The pre-treatment of wastes requires a number of different processes such as crushing, drying and deodorizing. An innovative hydrothermal pre-treatment system called Resource Recycling System (RRS) had been developed that can perform these three pre-treatment functions in one step using high pressure saturated steam. This technology is characterized by low energy requirements for drying. Figure 1 shows a schematic process flow diagram of the RRS hydrothermal treatment process. Figure 2 shows a photograph of a commercial hospital wastetreatment facility using the RRS technology in Japan. The inner volume of the reactor is 3 cubic meters and this facility can treat 50-60 hospital waste boxes per batch. The average weight of one box is about 7 kg and one batch requires about 4 hours. The facility has been commercially operating for two years.
Solid wastes are fed into the reactor and then saturated steam at a temperature of 2000C and pressure of 2 MPa is supplied into the reactor for about 30 minutes. The blades installed inside the reactor rotate to mix the wastes for about 10 minutes. The product is discharged after extracting steam. The product is a powder-like substance with moisture content similar to that of the raw material but dries easily upon exposure to the surroundings or under the sun. By producing a product that dries easily, the process results in low energy consumption. The product has no bad smell and can be used as liquid and solid organic fertilizer (if the feedstock is sewage sludge or food residue) or solid fuel (if the feedstock is mixed municipal solid wastes or cellulosic biomass such as wood) that can be mixed with coal for power generation or cement production. For the treatment of municipal solid wastes, the RRS technology has significant technical and commercial advantages over conventional incineration technologies since it is virtually emission free (no emission of dioxins, NOx, SOx, dust). The product can be utilized as a solid fuel for co-firing with coal and the capital and operating costs are just half of conventional incinerators. By increasing the pressure of the saturated steam to 2.5MPa, PVC can be converted into a harmless inorganic salt by reaction with the alkaline contents in the waste. Thus there is no chlorine emission or dioxin formation as in the case of conventional incineration.