Purification And The Development As Water-soluble Fertilizer Of Biogas Slurry Of Cattle Dung

The scale of livestock and poultry industry has been ranked at first in the world. A large number of fanning waste discharge has caused extensive concern in society. In recent years, it has become a hot study topic particularly that farms in scale of dispersed and small are discharging the wastes. Generally, anaerobic fermentation is the preferred technique for different scale farms to dispose the liquid waste. Anaerobic fermentation can reduce pollution of the liquid wastes and produce biogas. But the weak point is that it produces a large amount of biogas slurry, which contains COD, ammonia nitrogen, total phosphorus, suspended solids, etc. Biogas slurry also contains a variety of trace elements, amino acids, GA and cytokinin. Because of pollution and the availability, the dispose of biogas slurry is becoming a focus of researcher increasingly. In this study, we develop a combined treatment technology to dispose the biogas slurry. The technology is coagulation-magnesium ammonium phosphate precipitation (MAP) and the application of water-soluble fertilizer. This technology dispose the biogas slurry which produced from the small-scale domestic livestock and poultry farms, decentralized distribution, high operating costs of processing investment. The composite technology based on coagulation-MAP method that is convenient, efficient and economical for purification and discharge of biogas slurry rapidly; based on the development of water-soluble fertilizer that achieve resource utilization of biogas slurry. We combine with purification and utilization of pollutant that achieve exhaustive disposal of biogas slurry. The main researches are as follows:1.Coagulation purification of biogas slurry:We used single factor experiment, orthogonal design optimization and statistics analysis to explore the impacts of coagulant type, coagulant dosage, pH of biogas slurry, polyacrylamide (PAM) dosage and factors of coagulation such as stirring time. Then we proposed optimal technical parameters. The optimal technical parameters were as follows:pH value was 5.5, ferric chloride dosage was 1120mg/L, PAM dosage was 3mg/L, speed of rapid stirring was 300r/min in 30s, then a speed of slow stirring was 50r/min in 15min, finally, settling time was 20min. After the optimal technical parameters, the COD value was 316.7mg/L, turbidity value was 13.1NTU and total phosphorus value was0.59mg/L that all reached the national emission standards except ammonia nitrogen.2.MAP advanced treatment of ammonia of biogas slurry:We used a complex precipitation (MAP method) as advanced treatment for residual ammonia after coagulation treatment of biogas slurry. With single factor experiment, orthogonal design optimization and statistics analysis, we proposed optimal technical parameters. The optimal technical parameters were as follows:pH value was 11, n(Mg2+): n(NH4+):n(PO43-)=1.1:1:1.2, reaction time was 13min, sedimentation time was 30min. In this case, the value of ammonia nitrogen and total phosphorus ware 39.4mg/L and 3.2mg/L that consistent with emission requirements from national.3.Optimize the preparation of the biogas slurry that applied to water-soluble fertilizer:At first, we used the biogas slurry of cattle dung as a raw material; then we went through test, filtering, synthetic and standing methods; finally we obtained two water-soluble fertilizers. They are N:P2O5:K2O mass ratio was 1:1:2 and 2:1:2 that meet with standard NY1106-2010. Producing one ton water-soluble fertilizer that N:P2O5:K2O mass ratio of 1:1:2 and 2:1:2 could eliminate biogas slurry of cattle dung was 800L and 600L; total cost of raw materials was 3995 yuan (RMB) and 3642 yuan (RMB). In this way, we not only achieved the reduction of livestock waste water, turn waste into treasure, but also created economic benefit.4.Application performance and parameter optimization of water-soluble fertilizer.Fertilizer efficiency test used water-soluble fertilizer which was N:P2O5:K2O=1:1:2 and 2:1:2 for ornamental sunflower, ornamental peppers and maidenhair. The two water-soluble fertilizers were diluted to 100 times,300 times,500 times,700 times and 900 times. The results showed that ornamental characteristics of each treatment was better than the control for the three kinds of garden plants significantly, in which N:P2O5:K2O=2:1:2 of water-soluble fertilizer was diluted to 500 times for Helianthus annuus and French Marigold and N:P2O5:K2O=2:1:2 of water-soluble fertilizer was diluted to 300 times for Capsicum frutescens.