THERMOCOMPOSTING: AN ALTERNATIVE WAY TO PRODUCE RENEWABLE HEATING FOR BUILDINGS IN DECENTRALIZED COMMUNITIES

The problems related with energy production and the increasingly higher energy demand, triggered the development of alternative and renewable energy sources for both economic and environmental reasons (Motora et al., 2020). There are various types of renewable energy sources available such as solar energy, wind energy, hydropower and biomass energy. Out of these sources, residual biomass, combined to waste management, represents an abundant and potentially sustainable source of energy. The renewable energy derived from biomass, can be called “bioenergy” (Dahiya, 2015). Bioenergy from residual biomasses is an interesting solution that allows to combine appropriate waste management strategies with energy generation, and this was the topic of the present PhD. Aerobic biodegradation of biomasses, most commonly known as composting process, is capable of releasing a consistent amount of heat, since microbial respiration of organic molecules is a strongly exothermal process (Zhao et al., 2017). This heat, when biomass residues are left on the ground, is usually dispersed into the environment, missing a great opportunity to recover renewable energy but through the implementation of innovative domestic scale systems, it can be recovered and used. Such systems are known in literature as Compost Heat Recovery Systems (CHRSs), Biomeiler, Thermo-composts (THC), or Compost Heaters (CHs). The recovered heat can power Underfloor Heating Systems (UHS) and/or Sanitary Hot Water Systems (SHWS). Traditionally, CHRSs mainly exploit residual biomasses resulting from forestry or agricultural activities, and they are employed to heat the water used in UHS, in rural or decentralized areas. These systems present several advantages, since they can be low-tech, sustainable and cost-efficient solutions of exploiting naturally available resources. Even though the recovery of energy from composting process has a long history, dating back to hotbeds systems used in ancient China 2000 years ago (Brown, 2014), these systems still present some limits. Their limits are mainly related to two aspects: on one side, once the biodegradation of the residual biomass used to feed the plant ends and the material has become mature compost, the operating time of the plant ends and the system must undergo a dismantling and reconstruction phase that requires time and money. On the other side, the volumetric thermal power generated per unit of volume of organic substance is quite low compared with the efficiencies of other domestic thermal energy plants. The overall objective of the present PhD research was to study and optimize traditional Compost Heat Recovery Systems, starting from the evaluation of the traditional CHRS configuration, passing through the study and implementation of possible technological optimizations, reaching a final saleable product to be brought on the market of domestic thermal energy plants. The evaluation of traditional CHRS configuration and functioning was performed through literature data collection and from the collection and processing of data from full-scale traditional plants built and monitored. Comparative analysis were performed between traditional CHRSs and other heating systems, proving that implementing a CHRSs is beneficial under both economic and environmental points of view. The research about possible CHRS optimizations was performed through experimental activities carried out at laboratory scale, pilot scale and full-scale and gave good results, that will be used for the filing of a patent about optimized CHRSs. Throughout the whole PhD course, CHRSs were re-discovered through innovative technological solutions that will be used for filing a patent in the near future, containing the optimizations studied. The patent will be necessary to achieve the final overall objective of the present research: to bring the optimized CHRS on the market of sustainable domestic heating systems.