The characteristics of household food waste in Hong Kong and their implications for sewage quality and energy recovery

Food waste (FW) is a worldwide environmental issue due to its huge production amount. FW separation from municipal solid waste followed by different treatment strategies has been widely accepted. Food waste disposer (FWD) is a promising approach to separate and collect household food waste (HFW), which has been widely applied in many countries. However, the feasibility of FWD application in many countries is still being debated due to the major concerns over the impact of FWD on the wastewater treatment plants. In order to investigate the feasibility of FWD application, FW characterization is a key work to be conducted in advance. Since the FW characteristics largely vary by region, reliable and representative FW characteristics in different countries should be investigated. To provide such information for further studies on FW management for Hong Kong, HFW was collected from Hong Kong typical households over one year and analyzed systemically in this study. The FW composition varied little from place to place or season to season, and the values observed were comparable with results reported from other countries and regions. Based on the reliable HFW characteristics obtained from one-year survey coupled with statistical analysis, simulated HFW for Hong Kong consisting of 50% fruits, 20% vegetables, 20% starchy food and 10% meat was proposed for future studies. On the other hand, the FWD treatment caused more than 50% of the biodegradable organic content in HFW to dissolve. With a ratio of 1 g food waste to 1 L sewage, total solids in the wastewater stream were predicted to increase by 73%, total chemical oxygen demand by 61%, soluble chemical oxygen demand by 110%, nitrogen by 6% and phosphorus by 16%. Theoretically, 22 million m³/year of additional methane could be generated if 50% of Hong Kong residential buildings equipped with FWD. That would certainly increase pollutant loading on the wastewater treatment plants, but also energy recovery potential.