Treatment of pesticide wastewater by moving-bed biofilm reactor combined with Fenton-coagulation pretreatment.
In order to treat pesticide wastewater having high chemical oxygen demand (COD) value and poor biodegradability, Fenton-coagulation process was first used to reduce COD and improve biodegradability and then was followed by biological treatment. Optimal experimental conditions for the Fenton process were determined to be Fe(2+) concentration of 40 mmol/L and H(2)O(2) dose of 97 mmol/L at initial pH 3. The interaction mechanism of organophosphorous pesticide and hydroxyl radicals was suggested to be the breakage of the P=S double bond and formation of sulfate ions and various organic intermediates, followed by formation of phosphate and consequent oxidation of intermediates. For the subsequent biological treatment, 3.2g/L Ca(OH)(2) was added to adjust the pH and further coagulate the pollutants. The COD value could be evidently decreased from 33,700 to 9300 mg/L and the ratio of biological oxygen demand (BOD(5)) to COD of the wastewater was enhanced to over 0.47 by Fenton oxidation and coagulation. The pre-treated wastewater was then subjected to biological oxidation by using moving-bed biofilm reactor (MBBR) inside which tube chip type bio-carriers were fluidized upon air bubbling. Higher than 85% of COD removal efficiency could be achieved when the bio-carrier volume fraction was kept more than 20% by feeding the pretreated wastewater containing 3000 mg/L of inlet COD at one day of hydraulic retention time (HRT), but a noticeable decrease in the COD removal efficiency when the carrier volume was decreased down to 10%, only 72% was observed. With the improvement of biodegradability by using Fenton pretreatment, also due to the high concentration of biomass and high biofilm activity using the fluidizing bio-carriers, high removal efficiency and stable operation could be achieved in the biological process even at a high COD loading of 37.5 gCOD/(m(2)carrierday).
Chen
Sheng
S
School of Municipal & Environmental Engineering, Harbin Institute of Technology, Harbin 150090, PR China. hitchensheng@126.com
Sun
Dezhi
D
Chung
Jong-Shik
JS
D018441:Biofilms; D019149:Bioreactors; D002126:Calcium Hydroxide / Q000737:chemistry; D005427:Flocculation; D006861:Hydrogen Peroxide / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry; D009943:Organophosphorus Compounds / Q000737:chemistry / Q000378:metabolism; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D010575:Pesticides / Q000737:chemistry* / Q000378:metabolism*; D020959:Polyethylene; D014865:Waste Disposal, Fluid / Q000379:methods*; D014874:Water Pollutants, Chemical / Q000737:chemistry* / Q000378:metabolism*; D018508:Water Purification / Q000379:methods
D009943:Organophosphorus Compounds; D010575:Pesticides; D014874:Water Pollutants, Chemical; D020959:Polyethylene; D006861:Hydrogen Peroxide; D007501:Iron; D002126:Calcium Hydroxide; D010100:Oxygen