Denitrification using polyhydroxybutyrate/cellulose blend (PHBC) as a carbon substrate

Abstract

The impact of cellulose on PHB’s biodegradability and denitrification performance was evaluated in a triplicated closed-loop (recirculating) format. Pure PHB bio-pellets were compared to PHB/microcrystalline cellulose blends (PHBC) containing 20, 30, and 40 % cellulose in terms of nitrate conversion rates, COD accumulation, cost of denitrification, and consumption rate. The results show that the PHBC60:40 and PHBC70:30 achieved average apparent peak nitrate conversion rates of 3.9 ± 0.80 kg NO₃−N/m³-d and 3.9 ± 0.24 kg NO₃−N/m³-d, respectively, on day 2. PHBC80:20 achieved an average apparent peak nitrate conversion rate of 3.7 ± 0.017 kg NO₃−N/m³-d on day 3, while PHB100 % attained an average apparent peak nitrate conversion rate of 3.4 ± 0.03 kg NO₃−N/m³-d on day 4. The peak nitrate conversion rates achieved by the four treatments are statistically different. The COD accumulated in the PHB100 %, PHBC80:20, PHBC70:30, and PHBC60:40 reservoirs on day 7 are 19 ± 2.9, 29 ± 4.2, 51 ± 8.6 and 58 ± 11.5, respectively, which was aggravated by the release of solids during backwashing. There is a significant difference in 7-day reservoir COD accumulation, which correlates with the cellulose content. PHB was consumed at a rate of 3.3 ± 0.54 kg PHB/kg NO₃−N, with the blended bio-pellets consumed at the rate of 3.5 ± 0.48 kg PHBC80:20/kg NO₃−N, 3.8 ± 0.13 kg PHBC70:30/kg NO₃−N, and 4.0 ± 0.12 kg PHBC60:40/kg NO₃−N, respectively. The cost of denitrification was estimated through the consumption rates and results showed that the blends are more cost-effective than PHB. PHBC blends can effectively reduce nitrate in water. A viable carbon substrate for remediating industrial wastewater and aquaculture systems where cellulose solubility will not be an issue. Future research will focus on using low-cost cellulose materials to produce more PHBC blends for more cost-effective denitrification.