Food waste (FW) management is an important issue in Hong Kong. An alternative to the current management system is needed to achieve sustainable FW treatment. Food waste disposer (FWD) has been proven is proved viable to divert FW away from the solid waste treatment stream to the wastewater treatment stream. This study comprehensively investigated the impacts of the use of FWD on greenhouse gas (GHG) emission and energy recovery potentials.

In the first phase of the study, household food waste (HFW) was sampled from three residential areas in Hong Kong and analyzed in the laboratory. Results showed little temporal and spatial variation in physical characteristics; however, large fluctuations in chemical characteristics were observed. Moreover, over 50% of COD, nitrogen and phosp...[ Read more ]

Food waste (FW) management is an important issue in Hong Kong. An alternative to the current management system is needed to achieve sustainable FW treatment. Food waste disposer (FWD) has been proven is proved viable to divert FW away from the solid waste treatment stream to the wastewater treatment stream. This study comprehensively investigated the impacts of the use of FWD on greenhouse gas (GHG) emission and energy recovery potentials.

In the first phase of the study, household food waste (HFW) was sampled from three residential areas in Hong Kong and analyzed in the laboratory. Results showed little temporal and spatial variation in physical characteristics; however, large fluctuations in chemical characteristics were observed. Moreover, over 50% of COD, nitrogen and phosphorus were released into soluble phase after FWD treatment. The results of these analyses suggest that COD in HFW may have a much higher influence on WWTP effluent quality compared with nitrogen and phosphorus in HFW after the use of FWD. The results also indicated increase of COD/TN and COD/TN ratios which should facilitate the biological nutrient removal in biological wastewater treatment facilities.

In the second phase of the study, based on the characteristics of local FW, a plant-wide steady state mathematical model was employed to comprehensively assess the potential overall impact of adding FW to the wastewater entering WWTPs. Given the combined influent characteristics of FW and WW, the effluent quality of WWTPs was not affected significantly in terms of COD and nitrogen. The use of FWD could produce substantial amounts of primary sludge and waste activated sludge in WWTPs. Methane production was dramatically improved with primary sludge as the main contributor. The surplus aeration required for treating the organic loading from the FW addition did, however, increase energy consumption. The overall energy balance was estimated to be positive with increased energy generation from the FW addition.

To advance the knowledge about the use of FWD for FW management, two FW treatment scenarios were compared in third phase of the study. To compare the pros and cons of these two FW treatment methods, life cycle assessment (LCA) was used to evaluate environmental performances from GHG generation and energy consumption perspectives. The results show that the use of FWD is significantly more environmentally friendly than landfilling. Using FWD (i.e., grinding food waste and diverting it into the wastewater stream) generates 50% less GHG and consumes 20% less energy compared with landfilling. The main reason is the increased methane recovery efficiency in aerobic digestion in WWTP with the use of FWD. When FW is sent to a landfill, methane produced escapes to the air; there is no methane recovery technique. The subprocess with high methane recovery ratio will both significantly decrease GHG emission and increase energy recovery. This work implies the potential installation of FWD, this integrated FW treatment method is not only mature in the technology, but also more environmentally friendly.