Biogas

As the global population is increasing, the generation of various waste materials (fats, oils and grease, fruit waste etc.) is increasing, which when landfilled, takes up valuable landfill space. Anaerobic digestion techniques have been developed that potentially convert these waste materials into energy and fertilizer, thus reducing landfill demand. It has been hypothesized that addition of high strength organic waste to conventional wastewater sludge can enhance the generation of onsite biogas at wastewater treatment plants, to meet the energy requirements of the plant partially or fully.
To determine the anaerobic biodegradability of fats, oils and grease and fruit waste residuals, lab scale ultimate digestibility tests were conducted for a period of 63 days under mesophilic conditions. High strength organic wastes, thickened waste activated sludge and inoculum were mixed at 9 different ratios, and the mixtures were incubated in 500 mL serum bottles. After 63 days, the highest methane yield of 280 mL/gVS and 243 mL/gVS were obtained with mixtures containing 10% FOG with 10% red apples and 10% FOG only respectively whereas the methane yield of inoculum was only 8 mL/gVS. Preliminary cost analyses were conducted using the laboratory derived data

The anaerobic biodegradability of food waste (FW), meat waste and FOG (fats, oils
and greases) with municipal primary sewage sludge was assessed using a laboratory scale
anaerobic digester and by ultimate sludge digestibility, at mesophilic conditions by varying
the inoculum to feedstock ratio (1:2-1:10) and solids retention time (SRT). Preliminary
analysis assessed the anaerobic digestion of food waste and meat at a biogas production
over 30 days at 1000 mL and 1400 mL, respectively. The maximum methane yield was
0.18 m3/kg VS and 0.50 m3/kg VS for 1:10 in meat and FOG, respectively in 28 days with
56-61% volatile solids of destruction and first order methane generation rate of 0.15 d-1 for
both meat and FOG. The optimal ratio for meat and FOG was determined to be beyond
highest ratio tested (1:10), and longer SRT should be considered to investigate the impact
of feedstock on methane yield. Preliminary modeling suggests that for one 1.74 MG
digester, diverting just 0.6% of the food waste generated in one-third of Palm Beach
County could produce enough methane to power 130-360 homes for one full month.