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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]

• We studied under-loaded performance of a full-scale WWTP to control overflow. • Long-term under-load of WWTPs didn't affect pollutant removal and shock resistance. • Under-loaded operation enlarged flocs size with overgrowth of filamentous bacteria. • Under-loaded operation slightly worsened sludge settleability and floc aggregation. • A remarkable increase in Thuricola confirmed the risk of flocs disintegration. Effects of low hydraulic loading rate (HLR) in dry weather and high HLR in wet weather on pollutant removal, microbial community, and sludge properties of a full-scale wastewater treatment plant (WWTP) were extensively studied to explore the risk of under-loaded operation for overflow pollution control. Long-term low HLR operation had an insignificant effect on the pollutant removal performance of the full-scale WWTP, and the system could withstand high-load shocks in wet weather. Low HLR resulted in higher oxygen and nitrate uptake rate due to the storage mechanism under the alternating feast/famine condition, and lower nitrifying rate. Low HLR operation enlarged particle size, deteriorated floc aggregation and sludge settleability, and reduced sludge viscosity due to the overgrowth of filamentous bacteria and inhibition of floc-forming bacteria. The remarkable increase in Thuricola and the contract morphology of Vorticella in microfauna observation confirmed the risk of flocs disintegration in low HLR operation. [ABSTRACT FROM AUTHOR]

Due to the importance of wastewater aeration in meeting treatment requirements and due to its elevated energy intensity, it is important to describe the real nature of an aeration system to improve design and specification, performance prediction, energy consumption, and process sustainability. Because organic loadings drive aeration efficiency to its lowest value when the oxygen demand (energy) is the highest, the implications of considering their dynamic nature on energy costs are of utmost importance. A dynamic model aimed at identifying conservation opportunities is presented. The model developed describes the correlation between the COD concentration and the α factor in activated sludge. Using the proposed model, the aeration efficiency is calculated as a function of the organic loading (i.e. COD). This results in predictions of oxygen transfer values that are more realistic than the traditional method of assuming constant α values. The model was applied to two water resource recovery facilities, and was calibrated and validated with time-sensitive databases. Our improved aeration model structure increases the quality of prediction of field data through the recognition of the dynamic nature of the alpha factor (α) as a function of the applied oxygen demand. For the cases presented herein, the model prediction of airflow improved by 20–35% when dynamic α is used. The proposed model offers a quantitative tool for the prediction of energy demand and for minimizing aeration design uncertainty. [ABSTRACT FROM AUTHOR]

• Fouling and cleaning of fine-pore diffusers operated for 10 years were studied. • Oxygen-affinity, filamentous and EPS-secreting bacteria enriched on diffuser surface. • External, internal and irrecoverable foulants accounted for 34.1%, 45.4% and 20.1%. • HCl cleaning dispersed organic foulants and failed to restore aeration performance. • NaClO cleaning before HCl had better recovery by eliminating organic foulants first. Fouling characterization and aeration performance recovery of fine-pore diffusers operated for 10 years in a full-scale wastewater treatment plant were investigated to elucidate fouling mechanisms and develop cleaning strategy. The performance decline of diffusers was observed with dynamic wet pressure increased by 3.2 times and standard oxygen transfer efficiency dropped to 73%, which contributed to 15.0% increase in total energy consumption. Oxygen-affinity, filamentous and extracellular polymeric substances secreting bacteria tended to accumulate on the diffuser surface. External (mainly biofilm growth), internal (organic and inorganic matters) and irrecoverable (mainly material aging) foulants accounted for 34.1%, 45.4% and 20.1% of total fouling, respectively. HCl cleaning failed to restore aeration efficiency because it eliminated structural support formed by inorganics, leaving organic foulants broken into smaller fragments and distributed more dispersed. NaClO showed better cleaning efficiency by effectively removing organic foulants. Sequential cleaning by NaClO and HCl, which achieved the best recovery, was recommended. [ABSTRACT FROM AUTHOR]

One of the main challenges in industrial wastewater treatment and recovery is the removal of sulfate, which usually coexists with Ca 2+ and Mg 2+ . The effect of Mg 2+ on sulfate removal by ettringite precipitation was investigated, and the process was optimized in the absence and presence of Mg 2+ . In the absence of Mg 2+ , the optimum conditions with sulfate removal of 99.7% were obtained at calcium-to-sulfate ratio of 3.20, aluminum-to-sulfate ratio of 1.25 and pH of 11.3 using response surface methodology. In the presence of Mg 2+ , sulfate removal efficiency decreased with increasing Mg 2+ concentration, and the inhibitory effect of Mg 2+ matched the competitive inhibition Monod model with half maximum inhibition concentration of 57.4 mmol/L. X-ray diffraction and Fourier transform infrared spectroscopy analyses of precipitates revealed that ettringite was converted to hydrotalcite-type (HT) compound in the presence of Mg 2+ . The morphology of precipitates was transformed from prismatic crystals to stacked layered crystals, which confirmed that Mg 2+ competes with Ca 2+ for Al 3+ to form HT compound. A two-stage process was designed with Mg 2+ removal before ettringite precipitation to eliminate the inhibitory effect, and is potential to realize sludge recovery at the same time of effective removal of sulfate and hardness. [ABSTRACT FROM AUTHOR]

This work aims at optimizing performance of the multimode anaerobic/anoxic/aerobic (AAO) system, which could be flexibly operated under AAO, reversed AAO (RAAO) and anoxic/aerobic (AO) modes, based on effluent quality and operating costs at low temperature of 12.5 °C. Influences of sludge retention time (SRT) on effluent quality, functional biomass and operating cost were evaluated for each mode. The AAO has a better performance than RAAO and AO at SRT of 5–25 d under the same operating cost for its higher pollutant removal efficiency and concentration of phosphorus-accumulating organisms. Furthermore, an operating region conforming to required discharge standards was established for the AAO mode by regulating returned activated sludge (RAS) and mixed liquor recirculation (MLR). Optimal condition was obtained using MLR ratio of 100%, RAS ratio of 50%, and SRT of 16 d. Dynamic simulation results showed that multi-criteria modeling was a useful tool in process optimization. [ABSTRACT FROM AUTHOR]

This paper describes a cost-effective method for phosphorus removal from reject water of sludge dewatering process by using supernatant from sludge lime stabilization (SLS) processes, which are extensively used in China. Supernatant from SLS processes contains high concentration of calcium and high alkalinity hindering COD and ammonium nitrogen removal but favoring phosphate precipitation. Effects of pH and dosing ratio between supernatant and reject water on simultaneous removal of phosphorus and organic substances were evaluated. Both pH and Ca/P ratio increased with increasing dosing ratio of supernatant and reject water. The phosphorus removal achieved 90% when dosing ratio maintained above 15%. COD and humic substances were also effectively removed from reject water by adding SLS supernatant. X-ray diffraction analysis and morphology of harvested precipitates revealed that when pH increased from 7.49 to 9.77, the crystallinity increased, and hydroxyapatite converted to tri-calcium phosphate simultaneously. This method not only saves costs for chemical precipitants, but also favors nutrient removal by increasing alkalinity for nitrification and adding carbon source for denitrification, meanwhile reduces risks of pipeline blockage in wastewater treatment plants. [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]

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]

This study investigated sulfate (SO 4 2−) removal by Mg–Al hydrotalcite-type (HT) compound (Mg 6 Al 2 SO 4 (OH) 16 • m H 2 O), and analyzed applicable condition of the method from techno-economic perspective. Under optimized condition of pH 8.80, molar ratio of Mg2+ and SO 4 2− (Mg/S ratio) of 6.63 and molar ratio of Al3+ and SO 4 2− (Al/S ratio) of 2.53, HT compound achieved a greatly lower concentration of SO 4 2− (3.76 mmol/L) than conventional gypsum precipitation. The composition and morphological analysis of precipitates showed that HT compound was transformed to Mg(OH) 2 at pH > 9.0, and Mg(OH) 2 , Al(OH) 3 and MgAl 2 (OH) 8 at Al/S ratio > 2.5. HT compound had better settleability than Mg(OH) 2 and ettringite, and was easier to be flocculated by anionic polyacrylamide to obtain a lower SV 30 of 16.4%. Turbiscan showed that HT compound had the highest instability and aggregation property among the three systems. Techno-economic analysis showed that HT compound coupled ettringite route was more economic than Mg(OH) 2 coupled ettringite route at Mg/S ratio > 6.08, but was not applicable when concentrations of Mg2+ and SO 4 2− were very low. The precipitated HT compound was recovered as demulsifier and showed more efficient COD removal than conventional demulsifier for chemical cleaning wastewater treatment. Image 1 • SO 4 2− removal by hydrotalcite-type (HT) compound (Mg 6 Al 2 SO 4 (OH) 16.• m H 2 O) was studied. • SO 4 2− was reduced to 3.76 mmol/L at pH 8.80, Mg/S ratio 6.63 and Al/S ratio of 2.53. • HT compound had better settleability and aggregation than Mg(OH) 2 and ettringite. • HT-Ett route was more economic than Mg(OH) 2 -Ett route at Mg/S ratio > 6.08. • HT compound was recovered as demulsifier with efficient COD removal from wastewater. [ABSTRACT FROM AUTHOR]