Effects of woody peat addition on maturity and gaseous emissions during pig manure composting

Abstract: The large amount of animal dung becomes a serious problem of environmental pollution with the development of large-size livestock farming. Aerobic composting, as an effective and accepted technology, has been often used to treat solid organic waste. However, the process of aerobic composting of pig manure faces several problems, such as low degree of maturity, severe nitrogen losses as well as large release of contamination gases, which can be controlled and mitigated by using different bulking agents. Peat is a natural and organic mineral resource and its application in composting is an important research site due to its better adsorption. Therefore, this research used woody peat as bulking agent and investigated the influence of different quantities of woody peat (with ratio of 5%, 10%, 15% and 20% on quality of wet mass) on pig manure compost maturity and CH4、NH3 and H2S emissions. The results showed that the composting matrix can be activated successfully for all treatments. In addition, the temperature entered into thermophilic phase on day 2~4, and the thermophilic phase lasted more than 7 d to completely meet the sanitary standard in all reactors; and after 28 d, the pH values of all compost were 8.0, the electrical conductivities (EC) were 1.47~1.82 mS/cm and the germination index (GI) were all larger than 80%. Therefore, all treatments can perform well and achieve the standard of ripe composting under the addition of woody peat. Moreover, according to the results, adding at least 15% woody peat could make a better compost product with better maturity, less physiology toxicity and more nitrogen element. In addition, the treatments with 15%~20% addition had more active microbial activities and higher biodegradation rate during 28 d, whose moisture content could decrease by 35% and degradation rate of dry material was around 22%. Compared with the 5% addition, woody peat addition at 15%~20% also reduced total CH4、NH3 and H2S emissions by 82.12%~89.48%, 53.47%~63.31% and 50.98%~62.76%, respectively. Consequently, these two treatments decreased total greenhouse gas emissions by 70.34%~83.26%. Furthermore, the effect of adding woody peat on keeping nitrogen was significant, and the 15%~20% addition could reduce total nitrogen losses by 44%~63%. Hence, woody peat is an alternative and good bulking agent for composting and the optimal addition of woody peat in the pig manure composting in this study is 15~20% of total wet weight.