Sludge Aeration Research Articles

Analysis of Activated Sludge Aeration Systems Following Primary Filtration With Microsieves

Analysis of Activated Sludge Aeration Systems Following Primary Filtration With Microsieves

How the nature of the compounds present in solid and liquid compartments of activated sludge impact its rheological characteristics

ABSTRACTAlthough the role of the solids concentration on the rheological characteristics of sludge is greatly documented in the literature, few studies focused on the impact of the nature of these solids. How the nature of solutes can modify the solid–liquid interactions and thus the rheological properties of the sludge are also slightly explored. Thus, the objective of this study is to investigate the rheological characteristics of activated sludge in relation with the nature of the compounds present in the solid and liquid phases. Rheological measurements were carried out on raw sludge and on sludge modified by mechanical actions and/or addition of solids or solutes. The rheological properties of raw and modified sludges were measured according to flow and dynamic measurements. Results demonstrated that if suspended solid concentration affected sludge rheological parameters, the nature of the solids was quite of importance. The key role of nature and molecular weight of solutes was also highlighted. The results contribute to a better knowledge of the relationship between sludge composition and its rheological properties, which is useful for the optimization of sludge mixing, pumping or aeration and also for the improvement of sludge dewatering, notably by a relevant choice of adjuvant.

A New Approach to Modeling Operational Conditions for Mitigating Fouling in Membrane Bioreactor.

Modeling and optimization tools play a key role in membrane fouling control in membrane bioreactor (MBR) systems by delineating the more important variables involved. In this study, the influence of sludge retention time (SRT), aeration rate and filtration mode on hollow fiber membrane fouling was investigated. Using the response surface methodology (RSM) for modeling and central composite rotatable design (CCRD) for design of experiments, mathematical models were developed for fouling rate and protein (P1, P2) and carbohydrate (C1, C2) concentrations in two layers of fouling. Results showed that sludge retention time (SRT) was the most important variable in most models followed by aeration rate. Aeration showed a more effective role on the models of the rinsed layer (P1, C1) than backwashed layer (P2, C2). Backwashed layer had more influence on total fouling rate than rinsed layer. The optimal point for MBR operation was: SRT = 30 days, aeration = 10.7 L/min, relaxation interval = 8.8 minutes, and relaxation duration = 41.8 seconds.

Development of a model for activated sludge aeration systems: linking air supply, distribution, and demand.

During the design of a water resource recovery facility, it is becoming industry practice to use simulation software to assist with process design. Aeration is one of the key components of the activated sludge process, and is one of the most important aspects of modelling wastewater treatment systems. However, aeration systems are typically not modelled in detail in most wastewater treatment process modelling studies. A comprehensive dynamic aeration system model has been developed that captures both air supply and demand. The model includes sub-models for blowers, pipes, fittings, and valves. An extended diffuser model predicts both oxygen transfer efficiency within an aeration basin and pressure drop across the diffusers. The aeration system model allows engineers to analyse aeration systems as a whole to determine biological air requirements, blower performance, air distribution, control valve impacts, controller design and tuning, and energy costs. This enables engineers to trouble-shoot the entire aeration system including process, equipment and controls. It also allows much more realistic design of these highly complex systems.

Real-Time Ultrafine Aerosol Measurements from Wastewater Treatment Facilities.

Airborne particle emissions from wastewater treatment plants (WWTP) have been associated with health repercussions but particulate quantification studies are scarce. In this study, particulate matter (PM) number concentrations and size distributions in the ultrafine range (7-300 nm) were measured from two different sources: a laboratory-scale aerobic bioreactor and the activated sludge aeration basins at Orange County Sanitation District (OCSD). The relationships between wastewater parameters (total organic carbon (TOC), chemical oxygen demand (COD), and total suspended solids (TSS)), aeration flow rate and particle concentrations were also explored. A significant positive relationship was found between particle concentration and WWTP variables (COD: r(10) = 0.876, p <.001, TOC: r(10) = 0.664, p <.05, TSS: r(10) = 0.707, p <.05, aeration flow rate: r(8) = 0.988, p <.0001). A theoretical model was also developed from empirical data to compare real world WWTP aerosol number emission fluxes with laboratory data. Aerosol number fluxes at OCSD aerated basins (9.8 × 104 lbs/min·cm2) and the bioreactor (7.95 × 104 lbs/min·cm2) were calculated and showed a relatively small difference (19%). The ultrafine size distributions from both systems were consistent, with a mode of ∼48 nm. The average mass concentration (7.03 μg/cm3) from OCSD was relatively small compared to other urban sources. However, the in-tank average number concentration of airborne particles (14 480 lbs/cm3) was higher than background ambient concentrations.

Low energy anaerobic membrane bioreactor for municipal wastewater treatment

Achieving low effluent BOD5 concentrations and stable performance while treating municipal wastewater at ambient temperature has been difficult for anaerobic biotechnology without using membranes. Membrane operation has typically required energy inputs greater than traditionally needed for activated sludge aeration, thus defeating one main objective of utilizing anaerobic biotechnology. However, new low-energy membrane operational strategies are being evaluated to make anaerobic membrane bioreactors (AnMBR) more energy efficient. In this study, four 3.3 L bench-scale AnMBRs using external crossflow tubular membranes were fed synthetic and real municipal wastewater at 10 and 25°C and evaluated on the basis of energy demand and organic removal. The membranes were operated at atypically low crossflow velocities of 0.018–0.3m/s, and with or without fluidized GAC, to reduce AnMBR energy demand. Use of GAC in membranes allowed for significant reduction in crossflow velocity without reducing membrane run-time between cleanings and resulted in energy demands of 0.05–0.13kWh/m3. The AnMBRs were able to produce permeate BOD5≤10mg/L at bioreactor HRTs of 4.2–9.8h, even at 10°C. When factoring in theoretical energy production, the AnMBR described herein is estimated to require 70–100% less energy compared to activated sludge, indicating net neutral energy demand may be feasible for BOD5 and nutrient removal from municipal wastewater.

Model predictive control of two-step nitrification and its validation via short-cut nitrification tests

ABSTRACTShort-cut nitrification (SCN) is shown to be an attractive technology due to its savings in aeration and external carbon source addition cost. However, the shortage of excluding nitrite nitrogen as a model state in an Activated Sludge Model limits the model predictive control of biological nitrogen removal via SCN. In this paper, a two-step kinetic model was developed based on the introduction of pH and temperature as process controller, and it was implemented in an SBR reactor. The simulation results for optimizing operating conditions showed that with increasing of dissolved oxygen (DO) the rate of ammonia oxidation and nitrite accumulation firstly increased in order to achieve a SCN process. By further increasing DO, the SCN process can be transformed into a complete nitrification process. In addition, within a certain range, increasing sludge retention time and aeration time are beneficial to the accumulation of nitrite. The implementation results in the SBR reactor showed that the data predicted by the kinetic model are in agreement with the data obtained, which indicate that the two-step kinetic model is appropriate to simulate the ammonia removal and nitrite production kinetics.

Municipal sludge characteristic changes under different aerating condition in a deep-shaft aeration system

A pilot-scale municipal sewage sludge deep-shaft aeration system was implemented in Lanzhou, Gansu Province of China. The reactor depth was 60 m with a diameter of 1.0 m and the sludge to be treated came from a wastewater plant in Lanzhou. In order to obtain the optimum operation conditions, analysis was conducted on the transformations of the volatile suspended solids (VSS), temperature, pH, oxidation-reduction potential (ORP) and pathogens in the deep-shaft reactor under different aeration conditions. Attention was paid to how operating conditions affected the removal efficiency of the VSS and the reaction temperature. As a result, higher volatile solids removal was gained at higher temperature, and the temperature could reach 50.8°C for a complete inactivation of bacteria in the first reaction zone when the deep-shaft aeration system was run for about 18 days. The sludge aeration rate was observed as 1.5 to 1.8 L/(h·L sludge) which enabled the volatile solids removal rate to reach 40.1%. The degradation of VSS occurred under a micro-oxygen environment, and the lowest ORP was found to be -256 mV in the digestive process. Not only aerobic bacteria but also anaerobic and facultative bacteria performed their functions in the reactor.

Study of the Products of Pyrolysis Recycling. Sewage Sludge in the Aeration Station Almaty, Kazakhstan

This article presents the results of experimental studies of the process of pyrolysis recycling of sewage sludge aeration station in Almaty. According to experimental studies have provided the basic characteristics of the products of pyrolysis of sewage sludge disposal.

Correlation among extracellular polymeric substances, tetracycline resistant bacteria and tetracycline resistance genes under trace tetracycline

Antibiotic resistance occurrences and proliferation in activated sludge have attracted more and more attention nowadays. However, the role which extracellular polymeric substance (EPS) plays on the antibiotic resistance is not clear. The changes and correlation among EPS, tetracycline (TC) resistant bacteria (TRB) and TC resistance genes (TRGs) of sequencing batch reactors (SBRs) were investigated. Performance of SBR without TC was compared with two other SBRs to which different amounts of TC were added. Total average EPS contents were found to increase significantly from 66mgg−1 VSS to 181mgg−1 VSS as the TC concentrations increased from 0 to 100μgL−1. As the EPS content increased, TRB in sludge of the three SBRs increased significantly from 105 to 106 colony forming unit mL−1 after being exposed to TC. In addition, the concentrations of three groups of TRGs (copies mL−1) were determined by real-time fluorescence quantitative polymerase chain reaction and followed the order: efflux pump genes>ribosome protected genes>degradation enzyme genes. The numbers of TRGs in the idle stage were larger than those in the aeration sludge. Correlation coefficients (R2) between EPS and TRB in sludge were 0.823 (p<0.01) while the correlation between EPS and total TRGs was poor (R2=0.463, p>0.05). But it showed the same tendency that EPS and TRGs in sludge increased with the increasing of TC.

Integration of microbial fuel cell with independent membrane cathode bioreactor for power generation, membrane fouling mitigation and wastewater treatment

A microbial fuel cell (MFC) was integrated with flat sheet membrane bioreactor (MBR) and studied for electricity generation, membrane fouling mitigation and artificial wastewater treatment. The cell potential was ∼0.2 V with 100 Ω external load during closed circuit operation. Batch tests identified that the sludge properties and aeration in cathodic chamber were the main affecting factors on electricity generation. Integration of microbial fuel cell can significantly alleviate membrane fouling, under closed circuit condition, membrane filtration lasted 21 days – 27 days and under the open circuit condition it lasted only 13 days - 15 days, before the transmembrane pressure (TMP) reached 0.03 MPa. The calculated electrostatic repulsion force between membrane surface and membrane foulant was about 2.5 × 10−14 N in this integrated reactor. The chemical oxygen demand (COD), ammonia nitrogen, phosphorus and offensive smell could be effectively removed by the sequential anaerobic-aerobic treatment system. The effluent pH was neutral and turbidity was very low.

Application of sewage sludge and intermittent aeration strategy to the bioremediation of DDT- and HCH-contaminated soil

Adding organic amendments to stimulate the biodegradation of pesticides is a subject of ongoing interest. The effect of sewage sludge on the bioremediation of dichlorodiphenyltrichloroethane (DDT) and hexachlorocyclohexane (HCH) contaminated soil was investigated in bench scale experiments, and intermittent aeration strategy was also used in this study to form an anaerobic–aerobic cycle. Bioremediation of DDT and HCH was enhanced with the addition of sewage sludge and the intermittent aeration. The removal rates of HCH and DDT were raised by 16.8%–80.8% in 10days. Sewage sludge increased the organic carbon content from 6.2 to 218g/kg, and it could also introduce efficient degradation microbes to soil, including Pseudomonas sp., Bacillus sp. and Sphingomonas sp. The unaerated phase enhanced the anaerobic dechlorination of DDT and HCH, and anaerobic removal rates of β-HCH, o,p′-DDT and p,p′-DDT accounted for more than 50% of the total removal rates, but the content of α-HCH declined more in the aerobic phase.

정수장 슬러지 폭기를 통한 방류수 수질 개선

So many drinking water treatment plants are under various difficulties by new reinforced effluent standards. Since the target turbidity, much higher than annual average, for designing sludge thickener have to be set to confront high turbidity season, the sludge at thickener should be put up for a long time during usual days. So the soluble manganese and chloroform may be formed under the anaerobic environment in the sludge thickener when the sludge retention time is longer with low turbidity. This phenomenon results in difficulties to keep regulatory level of the discharged effluent. For an effort to overcome the problems, a sludge aeration was successfully implemented into the thickening process. As a result, the final effluent quality and sludge volume were much improved; 41 % of manganese, 62 % of chloroform and 35 % of sludge volume. Additionally, effluent quality was improved ; 61 % of Manganese on aeration with pH control and we could make sure of stability effluent quality despite a long sludge retention time. We recommended the standard of installation sludge aeration equipment to nationally supply water treatment plant under effluent water quality problem ; Manganese, Chloroform, etc.

Optimization method for the treatment of Tehran petroleum refinery wastewater using activated sludge contact stabilization process

ABSTRACTThis paper describes the results of side by side large scale testing of contact stabilization and extended aeration activated sludge processes on the petroleum refinery wastewater at Tehran (Iran) oil refinery by using continuous large scale experiments during the three month investigation period. The process optimization for performance evaluation was studied. Sampling results indicated that the contact stabilization process shows more effective performance than extended aeration process in removing chemical oxygen demand (COD) and biological oxygen demand (BOD), and also the mixed liquor volatile suspended solids were less in contact stabilization as compared to those in the extended aeration process. The excess sludge production was affected by the amount of sludge loading rate and aeration. The applied aeration to the mixed liquor and the sludge recycle rate were found to be critical parameters in the successful optimization of the contact stabilization process. The appropriate optimized opera...

Co-treatment of acid mine drainage with municipal wastewater: performance evaluation

Co-treatment of acid mine drainage (AMD) with municipal wastewater (MWW) using the activated sludge process is a novel treatment technology offering potential savings over alternative systems in materials, proprietary chemicals and energy inputs. The impacts of AMD on laboratory-scale activated sludge units (plug-flow and sequencing batch reactors) treating synthetic MWW were investigated. Synthetic AMD containing Al, Cu, Fe, Mn, Pb, Zn and SO4 at a range of concentrations and pH values was formulated to simulate three possible co-treatment processes, i.e., (1) adding raw AMD to the activated sludge aeration tank, (2) pre-treating AMD prior to adding to the aeration tank by mixing with digested sludge and (3) pre-treating AMD by mixing with screened MWW. Continuous AMD loading to the activated sludge reactors during co-treatment did not cause a significant decrease in chemical oxygen demand (COD), 5-day biochemical oxygen demand, or total organic carbon removal; average COD removal rates ranged from 87-93%. Enhanced phosphate removal was observed in reactors loaded with Fe- and Al-rich AMD, with final effluent TP concentrations<2 mg/L. Removal rates for dissolved Al, Cu, Fe and Pb were 52-84%, 47-61%, 74-86% and 100%, respectively, in both systems. Manganese and Zn removal were strongly linked to acidity; removal from net-acidic AMD was <10% for both metals, whereas removal from circum-neutral AMD averaged 93-95% for Mn and 58-90% for Zn. Pre-mixing with screened MWW was the best process option in terms of AMD neutralization and metal removal. However, significant MWW alkalinity was consumed, suggesting an alkali supplement may be necessary.

Effect of process variables on the production of Polyhydroxyalkanoates by activated sludge.

Polyhydroxyalkanoates are known to be temporarily stored by microorganisms in activated sludge, especially in anaerobic-aerobic processes. Due to the problems resulted from the disposals of plastic wastes and excess sludge of wastewater treatment plants, the production of polyhydroxyalkanoates by treating activated sludge and determining the effect of process variables were the main issues of this paper. In this research, an anaerobic-aerobic sequencing batch reactor was used to make microorganism adapted and a batch aerobic reactor was used for enriching them. The variables affecting polyhydroxyalkanoates production including aeration time, sludge retention time, and volatile fatty acids concentration of the influent in sequencing batch reactor, and also carbon to nitrogen ratio and cultivation time in polymer production reactor, were investigated using Taguchi statistical approach to determine optimum conditions. The maximum polymer production of 29% was achieved at sludge retention time of 5–10 days, aeration time of 2 hours, supplementation of 40% of volatile fatty acids in the influent and increasing of carbon to nitrogen ratio of polymer production reactor to above 25 g/g. Based on the results, in optimum conditions, the volatile fatty acids concentration which increased the production of polyhydroxyalkanoates up to 49% was the most effective variable. Carbon to nitrogen ratio, sludge retention time and aeration time were ranked as the next affecting parameters. Although the polyhydroxyalkanoates content achieved in present study is much lower than that by pure culture, but the proposed method may still serve well as an environmental friendly means to convert waste into valuable product.

Aeration prevents methyl mercury production in dental wastewater

Although research has demonstrated that Hg is methylated in the reducing conditions of the dental clinic wastewater collection system, studies are inconclusive as to whether further methylation occurs in the aeration basin of activated sludge wastewater treatment plant (WWTP) which typically treats this waste. Given the high levels of methyl Hg reported in dental wastewater (DWW), it is important to determine whether additional methylation occurs once it enters the WWTP. To achieve this objective, we incubated DWW under conditions designed to mimic the oxidized conditions of the activated sludge aeration basin in a WWTP. Duplicate bioreactors were charged with raw DWW collected from a 12-chair dental clinic and incubated both with and without aeration. Aeration was continued for 15 days, consistent with the typical mean cell residence time (MCRT) necessary for both heterotrophic carbon oxidation (typically 5–6 days) and nitrification (typically 12–15 days), thus ensuring that incubation time exceeded those for most conceivable MCRTs used in the activated sludge process. Results demonstrate a rapid increase in pH concomitant with an increase in dissolved oxygen (DO) to near saturation in the aerated reactor. The non-aerated reactor remained low or at zero DO due to low surface reaeration coupled with the high levels of organic matter. The rate of mercury methylation increased in the unaearated reactors rapidly upon incubation, reaching highest levels when DO was at the lowest levels during the experiment. In great contrast, methyl mercury levels were much lower and net mercury methylation does not appear to occur at any significant rate under aeration. These results imply that although some mercury methylation may occur in the sewer collection system (or anaerobic digesters), net methylation is unlikely to occur in the aeration basin in activated sludge WWTPs, and thus methyl Hg influent levels from DWW represent an upper bound on effluent levels.

Modeling membrane fouling in a submerged membrane bioreactor by considering the role of solid, colloidal and soluble components

Activated sludge is a complex mixture of solid, colloidal and soluble components. Their respective contributions to membrane fouling process in membrane bioreactor (MBR) have been investigated by the fractioning method. The synergistic effects among these components on membrane fouling are neglected by using the method. A mathematical model was developed to simulate fouling that included the mixed liquor suspended solids (MLSS), soluble and colloidal components, the activated sludge floc size distribution (FSD) and aeration intensity. The membrane fouling was divided into cake layer formation and pore fouling. The cake layer is assumed to be formatted by MLSS and consolidated by the entrapment of colloidal components, resulting in the decreasing in cake porosity and increasing in specific cake resistance. The addition of activated sludge FSD in the model development allows the probability and deposition rate of individual solid sizes to be considered. The developed model was calibrated and validated using experimental data from different aeration intensities. It provides a valuable tool for analyzing the synergistic fouling effects from solids, colloidal and soluble components within activated sludge.

Biogas availability and its energy use in combined wastewater treatment plants (CWWTP)

CWWTP are sanitation facilities formed by the coupling of an aerobic post-treatment (i.e. activated sludge, extended aeration, etc.) with a primary anaerobic treatment (i.e. UASB). In these combined arrangements, usually biogas produced in the UASB units is used to drive mechanical energy for aeration requirements in the secondary treatment (i.e. Activated Sludge, AS). Quality of effluents from CWWTP is similar to those from AS processes but combined treatments could become completely self-sufficient in energy consumption. In this manner, CWWTP improve the carbon-sequestration potential in the sanitation sector by increasing the capture of methane-rich biogas and its energy utilization. This study show how effluent quality parameters and energy demand in the AS unit can be influenced by control, sludge external recirculation and aeration strategies. Modelling and simulation tests, have allowed identifying operational conditions for potential energy savings and rational use of the biogas energy available in a full-scale CWWTP treating municipal sewage.

Study of Treating High Ammonia-N Domestic Wastewater with CASS Process

Abstract The study of treating high ammonia-N domestic wastewater is in the initial stage at home. The removal rate of nitrogen is still at a low level. In the experiment, the CASS process was used to treat high ammonia-N domestic wastewater. The influence of these factors on nitrogen removal, including sludge load, reflux ratio, aeration time, dissolved oxygen and aeration time, were studied and discussed. And then find the optimum conditions.