Conventional Activated Sludge Treatment Plant Research Articles

Linking conventional activated sludge treatment plant performances for micropollutants removal to environmental risk and SimpleTreat model assessment

The attention to the contaminants of emerging concerns or micropollutants is continuously rising, also stimulated by the new initiatives at European level. The present study focuses on the removal of target micropollutants in a conventional activated sludge wastewater treatment plant which is the most common system and considered a source of micropollutants to the environment. The aims were to evaluate the removal efficiency of different stages of the wastewater treatment plant and to conduct the Environmental Risk Assessment on the final effluent. As indicated by the European’s guidelines on Environmental Risk Assessment, the SimpleTreat4.1 model was applied to this purpose: different values of the biodegradation constant, which represents the key factor for modelling, were applied, and the effects on the quality of prediction were evaluated. The evaluations were carried out thorough 3-year monitoring activity in a full-scale wastewater treatment plant on 10 micropollutants belonging to the classes of illicit drugs, pharmaceuticals and psychoactive. The model was found statistically not satisfactory for most of the investigated micropollutants. A better prediction was obtained when the biodegradation constant was calculated based on the full-scale data. Nonetheless, the results obtained in terms of risk were considered acceptable and comparable among each other.Graphical abstract

Estimating the impact of inhibitory substances on activated sludge denitrification process

Abstract Industrial wastewater frequently contains substances which inhibit activated sludge treatment processes. Inhibitory characteristics of different substances are usually evaluated based on testing the impact of respective substance on activated sludge nitrification or oxygen uptake rates. However, denitrification is always before aerobic processes in conventional activated sludge treatment plants and thereby more exposed to inhibitory compounds. There is no easily applicable and validated method available for determination of denitrification process efficiency and inhibition. In this study, a method for evaluation of inhibition on the activated sludge denitrification process was developed and validated using 3,5-dichlorophenol (3,5-DCP) as a model inhibitory compound and additionally controlled with real wastewater produced in the shale oil industry. Average IC50 value (5.5 ± 2.2 mg L−1) for 3,5-DCP showed that denitrifiers were less sensitive than nitrifiers (IC50 = 2.9 ± 0.7 mg L−1) and more sensitive than aerobic heterotrophs (IC50 = 7.2 ± 2.4 mg L−1). Methodological aspects like accumulation of nitrite nitrogen, acclimatization of biomass and technical issues were discussed. Achieved validation characteristics were similar with ISO Standards estimating activated sludge nitrification and oxygen uptake rates, which proves the reliability of the method: standard deviation, 95.4% confidence level, relative standard deviation were calculated to be 2.2 mg L−1, 1.2 … 9.8 mg L−1 and 39.2%, respectively.

Optimization of mesophilic anaerobic digestion of a conventional activated sludge plant for sustainability

Potential of nutrient recovery as struvite (NH4MgPO4·6H2O) with sole waste activated sludge (WAS) of a conventional activated sludge treatment plant has been investigated using computational modelling supported by laboratory experiments. Predicted key outcomes using Bio-Win modelling tool indicated that anaerobic digestion of WAS could produce a supernatant consisting of 300–420 mg/L ammonia , 100–200 mg/L phosphate and 12–30 mg/L magnesium and laboratory experiments confirmed that struvite can be precipitated using these nutrient concentrations. Study of sludge retention time (SRT 15–30 days) and temperature (34–38 °C) on the nutrient concentrations of digester supernatant revealed that ammonia and phosphate concentrations of supernatant increased with SRT and temperature. The removal efficiencies of magnesium and phosphate in struvite precipitation reactions were 91% and 50% respectively, indicating that magnesium addition is required for extra phosphate removal in the digester supernatant. It was found that a substantial excess ammoniac nitrogen would remain and need alternative method to remove and recover, if sustainability is to be achieved. The outcome of this study confirms that WAS from conventional wastewater treatment plants such as Loganholme can be successfully upgraded towards a nutrient recovery facility by optimizing anaerobic digester parameters. Modelling is a suitable first approach for planning and decision-making.

Novel process concept alternatives for improved removal of micropollutants in wastewater treatment

Abstract Conventional activated sludge treatment plants have limited capability to remove micropollutants from municipal wastewater, and as a consequence, concentrations of micropollutants in water bodies are increasing. This creates concerns due to their potentially harmful effects on the aquatic environment, as well as needs to improve or replace the traditional wastewater treatment processes with novel process concepts. In this study, two novel process concept alternatives for enhanced removal of micropollutants are examined. The experiments were done in pilot scale with real wastewater of a small municipality. In the first concept, a membrane bioreactor process (MBR) without phosphorus precipitation was combined with high permeability nanofiltration (NF), and in the other, the MBR with the precipitation of phosphorus was combined with advanced oxidation implemented by pulsed corona discharge (PCD). The results showed that the MBR processes were insufficient for removing unreadily biodegradable micropollutants, such as carbamazepine and diclofenac. However, combining the nanofiltration or PCD oxidation step with the MBR enabled significant enhancement in the removal of micropollutants. Over 84% removal was reached with nanofiltration (NF270) for most of the studied micropollutants, except caffeine and hydrochlorothiazide. The performance of PCD oxidation (oxidation energy 0.2 kWh/m 3 ) in the removal of micropollutants exceeded the one of nanofiltration; over 90% removal of most of the studied micropollutants was reached, and the pollutants were degraded below 0.1 µg/L concentration. Thus, the total removal of micropollutants was better in the concept combining MBR and oxidation treatment. However, the concept combining MBR and nanofiltration provided better overall removal of organic compounds (removal of COD and DOC > 99%), and it also enabled the recovery of phosphorus as a concentrated solution.

Biological stability and dewaterability of CAS and MBR sludge

This paper investigates and compares the characteristics of sludges produced by membrane bio-reactor (MBR) and conventional activated sludge (CAS) systems. Stability and dewaterability of full-scale MBR and CAS treatment plants are measured and compared. Obtained results show that specific methane production is higher in CAS sludge compared to MBR sludge, although one of the CAS sludges investigated had a sludge retention time (SRT) higher than the two MBR sludges investigated. Nonetheless, MBR sludge results to be characterized by a non-negligible biometanation potential (BMP). Methane production measured during BMP tests is around 200 NmL/gVS for MBR sludge, equaling 2/3 of methane production obtained, in similar condition, for CAS sludge. Dewaterability of the sludge resulted to be linearly correlated with the SRT and the sludge extracellular polymeric substances (EPS) concentration. The higher the SRT and the lower the sludge EPS concentration, the lower the specific resistance to filtration.

Full scale performance of the aerobic granular sludge process for sewage treatment

Recently, aerobic granular sludge technology has been scaled-up and implemented for industrial and municipal wastewater treatment under the trade name Nereda®. With full-scale references for industrial treatment application since 2006 and domestic sewage since 2009 only limited operating data have been presented in scientific literature so far. In this study performance, granulation and design considerations of an aerobic granular sludge plant on domestic wastewater at the WWTP Garmerwolde, the Netherlands were analysed. After a start-up period of approximately 5 months, a robust and stable granule bed (>8 g L−1) was formed and could be maintained thereafter, with a sludge volume index after 5 min settling of 45 mL g−1. The granular sludge consisted for more than 80% of granules larger than 0.2 mm and more than 60% larger than 1 mm. Effluent requirements (7 mg N L−1 and 1 mg P L−1) were easily met during summer and winter. Maximum volumetric conversion rates for nitrogen and phosphorus were respectively 0.17 and 0.24 kg (m3 d)−1. The energy usage was 13.9 kWh (PE150·year)−1 which is 58–63 % lower than the average conventional activated sludge treatment plant in the Netherlands. Finally, this study demonstrated that aerobic granular sludge technology can effectively be implemented for the treatment of domestic wastewater.

Effect of Anaerobic Digestion on Rheological Parameters and Dewaterability of Aerobic Sludges from MBR and Conventional Activated Sludge Plants

The paper investigates and compares the characteristics of sludges produced by membrane Bio-Reactor (MBR) and Conventional Activated Sludge (CAS) systems. Stability and dewaterability of full-scale MBR and CAS treatment plants are measured and compared. Obtained results show that specific methane production is higher in CAS sludge compared to MBR sludge because of the higher solid retention time of the MBR. Nonetheless MBR sludge results to be characterized by a non-negligible biometanation potential (BMP). Methane production measured during BMP tests is around 250 NmL/gVS for MBR sludge, equaling 2/3 of methane production obtained, in similar condition, for CAS sludge. Dewaterability is evaluated by Specific Resistance to Filtration (SRF), Capillary Suction Time (CST) and Time To Filter (TTF) tests. Data obtained before and after the anaerobic digestion of the sludges show that the stabilization process affects much more the resistance to filtration of CAS sludge than the resistance to filtration of MBR sludge. The same trend is observed, for the other measured parameters. This is attributed to the variation of the rheological characteristics of the two sludges during the stabilization process, and to the different initial rheological properties of them due to the different selection process of the biomass deriving from the different biomass retention methods of MBR and CAS systems.

Occurrence of Clostridium difficile in two types of wastewater treatment plants.

Wastewater is a potential environmental source of Clostridium difficile, although a direct link with community-acquired C. difficile infection (CA-CDI) in humans has not yet been established. The present study was performed to determine the occurrence of C. difficile in two types of wastewater treatment plants (WWTPs) in Isfahan, Iran. A total of 95 samples were taken from a conventional activated sludge treatment plant and a waste stabilization ponds system, and analyzed for the presence of C. difficile. C. difficile was found in 13.6% (3/22) of digested sludge samples. However, no C. difficile was detected in inlet and outlet samples or in raw sludge of activated sludge. C. difficile was also detected in 5% (2/40) of the samples from waste stabilization ponds. Polymerase chain reaction (PCR) analysis showed that all strains of C. difficile detected were toxigenic (tcdB gene positive). This study shows that C. difficile was present in WWTPs, which might constitute a potential source of community-acquired C. difficile infection.

MBR technology for textile wastewater treatment: First experience in Bangladesh

For the first time in Bangladesh, a bench scale membrane bioreactor (MBR) unit was tested in treating a textile wastewater in the industry premises of EOS Textile Mills LTD, Dhaka for three months. The performance of the unit was compared with that of the conventional activated sludge treatment plant, which is in operation in the same premises. The COD and BOD removal efficiency of the MBR unit reached to around 90% and 80% respectively in 20 days whereas the removal efficiency of the conventional treatment plant was as low as 40-50% and 38-40% respectively. The outlet COD and the BOD level for the MBR unit remained stable in spite of the fluctuation in the feed value, while the conventional effluent treatment plant (ETP) failed to keep any stabilized level. The performance of the MBR unit was much superior to that of the functional ETP and the water treated by the MBR system can meet disposal standard.

Effect of Cr(III) on process performances of MBR systems

The paper investigates the effect of Cr(III) on the heterotrophic biomass of membrane bioreactors (MBRs) to understand the consequences on process performances. Respirometric tests are conducted to evaluate the consequences of chromium injection on oxygen consumption and oxygen uptake rate for the sludge sampled from a MBR pilot plant and, comparatively, for the sludge sampled from a conventional activated sludge treatment plant. MBR sludge is found to be more resistant to chromium injection than conventional activated sludge. Measurements of residual metal concentration are carried out to understand the mechanism of chromium adsorption and assimilation. The release of soluble microbial products, which play an important role on membrane fouling, is also investigated. Obtained information is completed by microscopic observations, aimed at identifying the variation of biomass structure and composition due to the presence of Cr(III).

Industrial Wastewater Treatment Using High Rate Activated Sludge and Alum Additive

The high rate activated sludge stage of the multiple-stage sludge treatment plant is characterized by high efficiencies of treatment, cost, and size, compared to conventional activated sludge treatment plants. A pilot plant with an industrial discharge flow of 135L/h was designed according to the highly loaded activated sludge stage (A-stage). The plant simulated the biological and chemical treatment of sludge by adding alum to the aeration tank in dosages of 100, 150, 200 and 250 mg/L. The results clearly indicate that the highly-loaded activated sludge, the A-stage of the absorption/bio-oxidation system, has a high efficiency for the elimination of organic and inorganic matters. Without adding aluminum salt, the chemical oxygen demand, the total phosphate and the total nitrate were approximately 52.43%, 47.82%, and 40.09% respectively. The chemical-biological process with a dosage of 200mg/L alum resulted in 76.07% reduced chemical oxygen demand and improved efficiency of phosphate and nitrate removal to 73.5% and 66.98% respectively compared with the biological process in the A-stage.

Comparison of the removal of phthalates and other organic pollutants from industrial wastewaters in membrane bioreactor and conventional activated sludge treatment plants

In recent years greater attention has been paid to the presence of pollutants in wastewater treatment plants, mainly because of strict environmental regulations and the possibility of reusing treated water in industrial processes. Since some organic pollutant compounds are not sufficiently removed in conventional activated sludge treatment (CAST) plants, new treatment processes have been developed, such as membrane bioreactors (MBRs). In this study a submerged membrane bioreactor (MBR) was used to treat mixed industrial wastewaters in parallel with a CAST plant. Two hydraulic retention times (HRT) of wastewater were tested as one of the operational conditions of MBR and the quality of effluents of the two processes were studied and compared. Several general quality parameters were analysed in wastewaters: chemical oxygen demand (COD), pH, conductivity, nitrogen, phosphate, suspended solids (SS) and turbidity. The two systems reduced COD by around 90%. SS was reduced by around 81% in the CAST plant and around 90% in the MBR plant. The results for the other general parameters were similar or better in the MBR process, which worked at a lower HRT. We also studied the removal of a group of six phthalates and bis(2-ethylhexyl)adipate ester by SPME/GC-MS in the two treatment plants. Most of these compounds were not completely removed in the two treatment plants and were identified at low microg l(-1) levels. We also tentatively identify some organic compounds in the wastewaters. Most of the compounds we found in the influent, MBR effluent and CAST effluent were benzene derivates, styrene, naphthalene and naphthalene derivates, and phenol derivates.

Evaluation of the Removal of Pollutants from Petrochemical Wastewater Using A Membrane Bioreactor Treatment Plant

A submerged membrane bioreactor (MBR) was used to treat two types of petrochemical wastewater: olefin process wastewater and total petrochemical wastewater. Various operational MBR conditions, such as influent pH and hydraulic retention time (HRT), were tested while these wastewaters were treated. The MBR treatment of olefin process wastewater reduced chemical oxygen demand (COD) and total organic carbon (TOC) by around 90% in both cases, and more than 90% of the suspended solids (SS) were removed. When MBR was used, the reduction in COD and TOC was also high for the total petrochemical wastewater, and was compared with the reduction obtained when the conventional activated sludge treatment plant was used (CASP). However, MBR effluent wastewaters showed high conductivity so for some reuse purposes subsequent reverse osmosis (RO) treatment would be needed. We characterized the MBR influent and MBR effluent wastewaters using a sequential solid phase extraction (SSPE) followed by gas chromatography-mass spectrometry (GC–MS) analyses. The main compounds that were tentatively identified were hydrocarbons, alkyl benzenes, phenols, acidic acids and esters, almost all of which could be partially or completely removed by MBR treatment.

Occurrence and reductions of pharmaceuticals and personal care products and estrogens by municipal wastewater treatment plants in Ontario, Canada

Occurrence and reductions of pharmaceuticals and personal care products and estrogens by municipal wastewater treatment plants in Ontario, Canada

Elevated precursor 16S rRNA levels suggest the presence of growth inhibitors in wastewater

Conventional activated sludge systems require bacteria to grow to avoid washout through decay and routine solids wasting. Recently we developed a procedure targeting precursor 16S ribosomal RNA to measure the in situ growth activity of phylogenetically defined microbial populations, and this procedure was used to study the growth of bacteria in activated sludge systems. The current study significantly expands this previous work by quantifying levels of precursor 16S ribosomal RNA within individual cells of pure cultures of bacteria exposed to various culture conditions. Initially, three ranges (Type I, Type II, and Type III) of precursor 16S ribosomal RNA levels were defined by whole cell fluorescence in situ hybridization of a pure culture of Acinetobacter calcoaceticusT prepared in three culture conditions. Low levels of precursor 16S ribosomal RNA (Type I) corresponded to a stationary phase culture prepared overnight in Luria-Bertani medium. Intermediate levels of precursor 16S ribosomal RNA (Type II) corresponded to a culture transferred into fresh Luria-Bertani medium, and high levels of precursor 16S ribosomal RNA (Type III) corresponded to a culture treated with the growth inhibiting antibiotic chloramphenicol. Subsequently, the abundance of individual cells of each Type were measured in four different pure cultures after exposure to 0.45-microm filtered primary effluent collected from four different conventional activated sludge treatment plants in Cincinnati, OH, USA. Individual cells of each Type were observed in the culture of A. calcoaceticusT exposed to each of the four primary effluents. Only Type I cells were observed in cultures of A. johnsoniiT, A. johnsonii strain 210a, and Escherichia coliT exposed to each of the four primary effluents. These results suggest that the growth of A. calcoaceticusT was inhibited by an unidentified component of filtered primary effluent present in each of the four wastewaters; whereas the growth of A. johnsoniiT, A. johnsonii strain 210a, and E. coliT were not inhibited. These results have significance for understanding the growth of phylogenetically defined microbial populations within activated sludge treatment systems. If the pattern of elevated p16S rRNA levels observed in A. calcoaceticusT is prevalent in many microbial populations in activated sludge systems, this may have implications for preventing washout of critical microbial populations that may be experiencing growth inhibition.

Pilot-plant comparative study of peracetic acid and sodium hypochlorite wastewater disinfection

Peracetic acid (PAA) use in wastewater disinfection was assessed by examining its performances in a pilot plant fed by the effluent from a conventional activated-sludge treatment plant. The influence of PAA initial concentrations (0.5–4.0 mg/l) and contact times (8–38 min) on the presence of seven microorganisms (total coliforms, fecal coliforms, fecal streptococci, Escherichia coli, Pseudomonas sp., Salmonella sp., and bacteriophages anti- E. coli) and on residual biocide and halogenated organic compound (AOXs) concentrations were evaluated. The data so obtained were compared to the corresponding results acquired using sodium hypochlorite (HYP) in the same experimental conditions. The biocide effect of PAA against total and fecal coliforms, E. coli, Pseudomonas sp. and Salmonella sp. was similar to that shown by HYP. The former disinfectant was, however, less efficient than the latter in the reduction of fecal streptococci and bacteriophages anti- E. coli. In both cases the biocide quantities initially introduced in the sewage resulted in the presence of significant concentrations at the end of the contact time. No significant variation of AOX content was detected in the effluent treated with PAA, whereas a progressive increment of such compounds was found when increasing quantities of HYP were added to the sewage.

Occurrence and Mass Balance of Polycyclic Aromatic Hydrocarbons in the Thessaloniki Sewage Treatment Plant

AbstractThe occurrence and the mass balance of the 16 EPA polycyclic aromatic hydrocarbons (PAHs) were investigated in a conventional activated sludge treatment plant. Polycyclic aromatic hydrocarbon concentrations were determined in wastewater and sludge samples from different treatment stages. The concentrations of PAHs in raw sewage were statistically analyzed to examine whether temporal factors (sampling period, day and hour of sampling) had a significant effect on the observed variance. Sampling period was the only factor that showed a significant impact. Principal component analysis (PCA) was used to assess similarities of the wastewater PAH pattern with possible source matrices (domestic effluents, urban runoff, and atmospheric particulates). The composition of wastewaters was found to be particularly similar to that of domestic effluents. Mass balances of PAHs were calculated for individual stages of wastewater treatment (primary treatment, secondary treatment, and chlorination), as well as for the whole treatment process. Relatively good mass balances were calculated in the primary clarifier for most PAHs. Lower molecular weight PAHs (Np, Ace, Ph, An, and Fl) showed substantial losses (>40%), in the secondary treatment probably due to biodegradation and volatilization. Good closures for all PAHs were found in the chlorination stage. Total mass balances indicated that only the lower PAHs are effectively removed, whereas the heavier compounds are rather resistant to the treatment process. Sorption was found to be the dominating removal process of PAHs—especially of the heavier ones—during primary treatment, while their removal during the secondary treatment is also governed by other processes, such as biodegradation and/or volatilization.

Oxygen utilization rates for continuous feed intermittently decanted activated sludge wastewater treatment plants

Abstract Activated sludge wastewater treatment plants can be operated in a sequential mode with continuous inflow of wastewater and an intermittent decant of the treated effluent. The biological activity of the mixed liquor as measured by oxygen utilization rates are relatively high at the inlet sections of these plants and with some wastewaters can approach 200 mg 02g‐1MISS h‐1. The rate of oxygen utilization decreases during the aeration sequence, after approximately one hour the values are similar to that observed in conventional activated sludge treatment plants. The rates of oxygen utilization were found to be a function of the instantaneous organic loading on a particular plant or section of a plant and the degradability of the wastewater. The high oxygen utilization rates in the inlet regions of some plants suggest the feasibility of lower overall hydraulic retention times.

The efficiency of heavy metal removal by a conventional activated sludge treatment plant

The total and dissolved concentration of cadmium, chromium, cobalt, copper, iron, lead, manganese, mercury, nickel and zinc at various points in a conventional activated sludge treatment plant have been measured. The analysis of raw sewage samples collected hourly over a 3-day period showed that metal input to the sewage treatment plant was not a continuous process but consisted of slugs of metal lasting for a discrete time. The efficiency of heavy metal removal by this model treatment plant was determined by monitoring the influent and effluent metal levels over a 4-week period.