Emission Pattern And In-situ Reduction Mechanism Of Sulfur Odors During Composting Of Livestock Manure

Odor issue from livestock manure composting is a big obstacle of the developing of composting.The extremely low olfactory threshold of sulfur odor makes it an unavoidable problem when controlling odors from composting.But little reaserch has been focused on this aera.Therefore,in this study,composting of livestock manure was choosen as the object of study,the effects of controllable conditions on 8 sulfur odors emission patterns were researched using specialized gas chromatography,the possible sources of sulfur odors were identified.Several in-situ reduction methods were developed and the microbial mechanism of two methods were studied using Illumina Miseq microbial sequencing.The 8 sulfur odors was COS?CS2?H2S?MeSH?EtSH?Et2S?Me2S and Me2SS.The results were as follows:1.Emission pattern:In total sulfur loss during composting of livestock manure,24.2?50.4%were lost in the form of the 8 sulfur odors.Me2S and Me2SS were the main sulfur odors among the 8 sulfur odors(>59.6%).The concentrations of COS,CS2,H2S,MeSH,EtSH and Et2S during composting were fairly low or incontinuous.Sulfur odors were only released during the first three weeks and the high concentrations occured in temperature rising phase and high temperature phase.Turning significantly affected the concentration of Me2S and Me2SS.Concentrations of these two compounds rose after turning.2.Influence of controlable parameters:The instantaneous concentrations of sulfur odors were lower with lower pig manure ratio,lower initial moisture content and higher aeration rate.In this study,instantaneous sulfur odors concentration was lowest when composting using 0.73 pig manure to corn stalk ratio(dry matter),60%initial moisture and 4 m3·m3·h-1 aeration rate.Increasing the aeration rate was an effective way to reduce the instantaneous concentration of sulfur odors.It was recommended to be used on temperature rising phase and after turning to minimize hazardous of sulfur odors to the environment.3.Sulfur odor sources:Both solid phase and liquid phase were the source of sulfur odors.Sulfur odors-S loss amount during pig manure solid phase composting was 69.0%of that during fresh pig manure composting.Met?Cys?SO32-and SO42-were all the potential precursor of sulfur odors.When these four sulfur containing compounds were added into the feedstocks respectively,Me2S and Me2SS were still the main sulfur odors.Transformation of SO42-to Me2S and Met to Me2SS were the most in the four compounds.4.In-situ reduction technology:Four common additives were added into composting to study their sulfur odor reduction effects which were pH modifier(NaOH and Ca(OH)2),adsorbent(Activated Carbon),oxidant(Potassium Permanganate)and precipitator(Fe2O3).pH modifier doesn't have any reduction effect.The other additives could reduce Me2S and Me2SS by as high as 45%(0.13 ‰Potassium Permanganate)and 32%(2.4%Activated Carbon),respectively.Me2S and Me2SS amounts could be reduced by 92.3%and 82.3%respectively when 2 mmol·L-1 Hexaammonium Heptamolybdate Tetrahydrate and 40 mmol·L-1 NO2-were added.Using mature compost as cover or mixing material could also reduce sulfur odors.The reduction effect was better when mature compost was mixed in the feedstocks compared with covering.Me2S and Me2SS amounts could be reduced by 70.8%and 41.0%respectively with mature compost mixing.5.In-situ reduction mechanism:When NRB activating agent were used,the relative abundance of dominant bacteria Bacillales which includes Me2S degration bacteria increased.The microbial community of cover mature compost was different from that of the bottom compost layer(? diversity difference>0.52).The difference remained relatively stable which means that the cover layer reduced sulfur odors continously.Region,composting time,composting method and feedstocks barely affect the microbial community of mature compost.Thus,all mature compost could be used as cover material.