Biogas : Production of clean compost from mixed MSW

The compostable fraction, consisting of organics and wastepaper/biodegradable plastics, is one of the largest components remaining in the rubbish bin after the recyclables and garden waste have been recovered. Therefore, these compostables represent the largest potential for increasing diversion and recycling. The SORDISEP technology combines dry anaerobic DRANCO digestion with wet refining of the digestate. Wet separation allows for fine screening and wet separation at a level that is not feasible in the conventional dry-composting process. The technology is proven on a large scale and has been running for over five years in the municipal waste processing facility in Bourg-en-Bresse (France). This facility treats about 66,000 metric tonnes of mixed waste and 7,500 metric tonnes of green waste on an annual basis. Due to the implementation of the well-engineered wet separation and clean-up process, this plant is able to produce high-quality compost from mixed household waste. The quality of the end products was assessed and the quality of the compost compared to compost derived from garden and food waste as well as from source-separated organics. It was found that the SORDISEP compost was low in heavy metals, plastics and other manmade impurities. Impurities >2 mm were even lower than the average of 744 samples of compost from source-separated organics. As a consequence, all parameters related to pollutants and impurities are within the range of compost from source-separated collection and well below EU fertiliser standards.

This technique is of particular interest for congested cities and areas with high-rise apartments. Separate organic waste collection becomes obsolete and will result in large savings in overall collection costs. The production of clean compost and recyclable fractions from mixed-waste organics is now feasible and represents a giant leap in the progress towards zero waste.