Vegetable and fruit market wastes as an appropriate source for biogas production via anaerobic digestion process

Urban waste management is a critical issue in today’s world. On the other hand, energy supply is a significant need, especially from renewable sources. In this paper, an efficient method is studied for the production of biogas from vegetable and fruit market wastes. A comprehensive study is presented on the production of methane in biogas from vegetable and fruit market wastes. For this purpose, a reactor was designed and vegetable and fruit market wastes were used as feed of the reactor for biogas production. For supplying the moisture during the gas formation, the feed was mixed with distilled water in 1:1 ratio. The mean cell residence time was set at 25 days. The results showed an intense sensitivity of the microorganism to the pH of the reactor. In acidic media, the produced biogas was very lower than neutral and slightly basic media. In addition, the percentage of the methane in the biogas showed to be increased by increasing pH from 6.3 to 7.6.

Survey on nitrogen removal and membrane filtration characteristics of Chlorella vulgaris Beij. on treating domestic type wastewaters

The main objective of this study is to evaluate the nitrogen assimilation and filtration characteristics of Chlorella vulgaris Beij. when treating domestic wastewaters. Chlorella could assimilate organic nitrogen, ammonia and nitrate in wastewater, and the mean cell residence time (MCRT) to achieve the maximum biomass content in a bioreactor was different for each individual nitrogen source used. The experimental results showed that using nitrate as the only nitrogen source was the most favorable for biomass growth. With ammonia and nitrate coexisting in the aquatic phase, Chlorella possibly utilized ammonia first, and this was unfavorable to subsequent biomass growth. Nitrifying bacteria in wastewaters significantly affected Chlorella growth as they possibly competed with Chlorella in assimilating ammonia and nitrate in domestic wastewater. In a submerged ultrafiltration (UF) membrane module, with an initial concentration of 850 mg/L of Chlorella, the optimized flux was 0.02 m3/(m2·h), and the filtration cycle was 30 min. A ‘dual membrane bioreactor (MBR)’ configuration using UF membranes for Chlorella incubation was proposed. MBR1 provides an environment with long MCRT for efficient nitrification. The converted nitrate is assimilated by Chlorella in MBR2 to sustain its growth. UF permeate from MBR1 is bacteria-free and does not affect the growth of Chlorella in MBR2. MCRT of Chlorella growth is controlled by the UF membrane of MBR2, providing the flexibility to adjust variations of nitrogen composition in the wastewater.