Effect of different types of sluggishness packings on ammonia stripping of piggery biogas slurry

Abstract: The treatment effect of ammonia stripping which is a pretreatment method of piggery biogas slurry is affected by many factors including pH value, temperature, air liquid ratio and packings etc. On the basis of previous studies, ammonia stripping effects of piggery biogas slurry in polyhedral hollow ball, pall ring and fluidized bed packing were studied in this article. Effects of adding sodium hydroxide and stripping in different types of packings on chemical oxygen demand, total solid and volatile solid of biogas slurry were also discussed. 50 L piggery biogas slurry which had been pretreated by flocculation, solid-liquid separation and paper tape filtration in turn was added to each tank. The same volume of polyhedral hollow ball packing, pall ring packing and fluidized bed packing were loaded in the air stripping tower respectively. The packings material are polypropylene plastics, whose diameter are both 25 mm. Biogas slurry was stripped for 5 hours under the conditions with pH value of 10.5, air liquid ratio of 2 000 and temperature of 30 ℃. 150 mL sample was taken from the tank every half hour during the stripping process. The stripping effects in different types of packings were analyzed. The results showed that the ammonia nitrogen average removal rates in polyhedral hollow ball packing and fluidized bed packing were significantly higher than that of pall ring packing (P<0.05) and the ammonia nitrogen average removal rates were 80.7%, 59.0% and 77.4%, respectively, when the air stripping tower ran for 2 hours. Considering the operational energy consumption and ammonia nitrogen and total nitrogen removal effects, polyhedral hollow ball packing was selected as the preferred material. The operation time should be controlled within 2 hours. The chemical oxygen demand of biogas slurry partial decreased on account of the compression of the twin electrical layer and coagulation after adding sodium hydroxide. The total solid and volatile solid of biogas slurry both increased because of the destruction of microorganism structure and the hydrolysis of macromolecular matters after adding sodium hydroxide. The chemical oxygen demand of biogas slurry partial increased, meanwhile, the total solid and volatile solid both decreased after ammonia stripping. The variations of chemical oxygen demand average removal rates and volatile solid average removal rates were different as a result of the differences in performance parameters of three types of packings, but they had no significant differences in three types of packings (P>0.05). The total solid average removal rate in fluidized bed packing was significantly higher than that of polyhedral hollow ball packing (P<0.05). 20 L piggery biogas slurry was stripped for 2 hours under the conditions with pH value of 10.5, air liquid ratio of 2 000 and temperature of 30 ℃ in polyhedral hollow ball packing and stripped ammonia was absorbed by 1 L sulfuric acid of 1, 1.5 and 2 mol/L, respectively. The average absorption rates were 35.8%, 36.7% and 32.4%, respectively, and they had no significant differences (P>0.05). Considering the absorption effect and economy, 1 mol/L sulfuric acid was selected as the preferred absorbent to absorb stripped ammonia.