Effect Of Sludge Retention Time Research Articles

Effect of culture history and carbon sources on polyhydroxyalkanoates production in activated sludge systems

ABSTRACT Polyhydroxyalkanoates (PHAs) are important and completely biodegradable alternatives to regular plastics, and they can be produced by activated sludge systems during wastewater treatment. Wastewaters with high organic content are being used for PHA production, which is an important resource recovery option. In this context, the effect of sludge retention time and different carbon sources, such as acetate, peptone-mixture and industrial wastewater (containing acetic acid (AA), lactic acid (LA) and propionic acid (PA)), on PHA storage was investigated. Oxygen utilisation rate (OUR) profiles were generated in respirometric tests and were evaluated by activated sludge modelling. Results showed that high storage (AA: 70%; LA: 49%; PA: 60% and industrial wastewater: 52%) was achievable in the feast phase even when the biomass was fed with a high organic acid content substrate to which it is not acclimated.

Effect of sludge retention time on the removal of fluoroquinolone antibiotics in wastewater treatment of activated sludge

In this study, the effect of the sludge retention time (SRT) (SRT = 15 d, 20 d, 30 d) on the removal of three typical fluoroquinolone antibiotics (norfloxacin (NOR), ofloxacin (OFL), ciprofloxacin (CIP)) and the role of microorganisms in the process was investigated. The removals of fluoroquinolone antibiotics were mainly removed by adsorption under all three sludge retention times, with average removal rates of 82.87 %, 62.53 % and 70.06 %, respectively. When the initial antibiotic concentration was higher than 3 mg/L, the biomass, total extracellular polymeric substance (EPS) and PN/PS showed a decreasing trend, and the sludge activity decreased. In the sequencing batch bioreactor, the removal efficiency of OFL increased from 59.24 % to 72.99 % as the SRT increased from 15 to 30 days. In addition, prolongation of SRT increased the diversity of active microorganisms while the relative abundance of K-strategic bacteria (Nitrospira, Glutamicibacter) increased under low food-to-microorganism (F/M) ratio conditions, which played a key role in the removal of fluoroquinolone antibiotics. Biodegradation removal increased from 7.89 % to 22.18 % and adsorption/biodegradation ratio decreased from 6.51 to 2.03.

Wastewater Remediation by Aerobic Membrane Bioreactor: Effect of Sludge Retention Time on Treatment Performance and Filtration Process

Wastewater Remediation by Aerobic Membrane Bioreactor: Effect of Sludge Retention Time on Treatment Performance and Filtration Process

Effect of sludge retention time (SRT) on micro-ecological niche competition kinetics between ammonia-oxidizing organisms (AOO) and nitrite-oxidizing organisms (NOO) in a single system

As a method for controlling the nitrification process, sludge retention time (SRT) control is based on the micro-ecological niche competition between ammonia-oxidizing organisms (AOO) and nitrite-oxidizing organisms (NOO). In this study, AOO and NOO were domesticated and cultured under different SRT conditions (40 d, 20 d, 10 d, and 5 d) in four continuous stirred-tank reactors (CSTRs) to investigate the relationship between their ecological niche shift and the typical environmental conditions. As the SRT decreased, the proportion of AOO colonies gradually increased and achieved spatial ecological niche competition superiority, which may be related to their maximum growth rate and ecological niche width. Moreover, the ecological niche width of the typical environmental impact parameters of AOO and NOO changed significantly with the SRT, which may be related to the changes in their internal flora. In addition, a micro-ecological niche competition model and kinetic systems were established and simulated on the basis of existing microbial biochemical models. The established model could be used to simulate and predict the ecological niche shift process of AOO and NOO under different SRT conditions in the CSTRs. In summary, this study explains the mechanism and basic kinetic parameters of SRT control in two-step nitrification based on micro-ecological niche competition theory. And a niche competition model has been established, providing a new method for controlling the process.

Enhancing Mesophilic Anaerobic Digestion of Waste-Activated Sludge through Heat Pretreatment and Kinetic Modeling

Sewage sludge is a useful raw material for the production of renewable energy due to its stable annual output. In this study, the enhancement of mesophilic anaerobic digestion of sewage sludge through heat pretreatment at 95 °C for 30 min was tested in an anaerobic moving bed biofilm reactor (hAMBBR). The sludge retention time was set at 20, 15, 10, and 5 days during 300 days of operation and compared to a traditional anaerobic continuous stirred tank reactor (AnCSTR) without pretreatment. Results of this research indicate that the digestion ratio of volatile soluble solids in the hAMBBR process could be improved by 50%, and the average conversion ratio of methane could be increased by 45%. When the sludge retention time (SRT) was shortened to 5 days, the methane production approached twice that of the contrast reactor. The expanded anaerobic digestion model, including activated sludge models, was utilized for operation simulation. The effect of sludge retention time (SRT) shortening on volatile suspended solids (VSS) digestibility and methane production was well reproduced with simulations. The research conclusion reveals the impact of pretreatment and reactor types on anaerobic digestion and provides the scientific basis for improving methane production and process efficiency in anaerobic digestion.

Effect of sludge retention time on bioregeneration of powdered activated carbon loaded with paracetamol

Effect of sludge retention time on bioregeneration of powdered activated carbon loaded with paracetamol

Effect of sludge retention time on the performance and sludge filtration characteristics of an aerobic membrane bioreactor treating textile wastewater

In this study, the impact of different sludge retention times (SRTs) on the wastewater treatment performance of an aerobic membrane bioreactor (MBR) was investigated using real textile industry wastewater. For this purpose, two laboratory-scale membrane bioreactors were operated in parallel. Under the same conditions, one of the systems was operated at an SRT of 30 d and, the other at SRTs of 20 d, and 10 d, respectively. The total chemical oxygen demand (COD), color and soluble total nitrogen (TN) of the wastewater averaged 927 ± 277 mg/L, 910 ± 287 PtCo and 39 ± 10 mg/L, respectively. COD removal efficiency remained above 90 % in all the tested SRTs. While the color removal efficiency was 55 % and 60 % at SRTs of 30 d and 20 d, respectively, it decreased to 50 % at SRT of 10 d. In addition, the impact of different SRTs on membrane filtration performance was studied. With the reduction of SRT to 10 d, an increase was observed in specific resistance to filtration (SRF) and supernatant filterability (SF) values, while viscosity decreased due to lower suspended solid (SS) concentration. According to gel permeation chromatography (GPC) analysis, the molecular weights of organic substances in the permeate distributed over a wide spectrum as SRT decreased. Also, signals given by the low molecular weight organic compounds were higher.

Effect of Sludge Retention Time on Bioregeneration of Powdered Activated Carbon Loaded with Paracetamol

Effect of Sludge Retention Time on Bioregeneration of Powdered Activated Carbon Loaded with Paracetamol

The effect of sludge retention time (SRT) on the Nitrifier typical kinetics at ambient temperature under the low ammonia density.

Sludge retention time (SRT) regulation is one of the essential management techniques for refined control of the main-sidestream treatment process under the low ammonia density. It is indispensable to understand the effect of SRTs changes on the Nitrifier kinetics to obtain the functional separation of the Nitrifier and the refined control of the nitrification process. In this study, Nitrifier was cultured with conditions of 35 ± 0.5 °C, pH 7.5 ± 0.2, DO 5.0 ± 0.5 mg-O/L, and SRTs were controlled for 40 d, 20 d, 10 d, and 5 d. The net growth rate (μm), decay rate (b), specific growth rate (μ), the yield of the Nitrifier (YA), temperature parameter (TA), and inhibition coefficient (KI) have been measured and extended with the SRT decreases. Instead, the half-saturation coefficient (KS) decreased. In addition, the limited value of pH inhibition occurs (pHUL), and the pH of keeping 5% maximum reaction rate (pHLL) was in a relatively stable state. The trade of kinetics may be induced by the change of species structure of Nitrifier. The Nitrosomonas proportion was increased, and the Nitrospira was contrary with the SRT decreasing. It is a match for the functional separation of Nitrifier when SRTs was 20 d at ambient temperature under the low ammonia density. The kinetics of ammonia-oxidizing organisms (AOO) and nitrite-oxidizing organisms (NOO) in Nitrifier under different SRT conditions should be measured respectively to the refined control of the partial nitrification process in future study.

Effect of sludge retention time on microbial succession and assembly in thermal hydrolysis pretreated sludge digesters: Deterministic versus stochastic processes

Thermal hydrolysis process (THP) assisted anaerobic digestion (AD) has been demonstrated to be an efficient approach to improve biogas production and solids reduction. Given the faster reaction kinetics in the THP-AD system, reduction of sludge retention time (SRT) is possible. However, a comprehensive understanding of the effects of sludge retention time (SRT) on microbial dynamics and community assemblages is still lacking in THP-AD systems. Thus, twelve THP-AD reactors were operated at different SRTs (10–30 d) to fulfill the knowledge gap. Results showed that, although all the bioreactors displayed good performance, shorter SRT reactors (SRT 10 d) took a longer time to reach the stable state. The total biogas production at SRT of 10 d was lower than that at other longer SRTs, attributing to the limited hydrolytic/fermentative capacities of AD microbiomes. Different SRTs resulted in distinct succession patterns of AD microbiomes. THP sludge reduced the microbial diversity in all the bioreactors over time, but longer SRTs maintained higher biodiversity. Null model analysis suggested that THP-AD microbial community assembly was predominately driven by deterministic selection at the tested SRT range, but stochasticity increased with elevated SRTs, likely attributing to the immigrants from the feedstock. Phylogenetic molecular ecological networks (pMENs) analysis revealed more stable network structures at longer SRTs, evidenced by the lower modularity, shorter harmonic geodesic distance, and higher connectivity. The potential keystone taxa under varied SRTs were identified, some of which were hydrolytic/fermentative bacteria (e.g., Peptostreptococcus, Lutispora, Synergistaceae), suggesting that these species related to organic hydrolysis/fermentation even with low-abundance could still play pivotal ecological roles in maintaining the THP-AD microbial community structure and functions. Collectively, this study provides comprehensive and in-depth insights into the mechanisms underlying community assembly in THP-AD reactors, which could aid in diagnosing system stability.

Shortening SRT of Intermittent Gradient Aeration to Realize Nitrogen and Phosphorus Removal in Short-range SNEDPR System

This study explored the effect of sludge retention time (SRT) on ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) under intermittent gradient aeration, as well as the effect of the short-range nitrification endogenous denitrification phosphorus removal system on the treatment of low C/N ratio domestic sewage. In this study, an SBR reactor was used to cultivate aerobic granular sludge, using actual domestic sewage as the influent substrate. As the SRT decreased from 50 d to 30 d, the specific ammonia oxidation rate increased from 3.16 mg·(g·h)-1to 4.38 mg·(g·h)-1, and the specific nitrite oxidation rate decreased from 3.4 mg·(g·h)-1to 1.8 mg·(g·h)-1. The activity of NOB decreased by about 44%, resulting in short-range nitrification within the system. With an SRT of 30 d, the maximum nitrite accumulation was 6.93 mg·L-1. Because the reduced SRT led to a slight decrease in sludge concentration within the system, an aeration reduction strategy was adopted after 40 d, according to the DO curve. When the final SRT was 30 d, the effluent COD concentration was 40.76 mg·L-1, the TN concentration was 12.4 mg·L-1, the TP concentration was 0.31 mg·L-1, and the simultaneous removal of C, N and P was realized. Thus, a stable short-range nitrification endogenous denitrification phosphorus removal system was finally obtained. At the same time, the EPS content of aerobic granular sludge was negatively correlated with SRT, the protein content increased from 66.7 mg·g-1 to 95.1 mg·g-1, and the polysaccharide content remained in the range of 12.1-17.2 mg·g-1, indicating that the decreased SRT had a great effect on the protein content. With an SRT of 30 d, the PN/PS value was maintained at approximately 6.2, and the structural stability of aerobic granular sludge can be maintained under such conditions.

Investigating organic nitrogen production in activated sludge process: Size fraction and biodegradability

The effect of sludge retention time (SRT) on the production of organic nitrogen (ON) fractions (particulate, colloidal and soluble) and the biodegradability of produced soluble ON in an activated sludge process was investigated. Synthetic wastewater with no ON was fed to the four laboratory-scale reactors operated at SRTs of 2, 5, 10 and 20 d, respectively. Effluent ON from each reactor was fractionated into particulate, colloidal, and soluble ON (pON, cON, and sON). The effluent total ON contained 5.7 to 11.9 mg/L pON, 3.6 to 3.8 mg/L cON, and 2.3 to 4.6 mg/L sON. cON fraction can be larger than sON fraction in the secondary effluent. Therefore, besides focusing on sON, water resource recovery facilities aiming to meet stricter effluent TN limits should also identify appropriate technologies to target cON. More than 50% of effluent sON was biodegradable under SRTs of 2, 5, and 10 d but the biodegradability decreased to 31% at 20-d SRT. Large fractions of non-biodegradable sON (69%) at SRT of 20-d could be contributed by extracellular polymeric substances and soluble microbial products, specifically biomass associated products due to endogenous respiration. Thus, sON generated at long SRTs may take longer to decompose in receiving waters.

The effect of sludge retention time and organic loading rate on performance and membrane fouling in membrane bioreactor

AbstractBACKGROUNDMembrane bioreactor (MBR) is commonly considered a promising technology for wastewater treatment due to its outstanding effluent quality, low sludge production, and smaller environmental footprint. However, membrane biofouling is regarded as the bottleneck of MBR processes preventing their universal application. Optimizing operating conditions and improving the antifouling properties of membranes have a substantial impact on the rate and characteristics of membrane fouling in MBR systems.RESULTSIn this study, a two‐step process was performed to mitigate membrane fouling by optimizing sludge retention time (SRT) and organic loading rate (OLR) and improving membrane characteristics in an MBR system developed for the treatment of pharmaceutical wastewater. At first, pure membrane fouling and sludge characteristics were examined in three identical MBRs at different OLRs (40, 100, and 160 mg chemical oxygen demand(COD)/L.d) under various SRTs (7.5, 22.5, and 37.5 days). The investigation indicated that high protein concentration in loosely bound extracellular polymeric substances (LB‐EPS) caused more irreversible fouling at the OLR and SRT of 40 mgCOD/L.d and 7.5 days, respectively. In the second stage, a modified anti‐biofouling membrane was installed into the optimized submerged MBR at OLR = 100 mgCOD/L.d and SRT of 22.5 days for further mitigation of membrane fouling. Membrane fouling significantly reduced as the protein and gram negative bacteria on the surface of the modified membrane decreased.CONCLUSIONThe results showed that the reversible and irreversible membrane fouling were controlled successfully through the proposed optimization of operational conditions and by improving the membrane characteristics in MBR. Finally, the protein of LB‐EPS is a vitally important factor affecting the irreversible membrane fouling. © 2020 Society of Chemical Industry (SCI)

Intermittent cycle extended aeration system pilot scale (ICEAS-PS) for wastewater treatment: experimental results and process simulation

Intermittent cycle extended aeration system is a modification of a conventional sequencing batch reactor system in which the system is operated under continuous feed. The objective of this research is to study the effect of sludge retention time and aeration pattern on the performance of intermittent cycle extended aeration system pilot scale for wastewater treatment. In addition, the process simulation using GPS-X software was conducted. Five different runs of sludge retention times of 10, 15, 20, 25 and 30 days were studied. The optimum sludge retention time for wastewater treatment by intermittent cycle extended aeration system pilot scale was 10 days, and under operating condition of sludge retention time of 10 days, effluent quality was 15.5 ± 3.8, 6.5 ± 1.1, 5.3 ± 1.6, 0.7 ± 0.2, 5.0 ± 1.4 mg/L and 1.4 ± 0.7 mg/L for COD, BOD5, TSS, NH4–N, TN and TP which amply met the local regulation of class A treated wastewater. GPS-X sensitivity analysis tool box was used to determine the most sensitive kinetic parameters affecting the intermittent cycle extended aeration system pilot scale performance. Out of about 50 kinetic parameters, YH, bH, μA, Ko, bA, Ka and μPAO appeared to the most sensitive kinetic parameters. The calibrated GPS-X model proved that the presence of anoxic phase in the cycle has a significant impact on nitrogen and phosphorus removal. In addition, intermittent aeration pattern achieved the highest performance compared with other patterns of aeration only, aeration/anoxic and anoxic/aeration.

Effect of Sludge Retention Time and pH on the Denitrifying Phosphorus Removal Process

In this work, the effects of the sludge retention time (SRT, 35, 25, or 15 d) and pH (7.5, 8.0, 8.5) on denitrifying phosphorus removal were investigated using denitrifying phosphorus bacteria (DPBs) enriched in a sequencing batch reactor (SBR). The results indicated that shortening the SRT from 35 d to 25 d resulted in a decrease in the mixed liquor volatile suspended solids (MLVSS) from 2821 to 2301 mg·L-1, while the sludge loading rate (F/M) increased from 0.256 kg·(kg·d)-1to 0.312 kg·(kg·d)-1. Although the quantity of net phosphorus release and net phosphorus uptake decreased at this stage, the rates of anaerobic phosphorus release, anoxic phosphorus absorption, and denitrification reached their highest levels with values of 25.07, 15.92, and 9.45 mg·(g·h)-1, respectively, due to the increased sludge activity. Consequently, the phosphorus content of the sludge increased from 4.78% to 5.33%, and the removal rate of PO43--P was stable at above 95% with an average effluent PO43--P concentration below 0.5 mg·L-1. When the SRT was further shortened to 15 d, the MLVSS decreased to values as low as 1448 mg·L-1, and the proportion of DPBs in the phosphorus accumulating organisms (PAOs) decreased from 82.4% to 65.7%, indicating that the DPBs were gradually washed out from the system due to the excessively short SRT. At this stage, the phosphorus content of sludge decreased to 3.43%, while the rates of phosphorus release, phosphorus absorption, and denitrification also decreased to some extent. When the pH was increased (7.5-8.0), the anaerobic phosphorus release rate and the anoxic phosphorus absorption rate also increased, and reached 25.86 mg·(g·h)-1 and 16.62 mg·(g·h)-1, respectively, at a pH of 8.0. When the pH exceeded 8.0, the phosphorus removal efficiency dropped rapidly, supposedly due to phosphorus chemical precipitation.

Effect of Sludge Retention Time on Biomass Production and Nutrient Removal at an Algal Membrane Photobioreactor

In this study, the effect of sludge retention time (SRT) on biomass production and nutrient removal was determined by constant hydraulic retention time (HRT) with mixed microalgae culture. The SRTs of 2, 3, 6, 12, and 24 days with constant 24 h HRT were studied in microalgae membrane photobioreactor (msMpBR) by using hollow fiber (HF) membranes with a pore diameter of 0.45 μm. According to the results, the best removal was achieved within 3 days of SRT. Chlorophyll-a/mixed liquor suspended solid (MLSS) ratios were found to be 0.033. Total nitrogen (TN) and phosphate phosphorus (PO4–P) removal rates were found to be 5.55 mg N/L day−1, and 0.4 mg PO4–P/L day−1, respectively. The volumetric microalgae production was found to be 0.118 g/L day−1. Also, Chaetophora sp. and Navicula sp. cultures were found to be dominant in steady state. The percentage of lipid and protein in dry biomass was obtained to be 8.94% and 30.34%, respectively. It is advisable to use algal membrane photobioreactor, and mixed microalgae cultures instead of specific microalgae cultures, which could be readily affected by seasonal changes and outdoor conditions in wastewater treatment.

Model-based energy and uncertainty analysis of membrane bioreactor to treat PVC production site wastewater

A pilot-scale membrane bioreactor (MBR) was developed to treat poly vinyl chloride (PVC) production site wastewater. Meanwhile, a simulation model based on activated sludge model No.1 (ASM1) was developed and calibrated for the MBR to evaluate performance in terms of effluent quality, energy consumption, and operation strategy reliability. Furthermore, a modified aeration model was proposed taking into consideration the effect of mixed liquor suspended solids (MLSS) on oxygen transfer. The results showed that the calibrated ASM1 was able to simulate NO3-N satisfactorily and simulate NH4-N and MLSS in the aerobic tank reasonably in both steady and dynamic states; the pilot-scale MBR consumed 0.73kWhm3 permeate production. After the calibration and validation of the MBR process model, a scenario analysis (SCA) was conducted to analyze the effect of sludge retention time (SRT), recirculation ratio (R), and dissolved oxygen (DO) on aeration energy demand and effluent quality. Moreover, Latin Hypercube Sampling (LHS) was performed to study the uncertainty of model parameters to judge the reliability of the operation strategy to meet certain criteria. It was evident that the current operation strategy was able to reach the target with an effluent NH4-N concentration lower than 2mgL−1 for about 97% chance.

Performance of thermal pretreatment and mesophilic fermentation system on pathogen inactivation and biogas production of faecal sludge: Initial laboratory results

The performance of thermal pretreatment of faecal sludge and biogas production of continuous stirred tank reactor (TPCSTR) system on faecal sludge was evaluated in the laboratory of the University of Science and Technology Beijing, China. First, the effectiveness of thermal pretreatment on the inactivation of pathogens and the relationship between complete inactivation time and TS were researched. Second, the effect of sludge retention time (SRT) on the TPCSTR performance of faecal sludge was investigated. Results demonstrated that the time it took for the complete inactivation of pathogens (i.e., faecal coliform, salmonella spp., faecal streptococcus) was 60, 60, 80, 80, 100, 100, and 100 min for the TS faecal sludge concentrations of 1%, 2%, 4%, 6%, 8%, 10%, and 12%, respectively. The experiments showed that the TPCSTR process was stable and efficient to inactivate pathogens under the operation conditions (i.e., TS = 8%, agitation speed = 120 rpm, and temperature = 37 ± 1 °C). The highest biogas production of faecal sludge was 453.21 L kg−1[TS] day−1 at SRT of 25 days.

Effect of sludge retention time on continuous-flow system with enhanced biological phosphorus removal granules at different COD loading

The effect of sludge retention time (SRT) on the continuous-flow system with enhanced biological phosphorus removal (EBPR) granules at different COD loading was investigated during the operation of more than 220days. And the results showed that when the system operated at long SRT (30days) and low COD loading (200mg·L−1), it could maintain excellent performance. However, long SRT and high COD loading (300mg·L−1) deteriorated the settling ability of granules and the performance of system and resulted in the overgrowth of filamentous bacteria. Meanwhile, the transformation of poly-β-hydroxyalkanoates (PHAs) and glycogen in metabolism process was inhibited. Moreover, the results of pyrosequencing indicated that filamentous bacteria had a competitive advantage over polyphosphate-accumulating organisms (PAOs) at high COD loading and long SRT. The PAOs specious of Candidatus_Accumlibater and system performance increased obviously when the SRT was reduced to 20days at high COD loading.

Effects of sludge retention time on oxic-settling-anoxic process performance: Biosolids reduction and dewatering properties

In this study, the effect of sludge retention time (SRT) on oxic-settling-anoxic (OSA) process was determined using a sequencing batch reactor (SBR) attached to external aerobic/anoxic reactors. The SRT of the external reactors was varied from 10 to 40d. Increasing SRT from 10 to 20d enhanced volatile solids destruction in the external anoxic reactor as evidenced by the release of nutrients, however, increasing the SRT to 40d did not enhance volatile solids destruction further. Relatively short SRT (10–20d) favoured the conversion of destroyed solids into inert products. The application of an intermediate SRT (20d) of the external reactor showed the highest sludge reduction performance (>35%). Moreover, at the optimum SRT, OSA improved sludge dewaterability as demonstrated by lower capillary suction time and higher dewatered cake solids content.