Biodegradation of phenol in batch and continuous flow microbial fuel cells with rod and granular graphite electrodes.

Phenol biodegradation was evaluated in batch and continuous flow microbial fuel cells (MFCs). In batch-operated MFCs, biodegradation of 100-1000 mg L-1 phenol was four to six times faster when graphite granules were used instead of rods (3.5-4.8 mg L-1 h-1 vs 0.5-0.9 mg L-1 h-1). Similarly maximum phenol biodegradation rates in continuous MFCs with granular and single-rod electrodes were 11.5 and 0.8 mg L-1 h-1, respectively. This superior performance was also evident in terms of electrochemical outputs, whereby continuous flow MFCs with granular graphite electrodes achieved maximum current and power densities (3444.4 mA m-3 and 777.8 mW m-3) that were markedly higher than those with single-rod electrodes (37.3 mA m-3 and 0.8 mW m-3). Addition of neutral red enhanced the electrochemical outputs to 5714.3 mA m-3 and 1428.6 mW m-3. Using the data generated in the continuous flow MFC, biokinetic parameters including µm, KS, Y and Ke were determined as 0.03 h-1, 24.2 mg L-1, 0.25 mg cell (mg phenol)-1 and 3.7 × 10-4 h-1, respectively. Access to detailed kinetic information generated in MFC environmental conditions is critical in the design, operation and control of large-scale treatment systems utilizing MFC technology.

Biokinetic evaluation of fatty acids degradation in microbial fuel cell type bioreactors.

Biodegradations of Na-lactate and Na-acetate were evaluated in microbial fuel cell (MFC) type bioreactors. Increase in lactate concentration from 1,000 to 5,000 mg L(-1) enhanced the biodegradation rate from 4.6 to 23.9 mg L(-1) h(-1). Sequential batch operation of MFC enhanced the lactate biodegradation rate. With acetate, neither increase in concentration nor sequential operation had a marked effect. Maximum power and current densities in MFCs operated batch-wise with lactate and acetate were 3.30 and 2.28 mW m(-2), and 48.2 and 40.2 mA m(-2), respectively. In the MFC operated continuously, increase in lactate loading rate caused the biodegradation rate to pass through maximum value of 1,668.2 mg L(-1) h(-1) (residence time: 1.2 h). Open circuit potential, power and current densities for continuous operation were 700 mV, 8.10 mW m(-2) and 43.0 mA m(-2), respectively. Using the experimental data, kinetic models for microbial growth and biodegradation of lactate and acetate in the MFC were developed.

Laboratory, semi-pilot and room scale study of nitrite and molybdate mediated control of H(2)S emission from swine manure.

The effects of manure age on emission of H(2)S and required level of nitrite or molybdate to control these emissions were investigated in the present work. Molybdate mediated control of H(2)S emission was also studied in semi-pilot scale open systems, and in specifically designed chambers which simulated swine production rooms. With fresh 1-, 3- and 6-month old manures average H(2)S concentration in the headspace gas of the closed systems were 4856+/-460, 3431+/-208, 1037+/-98 ppm and non-detectable, respectively. Moreover, the level of nitrite or molybdate required to control the emission of H(2)S decreased as manure age increased. In the semi-pilot scale open system and chambers, average H(2)S concentration at the surface of agitated fresh manure were 831+/-26 and 88.4+/-5.7 ppm, respectively. Furthermore, 0.1-0.25 mM molybdate was sufficient to control the emission of H(2)S. A cost study for an average size swine operation showed that the cost of treatment with molybdate was less than 1% of the overall production cost for each market hog.