Pretreatment Doubles Food Waste Throughput of Anaerobic Digesters

Pretreating food waste with a combination of steam and pressure, in a machine known as an autoclave, will double the throughput of an anaerobic digester and significantly reduce the amount of ammonia concentrations by denaturing proteins, according to research by AeroThermal Group.

For the plant operator, this means that by using an autoclave, they can potentially double the throughput of the plant and in doing so, they would double revenues for only a marginal increase in operating costs, since the autoclave uses waste heat from the CHP process.

AeroThermal says this makes for an attractive proposition to food waste AD plant operators, in a market where gate fees continue to fall.

The trials have been run more than 580 days to date.

This increase in performance of the digesters was maximized when the autoclave operated at a temperature of 140oC and the digesters were run at an Organic Loading Rate (ORL) of >5kgVS/m3/day.

The experiments have shown that autoclaving has the effect of producing a feedstock for AD, which allows stable digestion at very high loading rates, without the addition of trace elements that could be harmful to the environment.

The autoclave can easily facilitate the co-processing and blending of different types of waste, since it pasteurizes, homogenizes and hydrolyzes the feedstock in one simple and highly effective process, the researchers say.

Last month a first-of-its-kind anaerobic digester in California began capturing methane from agricultural waste and turning it into clean biogas to power an ethanol facility in Tulare County.