The impact of nitrogen control strategies and of biopackaging degradation on the implementation of the anaerobic digestion of selected MSW fractions

Anaerobic digestion (AD) offers a sustainable route to resource recovery from management of municipal solid waste (MSW) in the form of biogas as a renewable fuel and digestate as source of plant nutrients. The thesis presents set of papers describing work carried out to investigate some specific issues in AD of some selected fraction of the municipal solid waste stream, such as source segregated food waste (SSFW), compostable bioplastics present in SSFW streams and residual MSW. Highlights include: The first long-term comparative study of thermophilic and mesophilic digestion of source segregated domestic food waste in a parallel trial supported by compositional analysis and stability and performance data, which identifies the ammonia inhibition thresholds in these conditions. The first demonstration of stable thermophilic operation with an undiluted SSFW substrate, using biogas stripping to control digestate ammonia concentrations below the inhibitory threshold. The first reported study on co-digestion of FW and card packaging with a range of compostable bioplastics. The results provide performance data and indicate that plastics degradation performance may be less good than expected. The study is also the first to note that the physical operating parameters of the digester may influence the retention time of plastic materials, and to highlight the potential effects of plastic density (floating and sinking). The first reported study on residual MSW degradation with feed addition and removal designed to simulate practice in a commercial AD plant that is facing the issue of low OLR. The addition of sewage sludge digestate as a co-substrate provided a novel and effective solution. Keywords: Anaerobic digestion; source segregated domestic food waste; ammonia inhibition; side-stream stripping; compostable bioplastics; residual municipal solid waste