AU2008200270A1 - Domestic Wastewater Treatment Plant - Google Patents

Description

00 1 SDOMESTIC WASTEWATER TREATMENT PLANT Field of the Invention.

ct 0 The present invention relates to wastewater treatment and particularly 00 to domestic wastewater treatment systems including an alkaliser recycle.

Background Art.

Activated sludge is a process in sewage treatment in which air or Soxygen is forced into sewage liquor to develop a biological floc which reduces the 00 organic content of the sewage. In all activated sludge plants, once the sewage has 00 Sreceived sufficient treatment, excess mixed liquor is discharged into settling tanks and S 10 the supernatant is run off to undergo further treatment before discharge. Part of the settled material, the sludge, is returned to the head of the aeration system to re-seed the new sewage entering the tank. This fraction of the floc is called R.A.S Return Activated Sludge. The remaining sludge, also called W.A.S Waste Activated Sludge, is further treated prior to disposal. (W.A.S is also sometimes called S.A.S Surplus Activated Sludge) Activated sludge is also the name given to the active biological material produced by activated sludge plants and which affects all the purification processes. This material, which in healthy sludge is a brown floc, is largely composed off saprophytic bacteria but also has an important protozoan flora mainly composed of amoebae, Spirotrichs, Peritrichs including Vorticellids and a range of other filter feeding species. Other important constituents include motile and sedentary Rotifers. In poorly managed activated sludge, a range of mucilaginous filamentous bacteria can develop including Sphaerotilus natans which produces a sludge that is difficult to settle and can result in the sludge blanket decanting over the weirs in the settlement tank to severely contaminate the final effluent quality. This material is often described as sewage fungus but true fungal communities are relatively uncommon.

Arrangement The general arrangement of an activated sludge process for removing carbonaceous pollution includes the following items: 1. Aeration tank where air (or oxygen) is injected in the mixed liquor.

2. Settling tank (usually referred to as "final clarifier" or "secondary settling tank") to allow the biological flocs to settle, thus separating the biological sludge from the clear treated water.

00 2 Treatment of nitrogenous matter or phosphate involve additional steps Swhere the mixed liquor is left in anoxic condition (no residual dissolved oxygen).

0There are many activated sludge treatment processes in the art. A 00 problem that all activated sludge treatment processes possess is the fragility of the process to acid levels as the process is dependant upon the biological activity of living organisms. Changes to the process conditions and particularly the level of acid in the Ssystem can kill or severely inhibit the activity of the bacteria that the system depends 00 upon for effectiveness.

00 SLimestone has been used in the past to raise the pH of wastewater (N 10 towards the neutral level for industrial or mine acidic wastewaters, however, the limestone addition is always used on the feed stream. This requires an ongoing source of fresh limestone to add to the feed stream and also has attendant problems particularly the coating the limestone in biologic slime reducing its effectiveness.

It will be clearly understood that, if a prior art publication is referred to herein, this reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country.

Summary of the Invention.

The present invention is directed to a domestic wastewater treatment plant, which may at least partially overcome at least one of the abovementioned disadvantages or provide the consumer with a useful or commercial choice.

In a first form, the invention resides in a domestic wastewater treatment plant including at least one anoxic treatment stage, and at least one recycle flow to return at least partially treated wastewater to the at least one anoxic stage of the process via at least one alkaliser stage.

In a second form, the invention resides in a domestic wastewater treatment plant including an activated sludge treatment process with at least one anoxic treatment stage, and at least one recycle flow to return at least partially treated wastewater to the at least one anoxic stage of the process via at least one alkaliser stage.

In a third form, the invention resides in a domestic wastewater treatment plant including a) a raw effluent inlet, b) at least one anaerobic treatment stage, 00 3 c) at least one anoxic treatment stage, d) at least one aerobic treatment stage, Se) at least one settling stage and 00 f) a treated water outlet and further including g) at least one recycle flow to return at least partially treated wastewater to the at least one anoxic stage of the process via at least one alkaliser stage.

In a fourth form, the invention resides in a domestic wastewater treatment plant including at least an aeration based wastewater treatment portion with 00 Sat least one of an anoxic, aerobic or anaerobic stage, and at least one recycle flow to S 10 return at least partially treated wastewater to at least one of the anoxic, aerobic or anaerobic stages of the process via at least one alkaliser stage.

In a fifth form, the invention resides in a domestic wastewater treatment plant including a) a raw effluent inlet, b) at least one anaerobic treatment stage, c) at least one anoxic treatment stage, d) at least one aerobic treatment stage, e) at least one settling stage and f) a treated water outlet and further including g) at least one recycle flow to return at least partially treated wastewater to the at least one anaerobic stage of the process via at least one alkaliser stage.

In a sixth form, the invention resides in a domestic wastewater treatment plant including at least one recycle flow to return at least partially treated wastewater from a later stage to an earlier stage of the process via at least one alkaliser stage.

There may be more than one recycle stream via an alkaliser stage in a single process stream. Where more than one recycle stream is used, the recycle streams will preferably originate at different process stages and be directed to different process stages or steps earlier in the process stream.

The influent pH has significant impact on wastewater treatment. It is possible to treat organic wastewaters over a wide pH range, however the optimum pH for microbial growth is between 6.5 and 7.5. It is interesting to note that bacteria grow 00 4 best at slightly alkaline water. Similarly, algae and fungi grow best in slightly acidic water. The response to pH is largely due to changes in enzymatic activity.

The present invention is largely directed toward the inclusion of an 00 alkalised recycle to the at least one anoxic stage of the process. However the full effect of the recycle on the process is best understood if the process steps are understood.

SThe plant of the present invention will typically be provided in a 00 prefabricated form able to be retrofit into association with an existing septic tank. The 00 Splant may provide one or more process steps in separate or combined process vessels.

N 10 Typically the vessels and attendant connecting pipe work will be modular in nature able to be connected together quickly and easily with a minimum of tools.

The plant of the present invention will typically be relatively small scale (for treatment of sewage for 10-12 persons) with optimum flow rates for that scale. However, scale-up of the plant is possible.

The plant of the present invention will preferably include or be based on an activated sludge water treatment process.

The preferred embodiment of the present invention includes at least one anaerobic treatment stage, at least one anoxic treatment stage, at least one aerobic treatment stage, and at least one settling stage.

Anoxic Stage Anoxic processes are typically used for the removal of nitrogen from wastewater. The process of biological nitrogen removal is known as denitrification.

Denitrification requires that nitrogen be first converted to nitrate, which typically occurs in an aerobic treatment process such as a trickling filter or aerated suspended growth system. In the preferred process of the present invention, the aerobic digestion stage is typically after the anoxic stage and a recycle line may be provided.

The nitrified water is then exposed to an environment without free oxygen. Organisms in this anoxic system use the nitrate as an electron acceptor and release nitrogen in the form of nitrogen gas or nitrogen oxides. A readily biodegradable carbon source is also needed for efficient denitrification processes to occur. It should be noted that sulfate can also be used as an electron acceptor, resulting in the formation of hydrogen sulfide.

Two common types of anoxic reactors are: 00 C, 1. Anoxic attachedgrowth reactors The basic form of the anoxic attached growth reactor is a submerged 00 basin filled with a support medium and, in some cases, carbon source. Anoxic upflow rock filters have been used for nitrogen removal from nitrified wastewater. Nitrified wastewater flows into the bottom of the filter and is mixed with the carbon source as it flows up through the fixed packing. The organic matter is septic tank effluent is the Smost common carbon source used because of its availability; however, methanol or an 00 alternate compound soap) may also be used to supply carbon.

2. Anoxic suspended growth reactors The suspended growth reactor is simply a tank in which nitrified wastewater is mixed with a carbon source, typically septic tank effluent. In some cases, nitrified wastewater is discharged back to the primary treatment stage, such as a septic tank, for denitrification. Nearly all of the suspended growth treatment systems and multi-pass trickling biofilter systems make use of an anoxic stage, through recycle of the aerobic stage effluent, to accomplish denitrification.

The anoxic stage of the present invention may be mixed but does not have to be and is preferably not aerated. The anoxic stage may be combined with and will preferably follow the anaerobic digestion stage of the process.

Nitrified process water flows into the anoxic reactor and is combined with a supplemental carbon source, typically a dilute methanol solution. Chemical is metered by calibration with an electrical signal from the feed pump. Treatment process includes devices for flow monitoring, float switches, and alarms. Effluent from the anoxic reactor is treated in a septic tank for solids removal before being discharged.

Anaerobic Stage Anaerobic digestion has long been used for the stabilization of wastewater sludges.

Its advantages over aerobic processes are the following: 1. Anaerobic digestion uses readily available CO 2 as an electron acceptor as its oxygen source. It requires no oxygen, the supply of which adds substantially to the cost of wastewater treatment.

2. Anaerobic digestion produces lower amounts of sludge (3 20 times less than aerobic processes), since the energy yields of anaerobic bacteria are relatively 00 6 low. Most of the energy derived from substrate breakdown is found in the final Sproduct, CH 4 As regards cell yields, 50% of organic carbon is converted to 0biomass under aerobic conditions. The net amount of cells produced per metric 00 ton of COD destroyed is 20-150kg, as compared to 400-600kg for aerobic digestion.

3. Anaerobic digestion produces a useful gas, methane. This gas contains about of the energy, and can be burned on site to provide heat for digesters or to 00 generate electricity. Little energy is wasted as heat. Methane 00 Sproduction contributes to the BOD reduction in digested sludge.

S 10 4. Energy required for wastewater treatment is reduced.

Anaerobic digestion is suitable for high-strength industrial wastes.

6. It is possible to apply high loading rates to the digester.

7. Anaerobic systems can biodegrade xenobiotic compounds such as chlorinated aliphatic hydrocarbons trichloroethylene, trihalomethanes) and 1 5 recalcitrant natural compounds such as lignin.

Anaerobic digesters are typically large fermentation tanks provided with mechanical mixing, heating, gas collection, sludge addition and withdrawal ports, and supernatant outlets. Sludge digestion and settling occur simultaneously in the tank. Sludge stratifies and forms the following layers from the bottom to the tip of the tank: digested sludge, actively digested sludge, supernatant, a scum layer and gas.

Higher sludge loading rates are achieved in the high-rate version, in which sludge is continuously mixed and heated.

Aerobic Stage Primary treated wastewater enters the aeration unit and is mixed with dissolved oxygen and suspended and/or attached microbes. The aerobic microbes convert organic compounds into energy, new cells and residual matter. As the water moves through the clarifier, a portion of the biological solids are separated out of the effluent and are retained within the stage. The biological solids settle back into the aeration chamber where they serve as seed for new microbial growth. Settled biomass and residuals will accumulate in the bottom of the chamber and must be removed with periodic maintenance.

As the biomass creates an oxygen demand, clarification is an important part of generating a high-quality effluent. The soluble BOD of the effluent is generally 00 7 below 5 mg/L, but the biomass solids carry over may produce an effluent BOD of Smg/L or greater. Many aerobic reactors have a conical-shaped clarifier to promote 0separation of the biomass. As the cross-sectional area of upflow increases, the fluid 00 velocity decreases. Once the settling velocity of the biomass is greater than the fluid velocity, the biomass will no longer move upward. During periods of no flow, the biomass will settle back into the aeration chamber. Other aerobic reactors may

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Sincorporate inline filters to separate the biomass from the effluent. Such filters require 00 periodic maintenance to remove the build up of solids.

00 SIn the aerobic process, organic nitrogen and ammonia are converted to N 10 nitrate. Under anoxic conditions (no molecular oxygen), the nitrate is denitrified to nitrogen gas. Some reactors are designed to also provide denitrification as part of their operation. Design modifications include intermittently supplying air and recirculate the nitrified wastewater into the anoxic regions within the treatment unit.

Most aerobic reactors operate as an intermitted-flow, complete mix tank, constant volume reactors. The flow is intermitted versus continuous because influent is not continuous. The contents of the aeration chamber are thoroughly mixed to maximize the contact between dissolved oxygen, microbes and wastewater.

Effluent moves out of the aeration chamber and into a clarifier. The rate of discharge is typically in direct response to the rate of inflow. The exception to this generalization is sequencing batch reactors.

In order to maintain aerobic conditions, large quantities of oxygen must typically be provided. If the influent to the reactor has an ultimate BOD of 100 mg/L, then 100 mg of dissolved oxygen per litre of influent must be provide in order to satisfy the oxygen demand. The primary function of the aeration system is to transfer oxygen to the liquid at such a rate that dissolved oxygen never becomes a limiting factor. Oxygen is only slightly soluble in water. Natural aeration cannot meet the demand of this high-rate unit process and therefore, oxygen transfer must be engineered into the treatment unit in order to maintain a minimum residual of I mg of dissolved oxygen per litre of water.

The passage of oxygen from the gas phase to the liquid phase is absorption. The driving force of oxygen transfer is the concentration gradient between the atmosphere and the bulk liquid. This gradient is created when there is a difference in the equilibrium concentration in the two phases. Thus the desire to obtain 00 8

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equilibrium drives the transfer of atmospheric oxygen into the water. The saturated concentration of dissolved oxygen changes with temperature, barometric pressure, 0 salinity, and with the concentration of water impurities. Designers of reactors have to 0O maximize the contact interface (surface area) between the gas and liquid phases in order to maximize the opportunity for oxygen transfer. In other words, systems must be designed so that the concentration gradient between the gas-liquid interface is high Oand therefore, the rate of transfer will be high.

ri Aeration units are evaluated on the mass of oxygen transferred per unit 00 of air introduced to the water. This is an efficiency rating. The goal is to maximize the mass of 2Oz transferred per unit of energy consumed by the device. The most common method of maximizing energy efficiency is to combine mixing with aeration.

Turbulent mixing is required to maximize the opportunity for microbes to come in contact with both soluble organic compounds and dissolved oxygen. If steady-state conditions can be maintained, the rate of oxygen transfer is equal to the rate of consumption by the microorganisms. Dissolved oxygen in the mixed liquor needs to be maintained at 1 to 3 mg/L. For residential strength wastewater, 2 to 7 grams per day of dissolved oxygen are needed for each gram of MLVSS.

For most reactors, the actual oxygen mass transfer efficiency is proprietary information. Manufacturers market specific reactor models based on organic and hydraulic loading. For a given unit, the aeration device is rated to provide sufficient dissolved oxygen for the given range of input oxygen demands (organic loading).

Typically, there are two types of aerators used by manufacturers of reactors diffused air systems and mechanical aeration systems.

Diffused air systems use submerged devices (sparkers) to inject air into the bulk liquid. Air injected below the surface has continuous contact with the liquid as it rises to the surface. The smaller the bubble, the greater the oxygen transfer rate.

Additionally, bubbles formed deep within the chamber will have more hydrostatic pressure to drive the oxygen transfer and more time-of-contact with the air-water interface. One method of creating small bubbles is with porous ceramic diffusers. The small-interconnected passageways inside the ceramic matrix create a tremendous loss of air pressure and many points of outflow. This combination produces streams of small bubbles over the surface of the ceramic diffuser.

00 9 A second method of injecting air is to machine orifices into pipes and plates. Many large-scale aerobic digesters use jet aerators. Streams of air serve to transfer oxygen and to provide vigorous mixing of the basin contents.

00 oO A third type of diffuse aerator is an aspirated mixer. A mixing-propeller is attached to a hollow shaft that is vented to the atmosphere. This paddle is located near the bottom of the aeration chamber. As the shaft spins, a venturi-type effect Screates a vacuum down the shaft and injects air into the water.

00 The mixing devices must balance the need for agitation while oO Sminimizing the shearing of floc. If shear is excessive, poor settling conditions in the 10 clarifier can result.

The system of the present invention typically incorporates fine bubble diffusers, normally two.

Settling Stage (Clarification) After thorough treatment is accomplished in the aeration chamber, hydraulic displacement forces the effluent into the clarifier. The settleable solids will settle down the slope of the clarifier and re-enter the mixing zone for further aerated treatment. The "polished" effluent will rise upwards through the clarifier to the discharge pipe.

The present invention preferably includes a two stage settling system with a pre-settler and a settler. The pre-settler preferably removes the majority of activated sludge. This heavy sludge is returned to the main aeration reactor. Following the pre-settler is the main settler where further settling of the finer sludge occurs. The sludge is collected via an airlift/eductor pump and fed back to the main aeration reactor. The clarified liquor that is left after sludge removal and return to aeration, is removed through separate pipes to two locations. The primary flow is to biocide treatment but a smaller secondary flow proceeds to the alkaliser.

Alkaliser Activated sludge process can be susceptible to generation of acidic conditions and by maintaining alkalinity with calcium carbonate, this condition is controlled. With pH modification, optimum biological processes and BOD removal is maintained. Furthermore, the addition of calcium allows higher proportion of phosphate precipitation. To ensure calcium and pH is modified at the early stages of 00 Sthe process, the recycle is fed to the anoxic chamber, also assisting in Nitrate and SNitrite conversion to nitrogen.

0 The alkaliser is typically a vessel holding a soluble form of calcium 00 carbonate. The calcium carbonate is preferably in solid form and a particularly preferred source is solid marble in crushed form. Any other relatively soluble form of marble can be used.

SThe system may further include a biocide treatment step. This step will 00 typically include the use of chlorine to kill any microorganisms present in the 00 Sdischarge water.

S 10 The system of the present invention preferably contains the above process steps in the order described.

According to the present invention, a portion of the treated wastewater is recirculated back to the anoxic chamber of an activated sludge process via a bed of crushed marble.

As previously stated, the design has sufficient internal capacity and processing capability to enable a number of different performance levels. The performance levels start with 10 equivalent persons, advanced secondary treatment with nutrient removal and progresses to 20 equivalent persons for secondary treatment for the same treatment plant. It is expected that the testing regime will prove these performance characteristics and allow approval under these set criteria.

The process has been implemented in a recirculation stream and towards the tail of the process because: 1) Doing this limits biological growth and coating the marble in bio-slime reducing its effectiveness; 2) Having it at the tail end allows for phosphate take up of activated sludge before precipitation; and 3) Adds to the denitrification recirculation stream and is lower in dissolved oxygen.

Thus reduces the formation of calcium oxide coating the marble/limestone that reduces the system's effectiveness.

Typically, the return or recycle stream of the product water flow will be a flow within the range of all approximately 5 to 25% of the product water flow.

However, the amount recycled will typically be dependent on the acidity level of the

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00 11 product water flow. The recycle stream may be returned to the inlet of the treatment Splant or alternatively to a section or process step or stage within the treatment process.

0The recycle stream via the alkalisation stage can be utilised with any 00 existing biological process, but is preferred for use with an aerobic treatment system and particularly an aerobic treatment system which utilises a chlorine/bromine or ultraviolet light this infection/sterilisation/biocidal process. Although focused on Sadaptation to a domestic treatment process of between 7 and 20 equivalent persons 0 processing capacity, the process can be utilised for systems of between 20 and 2000 00 Sequivalent persons; however, not limited to this equivalent treatment capability.

The inclusion of a recycle via alkaliser stage will preferably not only incorporate contact with solid calcium carbonate will preferably also incorporate contact with an iron source. Without wishing to be limited by theory, a process including an alkalisation stage with iron contact source will typically be more effective in retarding biological growth on the calcium carbonate as it has biocide present and a much lower biological organism concentration in the process stream.

According to a particularly preferred embodiment, the process will include a biocide treatment stage. The product biocide/sterilised treated water which may be used as a recycle will preferably be recycled through the alkaliser stage, reducing acidity and increasing alkalinity and calcium concentrations within the water.

Some of the biocide is lost due to chemical reactions with the alkaliser stage.

The alkalisation stage will preferably include a number of subprocesses. According to a particularly preferred embodiment will be an inlet or feed into the alkali stage will preferably enter a vessel in which the process fluid will contact an alkali source such as a calcium carbonate source of which crushed marble or limestone is preferred.

The alkali treated process fluid will then preferably continue into a biocide treatment stage. Preferably the biocide treatment stage will typically be or include a chlorine-based biocide removal process step. Most preferably the process fluid will be contacted with an iron or steel source to form Ferric chloride which, whilst not wishing to be limited by theory, typically aids in the settling of activated sludge and also in the production of a product fluid having a lower amount of suspended solids.

The process fluid will preferably then enter a holding vessel with a 00 12 N residence time determined to allow the natural destruction or degradation of the biocide.

0The exit stream from the holding vessel will then preferably be 00 returned to either the anaerobic section, the anoxic section or the aerobic section of the waste water treatment process, these three sections listed in order of preference as the destination of the treated recycle water.

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SAccording to the most preferred embodiment, the at least one 0 alkalisation stage referred to in this application will include the three process stages 00 Sdescribed above, namely a vessel to contact the water with an alkali source, a biocide N 10 removal stage in a separate vessel and then a holding vessel.

Preferably, the water exiting the calcium carbonate bed is contacted with iron or steel. In the case of chlorine or bromine biocidal treatments, the remaining chemical is removed allowing safe levels for return to the wastewater treatment process. Chlorine being the most common biocidal treatment allows for ferric chloride to form. The product water that is at a more neutral pH after contact with the calcium carbonate and having the biocide stripped from solution is held in a holding vessel prior to return to the wastewater treatment plant.

The degree of recycled water applied to the Alkaliser is dependent of the levels of acidity of the process. The degree of recycle will be between 25% in severe acid water cases to 5% for minimal treatment systems.

The advantages of this design include: 1) improved pH control to keep the solution from being acidic and to optimise the biological processes; 2) additional calcium carbonate to buffer pH changes, that is to increase alkalinity; 3) additional calcium to assist in the Sodium Absorption Ratio of the treated water to be irrigated, that is to assist in maintaining soil quality and to assist soils high in clay; 4) increased concentration of calcium to force calcium phosphate precipitation; the production of ferric chloride for chlorine based biocidal treatment plants, aids in the settling of activated sludge and aids in the production of lower suspended solid product water; and 6) Increased calcium concentrations aids in the production of stronger, more robust biological flocs.

Definitions 00 13 Raw water water entering the system SMixed liquor the mix of raw water and activated sludge.

SReturn activated sludge activated sludge extracted from the system 00 and mixed with raw water to form the mixed liquor.

Waste activated sludge activated sludge in excess that is extracted from the system to be directed to sludge treatment.

O Sludge age the average time biological sludge stay in the system. In simpler 00 words, it can be defined as the average age of a bacteria in the system.

00 O Brief Description of the Drawings.

S 10 An embodiment of the invention will be described with reference to the following drawings, in which: Figure 1 is a flow diagram of the process according to a first preferred embodiment of the present invention.

Figure 2 is a flow diagram of a process according to a second preferred embodiment of the present invention.

Figure 3 is a flow diagram of a process according to an embodiment of the present invention utilised in a generic waste water treatment system.

Figure 4 is a flow diagram of a preferred embodiment of an alkalisation stage located in a recycle stream of a wastewater treatment system.

Detailed Description of the Preferred Embodiment.

According to a preferred embodiment of the present invention, a domestic wastewater treatment plant is provided.

A process flow diagram of a particularly preferred embodiment is included as Figure 1. This PFD and following equipment sizes relate only to a system for flow and stream characteristics for the treatment of effluent from 10 to equivalent persons of advanced secondary quality with nutrient removal.

The process involves between 22 and 42 hours of anaerobic digestion in a standard 3800-litre septic tank. From the primary, anaerobic treatment the wastewater flows to an anoxic chamber of the order of 800 litres volume where a culture of anoxic bacteria further treats the waste to convert nitrate and nitrite to nitrogen. To enable digestion of nitrate and nitrite a recycle stream of the order of 000 litres per day is fed to the anoxic chamber from the aeration chamber. The recirculation rate is of the order of between 5:1 to 20:1 compared to influent flow.

00 14 Another stream of Alkaliser Recycle, of considerably lower flow rate is also fed to the Sanoxic chamber. The recirculation is accomplished by an air-lift/eductor pump driven 00 with compressed air.

The combined flow of primary treated effluent, alkaliser recycle and anoxic recycle is fed to the aeration chamber. Via two fine bubble air diffusers, air is fed to the Aerobic digestion chamber to enable suspension and growth of activated Ssludge. This sludge performs the primary BOD removal of the process. The activated 0 sludge process occurs in a chamber of approximately 1790 litres of capacity. Two 00 Sactivated sludge return streams are also recycled back to the activated sludge chamber to maintain biomass concentration.

From the aerobic chamber, the mixed liquor is fed to the settling process. The settling process is two stage, with a 200 litre pre-settler to remove the majority of activated sludge. This heavy sludge is returned to the main aeration chamber. Following the pre-settler is the main settler where further settling of the finer sludge occurs. The sludge is collected via an airlift eductor pump and fed back to the main aeration chamber. The clarified liquor that is left after sludge removal and return to aeration, reports to essentially two locations. The primary flow is to biocide treatment and the pump out chamber. A smaller secondary flow reports to the alkaliser.

The alkaliser is a vessel of the order of between 100 and 200 litres and is 75% filled with crushed marble, a reasonably soluble form calcium carbonate.

Biocide treatment is accomplished by contacting treated effluent with trichloroisocyanuric acid tablets where free chlorine is released into the water oxidising microorganisms. The chlorinated water is collected in the pump-out chamber whereby a pump discharges on level basis. The pump-out system is fitted with a pressure gauge and pressure relief. The pressure relief protects pump from running dry in the case of level control failure or downstream faults.

The Anasalk Plant is fitted with an emergency overflow that in the event of pump or power failure water is discharged below ground in either a transpiration trench or immediately around the installed treatment plant in an area filled with aggregate. This allows for fail-safe condition.

The design is also fitted with a manual level device that yields visual warning of a fault condition, also indicating possible system power loss and pump 1 00 failure. This level indication system is custom fitted to the system's vent system. All system vents are fitted with mosquito and insect proof fittings.

The plant supplies all of its air uses with a Nitto 120 I/min air 00 compressor. The compressor supplies two fine bubble air diffusers and three airlift/eductor pumps. Air supply is monitored by pressure and in the situation of failure, a warning light is activated.

(,i The power supply is designed with residual current protection so that 00 any pump or compressor fault that results in earth leakage, results in tripping of the 00 Sresidual current device. This inclusion reduces reliance on the site's protection devices, if in existence.

One advantage of the Anasalk Plant is that other than the anaerobic chamber/septic tank, all other processes are retrofitted to a septic tank and can be added to existing septic only sites to enable increased wastewater treatment quality.

The Anasalk Plant can also be installed in above ground vessels where site characteristics may warrant above ground installation due to factors such as high subsurface rock content and high water table levels.

The pump-out pump is a high-pressure lower flow pump allowing for feed to a Netafim-type or other subsurface irrigation system, often a preference in water disposal for irrigation systems.

There are two types of internal fabrication for the Anasalk Plant; the initial type proposed for the trial has internal partitions to obtain the volumed sections for the Anoxic and Settling Chambers. The second type of design is where all internal chambers are fabricated from sections of pipe.

The design has sufficient internal capacity and processing capability to enable a number of different performance levels. The performance levels start with equivalent persons, advanced secondary treatment with nutrient removal and progresses to 20 equivalent persons for secondary treatment for the same treatment plant. It is expected that the testing regime will prove these performance characteristics and allow approval under these set criteria.

Materials of Construction Materials of construction for the internals of the retrofitted modified 3800 litre septic tank will be either PVC, Poly Ethylene, or resin coated marine ply in the case of partitions or baffles. All screws and metal fittings are to be of 304 00 16 C, Stainless Steel.

SAncillary Equipment Components The key components utilised in the process are the compressor, fine bubble diffusers, pump and relief valve on the pump's discharge.

Compressor Nitto Kohki Australia Pty Ltd Model: LA-120 00 Rated Air Flow: 120 1/min Rated Pressure: 0.018 MPa Discharge Treated Effluent Pump Grundfos Model: Hilift Max Pressure: 350 kPa Max Flow: 5 m 3 /h Standard Operating Point: 250 kPa at 2.5 m 3 /h Pressure Relief Spraying Systems Co.

Model 2310 A Size: /4" Set Pressure: 300 kPa Membrane Air Diffuser AIR+ Membrane Air Diffuser Model: M250 Air Rate: 1.7 to 4.2 m 3 /h Diffusion Area: 0.043 m 2 Number of holes: 6000 A variation of the process illustrated in Figure 1 is illustrated in Figure 2. According to the alternative process illustrated in Figure 2, the recycle including the alkalisation stage may be used as well as, or instead of, the recycle illustrated in Figure 1. As can be seen from Figure 2, the alternative/additional recycle stream removes a portion of the partially treated process water from the biocide treatment stage and returns this water to the anaerobic treatment stage via the alkalisation stage.

Alternatively, the alkalisation stage may be used according to the 00 17

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process flow diagram illustrating Figure 3 wherein fluid is removed from the end of a generic waste water treatment system and returned, via an alkalisation stage, to either the system feed line or to a section within the treatment system.

0O A particularly preferred alkalisation stage is illustrated in Figure 4 as including a number of sub-processes. The preferred alkalisation stage includes three process stages. According to the illustrated set of sub-processes, the inlet or feed into (,i Sthe alkalisation stage enters a vessel in which the process fluid contacts an alkali 0 source such as a calcium carbonate source, of which crushed marble or limestone is 0O preferred.

N 10 The alkali treated process fluid then continues into a biocide treatment stage. The biocide treatment stage will illustrated is a chlorine-based biocide removal process step in which the process fluid iscontacted with an iron or steel source to form ferric chloride which typically aids in the settling of activated sludge and also in the production of a product fluid having a lower amount of suspended solids.

The process fluid then enters a holding vessel with a residence time determined to allow the natural destruction or degradation of the biocide prior to reintroduction into the process stream.

The exit stream from the holding vessel is returned to either the anaerobic section, the anoxic section or the aerobic section of the waste water treatment process, these three sections listed in order of preference as the destination of the treated recycle water.

In the present specification and claims (if any), the word "comprising" and its derivatives including "comprises" and "comprise" include each of the stated integers but does not exclude the inclusion of one or more further integers.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more combinations.

In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. It is to be 00 18 N, understood that the invention is not limited to specific features shown or described Ssince the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims (if any) appropriately interpreted by those skilled in the art.

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Claims (15)

1. 2. A domestic wastewater treatment plant including i. a raw effluent inlet, ii. at least one anaerobic treatment stage, N0 iii. at least one anoxic treatment stage, 00 iv. at least one aerobic treatment stage, v. at least one settling stage and vi. a treated water outlet and further including vii. at least one recycle flow to return at least partially treated wastewater to the at least one anoxic stage of the process via at least one alkaliser stage.
2. 3. A domestic wastewater treatment plant including at least an aeration based wastewater treatment portion with at least one of an anoxic, aerobic or anaerobic stage, and at least one recycle flow to return at least partially treated wastewater to at least one of the anoxic, aerobic or anaerobic stages of the process via at least one alkaliser stage.
3. 4. A domestic wastewater treatment plant including i. a raw effluent inlet, ii. at least one anaerobic treatment stage, iii. at least one anoxic treatment stage, iv. at least one aerobic treatment stage, v. at least one settling stage and vi. a treated water outlet and further including vii. at least one recycle flow to return at least partially treated wastewater to the at least one anaerobic stage of the process via at least one alkaliser stage.
4. 5. A domestic wastewater treatment plant including at least one anoxic treatment stage, and at least one recycle flow to return at least partially treated wastewater to the at least one anoxic stage of the process via at least one alkaliser stage. 00
5. 6. A domestic wastewater treatment plant including an activated sludge treatment Sprocess with at least one anoxic treatment stage, and at least one recycle flow to return at least partially treated wastewater to the at least one anoxic stage of 00 the process via at least one alkaliser stage.
6. 7. A domestic wastewater treatment plant according to any one of the preceding claims wherein the at least one alkaliser stage includes the sub-steps of contacting the wastewater with an alkali source, a biocide treatment stage and (N a holding vessel with a residence time determined to allow the natural 00 Sdegradation of the biocide. (N 10 8. A domestic wastewater treatment plant according to any one of the preceding claims including more than one recycle stream via an alkaliser stage in a single process stream.
7. 9. A domestic wastewater treatment plant according to any one of the preceding claims provided in a prefabricated form able to be retrofit into association with an existing septic tank. A domestic wastewater treatment plant according to any one of the preceding claims wherein the plant includes an activated sludge water treatment process.
8. 11. A domestic wastewater treatment plant according to any one of the preceding claims wherein the at least one alkaliser stage includes a vessel holding a soluble form of calcium carbonate.
9. 12. A domestic wastewater treatment plant according to claim 11 wherein the calcium carbonate is in solid form.
10. 13. A domestic wastewater treatment plant according to any one of the preceding claims further including a biocide treatment stage including the use of chlorine.
11. 14. A domestic wastewater treatment plant according to any one of the preceding claims wherein a portion of treated wastewater is recirculated back to an anoxic chamber of an activated sludge process via a bed of crushed marble. A domestic wastewater treatment plant according to any one of the preceding claims wherein the recycle flow is within the range of approximately 5 to of product water flow.
12. 16. A domestic wastewater treatment plant according to either one of claims 7 or 13 wherein the biocide treatment stage includes contact with an iron source. 00 21
13. 17. A domestic wastewater treatment plant according to claim 16 wherein the Swastewater exiting the biocide treatment stage enters a holding vessel with a residence time determined to allow the degradation of the biocide. 00
14. 18. A domestic wastewater treatment plant according to claim 18 wherein the recycle flow exit stream from the holding vessel is returned to either an anaerobic section, an anoxic section or an aerobic section of a waste water (Ni Streatment process, these three sections listed in order of preference as the N0 destination of the recycle flow. 00
15. 19. A domestic wastewater treatment plant substantially as described herein with reference to the accompanying figures.