Mitigation of Environmental Impact of Intensive Animal Farming through Conversion of Animal Wastes to Value-Added Products

The environmental impact of concentrated animal farming operations has become serious social issues, with the livestock wastes contaminating waterways and groundwaters and generating greenhouse gas (GHG) emissions that are responsible for more than half the total GHG emissions in agricultural activities in the U.S. These impacts are mostly due to the current practice of spraying manure or manure digestate on croplands. We have recently developed two novel processes not only to mitigate the impacts stemming from the current manure management practice but also to bring in extra revenues to livestock farmers, which should provide an incentive to the farmers, by recovering value-added products from livestock manure or manure digestate. In this review, we discuss the effectiveness of the processes to produce two products: protein hydrolysate feed additives from the manure-digestate solid by one process and renewable ammonia from the manure-digestate liquid by another. One process uses thermal hydrolysis to extract protein from manure-digestate solid at a moderate recovery rate of more than 60%. Another employs acid-base reactions to strip NH3 from manure-digestate liquid and dissolve the stripped NH3 gas into the water at a high recovery rate of 90%. By repeating this stripping process, the nitrogen concentration in the water can reach as high as 18%.