A. Mitra

Effect of presence of cellulose in the freshwater sediment on the performance of sediment microbial fuel cell.

The performance of sediment microbial fuel cells (SMFCs) was evaluated in the presence of cellulose in the aquaculture pond sediment as 2% (w/w) in SMFC-2, 4% in SMFC-3 and without adding cellulose in SMFC-1. From aquaculture water, average chemical oxygen demand (COD) and total nitrogen (TN) removal efficiencies of 80.6±0.3% and 83.0±0.01% were obtained in SMFC-1, 88.2±0.5% and 89.6±0.8% in SMFC-2 and 83.1±0.3% and 64.5±1.6% in SMFC-3, respectively. During the complete experimental period, acetic acid was the only short chain fatty acid detected in all three SMFCs. Sediment organic matter removal in SMFC-1, SMFC-2 and SMFC-3 were 16%, 22% and 18.6%, respectively. SMFCs demonstrated effective cellulose degradation from aquaculture pond sediment and maintained the oxidized sediment top layer favourable for aquaculture.

Sewage treatment in integrated system of UASB reactor and duckweed pond and reuse for aquaculture

The performance of a laboratory-scale upflow anaerobic sludge blanket (UASB) reactor and a duckweed pond containing Lemna gibba was investigated for suitability for treating effluent for use in aquaculture. While treating low-strength sewage having a chemical oxygen demand (COD) of typically less than 200 mg/L, with an increase in hydraulic retention time (HRT) from 10.04 to 33.49 h, COD removal efficiency of the UASB reactor decreased owing to a decrease in organic loading rate (OLR) causing poor mixing in the reactor. However, even at the lower OLR (0.475 kg COD/(m3·d )), the UASB reactor gave a removal efficiency of 68% for COD and 74% for biochemical oxygen demand (BOD). The maximum COD, BOD, ammonia-nitrogen and phosphate removal efficiencies of the duckweed pond were 40.77%, 38.01%, 61.87% and 88.57%, respectively. Decreasing the OLR by increasing the HRT resulted in an increase in efficiency of the duckweed pond for removal of ammonia-nitrogen and phosphate. The OLR of 0.005 kg COD/(m2·d ) and HRT of 108 h in the duckweed pond satisfied aquaculture quality requirements. A specific growth rate of 0.23% was observed for tilapia fish fed with duckweed harvested from the duckweed pond. The economic analysis proved that it was beneficial to use the integrated system of a UASB reactor and a duckweed pond for treatment of sewage.

Effect of pH and distance between electrodes on the performance of a sediment microbial fuel cell.

The performance of three sediment microbial fuel cells (SMFCs) was evaluated at different feed water pH and electrode spacing for chemical oxygen demand (COD) removal, total nitrogen (TN) removal, and power density; while offering in situ remediation of aquaculture pond water. SMFC-A was operated at the feed water pH of 6.5 and spacing between the electrodes of 100 cm. SMFC-B and SMFC-C were operated at feed water pHs of 8.5 and 6.5, respectively, and distance between electrodes of 50 cm. The anode and cathode were connected with concealed copper wire through an external load of 100 Ω. The average amount of total COD removal rate and TN removal rate, per unit area of cathode, were 1.72 ± 0.06 and 0.021 ± 0.007 g/m(2) d in SMFC-A, 1.03 ± 0.08 and 0.024 ± 0.005 g/m(2) d in SMFC-B, and 1.14 ± 0.01 and 0.017 ± 0.001 g/m(2) d in SMFC-C, respectively. SMFC-A, operated with higher distance between electrodes, demonstrated better removal of organic matter and highest open circuit voltage of 0.903 V. SMFCs with less feed pH (6.5) gave higher COD removal and feed pH of 8.5 gave higher TN removal. SMFCs operated with lesser distance between electrodes gave higher power density.