GB2320492A

GB2320492A - Wastewater treatment plant

Info

Publication number: GB2320492A
Application number: GB9626634A
Authority: GB
Inventors: Michael Jeremy Lenn; Colin Devonshire
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-12-21
Filing date: 1996-12-21
Publication date: 1998-06-24
Also published as: GB9626634D0

Abstract

A waste water treatment plant, especially for oil-containing waste water, comprises a bioreactor 9 having a matrix 12 on which microbes are retained and an ultrafiltration unit 21 downstream of the bioreactor. Fluid from the bioreactor is forced through the ultrafiltration unit with the filtrate being removed to a drain and the fluid (eg oil) retained by the ultrafiltration unit being returned to the bioreactor for further treatment. Preferably the plant also includes a pre-treatment unit 1 upstream of the bioreactor and a reservoir 6 containing emulsifying agents or surfactants 5 which are added to the pre-treatment unit to assist degradation of pollutants. Preferably, in use fluid retained by the ultrafiltration unit is returned to the bioreactor via the pretreatment unit. The bioreactor may be aerobic or anaerobic.

Description

Wastewater Treatment Plant and Method of Use Therein This invention relates to a wastewater treatment plant in which biological treatment and filtration are combined to allow re-use of treated water or disposal to sewer.

A number of technologies are available for the treatment and disposal of wastewaters containing both oils and water soluble contaminants. One of the most commonly used methods is ultrafiltration. By this method, water and low molecular weight water soluble contaminants in the waste fluid are forced through a membrane under pressure, whilst the oily components and high molecular weight contaminants do not pass through the membrane. Thus the water is separated from the oil and can.be disposed to foul drain or sewer. The oil fraction remains to be disposed of by incineration or landfill. This method has several drawbacks. Firstly, the disposal of the oil fraction by these methods has major economic environmental implications. Secondly, the increase in oil concentration within the filter system gradually blinds the filter membrane and oil can eventually pass through such that the treated fluid requires reprocessing. The volumes of oily concentrate are thus fairly high, typically 15 -20% of the total waste volume. Thirdly, the accumulation of oil on the membrane requires that the system is frequently cleaned, requiring that the unit is taken out of operation for short periods.

Biological treatment of wastewaters and oily wastes is a well established approach. Biological treatment of oily wastes can be advantageous compared to filtration because the oil components can be completely degraded to harmless water and carbon dioxide, allowing for disposal of the total liquid volume processed. In addition, many of the toxic water soluble chemicals in wastewaters can be biologically degraded. However, biological treatment of oils occurs relatively slowly, such that the rate of throughput is limited. Also biologically treated water may not be suitable for recycling due to the presence of bacteria and solids.

The object of the present invention is to combine the benefits of filtration and biological technologies in an integrated system, thereby providing for a continuous process allowing for high efficiency processing of oily wastewaters and allowing for re-use of the treated water.

According to the invention there is provided a liquid waste treatment plant comprising a waste pretreatment tank, a biological treatment tank (bioreactor) and a filtration unit. The pre-treatment tank serves as a reservoir in which wastes of different composition may be mixed and balanced, and in which suitable pre-treatments may take place if required. Alternatively, the pre-treatment tank may not be required if the effluent is of a reasonably consistent volume and composition. The bioreactor ensures that a proportion of the oils and other waste components are degraded before filtration treatment, such that the filtration unit receives a reduced concentration of contaminants. The system is configured such that components of the effluent that do not pass through the filter membrane can be retumed to the storagelpre-treatment tank for further treatment. Thus the system can be configured to operate continuously.

The pre-treatment tank may be dosed with a product to assist the further treatment of the waste.

Typically this could be a solution with surfactant properties to emulsify the oily components of the waste. The formation of an emuision allows for increased efficiency of oil breakdown in the bioreactor. The contents of the pre-treatment tank may be agitated or aerated by means of a mixing device, such as an overhead mixer, submersible pump, direct aeration or an extemal circulatory pump. This will provide for complete mixing of the dosed product and prevent accumulation of solids in the tank.

The pre-treatment tank is constructed of any materials that are chemically compatible with the components of the waste to be treated. The pre-treatment tank can be sized according to the type and volumes of waste to be processed. Waste may typically be pumped into the pre-treatment tank from a factory waste liquid storage facility, which would typically comprise a tank of larger volumetric capacity than the pretreatment tank. Altematively, the pre-treatment tank may receive waste liquids directly. Waste effluent will normally pass through a coarse filter before entering the pre-treatment tank. The pre-treatment tank is fitted with a float switch to prevent the system overfilling.

The bioreactor may comprise either an aerobic or anaerobic system. An aerobic system requires an arrangement to disperse air from a mechanical compressor or air blower throughout the liquid waste in the bioreactor. The bioreactor may be designed as either an attached growth system, in which a suitable solid support material is placed to retain microbes within the system, or as suspended growth system in which microbes are dispersed within the liquid in the bioreactor.

Suitable microbes for effecting the degradation in the bioreactor include bacteria, fungi and protozoa. The bioreactor performs three essential functions of the invention.

(i) Many of the organic components in the waste stream are degraded to harmless products such as carbon dioxide and water. Thus the final processed effluent will contain a lower organic carbon content.

(ii) Microbes in the bioreactor will degrade many toxic compounds in the effluent.

(iii) Microbes in the bioreactor will degrade oils contained within the effluent. This prevents accumulation of oils in the subsequent filtration stage, thus allowing for greatly enhanced efficiency of processing.

Waste effluent passes into the bioreactor near the base of the tank and exits near the Eoc tithe tank, in which case the effluent passes through the reactor in a upward direction in common with the airflow through the tank. Alternatively, the waste effluent may enter near the top of the bioreactor tank and exit near the base. In this configuration the system is said to be configured in a countercurrent mode.

In order for the microbes to reproduce it is necessary to maintain a minimum nutrient level in the bioreactor. In addition, the bioreactor performance may be enhanced by the frequent or continuous addition of appropriate cultures of bacteria which are available commercially as either liquids or dried preparations. Accordingly the plant preferably includes the facility for dosing of nutrients and/or additional bacteria into the bioreactor.

As any particular type of microbe will degrade the waste components most effectively at a particular acidity level, the plant preferably includes a method to control the acidity in the bioreactor.

Waste fluid from the bioreactor is fed to the ultrafiltration unit either by pump or gravity feed. The ultrafiltration unit comprises a system of the type currently available for treatment and disposal of waste industrial fluids. Typically, the ultrafiltration unit will comprise a waste collection tank and a filtration module which can be fitted with a variety of interchangeable membranes according to the application. The membranes can be specified according to the nature of the effluent to be treated, with membranes possessing different pore sizes available. The range of membranes used for this invention will typically have pores designed to allow molecules to pass having a molecular weight of between 4,000 to 100,000 kDa. A proportion of the water and low molecular weight contaminants are forced through the membrane under pressure. This fraction of the fluid is known as the filtrate.

The filtrate can then be disposed to drain/sewer, or may be used for other industrial purposes. Oils, and unprocessed water and other components that do not pass through the membrane (the retentate) are returned to the pre-treatment tank and reprocessed through the complete system.

The invention can additionally be provided with an oil coalescing function. This is provided in instances when the effluent to be processed is known to intermittently contain large amounts of oils which could interfere with operation of the bioreactor. The coalescing unit receives the waste fluid upstream of the pretreatment tank. Free oil in the effluent is separated and deposited in an oil reservoir. Oil collected in the oil reservoir can either be reused or dosed into the pretreatment tank at a controlled rate.

The invention may optionally be constructed to fit onto a trailer such that the complete system can be transporied and towed by a vehicle to a factory or other site where waste treatment is required.

A specific embodiment of the invention will now be described by way of example with reference to Figure 1, which shows a schematic overview of the process.

The pretreatment tank comprises a sealed, vented tank constructed of polypropylene (1).

Altematively, the pretreatment tank may be manufactured from steel, polyethylene, glass reinforced plastic or any other material that is chemically compatible with the components of the effluent stream. Waste engineering coolants, lubricants and metal-cutting fluids are pumped into the pretreatment tank from a factory waste storage facility, preferably through a coarse filter (2) to remove any large particles. The liquid is drawn via a charge pump (3) which is triggered by a float switch in the pretreatment tank. When the pretreatment tank is filled to a defined level, a second float switch activates a solenoid valve (4). This stops the incoming effluent feed and causes the charge pump to recirculate and mix the fluid within the pretreatment tank. An emulsifying agent or surfactant (5) is dosed into the pre-treatment tank from a reservoir (6) via a peristaltic pump (7) to allow for more efficient degradation of oil components in the bioreactor.

The pre-treatment tank is sealed, and fitted with a vent to atmosphere. This feature allows for pressure equalisation within the system whilst preventing the escape of noxious odours into the immediate surrounding area.

Fluid is transferred from the pre-treatment tank into the bioreactor by means of a pump (8). The bioreactor vessel (9) comprises a polypropylene cylindrical tank. Alternatively, the bioreactor could be manufactured from steel, polyethylene, glass reinforced plastic or any other material that is chemically compatible with the components of the effluent stream.

Organic components in the waste fluids are degraded by the action of aerobic microorganisms.

Aeration and fluid mixing within the bioreactor vessel are provided by means of a compressor (10) from which air passes through diffusers (11) situated in the base of the bioreactor vessel. The reactor contains a plastic matrix (12) to which bacterial cells adhere and become entrapped.

Measurement of pH in the bioreactor is achieved by means of a pH probe (13) connected to an electronic pH control unit (14). The pH control unit doses acid or alkali (15) into the bioreactor, as required, via a peristaltic pump (16).

Microbial activity within the bioreactor is enhanced by the addition of a commercial preparation of bacteria and nutrients which is dosed into the bioreactor via a peristaltic pump (17) from a reservoir (18).

The lid of the bioreactor is sealed to prevent escape of gases or release of microbes to the localised area. A vent pipe to atmosphere is fitted.

Fluid exits the bioreactor by gravity feed into the ultrafiltration process tank (19). Fluid in the ultrafiltration process tank is forced through the ultrafiltration unit by a pump (20). Processed filtrate can then be disposed to foul drain. The retentate fluid then passes back to the ultrafiltration process tank from which a gravity overspill feeds back to the pretreatment tank for recycling through the system.

A second embodiment of the invention, shown in figure 2, is intended for treatment of wastes that may intermittently contain large amounts of oil. This embodiment includes an oil coalescing unit (22) which removes the majority of the oil from the fluid in the incoming effluent. The oil removed by the coalescer unit is stored in an oil reservoir (23). Oil from the reservoir is fed into the bioreactor at a controlled rate via a dosing pump (24) to maximise the efficiency of oil degradation.

Claims

Claims

1. A wastewater treatment plant comprising a biological reactor containing a physical matrix to retain microbes and an ultrafiltration unit configured such that wastewater is treated in the biological prior to treatment by ultrafiltration. The final effluent from the wastewater treatment plant comprises the filtrate from the ultrafiltration unit. The fluid retained by ultrafiltration is returned to the bioreactor for further treatment.

2. A treatment plant as claimed in Claim 1 characterised in that fluid is received in a pre treatment tank prior to entering the biological reactor.

3. A treatment plant as claimed in Claim 2 characterised in that the ultrafiltration retentate fluid is returned to the pretreatment tank.

4. A treatment plant as claimed in any preceding claim which is characterised by acidity control means for controlling conditions in the biological reactor or pre-treatment tank.

7. A treatment plant as claimed in any preceding claim which is characterised by a means of dosing and mixing emulsifying agents or surfactants in the pretreatment tank.

5. A treatment plant as claimed in any preceding claim which is characterised in that the biological reactor or pre-treatment tank is provided with nutrient supply means 6. A treatment plant as claimed in any preceding claim which is characterised by a means of dosing microbes into the biological reactor.

8. A treatment plant as claimed in any preceding claim in which the biological reactor contains microbes including bacteria, fungi or protozoa.

10. A treatment plant as claimed in any preceding claim which is characterised by an oil coalescing unit seperate free oil from the wastewaster and transfer the oil into a reservoir from which oil is dosed into the pretreatment tank at a defined rate.

11. A treatment plant as claimed in any preceding claim in which the fluid in the biological reactor is aerated to facilitate growth of aerobic microbes.

12. A treatment plant as claimed in any preceding claim in which the fluid in the biological reactor is maintained under anaerobic conditions to facilitate growth of anaerobic microbes.

13. A treatment plant as claimed in any preceding claim in which all components are affixed to a trailer suitable for towing behind a vehicle.