Search

Abstract 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. [ABSTRACT FROM AUTHOR]

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 (HRT A ) and to elucidate sludge reduction mechanisms in ASSR-MBRs. Increasing HRT A 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 HRT A 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. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate membrane fouling performance of anaerobic side-stream reactor (ASSR) coupled membrane reactors (MBR), and effects of representative enhancement strategy, namely packing carriers and low-strength ultrasonication, on sludge properties and membrane fouling by four pilot-scale MBRs. Compared to anoxic/oxic MBR (AO-MBR) for control, ASSR coupled AO-MBR (ASSR-MBR), ASSR-MBR with ASSR packed with carriers (AP-MBR) and AP-MBR with part of sludge ultrasonicated before fed into ASSR (AUP-MBR) reduced sludge production by 8.4%, 17.5% and 32.9% with efficient pollutants removal. ASSR-MBR showed more severe membrane fouling because inserting ASSR disintegrated sludge floc structure, increased the secretion of extracellular polymeric substances (EPS) and deteriorated viscoelastic property of sludge. Packing carriers in ASSR alleviated membrane fouling of ASSR-MBR by inhibiting EPS-secreting bacteria (Flavobacteriia, γ-Proteobacteria, δ-Proteobacteria and norank_Saccharibacteria), enlarging particle size and improving dewaterability. AUP-MBR showed the most severe membrane fouling and obvious cake layer fouling because ultrasonication disintegrated sludge to small particles, increased adherence property of EPS, and deteriorated dewaterability and viscoelastic property of sludge. MiSeq sequencing revealed Proteobacteria and Bacteroidetes were responsible for membrane fouling at the phylum level, and norank_Neisseriaceae , Arcobacter , norank_Parcubacteria and Mycobacterium were dominant genera easily attached on membrane surface. Image 1 • Membrane fouling (MF) of anaerobic side-stream reactor (ASSR) - MBR was studied. • ASSR-MBR deteriorated MF, dewaterability and flowability due to sludge reduction. • Carriers in ASSR alleviated MF by inhibiting EPS secretion and enlarging particles. • Ultrasonication caused severe MF due to flocs disintegration and high EPS adhesivity. • MiSeq sequencing revealed dominant bacteria easily attached on membrane surface. [ABSTRACT FROM AUTHOR]

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 NH 4 + 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. Graphical abstract Image 1 Highlights • Enhancement of sludge reduction in anaerobic side-stream reactor (ASSR) was studied. • Packing carriers enhanced sludge reduction from 8.2% to 17.1% at 1.0–9.0 °C. • Combining ultrasonication and packing carriers enhanced sludge reduction by 297%. • Combination enhanced cell rupture and protease activity, and reduced ATP content. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • DO effect on sludge reduction was studied by side-stream reactor (SSR) coupled MBR. • Anaerobic and micro-aerobic SSR-MBR obtained higher nitrogen removal than aerobic. • Micro-aerobic SSR-MBR had higher sludge reduction (61.1%) than anaerobic and aerobic. • Anaerobic SSR favored hydrolysis and fermentation, and aerobic enriched slow growers. • Micro-aerobic SSR benefited hydrolytic, fermentative and slow-growing bacteria. Abstract An anoxic/oxic membrane bioreactor (MBR) and three side-stream reactor (SSR) coupled membrane bioreactors were operated in parallel to investigate effects of dissolved oxygen (DO) level in SSR on sludge reduction and microbial community structure of SSR-MBRs. The four MBRs were equally efficient in COD and ammonium nitrogen removal. The anaerobic and micro-aerobic SSR favored nitrogen removal through denitrification, simultaneous nitrification and denitrification and autochthonous substrate release as carbon source. The micro-aerobic SSR achieved greatly higher sludge reduction efficiency (61.1%) than anaerobic (37.3%) and aerobic SSR (7.9%). Micro-aerobic SSR obtained the highest endogenous decay constant (0.035 d−1) compared to anaerobic (0.023 d−1) and aerobic SSR (0.015 d−1). High-throughput sequencing results revealed that anaerobic SSR enriched hydrolytic and fermentative bacteria, aerobic environment favored the growth of slow-growing bacteria, and micro-aerobic SSR stimulated biological activities of both anaerobic and aerobic bacteria. [ABSTRACT FROM AUTHOR]

A micro-aerobic side-stream reactor (MSSR) was inserted in returned sludge line of a membrane bioreactor (MBR) for sludge reduction. Three MSSR coupled MBRs (M-MBRs) and an anoxic/oxic MBR (AO-MBR) were operated in parallel to investigate effects of micro-aerobic condition and hydraulic retention time (HRT) of MSSR (HRT M ) on process performance. M-MBRs and AO-MBR were equally effective in COD and NH 4 -N removal. Rising HRT M from 3.3 to 6.7 h increased sludge reduction from 10.8% to 47.5%, and promoted dissolved organic matters release and utilization by enriching hydrolytic, fermentative and predatory bacteria. M-MBR at HRT M of 3.3 h obtained the highest nitrogen removal, and enriched denitrifiers ( Thauera and Hyphomicrobium ) in the MSSR. The highest relative abundance of polyphosphate-accumulating organisms was observed in M-MBR at HRT M of 5.0 h, which achieved the highest phosphorus removal. Prolonging HRT M to 6.7 h improved sludge dewaterability by enriching floc-formation bacteria ( Nannocystis ) and inhibiting filamentous bacteria ( Candidatus_Alysiosphaera ). [ABSTRACT FROM AUTHOR]

Membrane fouling is the major obstacle for membrane bioreactors operated at a long sludge retention time to reduce sludge production. In this study, a sludge process reduction (SPR) module, consisting of a microaerobic tank and a settler, was inserted before an anoxic/oxic MBR (AO-MBR) to achieve dual objectives of fouling alleviation and sludge reduction. Three SPR-MBRs were operated to investigate influences of sludge recirculation ratios from the SPR settler to the microaerobic tank on process performance. Compared to AO-MBR, the SPR-MBRs reduced sludge production by 43.1–56.4% by maintaining sludge retention times above 175 d, and decreased foulant layer resistance and pore clogging resistance. Inserting SPR reduced the accumulation of dissolved organic matters and extracellular polymeric substances, enlarged sludge flocs, and decreased sludge viscoelasticity. However, increasing R SPR stimulated outward diffusion of extracellular polymeric substances and increased sludge viscosity. SPR-MBRs achieved effective sludge reduction by enriching hydrolytic (Trichococcus and Aeromonas) and fermentative genera (Lactococcus , Paludibacter , Macellibacteroides , and Acinetobacter) in the SPR, and alleviated membrane fouling by prohibiting the growth of extracellular polymeric substance-secreting bacteria and enriching filamentous bacteria to enlarge particle size. The results revealed that the SPR-MBR maximized sludge reduction with a very long sludge retention time, and alleviated membrane fouling synchronously. • An SPR-MBR was proposed to reduce sludge production and alleviate membrane fouling. • SPR-MBR achieved sludge reduction of 43.1–56.4% by maintaining SRTs ≥175 d. • SPR-MBR alleviated membrane fouling by reducing sticky organics and enlarging flocs. • SPR-MBR enriched abundant hydrolytic and fermentative bacteria for sludge reduction. • SPR-MBR reduced EPS secretion and enriched filamentous bacteria to alleviate fouling. [ABSTRACT FROM AUTHOR]

A sludge process reduction activated sludge (SPRAS), with a sludge process reduction module composed of a micro-aerobic tank and a settler positioned before conventional activated sludge process, showed good performance of pollutant removal and sludge reduction. Two SPRAS systems were operated to investigate effects of micro-aeration on sludge reduction performance and microbial community structure. When dissolved oxygen (DO) concentration in the micro-aerobic tank decreased from 2.5 (SP H ) to 0.5 (SP L ) mg/L, the sludge reduction efficiency increased from 42.9% to 68.3%. Compared to SP H , activated sludge in SP L showed higher contents of extracellular polymeric substances and dissolved organic matter. Destabilization of floc structure in the settler, and cell lysis in the sludge process reduction module were two major reasons for sludge reduction. Illumina-MiSeq sequencing showed that microbial diversity decreased under high DO concentration. Proteobacteria , Bacteroidetes and Chloroflexi were the most abundant phyla in the SPRAS. Specific comparisons down to the class and genus level showed that fermentative, predatory and slow-growing bacteria in SP L community were more abundant than in SP H . The results revealed that micro-aeration in the SPRAS improved hydrolysis efficiency and enriched fermentative and predatory bacteria responsible for sludge reduction. [ABSTRACT FROM AUTHOR]

To understand process performance and microbial community structure in oxic-settling-anaerobic (OSA) sludge reduction process, an anoxic–OSA (A + OSA) system and a conventional anoxic–oxic (AO) system were operated for 200 days. Both systems were almost equally effective in the removal of COD and ammonium nitrogen, but A + OSA system showed higher nitrogen removal efficiency owing to denitrification and the release of soluble organic matters in the sludge holding tank (SHT). A + OSA process reduced sludge production by 30.4% with observed sludge yield of 0.179 gSS/gCOD. Pyrosequencing results revealed that although core populations were shared with highly functional organization, the relative abundance and stability of microbial communities in A + OSA system were higher than AO system. Classes Anaerolineae and Actinobacteria responsible for hydrolysis and fermentation of organic matters were enriched in SHT and played an important role in sludge reduction of A + OSA process. Specific comparison down to the genus level revealed the enrichment of anaerobic fermentative bacteria ( Azospira , Propionivibrio and Sulfuritalea ) and slow growers ( Trichococcus ) in A + OSA system. [ABSTRACT FROM AUTHOR]

Three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy and gel permeation chromatography (GPC) analysis were employed to investigate the distribution and transformation of dissolved organic matter (DOM) in the anoxic–oxic-settling-anaerobic (A + OSA) process for sludge reduction. The A + OSA process showed a good performance in nitrogen and organic pollutants removal efficiency, and reduced sludge yield by 32% under a sludge retention time of 6 h in the anaerobic sludge holding tank (SHT). Parallel factor analysis was used to assess DOM composition from EEM spectra and three fluorescent components were identified: two humic-like components and one protein-like component. In the A + OSA process, the humic-like components were difficult to degraded, while the protein-like component was easily hydrolyzed and adsorbed under anoxic conditions. The fluorescence intensities of the humic-like and protein-like components were both strengthened in the SHT owing to sludge decay under the anaerobic condition. GPC analysis of the A + OSA system showed that the majority of molecules in the influent wastewater with molecular weight (MW) in the range of >250 and 30–50 kDa were mainly transformed into small molecules with MW in the range of 30–250 and <0.5 kDa in the effluent by microorganisms. The DOM in the SHT effluent demonstrated a broader MW distribution and higher intensity than that in the SHT influent, and the percentage of MW between 10 and 30 kDa in the SHT effluent were significantly increased owing to cell lysis and decay in the SHT. [ABSTRACT FROM AUTHOR]

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 (HRT SR) on membrane filtration performance and fouling tendency. ASSR-MBR with HRT SR 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) > ASSR 2.5 -MBR (5.39 ± 0.30 × 1012 m−1) > ASSR 6.7 -MBR (3.33 ± 0.42 × 1012 m−1) > ASSR 5.0 -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 HRT SR of 2.5 and 6.7 h, respectively. CLSM results indicated that ASSR-MBR with HRT SR 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. [Display omitted] • The alleviation of membrane fouling was observed in carrier-enhanced ASSR-MBRs. • Carrier-enhanced ASSR improved dewaterability and rheological property of sludge. • Proteins of EPS were responsible for improving membrane filtration in ASSR-MBRs. • ASSRs-MBR enriched fouling-eased bacteria to mitigate membrane fouling. • Relation between fouling and metabolism of membrane surface microbes is uncovered. [ABSTRACT FROM AUTHOR]

• Roles of filling fraction of carriers in anaerobic side-stream reactor was studied. • Carriers with filling fraction of 25% achieved the highest sludge reduction of 50.5%. • Packing carriers accelerated enzyme secretion and enhanced hydrolysis and cell lysis. • Enhancement by carriers themselves and to the bulk sludge accounted for 25% and 75%. • Excessive carriers had negative effect on biomass stability and movement of carriers. An anoxic/oxic membrane bioreactor (AO) and three pilot-scale anaerobic side stream reactors (ASSR) coupled MBRs (ASSR-MBRs), packed with 0%, 25% and 50% carriers in ASSRs, were continuously operated to study the mechanisms for sludge reduction. Four systems showed efficient COD and NH 4 +-N removal, while packing carriers significantly enhanced nitrogen removal. 25% filling fraction (AP 25) achieved the highest sludge reduction efficiency of 50.5% compared to 0% (21.7%) and 50% (39.7%). Compared to ASSR-MBR, carriers enhanced the release of dissolved organic matters, and accelerated the secretion of enzyme for cell lysis and hydrolysis. In AP 25 , the presence of carriers prompted the formation of environment propitious to sludge reduction in bulk sludge. AP 25 tended to enrich hydrolytic, fermentative and denitrifying bacteria to accelerate hydrolysis process, while excessive carriers had negative effect on biomass stability and movement of carriers. [ABSTRACT FROM AUTHOR]