WO1995027682A1

WO1995027682A1 - Plant and method for local treatment of water and sewage

Info

Publication number: WO1995027682A1
Application number: PCT/SE1995/000378
Authority: WO
Inventors: Kettil Genmarker
Original assignee: Swedish Müüma International Ab
Priority date: 1994-04-08
Filing date: 1995-04-07
Publication date: 1995-10-19
Also published as: SE9401171D0; AU2270795A

Abstract

A system and a method for locally handling the water and sewage emissions from a group of consumer units are characterized by placing a smaller first treatment unit adjacent each consumer unit. The treatment unit may be a multi-compartment septic tank type unit and is optionally equipped with aeration and agitation means. The outlet from the smaller first treatment unit is connected in an air-free manner to a larger second treatment unit by means of pipes which can be pressurized selectively to a pressure level corresponding to the pressure level of clean water pipes, these pipes having a small diameter in relation to conventional pipes. The larger second treatment unit is common to all the consumer units of the group and part of the treated water taken from the larger second treatment unit is returned to the consumer units for usages that do not require a clean water quality. The treated water exiting from the second treatment unit is connected with the consumer unit sewage system, water closets, water seals and to junction points in the sewage network. The entire system will thereby assist in cleansing the sewage water, by virtue of the introduction of microorganisms to the system sewage network via the treated water exiting from the second treatment unit.

Description

PLANT AND METHOD FOR LOCAL TREATMENT OF WATER AND SEWAGE.

The present invention relates to a system for handling local water and sewage deriving from a group of consumer units.

TECHNICAL FIELD

Effective and rational handling of water and sewage is a central concern in the endeavour to achieve an environmentally friendly society. In Sweden, a typical family will consume about 150-200 litres of water per person and day, i.e. so-called BDL-water (bathing, dishwashing and laundering water) and water used to flush water closets or toilets. When water is in limited supply, or when sewage treatment facilities are limited, it is essential to use water sparingly. This applies, for instance, to domestic dwellings that are located outside densely built-up areas, such as leisure centres and like building complexes. The interest in so-called ecovillages, i.e. ecologically adapted building complexes contained within a densely populated area, also require water and sewage to be handled in a manner which is more friendly to available resources.

Sewage systems of the kind comprising multi-compartment septic tanks connected to an individual consumer unit have long been known to the art. These systems function as sludge separators and as fermentation tanks. Decomposition in a multi-compartment septic tanks is anaerobic. Drawbacks with this type of system include the limited extent to which the sewage is cleansed, the bad odours that are emitted, and the danger of the system drying up, for instance during summer vacation periods, resulting in operating problems.

WO 94/18129 describes an aerated three-compartment system intended for handling sewage water taken from one or more consumer units.

A Swedish article entitled "Ekologiska utgangspunkter for planering och byggande", the Council of Building Research, 1992 (Bjorn Malbert, editor) , describes the recycling of partially cleansed BDL-water and rain water, for use when flushing toilets, the toilet sewage then being passed to a conventional, central treatment plant. This system presumes that the building has been provided with a double sewage system: one system for BDL-water and one system for toilet sewage.

The technique of pressurizing rain water conduits with the aid of pumps or high-level water reservoirs is a well-tested technique.

It is also known to finely divide particles and solid substances in sewage water mechanically. This enables small low-pressure flows to be used. On the other hand, it is normally not possible to pressurize sewage pipes or conduits, due to the risk of the pipes becoming blocked and because of the explosion risk of gases generated by decomposition processes. Conventional sewage pipes are therefore given large diameters, which result in high system costs.

It is therefore desirable to provide a system in which less expensive and simpler conduits or pipes of smaller dimensions can be used, while enabling, at the same time, the pipes to be pressurized to pressure levels corresponding to the pressure levels that prevail in clean water pipes, so as to obtain volumetric flow rates which correspond to the flow rates in clean water pipes. The costs entailed by laying such pipes are also lower than the costs entailed by laying conventional pipes.

It is also desirable to make the microbiological decomposition in conventional sewage systems more effective.

OBJECT OF THE PRESENT INVENTION

The object of the present invention is to provide a system for reusing treated sewage water from consumer units in a limited area, by recycling treated sewage water, said recycled water being returned to the consumer units in pressurized pipes for purposes which do not require the use of clean water qualities. By clean water is meant here potable pipe carried water that has been purified to clean water standards.

It has been surprisingly found that this object can be achieved with a system for handling locally the water and sewage effluent from a group of consumer units, this system being characterized in that a relatively small first treatment unit is positioned in connection with each consumer unit; in that the outlet from said smaller first treatment unit is connected in an air-free manner to a larger second treatment unit by means of pipes which have a small diameter in relation to conventional pipes, wherein the second larger treatment unit is common to all of the consumer units in said group; and wherein part of the cleansed water exiting from the second larger treatment unit can be returned to the consumer units and used for purposes that do not require a clean water quality.

The smaller first treatment unit may be of the multi-chamber well kind and is optionally equipped with aerating and agitating means. A grid or some similar device is placed suitably at the inlet to the treatment unit, for mechanical separation of larger particles and objects. The tank will preferably have a volumetric capacity of at least 2 π , normally about 4 m . Such a water treatment unit is able to cleanse sewage water to a degree of 80-90% with regard to suspended substances (SS) and biological oxygen demand (BOD) .

No modifications are required to the consumer unit sewage system, with the exception of supplementing the system with water recycling pipes or conduits. All sewage outlets from the consumer unit lead to the smaller first treatment unit, in other words no separate pipes are required to conduct toilet sewage. The first treatment unit shall not be allowed to operate empty or to dry-out. A certain degree of recycling can be maintained constantly in the system, even during vacation periods and corresponding periods.

The pipes which connect the small first treatment units to the larger second treatment unit may be pressurized to a pressure level that corresponds to the pressure in the clean water pipes, i.e. up to an overpressure of about 10 atm, and have a volumetric flow rate (ιτr/h) that corresponds to the volumetric flow rate in clean water pipes. This enables the same type of pipe to be used for both clean water and recycled treated sewage water.

By pressurized pipe is meant here and in the following Claims a pipe which has been intentionally placed under pressure, for instance with the aid of one or more pumps, or by creating a pressure head. When pumps are used, the pumps may be positioned as required at the outlet from the first water treatment unit or at different locations in the sewage network. Check valves are suitably fitted downstream of the pumps. The pipes are kept constantly filled with sewage water.

The larger second treatment unit may be a conventional water treatment plant of the kind in which mechanical, biological and chemical purification can be included in selective combinations. The plant may include pressure tanks for equalizing variations in clean water consumption and recycled treated sewage water. This second treatment stage enables sewage to be cleansed to a total extent of about 95% with respect to SS and BOD in the first and second stages together. However, the extent to which the sewage is cleansed may be adapted to the requirement of a given water quality. A degree of purification as high as 95% with respect to SS and BOD is not always desirable. This applies, for instance, when using the recycled water for irrigation purposes.

The sewage water recycling pipes are suitably pressurized, and may be of the same type as the pipes used between the first and the second treatment units. These pipes are also kept constantly filled with sewage water.

Safety valves and aerating devices are mounted at suitable locations in the plant pipe system.

The pipes used in the inventive system may have a diameter as small as about 16 mm. A pipe diameter of about 25 mm is typical for water recycling pipes, while the pipes through which sewage is taken from the consumer units will have a diameter of 54 mm. These diameters correspond to about one-tenth of the pipe diameters of conventional sewage systems. The pipes are conveniently made of plastic, for instance polyethylene.

The various pipes for conducting clean water, untreated sewage water and recycled adequately cleansed sewage water may be placed together in boxes insulated with polystyrene foam, for instance. The boxes may be buried to a depth of about 2 dm in the ground plot and to a depth of about 5 dm beneath road surfaces. The pipes need not be buried to the same depth as that necessary in the case of conventional underground pipes, which is also an advantage because less the surrounding terrain will be disturbed to a commensurate lesser extent. This assumes that the pipes are protected against frost. The pipe trenches may optionally be heated electrically as a protection against frost. Alternatively, the pipes, or conduits, may be protected against frost by heating the treated sewage water from the larger second treatment unit prior to recycling the water. Heating of the sewage water will also accelerate the process of decomposition in the sewage water, by imparting a favourable temperature to the water already at the sewage outlet source. The decomposition rate is dependent on the temperature of the sewage water.

The smaller first treatment unit is conveniently provided with a heat exchanger and the treated recycled sewage water is allowed to pass in pipes through the treatment unit to take up heat from the decomposition process in the tank, prior to being conveyed to the consumer unit.

Microorganisms can be added to the larger second treatment unit, as conventional. These microorganisms will be dispersed throughout the system, including the sewage system of the consumer units, by the recycled treated sewage water, so that decomposition of sewage substances will commence already at source. For instance, the recycled treated sewage water may be piped to the toilets (water closets) of the consumer units, to the water seals of waste mills or to locations downstream of water seals, and to washing machines, dishwashers, bath and shower outlets, etc., and may also be piped to junction points in the sewage network. In this way, the entire sewage water treatment system, including pipes and conduits will assist in the decomposition of sewage, and not solely the sewage tanks of a central sewage treatment plant.

Depending on requirements, different substances may be added to the treated waste water, which is then piped to different user sites: for use in the sewage system in accordance with the above, for irrigation purposes, fire-fighting, etc. One advantage with the use of treated waste water for irrigation purposes is that the water will introduce nutrients into the soil to a greater extent than will clean water. Irrigation can therefore be effected with the intention of fertilizing the soil. Substances that are required by the soil, such as lime, may also be added to the recycled water when this water is used for irrigation purposes.

It should be possible to recycle at least 30% of the treated sewage water. This will result in a corresponding decrease in the consumption of clean water, which is particularly beneficial in rural areas, leisure areas, areas which are sensitive to heavy road haulage vehicles used in conjunction with emptying sewage tanks, etc. This reduction in the need to empty sewage tanks is able to provide an annual savings of about SEK 1,200.00 to SEK 3,000.00 per consumer unit.

The treated waste water that is not recycled in the system is passed to a filtering station or to a recipient. This waste water can also be passed to the municipal wastewater network. The water is filtered before optionally heating the water or metering nutrients, etc., to the cleansed waste water.

The sewage water may also be stored in tanks which are emptied by tank trucks.

A fully controllable system can be obtained with the aid of conventional control techniques. The degree of recycling, filtra¬ tion, the introduction of additives at different points in the sewage network, tapping of water to cover local requirements in the vicinity of the consumer units, rates of flow, volumes, pressures and temperatures in tanks and conduits or pipes, etc., can be controlled, monitored, registered and optimized within the system. The system may be run manually either totally or partially, although it may also be conveniently automated. The system is thus very flexible and can be quickly regulated and optimized for effective sewage handling. In the event of a pipe fracturing or malfunctioning in some other way, the pipe can be shut-off and the reserve capacity (about 1 irr) of the smaller first treatment unit can be used. There is no need to release untreated sewage.

Because the load of each consumer unit on the water and sewage network is measured, there is an economic incitement to economize on water, and to choose environmentally friendly detergents, etc. The water and sewage handling costs can be calculated separately for each consumer unit.

The inventive system enables a dwelling area to become self- supporting from the aspect of water treatment. The water builds a closed cycle in such a fully ecologically adapted system. This presumes that sufficient water is available to cover the needs of the dwelling area and also that the wastewater that is not recycled can be filtered.

The inventive system is thus suitable for residential units and consumer units located outside the municipal sewage network, for ecovillages and for general use where there is a need to minimize water consumption and the quantities of sewage water effluents. The inventive system may also be used as an alternative in expanding existing sewage systems and sewage plants in newly erected buildings in a dwelling area.

Claims

1. A system for handling locally the water and sewage emissions from a group of consumer units, characterized in that a smaller first water treatment unit is positioned adjacent each consumer unit; in that the outlet from the smaller first treatment unit is connected in an air-free manner to a larger second treatment unit by means of pipes which have a small diameter in relation to conventional pipes, wherein the larger second treatment unit is common to all the consumer units of said group; and in that part of the treated water exiting from the larger second treatment unit can be returned to the consumer units for a use which does not require a clean water quality.

2. A system for locally handling water and sewage emissions from a group of consumer units according to Claim 1, characterized in that the smaller, first treatment unit is of the multi-compartment tank kind.

3. A system for handling locally the water and sewage emissions from a group of consumer units according to Claim 1 or Claim 2, characterized in that the smaller first treatment unit is equipped with aeration and agitation means.

4. A system for handling locally the water and sewage emissions from a group of consumer units according to any one of the preceding Claims, characterized in that the pipes connecting the smaller first treatment units to the larger second treatment unit can be pressurized to a pressure level corresponding to the pressure level of clean water pipes, so as to obtain a volumetric flow rate which corresponds to the volumetric flow rate in clean water pipes.

5. A system for handling locally the water and sewage emissions from a group of consumer units according to any one of the preceding Claims, characterized in that the treated water exiting from the second treatment unit is connected with the consumer unit sewage system, water closets, water seals and with junction points in the sewage network, whereby the entire system assists in cleansing the sewage water by virtue of microorganisms being introduced to the system sewage network through the cleansed water from the second purification unit.

6. A method for locally handling the water and sewage emissions from a group of consumer units, characterized in that a smaller first water treatment unit is positioned adjacent each consumer unit; in that the outlet from the smaller first treatment unit is connected in an air-free manner to a larger second treatment unit by means of pipes which have a small diameter in relation to conventional pipes, wherein the larger second treatment unit is common to all the consumer units of said group; and in that part of the treated water exiting from the larger second treatment unit can be returned to the consumer units for a use which does not require a clean water quality.

7. A method for locally handling the water and sewage emissions from a group of consumer units according to Claim 6, characterized in that the smaller, first treatment unit is of the multi- compartment tank kind.

8. A method for locally handling the water and sewage emissions from a group of consumer units according to Claim 6 or Claim 7, characterized in that the smaller first treatment unit has the form of apparatus equipped with aeration and agitation means.

9. A method for locally handling the water and sewage emissions from a group of consumer units according to any one of the preceding Claims, characterized in that the pipes connecting the smaller first treatment units to the larger second treatment unit can be pressurized to a pressure level corresponding to the pressure level of clean water pipes, so as to obtain a volumetric flow rate which corresponds to the volumetric flow rate in clean water pipes.

10. A method for locally handling the water and sewage emissions from a group of consumer units according to any one of the preceding Claims, characterized by introducing microorganisms into the consumer unit sewage system, water closets, water seals and junction points in the sewage network through the medium of the treated water taken from the second treatment unit, whereby the whole of the system assists in cleansing the sewage water.