Modelling the hydrothermal carbonization of cheese whey wastewater in Lesvos island: an application of the 3-step evolution model

Lesvos island has an extensive dairy production sector, and -at present- eighteen dairy processing facilities are operating. Efficient management of the liquid biowaste effluents has been an issue of interest since the scope is the minimization of the environmental impact. The operating dairy processing facilities have an estimated total production of cheese whey wastewater that exceeds the value of 25 thousand cubic meters annually. Hydrothermal carbonization of cheese whey wastewater can be a viable option for reducing the organic load and at the same time produce hydrochar, which is a material that can be utilized in several downstream processes. Experiments for the hydrothermal carbonization of locally sampled cheese whey wastewater have been performed in a hydrothermal autoclave reactor under subcritical conditions, i.e. 200 – 230 °C and 15- 20 bar. The process has been analyzed by implementing mass balances and by conducting analysis experiments, e.g. COD measurements and conductivity assessment. The main scope of this study is the development of a modelling simulation of the hydrothermal carbonization of cheese whey wastewater for different operating conditions. For this purpose, the novel 3-step evolution model is being used and calibrated for the specific case of cheese whey wastewater. The model performs a series of “char-gas” reactions for the final calculation of the hydrochar. The model reports values of 50% -80% final hydrochar yields depending on the operational conditions and the residence times. The model also has the ability to simulate the produced gaseous products with the biggest fraction, i.e. > 93%, being carbon dioxide. The aim of this study is to identify the effect of operating conditions on the production of hydrochar from cheese whey wastewater by means of hydrothermal carbonization with the goal to potentially develop a small commercial unit in Lesvos.