Study On Pilot-scale Purification Of Biogas Slurry And Agricultural Application Of Purification Byproducts

With the application and promotion of anaerobic fermentation technology in livestock and poultry manure treatment in farms,the production of biogas slurry increased linearly.Although biogas slurry is rich in organic matter,ammonia nitrogen and biologically active substances,it can be directly used as liquid fertilizer in theory.However,due to the large output of biogas slurry and the contradiction between the seasonality of crop fertilizer requirements and the continuous discharge of biogas slurry,the direct use of biogas slurry as liquid fertilizer in the south is very limited.On the contrary,in reality,it has become the main source of pollution for the eutrophication of water bodies such as rice fields,streams,lakes,and rivers,so the purification of biogas slurry has become an urgent issue to be solved for large-scale farms.In this study,a pilot-scale study ofcoprecipitation-electrodialysis ’ purification process for biogas slurry was carried out,and the relevant technical parameters were optimized.The by-product of biogas slurry purification-sediment and concentrated ammonium water were explored for resource utilization,so that the biogas slurry was completely harmed.In view of the characteristics of sediment and concentrated ammonium water produced after biogas slurry purification,sediment was intended to be used as the conditioner of flower potted nutrient soil,and concentrated ammonium water was used as the nitrogen source of hydroponic vegetables.Experiments were carried out to test their resource utilization effect in specific directions.In the experiment of using the sediment as a conditioning agent,take the Epipremnum aureum as an example,the effect of sediment application on transpiration rate and root activity of Epipremnum aureum was studied,and its effect on water holding capacity of pot nutrient soil was tested.In the study of using concentrated ammonium water as nitrogen source of hydroponic vegetables,we took the Gynura cusimbua and Ipomoea aquatica Forsk as examples to study the effects of concentrated ammonium water on the biomass,quality and edible safety of hydroponic vegetables.The results of the study are as follows:(1)The ratio of AlCl3-CaO co-precipitation agent is 1:3,the volume ratio of co-precipitation agent and biogas slurry is 1:6,pH=9,reaction time is 60 minutes,co-precipitation treatment can effectively remove more than 94%of organic matter in biogas slurry.Using electrodialysis to treat the primary treatment solution:when the voltage is 20 V,the inflow is 30 L/h,the pH is 8.5,and the hydraulic retention time is 15 minutes,the removal rate of ammonia nitrogen is as high as 96%.(2)The biogas slurry is purified by the "co-precipitation-electrodialysis" method to produce sediment for potted nutrient soil improvement.After 30%sediment is used,the field water holding capacity of potted nutrient soil will increase by 35.71%,and the pH will increase from 5.6 to 6.4.Compared with single nutrient soil treatment and 30%red soil improvement treatment,the root activity of green radish increased by 36.2%～53.4%,the photosynthetic rate increased by 29.5%～44.2%,and the transpiration rate increased by 13.6%～39.6%.(3)The biogas slurry is purified by the "co-precipitation-electrodialysis" method to produce concentrated ammonium for hydroponic vegetable nitrogen source.After treatment with different nitrogen sources,the vegetable biomass,soluble sugar content and vitamin C content from high to low is:biogas slurry treatment>concentrated ammonium water treatment>ammonium bicarbonate treatment.(4)The concentrated ammonium produced by the "co-precipitation-electrodialysis"method to purify the biogas slurry is used in the production of hydroponic vegetables.In terms of vegetable safety,the content of heavy metals,nitrates and antibiotics in vegetables treated with concentrated ammonium nitrogen sources are in line with national food safety standard.Compared with the treatment of biogas slurry,the content of antibiotics in Gynura cusimbua after the treatment of concentrated ammonium water was reduced by more than 8 times,and the content of antibiotics in Ipomoea aquatica Forsk was reduced by more than 2.5 times.Based on the above research results,the pilot test parameters of the biogas slurry"co-precipitation-electrodialysis" purification process have been further optimized,and the pilot test results have reached the target requirements.The sediment produced by purification process was used in potted nutrient soil to increase the effective water content of potted nutrient soil and enhance plant life activities.The purification process produces concentrated ammonium water for hydroponic vegetable nitrogen source,which can promote the growth of vegetables and improve the quality and safety of vegetables.