Perspectives on the Fate of Absorbed Nitrogen in Dairy Farms

The demand for milk rises dramatically due to the increased global population without damaging the standard of living. As a result, the scale of the dairy industry in the world is growing rapidly. Consequently, a concomitant problem that needs to be faced is the environmental impact of the by-products produced during the operation of the dairy farm. Among the substances produced in dairy farms, the most harmful pollutant to the environment is nitrogen (N). In addition, the N pollution from dairy farms is significant and N has a great danger to human health and society. This study provides a systematic review on how to alleviate N pollution from dairy cows during milk production and the removal of ammonia and nitrate from dairy wastewater via biochar adsorption. First, from a physiological perspective, the metabolic pathways of amino acids and ammonia in the rumen, portal-drained viscera, liver, and mammary gland of dairy cows are elaborated, as well as the measures to improve N utilization. In the second part, the progress of research on the removal of ammonia and nitrate by biochar adsorption and the involved mechanisms are summarized. Modified biochar has a significant improvement in nitrate removal due to weakening the repulsive effect of ions. Based on the review of this paper, it can provide relevant theoretical support for future studies on N pollution mitigation from dairy farms.