A passive continuous flow pasteurisation process designed for solar application. Part I: Indoor experiments for thermal characterization and bacteria inactivation

Abstract

Within the framework of the WHO's universal sanitation policy, water disinfection processes with low manufacturing and maintenance costs must be developed. This is the case with solar pasteurisation, the effectiveness of which, at 50–70 °C, has been already demonstrated in the literature. To be fully acceptable, the process must be appropriately energy efficient and be able to adapt to natural fluctuations in solar radiation. An experimental indoor test platform under controlled conditions, with thermal powers supplied similar to those of a future solar application with a standard thermal panel, was designed. Experimental results highlighted the specific thermal energy consumption (SECtherm), which is highly dependent on the effectiveness of a deliberately oversized heat recovery exchanger. The operation under both stationary and dynamic regimes underscored the role of the thermostatic valve which autonomously calibrated the flow of the fluid according to the injected available power. For the temperature range sufficient to inactivate microorganisms [50–70 °C], the specific thermal energy consumption reached values between 3.5 and 6 kWhtherm.m−3. The bacterial indicators, Escherichia coli and Enteroccocus, currently present in surface waters in the south of France, were no longer detected (<10 MPN.100 mL−1) after one-minute of pasteurisation at 55 °C and 60 °C, respectively.