Nitrogen removal from shrimp farm wastewater by aerobic and anoxic recirculation systems

Abstract

Although wastewater from shrimp culture production contains high amount of ammonia nitrogen, normally toxic to shrimps, it is required to be reused because of other available substances in this wastewater. With this reason, the ammonia nitrogen should be removed before reusing this wastewater until its amount less than the toxic level. The objective of this research was to find the removal efficiency of ammonia nitrogen by aerobic and anoxic recirculation systems. The experiments were conducted at shrimp culture production farm located at Chachoengsao Province in Thailand. The shrimp production wastewater contained the ammonia nitrogen of 13.14+3.54 mg/L was passed through the designed reactors with sizing of 6 L. Air requirement for nitrification was added to the reactor at 2.5 l/min for 10 days to complete the nitrification process. In this experiment, it was found that ammonia nitrogen was converted to nitrate about 98%. Compare to the control group, ammonia nitrogen was converted to nitrate nitrogen with 26%. The results also showed that nitrate was converted to nitrogen gas and total nitrogen was removed with 5% and 84% for control and treatment group, respectively. For the long period operation, nitrate was consistently remained in the effluent with the concentration below 0.38 mg-N/l. Also, the rate nitrogen gas produced was approximately 68 ml/m3/day. The C/N ratio for the anoxic period was approximately 0.1 g of TOC/g of nitrate nitrogen. For the aerobic system, the percent survival of shrimp under control and treatment group experiments was 34% and 54%, respectively while for the recirculation system, the percent survival was decreased to 26% and 49% for control and treatment group, respectively. This finding showed that the recirculation of water after the aerobic and anoxic systems slightly affected the shrimp survival but the shrimp were significantly affected for control group (p<0.05).