This study aimed to evaluate the two-stage and one-stage anaerobic co-digestion of vinasse and spent brewer yeast cells (SBY) for biohydrogen and methane production. Optimization of the vinasse-to-SBY ratio and fly ash concentration of the two-stage and one-stage production processes was investigated. In the two-stage process, the vinasse-to-SBY ratio and fly ash concentration were optimized, and the leftover effluent was used for methane production. The optimum conditions for biohydrogen production were a vinasse-to-SBY ratio of 7:3% v/w and fly ash concentration of 0.4% w/v, in which the maximum hydrogen yield was 43.7 ml-H2/g-VSadded. In contrast, a vinasse-to-SBY ratio of 10:0% v/w and fly ash concentration of 0.2% w/v were considered optimal for methane production, and resulted in a maximum methane yield of 214.6 ml-CH4/g-VSadded. For the one-stage process, a vinasse-to-SBY ratio of 10:0% v/w and fly ash concentration of 0.1% w/v were considered optimal, and resulted in a maximum methane yield of 243.6 ml-CH4/g-VSadded. In the two-stage process, the energy yield from hydrogen (0.05-0.47 kJ/g-VSadded) was 0.62%-11.78%, and the major fraction was approximately 88.22%-99.38% gain from methane (3.19-7.73 kJ/g-VSadded). For the one-stage process, the total energy yield distribution ranged from 4.20 to 8.77 kJ/g-VSadded.
Purple non-sulphur bacteria can only capture up to 10 % light spectra and only 1-5 % of light is converted efficiently for biohydrogen production. To enhance light capture and conversion efficiencies, it is necessary to understand the impact of various light spectra on light harvesting pigments. During photo-fermentation, Rhodobacter sphaeroides KKU-PS1 cultivated at 30 °C and 150 rpm under different light spectra has been investigated. Results revealed that red light is more beneficial for biomass accumulation, whereas green light showed the greatest impact on photo-fermentative biohydrogen production. Light conversion efficiency by green light is 2-folds of that under control white light, hence photo-hydrogen productivity is ranked as green > red > orange > violet > blue > yellow. These experimental data demonstrated that green and red lights are essential for photo-hydrogen and biomass productions of R. sphaeroides and a clearer understanding that possibly pave the way for further photosynthetic enhancement research.
Seven sulfonamides, trimethoprim, five macrolides, lincomycin and three tetracyclines were measured in 150 water samples of sewage, livestock and aquaculture wastewater, and river and coastal waters, in five tropical Asian countries. The sum of the concentrations of the target antibiotics in sewage and heavily sewage-impacted waters were at sub- to low-ppb levels. The most abundant antibiotic was sulfamethoxazole (SMX), followed by lincomycin and sulfathiazole. The average concentration of SMX in sewage or heavily sewage-impacted waters was 1720 ng/L in Vietnam (Hanoi, Ho Chi Minh, Can Tho; n=15), 802ng/L in the Philippines (Manila; n=4), 538 ng/L in India (Kolkata; n=4), 282 ng/L in Indonesia (Jakarta; n=10), and 76 ng/L in Malaysia (Kuala Lumpur; n=6). These concentrations were higher than those in Japan, China, Europe, the US and Canada. A predominance of sulfonamides, especially SMX, is notable in these tropical countries. The higher average concentrations, and the predominance of SMX, can be ascribed to the lower cost of the antibiotics. Both the concentration and composition of antibiotics in livestock and aquaculture wastewater varied widely. In many cases, sulfamethazine (SMT), oxytetracycline (OTC), lincomycin, and SMX were predominant in livestock and aquaculture wastewater. Both human and animal antibiotics were widely distributed in the respective receiving waters (i.e., the Mekong River and Manila Bay). SMT/SMX ratios indicate a significant contribution from livestock wastewater to the Mekong River and nearby canals, with an estimated ~10% of river water SMX derived from such wastewater. Mass flow calculations estimate that 12 tons of SMX is discharged annually from the Mekong River into the South China Sea. Riverine inputs of antibiotics may significantly increase the concentration of such antibiotics in the coastal waters.