Effect of hydraulic retention time of sponge-based trickling filter for shrimp culture recirculating tank

Abstract

This study examined the effect of hydraulic retention time (HRT) of the sponge-based trickling filter in the recirculating aquaculture system (RAS) during the 85-day Penaeus vannamei cultivation at 1–3 kg/m3, comparing low (0.04 h; control) and high (1 h; treatment) HRTs. Operating the system at low HRT with a recirculation rate of 1.08 m3/h provided preferable conditions for nitrification, as low total ammonia nitrogen (TAN) and nitrite levels (<0.1 mg-N/L) were maintained throughout shrimp cultivation period. Likewise, the indices of TAN removal rates were higher (0.16–0.20 kg-N/m3-sponge d) with higher relative abundance of nitrifiers, including Candidatus Nitrosocosmicus (0.11–3.43 %), Nitrosomonas (0.00–0.09 %) and Nitrospira (0.17–0.70 %). On the other hand, high HRT with a recirculation rate of 0.042 m3/h contributed to solid accumulation, which was favorable for denitrification. A lower final nitrate level (31.7 mg-N/L less than control tank) was obtained, with higher nitrate removal rate indices of 0.017–0.020 kg-N/m3-sponge d. The dominant denitrifying genera included Marinicella (0.00–1.67 %), Flavobacterium (0.00–0.67 %), and Pseudomonas (0.00–0.37 %). With this process, alkalinity was generated, helping maintain pH stability (7.4 ± 0.4) and minimizing the need for bicarbonate supplementation.