Effects of lactic acid on modulating the ammonia emissions in co-composts of poultry litter with slaughter sludge

[Display omitted] •NH3 emissions were calculated using an online monitoring method.•NH3 emission rates and times can be expressed as curvilinear and power equations.•1% lactic acid provided lowest NH3 emissions and nitrogen loss.•Addition of lactic acid could promote the relative abundance of Lactobacillales. The aim of this work was to study the feasibility of lactic acid addition during poultry litter and slaughter sludge composting for controlling NH3 emissions. The results indicated that lactic acid addition reduced NH3 emissions and promoted the maturity of the composting product. Compared to the blank, nitrogen loss in the form of NH3 emissions in the 0.4%, 0.7%, and 1.0% lactic acid treatments decreased by 3.36%, 8.29%, and 14.65%, respectively. Moreover, lactic acid addition promoted the relative abundance of Lactobacillales, while the microbial community of the blank was dominated by Bacillales. The mechanism behind the control of NH3 emissions via the addition of lactic acid involved the secretion of large amounts of lactic acid by Lactobacillales, which lowers the pH of the initial compost pile. This study suggests that lactic acid is a suitable additive for composting.