Evaluation of biofilter performance with alternative local biomedia in pilot scale recirculating aquaculture systems

Abstract

Plastic is commonly used as biofilter media in recirculating aquaculture systems. Because plastic is relatively expensive and may erode and emit microplastics to the environment, efforts are being made to test and develop more sustainable materials. Five alternative locally available biofilter media were compared with commercial plastic media and evaluated in duplicate in 1 m3 two pilot scale Recirculation aquaculture system. Ammonium chloride and sodium nitrite were added to the systems for 4 weeks followed by stocking 20 kg of Nile tilapia in each system. Volumetric total ammonia nitrogen (TAN), nitrite and oxygen conversion rates were assessed for ten weeks. All biofilters with local media matured and reached full capacity after six weeks, while commercial plastic biomedia matured after seven weeks. This study found that the performance of commercial plastic biomedia was similar to performance of coconut shells in terms of volumetric TAN conversion rate (VTR), volumetric nitrite conversion rate (VNR) and volumetric oxygen conversion rate (VOCR). The highest VTR recorded in this study was 599 ± 15.8 g TAN/m3/d from coconut shells while the lowest was 343 ± 8.9 g TAN/m3/d from cattle horns. Biofilters with commercial plastic media had the highest VNR (704 ± 50.3 g NO2–N/m3/d) while media made of cattle horns was the lowest (457 ± 46.1 g NO2–N/m3/d). Biofilters containing coconut shells demonstrated the highest oxygen consumption around 3.0 g/m3/d and biofilters containing charcoal consumed less than 1.0 g/m3/d of oxygen. This study suggests that coconut shells can be used in place of plastic materials in simple recirculation aquaculture system biofiltration. This study also recommends further studies on comparing coconut shells with other biomedia and assessing its effects on water quality parameters and durability.