Performance of a Modified Trickling Filter Packed with Different Substrates in Polishing Aquaculture Wastewater

Abstract

: Sustainable use of natural resources is one of the most critical aspects in today’s world, water monument being one of them. There is a high demand for water in domestic, agricultural and industrial sector. As a result of these there is an increased rate of wastewater generation. To ensure sustainable use of the resource, there is need for wastewater management that will ensure reuse and reduce pollution to the water resource. The aim of the study was to evaluate the performance of different locally available substrate materials in polishing aquaculture wastewater before it is discharged to the receiving bodies and to determine the substrates’ optimal treatment conditions in a modified trickling filter system. The wastewater was characterized with high levels of nitrates, nitrites and phosphates which are nutrients responsible for the degradation of water resources through eutrophication. A modified trickling filter system was fabricated and woodchips, maize cobs and sugarcane bagasse were each packed in three different reactor tanks. These substrates were subjected to similar operating conditions of substrate column heights of 14 cm, 18 cm and 22 cm, varied HRT (Hydraulic Retention Time) at 12 h, 24 h, 48 h and 60 h respectively. Wastewater was collected from a fish pond and passed through the modified trickling filter system for a specified period of time. Samples of the effluent were collected and tested for nitrates, nitrites and phosphates using a UV VIS (Ultraviolet-visible) spectrometer. The results obtained showed that the contaminant with the highest concentration was nitrates. Nitrites was converted into nitrates during the treatment process hence it was not a suitable parameter to be used to make conclusions. Phosphate was present in lower concentrations compared to nitrates hence the desired level was achieved. The most suitable substrate in the removal of all the contaminants was the woodchips with an efficiency of 94% at an operating condition of 18 cm and 22 cm substrate column height for the small and large woodchip particles at 48 and 60 h HRT respectively. Maize cobs and sugarcane bagasse both yielded an efficiency of 92% at 22 cm substrate column height and 60 h HRT .