A multi-waste management concept as a basis towards a circular economy model

This study proposes the use of a waste management procedure based on the technical development and practical implementation of a “Multi-Waste Plant” concept. A final point of this model is to reduce the costs related to waste treatment processes, thus optimizing its management, from the ecological viewpoint, as well as from the money related perspective. To this end, it is proposed: 1. Treatment, in the same facility, of various types of waste: municipal, industrial, biomass; 2. Energy and mass integration of individual waste treatment processes (anaerobic digestion and pyrolysis) to obtain a single integrated process more economical; 3. Complete recuperation of waste as energy (biogas, syngas and carbon pellets) and slow-release fertilizers (struvite). As a result, stable codigestion of a mix of poultry manure, pig manure, and vegetable waste (40/40/20 w/w) was achieved in a two-phase biodigester with production of biogas (65%CH4, energy content 6.5kWhm−3) and non-harmful digestate with phytotoxicity less than 25 Equitoxm−3, later transformed in struvite fertilizer with up to 95,4% of nutrients recovery. In parallel, the pyrolysis of a mix of organic fraction, waste biomass, plastic waste and other industrial waste (15/15/50/20 w/w) at 420-450°C produced non-condensable gas (86.2%, LHV 8.5kWhm−3), char (9%) and a liquid phase (4.8%). A Pinch analysis reveals that an energy integration process in the plant will make possible to cover energy needs of the whole facility. The “Multi-Waste Plant” concept along these lines turns into an unmistakable example of the circular economy model.