GB2279887A - Waste water treatment - Google Patents

Abstract

A waste water treatment system includes a preliminary first stage separator for separating an aqueous phase from other materials. A pressure vessel sedimentation follows for removing most of the remaining solids from the waste material. The liquid and a minor fraction of the solids then pass on to an evaporation vessel where water vapor is removed, compressed and passed through a condenser inside the evaporator vessel to recycle heat to the evaporator. The condensate then passes through a second heat exchanger that heats the liquid flowing into the evaporator. The effluent water has been purified by the evaporation. The residual solids are heat treated to evaporate residual moisture and to sterilize the solids using a steam-jacketed auger. The resulting solids are used as fertilizer.

Description

SEWAGE TREATMENT PROCESS The present invention relates to pollution reduction and more particularly to the treatment of contaminated waste water, including industrial pollutants and sewage.

Planet Earth should be our most prized possession. However, each and every day our environment is being polluted to a greater extent with industrial waste and human sewage.

Cities and towns, when economically feasible, do employ primary and secondary waste water treatment methods. However, the effluent from these methods is often still a contaminant that cannot be discharged to surface or subsurface waters without contaminating or reducing the quality of the carrier or solvent waters.

Coastal cities pipe so-called secondary treatment effluents miles into the ocean and discharge them as deeply as possible in hopes of reducing pollution by dilution. Inland cities, where possible, discharge effluents deeply into lakes and rivers. To date, there has been no economically feasible way to purify sewage and for certain, the Solution to Pollution is not Dilution.

The invention disclosed herein includes a process and an apparatus which can now economically treat sewage and contaminated waters to a high degree of purity. Preferably, treated water is of sufficient purity that it may be used for human consumption.

It is an objective of this invention to achieve the aforementioned treatment without the use of chemicals, thereby eliminating chemical pollution from the treatment and reducing operating costs.

According to one aspect of the present invention there is provided a waste water treatment evaporator comprising: a closed vessel; a waste inlet to the vessel; a water vapor outlet from the vessel; a solids outlet from the vessel; pump means for pumping water vapor from the water vapor outlet; a first heat exchanger within the vessel having an inlet connected to the pump means for receiving water vapor therefrom and an outlet for discharging condensed water vapor; and a second heat exchanger externally of the vessel and having a first heat exchange passage for waste upstream of the waste inlet to the vessel and a second heat exchange passage for condensed water vapor downstream from the vessel.

The apparatus heats the waste water and distills the water component. Heat recovery from the condensed water vapor in the two heat exchangers makes the apparatus economically effective to operate.

According to another aspect of the present invention there is provided pasteurization apparatus for waste solids, comprising: an auger tube having an inlet and outlet; auger flighting along the tube for feeding waste solids through the tube from the inlet to the outlet; and heating means for heating the auger tube.

This secondary apparatus sterilizes the waste solids from the primary distillation equipment.

According to a third aspect of the present invention there is provided a method of treating waste water comprising: passing the waste water into an evaporator vessel so as to maintain a substantially uniform quantity of waste water therein; evaporating water from the waste water in the vessel; withdrawing water vapor from the vessel; compressing the withdrawn water vapors; extracting heat from the compressed water vapor to condense the vapor; adding the extracted heat to the waste water in the evaporator vessel; and transferring heat from the condensed water vapor to the waste water before the waste water enters the evaporator vessel.

In the accompanying drawings, which illustrate an exemplary embodiment of the present invention, Figure 1 is an overall schematic illustrating the process and apparatus; and Figure 2 is a detailed schematic illustrating the heat exchange and the evaporation portions of the system.

Referring to the accompanying drawing, especially Figure 1, there is illustrated a multi-stage waste water purification system. In the first stage a separator 10 receives raw waste water through an inlet 12. The waste water is subjected to a four-phase separation in which gases, solids and water immiscible liquids such as oils are separated from the water borne fraction of the waste. As will be appreciated, this is not a complete separation of all suspended matter but rather a preliminary separation stage.

Subsequently, the water based waste is withdrawn through an outlet 14.

The solids are discharged through an outlet 16.

The liquid component withdrawn from the separator 10 is passed to an accumulator tank 18 through its inlet 20 A further liquid-solid separation is carried out by gravity settling in the accumulator tank. The liquid is withdrawn through an outlet 22, while settled solids are withdrawn through a solids outlet 24.

The liquid component from the accumulator tank is passed through a heat exchanger 26 to an evaporator vessel 28. This vessel is illustrated schematically as having a pure water outlet 30 and a solids outlet 32. The solid materials discharged from the separator, the accumulator tank and the evaporator are all collected on a sludge condenser and dryer 34 where they are dried for subsequent collection in a collector 35 for use as fertilizer.

Figure 2 illustrates the portion of the apparatus downstream from the separator 10. This includes the pressure separator 18 with its inlet 20 and bottom solids discharge 24. Liquid from the pressure separator passes through the heat exchanger 26 to the evaporator vessel 28.

The evaporator vessel has an inlet valve 38 that is controlled by a float or other level control 40 to maintain a constant liquid level in the evaporator. A head space 42 is provided above the liquid surface 44.

Submerged in the liquid in the evaporator vessel is a heat exchanger 46 composed of a series of thin walled plates 48. Alternate pairs of the plates are connected to provide condensation chambers 50 spaced apart by evaporation chambers 52. Evaporation chambers 52 are filled with the waste liquid in the evaporator. A solids outlet 54 is provided in the bottom of the evaporator to discharge solids that accumulate at the bottom of the evaporator.

A vapor pump 56 withdraws vapor from the head space 42 and compresses that vapor. The compressed vapor is returned to the evaporator vessel to pass through the condensation chambers 50 of the heat exchanger 46. In passing through the condensation chambers, the vapor is condensed, yielding its latent heat of vaporization to the incoming liquid waste. This recovers most of the heat expended in evaporating the water from the liquid waste into the head space 42 so that it may be withdrawn and compressed by the pump 56. From the heat exchanger 46, the condensate passes to the heat exchanger 26, where it yields further heat to the incoming liquid waste.

The evaporator 28 is equipped with appropriate instrumentation and controls to allow its operation at various desired pressures and temperatures.

A vortex breaker is provided at the inlet to the vapor pump or compressor 56 to prevent any cyclonic action within the head space of the evaporator. This ensures that an equal vapor pressure is exerted over the entire liquid-vapor interface.

In a computed example of the system, liquid enters the pressure vessel 18 at a flow rate of approximately 450 litres/hour, a pressure of about 170 kPa and a temperature of about 4.50C. The pump 56 increases the pressure of the water vapor by approximately 20.7 kPa.

The approximate water yield from the heat exchanger 26 is 447.8 litres/hour at 5.60 C. The temperature difference between the incoming waste water and the discharged, purified, treated water is about 1 0C, a limited heat loss.

Returning to Figure 1, the sludge dryer 34 is, in the preferred embodiment, a close tolerance auger with an auger tube having an inlet or inlets for receiving the solid sludge and close fitting auger flighting extending the length of the tube for delivering the sludge from the inlet to the outlet. The auger tube is fitted with a steam jacket so as to heat the sludge and drive off the moisture, so that the solid is dried and pasteurized prior to discharge.

While one embodiment of the present invention has been described in the foregoing, it is to be understood that other embodiments are possible within the scope of the invention.

Claims (8)

CLAIMS:

1. A waste water treatment evaporator comprising: a closed vessel; a waste inlet to the vessel; a water vapor outlet from the vessel; a solids outlet from the vessel; pump means for pumping water vapor from the water vapor outlet; a first heat exchanger within the vessel having an inlet connected to the pump means for receiving water vapor therefrom and an outlet for discharging condensed water vapor; and a second heat exchanger externally of the vessel and having a first heat exchange passage for waste upstream of the waste inlet to the vessel and a second heat exchange passage for condensed water vapor downstream from the vessel.

2. An evaporator according to Claim 1 wherein the first heat exchanger comprises a plurality of thin walled, substantially vertically oriented plates in the vessel, the plates being connected to provide alternate condensing and evaporation chambers across the vessel.

3. An evaporator according to Claim 2 including liquid level control means for maintaining a predetermined liquid level in the vessel, and wherein the plates are located below the liquid level so as to remain fully submerged in the liquid.

4. An evaporator according to Claim 1, 2 or 3 including a solids discharge for discharging solids from the vessel.

5. Pasteurization apparatus for waste solids, comprising: an auger tube having an inlet and outlet; auger flighting along the tube for feeding waste solids through the tube from the inlet to the outlet; and heating means for heating the auger tube.

6. Apparatus according to Claim 5 wherein the heating means comprise a steam jacket around the auger tube.

7. A method of treating waste water comprising: passing the waste water into an evaporator vessel so as to maintain a substantially uniform quantity of waste water therein; evaporating water from the waste water in the vessel; withdrawing water vapor from the vessel; compressing the withdrawn water vapors; extracting heat from the compressed water vapor to condense the vapor; adding the extracted heat to the waste water in the evaporator vessel; and transferring heat from the condensed water vapor to the waste water before the waste water enters the evaporator vessel.

8. A method according to Claim 7 including the preliminary step of separating immiscible liquids, solids and gases from the waste water.