ABSTRACT Water and Air Quality Performance of a Reciprocating Biofilter Treating Dairy Wastewater Seppi Matthew Henneman Agricultural non-point source pollution is the leading water quality problem in surface water and the second leading problem in ground water in the US. Among the contaminants, nutrients (such as nitrogen, phosphorus, potassium) can be transported from agricultural fields when cropland is not managed properly. In California, dairy manure application to cropland has become tightly regulated with the goal of decreasing such nutrient pollution. Dairies unable to balance their manure nutrient supply with cropland application area may benefit from a nitrogen removal technology. One such technology is the reciprocating biofilter, known as the ReCip® technology. A pilot-scale ReCip® unit was installed at the Cal Poly dairy to evaluate its treatment efficacy, in particular for nitrogen removal, when treating wastewater from flush dairies. This pilot-scale system was the first application of the ReCip® technology to dairy wastewater, and recently it was found to be effective for removal of ammonium, total nitrogen, and biochemical oxygen demand (BOD). In the ReCip®, wastewater is repeatedly pumped back and forth between two gravel-filled basins. This reciprocation creates two treatment environments: an aerobic environment, which promotes reactions such as nitrification and BOD oxidation, and an anoxic/anaerobic environment, which promotes reactions such as denitrification of nitrate into nitrogen gas and methanogenesis. At Cal Poly, the ReCip® treated storage lagoon water, and ReCip® effluent containing nitrate was returned to the lagoon, possibly contributing to odor control. Emission of air pollutants is a concern about dairy waste in general (volatile organic compounds, hydrogen sulfide, methane, etc.) and for nitrification-denitrification systems in particular (nitrous oxide). In the present work, the first detailed air emission study was conducted on ReCip®. Emissions of air pollutants were measured with flux chambers during different seasons, and, simultaneously, the water quality within the pore volume of the gravel beds was measured to explore whether pore water quality correlated to air emissions. These air emissions studies were performed within a yearlong study of overall ReCip® treatment performance. Water quality constituents measured were pH, alkalinity, temperature, dissolved oxygen (DO), total ammonia nitrogen (TAN), soluble nitrogen, soluble non-purgeable organic carbon, nitrite, and nitrate. During the submerged phase of the reciprocation cycle, pore water DO generally declined from 1-2 mg/L to <0.1 mg/L, while TAN declined and nitrate accumulated, although total nitrogen also declined due to denitrification. The extent of denitrification was correlated to influent BOD loading. The average removals by the ReCip® were 93% TAN, 61% CBOD5, 74% TKN, and 57% TSS. A simple CBOD5 removal model was developed that described and predicted CBOD5 ­removal in the system. Key air pollutants emitted by the ReCip® and their annual mean concentrations were nitrous oxide (0.74 ppm), ammonia (0.15 ppm), and methane (3.85 ppm). The air emission potential of the lagoon water influent was compared to that of the ReCip® effluent. The decreases in emission potential were 82% for ammonia, 93% for methane, and 99% for hydrogen sulfide. The average masses emitted (g emitted/kg loaded into system) by the ReCip® were 1.7 g N2O/kg N, 0.15 g NH3/kg N, 2.1 g CH4/kg CBOD5, 1.0 g ethanol/kg CBOD5,and 0.004 g H2S/kg CBOD5.