Conventional Activated Sludge Unit Research Articles

LCA of a Membrane Bioreactor Compared to Activated Sludge System for Municipal Wastewater Treatment.

Membrane bioreactor (MBR) systems are connected to several advantages compared to the conventional activated sludge (CAS) units. This work aims to the examination of the life cycle environmental impact of an MBR against a CAS unit when treating municipal wastewater with similar influent loading (BOD = 400 mg/L) and giving similar high-quality effluent (BOD < 5 mg/L). The MBR unit contained a denitrification, an aeration and a membrane tank, whereas the CAS unit included an equalization, a denitrification, a nitrification, a sedimentation, a mixing, a flocculation tank and a drum filter. Several impact categories factors were calculated by implementing the Life Cycle Assessment (LCA) methodology, including acidification potential, eutrophication potential, global warming potential (GWP), ozone depletion potential and photochemical ozone creation potential of the plants throughout their life cycle. Real data from two wastewater treatment plants were used. The research focused on two parameters which constitute the main differences between the two treatment plants: The excess sludge removal life cycle contribution—where GWPMBR = 0.50 kg CO2-eq*FU−1 and GWPCAS = 2.67 kg CO2-eq*FU−1 without sludge removal—and the wastewater treatment plant life cycle contribution—where GWPMBR = 0.002 kg CO2-eq*FU−1 and GWPCAS = 0.14 kg CO2-eq*FU−1 without land area contribution. Finally, in all the examined cases the environmental superiority of the MBR process was found.

Influence of Landfill Leachate on Organic Matter Removal in Activated Sludge and Activated Sludge with Carrier Processes

Abstract This study assessed the performance of two pilot units, a conventional activated sludge (CAS) and an Integrated Fixed-Film Activated Sludge (IAS), in the treatment of leachate from sanitary landfill combined with domestic sewage, with the aim of removing organic substances. In order to assess the possible impacts on treatment, three experimental phases were designed using influent leachate contributions of 5%, 10%, and 20% of the total BOD load. Overall, the results showed that no significant changes in the behavior of biological processes. The IAS unit presented average BOD removal efficiencies of above 88%, 87% and 80% for the three leachate load contributions of 5%, 10% and 20% studied. The CAS unit presented lower average efficiency with a 5% leachate contribution (64%), but displayed a similar performance to the IAS unit in the other phases (82% and 80%); similar quantitative aspects were observed for both treatment processes with regards to biomass composition analysis. The kinetic coefficients related to heterotrophic metabolism did not indicate negative effects on treatment efficiency as a result of the increase in leachate addition, with values of 2.8; 2.8 and 2.7 d-1 obtained respectively for each phase with the CAS unit, and 2.0; 1.5 and 1.6 d-1 with the IAS unit, representing similar values to those found in the literature (1.5 a 5.0 d-1). The results reinforced the conclusion that the leachate load introduced did not cause inhibition or significant alterations to heterotrophic metabolism, and, therefore, to the removal of organic matter.

Improvement of the Overall Biodegradability of Ciprofloxacin by Pre-treatment with Photocatalytic Oxidation of Wastewaters

In this study, photocatalytic degradation of ciprofloxacin (CIP) was investigated. CIP is a widely used quinolone antibiotic. Removal of CIP in the dark is negligible. The removal efficiency by photolysis of CIP was 25.3%. The removal efficiencies after 30 min irradiation were 85%, 93.5% and 97% at pH values 3, 6 and 9 in the presence of 0.5 g/L TiO2, respectively. Modified form of the Langmuir-Hinshelwood equation has been successful as a quantitive model to describe solid-liquid interactions. Kinetic constant k is reactivity constant, K is the adsorption equilibrium constant and kap (kK) is the apparent first order reaction constant, these were determined as 0.673 mg/L min, 0.662 L/mg and 0.445 (1/min), respectively. The results showed that after 30 min irradiation of CIP, solution was degraded 95%, whereas COD removed was 40.3%. The enhancement of biodegradability, evaluation in terms of the BOD5/COD ratio, increased from 0.043 to 0.403. This increase is not sufficient for treatment in conventional activated sludge unit. Additionally, the biodegradability of CIP photo-transformation products was assessed by BOD test. k (1/d), BOD reaction rate constants were determined as 0.0857 (1/d) and 0.1778 (1/d) for untreated and treated CIP solution, respectively.

A test for adequate wastewater treatment based on glutathione S transferase isoenzyme profile

Discharge to the environment of treated or non-treated municipal wastewater imposes several threats to coastal and estuarine ecosystems which are difficult to assess. In our study we evaluate the use of the isoenzyme profile of glutathione S transferase (GST) in combination with the kinetic characteristics of the whole enzyme and of heme peroxidase, as a test of adequate treatment of municipal wastewater. For this reason, Artemia nauplii were incubated in artificial seawater prepared by wastewater samples, such as secondary municipal effluents produced by a conventional activated sludge unit and advanced treated effluents produced by the employment of coagulation, activated carbon adsorption and chlorination as single processes or as combined ones. Characteristic changes of the isoenzyme pattern and the enzymes' kinetic properties were caused by chlorinated secondary municipal effluent or by secondary non-chlorinated effluent. Advanced treatment by combination of coagulation and/or carbon adsorption resulted to less prominent changes, suggesting more adequate treatment. Our results suggest that GST isoenzyme profile in combination with the kinetic properties of the total enzyme family is a sensitive test for the evaluation of the adequateness of the treatment of reclaimed wastewater and the reduction of potentially harmful compounds. Potentially, it may offer a ‘fingerprint’ characteristic of a particular effluent and probably of the treatment level it has been subjected.

Influence of the employment of adsorption and coprecipitation agents for the removal of PPCPs in conventional activated sludge (CAS) systems

Three activated sludge reactors were operated to improve the removal of organic micropollutants such as Pharmaceutical and Personal Care Products (PPCPs). Reactor 1 (R1) was operated as a Conventional Activated Sludge reactor (CAS), Reactor 2 (R2) consisted of a CAS unit that was continuously fed with FeCl3 whereas granular activated carbon (GAC) was fed directly into the mixed liquor of Reactor 3 (R3) in order to attain concentrations in the range 100-1,000 mg/L. PPCPs removal rates varied depending on the compound present in each reactor during the entire 220 days of operation. Some substances showed the same behaviour in all reactors, such as the acidic pharmaceuticals naproxen and ibuprofen, which were almost completely removed (> 90%). More hydrophobic organic substances, like musk fragrances, were about 90% removed after 40 days of operation in all of the reactors. The main difference between the three reactors was obtained in R3 when the GAC concentrations in the aeration tank were around 500-1,000 mg/L. Under these conditions, the more recalcitrant compounds like diazepam and carbamazepine could be removed by up to 40%, and diclofenac up to 85%. Adsorption isotherms for PPCPs were obtained with activated carbon, and the results were successfully fitted to the Freundlinch equation. The more recalcitrant compounds (carbamazepine, diazepam and diclofenac) had the highest adsorption capacities onto GAC, which is consistent with the behaviour observed in R3 and helps to identify the removal mechanism (adsorption for these compounds, whereas absorption for fragrances).

Comparative Analysis of Nitrifying Bacteria in Full–Scale Oxidation Ditch and Aerated Nitrification Biofilter by Using Fluorescent In Situ Hybridization (FISH) and Denaturing Gradient Gel Electrophoresis (DGGE)

In this study, nitrification performances and composition of nitrifying populations in a full–scale oxidation ditch and a high–rate submerged media nitrification biofilter were comparatively analyzed. In addition to different reactor configurations, effects of differing operational conditions on the nitrification efficiency and bacterial diversity were also explored and evaluated thoroughly. In microbial analysis of sludge samples fluorescent in situ hybridization (FISH) and denaturing gradient gel electrophoresis (DGGE) techniques were used complementary to each other. The extended aeration oxidation ditch subjected to the study is operated as a nitrogen and phosphorus removal system consisting of anaerobic, anoxic, and aerobic zones. The high–rate submerged media aerated filter is operated as nitrification step following the conventional activated sludge unit and the nitrified wastewater is discharged to the sea without complete nitrogen removal. In situ hybridization results have indicated that Nitrosomonas–like ammonia oxidizing and Nitrospira–related nitrite oxidizing bacteria were intensively present in vigorous flocs in nitrification biofilter while carbonaceous bacteria belong to beta subclass of Proteobacteria were considerably dominant in oxidation ditch. Low quantities of nitrifiers in oxidation ditch were also confirmed by the dissimilarity in intensive bands between two systems obtained with DGGE analysis.

Evaluation of increased denitrification in an anoxic activated sludge using zeolite

Zeolite added activated sludge unit (ZU) under anoxic conditions improved nitrate removal efficiency by 48% (i.e., equivalent to approximately 10 mg/l) greater than that of a conventional activated sludge unit (CU) regardless of varying C/N ratio ranging from 0 to 4.8. For a C/N ratio of 4, no significant differences of denitrification rate were found between two units showing a range of 6.7 to 6.9 mg NO3 - -N/g VSS (volatile suspended solids) hr. However, a C/N ratio decrease to 1.6 was ascribed to considerable differences in denitrification rate showing 4.15 mg NO 3 - -N/g VSS·hr for the ZU, which was 39% greater than that of the CU presenting at 2.98 mg NO 3 - -N/g VSS·hr. It was decided that the presence of greater concentration of MLVSS (mixed liquor suspended solids) in the ZU can be efficiently used for enhanced denitrification as a potential carbon source due to autolysis, although a lower concentration of COD (i.e., less than 1.6 of C/N ratio) is introduced.

Decolorization of simulated textile wastewater in an anaerobic–aerobic sequential treatment system

The effects of hydraulic retention time ( θ H=12–72 h), initial COD concentration (COD 0=1000–8000 mg l −1) and initial dyestuff concentration ( D 0=50–400 mg l −1) on COD removal and decolorization of vinylsulfone/monochlorotiazine bifunctional, monoazo type textile dyestuff, Reactive Red 195, Sumifix Supra Br Red 3BF 150% gran in a sequential anaerobic–aerobic treatment system were investigated in this study. A facultative anaerobic PDW was used as dominant microbial culture in the anaerobic unit for decolorization. The system was operated continuously at room temperature ( T=19–22 °C). It consisted of an anaerobic packed column and a conventional activated sludge unit which was fed with effluent from an anaerobic unit. Metal mesh particles were used as microorganism support material in the anaerobic packed column. Experimental results indicated that the system could be operated at θ H=18 h, 3000 mg l −1 initial COD concentration and 100 mg l −1dyestuff concentration to obtain over 85% decolorization efficiency in an anaerobic reactor. No significant colour removal (15%) was observed under aerobic conditions while COD removal was mainly obtained in the aerobic unit with maximum 90% efficiency.

Treatment of a petrochemical wastewater in sequencing batch reactors

AbstractThe response of sequencing batch reactors (SRB's) in an industrial application was investigated. Four bench‐scale SBR's and a bench‐scale conventional activated sludge unit were operated with wastewater from a petrochemical complex. In terms of the degradation of BOD material and nitrification, the performance of the SBR's was comparable or slightly superior to that of the conventional activated sludge unit. However, for high strength wastes with BOD5 &gt; 300 mg/l and under organic shock loading conditions, effluent from an SBR may have a high solids content as a result of abundant dispersed‐cells growth. The SBR reacted well to a series of phenolic shock loadings; phenols were degraded from initial concentrations ranging from 200 to 950 mg/l to &lt;0.1 mg/l. A model of the SBR, which incorporated the Monod kinetics, was presented as a design aid.

Bacterial aerosols generated by a package treatment plant

Abstract Airborne bacteria were monitored near the aeration tank of a package sewage treatment plant serving a mobile‐home community. The concentrations of airborne coliforms were similar to those found at a conventional activated sludge unit. HC type Millipore filters were found to be the most efficient for the recovery of airborne fecal coliforms.

Disposal of dairy whey by two stage biological treatment—I kinetic studies of the aerobic stage

A two stage biological treatment process has been proposed for the treatment of whey discharged from cheese and casein factories. The system consists of high rate anaerobic digestion followed by stabilization of the waste in a conventional activated sludge unit. This work embodies the determination of the kinetic parameters describing the second stage—the aerobic biological process. The relationships chosen to describe the system are based on the Monod empirical model describing biological oxidation processes.