A new approach to obtain energy from wet organic waste
Composition of Municipal Solid Waste (MSW) depends on many factors such as climate, geography, population, and also social and economical features of the countries.
Landfilling is the most common solid waste disposal technique in Turkey. Because of increasing population, waste production rates and available organic waste properties, composting is an alternative method for reduction of the amount of waste that will be disposed of in the landfill areas. Due to the high water content (65-85%) of the biodegradable wastes that brings high operational costs because of the fuel requirements, in Turkey, incineration or other thermal methods are not taken into account by the authorities. Furthermore, The Ministry of Environment and Forestry declared that composting is their priority disposal method for biodegradable waste.
The mass balance in the composting facilities shows that almost 65% of the product is screened and removed to be disposed of in the landfill area, because of its improper particle size. On the other hand, when we look at the process, it can easily be seen that the solid waste water content decreases significantly during the composting process. As an initial study, the compost particles with lower water content are used here to produce refuse derived fuel (RDF). A completely closed thermal chamber used for RDF studies under different temperatures and time intervals.
Solid waste samples were collected from Menemen CP for the study. One of the samples was collected from the material received by the fermentation area and the other sample was collected from the material <20 mm which would be sent to landfill area. Both samples were homogenized and 2 kg representing material from each of the samples was placed in composting reactors installed with surrounding water jackets that allow arranging desired temperature in the reactor. The sample from fermentation area was composted aerobically (25ºC) and the sample from the waste smaller than 20 mm was composted anaerobically (35ºC). Aerobic composting was used for material between 40 and 20 mm diameter to simulate fermentation area, while anaerobic composting was preferred for the material smaller than 20 mm to reduce operational costs for the large mass of (296 tons/day) partially processed waste. Aerobic reactor was aerated and mixed on a weekly basis during composting, while anaerobic reactor, which has a valve at the top to remove produced gas, was sealed and opened at the end of the composting time. Both reactors were operated for 40 days.
Both aerobic and anaerobic composting processes decreased the water content and organic matter content of the waste. Lost in water content is higher in aerobic reactor. A slight increase in calorific values of the material is seen after composting. Weight losses recorded for aerobic and anaerobic reactors are 39% and 24%, respectively. Composted materials provided from the reactors then sieved from 15 mm to obtain the samples for RDF study.
RDF reactors with 26 ml internal volume and having circular cross sections used for this study are made of stainless steel and bolted at the two ends. 5 g of composted material was placed into the RDF reactor and the reactor was placed in a muffle furnace after it was sealed. Furnace temperatures of 300ºC and 400ºC were tried at the study with a constant heating time of 30 minutes. At the end of the heating duration the reactors were allowed to cool before they were opened.
Composted waste residues and the anaerobically composted residue from screening from 20 mm are used to produce RDF here. As early inspiring outcomes of the study, thermal processing of this waste in a closed chamber under moderate temperatures was resulted with a product that has calorific value of 2400-3400 kcal/kg dw. The produced gases during the thermal process and their control should be studied in the future as well as extending the study by working many more samples by modifying the thermal chamber.
