GB2138797A

GB2138797A - Compact sewage purification plant

Info

Publication number: GB2138797A
Application number: GB08313812A
Authority: GB
Inventors: William Henry Taylor Griffin
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-02-17
Filing date: 1983-05-19
Publication date: 1984-10-31
Also published as: GB8313812D0; GB2138797B

Abstract

The plant comprises two concentric tubes. Sewage is received into an aerated suspension of aerobic biological sludge which may be mixed with circulating sand particles, or circulating through static plastic media, around the annulus. The solids are maintained in suspension by a ring shaped diffuser and the circulation sustained by an air lift. Effluent and sludge pass to the inner tube for settlement and clarified effluent is removed by airlift which buffers hydraulic fluctuations by permitting variable operating levels. The sand particles or plastic media provide support to accommodate high biomass concentrations to reduce the volume of the aeration annulus. A constantly recycled flow from the settlement tube improves the quality of the cesspit liquor. <IMAGE>

Description

SPECIFICATION Compact sewage purification plant I, William Henry Taylor Griffin, of 29, Larkway, Bedford, do hereby declare this in vention and request that a patent be granted to me This invention relates to a compact unit for the biological purification of the settled sew age.

There are many properties which it is im practical or too expensive to connect by public sewer to a public sewage treatment works.

Many of these rely on cesspits or septic tanks for the retention or partial treatment of domestic sewage. The cost of removal of the stored sewage from cesspits is a continuous expense, and the discharge from septic tanks may create a pollution nuisance.

The invention described is designed to fit within the volume of a cesspit serving a single house and to purify the settled contents of the pit biologically to a quality acceptable in local water-courses. The sludge naturally accumulating in the pit will need to be removed, but the frequency of removal will be in the order of one tenth of the frequency of normal cess pit emptying. The invention is also applicable to improving the quality of effluents from septic tanks and by its compact nature will prove a competitive method for the treatment of sewage from larger communities.

For a detailed description I refer to the accompanying drawings: Figure I Sectional Elevation Figure II Sectional Plan Figure III Shows a typical installation within a cesspit.

Referring to the drawings, Fig. I shows a vertical section through the unit which comprises an annular reaction tank (1) fitted with an air lift tube (2). The outer wall has inlet holes (3) of approximately 10 mm diameter arranged in a group.

Around the base of the reaction tank (1) is a finely perforated aeration pipe ring (4).

Near the base of the reaction tank (1) is a perforated diaphragm (5) which locates the airlift (2) and the aeration ring (4) and supports plastic media should this be selected for suporting the biomass.

The inner wall of the annulus forms the settlement zone (6). This wall is suspended above the base of the annulus and the gap created leads to an annular passage (7) between the reaction tank (1) and settlement zone (6). A conical sludge hopper (8) is formed in the base of the settlement zone (6).

Three airlifts are provided: the first (9) lifts from the centre of the sludge hopper (8) and discharges into reaction tank (1). The second (10) has an inlet position determined by the minimum operating level selected and discharges from the unit at a chosen level a little above the maximum operating level. The third airlift (11) lifts from a level approximately 40% up from the base to the minimum operating level and discharges to the cesspit or septic tank.

Fig. II is a sectional plan showing the disposition of the airlifts. Fig. Ill shows a typical installation for a single house (up to 5 persons capacity) with a correspondingly sized unit situated within a cesspit.

The operation of the invention is as follows.

With the unit placed inside a cesspit or septic tank, settled sewage enters the reaction tank (1) through the holes (3). (or if constructed externally to the septic tank, sewage is piped into the reaction tank at the same level as the holes (3).) The reaction tank contains a measured volume of sand (graded 0.3 mm to 0.03 mm) or of plastic media. Air is diffused from the aeration ring (4) to maintain the solids freely in suspension, and air injected into the base of the airlift (2) aerates, mixes and lifts the suspension of settled sewage, biological solids and sand (if used). This mixture is discharged horizontally from the airlift to create a spiralling flow around the reactor annulus (1).In the aerobic conditions thus created an aerobic biological sludge develops which partially clings to the surface of the sand particles or plastic media and the biological purificatiion process becomes established. The relatively slow flow through the unit induced by the airlifts (9) (10) and (11) carries the aerated mixture through the annulus (7) to the settlement zone (6) in which suspended particles settle in the hopper (8) as the water rises more slowly than the settling speed of the sludge to the inlet of the effluent discharge airlift (10).

The size and levels of this airlift are chosen so that a constant rate of air supply regulates the rate of effluent pumped in accordance with the level in the tank. The operating levels are chosen to vary over a range of approximately 0.5 m. This range of depth in the unit is arranged to correspond with a substantial storage capacity in the cesspit or septic tank which adequately buffers the unit from rapid hydraulic fluctuations, enhanced by the gradual and progressive change in discharge rate of the airlift as the levels vary. Combined with the beneficial dilution effect achieved by the recycled effluent from airlift (11) the unit is extremely well protected against shock loads which are the major souce of operational difficulties in small activated sludge plants.

Surplus sludge above the predetermined inlet level is automatically removed from the settlement zone by airlift (11). Sludge from the hopper (8) is returned to the reaction tank (1).

The energy supply is by compressed air line from a remote compressor and no electrical connection to the unit is required.

Claims

1. A biological sewage purification unit with no moving parts which operates with water levels varying substantially and simultaneously on all treatment zones and in which a buffered gravity flow through the succeeding treatment zones is induced by a controlled rate of removal of purified effluent from the final settlement zone.

2. A unit is claimed in (1) in which a high concentration of activated sludge is sustained by the use of a circulating suspension of sand particles or a static bed of plastic media.

3. A unit as claimed in (1) and (2) for full biological treatment of sewage by insertion within the space of a cesspit or septic tank or supplementary to a septic tank or primary sedimentation tank.