Secondary sewage treatment system

Claim 1

A process for secondarily treating waste water liquor containing food preparation wastes from which waste solids have been settled out comprising the steps of providing a vertical waste water treatment region having an upper turbulent zone, an intermediate mixing zone, a lower settling zone, and a bottom sludge-collecting zone below said settling zone, each extending across the region with said settling zone and said sludge-collecting zone occupying a major portion of said region; providing a plurality of vertical aerating zones extending through said mixing zone and being in fluid communication with the bottom of said mixing zone and with said turbulent zone; providing a barrier between said turbulent and mixing zones to retain a bouyant media within said mixing zone and prevent such bouyant media from escaping into said turbulent zone; providing a bouyant media in sufficient volume to substantially fill said mixing zone; introducing waste water liquor into said treatment region in said turbulent zone to fill said treatment region up to and including said turbulent zone, and to float said bouyant media into occupancy of said mixing zone, beneath said barrier; introducing air into said aerating zones in sufficient quantity to create a pumping effect of a magnitude that will continuously draw waste liquor from the bottom of said mixing zone, aerate the withdrawn waste liquor portion and expel the aerated portion into said turbulent zone with sufficient force to create turbulence within said turbulent zone, and that will cause waste liquor to pass through said barrier and into and gently downwardly through said mixing zone whereby aerobic microbial growth on said bouyant media will be established; regulating air introduction into said aerating zones to establish a non-turbulent flow rate of waste liquor through said mixing zone sufficient to enable said bouyant media to be self-cleaning but insuffient to wash said microbial growth off said bouyant media; permitting treated waste liquor to settle from said mixing zone into said settling zone in the absence of aeration below said mixing zone; permitting waste liquor portions to settle out from said settling zone into said sludge-collecting zone in the absence of aeration; and drawing off treated waste liquor from within said settling zone.