Potential of methane production by co-digestion of food waste with saline sludge produced from sewage receiving seawater toilet flushing was investigated to determine its suitability for food waste management in Hong Kong by making use of excess design capacity of sludge digesters. High salinity of saline sludge (12.8 mS/cm) affected degradation of organic compounds resulting in an increase in sCOD by 135% as compared to an increase by 283% in treatments with non-saline sludge (4.2 mS/cm) co-digestion. This inhibitory effect was also evident by lower VS removal efficiency of 32.65% for saline versus 54.23% for non-saline sludge based co-digestion. Furthermore, non-saline sludge gave a 3.4-fold higher methane yield than saline sludge co-digestion. It is concluded that co-digestion of food waste with both sludges could be adopted as a potential strategy to make use of excess digestion capacity of existing wastewater treatment facilities but is more viable for non-saline sludge.