Mathematical modelling of 4-chlorophenol inhibition on COD and 4-chlorophenol removals in an activated sludge unit.
ABSTRACT A mathematical model was developed for an activated sludge unit treating 4-chlorophenol (4-CP) containing synthetic wastewater composed of diluted molasses, urea, KH(2)PO(4) and MgSO(4) with COD and 4-CP contents of 2500 and 500 mg l(-1), respectively. The model included 4-CP inhibition on COD and 4-CP removals. Experimental data obtained at different hydraulic residence times (HRT=5-30h) and sludge ages (SRT, 3-30 days) were used to estimate the kinetic and inhibition constants for COD and 4-CP removal rates. 4-CP inhibition on COD removal was negligible while the inhibition on 4-CP removal was significant. The specific rate constant (k), saturation constant (K(s)) for COD oxidation were found to be 2.64 day(-1) and 559 mg l(-1), respectively. A similar model was used for 4-CP oxidation in the activated sludge unit and the constants were found to be k'=1.44 day(-1), K'(s)=25.7 mgl(-1), K"(CP)=559 mg l(-1),and K(I,CP)=17 mg l(-1). Increases in death rate constant because of 4-CP inhibition was also quantified and the inhibition constants were determined for both COD and 4-CP removals. Model predictions with the estimated kinetic constants were in good agreement with the experimental data. Developed model can be used to estimate the performance of an activated sludge unit treating 4-CP containing wastewater under the specified experimental conditions.
- SourceAvailable from: Evans M N Chirwa[Show abstract] [Hide abstract]
ABSTRACT: Process water from nuclear fuel recovery unit operations contains a variety of toxic organic compounds. The use of decontamination reagents such as CCl4 together with phenolic tar results in wastewater with a high content of chlorophenols. In this study, the extent of dehalogenation of toxic aromatic compounds was evaluated using a photolytic advanced oxidation process (AOP) followed by biodegradation in the second stage. A hard-to-degrade toxic pollutant, 4-chlorophenol (4-CP), was used to represent a variety of recalcitrant aromatic pollutants in effluent from the nuclear industry. A UV-assisted AOP/bioreactor system demonstrated a great potential in treatment of nuclear process wastewater and this was indicated by high removal efficiency (>98%) under various 4-CP concentrations. Adding hydrogen peroxide (H2O2) as a liquid catalyst further improved biodegradation rate but the effect was limited by the scavenging of OH• radicals under high concentrations of H2O2.International Journal of Chemical Engineering 01/2010;
- [Show abstract] [Hide abstract]
ABSTRACT: BACKGROUND: This study is focused on the application of intensified biological systems for the degradation of halogenated organic compounds. The single and combined effects of cometabolism and bioaugmentation with Pseudomonas putida on the aerobic degradation of 4-chlorophenol (4-CP) in sequencing batch reactors was studied. Phenol was added as growth substrate to enhance 4-CP biodegradation through cometabolic transformation. RESULTS: Adaptation of activated sludge by increasing 4-CP loads aimed at a progressive acclimation to that compound, which could be successfully degraded at loading rates below 55 mg g−1 VSS d−1. Using phenol as cosusbtrate allowed almost a threefold decrease of the time required for the exhaustion of 4-CP. The addition of phenol also reduced the toxic effect of 4-CP over P. putida. The bioaugmentation of the SBR with P. putida enhanced the 4-CP removal rate, allowing the SBR to deal with 4-CP loads up to 120 mg g−1 VSS d−1. CONCLUSION: Bioaugmentation of SBR with P. putida improves the capacity of this system to withstand high toxic shocks. Cometabolic degradation of 4-CP with phenol improves the removal rates achieved by the SBR at similar 4-CP loads. Both strategies are more convenient intensification techniques than acclimation for the biological treatment of 4-CP. Copyright © 2012 Society of Chemical IndustryJournal of Chemical Technology & Biotechnology 09/2012; 87(9). · 2.50 Impact Factor