title: Para-chlorophenol containing synthetic wastewater treatment in an activated sludge unit: effects of hydraulic residence time.
abstract: Due to the toxic nature of chlorophenol compounds present in some chemical industry effluents, biological treatment of such wastewaters is usually realized with low treatment efficiencies. Para-chlorophenol (4-chlorophenol, 4-CP) containing synthetic wastewater was treated in an activated sludge unit at different hydraulic residence times (HRT) varying between 5 and 30 h while the feed COD (2500 mg l(-1)), 4-CP (500 mg l(-1)) and sludge age (SRT, 10 days) were constant. Effects of HRT variations on COD, 4-CP, toxicity removals and on settling characteristics of the sludge were investigated. Percent COD removals increased and the effluent COD concentrations decreased when HRT increased from 5 to 15 h and remained almost constant for larger HRT levels. Nearly, 91% COD and 99% 4-CP removals were obtained at HRT levels above 15 h. Because of the highly concentrated microbial population at HRT levels of above 15 h, low effluent (reactor) 4-CP concentrations and almost complete toxicity removals were obtained. High biomass concentrations obtained at HRT levels above 15 h were due to low 4-CP contents in the aeration tank yielding negligible inhibition effects and low maintenance requirements. The sludge volume index (SVI) decreased with increasing HRT up to 15 h due to high biomass concentrations at high HRT levels resulting in well settling sludge with low SVI values. Hydraulic residence times above 15 h resulted in more than 90% COD and complete 4-CP and toxicity removals along with well settling sludge.
authors.affiliation: Department of Environmental Engineering, Dokuz Eylul University, Buca, Izmir, Turkey. fikret.kargi@deu.edu.tr
authors.forename: Fikret
authors.initials: F
authors.lastname: Kargi
authors.forename: Isil
authors.initials: I
authors.lastname: Konya
mesh_terms: D001419:Bacteria / Q000187:drug effects / Q000378:metabolism*; D001673:Biodegradation, Environmental; D018533:Biomass; D019149:Bioreactors; D002733:Chlorophenols / Q000378:metabolism* / Q000633:toxicity; D012722:Sewage / Q000382:microbiology*; D013997:Time Factors; D014865:Waste Disposal, Fluid; D018505:Waste Management; D014874:Water Pollutants, Chemical / Q000378:metabolism* / Q000633:toxicity
chemical_list: D002733:Chlorophenols; D012722:Sewage; D014874:Water Pollutants, Chemical; C029107:4-chlorophenol