Study On AF-BAF Process In Treatment Of Piggery Wastewater

The rapid development of Livestock and poultry breeding industry have provided socialmaterial wealth and economic benefit, but environmental pollutions caused by livestock andpoultry breeding waste water is becoming to be an increasingly serious problem at the sametime. Exploring an economic and effective piggery wastewater treatment technology whichsuits our national condition is the hot spot and difficulty of polluted water controlling. Thechemical oxygen demand (COD), ammonia (NH₃-N) and Suspended matter(SS)concentrations in piggery wastewater are high. A treatment process of anaerobic filter (AF)plus biological aerated filter (BAF) was used.The objective was to study the effect ofAF-BAF process on wastewater COD, NH₃-N and SS content. The results could provide anew technology for the treatment of livestock and poultry cultivation wastewater. Wastewaterfrom a pig farm of Ben xiang group in Shaanxi Yangling was studied. COD, NH₃-N and SSremoval rates were selected as determination standard. After starting the AF and BAF reactors,the optimum operational parameters were determined. Next, the AF-BAF system wasoperated under these optimum conditions to determine the COD, NH₃-N removal rates fromwastewater. The main conclusions are as follows:(1)The water quality indices(COD, NH₃-N, SS) of the effluent meet the DischargeStandard of Pollutants for Livestock and Poultry Breeding(GB18596—2001)after treatmentof AF-BAF. The process is effective for the treatment of piggery wastewater. On average, thetreatment process removed94.69%of the COD,87.72%of the NH₃-N and79.67%of the SS.(2)At30³5℃, theAF reactor required89days for start-up. Organic load forAF canreach6.5kg/(m3·d). When AF operate stable, the treatment process removed81.13%of theCOD and18.93%of the NH₃-N on average. The COD of the influent ranged from5500to6500mg/L and the NH₃-N concentration ranged from380to460mg/L. After treatment, theCOD of the effluent ranged from960to1308mg/L and the NH₃-N concentration rangedfrom290to380mg/L.(3)The optimum temperature for theAF was30³5℃. At30³5℃, the removal rate of COD is supreme. The increasing and decreasing of temperature can cause COD removalrate decline. The optimum hydraulic retention time (HRT) for the AF was18h. HRT <18h,the COD removal rate increased with HRT, when HRT>18h, the increase of COD removalrate was not significantly.(4)The influent pH value ranged form7.02to8.26inAF, the average is7.66. Theeffluent pH value ranged form6.06⁷.80, the average is7.17.The pH value was stable in AFreactor during the whole operation process and acidification did not appear.(5)COD removal rate increased with organic load elevation inAF reactor. The removalrate of COD and organic loading meet the relationships: y=3.5942x+56.271, when organicload increased from0.5to6.5kg/(m3·d). The COD removal rate did not decline when AFreached the maximum load that showed the maximum capacity of AF has not reached.(6)Anaerobic ammonia oxidation occurs inAF reactor. The average removal rate ofNH₃-N is18.93%. Part of ammonia nitrogen depredated. When AF operate stable, the NH₃-Nof influent concentration ranged from380to460mg/L. After treatment, the NH₃-N ofeffluent concentration ranged from290to380mg/L.(7)BAF reactor required25days for start-up. When BAF operate stable, the treatmentprocess removed77.38%of the COD and86.42%of the NH₃-N on average. The COD of theinfluent ranged from960to1300mg/L and the NH₃-N concentration ranged from290to380mg/L. After treatment, the COD of the effluent ranged from190to340mg/L and the NH₃-Nconcentration ranged from40to70mg/L.(8)For the BAF, the optimum temperature was25℃, the optimum HRT was10and theoptimum gas to water ratio was7.Raise of temperature, gas water ratio and HRT can makethe pollutants depredate fully and COD and NH₃-N removal rate increase.But when theparameter values above the optimum value will cause decline of activated sludge andincreasing of energy consumption.(9)The influent pH value ranged form6.06to8.80in BAF, the average is7.17. Theeffluent pH value ranged form7.03⁸.11, the average is7.46. The pH values were stable inBAF reactor during the whole operation process and basically meet the needs of nitrificationand denitrification.