MITIGATION OF AMMONIA EMISSIONS FROM CONFINED DAIRY OPERATIONS

Abstract

Over the past few decades, livestock agriculture in the United States (U.S.) has undergone rapid transformations. In general, concentrated animal feeding operations (CAFOs) have not only grown in size but also in tendency to concentrate in smaller geographical regions for economies of scale. Consequently, ammonia (NH3) and other emissions from these CAFOs have prompted serious concerns because of potential adverse effects on human health and the environment. Therefore, there is a critical need to develop efficient and cost-effective technologies for mitigating NH3 and other emissions from CAFOs. This thesis presents technologies or techniques for mitigating NH3 emissions from dairy operations, which include: (1) management of manure-pH, (2) anaerobic digestion and solids-liquid separation, and (3) an enhanced aerobic biological processing. The first study examined potential mitigations of NH3 emissions from the barn and manure storage, when a pH < 6 is maintained in a closed-loop recycle of flush water as well as the effective cost reduction accruing from repetitive acid dosing. Results, from this study, revealed significant potential mitigations of NH3 emissions from dairy barns as well as in subsequent storage of effluents. Operating the flushing system in a closed-loop also indicated significant cost-benefit accruing from reduced acid dosages. The second study evaluated, in lab and field studies, the effects of anaerobic digestion (AD) and solids-liquid separation on emissions during subsequent storage and land application of effluents. Although the AD process exacerbated NH3 emissions from storage of AD liquid effluents, significant reduction of NH3 emissions were observed during and after land application of AD effluents. Solids/liquid separation proved to be an effective means to not only reduce solids loading to storage facilities but also in reduction in NH3 losses. The third component of this research explored an enhanced biological removal of NH3 from dairy wastewater. This bioprocess utilized bacterium Alcaligenes faecalis strain No. 4, which has an ability to carry out heterotrophic nitrification and aerobic-denitrification simultaneously in a single tank. Removal of TAN from dairy wastewater by A. faecalis strain No. 4 was rapid and efficient thus ensuring mitigation of NH3 emissions from treated effluent. For this bioprocess to achieve high efficiency of TAN removal, however, addition of external carbon to the dairy wastewater, as well as adequate oxygen supply are necessary.