Study On The Recovery Utilization Of Nitrogen And Phosphorus From Biogas Slurry Through Biochar Adsorption

In recent years,with the intensive and standardized development of livestock and poultry farming in China,the production of livestock and poultry manure has been increasing year by year.Anaerobic fermentation to produce biogas is one of the mainstream technologies for the energy and resourceful treatment of livestock and poultry manure.However,the biogas slurry by fermentation has a huge yield,and its chemical oxygen demand(COD),nitrogen(N)and phosphorus(P)concentration are high,and improper disposal can easily cause soil and water pollution.However,various nutrients such as nitrogen,phosphorus,and organic substances in the biogas slurry are also beneficial nutrients,which can be used by plants.China’s straw resources are extremely rich but more waste,and in recent years,biomass pyrolysis carbonization technology has been widely used in agricultural waste treatment.The product biochar can be used as adsorbent material to absorb nutrients in the biogas slurry.Therefore,this paper uses straw pyrolysis carbonization product biochar to treat the biogas slurry and re-apply it to the soil to observe its nutrient release,so as to realize the nutrients recovery and resource utilization in biogas slurry,and strive to achieve " treating pollution with waste " and resource utilization of wastes and pollutants.In this paper,corn stalks,bamboo shavings,rice husks,and pine wood were used as raw materials and pyrolyzed at 300-700 ℃ to study the effect of static adsorption process parameters on the adsorption and the effects of different biomass and pyrolysis temperatures on the adsorption effect of biogas slurry.Simulation of the dynamic adsorption effect of biogas slurry for practical application using optimized biochar.Finally,the release pattern of nutrients in soil after re-application of biochar to soil after adsorption of biogas slurry was studied,and the results showed that:(1)Corn stalk biochar obtained by pyrolysis at 500 ℃ can adsorb COD,ammonia nitrogen and total phosphorus in the biogas slurry well.The adsorption effect was greatly influenced by different addition amounts.Adding 15 g/L corn stalk biochar has the best adsorption effect on COD,15 g/L for ammonia nitrogen and 5 g/L for total phosphorus.The oscillation time also effected the adsorption results.COD adsorption reached saturation at 120 min,but ammonia nitrogen adsorption reached saturation at 15 min,while total phosphorus did not reach adsorption saturation until 480 min.In summary,in actual use,the amount of biochar added was 15 g/L,and the oscillation equilibrium time was 480 min to achieve a good adsorption effect of biochar on biogas slurry.(2)Different biomass(corn stalks,bamboo shavings,rice husks,pine wood)and different pyrolysis temperatures(300-700 ℃,temperature gradient 100 ℃)had significant effects on the physicochemical properties of biochar and the adsorption of nutrients from biogas slurry.Significantly affected.As the pyrolysis temperature increased,the yield of biochar decreased,the ash content,the p H and the specific surface area increased,the pore structure was enriched,the C element content increased,the H/C and O/C molar ratio decreased,and the aromaticity of biochar gradually increased.Biogas slurry adsorption experiments were conducted on 20 types of biochar(4 raw materials and 5pyrolysis temperatures),and the results showed that the best adsorption effect of each biomassprepared biochar on biogas slurry was Y700,Z600,D500 and S400.(3)The results of using dynamic adsorption to simulate the actual application of treating biogas slurry showed that Y700 has the best adsorption effect on biogas slurry.The tandem dynamic adsorption was significantly better than the normal dynamic adsorption and the aging rate was also significantly slower.The adsorbed biomass char was lyophilized and applied to the soil.Compared with the the pre-adsorption biochar,it could increase the p H of the soil by 0.12.The content of DOC,ammonia nitrogen and effective phosphorus were significantly increased to 70.42 mg/kg,58.12 mg/kg and 8.78 mg/kg,respectively,where the release rate of adsorbed ammonia nitrogen could reach 61.59%and total phosphorus was 94.24%.It shows that biochar can well release the adsorbed nutrients into the soil environment and improve the soil fertility characteristics.This is not only realizes the resourceization of waste straws,but also realizes the recirculation of nutrients,so as to achieve the co-resource utilization of agricultural and forestry waste and biogas slurry.