Recovery of essential nutrients from municipal solid waste - Impact of waste management infrastructure and governance aspects

Every year 120-140. million tonnes of bio-waste are generated in Europe, most of which is landfilled, incinerated or stabilized and used as covering material in landfill operation. None of these practices enables the recovery of essential nutrients such as phosphorus (P) and nitrogen (N), which are in great demand for agricultural production. Recovery of these nutrients is a matter of international concern considering the non-renewable nature of P sources and the energy intensive production process required for the synthesis of N fertilizers. The objective of this research is to understand the relation between the municipal solid waste management (MSWM) system, both its the physical components and governance aspects, and the recovery of nutrients in Vitoria-Gasteiz (Basque Country) as a benchmark for European medium-size cities. The analysis shows that the existing physical infrastructure and facilities for bio-waste have high potential for nutrient recovery, 49% for N and 83% for P contained in bio-waste. However, governance aspects of the MSWM system such as legislation and user inclusivity play an important role and decrease the actual nutrient recovery to 3.4% and 7.4% for N and P respectively

A Biowaste Treatment Technology Assessment in Malawi

In the city of Blantyre, much of the generated municipal waste is biowaste, typically mixed with other waste fractions and disposed at the city’s dumpsite. Energy and nutrients could be recovered; however, with many biowaste options available, choosing what technology to implement is difficult. Selecting Organic Waste Treatment Technology (SOWATT) is a tool that supports decision making for selecting a biowaste treatment option considering social, technical, and environmental aspects. SOWATT was used to evaluate options for Blantyre’s Limbe Market. Anaerobic digestion, black soldier fly processing, slow pyrolysis, in-vessel composting, windrow composting, vermicomposting, and wet-biomass-briquetting were considered as options. The performance of each alternative was assessed based on five objectives by government, NGO, and market-based stakeholders in order to determine the most acceptable option for the greatest number of people: something that is rarely done, or if it is the preferences are not rigorously quantified (e.g., stakeholder workshops) and/or weighted against specific objectives. However, given the novelty of the ranking-solicitation process, some participants struggled with the variety of options presented, and further iterations of SOWATT will address this limitation. Ultimately, vermicomposting scored highest of all alternatives and could best achieve the five objectives as prioritized by the stakeholders when implemented

Improving the energy-related aspects of biowaste treatment in an experimental hydrothermal carbonization reactor

Hydrothermal carbonization (HTC) is a thermochemical conversion process with the potential to treat the prevalent wet urban biowaste in low- and middle-income countries. The generated hydrochar solids are a hygienic, homogenized, carbon rich and energy dense product with economic value that can be used as an alternative to wood-based charcoal or fossil fuel. Obtaining a satisfactory energy efficiency of the process is, however, one of the prerequisites for the possible breakthrough of this technology. In an experimental HTC reactor, a model kitchen/market waste feedstock (17.8 MJ/kgdb) was hydrothermally carbonized with varying loading rates (TS 20 and 25%) under mild operational conditions with peak temperatures of 160-190°C and process times of 2-10 h above 160°C. The aim was to evaluate the energy ratio of the process under these conditions while examining the impact on the hydrochar quality. Results show that the chemical properties of the produced hydrochar and its heating value were of moderate quality (21.1-24.4 MJ/kgdb), showing similar characteristics like torrefied products. HTC of a 25% TS-load during 2 h at 180 °C and maximum pressure of 18.3 bar resulted in a char chemical output energy that is twice as high as the electrical energy consumed in the process. If considering the theoretical methane potential of the process water, the energy ratio could be increased to 2.6; while reactor insulation could further enhance this ratio to 3. This article reveals the merits of mild HTC and provides relevant knowledge for attaining an optimized, energy efficient HTC system