Treatment of volatile organic substances at waste water treatment plants

Claim 1

In a method for purifying industrial waste effluent including both waste water and off-gases containing volatile organic solvents by an aerobic biological waste water treatment system containing an aerobic treatment zone comprising a mixture of biologically active solids and activated carbon for treating the waste water, which involves subjecting the industrial waste water to a primary treatment to at least adjust the pH of the industrial waste water and remove the solids therefrom, subjecting the thus treated waste water to treatment in an aerobic biological treatment zone, supplying the biological treated waste water to a separation zone to separate the sludge produced in the aerobic treatment zone from the waste water to purify the waste water, transferring at least a portion of this sludge to an aerobic digesting zone, wherein the sludge is reduced in volume by action of aerobic microorganisms located therein, the improvement comprising concurrently collecting the off-gases containing volatile organic solvents in the industrial waste water primary treatment system, directing the thus collected off-gases to either the aerobic treatment zone or the aerobic digesting zone or to both the aerobic treatment zone and the aerobic digesting zone to biologically degrade and substantially eliminate the volatile organic solvents in the off-gases.