J. Agric. Food. Tech., 4(2)6-12, 2014 © 2014, TextRoad Publication ISSN 2090 – 424X Journal of Agriculture and Food Technology www.textroad.com *Corresponding Author: Akeem Babatunde DAUDA, Department of Fisheries and Aquacultural Technology, Federal University Dutsin-Ma, Dutsin-Ma, Katsina State, Nigeria. Email: dedabak03@yahoo.com +2348062085120 Biodenitrification of Aquaculture Wastewater at Different Drying Times in Water Reuse System Akeem Babatunde DAUDA 1* , Ayoola Olusegun AKINWOLE 2 and Latifat Kehinde OLATINWO 3 1 Department of Fisheries and Aquacultural Technology, 3 Department of Agricultural Economics and Extension Federal University Dutsin-Ma, Dutsin-Ma, Katsina State, Nigeria 2 Department of Aquaculture and Fisheries Management, University of Ibadan, Ibadan, Nigeria ABSTRACT Introduction of denitrification in water recirculating system to remove nitrate-nitrogen which is produced by nitrification and tend to be toxic at high concentration has been investigated by some researchers but mostly for temperate aquaculture and information on the time for readiness of the system is virtually not available. Therefore this study examined the biodenitrification of aquaculture wastewater from a tropical fish species at different drying times. Aquaculture effluent from monoculture of Clarias gariepinus was passed through nitrifying followed by denitrifying biofilter at three drying times (24, 72 and 144 hours). Water quality parameters; Temperature, Dissolved oxygen (DO), pH, Total ammonia-nitrogen (TAN), Nitrite-nitrogen (NO 2 -N) and Nitrate-nitrogen (NO 3 -N) were measured in the filtrates of the nitrification and denitrification column to assess the change in water quality. Denitrification efficiency of the biofilter was determined using Percentage nitrate-nitrogen removed (PNR) and Volumetric nitrate-nitrogen conversion rate (VNR). The result showed that all the water quality parameters were within the range for fish culture but the nitrate-nitrogen in the nitrification is higher than the recommended level for discharge into the environment. The PNR recorded were 33.33±57.74%, 47.87±4.19 % and 59.09±7.87% while the VNR recorded were 3116.88±599.60 mgNO 3 -N/m 3 d, 14125.26±746.55, 58775.51±7068.43 mgNO 3 -N/m 3 d for the 24, 72 and 144 hours drying time respectively. The study revealed that biodenitrification increases with drying time and prevented NO 3 -N accumulation in the system. The incorporation of denitrification column in recirculating system will enhance sustainable aquaculture production and save the aquatic environment from eutrophication. KEYWORDS: Aquaculture effluents, Nitrate removal, Drying time, Total ammonia nitrogen, Recirculating system. INTRODUCTION The trend in fish culture has been to move from conventional open systems to high density and highly productive land-based systems in which recirculation aquaculture system (RAS) is one of them. The use of recirculating system has been tested both at experimental and pilot scale and it is now growing in number in commercial scale. The use of recirculation system is growing in the fast developing urban and peri-urban aquaculture in Nigeria [2]. Recirculating aquaculture systems (RAS) are used to rear high densities of fish while employing water conservation techniques by continuously recycling the culture water. The percentage of the total system volume that is recycled varies with system operation, but for completely closed systems water replacement compensates mainly for evaporation and splash out losses [19]. In most recirculating systems, total ammonia (referring to NH 3 and NH 4 + ) removal by nitrification, sludge removal by sedimentation or mechanical filtration, and water exchange are the vital forms of water treatment [20]. High pollutant load results in the water drained from the inland aquaculture systems [15], and may be due to nitrate and phosphate in RAS. The removal of toxic ammonia from fish water is carried out mainly by biofilters, the less toxic nitrate resulted from conversion of ammonia by biofilters may accumulates over time to the extent of becoming a limiting factor to fish production. High nitrate concentration in the recirculating system can be toxic to fish species and for tropical fresh water fish species less than 250mg/L is recommended [21]. Increased efforts are now directed toward nitrate control in recirculating systems which apart from the direct toxic effect on fish at high concentrations can also lead to environmental degradation. Nitrates can be reduced in RAS if the conventional nitrification is followed by denitrification [17]. Biological denitrification can be used to remove nitrates from recirculating aquaculture system waters and this is done in anoxic condition by heterotophic bacteria and nitrates is used as terminal electron acceptor in the presence of carbon and energy source [13] . Biodenitrification has been experimented by some researchers but mainly for temperate fish species, therefore this study investigated biodenitrification of wastewater from Clarias gariepinus 6