| Composting is the main measure for utilizing the resource and harmlessly treating livestock waste,but a large quantity of ammonia(NH3)and other gases are generally emitted from the composting process.In order to deal with ammonia which is the compost tail gas,biofiltration is often used as an important method.However,studies related to the biofiltration treating NH3 emitted from composting mostly focused on the laboratory experiments,and there were few on-site measurements.In addition,the research of engineering tests using decomposed compost as filter material were still particularly rare To fill this research gap,the aims of this study were to explore the removal effect of NH3 in an industrial biofilter filled with mature compost.The NH3 for the biofiltration were from a composting plant which used swine manure biogas residue as feedstock and was built with a real-time NH3 monitoring system.The NH3 emissions from the composting plant were characterized and NH3 removal of the biofilter was investigated.The main conclusions of the study are as follows:(1)NH3 concentrations in the composting plant during a composting period(38 days)ranged from 0.85 to 22.40 mg·m-3.The NH3 concentrations in the composting plant fluctuated greatly during different time periods,in which the values of the daytime were higher than those of the nighttime.In the daytime,the highest mean value of 6.77 mg·m-3 and the lowest mean value of 2.03 mg·m-3 were found during time of 12:00-16:00 and time of 4:00-8:00,respectively.The mean value during the whole process was 3.63 mg·m-3,however,most of the time,the NH3 concentration was higher than the limit value of the "Emission Standard for Odor Pollutants".Therefore,the reasonable and effective measures are required to take for controlling the emissions.During the whole composting process,the NH3 emission flux and cumulative emission per compost volume unit were 103.99±37.93 mg·m-3·h-1 and 94.84 g·m-3,respectively.(2)Using mature compost of swine manure biogas residue as the filter material,the biofilter had high removal rate of NH3 emissions(more than 80%)under low temperature conditions in winter.The highest(up to 91.75%)and the lowest(up to 84.11%)removal rate were found during time of 12:00-16:00 and time of 8:00-12:00,respectively.During the experiment,the NH3 removal rate was positively correlated with the NH3 intake concentration(R=0.761,P<0.01).After the treatment of biofilter,the NH3 concentrations were reduced to a value between 0.55 and 4.92 mg·m-3,with the mean concentration of 1.69 mg·m-3,which can meet the requirement of the secondary emission standard(2.0 mg·m-3)of NH3 gas in the "Emission Standards of Odor Pollutants".(3)The operational cost of this biofilter for per kilogram composting NH3 gas treatment is ? 7.80.Mature compost can not only be used as the filter material in the biofiltration to remove NH3 gas,but be recycled as a high-value organic fertilizer saturated with aqueous ammonia after secondary composting.However,it should be noted that when the outdoor temperature is lower than 0?,the freezing will affect the microbial activity of the biofilter and reduce the treatment efficiency.It is recommended to properly choose and operate biofilters according to local climatic conditions. |
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