Performance Of A Packed-Bed A/O Process In Pollutants Removal From Manure-free Piggery Wastewater

The Manure-free piggery wastewater the typical characteristics of high ammonia nitrogen（NH₄⁺-N）and low carbon nitrogen ratio（COD/TN）.It is difficult to achieve effective biological denitrification by using the traditional A/O process.A variety of antibiotics in the wastewater may induce microorganisms to produce antibiotic resistance genes and endanger ecological security and human health through transmission.The removal of antibiotics in the wastewater treatment system is also a frontier hot topic in the direction of pig wastewater treatment.In this paper,a packed-bed anaerobic-aerobic reactor（PBAOR）consisting of two anaerobic compartments and two aerobic compartments was constructed based on the water quality characteristics and emission standards of manure-free piggery wastewater from dry pig manure（GB18596-2001）.The reactor was started up and operated continuously under the conditions of hydraulic retention time（HRT）of 32 h,reflux ratio of 200%and 25°C.The removal performance of COD,NH₄⁺-N,TN and various antibiotics in manure-free piggery wastewater from dry pig manure was mainly investigated.The results show that PBAOR can be successfully started within 60 days and achieve stable operation.In the follow-up continuous operation,although the influent COD,NH₄⁺-N and TN fluctuated greatly between 440.8～818.6 mg/L,166.5～451.1 mg/L and 167.0～456.3 mg/L,the removal rates were about 86.0%,98.2%and 87.4%,and the effluent concentrations were only about 81.7 mg/L,5.7 mg/L and38.2 mg/L,which fully met the requirements of national emission standards.During the study,12 veterinary antibiotics were detected in three categories（tetracycline antibiotics,fluoroquinolone antibiotics and sulfonamide antibiotics）from wastewater.PBAOR had a significant removal effect on tetracycline antibiotics and sulfonamide antibiotics,and the average removal rates were 63.1%and 83.4%,respectively.However,fluoroquinolone antibiotics showed an accumulation trend in the reactor.During the 30d operation after the successful start of PBAOR,no residues of sulfonamide antibiotics were detected in the effluent.It was found that the removal of COD from manure-free piggery wastewater by PBAOR mainly occurred in the front-end anaerobic cell,and the contribution rate of PBAOR to the total removal of COD was as high as 70.1%.The removal of NH₄⁺-N and TN mainly occurred in the back-end aerobic cell,and the contribution rates of the total removal amount of the system reached 77.3%～83.0%and 54.7%～70.5%,respectively.In the case of serious shortage of organic carbon sources,the efficient biological denitrification in the aerobic cell should be mainly removed through the combined effect of aerobic ammonia oxidation and anaerobic ammonia oxidation.The analysis of the removal characteristics of antibiotics showed that the degradation of tetracycline antibiotics and sulfonamide antibiotics by PBAOR mainly occurred in the anaerobic chamber,and the contribution rates of PBAOR to the total degradation of the system reached 69.2%and 71.0%,respectively.The accumulation of fluoroquinolone antibiotics mainly occurred in the aerobic compartment,and the average accumulation was about 60.5%.Although the removal of NH₄⁺-N and TN by PBAOR and the degradation or accumulation mechanism of antibiotics remain to be further explored,this study has proved that this treatment process is efficient and stable for the treatment of manure-free piggery wastewater with dry manure,and it is a manure-free piggery wastewater treatment technology with good application prospects.