Effect of FeCl3 concentration in chemically enhanced primary treatment on the performance of a conventional wastewater treatment plant. A case study.

The effect of coagulant dosage in a chemically enhanced primary treatment (CEPT) on the performance of a conventional wastewater treatment plant (WWTP) has been investigated. Lab-scale experiments simulations were carried out in order to evaluate the effect of coagulant addition on the primary settling performance. In these experiments, FeCl3 was used as coagulant. Later, the WWTP was theoretically simulated using a commercial software (WEST®) to evaluate the effect of coagulation/flocculation on the global system, based on the results obtained at lab-scale. According to these results, the CEPT modifies the organic matter balance in the WWTP, decreasing the contribution of readily (SS) and slowly (XS) biodegradable fractions of COD to the aerobic biological process up to 27.3% and 80.8%, respectively, for a dosage of FeCl3 of 24 mg L-1. Consequently, total suspended solids in the aerobic reactor and the secondary purged sludge decreased up to 33% and 13%, respectively. However, the influence on effluent quality was negligible. On the contrary, suspended solids concentration in the sludge to be treated by anaerobic digestion increased, mainly regarding the Ss and Xs fractions, which caused an 8.1% increase in biogas production potential, with approximately 60% of CH4 concentration.

Advanced treatment of dye manufacturing wastewater by electrocoagulation and electro-Fenton processes: Effect on COD fractions, energy consumption, and sludge analysis.

This study investigated chemical oxygen demand (COD), color number (CN), and UV254 removal from dye manufacturing wastewater via electrocoagulation (EC) and electro-Fenton (EF) processes. The effects of current density, initial pH, reaction time, and H2O2/COD ratio on the EC and EF processes were evaluated and optimum operating conditions were determined. The effects of EC and EF processes on COD fractions and the specific energy consumption of both processes were evaluated. Sludge analyses were conducted by organic removal to sludge ratio (ORSR) and Fourier Transform Infrared Spectroscopy spectra were assessed for characterization of generated sludge. Optimum operation conditions for the EC process were 21 mA/cm2 current density, 7.3 initial pH, and 25 min reaction time while they were 21 mA/cm2 current density, 3.5 initial pH, 1.25 H2O2/COD ratio, and 35 min reaction time for EF process. Under optimum conditions COD, CN, and UV254 removal efficiencies were 38.5%, 90.1%, and 52.5%, respectively in EC process and 54.8%, 94.2%, and 88.1%, respectively in EF process. Both processes have a positive effect on the increase of biodegradable and soluble COD fractions. Higher ORSR and lower specific energy consumption were provided by the EF process under optimum conditions. The EF process is more effective when pollutant removal efficiencies, ORSR, and specific energy consumption are considered.

Sludge reduction by ozone: Insights and modeling of the dose-response effects.

Applying ozone to the return flow in an activated sludge (AS) process is a way for reducing the residual solids production. To be able to extend the activated sludge models to the ozone-AS process, adequate prediction of the tri-atoms effects on the particulate COD fractions is needed. In this study, the biomass inactivation, COD mineralization, and solids dissolution were quantified in batch tests and dose-response models were developed as a function of the reacted ozone doses (ROD). Three kinds of model-sludge were used. S1 was a lab-cultivated synthetic sludge with two components (heterotrophs XH and XP). S2 was a digestate of S1 almost made by the endogenous residues, XP. S3 was from a municipal activated sludge plant. The specific ozone uptake rate (SO3UR, mgO3/gCOD.h) was determined as a tool for characterizing the reactivity of the sludges. SO3UR increased with the XH fraction and decreased with more XP. Biomass inactivation was exponential (e-ß.ROD) as a function of the ROD doses. The percentage of solids reduction was predictable through a linear model (CMiner + Ysol ROD), with a fixed part due to mineralization (CMiner) and a variable part from the solubilization process. The parameters of the models, i.e. the inactivation and the dissolution yields (ß, 0.008-0.029 (mgO3/mgCODini)-1 vs Ysol, 0.5-2.8 mg CODsol/mgO3) varied in magnitude, depending on the intensity of the scavenging reactions and potentially the compactness of the flocs for each sludge.

Optimizing anaerobic technology by using electrochemistry and membrane module for treating pesticide wastewater: Chemical oxygen demand components and fractions distribution, membrane fouling, effluent toxicity and economic analysis.

Optimization in performance and membrane fouling of an electrochemical anaerobic membrane bioreactor (R1) for treating pesticide wastewater was investigated and compared with a conventional anaerobic membrane bioreactor (R2). The maximum COD removal efficiency of R2 was 80.1%, 80.0%, 67.4%, 61.1% with HRT of 96, 72, 48 and 24 h, which of R1 was enhanced to 84.7%, 84.3%, 82.0% and 66.3%. These results demonstrated that the optimum HRT of R1 was shortened to 48 h, which of R2 required 72 h. R1 reduced the contents of particulate and colloidal COD, and the fraction of COD converted to sludge was 5.0-8.2% lower than that of R2. The fouling rate was 0.99-1.44 kPa/d and reduced by 31.0%-38.5% compared with R2. Detoxification was enhanced by 7.8-47.7% with the assistance of bio-electrochemistry. Ultimately, ensuring similar performance, R1 achieved a 65.6% improvement in environmental benefit, a 26.3% and 38.9% reduction in unit capital and operating costs.

A New Activated Sludge Model with Membrane Separation-Implications for Sewage and Textile Effluent.

A new model for the activated sludge process with membrane separation is presented, based on the effective filtration size. A new size threshold is imposed by the membrane module. The model structure requires a modified fractionation of the chemical oxygen demand and includes chemical oxygen demand fractions entrapped in the reactor or in the flocs as model components. This way, it offers an accurate mechanistic interpretation of microbial mechanisms taking place in membrane activated sludge systems. Denim processing wastewater was selected for model implementation, which emphasized the significance of entrapped fractions of soluble hydrolysable and soluble inert chemical oxygen demand responsible for better effluent quality, while underlining the shortcomings of existing activated sludge models prescribed for systems with conventional gravity settling. The model also introduced particle size distribution analysis as a new experimental instrument complementing respirometric assessments, for an accurate description of chemical oxygen demand fractions with different biodegradation characteristics in related model evaluations.

Impact of paint shop decanter effluents on biological treatability of automotive industry wastewater.

A lab-scale Sequencing Batch Reactor (SBR) was implemented to investigate biological treatability and kinetic characteristics of paint shop wastewater (PSW) together with main stream wastewater (MSW) of a bus production factory. Readily biodegradable and slowly biodegradable COD fractions of MWS were determined by respirometric analysis: 4.2% (SS), 10.4% (SH) and 59.3% (XS). Carbon and nitrogen removal performance of the SBR feeding with MSW alone were obtained as 89% and 58%, respectively. When PSW was introduced to MSW, both carbon and nitrogen removal were deteriorated. Model simulation indicated that maximum heterotrophic growth rate decreased from 7.2 to 5.7day-1, maximum hydrolysis rates were reduced from 6 to 4day-1 (khS) and 4 to 1day-1 (khX). Based on the dynamic model simulation for the evaluation of nitrogen removal, a maximum specific nitrifier growth rate was obtained as 0.45day-1 for MSW feeding alone. When PSW was introduced, nitrification was completely inhibited and following the termination of PSW addition, nitrogen removal performance was recovered in about 100 days, however with a much lower nitrifier growth rate (0.1day-1), possibly due to accumulation of toxic compounds in the sludge. Obviously, a longer recovery period is required to ensure an active nitrifier community.

Effect of persulfate and persulfate/H2O2 on biodegradability of an anaerobic stabilized landfill leachate.

The current study investigated the effects of S2O8(2-) and S2O8(2-)/H2O2 oxidation processes on the biodegradable characteristics of an anaerobic stabilized leachate. Total COD removal efficiency was found to be 46% after S2O8(2-) oxidation (using 4.2 g S2O8(2-)/1g COD0, at pH 7, for 60 min reaction time and at 350 rpm shaking speed), and improved to 81% following S2O8(2-)/H2O2 oxidation process (using 5.88 g S2O8(2-) dosage, 8.63 g H2O2 dosage, at pH 11 and for 120 min reaction time at 350 rpm). Biodegradability in terms of BOD5/COD ratio of the leachate enhanced from 0.09 to 0.1 and to 0.17 following S2O8(2-) and S2O8(2-)/H2O2 oxidation processes, respectively. The fractions of COD were determined before and after each oxidation processes (S2O8(2-) and S2O8(2-)/H2O2). The fraction of biodegradable COD(bi) increased from 36% in raw leachate to 57% and 68% after applying S2O8(2-) and S2O8(2-)/H2O2 oxidation, respectively. As for soluble COD(s), its removal efficiency was 39% and 78% following S2O8(2-) and S2O8(2-)/H2O2 oxidation, respectively. The maximum removal for particulate COD was 94% and was obtained after 120 min of S2O8(2-)/H2O2 oxidation. As a conclusion, S2O8(2-)/H2O2 oxidation could be an efficient method for improving the biodegradability of anaerobic stabilized leachate.