Patent ID: 7785469

Claim:
An aerated biological filtration system for treating waste water, the system comprising: a treatment vessel through which waste water to be treated will pass, said treatment vessel having an upper inlet and a lower outlet; a circulating filter bed located in said treatment vessel between the inlet and the outlet, said circulating filter bed being arranged to trap solids from the waste water within said bed and comprising of a particulate filter material having a specific gravity of greater than 1, individual particles having a surface or pore structure selected or adapted to facilitate the attachment of micro-organisms on said particles; and aeration means adapted to diffuse air countercurrently through said filter bed either continuously or intermittently whilst waste water is being treated in said filter bed; wherein the structure and the operating characteristics of the treatment vessel, the circulating filter bed and the aeration means are selected such that the particles are able to move relative to each other within the circulating filter bed; and operation of the filtration system will cause a substantial portion of the particulate material to circulate within the circulating filter bed over time to promote distribution of the trapped solids within said bed.