Acidification of animal slurry in housing and during storage to reduce NH3 and GHG emissions-recent advancements and future perspectives

Abstract

Ammonia and greenhouse gas emissions are an environmental issue associated with animal manure management. Concrete, practical, and economic solutions are needed for farmers and other stakeholders around the globe to solve this issue. Decreasing slurry pH with the help of acids or other compounds is a well-documented technique to reduce ammonia and methane emissions from slurry. However, the effect of manure acidification on N₂O emissions is still not clear. Recently, acidifying agents other than the previously used mineral acids have been tested such as e.g. organic acids, bio-waste materials, and microbial inoculations. However, the effectiveness of these acidifying agents in reducing the slurry pH and mitigation of gaseous emissions further needs to be reviewed. Also, the effectiveness of acidification in combination with other manure treatments such as composting, solid–liquid separation, and anaerobic digestion requires consideration in whole-system solutions. Here, recent studies have been compiled and reviewed to determine the applicability of acidification options for slurry management to deepen our understanding of the environmental impact of slurry acidification. The literature review revealed that temperature fluctuations have a substantial impact on the acidified slurry’s performance during storage. A viable substitute for conventional mineral acids could be organic acids and biomaterials like sugars whey, and microbes. Furthermore, apple pulp, sugar beet molasses, and grass silage are examples of bio-waste products that exhibit promise as acidifying agents. However, to gain a better understanding of the viability and usefulness of the recently evaluated acidifying compounds, more research is still required.