Characterisation of food service establishment wastewater and its implication for treatment

Essential for the selection of a reliable treatment system is the characterisation of the effluent to treat. Kitchen wastewater (KWW) from food service establishments (FSEs) is a strong organic and fat-rich effluent whose characterisation has not been sufficiently addressed. KWW composition is highly variable and linked to the FSE's size, the type of meals prepared and the amount of water used during the cleaning. COD, TSS and fat content (FOG) are the most common parameters found in literature. However, other physical and chemical parameters (e.g. temperature, pH, oil droplets characteristics and trace elements), correlated to commercial kitchen cleaning practices rather than the specific effluent, but equally influential on the treatment efficiencies of both physical and biological methods, have hardly been investigated. A comprehensive characterisation of wastewaters from three food service establishments was used to generate data to support the selection of appropriate FOG mitigation methods. Two novel analytical methods were used to quantify the proportion of emulsified FOG and associated droplet size from different kitchen washing effluents. The results showed that more than 90% of the FOG from the dishwasher effluent and around 35% of sink one was emulsified, with droplet sizes less than 100 μm, well below the removal capabilities of conventional grease interceptors, but easily removed using biological means. From the WW composition results, a formula for predictive modelling was derived to represent average organic matter composition for kitchen wastewater as C20H38O10N, applicable in remediation processes. These results offer a good starting point for the design, operation, and optimisation of wastewater treatment systems of oil-rich KWW.