Nitrogen and organic matter removal in an intermittently aerated fixed-bed reactor for post-treatment of anaerobic effluent from a slaughterhouse wastewater treatment plant

Abstract This study evaluated the performance of a lab scale, fixed-bed reactor exposed to intermittent aeration for the removal of organic matter and nitrogen from anaerobic reactor effluent. The reactor was continuously fed with effluent from a UASB reactor used to treat wastewater from a poultry slaughterhouse. The hydraulic retention time (HRT) was maintained at 24 h during the five operational phases that the reactor was subjected to. The phases differed only for the duration of periods with and without aeration. The best results regarding nitrogen removal efficiency were obtained in phase V (8 daily cycles of 1 h of aeration and 2 h without aeration). Under these conditions, for influent with total COD of 418 mg L −1 , 169 mg L −1 of TKN and 112 mg L −1 of NH 4 + -N, effluent with a total COD of 22 mg L −1 , 6.4 mg L −1 of TKN, 6.4 mg L −1 of NH 4 + -N and 58 mg L −1 of NO 3 -N was obtained and NO 2 -N was not detected. During this phase, the average nitrogen removal efficiency was 62%. Optical microscopy and molecular biology analyses associated with the study of microbial activity detected the activity of bacteria that perform anammox, thereby contributing to the understanding of the processes involved.