Removal of nitrogen in wastewater by polyvinyl alcohol (PVA)-immobilization of effective microorganisms

To remove nitrogen and carbon simultaneously from municipal wastewater, a mixture of effective microorganisms (EM) was immobilized in polyvinyl alcohol (PVA) hydrogel beads. The modified PVA beads with calcium alginate show characteristic pores and mechanical stability and flexibility. The EM-immobilized PVA system was established in a 3 L sequential batch reactor (SBR) with a synthetic wastewater and operated at an HRT of 12 h with COD loading rate of 0.5–2.4 g COD/L·d. In this system, intermittent aeration is more efficient than continuous aeration, and removal rates of COD and total nitrogen (T-N) were increased as the feed COD/N ratio was increased from 1.9 to 5.6. At an optimal condition, 73% of total nitrogen and 93% of COD were stably removed at a COD loading rate lower than 2.4 g COD/L·d and at 3: 1 ratio of aerobic time to anoxic time.