WO1992008676A1

WO1992008676A1 - Waste water treatment plant

Info

Publication number: WO1992008676A1
Application number: PCT/GB1991/001991
Authority: WO
Inventors: Geoffrey Harold Jensen; Michael Ian Robert Smith
Original assignee: Klargester Environmental Engineering Limited; G.H. Jensen Ltd.
Priority date: 1990-11-14
Filing date: 1991-11-12
Publication date: 1992-05-29
Also published as: GB9024724D0; AU8928491A

Abstract

Waste water treatment plant has a tank (10) with a bulbous lower portion (12) divided into upper (22) and lower (24) chambers by a partition (20). Waste water to be treated enters the lower chamber (24) via an inlet (28) and leaves the upper chamber via an outlet (44). While in the tank, the waste water is cycled periodically through biomass on plates (40) in the upper chamber (22) by injecting air from a blower (36) into the lower chamber to contact further biomass located on plates (34) therein.

Description

WASTE WATER TREATMENT PLANT

Field of the Invention

1. Technical Field

This invention relates to waste water treatment plant and is particularly, but not exclusively, concerned with sewage treatment plant contained in a tank suitable for installation below ground for a single dwelling or for a small community of dwellings as a substitute for a cesspool or septic tank used where a main sewage drainage system is not available.

2. Background Art

A cesspool^' is generally unsatisfactory and its use involves several problems and disadvantages, including a tendency to generate odours, to pollute the surroundings if it overflows and the- need for regular emptying (e.g. by a road vehicle). A septic tank is liable to cause pollution when it is installed in an area where the ground conditions are not suitable. People living in areas where sewage drainage via a main is not available, have a need for an improved form of apparatus for the treatment of sewage. The present invention provides a way of meeting this need.

The invention makes use of a tidal flow concept of sewage treatment disclosed in the specification of European Patent Application 0326731 by virtue of which biomass support means is alternately contacted by liquid sewage and by gas by a periodic artificial raising and lowering of the level of the free surface of a body of liquid sewage (-i.e. creation of artificial "tides").

Summary of the Invention According to this invention waste water treatment plant comprises a tank containing a partition dividing the tank into upper and lower chambers, means to feed waste water containing organic contaminants to the lower chamber, means to allow waste water to flow from the lower chamber to the upper chamber and means to allow treated water to flow out of the tank from the upper chamber, characterised in that the tank has a bulbous lower portion and a narrower neck leading to an openable upper end, the bulbous lower portion being divided into said upper and lower chambers, biomass support means in each of the upper and lower chambers , and means to periodically create a volume of gas below the partition in the lower chamber, whereby the biomass support means therein are alternately contacted by liquid and by gas.

Conveniently the partition is shaped to create an annular volume of gas in the lower chamber. Suitably the means to feed waste water to the lower chamber, includes an inlet tube which extends downwardly into the bulbous portion through the neck. The inlet tube suitably includes a screen (e.g. a basket)- to collect non-biodegradable articles that may enter the tank with the waste water.

Desirably, the means to create the volume of gas is an electrically powered air blower which may be mounted on the neck, to one side of the neck or any other convenient location where the possibility of flooding is remote. The air blower or the like feeds its output air down through the partition into the lower chamber. The output from such a blower can be used to agitate material trapped on an inlet screen to prevent clogging of the latter between screen- cleaning operations.

The upper chamber may include filter media which, in a liquid flow direction, are located downstream of the biomass support means in the upper chamber. The means to allow treated water to flow out of the tank can be a weir- controlled outlet upstream of such filter media.

The effect of the periodic creation of a volume of gas in the lower chamber causes the liquid level in the upper chamber to rise and fall whereby the biomass support means in the lower chamber can be increasingly located in gas as the biomass support means in the upper chamber is increas- ingly located in liquid, and vice versa. By this process pollutants in the liquid to be treated are adsorbed and absorbed into the biomass supported on the support means and then oxidised to reduce pollutants to harmless substances and plant nutrients. Further by cultivating facultative organisms and denitrifiers on one (or part of one) biomass support means it is possible to effect a degree of denitrification as part of the waste water treatment performed in the tank. Humus sludge that collects in the tank can be recirculated for further oxidation so that during periods of no or low inflow of fresh pollutants, endogenous respiration of the total biomass occurs, hence reducing total sludge production.

Each biomass support means preferably comprises a plurality of upright or inclined contactor plates of corrugated, or dimpled or other raised surfaces. The plates are suitably situated so that they form a large number of upright or inclined channels by alternate reversal of the plates or other displacement that ensures the plates touch at high points only. Such contactor plates are preferably made from polypropylene or other suitable material, vacuum formed or pressed to the desired shape, so that when they are joined together they form a mesh struc¬ ture of sufficient strength to resist the forces caused by the movement of liquid through the structure and the weight of biomass adhering on the plates. Alternatively the biomass support means could be formed from random or regular polymer fibres or strands between 1 and 3000 microns diameter with a percentage of voids between the fibres in excess of 90% by volume. The layers should be disposed substantially vertically to allow drainage.

Conveniently, the upper chamber contains an outer ring of biomass support means and an inner annular core of filter media forming the final stage of water treatment for the liquid passing through the tank. The annular core can be arranged so that the liquid path through the filter media is an inwardly directed spiral path. A non-return valve can be located in the partition allowing flow down from the filter region back into the lower chamber but not upward flow from the lower chamber directly into the filter region.

Brief Description of Drawings

Two embodiments of waste water treatment plant in accordance with this invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a sectional side elevation of a first embodiment of plant according to the invention,

Figure 2 is a horizontal section on the line A - A of Figure 1,

Figure 3 is a horizontal section on the line B - B of - Figure 1,

Figure 4 is a sectional side elevation of a second embodiment of plant according to the invention, and

Figure 5 is a section on the line A - A of Figure 4.

Description of Preferred Embodiments Figures 1 to 3 show a sewage treatment plant based on a single tank 10 (e.g. of glass-reinforced plastics mater¬ ial) having a bulbous lower portion 12 and a narrower neck 14 leading to an upper end 16. The tank is designed to be buried in the ground to the level of the upper end 16 which will be closed by a removable lid 18.

A partition 20 divides the interior of the tank 10 into an upper chamber 22 and a lower chamber 24.

An inlet tube 26 passes through the partition 20 and creates annular treatment zones in both chambers 22 and 24. The tube 26 connects to an inlet pipe 28 so that raw sewage can flow down (via a removable screening basket 30) to the lowermost part of the tank 10 where a settled humus zone 32 is formed.

Surrounding the tube 26 in the lower chamber 24 is an array of biomass support plates 34. In known manner, these plates are colonised by soil bacteria and other microor¬ ganisms that breed by feeding on the pollutants in the sewage entering the plant forming biomass that purifies the sewage .

An air blower 36 is periodically operated to feed air into the lower chamber via pipes 38 and optionally also (via a pipe not shown) to the basket 30.

The upper chamber 22 is divided into two zones. An outer zone 23 contains an array of biomass support plates 40 and an inner zone 25 contains an annular mass of filter media 42. An outlet 44 from the tank leads from an upper part of the zone 25 containing the media 42.

Interconnection between the lower and upper chambers 24, 22 is via an annular passage 27 and communication between the zones 23 and 25 is via openings in an upper part of an outer .wall of the zone 25 and wall ducts 29 lining the perimeter of zone 25. Non-return valves 50 (e.g. lengths of lay-flat tubing) permit flow down from the lower part of the inner zone 25 to the lower chamber.

The plant operates as follows:

After screening the raw sewage for non-degradable coarse material in the basket 30, the sewage enters the lower chamber 24 via the humus zone 32. In commissioning, the tank is filled with liquid to above the partition 20. Thus when the blower 36 operates air collects below the partition 20 in the form of a growing annular bubble. The creation of the bubble puts the upper parts of the plates 34 in air and displaces liquid up through the passage 27 into the zone 23 where, from the bottom up, it wets the plates 40. The final volume of air supplied to form the bubble can spill into the lower end of the tube 26 where it will flow up to agitate the contents of the basket and break-up any soft-friable material contained therein.

After creating the bubble, the blower 36 ceases and the gas leaks away causing the "tide" to fall in the chamber 22 and rise in the chamber 24. Thus the plates 40 return to being in air and the plates 34 return to being fully submerged. The periodic exposure to sewage and air creates ideal conditions for aerobic degradation of carbonaceous material on the plates 34, 40. The lower part of the lower chamber 24 (i.e. adjacent to the zone 32) becomes an anoxic zone in which facultative denitrifying organisms can multiply so that in the lower chamber aerobic break-down of organic particles in the sewage and anoxic removal of nitrates in the liquid can occur. The filter media 42 can be packs of spiral brush media arranged in four 90° sectors around the inlet tube 26 and flow can be sequenced around the sectors if required.

Alternatively, the media 42 can be arranged to en¬ courage inward spiral flow of the overflow liquid on its way to the outlet 44 or an upward flow which is generally parallel to the axis of the tube 26.

The sewage will be added to the tank periodically as waste-generating equipment in the one or more houses connected to the pipe 28 is used. Eventually "high tide" in the upper chamber will cause liquid to flow through the opening 29 into the final zone 25. As the overflow liquid builds up in the zone 25 it is filtered by the media 42 on its way to the outlet 44 from whence it leaves the tank 10. When the "tide" falls, nitrified effluent and any humus solids are returned from the final filter via non-return valves 50 to the lower chamber 24 where during anoxic conditions, denitrification can occur. For cleaning purposes, the media 42 and^' basket 30 are conveniently removable through the upper end 16. The tube 26 may also be removable.

Locating the basket 30 in the tube 26 ensures that there is a measure of backwashing each time the "tide" rises due to the injection of air below the partition 20, this backwashing reducing the amount of biodegradable material which could otherwise become trapped on the non- biodegradable material trapped in the basket 30.

Access to the humus zone 32 via the open upper end 16 is desirable since periodic desludging may be required in some circumstances.

Figures 4 and 5 show a second embodiment of plant with many features that^' are common to those described with reference to the first embodiment and for convenience the same reference numerals have been used in both embodiments to designate similar items.

The second embodiment uses the central inlet tube 26 as the flow path from lower chamber 24 to upper chamber 22 when the "tide" rises and has flap valves 50 in place of the lay flat tubes. Only two sectors of the final zone 25 contain filter media in the second embodiment.

In a typical case, the diameter of the bulbous part of the tank could be 1800 mm, the overall height 2500 mm and the diameter of the inlet tube 26. some 450 mm. The neck 14 could have a diameter of around 900 mm. The inlet and outlet pipes could have a diameter of around 110 mm.

Claims

1. According to this invention waste water treatment plant comprising a tank containing a partition dividing the tank into upper and lower chambers, means to feed waste water containing organic contaminants to the lower chamber, means to allow waste water to flow from the lower chamber to the upper chamber and means to allow treated water to flow out of the tank from the upper chamber, characterised in that the tank has a bulbous lower portion and a narrower neck leading to an openable upper end, the bulbous lower portion being divided into said upper and lower chambers, biomass support means in each of the upper and lower chambers, and means to periodically create a volume of gas below the partition in the lower chamber, whereby the biomass support means therein are alternately contacted by liquid and by gas.

2. Plant as claimed in claim 1, characterised in that the partition is shaped to create an annular volume of gas in the lower chamber.

3. Plant as claimed in claim 2, characterised in that the means to feed waste water to the lower chamber includes an inlet tube .which extends downwardly into the bulbous portion through the neck.

4. Plant as claimed in claim 3, characterised in that the inlet tube includes a screen to collect non- biodegradable articles that may enter the tank with the waste water.

5. Plant as claimed in claim 1, characterised in that the means to create the volume of gas is an electrically powered air blower which feeds its output air down through the partition into the lower chamber.

6. Plant as claimed in claim 5, characterised in that the output from the blower is used to agitate material trapped on an inlet screen, which screen is backwashed by the liquid moving into the upper chamber on the occasion of the creation of a volume of gas below the partition thereby to reduce the risk of clogging of the screen between screen- cleaning operations.

7. Plant as claimed in claim 1, characterised in that the upper chamber includes filter media which, in a liquid flow direction, are located downstream of the biomass support means in the upper chamber.

8. Plant as claimed in claim 7, characterised in that the means to allow treated water to flow out of the tank is a weir-controlled outlet upstream of such filter media.

9. Plant as claimed in claim 1, characterised in that ^• the upper chamber contains an outer ring of biomass support

• means and an inner annular core of filter media forming the final stage of water treatment for the liquid passing through the tank.

10. Plant as claimed^' in claim 1, characterised in that a non-return valve is located in the partition allowing flow down from a filter region back into the lower chamber but not upward flow from the lower chamber directly into the filter region.