West Coast supermarket chain Ralph’s uses leftover fruit and expired meat and milk from its stores to keep generate electricity. The closed-loop system, to which it is referred, was developed by the Boston start-up Feed Resource Recovery and offsets more than 20% of Ralph’s Compton, CA distribution center’s energy demands.
In Ralph’s distribution center that it shares with its Kroger Co. subsidiary Food 4 Less, rerouted food waste is used to power the facility’s energy grid. Kroger believes it is the first supermarket to both cut down on food waste and use alternative energy.
An anerobic digester system grinds the waste, pulverizes it, and sends it to a pulping machine. The machine then filters out inorganic materials – glass, metal, etc. – and creates a sludgy substance by mixing in hot wastewater from a nearby dairy creamery.
Then, mulch is added to a 250,000 gallon staging tank with the sludge and is slowly fed into a 2-million-gallon silo. The inside of the silo contains no oxygen, enabling bacteria to quickly attack the liquid refuse thereby converting it into methane gas. The methane then rises to the top of the tank and is siphoned out to power three turbine engines at the facility.
Experts note that the 13 million kilowatt-hours of electricity produced annually could power more than 2,000 California homes over the same period.
The leftover sludge is used as nutrient-rich fertilizer, and enough is produced for use on 8,000 acres of soil.