Green energy from chicken waste

Technology to reduce retention times

Food processing and other organic waste streams are often high in energy potential and produced in significant quantities. Trade waste is an expense and green credentials are gaining importance in the eyes of the consumer.

Anaerobic digestion is an appropriate technology to recover water and energy, however, extended retention times, often as long as 24 days, can be a major problem where space is at a premium and storage of millions of litres of waste material simply not feasible. Disposal of sludge is a further cost.

Recognising not only the potential of energy and water recovery from organic waste but also the limitations of current technology, Active Research has introduced technology to reduce retention times to hours rather than days. At the same time making the digestion of product, often regarded as difficult, suitable for digestion. For example, offal and wastewater produced as a by-product of poultry processing can be economically converted to biogas for further conversion to electrical and thermal energy in an environmentally sound manner.

Technology improvements include the use of ultrasound to lyses cells leading to reduced retention time, reduced sludge generation and additional gas generation. Fixed-film technology minimises washout of methanogens from the reactor.

A trial recently undertaken over a period of six weeks using the Active Research pilot plant at a Melbourne-based chicken processing plant demonstrated the potential for the host company to become almost self sufficient in electrical and thermal energy requirements. Potentially, the recovered energy may lead to the replacement of a propane-fired boiler.

The pilot plant with an onboard high-rate, fixed-film anaerobic digester using ultrasound as part of the influent preparation process was used. The reactor is of 3000 L capacity, constant stir and heated.

Initial results clearly demonstrated the capability of the technology used to digest the influent - viscera, blood, fat, heads, feet and factory wash water to produce high-quality biogas (73% methane) and water for re-use. Retention time was 48 h on establishment and development of the microbial population. This time lag will reduce further as the microbial population increases.

The trial demonstrated 2670 m³ methane would be produced daily from an influent input of only 10 tonnes of by-product and 120 kL factory wash water. As an indicator of the dollar value of the gas, it would be sufficient to power a cogeneration plant producing 200 kW/h electricity plus 240 kW thermal energy 24 hours per day. Taken over 300 days per annum this equals 1440 MWh at roughly $120.00/MWh plus the value of RECs.

Added to this is the value of the thermal energy produced and trade waste cost reduction, compared to no financial benefit as is currently the case. Suspended solids in discharge water were reduced from 2100 mg/L to <200 mg/L and BOD from 1900 mg/L to <300 mg/L.

Payback on a full-scale facility is estimated at 2½-3 years.