Research On Removal Of NH₃and H₂S Derived From Livestock Farm By Biological Activated Carbon

With the rapid expansion of livestock and poultry breeding, the people’sliving standard raises obviously, at the same time, environmental pollutionsderived from livestock also cause great concern. Especially the ordor gases fromlivestock farms, which arouse people’s antipathy easily, do damage to humanand animal health. The ordor gases can be removed by physical, chemical andbiological methods.Biological removal of odorous pollutants with green, highefficiency, high removal rate, easy automation, becomes research hotspot in theworld. By simulating livestock farms ordor atmosphere with mixture of NH3andH2S, the removel of NH3and H2S had been investigated in a homemadebiological activated carbon reactor system in this paper.The experiment resultsand conclusions were as follows:(1)After comparision of two different biofilm formation process byspraying nutrient solution into fresh activated carbon and saturated activatedcarbon directly,at temperature of30℃, gas velocity of0.2m3/h, nutrientsolution spraying rate60ml/min, the initial pH value of7.0, inports of NH3200mg/m3, H2S70mg/m3, the results showed that biofilm formation by spraying nutrient solution into saturated activated carbon directly was easierthan that of by spraying nutrient solution into fresh activated carbon directly.After10days the reactor started successfully. The removal rates of NH3and H2Swere all above98%, the conversion rate of nitrogen maintained75%andsulfur conversion rate remained above95%. After the biological activatedcarbon reactor started successfully, the final nitrogen conversion rate andsulfur conversion rate of two methods had no obvious difference.(2) The effect of different environment factors on the degradation ofbiological activated carbon had been investigated in this paper.Temperature, gasspace velocity, nutrient solution spray rate, initial pH value were selected asfactors. Some valuable results and conclusions were obtained.When the reaction temperature increased from20℃to25℃，30℃,40℃gradually, the removal rates of NH3and H2S were above98%all the time. Attemperature30℃, the nitrogen conversion rate and sulfur conversion rate werehigher than that of at other temperature. They reached60%and97%respectively.30℃was considered as the optimal temperature of biologicalactivated carbon reator.When the gas space velocity varied from0.2m3/h to0.25m3/h,0.3m3/h,0.35m3/h, the removal rates of NH3and H2S at0.2m3/h and0.25m3/h werehigher than that of at other space velocity conditions, which reached98%.At thespace velocity of0.2m3/h and0.25m3/h, the nitrogen conversion rate andsulfur conversion rate reached70%and96%respectively. In consideration of practical operation,0.25m3/h was more efficient than0.2m3/h per unit time.So0.25m3/h was the best gas space velocity of biological activated carbon reactor.When the nutrient solution spray rate varied from40ml/min to60ml/min,80ml/min,100ml/min, the removal rates of NH3and H2S increased as thenutrient solution spray rate increased. At the nutrient solution spray rate80ml/min and100ml/min, the nitrogen conversion rate and sulfur conversionrate reached65%and95%respectively, which were higher than that of at otherspray rates. In consideration of economic factors,80ml/min was more suitablethan100ml/min for biological activated carbon reator.Different initial pH values4.0,7.0,11.0were seted in the experiment. Theresults showed that the removal rates of NH3and H2S were superior to the initialenvironment of acidic and alkaline when initial pH was neutral environment7.0.The nitrogen conversion rate and sulfur conversion rate were significantlyhigher than that of acidic and alkaline environment, which reached65%and95%respectively. The initial pH7.0was considered as the optimal initial pHvalue of biological activated carbon reator.(3) The effect of H2S concentration on NH3removal rate was investigatedin this experiment. At the inlet concentration of NH3200mg/m3, H2Sconcentration changed from70mg/m3to150mg/m3,300mg/m3. The resultsshowed that the removal rates of NH3didn’t chang significantly with theincrease of H2S concentration, but the nitrogen conversion rates decreasedwith the increasing H2S concentration. Under the same experiment conditions, the effect of NH3concentration on H2S removal rate was investigated.At theinlet concentration of H2S70mg/m3, NH3concentration changed from200mg/m3to400mg/m3,600mg/m3. The results showed that the removal rates ofH2S had no obvious difference with the increase of NH3concentration, butsulphur conversion rates decreased obviously with the increase of NH3concentration.(4) By conducting the blank experiment of spraying distilled water intofresh activated carbon, sulfur and nitrogen balance calculation, acid and alkalinefunctional group titration analysis of fresh activated carbon, adsorptionsaturation activated carbon and biological activated carbon, the mechanism ofdegradation of NH3and H2S in was investigated. The biological degradation ofNH3and H2S in biological activated carbon reactor followed three processes ofdissolve adsorption, activated carbon adsorption/biological degradation andbiodegradation, which was the results of combined action by microbialdegradation, extracellular enzymes and concentration gradient.Due to time limit, it is suggested that the mathematical modeling, thedegradation mechanism of the biological activated carbon need more work forfurther research in the future.