (NRE) of the nitrification-sludge fermentation coupled denitrification (NSFD) pilot system increased from 67.1 ± 0.2 % to 96.7 ± 0.1 %, and the sludge reduction efficiency (SRE) rose from 40.2 ± 0.5 % to 62.2 ± 0.9 %. Longer SRT enhanced predation and energy dissipation, reducing intact cells from 99.2 % to 78.0 % and decreasing particle size from 135.2 ± 4.6 μm and 19.4 ± 2.1 μm to 64.5 ± 3.5 μm and 15.5 ± 1.6 μm, respectively. It also created different niches by altering the biofilm’s adsorption capacity, with interactions between these niches driving improved performance. In conclusion, extending SRT optimized the microbial structure and enhanced the performance of the NSFD system.

Synchronous in-situ sludge reduction and enhanced denitrification through improving electron transfer during endogenous metabolisms with Fe(Ⅱ) addition

The creation of large amounts of excess sludge and residual nitrogen are critical issues in wastewater biotreatment. This study introduced Fe(II) into an oligotrophic anaerobic reactor (OARFe) that was implemented to modify an anoxic-oxic process to motivate in-situ sludge reduction and enhance denitrification under an effective electron shuttle among organic matter, nitrogen, and Fe. The addition of 15 mg L−1 Fe(II) resulted in a sludge reduction efficiency reached 32.0% with a decreased effluent nitrate concentration of 33.3%. This was mostly attributed to the electron transfer from Fe(II) to organic matters and nitrogen species in OARFe. The participation of Fe(II) led to the upregulation of Geothrix and Terrimonas, which caused active organic matter hydrolysis and cell lysis to stimulate the release of extracellular polymeric substances (EPS) and substance transfer between each layer of EPS. The higher utilization of released bioavailable dissolved organic matter improved endogenous denitrification, which can be combined with iron autotrophic denitrification to realize multiple electron donor-based nitrogen removal pathways, resulting in an increased nitrate removal rate of 58.2% in the absence of external carbon sources. These functional bacteria associated with the transformation of nitrogen and carbon and cycling between ferrous and ferric ions were enriched in OARFe, which contributed to efficient electron transport occurred both inside and outside the cell and increased 2,3,5-triphenyltetrazolium chloride electronic transport system activity by 46.9%. This contributed to the potential operational costs of chemical addition and sludge disposal of Fe-AO being 1.9 times lower than those of conventional A2O processes. These results imply that the addition of ferrous ions to an oligotrophic anaerobic zone for wastewater treatment has the potential for low-cost pollution control.

A pilot study of situ sludge fermentation-driven multiple biological nitrogen removal pathways (SFBNR): Revealing microbial synergy mechanism based on co-occurrence network analysis

The sludge fermentation-driven biological nitrogen removal (SFBNR) has garnered increasing attention due to its efficient carbon resource utilization from waste activated sludge (WAS). This study successfully extended the application of this technique to a 38 m3 reactor, facilitating a daily ultra-low carbon to nitrogen ratio (<1) wastewater treatment capacity of 16 tons and a WAS capacity of 500 L. After 185-days operation, the system demonstrated commendable performance with a denitrification efficiency (DNE) of 93.22 % and a sludge reduction efficiency (SRE) of 72.07 %. To better understand the potential mechanisms, various functional bacteria interactions were revealed by co-occurrence network analysis. The results unveiled module hubs (e.g., Anaerolineaceae, Denitratisoma, and Candidatus Brocadia) and connectors (e.g., Tuaera and Candidatus Alysiosphaera) in the network exhibited synergistic relationships facilitated by carbon metabolism and nitrogen cycling. Furthermore, the interaction between biofilm sludge (BS) and suspended sludge (SS) contributed to the in-situ enrichment of anaerobic ammonium oxidizing bacteria (AnAOB), whose abundance in BS reached 1.8 % (200-times higher than in SS) after six months, and the suspend-biofilm interface served as a hotspot for anammox activity.

Sludge lysis by thermophilic bacteria community enhances nutrient removal, sludge reduction, and modulates microbial community in anaerobic-anoxic-oxic process

Excess sludge generated during the biological treatment of wastewater is returned to the biochemical tank after being lysed, which is considered to be a feasible strategy for reducing sludge. In this study, an in-situ sludge reduction technology combining sludge lysed based on thermophilic bacterial community (LTBC) and anaerobic-anoxic-oxic (AAO) process (i.e., LTBC-AAO process) was proposed for the first time and the sludge reduction efficiency of the LTBC-AAO process was evaluated. In LTBC reactor, the average removal efficiency of volatile suspended solids of sludge was 52.1 ± 3.2 %. Thermophilic bacteria involved in sludge lysis included Thermus, Fervidobacterium and Caldanaerobacter with relative abundances of 51.5 %, 20.3 % and 8.72 %, respectively. The excess sludge of LTBC-AAO was reduced by 64.7 % compared with that of conventional AAO. The COD removal efficiencies of LTBC-AAO and AAO were 93.4 ± 1.8 % and 93.1 ± 2.1 %, respectively, and there was no significant difference. The TN removal efficiency of LTBC-AAO was 65.7 ± 4.2 %, which was 10 % higher than that of AAO (55.7 ± 3.2 %). Furthermore, 65.7 % substrate in lysed sludge supernatant was readily biodegradable, and the denitrification rate of these substrates as carbon source was 6.33 mg N/g VSS-h. Microbial community structure analysis revealed increased microbial diversity of activated sludge due to lysed sludge reflux, with enrichment of denitrification-related species Delftia and Acinetobacter in LTBC-AAO contributing to the improvement in nitrogen removal efficiency. These findings suggest that the LTBC-AAO process is a promising technology for sludge reduction and nutrient removal in municipal wastewater treatment plants.

Enhanced in-situ sludge reduction of the side-stream process via employing micro-aerobic approach in both mainstream and side-stream

Side-stream reactor (SSR), as an in-situ sludge reduction process with high sludge reduction efficiency (SRE) and less negative impact on effluent, has been widely researched. In order to reduce cost and promote large-scale application, the anaerobic/anoxic/micro-aerobic/oxic bioreactor coupled with micro-aerobic SSR (AAMOM) was used to investigate nutrient removal and SRE under short hydraulic retention time (HRT) of SSR. When HRT of SSR was 4 h, AAMOM system achieved 30.41% SRE, while maintaining carbon and nitrogen removal efficiency. Micro-aerobic in mainstream accelerated the hydrolysis of particulate organic matter (POM) and promoted denitrification. Micro-aerobic in side-stream increased cell lysis and ATP dissipation, thus increasing SRE. Microbial community structure indicated that the cooperative interactions among hydrolytic, slow growing, predatory and fermentation bacteria played key roles in improving SRE. This study confirmed that SSR coupled micro-aerobic was a promising and practical process, which could benefit nitrogen removal and sludge reduction in municipal wastewater treatment plants.

Improvement of the Sludge Decomposition and Nutrients Release by a Treatment with Potassium Permanganate Combined with an Ultrasonic Process

Ultrasonic decomposition of sludge is a popular method for sludge treatment. Potassium permanganate (KMnO4) was added to promote the reduction of sludge and hydrolysis efficiency. The effect of ultrasonic treatment (ULT) combined with potassium permanganate (KMnO4) preprocessing on the disintegration of waste activated sludge (WS) was studied in this survey. The results indicated that the combined pretreatment of KMnO4 and ULT (150 W, 20 min) significantly improved the decomposition efficiency and nutrient release efficiency of sludge. The volatile suspended solids (VSS) were lessened by 15.22%, which was 56.8% larger than that of raw sludge. The soluble proteins, soluble chemical oxygen demand (SCOD), polysaccharides, and volatile fatty acids (VFAs) were improved by 2005.1%, 464%, 669.8%, and 719.9% respectively. The deliquescent organic matter in sludge products also effectively decreased, demonstrating the effective promoting effect of KMnO4 + ULT. Mechanistic studies showed that ULT united with KMnO4 pretreatment could improve the biodegradability of soluble organic matter by generating reactive radicals, effectively disrupt the structure of cell walls, lyse extracellular polymers, and accelerate the liberation of organic matter. The composite sludge decomposition process further mitigates the harm of sludge to the environment and provides a cleaner and more efficient sludge reduction and utilization method.

Superior nitrogen removal and efficient sludge reduction via partial nitrification-anammox driven by addition of sludge fermentation products for real sewage treatment

Efficient retention and enrichment of anammox bacteria (AnAOB) are essential for the application of municipal wastewater anammox. Herein, an innovative process for highly enriching AnAOB within suspended carrier was developed in a single-stage anaerobic/oxic/anoxic reactor with 5.5 % carrier filling ratio for real sewage. Addition of sludge fermentation products promoted stable maintenance of partial nitrification (nitrite accumulation rate > 90.0 %) and achieved efficient external sludge reduction (27.6–37.9 %). Continuous nitrite supply and carrier addition promoted AnAOB enrichment (2.4 × 1011 gene copies/g dry sludge). Candidatus Brocadia was the predominant bacteria in carriers (18.6 %). The average effluents of total inorganic nitrogen (TIN) and NH4+-N were 1.9 and 0.8 mg/L with removal rates of 97.0 % and 98.7 %. In the anoxic stage, TIN removal rate reached 71.5 %, and the proportion of anammox to nitrogen removal accounted for 82.7 %. This study broadens the application of mainstream sewage anammox and the resource utilization of waste activated sludge.

Nitrogen Removal and Sludge Reduction in Anoxic-Aerobic Sequencing Batch Reactor with Alkaline-H2O2 Disintegration

Abstract In this study, alkaline-H2O2 sludge disintegration was combined with anoxic-aerobic sequencing batch reactor (SBR). The carbon obtained by alkaline-H2O2 sludge disintegration was used in the denitrification process and sludge reduction was achieved in the SBR process. In the SBR process, a 9 % increase in nitrogen removal efficiency was achieved with the improvement in the denitrification process. A sludge reduction efficiency of 43 % was obtained in the SBR process with alkaline-H2O2 sludge disintegration. A synergistic effect was obtained in the combination of alkaline and H2O2 methods and the sludge reduction increased by 8 %. By combining sludge disintegration into the SBR process, it is possible to reduce the amount of sludge formed, which is an important environmental problem, and to provide carbon source for the denitrification process.

A metabolomic view of how the anaerobic side-stream reactors achieves in-situ sludge reduction

Anaerobic side-stream reactors (ASR), which were inserted in the sludge recirculation line of activated sludge process, can achieve in-situ sludge reduction. The lysis-cryptic growth occurred in ASR was accompanied with the release and reuse of dissolved organic matter (DOM), resulting in changes in DOM characteristics and affecting the microbial metabolic strategies, ultimately causing lower sludge yield in ASR. However, the variations in metabolic strategies of microorganisms in response to DOM changes in ASR systems remained unclear. Here, the sludge morphological feature, molecular properties of DOM and microbial metabolomics were analyzed to investigate the phenotype discrepancies and intrinsic causes of low biomass yield. Results showed that ASR systems achieved 22.9% sludge reduction efficiency. In the ASR system, the decreased microbial activity (adenosine triphosphate decreased by 10.3%) and unstable flocs structure implied the sludge destruction, causing the accumulation of proteins in extracellular polymeric substances (increased by 58.3%). The microorganisms in stressed ASR tended to utilize some tough aromatic carbon sources in DOM, finally affecting biomass growth. At the metabolite level, decreased lipid and purine/pyrimidine metabolism pathways activities provided less nucleic acids for synthesis of cellular structure and bacterial proliferation in the mainstream aerobic tank of ASR system, respectively. Microbes facilitate the metabolism of cheaper amino acids rather than costly ones due to the weaker cell activity. Notably, this change of amino acid utilization strategy would lead to the low level of nucleic metabolism, thus restraining the biomass yield. This study unraveled the low biomass yield mechanisms on sludge-reduction bacteria in response to the change of DOM molecular characteristics, which will help provide a deep theoretical foundation for promoting its full-scale applications.

Integrating electrochemical pretreatment (EPT) and side-stream sulfidogenesis with conventional activated sludge process: Performance, microbial community and sludge reduction mechanisms

• Coupling EPT and sulfidogenic side-stream reactor (ESSR) with CAS process was studied. • EPT at 15 V/5min with 125 mg S/L of SO 4 2− dosage improved sludge reduction. • The ESSR could be designed with a very short SRT of 2.5 days. • The integrated process (ESSR-CAS) was operated over 200 d with good performance. • Possible reasons for fast sludge hydrolysis in ESSR-CAS were discussed. Recently, inserting an anaerobic side-stream reactor into a conventional activated sludge (CAS) process for upgrading biological wastewater treatment plants with in-situ sludge reduction function has been extensively studied. A typical example is an oxic-settling anaerobic (OSA) process, which can achieve efficient sludge reduction, but requires ample space, limiting its application potential. Optimizing the conventional OSA process towards compact and energy-efficient is necessary. This paper studied a new method by integrating electrochemical pretreatment (EPT) and sulfidogenesis-enhanced anaerobic treatment with a conventional OSA process to achieve considerable in-situ sludge reduction with a limited side-stream size requirement (i.e. short sludge retention time (SRT)). The proposed idea was verified experimentally – first, batch experiments were conducted to determine the effective sulfate concentration for the EPT and sulfidogenic side-stream reactor (ESSR); then, the ESSR-CAS process (upgrading CAS with a new ESSR) and a stand-alone CAS process (control) were operated in parallel for 200 days. The experimental results showed that: The new ESSR, with approximately 125 mg S/L of sulfate dosed and 5 min electrochemical sludge pretreatment at 15 V, can successfully accelerate anaerobic reactions, resulting in a short SRT of 2.5 days. The ESSR-CAS process can reduce sludge production by 61%, with high soluble chemical oxygen demand (SCOD) and total nitrogen (TN) removal efficiencies of 96% and 70% respectively. The possible mechanisms of ESSR for the augment of sludge hydrolysis (sludge floc disintegration, extracellular polymer destruction, and cell structure breakage) as well as the economic considerations of this new sulfur-cycle bioprocess are discussed.

A novel partial denitrification, anammox-biological phosphorus removal, fermentation and partial nitrification (PDA-PFPN) process for real domestic wastewater and waste activated sludge treatment

A novel process was developed for real domestic wastewater and waste activated sludge (WAS) treatment based on partial denitrification, anammox-biological phosphorus removal, fermentation and partial nitrification (PDA-PFPN). After 246 days of operation, the effluent concentrations of NH4+-N, NO2−-N and NO3−-N were below detection limits (0.1 mg/L), and the effluent concentration of PO43−-P was 0.1 mg/L without the addition of external carbon source in PDA-PFPN system. Moreover, the sludge reduction efficiency reached 48.1% due to fermentation. The nitrite accumulation ratios by ammonia oxidation and nitrate reduction pathway were 60.6% and 87%, respectively. Intracellular metabolites measured by liquid chromatography mass spectrometer (LC-MS/MS) suggested that different intracellular amino acids were stored and consumed at different duration, and intracellular Valine, Glycine and Lysine were not utilized in oxic stage. Results of flow cytometry showed that the proportion of intact cells decreased from 94.7% to 82.9%, and necrotic cells increased from 5.3% to 17.1% with the increase of DNA content in sludge supernatant and cell decay rate, indicating the occurrence of cell death and lysis and leading to WAS reduction. Analysis of transcriptional community composition revealed that partial denitrification bacteria (Thauera), anammox bacteria (Candidatus Brocadia and Candidatus Kuenenia), simultaneous phosphorus removal and fermentation bacteria (Tetrasphaera) and partial nitrification bacteria (Nitrosomonas) coexisted and actually worked in PDA-PFPN system. The novel PDA-PFPN process simultaneously achieved highly efficient nitrogen and phosphorus removal and WAS reduction without the addition of external carbon source, which greatly reduced the operation cost of carbon source dosing and WAS treatment in wastewater treatment.

Performance assessment of ultrasonic sludge disintegration in activated sludge wastewater treatment plants under nutrient-deficient conditions

Although biological oxidation is a commonly applied technique for the removal of pollutants in industrial and municipal wastewater, one major drawback is its excess sludge production, having both an environmental and economic impact. The integration of ultrasonic sludge disintegration in a conventional biological wastewater treatment plant was explored experimentally via assessing the long-term effects on excess sludge reduction by conducting on-site pilot tests at a food processing company and a biodiesel production plant. Two sequencing batch reactors, each with a maximum active volume of 700 L, were operated in parallel for the treatment of industrial wastewater with nutrient deficient characteristics (COD/N/P ratio of 100/1.4/0.12) for over 6 months. One of the reactors was equipped with a side-stream recirculation system to enable the ultrasonic treatment of part of the settled sludge, whereas the other was operated in a conventional way as a reference. The experimental results show a reduction of the observed sludge production yield by 15% to 45% for the ultrasonically treated sequencing batch reactor compared to the conventional one, at a relatively low specific energy of less than 6,000 kJ/kg DS when 15 to 30% of the total sludge mass is treated per day. It was proven that the sludge reduction efficiency is directly proportional to the applied sludge retention time, suggesting that the ultrasonic treatment converts part of the hardly biodegradable particulate material in the activated sludge and improves its biodegradability. During the long-term pilot experiment at the biodiesel production plant, the electrical energy needed for decreasing the excess sludge production by 1 ton could be reduced by more than 80% when the sludge retention time was increased from 11 to 44 days. In addition, the sludge settling characteristics at the food processing company were considerably improved by the ultrasonic treatment, enabling to reduce or even avoid the need for external addition of expensive nutrients to prevent sludge bulking. Finally, an improved effluent quality was observed. Improvements of 7 to 17%, 9 to 20% and 17 to 30% for COD, nitrogen and phosphorus removal, respectively, were established.

Pilot-scale demonstration of a novel process integrating Partial Nitritation with simultaneous Anammox, Denitrification and Sludge Fermentation (PN + ADSF) for nitrogen removal and sludge reduction

Anammox process is a cost-effective solution for nitrogen removal, whereas unsatisfactory effluent with nitrate accumulation is usually achieved in treating domestic sewage, owning to the unwanted prevalence of nitrite-oxidizing bacteria (NOB) and the intrinsic nitrate production by anammox bacteria. Herein, a pilot-scale system integrating Partial Nitritation and simultaneous Anammox, Denitrification and Sludge Fermentation (PN + ADSF) process was developed to treat real municipal wastewater. In this process, PN was accomplished in a sequencing batch reactor (SBR) using the strategy of intermittent hydroxylamine addition, while ADSF coupling anammox and heterotrophic denitrification was conducted in an up-flow anaerobic sludge blanket reactor (UASB) to further remove nitrogen. The pilot-scale system achieved total inorganic nitrogen (TIN) concentrations of 10.0 mg N/L in effluent and sludge reduction efficiency of 42.3% simultaneously. The characterization on microbial communities revealed that Candidatus Kuenenia and Thauera were the dominant functional bacteria for anammox and denitrification, respectively. Supported by the slow-release carbon sources from sludge fermentation, heterotrophic denitrification contributed to about 28% of nitrogen removed from the UASB, while anammox played a more important role in nitrogen removal. The pilot-scale demonstration confirmed that the PN + ADSF process is technically feasible for enhanced nitrogen removal and sludge reduction.

Recirculation of reject water in deep-dewatering process to influent of wastewater treatment plant and dewaterability of sludge conditioned with Fe2+/H2O2, Fe2+/Ca(ClO)2, and Fe2+/Na2S2O8: From bench to pilot-scale study

Deep dewatering of sewage sludge pretreated with advanced oxidation processes (AOPs) is a strategy for efficient sludge reduction and subsequent disposal. The pretreatment and dewatering performance of sludge conditioned with three types of AOPs (Fe2+/H2O2, Fe2+/Ca(ClO)2, and Fe2+/Na2S2O8), compared with sludge conditioned with traditional conditioner (Fe3+/CaO), were investigated in both bench and pilot-scale tests. All of those conditioner systems could reduce the water content of dewatered sludge cake to below 60 wt% in bench-scale (about 16 kg raw sludge per round) and pilot-scale (approximate 800 kg raw sludge per round) diaphragm filter press dewatering. Compared with raw sludge, the deep-dewatering filtrate after different conditioning and dewatering processes had higher ammonia nitrogen (NH4+-N) and chemical oxygen demand (COD) contents due to the degradation of organic matter, and much lower total phosphorus (TP) content due to the formation of iron phosphate precipitate. A better biodegradability (i.e. higher BOD5/COD ratio) was found in the deep-dewatering filtrate of sludge conditioned with Fe2+/H2O2 (25.2 %) and Fe2+/Ca(ClO)2 (17.4 %). Most of the heavy metals (Cr, Cu, Ni, and Pb) (>79 wt%) have remained in the dewatered sludge cake, and most of the Cl element (>90 wt%) in the sludge pretreated by Fe2+/Ca(ClO)2 and Fe3+/CaO was kept in the filtrate, rather than the dewatered sludge cake. Based on the pilot-scale experimental results, if all the filtrate in the deep-dewatering process returned to the influent of WWTP, the loading ratios of TP, NH4+-N, COD in the four conditioner systems were less than 3 wt%. The above results proved that the AOPs conditioned sludge could achieve deep-dewatering in pilot-scale and the direct recirculation of deep-dewatering filtrate to the influent of wastewater treatment plant was feasible.

Membrane fouling in anoxic/oxic membrane reactors coupled with carrier-enhanced anaerobic side-stream reactor: Effects of anaerobic hydraulic retention time and mechanism insights

Membrane fouling mechanism of membrane reactors (MBR) coupled with anaerobic side-stream reactor (ASSR) has been extensively studied, while the homologous mechanism in carrier-enhanced ASSR process remained unclear. Anoxic/oxic MBR and three carrier-enhanced ASSR coupled anoxic/oxic MBRs (ASSR-MBRs) were operated in parallel to investigate the effect of hydraulic retention time of ASSR (HRTSR) on membrane filtration performance and fouling tendency. ASSR-MBR with HRTSR of 2.5, 5.0 and 6.7 h achieved the sludge reduction efficiency of 24.6%, 32.2%, and 41.0%. The foulant layer resistances were in the order of anoxic/oxic MBR (5.40 ± 0.32 × 1012 m−1) > ASSR2.5-MBR (5.39 ± 0.30 × 1012 m−1) > ASSR6.7-MBR (3.33 ± 0.42 × 1012 m−1) > ASSR5.0-MBR (2.38 ± 0.45 × 1012 m−1). The improved sludge dewaterability and more stable sludge structure in carrier-enhanced ASSR caused membrane fouling less severe than that in anoxic/oxic MBR. The results of extracellular polymeric substances identified incomplete and over hydrolysis of cell lysate at HRTSR of 2.5 and 6.7 h, respectively. CLSM results indicated that ASSR-MBR with HRTSR of 5.0 h achieved the best filtration performance because of the enhanced protein degradation ability of membrane surface microbes. MiSeq sequencing indicated that fouling-eased group bacteria (responsible for the alleviation of membrane fouling) were enriched in ASSR-MBRs, while fouling-caused group bacteria (responsible for the aggravation of membrane fouling), such as filamentous bacteria, were dominant in anoxic/oxic MBR. This study bridged a gap between sludge redcution and membrane fouling in carrier-enhanced ASSR-MBR.

Achieving enhanced biological phosphorus removal utilizing waste activated sludge as sole carbon source and simultaneous sludge reduction in sequencing batch reactor

Achieving enhanced biological phosphorus removal dominated by Tetrasphaera utilizing waste activated sludge (WAS) as carbon source could solve the problems of insufficient carbon source and excessive discharge of WAS in biological phosphorus removal. Up to now, the sludge reduction ability of Tetrasphaera remained largely unknown. Furthermore, the difference between traditional sludge fermentation and sludge fermentation dominated by Tetrasphaera was still unclear. In this study, two different sequencing batch reactors (SBRs) were operated. WAS from SBR-parent was utilized as sole carbon source to enrich Tetrasphaera with the relative abundance of 91.9% in SBR-Tetrasphaera. PO43−-P removal and sludge reduction could simultaneously be achieved. The effluent concentration of PO43−-P was 0, and the sludge reduction efficiency reached about 44.14% without pretreatment of sludge. Cell integrity detected by flow cytometry, the increase of DNA concentration in the sludge supernatant and decrease of particle size of activated sludge indicated that cell death and lysis occurred in sludge reduction dominated by Tetrasphaera. Stable structure of activated sludge was also damaged in this process, which led to the sludge reduction. By analyzing the excitation-emission matrix spectra of extracellular polymeric substances and the changes of carbohydrate and protein concentration, this study proved that slowly biodegradable organics (e.g., soluble microbial byproduct, tyrosine and tryptophan aromatic protein) could be better hydrolyzed and acidized to volatile fatty acids (VFAs) in sludge fermentation dominated by Tetrasphaera than traditional sludge fermentation, which provided carbon source for biological nutrients removal and saved operation cost in wastewater treatment.

Pilot-Scale Airlift Bioreactor with Function-Enhanced Microbes for the Reduction of Refinery Excess Sludge.

A pilot-scale airlift bioreactor (ALBR) system was built and operated continuously for refinery excess sludge (RES) reduction. Combined ALBR and function-enhanced microbes (composed of photosynthetic bacteria and yeast) were integrated into the system. The pilot-scale ALBR was operated for 62 days, and the start-up time was 7 d. Continuous operation showed that the sludge reduction efficiency was more than 56.22%, and the water quality of the effluent was satisfactory. This study focused on investigating the effects of hydraulic retention time (HRT) on the stability of the system and the effect of sludge reduction. Under different HRT conditions of 40, 26.7, 20, and 16 h, the sludge reduction rates reached 56.22%, 73.24%, 74.09%, and 69.64%, respectively. The removal rates of chemical oxygen demand (COD) and total nitrogen (TN) decreased with decreasing HRT, whereas the removal rate of NH4+-N increased. The removal rate of total phosphorus (TP) was approximately 30%. Results indicate that the ALBR and function-enhanced microbe system can reduce sludge and treat sewage simultaneously, and the effluent is up to the national emission standard. Addition of function-enhanced microbes can promote the degradation of petroleum hydrocarbon substances in the sludge, especially alkanes with low carbon numbers. This study suggests that the optimal HRT for the system is 16 h. The total operation cost of the ALBR combined with the function-enhanced microbe system can be reduced by 50% compared with the cost of direct treatment of the RES system.

Achieving synergetic treatment of sludge supernatant, waste activated sludge and secondary effluent for wastewater treatment plants (WWTPs) sustainable development

A novel process that combines partial nitrification, fermentation and Anammox-partial denitrification (NFAD) was proposed to co-treat ammonia rich sludge supernatant (NH4+-N = 1194.1 mg/L), external WAS (MLSS = 22092.6 mg/L) and WWTP secondary effluent (NO3–-N = 58.6 mg/L). Three separated reactors were used for partial nitrification (PN-SBR), integrated fermentation and denitrification (IFD-SBR) and combined Anammox-partial denitrification (AD-UASB), respectively. The process resulted in excellent nitrogen removal efficiency (NRE) of 98.7%, external sludge reduction efficiency (SRE) of 44.6% and external sludge reduction rate of 4.1 kg/m3 after 200 days of continuous operation. IFD-SBR and AD-UASB contributed towards 89.4% and 9.2% nitrogen removal, respectively. In AD-UASB, cooperation between Anammox bacteria (4.1% Candidatus Brocadia) and partial denitrifying bacteria (3.2% Thauera) resulted in significant stability of Anammox pathway, which contributed up to 84.1% nitrogen removal in the combined Anammox-partial denitrification process. NFAD saved up to 100% organic resource demand and 25% of aeration consumption compared with the traditional nitrification–denitrification process.

A novel anoxic/aerobic process coupled with micro-aerobic/anaerobic side-stream reactor filled with packing carriers for in-situ sludge reduction

Activated sludge process with anaerobic side-stream reactors (SR) in the sludge recirculation line can achieve in-situ sludge reduction. But sludge reduction efficiency (SRE) is limited with low cell lysis and particle organic matter hydrolysis rates under short hydraulic retention time of SR for practical application. This study firstly inserted alternating micro-aerobic/anaerobic conditions (AMAC) and packing carriers into SR with low hydraulic retention time for improving SRE. The effects of AMAC and packing carriers on sludge rheology properties, molecular characteristics of dissolved organic matter (DOM) and microbial communities were investigated. Results showed that AMAC coupled packing carriers achieved SRE by 51.09% with efficient effluent pollutant removal. AMAC specialized inactive particle organic matter hydrolysis and active cell lysis in the micro-aerobic and anaerobic SR, respectively. Packing carriers intensified this function division effect. This effect weakened colloidal entanglement of flocs. It intensified the cell lysis in mainstream aerobic tank, causing the accumulation of refractory lignins in DOM. The higher utilization of released bioavailable DOM decreased microbial activity. Overall, the improved SRE favored the declined DOM bioavailability by inserting AMAC and packing carriers in SR. The sludge reduction-related bacteria like slow growing (Dechloromonas), predatory (Norank_Saprospiraceae), and hydrolytic/fermentative bacteria (Chelatococcus, Pseudomonas, Tolumonas, and Unclassified_Bacteroidia) were involved in decreasing DOM bioavailability. This study advanced our knowledge about the effects of AMAC and packing carriers on in-situ sludge reduction systems. This research also showed how AMAC and packing carriers enhanced the sludge lysis/hydrolysis for sludge reduction.