Fruit and vegetable wastes are produced in large quantities in Iran, and constitute a source of nuisance in municipal landfills. The objective of this study was to optimize the applications of anaerobic digestion for the treatment of municipal organic wastes. We studied the effect of organic loading rates on anaerobic digestion of vegetable wastes. The complete-mix, pilot-scale digester with working volume of 70 l was used. The experiments were conducted at 34oC with a fixed hydraulic retention time of 25 days. The digester was operated at different organic feeding rates of 1.4, 2 and 2.75 kg VS/(m.d). The biogas produced had methane composition of 49.764% and biogas production rates of 0.12-0.4 m/(kg VS). The reactor showed stable performance with highest biogas production (0.4 m/kg VS) and VS reduction of around 88% during loading rate of 1.4 kg VS/(m3.d). The chemical oxygen demand (COD) reduction, VS removal and methane concentration in biogas was decreased when the organic loading rate was increased. Based on the data obtained from this study, OLR of 1.4kg VS/(m.d) is suggested as design criteria with biogas production rate of 0.4 mbiogas/(kg VS).
Firstly; fourteen variations of six general energy concepts have been developed and calculations conducted on the energy neutrality by means of an Excel model designed for this purpose.
In order to obtain basic design criteria for anaerobic digestion of a mixture of poultry manure and wheat straw, the effects of different temperatures and organic loading rates on the biogas yield and methane contents were evaluated. Since poultry manure is a poor substrate, in term of the availability of the nutrients, external supplementation of carbon has to be regularly performed, in order to achieve a stable and efficient process. The complete-mix, pilot-scale digester with working volume of 70 L was used. The digestion operated at 25°C, 30°C and 35°C with organic loading rates of 1.0, 2.0, 2.5, 3.0, 3.5 and 4.0 kg Volatile solid/m3d and a HRT of 15 days. At a temperature of 35°C, the methane yield was increased by 43% compared to 25°C. Anaerobic co-digestion appeared feasible with a loading rate of 3.0 kg VS/m3d at 35°C. At this state, the specific methane yield was calculated about 0.12 m3/kg VS with a methane content of 53-70.2% in the biogas. The volatile solid (VS) removal was 72%. As a result of volatile fatty acid accumulation and decrease in pH, when the loading rate was less than 1 or greater than 4 kg VS/m3d, the process was inhibited or overloaded, respectively. Both the lower and higher loading rates resulted in a decline in the methane yield.
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