Optimizing municipal biodegradable waste management system to increase biogas output and nutrient recovery: a case study in Lithuania

Abstract

Despite large investments to modern centralised mixed municipal waste (MMW) management plants (mechanical biological treatment (MBT)), environmental impact has been decreased less than was expected due to several determined reasons in Lithuania. Energy consumption for MMW management exceeds production volume of alternative energy in municipal biodegradable waste (BDW) fermentation equipment. Produced “technical compost” does not correspond to the requirements for contamination and quality of compost to be used in agriculture and can be used only as a stabilate for overlay of landfill layer and landfill restoration. This article presents the results of optimization possibilities of municipal BDW management in one of the Lithuanian regions. A few alternatives were suggested, but the source separation of municipal BDW from individual household was selected for implementation as the best available alternative for the target region from a technical, environmental, and economic point of view. The results of the carried out experiment with the source separation of municipal BDW and processing in the tunnel of the existing MBT plant have shown that biogas output can increase up to 114 m3 per tonne of the municipal BDW. This approach would allow increasing alternative energy production in MBT plant by 4.9 times and producing compost instead of the stabilate. In case of the target region, overall alternative energy production would exceed energy demand (including for BDW transportation), by over 7 thousand GJ per year. Thus GHGs (without biogenic CO2) would decrease by approximately 600 tonnes per year.