Study On Ammonia Stripping Process Of Biogas Slurry With Membrane Concentration Treatment

The biogas project using anaerobic fermentation to treat livestock and poultry manure is developing rapidly while the biogas slurry produced in the biogas project still needs to be treated or utilized later because of the large amount of concentrated residue.Biogas slurry produced after anaerobic fermentation of livestock and poultry manure has complex composition,low carbon nitrogen ratio,high ammonia nitrogen concentration,poor biodegradability.The subsequent processing of it is difficult to meet the emissions standards.Ammonia stripping process is suitable for the pretreatment of various types of high ammonia nitrogen sewage.This process can greatly reduce the concentration of ammonia nitrogen in sewage but the treatment effect is affected by many factors.The pig farm biogas slurry pretreated by flocculation precipitation,solid-liquid separation and paper belt filtration,as well as the hollow fiber membrane permeate and the nanofiltration membrane permeate were taken as the objects.This paper studied the influence of operating parameters such as packing type,stripping time,pH value and gas flow rate on ammonia stripping effect of biogas slurry in different membrane concentration stages and analyzed the interaction between operating parameters synthetically to determine the optimized combination parameters.The absorption effect of ammonia in exhaust gas was also studied by absorbent with different molar concentration,volume and type.The purpose of this paper was to provide basic parameters for reducing environmental pollution.The main conclusions are as follows:1.In the single factor influence experiments on ammonia stripping effect of biogas slurry,the results showed that the ammonia nitrogen average removal rates in polyhedral hollow ball packing and fluidized bed packing were significantly higher than pall ring packing(P<0.05)and the ammonia nitrogen average removal rates were 80.7%,77.4%and 59.0%,respectively,when the air stripping tower ran for 2 hours.Under the conditions of the packing of polyhedral hollow ball,the pH value of10.5,the gas flow of 20 m~3/h,the gas liquid ratio of 2000,the temperature of 30?,20 L biogas slurry was stripped for 30 minutes,the ammonia nitrogen average removal rate was 54.4%and only increased by 12.1%when stripped for 2 hours.At the same stripping time,the ammonia nitrogen average removal rate increased with the increase of pH value.Within the range of 11~12,there was no significant difference in ammonia nitrogen removal effect with different pH values(P>0.05).The ammonia nitrogen average removal rate with the change of gas flow rates was 24>28>20 m~3/h but there was no significant difference(P>0.05).2.The multi-factor parameters optimization experiment of ammonia stripping effect in biogas slurry was carried out.A quadratic polynomial regression model with ammonia nitrogen removal rate as the response value was established by Box-Behnken design.The interactions among stripping time,pH value and gas flow rates were analyzed by contour plots and response surface plots.The interaction between stripping time and pH value and interaction between stripping time and gas flow rate were both not significant(P>0.05),while the interaction between pH value and gas flow rate was significant(P<0.05).The optimized combination parameters of ammonia stripping process were the packing of polyhedral hollow ball,the stripping time of 90 min,the pH value of 11,the gas flow rate of 28 m~3/h,the gas liquid ratio of 2000,the temperature of 30?.The maximum value of the corresponding response value was 78.13%and the ammonia nitrogen average removal rate was 73.93%in verification experiment.3.The same batch of pretreated biogas slurry,the hollow fiber membrane permeate and the nanofiltration membrane permeate were stripped by the optimized combination parameters.The ammonia nitrogen average removal rates in pretreated biogas slurry and the hollow fiber membrane permeate had no significant differences(P<0.05)but they were both significantly higher than the nanofiltration membrane permeate(P<0.01).The best effect was obtained in stripping pretreated biogas slurry directly.4.The biogas slurry was stripped by the optimized combination parameters and the 1.5 mol/L sulfuric acid absorbent was the appropriate choice when the volume ratio of biogas slurry to absorbent was 10:1.The absorption rate of ammonia from 20 L biogas slurry exhaust gas reached 77.6%with 2 L1.5 mol/L sulfuric acid absorbent.Compared with the sulfuric acid absorbent,the absorption effect of the membrane concentrate and sulfuric acid mixed absorbent was better.The absorption rates of mixed absorbent to ammonia from exhaust gas stripped in the hollow fiber membrane permeate and the nanofiltration membrane permeate were both more than 80%.