Fig. 1

A Experimental set-up: double-walled reactors (1) with a volume of 5 l each. Each reactor was filled through an input port (2), and acidified hydrolysate was removed through a port at the bottom (3). For heating, a water pipe was connected to the input (9) and output (10) ports of the double-wall clearance. Water was heated using a thermostat (6). The gas produced was measured by a MilliGascounter (5), connected to a tube (4), and stored in a gas bag (7). The time-resolved gas production was recorded with an Arduino (8) connected to the gas counter. B Average incubation time for heat shock up to a minimum of 80 °C for pre-treatment with oven (set to 130 °C) and microwave (set to 1000 W). C Substrate variation tests: Comparison of hydrogen production with sucrose, mixed rye bread, gelatine and coconut oil as feeding substrates and sewage sludge as inoculum. Both control and heat shock (oven and microwave) scenarios were tested