Performance of a Modified Trickling Filter Packed With Organic Substrates for Treatment of Aquaculture Wastewater

Abstract

Globally, environmental sustainability is the most critical aspect of humanity. In order to achieve a sustainable environment, technologies of waste and wastewater management have been improving over the years. The development of wastewater treatment infrastructure lags behind the rates of urbanization. There is a need to come up with innovative and effective approaches of wastewater treatment to complement the existing wastewater treatment systems. Aquaculture wastewater is characterized by high nutrients and organic load. The organic compounds are broken down to simpler structures of carbon (IV) oxide and water at the secondary stage of treatment. It is therefore important to polish the water to remove contaminants so as to avoid pollution and eutrophication of receiving water bodies. The main objective of the study was to evaluate the performance of a bioreactor trickling filters packed with different substrates in polishing aquaculture wastewater effluents using locally available materials (woodchips, sugarcane bagasse and maize cobs) as substrate. These organic materials are suitable for bioreactors as they act as substrate for the microorganisms. The wastewater was obtained from the outlet of a fish pond. The bioreactor variables studied include; substrate column height, hydraulic retention time, particle sizes. The most suitable operating conditions was determined for all the three substrates. Wastewater was analyzed before and after treatment. The raw wastewater compositions were; nitrates, 208±1.24 mg/l 24.5±0.4mg/l nitrites and 20.66±0.31mg/l Phosphates. Other parameters Such as temperature and pH were within normal range of 19oc and 6 respectively. These values are higher acceptable discharge standards set by GOK indicating need for polishing before discharge. The model wastewater bioreactor had a capacity of 12 liters. Each bioreactor unit was packed with different particle sizes of woodchips, maize cobs and sugarcane bagasse at various column heights; 14cm, 18cm and 22cm. The hydraulic loading rate and thus hydraulic retention time were varied at intervals of 12hour, 24hours, 48 hours and 60 hours. Samples were then collected and analyzed for nitrates, nitrites and phosphates using a UV VIS spectrophotometry. Data was analyzed to determine the efficiency of each substrate in the removal of contaminants. An analysis of the performance of each substrate at varied particle size and contact time was done. Wood chips was the most efficient substrate in the removal of contaminants at 22cm substrate column height, the smaller particles of woodchip (30-38mm) was the most efficient with 94%, efficiency in the removal of nitrates. Maize cobs was slightly more efficient compared to sugarcane bagasse in the removal of phosphates because of its adoptive properties. The optimal HRTs were as follows: For the woodchip at 22cm substrate column height 45 hours is required and in the 18cm substrate column height 72 hours: For the maize cobs and sugarcane at 22cm height of substrate 65 hours and 67 hours were the optimal HRTs. It is recommended that policy makers adopt this finding in developing regulations of unconventional water treatment in the country.