Biofiltration in an aquaponic system using spinach (ipomea oleracea) cultivation on biochar

Abstract

The efficiency of biochar as a substrate in biofiltration in an aquaponic system was investigated. The study was carried out at RA Cell company in Kirinya- Bweyogerere and it involved the use of plants as biological filters for uptake of nutrients from the water and these were cultivated on both biochar and sawdust. Fish tanks of 40litres of water were stocked with 200 juveniles of African catfish (Clarias gariepinus) having an initial weight of 1g which were fed on commercial fish feed 3 times a day. Water from the fish tanks was channeled to the growing beds which composed of both biochar and sawdust as the growth substrate for spinach (Ipomea oleracea). Water quality parameters such as dissolved oxygen levels, total dissolved solids (TDS) and ammonia levels were assessed before biofiltration and after biofiltration in growing beds with biochar and saw dust during the study period. Biofiltration in growing beds with biochar as a growth substrate gave low levels of dissolved oxygen which were in the range of (2.9-3.8) mg/L and an average of (3.2±0.3) after biofiltration compared to biofiltration in growing beds with sawdust as a growth substrate which were in a range of (3.6-4.0)mg/L with an average of (3.8±0.1). The plant beds with biochar gave a low range of (200-325) ppm total dissolved solids with an average (264.5±39.6) after biofiltration compared to a range of (222-380) ppm and an average (312.1± 56.2) obtained after biofiltration in plant beds with sawdust as a growth substrate. The plant beds with biochar gave a very low range of ammonia levels (0.0-0.2) mg/L and an average of (0.09±0.1) after biofiltration compared to a range of (0.1-0.5) mg/L and an average of (0.2± 0.1) obtained after biofiltration in plant beds with sawdust as a growth substrate. This study suggests that biochar when used as a substrate in growing beds (biofilters) is efficient for biofiltration in aquaponics due to presence of nitrifying bacteria to convert toxic ammonia into nitrite (NO2-) followed by nitrate (NO3-) which are needed to support plant life. Therefore biofiltration with biochar as a growth substrate greatly reduces ammonia levels and total dissolved solids in fish tank effluents.