Recycling agricultural waste

Pigs are able to utilize only 50% of the feed they consume, the rest of which is returned as waste. In management terms this is considered a poor return on investment as well as poor use of resources.

The Berrybank Farm piggery in Victoria, Australia, produces a daily average of 275,000 liters of sewage effluent with an organic solids content of approximately 2%. This compares to the sewage output of a town with a population of about 50,000 people. The waste management system developed at Berrybank Farm recovers all the waste and transforms it into various by-products that can be used on the farm, such as flush water for farming, gas for electricity, and fertilizer. The system is a seven stage process comprised of (1) automatic continuous collection; (2) grit removal; (3) slurry thickening; (4) primary digestion; (5) secondary digestion; (6) biogas purification; and (7) a co-generation thermic plant. Initiated in 1989, the waste management process of Berrybank Farm started producing electricity in 1991. Each day the farm recovers: approximately 7 tons of waste solids at 35% dry matter, to be used as fertilizer; 100,000 liters of recyclable water; 100,000 liters of mineralized water, used as fertilizer; and, 1,700 cubic meters of biogas, able to run a co-generation electricity program with a daily output of 2,900 kW of electricity.