Study On Treatment Of High Concentration Biogas Fermentative Liquid From Pig Farm By MAP Percipitation And Ozone Oxidation

A high concentration of wastewater discharges with the number of scaled hoggery increasing. Swine wastewater has become an important source of agricultural pollution due to the high concentration of ammonia nitrogen and oragincs, which is very difficult to remove by using the common methods. In this study, using biogas fermentative liquid from pig farm, Magnesium Ammonium Phosphate(MAP) and ozone oxidation method were applied to investigate the optimum reaction conditions of MAP for the removal of ammonia nitrogen and the efficiency of ozone oxidation on the organics removal and biodegradability changes. The main results were as follow:In the MAP experiment, the influence of pH value, phosphate-nitrogen ratio, magnesium-nitrogen ratio, and original concentration of ammonia nitrogen on the ammonia nitrogen removal and phosphate utilization rate were analyzed by orthogonal and single factor experiment systematically. Results indicated that the optimum conditions of MAP reaction was: n(P):n(N) at 1.0, n(Mg):n(N) at 1.1, the original concentration of ammonia nitrogen at 800 mg/L, pH value at 10.0. At this time, the removal rate of ammonia nitrogen was 85%, and the phosphate utilization rate reached 95%, while the residual ammonia nitrogen and phosphate concentration were 150~210 mg/L and 10~30 mg/L, respectively. Then n(P):n(N) ratio was the key factors affecting MAP precipitation, which indicated that the best way to increase the removal rate of ammonia nitrogen was to improve the dosage of phosphate.Based on the MAP precipitation, the ozone oxidation experimet was designed and carried out with four ozone dosages including 0, 4, 6, and 8 mg/L. Results showed when the ozone dosage was 4 mg/L, 6 mg/L, 8 mg/L, the best removal effectiveness of CODCr and UV254 were recorded at 40 mins. After 40 mins, no increase in the removal rate of CODCr and UV254 was recorded resulting from the organic matter mineralization, which may be caused by low value of pH in the reaction system. Particularly, when the ozone dosage was 6 mg/L, CODCr and UV254 removal rate was superior to the 4 mg/L and 8 mg/L, meanwhile the maximum CODCr and UV254 removal rate would reach 21.7% and 60%, respectively. Additionally, BOD5/CODCr rate also increase from 0.24 to 0.41 at the ozone dosage of 6 mg/L, which significantly improved the biodegradability of the biogas fermentative liquid. After 40 min, though no change of BOD5/CODCr ratio occurred, the ratio was still higher than 0.3, which could meet the needs of subsequent biological availability. Indeed, ozone oxidation could not remove the nitrogen completely, but it could transform from the ammonium nitrogen into nitrate nitrogen.Additionally, economic analysis, which includes chemical reagents costs, power consumption and sediment gains, were conducted. Results revealed 1 ton biogas fermentative liquid from pig farm to produce the economic value of about 16.69 yuan/ton, which fully illustrated there is a great potential to treat the biogas fermentative liquid and reduce its pollution by the combination of Magnesium Ammonium Phosphate(MAP) and ozone oxidation.