Valorization of cheese-making residues in biorefineries using different combinations of dark fermentation, hydrothermal carbonization and anaerobic digestion

Dark fermentation (DF), hydrothermal carbonization (HTC) and anaerobic digestion (AD) are applied, in different combinations, to cheese whey (CW), which is the liquid effluent from the precipitation and removal of milk casein during the cheese-making process. The aim and novelty of this research is to investigate the production of various biofuels (H2-rich gas, hydrochar and biogas) in cascade, according to the waste biorefinery concept. The simplest case is the direct AD of CW. The second investigated possibility is the preliminary HTC of CW, producing hydrochar, followed by the AD of the process water from which hydrochar is separated by filtration. The third possibility is based on DF of CW, followed by the AD of the fermentate (F) from DF. The final possibility is based on DF of CW, followed by HTC of the F, and then AD of the process water. Accordingly, the physical and chemical properties of CW, F, resulting hydrochar and process water (PW), and biomethane potentials of CW, F, and process waters are studied to determine the energy and carbon balances of all variants. In brief, the first variant, direct AD of CW, is believed to be the most energy efficient method

Preliminary environmental evaluation of cheese whey biorefinery

An integrated biorefinery process for cheese whey is proposed and evaluated. The cheese whey is fed to a first step of dark fermentation, to produce a biogas mainly composed by hydrogen and carbon dioxide. The biogas is processed by physical/chemical absorption, with the aim of producing an almost pure hydrogen stream for further use. The separated carbon dioxide is stored by the accelerated carbonation of industrial residues. The fermentate, exiting the dark fermentation, still rich in organic contents is fed to hydrothermal carbonization (HTC), producing hydrochar, to be used as biofuel or soil amendant. Basing on some already available laboratory test results, a preliminary environmental evaluation, by Life Cycle Assessment, was performed aimed at highlighting the main contributions of the biorefinery sub-process to the overall value of some selected environmental indicators. Results for Climate Change indicators show that biorefinery system provides negative impact; the main environmental credits come from CO2 storage and HTC process, while DF is the most critical process for the biorefinery supply chain