Biochar and zeolite as alternative biofilter media for denitrification of aquaculture effluents

Abstract

Denitrification processes are crucial in aquaculture as they convert the undesirable nitrate to safer forms of nitrogen. Conventionally, plastic media are used for the biofiltration of wastewater. However, alternative media may be as effective/better than plastic and enhance the sustainability of the system. This study evaluated biochar and zeolite as alternatives for the denitrification of aquaculture effluents. Triplicates of laboratory-scale bioreactors were fabricated to compare the denitrification efficiencies of biochar and zeolite to that of plastic. The bioreactors were fed synthetic aquaculture wastewater having nitrate loading rates of 50, 125, and 150 mg/L. Zeolite exhibited highest values of surface roughness in terms of arithmetic mean height (0.89 µm), maximum height (6.52 µm), and root-mean-square height (1.17 µm), as corroborated by surface profilometry and scanning electron microscopy. The results revealed that under pseudo-steady-state conditions, zeolite displayed the highest nitrate removal efficiency (maximum 95.02 ± 0.01%), which was followed by biochar and plastic (maximum 92.91 ± 0.01% and 92.57 ± 0.02%, respectively) due to its extraordinary surface roughness that provided better adhesion to the bacteria. However, by the end of the study, all the media exhibited comparable rates. Thus, both zeolite and biochar are sustainable alternatives of biomedia for nitrate removal. However, time and labor constraints must be accounted for to scale-up such bioreactors.