Cost Effectiveness of Low-Density Polyethylene Pellets as Biofiltration Media in a Recirculating Aquaculture System

Abstract

This study was carried out at facilities of FreshAcres Agriventure (P) Ltd. in Hattiban, Lalitpur to assess the performance, cost per Kg of ammonia conversion and cost effectiveness of a locally available Low-Density Polyethylene (LDPE) pellets, as an alternative to K1 commercial biomedia in a domestically developed Recirculating Aquaculture system (RAS). Three fiber reenforced plastic tanks T1, T2 and T3 of 1.5m height and 3m diameter with viewing windows were built. Locally available 3000L water tank was used as biofilter chamber. Rotary drum filter with 100micron mesh screen was built for mechanical filtration of suspended solids. 600 common carp fingerlings were purchased from Centre for Aquaculture research and production in Kathar, Chitwan and transported to the study site in oxygenated packaging. Fingerlings were acclimatized, disinfected, quarantined and transferred to the three study tanks equally. Three trial sets TS1, TS 2 and TS3 were consecutively run for 6 months. The fish were fed at 3% body weight. The feeding stages were divided into S1, S2 and S3 according to their growth stages as fingerling, juvenile and adult respectively. Based on the biomass of the fish, feed rate and crude protein percentage of the feed, TAN was calculated for feeding stages S1, S2 and S3. Using this value, the theoretical required volume of LDPE pellet was calculated and used in the system. TAN level was every day and 1mg/L was taken as the base line level. Every time TAN increased by 0.1mg/L, one liter of LDPE pellets was added to the biofilter chamber until the level dropped down to base line level. Then the actual volume of the LDPE pellets required was used to calculate the cost per KG of TAN conversion into Nitrate which was found to be Rs.2208.77/KG. This number, although low compared to the cost per KG TAN conversion to nitrate using commercial biomedia K1, was still very high to be favorable for the Nepalese market. Nevertheless, this study will be a starting point for many more studies on RAS in Nepal. The fact that commercial biomedia is not available in Nepal and very expensive when it is available, makes this study valuable for the Nepalese aquaculture industry. This study also opens a pathway for modernization of the aquaculture industry in Nepal with domestically developed, low-cost technology.