Analysis of greenhouse gas emission reductions by collaboratively updating equipment in sewage treatment and municipal solid waste incineration plants

An analysis of energy balance and greenhouse gas emissions was conducted to compare alternative systems for the disposal and recycling of sewage sludge and food waste. Although the conversion of dewatered sludge to solid fuel has been a recent research focus, it is difficult to ensure that the solid fuel is needed and can be delivered to plants that can use it, such as coal-fired power plants. We therefore evaluated the effects of introducing various collaborative systems when updating existing sewage treatment plants and municipal solid waste incineration plants in Japan. Several cases were proposed and compared with a base case. In case Y, low-temperature carbonization equipment is introduced into a sludge conversion plant and dewatered sludge is converted into solid fuel. In case Z, dewatered sludge is dried to a moisture content of 40% with useable steam heat in a municipal solid waste incineration plant; the dried sludge is then combusted with municipal solid waste. Relative to the base case, greenhouse gas emissions were reduced by 25% in case Y and 26% in case Z. Therefore, a similar level of greenhouse gas reduction can be achieved by introducing a co-combustion system in a municipal solid waste incineration plant, even if there is no production of solid fuel to use in collaboration with coal-fired power plants.