IES20030654A2 - A domestic sewage treatment system - Google Patents

Abstract

The sewage treatment system (1) includes a sewage holding tank (2) for reception of raw sewage from a domestic dwelling. A diffuser assembly (7) at the bottom of the tank (2) is operable for a preset period to aerate sewage liquid in the tank (2). After aeration and a subsequent settling period a discharge pump (6) is operable to discharge a preset amount of treated liquor from the tank (2) for dispersal through an irrigation system buried in the ground remote from the tank (2). <Figure 1>

Description

“A Domestic Sewage Treatment System11 This invention relates to a domestic sewage treatment system and process.

Where domestic sewage systems cannot be connected to a main sewer some other method of handling the sewage waste must be provided. One typical system involves the use of a septic tank through which sewage flows. Such septic tanks generally have two or more chambers in which the waste is allowed to settle before discharging purified liquor into an irrigation system or the like buried in a field. On a regular basis sludge which collects in the septic tank must be pumped out for safe disposal elsewhere. This is relatively expensive and somewhat inconvenient. Also this sludge is a nuisance as it has a very unpleasant odour caused by hydrogen sulphide gas (rotten egg smell).

The present invention is directed towards overcoming these problems.

According to the invention there is provided a domestic biological sewage treatment system including a sewage holding tank having an inlet for reception of raw sewage and an outlet for discharge of treated liquor, a diffuser mounted in the holding tank, said diffuser having an inlet connected to an air supply means, said diffuser having a plurality of outlet openings for discharging air into the holding tank, a treated liquor discharge pump having an inlet communicating with an interior of the holding tank and an outlet which is connected to a liquid discharge line for discharge of treated liquor from the holding tank.

In one embodiment of the invention a 3-way discharge valve is mounted in the liquid discharge line, said 3-way valve having an inlet, a first outlet and a second outlet, said valve inlet being connected to the discharge pump outlet, said valve first outlet being connected to a recirculating line having an outlet which discharges into the holding tank, and said valve second outlet being connected to a discharge pipe for discharge of treated liquor from the holding tank, said valve being operable such that when the first outlet is open the second outlet is closed and when the first outlet is closed the second outlet is open. —.........

OPEN TO PUBLIC INSPECTION UNDER SECTION 28 AND RUUE23 - 2 ΐε 0 306 s 4 In a further embodiment means is provided for controlling delivery of air from the air supply means to the diffuser. Preferably said means is operable to continuously supply air to the diffuser during an aerating period.

Conveniently the air supply means is a blower mounted on the holding tank.

In another embodiment the discharge pump is a submersible pump mounted within the holding tank.

In another embodiment a pump cut-out switch is provided associated with the discharge pump, said cut-out switch operable to switch off the pump when the liquid level in the holding tank falls to a predetermined level.

In another embodiment the liquid discharge line is connected to an irrigation system outside the holding tank for disposal of treated liquid.

In a further embodiment control means is provided for regulating operation of the air supply to the diffuser, for regulating operation of the discharge pump and for regulating operation of the discharge valve. Said control means may conveniently be provided by a pre-programmed PLC.

It is desirable that the controller, the blower and electrical controls for the blower and the discharge pump are housed in a weatherproof kiosk which is mounted on top of the holding tank.

In another aspect the invention provides a domestic biological sewage treatment process, including: delivering sewage waste to a sewage holding tank forming a reservoir of sewage liquor, aerating the sewage liquor in the holding tank for a preset aerating period, after aerating allowing the aerated sewage liquor to settle in the holding tank for a preset settling period, and discharging a quantity of treated liquid from the holding tank.

In another embodiment the process includes aerating the waste continuously during the aerating period.

In a preferred embodiment the aerating period is between 8 hours and 16 hours, and most preferably is about 12 hours.

In another embodiment the process includes aerating the sewage liquor by finely diffusing air into the sewage liquor during the aerating period.

In a further embodiment the sewage liquor is aerated by generating a pressurised air supply and discharging said air supply through a diffuser located at a bottom of the holding tank during the aerating period.

In another embodiment the process includes discharging treated liquid from the holding tank by initially recirculating treated liquor through a discharge line and back to the holding tank and subsequently discharging treated liquor through the discharge line for disposal outside the holding tank.

In another embodiment the process includes disposing of the treated liquor by delivering the treated liquor through an associated irrigation system connected to the discharge line outside the holding tank.

In another embodiment the settling period for the aerated sewage liquor is between 6 hours and 10 hours, and most preferably the settling period is about 8 hours.

In a further embodiment the process includes settling the liquid for an initial primary settling period, recirculating a quantity of treated liquor through the discharge pump and back to the holding tank during a brief recirculating period, and - 4 ΙΕ η3 06 54 thereafter settling the sewage liquor in the holding tank for a secondary settling period before discharging treated liquor from the holding tank.

In another embodiment each of the primary settling period and the secondary settling period is at least 1 hour, and preferably at least 2 hours duration. Ideally, the primary settling period is about 6 hours and the secondary settling period is about two hours duration.

The recirculating period should be sufficient to flush through the discharge pump and the discharge line upstream of a discharge valve which controls discharge of treated liquor from the holding tank. Typically the recirculating period is less than 1 minute and preferably is of the order of 20 to 30 seconds.

The invention will be more clearly understood by the following description of some embodiments thereof, given by way of example only, with reference to the accompanying drawings, in which; Fig. 1 is a sectional elevational view of a domestic sewage treatment system according to the invention; Fig. 2 is a plan view of the sewage treatment system; and Fig. 3 is a detail sectional elevational view taken along the line III - III of Fig. 1 showing portion of the sewage treatment system; Fig. 4 is a sectional elevational view of a sewage treatment system of the invention retrofitted to an existing septic tank; Fig. 5 is a plan view of the system shown in Fig. 4; Fig. 6 is a plan view of the septic tank; and Fig. 7 is a sectional elevational view of the septic tank. - 5 IE 03 06 5 4 Referring to the drawings, and initially to Figs. 1 to 3 thereof, there is illustrated a domestic biological sewage treatment system according to the invention indicated generally by the reference numeral 1. The system 1 comprises a sewage holding tank 2 having an inlet 3 for reception of raw sewage delivered through a raw sewage inlet pipe 4 which is connected to a domestic dwelling. A holding tank outlet for discharge of treated liquor comprises a discharge line 5 which delivers treated liquor to an irrigation system located downstream of the holding tank 1. A treated liquor discharge pump 6 is located within the holding tank 2 to discharge treated liquor from the holding tank 2 through the discharge line 5. A diffuser assembly indicated generally by the reference numeral 7 is mounted at a bottom of the holding tank 2 for aerating liquid within the holding tank 2.

The holding tank 2 has a base 10 with an upstanding side wall 11 and a top 12. The top 12 has an access opening 13 closed by a cover 14. A through hole 16 is provided in the top 12 for through passage of pipework, cabling and the like. A weatherproof control kiosk 17 is mounted directly above the opening 16.

The discharge pump 6 is suspended centrally within an upper portion of the holding tank 2 by means of a chain 20 and hanger 21 attached to an inside face of the top 12 of the holding tank 2. A power supply cable 22 for the pump 6 passes up through the hole 16 to the control kiosk 17 within which is housed electrical contactors for connection to a power supply and a controller for operation of the discharge pump 6. The discharge pump 6 has an inlet 24 and an outlet connected to a discharge pipe 25. This discharge pipe 25 feeds up through the hole 16 to a 3-way valve (not shown) housed within the control kiosk 17. An outlet end of the discharge pipe 25 connects to an inlet of the 3-way valve. This 3-way valve has a first outlet which is connected to a recirculation line 26 which feeds back down through the hole 16 for discharge adjacent the base 10 of the tank 2. A second outlet of the 3-way valve is connected to the discharge line 5 for discharging treated liquor to the irrigation system externally of the holding tank 2. This 3-way valve is electrically operated for switching between the recirculation line 26 and the discharge line 5 as will be described in more detail later. The controls for the 3-way discharge valve are also housed within the control kiosk 17. - 6 IE 03 os The diffuser assembly 7 is mounted centrally on the base 10 of the holding tank 2. The diffuser assembly 7 connects by means of an air line 30 with an electrically operated blower (not shown) which is mounted in the control kiosk 17 together with controls for the blower. The blower delivers air through the air line 30 and through arms 31 of the diffuser assembly 7 which have outlet openings to diffuse the air as fine bubbles into an interior of the holding tank 2 for aeration of liquid retained within the holding tank 2 in use.

The holding tank 2 is mounted below ground adjacent a domestic dwelling with the control kiosk 17 projecting upwardly from ground level 18 as shown in Fig. 1. The sewage inlet 3 of the holding tank 2 is connected to a raw sewage pipe 4 coming from the domestic dwelling for delivery of domestic sewage into the holding tank 2. During the day, typically between 8am and 8pm the blower is operated continuously for continuous aeration of sewage liquor within the holding tank 2. Fine bubbles of air are diffused up through the sewage liquor within the holding tank 2 for biological treatment of the sewage by aerobic bacteria present within the holding tank 2. The aerobic bacteria digests the sewage, reducing the biochemical oxygen demand (BOD) by converting the organic content of the sewage to a chemically and organically inert sludge. The oxygen input delivered in the air through the diffuser assembly 7 is calculated to supply sufficient oxygen to support the bacteria colony in the activated sludge within the holding tank 2 in addition to creating nitrifying bacteria and to provide for simultaneous sludge stabilisation.

After the desired aeration period has been completed, that is at 8pm, a controller in the control kiosk 17 switches off the blower and the sewage liquor within the holding tank 2 is allowed to settle for a primary settling period. In the early morning hours when little or no sewage inflow occurs, that is at about 2am the discharge pump 6 is switched on for a brief recirculation period of about 20 to 30 seconds. The 3-way discharge valve is switched to the recirculation position so that treated liquor is discharged by the pump 6 back through the recirculation line 26. This flushes through the pump 6 and discharge pipe 25 to clear the pump 6 and discharge pipe 25 of any mixed liquor that might have entered during the aeration period.

Settlement of the sewage liquor within the holding tank 2 then continues for a IE 0 3 0654 - 7 secondary settlement period until about 4am and then the discharge valve is switched to the discharge line 5 and the discharge pump 6 is operated to discharge treated liquor from the holding tank 2 through the discharge line 5 to the irrigation system for disposal of the treated liquor. The discharge pump 6 is automatically stopped by a float switch associated with the pump 6 when the sewage liquor within the holding tank 2 falls to a predetermined level. The position of the float switch is arranged to avoid discharge of any floating material from the holding tank 2. The discharge pump is sized such that it will discharge the previous days inflow sewage volume in up to 3 hours.

Automatic control of the air blower for the diffuser assembly 7, the 3-way discharge valve and the discharge pump 6 is by way of a pre-programmed PLC. Electncal controls for the blower, the pump 6 and the 3-way discharge valve such as miniature circuit breakers and the PLC together with the blower and the 3-way discharge valve are all housed in the weatherproof control kiosk 17.

It will be appreciated that the invention provides a compact and efficient prefabricated domestic biological sewage treatment system for the efficient handling and disposal of domestic sewage waste. Any sludge produced is aerobic and odourless. The sewage is simply treated in a single tank.

Conveniently the sewage treatment system of the invention may be retrofitted to suitable existing septic tanks obviating costly and disruptive excavations and construction work in mature gardens for example.

Referring to Figs. 4 to 7 there is shown a sewage treatment system of the invention retrofitted to an existing septic tank. The sewage treatment system is indicated generally by the reference numeral 40. Parts similar to those described previously are assigned the same reference numerals. In this case the system is fitted to an existing septic tank 42 which forms the sewage holding tank. This conveniently avoids the need to dig up a garden or the like to install a new tank.

The invention is not limited to the embodiments hereinbefore described which may be varied in both construction and detail within the scope of the appended claims.

Claims (5)

1. A domestic biological sewage treatment system including a sewage holding tank having an inlet for reception of raw sewage and an outlet for discharge of treated liquor, a diffuser mounted in the holding tank, said diffuser having an inlet connected to an air supply means, said diffuser having a plurality of outlet openings for discharging air into the holding tank, a treated liquor discharge pump having an inlet communicating with an interior of the holding tank and an outlet which is connected to a liquid discharge line for discharge of treated liquor from the holding tank.

2. A system as claimed in claim 1 wherein a 3-way discharge valve is mounted in the liquid discharge line, said 3-way valve having an inlet, a first outlet and a second outlet, said valve inlet being connected to the discharge pump outlet, said valve first outlet being connected to a recirculating line having an outlet which discharges into the holding tank, and said valve second outlet being connected to a discharge pipe for discharge of treated liquor from the holding tank, said valve being operable such that when the first outlet is open the second outlet is closed and when the first outlet is closed the second outlet is open, the air supply means is a blower mounted on the holding tank, the discharge pump is a submersible pump mounted within the holding tank, a-pump cut-out switch is provided associated with the discharge pump, said cut-out switch operable to switch off the pump when the liquid level in the holding tank falls to a predetermined level, control means is provided for regulating operation of the air supply to the diffuser, for regulating operation of the discharge pump and for regulating operation of the discharge valve, the controller, the blower and electrical controls for the blower and the IE Ο 30654 discharge pump are housed in a weatherproof kiosk which is mounted on top of the holding tank.

3. A domestic biological sewage treatment system substantially as hereinbefore 5 described with reference to the accompanying drawings.

4. A domestic biological sewage treatment process, including: delivering raw sewage waste to a sewage holding tank forming a 10 reservoir of sewage liquor, aerating the sewage liquor in the holding tank for a preset aerating period, 15 after aerating allowing the aerated sewage liquor to settle in the holding tank for a preset settling period, and discharging a quantity of treated liquid from the holding tank. 20

5. A domestic biological sewage treatment process substantially as hereinbefore described with reference to the accompanying drawings.