Abstract: A treatment vessel (10) for a waste water treatment process system. The vessel (10) including a first section (12) and a second section (14). The first section (12) has a substantially constant first cross sectional area and is adapted for housing a granulated aerated charcoal biofilter material. The second section (14) has a substantially constant second cross sectional area, is below the first section (12) and is in fluid communication with the first section (12). The second section (14) is adapted for housing a sand filter material. The second cross sectional area is about 30 to 70% of the first cross sectional area.

Abstract: An aerated biological filtration system (10) for treating waste water includes a treatment vessel (11) of elongated configuration which incorporates a circulating filter bed (23) and a static filter bed (24). The circulating filter bed incorporate a particulate material such as granulated activated carbon having a specific gravity in the range of 1.2 to 1.4 and effective size of 0.6 mm to 1.5 mm. The circulating filter bed is disposed above the static filter bed and an aeration system (27) is disposed between the filter beds. The aeration system is arranged to diffuse air through the circulating bed either continuously or intermittently so as to provide oxygen to micro-organisms attaching to the particulate material and to cause slow circulation of that particulate material. The system has particular application for domestic recycling of grey water.