Performance Of Activated Sludge Research Articles

Wastewater treatment plant serves as a potentially controllable source of microplastic: Association of microplastic removal and operational parameters and water quality data

Wastewater treatment plant (WWTP) has great potential to regulate microplastics (MPs) emissions, but few studies have focused on this subject. The present study performed a long-term investigation in a typically combined sewers WWTP. Compared to dry weather, rainfall contributed approximately 1.5 times more MPs to the inlet of the combined WWTP. The equalization tank served as a primary site for MPs' removal, with a 46.67-87.91% removal rate. Decreasing surface overflow rate (SOR) was an effective measure for improving MPs removal, and a suitable SOR was recommended at ~11 m 3 (d·m 2 ) -1 ) in the equalization tank. However, MPs' existing settling/rising velocity models failed to obtain a theoretical SOR. In cyclic activated sludge systems, reducing sludge wastage was proposed to facilitate the removal of MPs. As a result, outlet MPs could be reduced by an order of magnitude by adjusting operational parameters on rainy days. Our study highlighted the potential for WWTP to operate as a controlled source of MPs by altering the operational parameters. We also advocated exploiting the mechanisms of MPs' removal by operational parameters and finding an equilibrium between MPs' removal and activated sludge performance. • MPs in WWTP can be mitigated 90% by adjusting operational parameters on rainy days. • Decreasing the SOR (or raising the HRT) improve MPs' removal in equalization tank. • Models were incapable to predict MPs’ velocities, failing to obtain suitable SOR. • Reducing sludge wastage enhanced MPs' removal in the CASS. • Balance the MPs’ removal and the activated sludge’s performance was needed in CASS.

Effect of antibiotic exposure on the characteristics of activated sludge in a landfill leachate biological treatment system

ABSTRACT Changes in the activated sludge performance in an anaerobic/aerobic biological treatment system for leachate was discussed under the condition of tetracycline (TC) exposure. The results show that a low concentration of TC did not have an obvious effect on the removal of chemical oxygen demand (COD) while a high concentration of TC had a certain promoting effect. Under the stimulation of TC, the particle size distribution of anaerobic/aerobic sludge tended to be more uniform, the particle size of anaerobic sludge decreased while the settleability increased; however, the particle size of aerobic sludge increased due to bulking. With the addition of TC, the concentration of most heavy metal ions in sludge samples increased.TC exposure results in the release of a large amount of extracellular polymeric substances (EPS), thus leading to a smoother surface of anaerobic sludge and a rougher surface of aerobic sludge. The high removal efficiency of COD under the high concentration of TC was also presumed to be due to EPS promoting the microbial absorption of anaerobic substances in the leachate. The results clearly showed that TC had a bacteriostatic effect. After antibiotic exposure, the abundance and diversity index of bacteria in each reactor decreased obviously, the microbial community evolved, and the dominant species at the genus and phylum levels of anaerobic/aerobic reactors changed. This study provides a better understanding the effect of TC on activated sludge and has reference value for the management of antibiotic exposure in leachate treatment facilities.

Study on the Balance of Oxygen in Supply and Demand in Wastewater Treatment Plant

In order to accurately evaluate the comprehensive operation efficiency of aerobic biological treatment system in wastewater treatment plants (WWTPs), the process state aeration performance tester and the specific oxygen uptake rate online monitoring device were used to measure the oxygenation performance and the activated sludge performance in aeration tank, and the comprehensive operation efficiency of aerobic tank was evaluated by combining physical-chemical indexes and water quality analysis of the treatment system. The results showed that the oxygen transfer efficiency (OTE) of aerators under process state are reduced by 13.07% and 14.48% respectively compared with that in clean water in the No.3-tank and No.6-tank, and the aeration uniformity index (IAU) is 4.86 and 1.46 respectively. The oxygen uptake rate (OUR) in the third corridor decreased significantly, but dissolved oxygen (DO) was a high level. Oxygen in supply (Qs) was much greater than oxygen in demand (Cs), which have resulted a large waste of energy consumption. Finally, the subsection regulation strategy was proposed based on the principle of oxygen balance. The results of this study will not only help the WWTP to achieve energy-saving and consumption-reducing, but also stable operation.

Phosphorus deficiency leads to the loosening of activated sludge: The role of exopolysaccharides in aggregation

Whether phosphorus deficiency in influent will affect the aggregation and sedimentation of activated sludge needs to be further clarified. This paper systematically studied the structure, aggregation and settlement of activated sludge, and the composition, properties and chemical structure of extracellular polymers and microbial community structure of sludge under different influent phosphorus contents to determine the causes of sludge aggregation and structural deterioration. The results show that phosphorus deficiency in influent leads to a decrease in the aggregation capacity and a loose structure of activated sludge, and the reduction of hydrophobic interactions is the main factor of sludge aggregation and structural deterioration. The content, functional groups and protein secondary structure of extracellular protein were almost unchanged. An increase in the content and hydrophilicity of extracellular polysaccharide (PS) results in a decrease in sludge hydrophobicity. Under phosphorus deficiency, the changes in microbial species related to PS secretion were the reasons for the increase in PS content and hydrophilicity. The negative effects of PS content and hydrophilicity on sludge aggregation and structure are important findings of this work and are expected to be useful for better understanding the restoration of activated sludge performance in the treatment of phosphorus-deficient wastewater.

Effects of long-term perfluorooctane sulfonate (PFOS) exposure on activated sludge performance, composition, and its microbial community

The widespread presence and persistence of perfluorooctane sulfonate (PFOS) in wastewater treatment plants, as well as its toxicity and bioaccumulation potential, necessitates the investigation on their impact on bioreactor performance. A 48-day exposure test was adopted to study the effects of low (10 μg L-1) and high (1000 μg L-1) PFOS concentrations in a sequencing batch reactor on the performance, composition, and microbial community of activated sludge. The results suggested that adding PFOS at low and high concentrations lowered the removal efficiency of total nitrogen by 22.48% (p < 0.01) and 16.30% (p < 0.01) respectively, while enhanced that of total phosphorus by 1.87% (p > 0.05) and 7.07% (p < 0.05) respectively, compared with the control group. The addition of PFOS also led to the deterioration of activated sludge dewatering performance. Composition and spectroscopic measurements revealed that the PFOS dosage changed the composition of the activated sludge. Furthermore, the PFOS altered the structure and function of the activated sludge microbial community as well as key enzyme activities.

Effect of polyethylene microplastics on activated sludge process - Accumulation in the sludge and influence on the process and on biomass characteristics

According to previous research, it has been proved that wastewater treatment plants (WWTPs) can retain more than 90 % of the MPs contained in wastewater. However, a significant fraction of the MPs removed in WWTPs is retained in the sludge floc and this may lead to an environmental issue since biosolids can be used as fertilizers. The purpose of this research was to evaluate how the presence of polyethylene (PE) could interfere with the activated sludge performance. For this, a sequencing batch reactor (SBR) was continuously fed during 93 days with synthetic sewage and PE microbeads. It was observed that 98 ± 2% of the total amount of MPs that entered SBR was accumulated in the activated sludge. Despite the high accumulation of MPs in the sludge, the depuration performance of the reactor was not compromised. However, the presence of MPs decreased the richness (Chao1) and abundance-based coverage estimators (ACE) and diversity (Shannon) of the bacterial community on day 93. Based on the analysis of the diversity indices and the relative abundances of microbial taxa, it was concluded that MPs had selective effects on activated sludge microbial community. However, MPs did not affect the abundance of nitrifying and denitrifying bacteria in the sludge.

New insight into the effect of short-term exposure to polystyrene nanoparticles on activated sludge performance

Microplastics have become a global concern because of their adverse effects on ecosystems. Although wastewater treatment plants (WWTPs) are considered a potential source of microplastics in the environment, the effect of polystyrene nanoparticles on activated sludge performance is not clear. In this study, the effect of short-term exposure to polystyrene nanoparticles (PS-NPs) on activated sludge activity and sedimentation was investigated, and the mechanism behind the effect was analysed. At 5 g/L, the PS-NPs could be adsorbed completely by activated sludge (2.8 g VSS/L) and could be transferred from the aqueous phase to the sludge phase in a short period. At a low concentration (0.1 g/L), the PS-NPs significantly inhibited the endogenous respiration in the sludge by causing bacterial death and affecting the mass transfer in the sludge. Changes in the zeta potential of the sludge surface and in the components of extracellular polymeric substance (EPS) resulted in low sludge aggregation. PS-NPs also caused sludge disintegration, so that when the PS-NP concentration reached 5 g/L, the sludge sedimentation decreased by approximately 50%. Short-term PS-NP exposure has a significant effect on the activity and sedimentation of activated sludge, which could affect the WWTP effluent quality. The findings of this study provide new insight for evaluating the potential risks posed by nanoplastics in WWTPs.

Physicochemical and Biological Effects on Activated Sludge Performance and Activity Recovery of Damaged Sludge by Exposure to CeO2 Nanoparticles in Sequencing Batch Reactors.

Recently, the growing release of CeO2 nanoparticles (CeO2 NPs) into sewage systems has attracted great concern. Several studies have extensively explored CeO2 NPs’ potential adverse impacts on wastewater treatment plants; however, the impaired activated sludge recovery potentials have seldom been addressed to date. To explore the physicochemical and biological effects on the activated sludge performance and activity recovery of damaged sludge by exposure to CeO2 NPs in sequencing batch reactors (SBRs), four reactors and multiple indicators including water quality, key enzymes, microbial metabolites, the microbial community structure and toxicity were used. Results showed that 10-week exposure to higher CeO2 NP concentration (1, 10 mg/L) resulted in a sharp decrease in nitrogen and phosphorus removal efficiencies, which were consistent with the tendencies of key enzymes. Meanwhile, CeO2 NPs at concentrations of 0.1, 1, and 10 mg/L decreased the secretion of tightly bound extracellular polymeric substances to 0.13%, 3.14%, and 28.60%, respectively, compared to the control. In addition, two-week recovery period assays revealed that the functional bacteria Proteobacteria, Nitrospirae and Planctomycetes recovered slightly at the phyla level, as analyzed through high-throughput sequencing, which was consistent with the small amount of improvement of the effluent performance of the system. This reflected the small possibility of the activity recovery of damaged sludge.

Global diversity and biogeography of bacterial communities in wastewater treatment plants.

Microorganisms in wastewater treatment plants (WWTPs) are essential for water purification to protect public and environmental health. However, the diversity of microorganisms and the factors that control it are poorly understood. Using a systematic global-sampling effort, we analysed the 16S ribosomal RNA gene sequences from ~1,200 activated sludge samples taken from 269 WWTPs in 23 countries on 6 continents. Our analyses revealed that the global activated sludge bacterial communities contain ~1 billion bacterial phylotypes with a Poisson lognormal diversity distribution. Despite this high diversity, activated sludge has a small, global core bacterial community (n = 28 operational taxonomic units) that is strongly linked to activated sludge performance. Meta-analyses with global datasets associate the activated sludge microbiomes most closely to freshwater populations. In contrast to macroorganism diversity, activated sludge bacterial communities show no latitudinal gradient. Furthermore, their spatial turnover is scale-dependent and appears to be largely driven by stochastic processes (dispersal and drift), although deterministic factors (temperature and organic input) are also important. Our findings enhance our mechanistic understanding of the global diversity and biogeography of activated sludge bacterial communities within a theoretical ecology framework and have important implications for microbial ecology and wastewater treatment processes.

Impacts of solids retention time and antibiotic loading in activated sludge systems on secondary effluent water quality and microbial community structure.

Solids retention time (SRT) is one of the most important factors in designing and operating activated sludge systems for biological wastewater treatment. Longer SRTs have been shown to alter the structure and function of microbial communities, thereby leading to improved treatment efficacy with respect to bulk and trace organics, nutrient removal, and membrane fouling. Research has also shown that longer SRTs and/or higher influent antibiotic concentrations may lead to increased prevalence of antibiotic resistance. However, it is unclear whether elevated, yet subclinical, concentrations of antibiotics also impact the overall microbial community. The purpose of this study was to characterize changes in microbial community structure in a laboratory-scale activated sludge system as a function of SRT (2-20days) and influent concentrations (1×-100× ambient) of ampicillin, sulfamethoxazole, tetracycline, trimethoprim, and vancomycin. Changes in microbial community structure were evaluated based on 16S rRNA gene sequencing, and microbial community function was evaluated based on changes in effluent water quality, including attenuation of bulk and trace organics. The results confirmed that longer SRTs-but not antibiotic loadings-had a significant impact on microbial community structure and effluent water quality. Therefore, moderate spikes in influent antibiotic concentrations are not expected to adversely impact biological wastewater treatment. PRACTITIONER POINTS: Longer SRTs lead to changes in microbial community structure, including alpha and beta diversity and relative abundance of various taxa. Enhanced TOrC attenuation at longer SRTs may be linked to biomass abundance rather than changes in microbial community structure. Moderate spikes in influent antibiotic concentrations do not impact activated sludge performance or microbial community structure. The phyla Proteobacteria and Bacteroidetes comprise a majority of the microbial community in primary effluent and mixed liquor.

Effect of sulfadiazine and trimethoprim on activated sludge performance and microbial community dynamics in laboratory-scale membrane bioreactors and sequencing batch reactors at 8°C.

The effect of antibiotics sulfadiazine and trimethoprim on activated sludge operated at 8°C was investigated. Performance and microbial communities of sequencing batch reactors (SBRs) and Membrane Bioreactors (MBRs) were compared before and after the exposure of antibiotics to the synthetic wastewater. The results revealed irreversible negative effect of these antibiotics in environmentally relevant concentrations on nitrifying microbial community of SBR activated sludge. In opposite, MBR sludge demonstrated fast adaptation and more stable performance during the antibiotics exposure. Dynamics of microbial community was greatly affected by presence of antibiotics. Bacteria from classes Betaproteobacteria and Bacteroidetes demonstrated the potential to develop antibiotic resistance in both wastewater treatment systems while Actinobacteria disappeared from all of the reactors after 60 days of antibiotics exposure. Altogether, results showed that operational parameters such as sludge retention time (SRT) and reactor configuration had great effect on microbial community composition of activated sludge and its vulnerability to antibiotics. Operation at long SRT allowed archaea, including ammonium oxidizing species (AOA) such as Nitrososphaera viennensis to grow in MBRs. AOA could have an important role in stable nitrification performance of MBR-activated sludge as a result of tolerance of archaea to antibiotics. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2708, 2019.

Impact of electrocoagulation on membrane filtration resistance under different proportions of industrial wastewater

AbstractBACKGROUNDThe principal purpose of the present work was to explore the mechanism of mitigation of membrane fouling in a periodic reversal submerged electro‐coagulation membrane bioreactor (SECMBR) with Fe–C electrodes. In this study, membrane resistance and activated sludge performance were compared in a SECMBR and a conventional submerged membrane bioreactor (SMBR).RESULTSAdsorption fouling had a strong direct correlation with the soluble microbial products (SMP) and carbohydrates in SMP and had a moderate correlation with the mixed liquor volatile suspended solids, viscosity and average particle size. SECMBR enhanced the flocculation of suspended sludge, decreased the absolute value of the ζ potential, and maintained microbial activities. With increasing proportion of oil shale wastewater, more soluble microbial products were secreted by microorganisms in the SECMBR than in the SMBR.CONCLUSIONElectrocoagulation technology has the capacity to increase the sludge particle size and decrease the absolute value of the ζ potential to alleviate cake layer fouling and total resistance. As the proportion of oil shale wastewater was increased, microbial activity in the conventional MBR was inhibited, leading to less secreted SMP and a lower adsorption fouling rate. The results provide insight into understanding the mechanism of mitigation of membrane resistance in an SECMBR. © 2018 Society of Chemical Industry

Biodegradation and toxicity of melamine at high activated sludge concentrations in a membrane bioreactor.

Melamine is recalcitrant and toxic to bacteria in conventional activated sludge systems. In this study, we investigated the degradation and toxicity of melamine in a membrane bioreactor (MBR) system operated at high activated sludge concentrations (∼8.5 g TSS/L). Melamine was dosed at 3 mg/L for about 100 days. The average melamine removal efficiency in the MBR system was 20 ± 11%. Meanwhile, batch studies showed the acclimated sludge from the MBR had higher removal efficiencies after the depletion of readily biodegradable substrate (acetate) while non-acclimated sludge did not remove any melamine. As acclimated sludge had removal efficiencies ranging from 33 ± 6% (by 1.7 g TSS/L biomass) to 41 ± 10% (by 8.5 g TSS/L biomass), microbial specialists with unique hydrolytic enzymes in the acclimated sludge were likely responsible for melamine degradation. Since bacteria prefer to use readily biodegradable substrates for growth in the MBR, the population of microbial specialists capable of degrading melamine or the capability of cometabolism appeared not to increase with an increase in biomass concentration. Nevertheless, because of high sludge concentrations and thus low mass ratio of toxic melamine to biomass in the MBR, the long-term melamine exposure did not affect MBR activated sludge performance.

Hazardous events in membrane bioreactors – Part 3: Impacts on microorganism log removal efficiencies

Under normal operation, membrane bioreactors (MBRs) produce high quality effluent leading to common application in water recycling schemes. When hazardous events, outside of normal operation, occur strategies must be in place to ensure that microbially safe water is consistently produced. Limited literature is available to quantify the consequence of hazardous events on microorganism log removal value (LRV) by MBRs. As a result, current MBR risk management practices cannot be based on sufficient quantitative evidence. In this study, MBRs were subjected to hazardous events designed to reflect a range of potential severe feed water variations and process failures. During these challenge events, removal of four microbial indicator organisms representing viruses, bacteria and protozoa were quantified. Hazardous event impacts were benchmarked against the 5th percentile of normal process LRV, determined via probabilistic techniques. Severe feed water variation decreased the efficacy of bio-predation due to adversely affected activated sludge performance. However, overall LRV was preserved due to the onset of fouling, aiding rejection by the membrane. Overall FRNA bacteriophage LRV significantly decreased to 0.3log units below the 5th percentile (LRV=4.1) after the NaCl shock, most likely due to inhibition of adsorption mechanisms. Fibre breakage resulted in a significant reduction in LRV, but was mitigated by suspended solids plugging the membrane lumen within 15min. The findings presented here can inform risk management strategies for MBRs by permitting control strategy prioritisation according to quantified event consequences.

Insights into the effect of mixed engineered nanoparticles on activated sludge performance.

In this study, the effects, fate and transport of ENPs in wastewater treatment plants (WWTP) were investigated using three parallel pilot WWTPs operated under identical conditions. The WWTPs were spiked with (i) an ENP mixture consisting of silver oxide, titanium dioxide and zinc oxide, and (ii) bulk metal salts. The third plant served as control (unspiked). ENP effects were evaluated for (i) bulk contaminant removal, (ii) activated sludge (AS) process performance, (iii) microbial community structure and dynamics and (iv) microbial inhibition. ENPs showed a strong affinity for biosolids and induced a specific oxygen uptake rate two times higher than the control. The heterotrophic biomass retained its ability to nitrify and degrade organic matter. However, non-recovery of ammonia- and nitrite-oxidizing bacteria such as Nitrosomonas, Nitrobacter or Nitrospira in the ENP spiked reactors suggests selective inhibitory effects. The results further suggest that ENPs and metal salts have antimicrobial properties which can reduce synthesis of extracellular polymeric substances and therefore floc formation. Scanning electron microscopy evidenced selective damage to some microbes, whereas lipid fingerprinting and 454 pyrosequencing indicated a temporal shift in the microbial community structure and diversity. Acidovorax, Rhodoferax, Comamonas and Methanosarcina were identified as nano-tolerant species. Competitive growth advantage of the nano-tolerant species influenced the removal processes and unlike other xenobiotic compounds, ENPs can hasten the natural selection of microbial species in AS.

Troubleshooting Activated Sludge Performance through Microscopic Observations: Five Case Studies

Troubleshooting Activated Sludge Performance through Microscopic Observations: Five Case Studies

Troubleshooting Activated Sludge Performance through Microscopic Observations: Five Case Studies

Troubleshooting Activated Sludge Performance through Microscopic Observations: Five Case Studies

Impacts of poly-aluminum chloride addition on activated sludge and the treatment efficiency of SBR

Coagulants addition to a bioreactor is a widely used technology for improving phosphorus removal. As a common and low-cost coagulant, poly-aluminum chloride (PAC) may be widely used for wastewater treatment. In this article, the impacts of PAC on activated sludge and the treatment efficiency of sequencing batch reactor were investigated over 100 d for domestic wastewater treatment. Parameters of chemical oxygen demand (COD), nitrogen, phosphorus, MLSS, oxygen uptake rate (OUR), and dehydrogenase activity (DHA) were used to assess the activated sludge performance. The addition of 40 mg PAC/L (R2) enhanced phosphorus removal from 73.3% in control with zero PAC (R1) to 92.4% due to simultaneous chemical precipitation. PAC addition improved COD removal slightly and did not affect the removal efficiency of nitrogen. The average removal efficiency of COD of the reactor increased slightly from 86.2 to 89.6% by PAC addition. In R1, TN removal was in the range from 86.3 to 90.8%. Nitrogen removal efficiency remained unaffected (slightly dropped) during simultaneous precipitation in R2 and was in the range from 84.5 to 86.8%. The average inhibition rate of DHA and OUR was 32.1 and 55.3%, respectively. PAC addition gave proof to the increase of MLSS by some 40%. Results obtained from the present work confirmed that PAC addition, despite the toxicity and inhibition on micro-organisms, favored phosphorus removal in wastewater treatment.

A review: inhibition of Ag NPs on wastewater treatment

This review summarizes and evaluates the present knowledge of the inhibition effect of silver nanoparticles (Ag NPs) on pollutants removal, activated sludge performance. The fate and behavior of Ag NPs in wastewater treatment plants (WWTPs) are also mentioned. Rapid progress in this area has been made over the last few years, but there are still some blanks in studies. Although some researches have been carried out on the inhibitory of Ag NPs on pollutants removal such as COD and nitrogen removal, most of them focus on microorganisms rather than treatment system. Few articles referred to impact of Ag NPs on phosphorus removal. Mechanisms of Ag NPs inhibition are still poorly understood although it seems clear that in some cases. As a well performance microcosmic ecosystem, the status of fungus, protozoa, and metazoan are also very important for activated sludge. However, little is known about the impact of Ag NPs on them. This review concludes with a set of recommendations for the advancement of understanding of the role of Ag NPs in WWTPs.

Bacterial response to a continuous long-term exposure of silver nanoparticles at sub-ppm silver concentrations in a membrane bioreactor activated sludge system

Silver nanoparticles (nanosilver or AgNPs) have excellent antimicrobial properties. Because of their increasing use, there is a concern about the potential impact of AgNPs in wastewater treatment systems. This study investigated the long-term effects of AgNPs (continuous loading for more than 60 days) on membrane bioreactor (MBR) activated sludge performance. At the influent AgNP concentration of 0.10 mg Ag/L, there was no significant difference in effluent water quality or bacterial activities before and after AgNP exposure. Nitrifying bacterial community structure was relatively stable before and after the long-term AgNP loading. Both ammonia-oxidizing bacteria (AOB) Nitrosomonas spp. and Nitrosospira spp. were present while Nitrospira spp. was the dominant nitrite-oxidizing bacterial species throughout this study. Abundance of silver resistance gene silE in the MBR, however, increased by 50-fold 41 days after the AgNP exposure, and then decreased with continuous AgNP exposure. The long-term nanosilver exposure did not change the membrane fouling rate although extracellular polymeric substances (EPS) concentration increased significantly after nanosilver dosing. The results suggest that AgNPs at the influent concentrations of 0.10 mg/L and below have almost no impact on activated sludge wastewater treatment performance, as activated sludge can effectively reduce nanosilver toxicity by adsorbing or precipitating AgNPs and silver ions (Ag+) released from the dissolution of AgNPs.