Mechanisms Of Sludge Reduction Research Articles

The anaerobic exposure time (AET) as a novel process parameter in the anaerobic side-stream reactor (ASSR)-based process for excess sludge minimization

Minimization of excess sludge produced by wastewater treatment plants has become a topical theme nowadays. One of the most used approaches to achieve this aim is the anaerobic side-stream reactor (ASSR) process. This is considered affected by the hydraulic retention time (HRT) of the anaerobic reactor, the anaerobic sludge loading rate (ASLR) and the sludge interchange ratio (SIR), although, studies available in the literature did not reflect a clear relationship with the sludge minimization yields.To overcome this, a novel parameter namely anaerobic exposure time (AET) was defined and related to reduction of the observed yield coefficient (Yobs) in a lab-scale plant implementing the ASSR process. Furthermore, the AET was validated by performing a detailed and thorough review of previous literature. Excess sludge production was successfully reduced (10–60 %) with the increase of the AET (7.9–13 h/d), although maintaining the same HRT in the ASSR and a constant sludge interchange ratio (SIR) (100 %). A strong correlation (Pearson = 0.763) was found between the AET, and the Yobs reduction reported in previous studies, also indicating a linear relationship (R2 = 0.92) between these parameters. Contrarily, the correlation between the Yobs with the ASLR and the ASSR-HRT resulted moderate (Pearson = 0.186) or weak (Pearson=−0.346), respectively. Overall, while operating at low AET (< 6 h), maintenance and uncoupling metabolism were found the main sludge reduction mechanisms. Increasing the AET (>8 h) favoured the occurrence of extracellular polymeric substances (EPS) hydrolysis and endogenous decay mechanisms, which improved excess sludge reduction. To conclude, the AET could be considered a reliable parameter to be used for design or control purposes for the ASSR-based process.

A comparative life cycle assessment (LCA) analysis of innovative methods employing cutting-edge technology to improve sludge reduction directly in wastewater handling units

Sludge reduction technologies can be used as an alternative plan to dispose of excess sludge in wastewater treatment plants, but the sustainability of these strategies is a challenging task. In this study, the potential environmental implications of innovative technologies based on lab-scale results published in the literature were assessed from the life cycle assessment (LCA) view point. Accordingly, three different scenarios using various sludge reduction mechanisms were selected and analyzed. The scenarios include (1) an integrated oxic-setting-anaerobic and ultrasound process; (2) a sequencing batch reactor (SBR) with an anaerobic side-stream reactor to its return activated sludge line; and (3) the anaerobic-anoxic-oxic system in conjunction with an ozone reactor. LCA was conducted through the CML-IA (baseline 2000) method. A sensitivity analysis was also done in order to determine how changes in the inputs are affecting the overall sustainability of the system. The environmental impact evaluation of three scenarios indicated that the integrated SBR with an anaerobic side-stream reactor was the most efficient and sustainable alternative in environmental terms. Although the upgraded SBR system was not the best alternative in terms of sludge reduction (65 % versus 78 % for Scenario 1 and 70 % for Scenario 3), it showed the highest overall performance and also demonstrated the lowest environmental impact compared to other scenarios. Because the scenarios studied were cutting-edge and provided novel sludge reduction strategies based on lab-scale results published in the literature, a comprehensive economic analysis and scale-up considerations are recommended to effectively assist decision-makers in guiding the development of emerging technologies.

The Performance and Mechanism of Sludge Reduction by the Bioaugmentation Approach

Simple SummaryActivated sludge-based wastewater treatment process is one of the most popular adopted systems in wastewater treatment plants around the world. Excess sludge is an inevitable byproduct of the process, and the enormous quantity has brought a significant burden on operational costs. Various physicochemical and biological methods have been developed. Biological-based methods are promising because of less chemical consumption and low operation cost comparing to physicochemical methods. Hence, the present study is aimed at searching for functional bacteria that could reduce sludge, enhance the performance of sludge reduction through optimization, and try to unveil the underlying mechanism during sludge reduction. A total of 19 strains that belong to Firmicutes, Proteobacteria, and Actinobacteria were successfully isolated and identified. Subsequently, the performance of sludge reduction by pure culture or mix-cultures was validated. In total, 21.2% and 13.9% of total suspended and volatile suspended solids were reduced within 48 h after optimization via response surface methodology. The three-dimensional excitation-emission matrix fluorescence spectrum and hydrolases test results revealed that the sludge reduction might be promoted by the strain mainly through hydrolysis via proteinase and amylase. The results obtained from the study could help us to find an effective and economical way to resolve the sludge issue.Millions of wastewater treatment plants (WWTPs) based on the activated sludge process have been established worldwide to help to purify wastewater. However, a vast amount of sludge is inevitably generated, and the cost of sludge disposal could reach over half of the total operation cost of a WWTP. Various sludge reduction techniques have been developed, including physicochemical, biological, and combinational methods. Micro-organisms that could reduce sludge by cryptic growth are vital to the biological approach. Currently, only limited functional bacteria have been isolated, and the lack of knowledge on the underlying mechanism hinders the technique development. Therefore, the present study is aimed at isolating sludge-reducing bacteria and optimizing the sludge reduction process through response surface methodology. Nineteen strains were obtained from sludge. The mix-cultures did not show a higher sludge reduction rate than the pure culture, which may be ascribed to the complicated interactions, such as competition and antagonistic effects. In total, 21.2% and 13.9% of total suspended and volatile suspended solids were reduced within 48 h after optimization. The three-dimensional excitation-emission matrix fluorescence spectrum and hydrolases test results revealed that the sludge reduction might be promoted by the strain mainly through hydrolysis via proteinase and amylase. The results obtained from the study demonstrate the potential of using micro-organisms for sludge reduction through cryptic growth.

In-Situ Sludge Reduction Performance and Mechanism in Sulfidogenic Anoxic-Oxic-Anoxic Membrane Bioreactors.

The excess sludge generated from the activated sludge process remains a big issue. Sustainable approaches that achieve in situ sludge reduction with satisfactory effluent quality deserve attention. This study explored the sludge reduction performance of sulfidogenic anoxic–oxic–anoxic (AOA) membrane bioreactors. The dynamics of the microbial community and metabolic pathways were further analyzed to elucidate the internal mechanism of sludge reduction. Compared with the conventional anoxic–oxic–oxic membrane bioreactor (MBRcontrol), AOAS150 (150 mg/L SO42− in the membrane tank) and AOAS300 (300 mg/L SO42− in the membrane tank) reduced biomass production by 40.39% and 47.45%, respectively. The sulfide reduced from sulfate could enhance the sludge decay rate and decrease sludge production. Extracellular polymeric substances (EPSs) destruction and aerobic lysis contributed to sludge reduction in AOA bioreactors. The relative abundance of Bacteroidetes (phylum), sulfate-reducing bacteria (SRB, genus), and Ignavibacterium (genus) increased in AOA bioreactors compared with MBRcontrol. Our metagenomic analysis indicated that the total enzyme-encoding genes involved in glycolysis, denitrification, and sulfate-reduction processes decreased over time in AOAS300 and were lower in AOAS300 than AOAS150 at the final stage of operation. The excess accumulation of sulfide in AOAS300 may inactive the functional bacteria, and sulfide inhibition induced sludge reduction.

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.

Identifying the mechanisms of sludge reduction in the sulfidogenic oxic-settling anaerobic (SOSA) process: Side-stream sulfidogenesis-intensified sludge decay and mainstream extended aeration

An energy-/cost-efficient and environment-friendly in-situ sludge reduction process, called the sulfidogenic oxic-settling anaerobic (SOSA) was developed recently. However, the underpinning mechanism of sludge reduction by the SOSA process remains elusive. This paper investigated the possible mechanisms of sludge reduction through biomass cultivation in three lab-scale experimental systems: one anoxic-oxic CAS process with a long sludge retention time (SRT) and extended aeration (EAO) process, and two EAO-based in-situ sludge reduction processes, i.e., the conventional oxic-settling anaerobic (COSA) process and the new SOSA process. These three comparative biosystems were operated with identical influent and reactor configurations as well as the same biomass concentrations and SRTs (approximately 5 g/L and 46 days, respectively), and the sludge interchange ratios (between the CAS and side-stream reactors) in COSA and SOSA were both 10% per day. Three systems all achieved high organic (>93%) and total nitrogen (TN) (>74%) removal efficiencies. SOSA produced 29% and 20% less sludge than EAO and COSA, respectively, simultaneously consumed 14% and 8% more oxygen than EAO and COSA, indicating that the sludge reduction in SOSA was not only caused by EAO-based aerobic digestion in the mainstream and conventional anaerobic reactions in the side-stream, but more importantly due to the bioaugmentation of sulfidogenesis. The roles of sulfidogenesis were further studied in batch tests, and the key findings were as follows: i) the SOSA biomass had a faster endogenous decay rate (0.097 d−1) than that of the COSA biomass (0.045 d−1), and ii) sulfidogenesis accelerated anaerobic solubilization, hydrolysis, acidogenesis and acetogenesis by 2.3 – 3.1 times, 6 – 22 %, 22 – 60% and 6 – 22%, respectively. Overall, the mechanisms of sludge reduction in SOSA were unraveled in this study which will help promote its full-scale application in future.

Pilot study on the upgrading configuration of UASB-MBBR with two carriers: Treatment effect, sludge reduction and functional microbial identification

Two kinds of biocarriers were adopted and a combined process of “AMC (Anaerobic microorganism carrier)-UASB and PBG (Porous bio-gel)-MBBR” was operated at the pilot scale for the treatment of real textile wastewater. The influence mechanism of the two carriers on the start-up, pollutant removal and sludge reduction were investigated within 118 days of operation. The dominant functional bacteria in anaerobic and aerobic systems were identified by high-throughput sequencing, and the possible ways and related mechanisms of nutrient removal and sludge reduction were analyzed based on the data. 37.0 ± 7.5 % and 53 ± 12.7 % of COD removal efficiencies were achieved in anaerobic system and aerobic system, respectively. Ammonia nitrogen concentration decreased from 20 to 45 to 3.49 ± 0.54 mg/L after treatment. An anaerobe was found to be closely related to color removal, which existed in both anaerobic and aerobic systems, achieving 84.0 % of color removal. With the operation of the system, the sludge yield decreased gradually. The sludge yields of anaerobic and aerobic systems were calculated individually and compared with similar studies. Aging biofilms were characterized to explore the factors associated with biofilm renewal.

Investigation of sludge solubilization and phosphorous release in anaerobic side-stream reactor with a low pressure swirling jet hydrodynamic cavitation treatment

In this study, the feasibility of a novel hydrodynamic cavitation (HC) system was evaluated to speed up the biological sludge reduction mechanisms of the anaerobic side-stream reactor (ASSR) process. In the first part of the research, HC was performed on ASSR sludge by using a low pressure swirling jet cavitation system, named Ecowirl – EW 25. The effects of the Ecowirl – EW 25 system, in terms of sludge solubilisation, disintegration degree and microbial activity, were investigated considering two different injection plates, respectively, with two and four injection slots and four different treatment times, from 10 to 80 minutes. The best results were achieved after 80 min of HC treatment, using the plate with two injection slots and with a specific supplied energy (SE) equal to 12670 kJ kg TSS-1. Respirometric tests showed an increase in the readily biodegradable COD through the HC treatment of sludge. Moreover, low endogenous decay rates (bH) were measured on the ASSR sludge for SE lower than 6340 kJ kg TSS-1 revealing that the sludge solubilization was due to a modification in the floc structure rather than a decrease in the biomass viability. In the second part of the research, the solubilized sludge, after HC treatment, was used as carbon substrate for the biological activity of bacteria into the ASSR, such as total phosphate accumulating organisms (TPAOs). Results revealed that the phosphorous releasing and uptake rate, obtained using the HC treated sludge as carbon source, were comparable with those obtained with the addition of a ready biodegradable carbon source such as acetate.

Pilot-scale textile dyeing wasted sludge reduction via microbial agent and aeration: Parameter optimization and mechanisms exploration

Abstract New methods to treat textile dyeing wasted sludge (TDWS) should be developed. In this study the sludge reduction induced by microbial agent addition and aeration in pilot-scale was studied. The one-off addition mode was employed in which better sludge reduction (i.e., 58.4%) and lower moisture content (i.e., 71.6%) were achieved. 25 L/min of aeration rate was best for sludge reduction and 52.8% of sludge reduction was achieved and aeration did play an important role in the sludge reduction. 15000 mg/L was determined as the suitable initial sludge concentration. The mechanisms of TDWS reduction were explored subsequently. As the results, the sludge particle size decreased with microbial agent addition while no such reduction was observed without microbial agent. The sludge would react with hydrolase to release organic substance and produce chemical oxygen demand (SCOD) in the liquid, which could be consumed by microorganisms. Finally, the change of microbial community was explored so as to further explain the mechanism of sludge reduction. The phylum Bacteroidetes increased from 33.30% to 45.37% with microbial agent addition which indicated the important role in sludge reduction. The genus Sphingopyxis, Thermomonas and Fluviicola would be the most relevant microorganisms with sludge reduction while the moisture content was most related with Dok59.

Treatment of post tanning wastewater with minimum sludge generation using sequential anoxic/oxic bioreactor and its microbial community profile

The conventional primary treatment use coagulants/flocculants to remove suspended and colloidal solids from post-tanning wastewater (PTWW) and it results in generation of huge quantity of primary chemical sludge. The present investigation was focused on the removal of suspended and colloidal solids from PTWW without addition of coagulants/flocculants using sequential anoxic/oxic bioreactor (SAOBR). The SAOBR was operated under continuous mode to investigate the removal of CODtot, CODdis, CODsus, CODcoll, TS, TDS & TSS by 35.7 ± 1.9 %, 20.2 ± 3.5 %, 84 ± 4.5 %, 82.4 ± 4.7 %, 10.9 ± 2.4 %, 1.4 ± 1.1 % and 78.8 ± 3.6 % at the optimum HRT of 9 h. The primary chemical sludge generated 5.27 ± 0.15 kg/m3of wastewater using conventional coagulants & flocculants and SAOBR has registered sludge generation of 0.293 ± 0.11 Kg/m3 of wastewater. The observed sludge yield (Yobs) in SAOBR was 0.188 g SS/ g COD & it showed 68 ± 9 % of sludge reduction. The change in microbial diversity profile was analyzed in SAOBR to understand the sludge reduction mechanism. The primary chemical sludge and SAOBR sludge were characterized using SEM-EDX, FT-IR, XRD, TGA and DSC analyses.

Characterization of sludge reduction and bacterial community dynamics in a pilot-scale multi-stage digester system with prolonged sludge retention time

Sludge reduction performance and bacterial community dynamics in a pilot-scale multi-stage digester system with prolonged sludge retention time were characterized. Throughout the operation period of 281days, the total loading sludge and the total digested sludge were 4700 and 3300kg-MLSS. After 114days of operation, the residual MLSS (RMLSS) in the reactors for sludge treatment was maintained at 18-25kg-RMLSS m-3, and the sludge reduction efficiency achieved 95% under the F/M ratio (kg-loading MLSS kg-RMLSS-1) of less than 0.018. Also, among the sludge components, both fixed suspended solids and volatile suspended solids were reduced. Based on the sludge reduction performance and the RNA-based bacterial community characteristics, the combined action of the maintenance metabolism, lysis-cryptic growth, and particulate inorganic matter is proposed as the sludge reduction mechanism in the multi-stage sludge treatment process.

Roles of hydrothermal-alkaline treatment in tannery sludge reduction: rheological properties and sludge reduction mechanism analysis.

The hydrothermal-alkaline treatment (HAT) is an efficient sludge reduction method. However, the roles of HAT in tannery sludge reduction are not very clear. In this study, the sludge reduction mechanism of HAT was explored. The results showed that HAT had good performance for the organic dissolution of tannery sludge. The reduction of the sludge mass was calculated by the mass of the separated wet sludge solid (4000 rpm, 10 min) before and after HAT. The HAT parameters for sludge reduction (SR) were optimized by the Box–Behnken, and the sludge reduction was 62.5% under optimal conditions (198 °C, 87 min and 8.7 g L−1 NaOH). The soluble organics, especially a polysaccharide (PS) and ammonia nitrogen (NH3–N), showed a close correspondence with the SR ratio. The rheological properties of the sludge indicated that the reticular structures in the sludge were destroyed after HAT. The tannery sludge solid became more pyknotic than raw sludge after the hydrothermal-alkaline treatment. The tannery sludge reduction can be attributed to the damage of reticular structures, organic dissolution and release of bound water.

Assessment of the Sludge Reduction of the Metabolic Uncoupler 3,3',4',5-tetrachlorosalicylanilide (TCS) in Activated Sludge Culture.

Batch experiments were completed to assess the sludge reduction of the metabolic uncoupler 3,3′,4′,5-tetrachlorosalicylanilide (TCS). The effects of various TCS concentrations on sludge yield were evaluated and the mechanisms associated with sludge reduction were assessed. We discovered that TCS addition resulted in a reduction in sludge. Furthermore, a low dose of TCS (≤3 mg/L) resulted in a slight reduction in the efficiency of the wastewater treatment system, while >3 mg/L TCS reduced matrix removal efficiency, with an especially remarkable inhibition effect on ammonia removal. An increase in TCS addition was associated with a gradual decrease in both the electron transport system (ETS) activity and the specific cellular ATP (SATP) in the TCS system. It was demonstrated that TCS plays an important role in metabolic uncoupling. However, with the addition of TCS, both contents and compositions were increased, and the protein content increased more than polysaccharide production in extracellular polymeric substances (EPS). At TCS concentrations of ≤3 mg/L, DNA content was stable, but it increased rapidly from 4.97 mg/L to 15.34 mg/L as the TCS concentration was elevated from 6 mg/L to 12 mg/L. This implied that the mechanisms of sludge reduction were different for different TCS concentrations, including uncoupling metabolism, maintenance metabolism and lysis–cryptic growth.

Determination and evaluation of kinetic parameters of activated sludge biomass from a sludge reduction system treating real sewage by respirometry testing

Oxic-settling-anoxic (OSA) process is one of the promising variants that produces lower amounts of sludge and has been applied to aerobic and nutrient removal systems. The only consequence on this modification is that supplementary research is advisable to fully understand the mechanism, which eventually leads to the development of a more realistic model. This study evaluated the characteristics of an OSA process as a sludge reduction system by calibration of kinetic coefficients of ASM1 model with some modifications. A series of respirometric tests were designed for the assessment of microbial kinetics and for further clarification of sludge reduction mechanism. The calibration results depicted that the decay rate is the most variable kinetic parameter depending on the system configuration. It was determined that this kinetic coefficient increased significantly after the system was modified into OSA configuration while other model parameters were almost kept constant. This may be referred to a change either in the microbial population or in the metabolism of the community. The active biomass ratio in the CAS reactor was found to be around 75%, while it was almost 2 times lower in the side-stream reactor. All results led to a conclusion that OSA process is encouraging endogenous decay and consequently lowers biomass viability in the reactor and achieves excess sludge reduction in the system. All experimental results confirmed that side-stream reactor accelerates decay rate of the community and causes the introduction of sludge with low viability to the main reactor.

The effects of a full-scale anaerobic side-stream reactor on sludge decay and biomass activity.

A full-scale anaerobic side-stream reactor (ASSR) for sludge reduction was monitored in terms of sludge production and compared with the previous conventional activated sludge configuration (CAS). A detailed solid mass balance was calculated on the whole full-scale plant to estimate the sludge reduction associated with the ASSR. The activity of the biomass, which undergoes alternation of aerobic and anaerobic conditions, was investigated by the respirometric test. The ASSR promoted a reduction of heterotrophic biomass activity and the substrate consumption rate in the activated sludge implemented with ASSR (AS + ASSR) was 36% smaller than in the CAS period. The solid mass balance indicated a sludge reduction of 28%. During the 270-day operation, the observed sludge yield passed from 0.438 kgTSS/kgCOD in the CAS to 0.315 in the AS + ASSR configuration. The solubilization of chemical oxygen demand (COD), NH4 +-N and orthophosphate were verified under anaerobic conditions. The results suggest that the possible mechanisms of sludge reduction were the increase of the system sludge retention time (SRT) by ASSR addition, and the reduction in heterotrophic biomass activity added to the organic compounds' hydrolysis.

Insight into the roles of packing carriers and ultrasonication in anaerobic side-stream reactor coupled membrane bioreactors: Sludge reduction performance and mechanism

The sludge in situ reduction process by inserting an anaerobic side-stream reactor (ASSR) in a sludge return line provides a cost-effective approach to reduce sludge production in activated sludge systems. In this study, four pilot-scale membrane bioreactors (MBRs), including an AO-MBR for control, ASSR coupled MBR (ASSR-MBR), a MBR with ASSR packed with carriers (AP-MBR) and an AP-MBR with part of sludge ultrasonicated before fed into ASSR (AUP-MBR) were operated in parallel to investigate enhancing effects of ultrasonication and packing carriers on sludge reduction and pollutants removal performance under both normal and low temperature. Low temperature showed negligible impact on COD removal, deteriorated NH4+N and TN removal from 98.3% to 69.7% at 21.6 °C to 92.5% and 48.8% at 2.6 °C, and decreased sludge reduction efficiency (SRE) in ASSR-MBR. Packing carriers and ultrasonication both enhanced sludge reduction, especially under low temperature with SRE values increased from 8.2% of ASSR-MBR to 17.1% of AP-MBR and 32.6% of AUP-MBR at 4.5 ± 2.5 °C. Packing carriers and ultrasonication increased cell rupture by 11.1% and 14.5% in aerobic MBR, enhanced protease activity in ASSR by 60.0% and 116.3%, and reduced ATP content for heterotrophic metabolism by 31.4% and 7.3%, respectively. MiSeq sequencing results showed that packing carriers enriched hydrolytic bacteria (Terrimonas, Dechloromonas and Woodsholea), slow growers (Sulfuritalea, Thauera and Azospira) and predatory bacteria (Bdellovibrio and norank_Saprospiraceae), while ultrasonication further enriched hydrolytic bacteria (norank_Saccharibacteria and Ferruginibacter). Packing carriers is more cost-effective than ultrasonication to enhance sludge reduction by partial damage to bacterial cells and promoting better interaction between bacteria, enzymes and substrates to favor particles hydrolysis.

Investigate of in situ sludge reduction in sequencing batch biofilm reactor: Performances, mechanisms and comparison of different carriers

Biofilm is an effective simultaneous denitrification and in situ sludge reduction system, and the characteristics of different biofilm carrier have important implications for biofilm growth and in situ sludge reduction. In this study, the performance and mechanism of in situ sludge reduction were compared between FSC-SBBR and SC-SBBR with constructed by composite floating spherical carriers (FSC) and multi-faceted polyethylene suspension carriers (SC), respectively. The variation of EPS concentration indicated that the biofilm formation of FSC was faster than SC. Compared with SCSBBR, the FSC-SBBR yielded 0.16 g MLSS/g COD, almost 27.27% less sludge. The average removal rates of COD and NH4+-N were 93.39% and 96.66%, respectively, which were 5.21% and 1.43% higher than the average removal rate of SC-SBBR. Investigation of the mechanisms of sludge reduction revealed that, energy uncoupling metabolism and sludge decay were the main factors for sludge reduction inducing 43.13% and 49.65% less sludge, respectively, in FSC-SBBR. EEM fluorescence spectroscopy and SUVA analysis showed that the hydrolytic capacity of biofilm attached in FSC was stronger than those of SC, and the hydrolysis of EPS released more DOM contributed to lysis-cryptic growth metabolism. In additional, Bacteroidetes and Mizugakiibacter associated with sludge reduction were the dominant phylum and genus in FCS-SBBR. Thus, the effect of simultaneous in situ sludge reduction and pollutant removal in FSC-SBBR was better.

Sludge reduction by a micro-aerobic hydrolysis process: A full-scale application and sludge reduction mechanisms

The process performance of a full-scale sludge process reduction activated sludge (SPRAS) system in long-term operation were investigated by inserting a micro-aerobic tank and a clarifier before conventional activated sludge process. The full-scale SPRAS for industrial park wastewater treatment achieved efficient pollutants removal and a low observed sludge yield of 0.074 g SS/g COD. Batch tests showed that influent feeding into the micro-aerobic tank favored sludge reduction, and obtained a sludge decay constant of 0.168 d−1. The SPRAS enriched slow growers and hydrolytic bacteria for sludge reduction, showed high simultaneous nitrification and denitrification efficiency in the micro-aerobic tank with abundant denitrifying bacteria, and improved sludge settleability by enriching floc-forming bacteria. Process configuration of the SPRAS was beneficial to enhance maintenance metabolism, cyclic micro-aerobic and anaerobic uncoupling, and lysis-cryptic growth for sludge reduction. Techno-economic analysis showed that the SPRAS greatly reduced sludge production with small footprint and low cost.

Effects of hydraulic retention time on process performance of anaerobic side-stream reactor coupled membrane bioreactors: Kinetic model, sludge reduction mechanism and microbial community structures

An anoxic/oxic membrane bioreactor (AO-MBR) and three anaerobic side-stream reactor (ASSR) coupled MBRs (ASSR-MBR) were operated to investigate the effects of hydraulic retention time of ASSR (HRTA) and to elucidate sludge reduction mechanisms in ASSR-MBRs. Increasing HRTA from 3.3 to 6.6 h improved nitrogen removal, and enhanced sludge reduction from 8.0% to 40.9% in ASSR-MBR. The sludge decay coefficient was 0.0221 d−1 in MBRs, and 0.0231–0.0345 d−1 in ASSRs. The measured lysis rate coefficient of heterotrophic biomass was 0.083–0.112 d−1 in MBRs and 0.079–0.111 d−1 in ASSRs. The hydrolysis rate coefficient of inactive particulate organic matters (POMs) in ASSRs significantly exceeded that in the MBR. At HRTA of 6.6 h, POMs hydrolysis in ASSR (38.6%) is the dominant route of sludge reduction, and cell lysis occurred principally in aerobic tanks. Illumina-MiSeq sequencing showed ASSR-MBRs enriched hydrolytic and fermentative bacteria, and confirmed that anaerobic hydrolysis contributed most to sludge reduction.

Respirometric anatomy of the OSA process: microbial basis of enhanced sludge reduction mechanism

AbstractBACKGROUNDExtensive research effort has been devoted to the performance of the OSA system. Despite all studies focused on the assessment of observed sludge yield values, their explanations of the mechanisms causing sludge reduction remained highly speculative. RESULTSA laboratory‐scale OSA system fed with peptone mixture was operated together with a system consisting only of a sequencing batch reactor. The experimental program focused on the assessment of the nature and characteristics of all streams by calibrating an appropriate model by oxygen uptake rate profiles obtained under different conditions. Results indicated that the interchange stream contained a significant fraction of heterotrophic biomass. Therefore, interpretations of the microbial functions in the OSA/oxic reactor should account for active heterotrophic input through the interchange stream. As also justified by corresponding mass balance expressions, the OSA/oxic reactor sustained a substantially higher active biomass concentration as compared with the control reactor. In this way, the relative magnitude of the endogenous decay was significantly increased with respect to microbial growth and the observed experimental results totally accounting for the excess sludge reduction in the tested lab‐scale OSA system.CONCLUSIONThe experimental results in this study provided conclusive proof that enhanced endogenous decay due to higher active biomass level sustained in the OSA/oxic reactor should be regarded as the major cause of excess sludge reduction in the OSA system. © 2018 Society of Chemical Industry