Study On Treatment Technology Of Biodiesel Wastewater

The quality of wastewater from biodiesel production is complex with high concentration pollutants and it is a kind of high concentration organic wastewater. The integrated “coagulation-floatation- hydrolytic acidification-biological contact oxidation” were used as treatment processes for biodiesel wastewater in this study, including design and operation control. The purification performance of different coagulants for wastewater treatment was investigated and the optimal coagulant and its dose were determined. In addition, the rapid start-up of large UASB reactor and the rapid sludge granulation were studied. The purification performance of integrated treatment process and each treatment unit was evaluated and the operation control characteristics of integrated treatment process were explored, to improve the operation control and overall technological level.The aluminum sulfate, polyaluminum chloride(PAC) and polyferric sulfate(PFS) were used as coagulants in the coagulation treatment of wastewater and PAC was determined to be optimal. The maximum COD removal rate was 41.2 % at PAC dose of 0.8 mg·L-1. When p H, COD, SS, animal and vegetable oils of influent were 7.5, 20160~21830 mg·L-1, 215~227 mg·L-1 and 412~436 mg·L-1, the qualities of treated water were COD of 11690~12660 mg·L-1, SS of 53~56 mg·L-1 and animal and vegetable oils of 80~85 mg·L-1 in the coagulation-floatation treatment. The average concentrations of COD, SS and animal and vegetable oils in the effluent were 11830 mg·L-1, 54.5 mg·L-1 and 82.1 mg·L-1, and their corresponding removal rates were 42.0%, 75.4% and 80.6%.The start-up conditions of anaerobic reactor were low concentration, high hydraulic loading and batch feeding. The start-up of anaerobic reactor was completed after 40 d operation at influent COD of 3000mg·L-1, organic loading rate of 1.0 kg COD·(m3·d)-1 and temperature of 34 ~ 36 ℃. After this, the organic loading rate increased to 12.0 kg COD·(m3·d)-1 gradually. The COD and BOD concentrations in the influent of anaerobic bioreactor were 11674~12623 mg·L-1 and 6873~7065 mg·L-1 during stable operation, and the average organic loading was 12.2kg COD·(m3·d)-1. The average COD, BOD5, SS and animal and vegetable oils in the effluent were 1129mg·L-1, 318 mg·L-1, 120 mg·L-1 and 43 mg·L-1. The average removal rates of COD, BOD5 and animal and vegetable oils were 90.6%, 95.8% and 51.2%.During this process, the sludge flocs formed in the reactor at organic loading rate of 3.0 kg COD·(m3·d)-1, then granular sludge appeared at organic loading rate of 9.0 kg COD·(m3·d)-1 and finally sludge granulation realized at organic loading rate of 12.0 kg COD·(m3·d)-1.The fiber carriers were filled in the biological contact oxidation reactor and batch feeding was carried out for its start-up at influent COD of 1176~1295 mg·L-1 and DO of 3~4 mg·L-1. The start-up of the biological contact oxidation reactor was completed when the stable COD removal rate was higher than 75.0 %. The average COD, BOD5, SS and animal and vegetable oils in the influent were 1276 mg·L-1, 308 mg·L-1, 110 mg·L-1 and 42.6 mg· L-1 during stable operation. The average p H, COD, BOD5, SS and animal and vegetable oils in the effluent were 7.1, 89.5mg·L-1, 18.3mg·L-1, 52 mg·L-1 and 6.0 mg· L-1. The average removal rates of COD, BOD5, SS and animal and vegetable oils were 93.0%, 94.3%, 52.7% and 85.9%. Alter treated, the effluent can comply with the Class A of Integrated Wastewater Discharge Standard(GB 8978- 1996). The sludge color changed from initial black to grey brown and finally yellow brown. The sludge concentration increased from initial 3 800 mg·L-1 to final 4500 mg·L-1. In the last operation phase, Nematode reduced in the reactor and Rotifer increased and became larger, indicating the system stable operation.The treatment capacity of this project was 200 m3·d-1 and the total investment was 1.9 million Yuan. The operation cost of wastewater treatment was 4.27 Yuan·m3. The total removal amounts of COD, BOD5, SS and animal and vegetable oils were 1315 t·a-1, 539 t·a-1, 12 t·a-1 and 30t·a-1. Therefore, the environmental benefit of this project was significant.