Integrating entrapped mixed microbial cell (EMMC) process for biological removal of carbon and nitrogen from dilute swine wastewater
Yang, P.Y., H.J. Chen, S.J. Kim
An entrapped mixed microbial cell (EMMC) process was used to investigate the simultaneous removal of carbon and nitrogen from dilute swine wastewater. Cellulose triacetate was used as the matrix for entrapping the mixed microbial cells. The EMMC process was tested under various oxygen supply conditions (ratios of aeration to non-aeration times) and two types of carrier sizes (large and medium). Also, various pre-treatments with chemical coagulation, screen separation, and ammonium crystallization prior to the EMMC process and post-treatment following the EMMC process were investigated. It was found that at a hydraulic retention time of 30 hours and 1 hour of aeration and 1 hour of non-aeration, the EMMC process packed with medium carriers after the pre-treatment of ammonium crystallization exhibited the best total nitrogen removal efficiency of 95.1 1.0% when compared to two other pre-treatment methods. The total chemical oxygen demand (TCOD) and soluble chemical oxygen demand removal efficiencies were 83.5 2.2% and 84.1 1.1%, respectively. Lime post-treatment provided TCOD and total phosphorus removal efficiencies of 59.6 2.7% and 98.0 0.5%, respectively. Thus, a cost analysis for ammonium crystallization pre-treatment, EMMC process, and post-treatment with lime was conducted. The unit cost for a 2,000-pig operation is $4.91/pig/year. For the application of the EMMC process with the proposed pre- and post-treatments, a suitable farm size needs to be greater than a 2,000-pig operation. Because of the high efficiency and the simple operation of simultaneous carbon and nitrogen removal, the EMMC process has the potential for treatment of dilute swine wastewater in a land-limited area and can be manufactured as pre-fabricated wastewater treatment units.