Field of the Invention

The invention relates to water and wastewater treatment and in particular, a system for reducing for instance, biological activity within said water or wastewater through oxidation.

Background

Conventional wastewater treatment processes involve, in the first instance, passing the wastewater through a settling tank so as to settle solids from the wastewater. The liquid phase is then passed through secondary treatment which involves aerating the wastewater so as to increase bacterial activity and subsequently break down, dissolve and/or suspend the organic solids. The solids are further settled and removed with the wastewater disposed of if the chemical oxygen demand (COD) is too high, then the wastewater may undergo further chemical treatment such as disinfection using chlorine.

Solids, in the form of sludge, removed during primary and secondary treatment are further treated in for instance, digestion tanks before disposal.

Conventional wastewater treatment is known to have some or all of the following disadvantages: i) Odour is released to the surrounding area, during primary and secondary treatment; ii) The biological treatment used in these processes is mostly inefficient in terms of both time taken and space required. iii) The treatment process, as a whole requires a large area and substantive infrastructure costs. iv) Because of the volume involved and potentially biological activity of the sludge, disposal is logistically difficult and expensive.

Despite these disadvantages, many industries and environment treatment providers use the conventional processes because of their proven technology and lack of viable alternatives. It follows therefore that there is a need for an improvement to the conventional process such as any of: requiring a reduction in odour, occupying less space or providing greater efficiency in the processing of the wastewater or management of the solids removed therefrom.

Summary of the Invention

In a first aspect the invention provides a system for the treatment of wastewater comprising a mixing chamber for receiving a flow of wastewater and an injection inlet for receiving an oxidising agent, said mixing chamber arranged to mix said oxidising agent into said flow of wastewater so as to oxidise and discharge said wastewater. In a second aspect the invention provides a method for treating wastewater comprising the steps of: flowing said wastewater into a mixing chamber; injecting an oxidising agent into said mixing chamber; mixing said oxidising agent into said flow of wastewater, and; discharging the oxidised water into a reservoir.

The invention varies from conventional water treatment processes by oxidising the wastewater at the primary treatment stage. Whereas in conventional processes the wastewater maintains a high COD until the completion of the secondary treatment stage, the present invention significantly reduces the COD of the wastewater. Because a bacterial process is not required, odour may be substantially reduced and the solids removed from the wastewater following the primary oxidation stage may also carry a lower COD and so avoid having to undergo secondary treatment. Thus the solids may be used immediately, and instead of presenting a logistical problem may in fact be used directly for application such as fertiliser, landfill or other preventive generating applications.

In one embodiment, the mixing chamber may be a common pipe through which the wastewater and oxidising agent pass before entering a reservoir. In a further embodiment, the mixing chamber may be an open ended housing having at least a portion located within the reservoir confining the area into which the oxidising agent and wastewater are received. Such a small area may provide for a good mixing environment before entering the larger volume of the oxidised wastewater reservoir. The means of adding the oxidising agent will depend on whether it is liquid such as oxidised water or a gas such as ozone is added. Such techniques of adding liquid and gas to large volumes of water are known, and may be used with respect to the present invention, particularly for water treatment. The present invention is not limited, other than in the manner described, to any particular method, with the skilled person capable of implementing an appropriate method in the circumstances.

In one embodiment, a mixing device may be located within the mixing zone to assist with inter alia, mixing of the wastewater and oxidising agent. This may be achieved by making the wastewater more turbulent by the mixing device. Such a mixing device may include rotating members for adding further turbulence to the mixing zone. Such a mixing device may include an air injection to further increase turbulence and thus facilitate further oxidisation of the wastewater. Alternatively, the mixing chamber may include baffles through which the wastewater flow, with the oxidising agent injected in the turbulent flow.

In a further embodiment, the mixing device may include an impeller, rotating blades or other rotating projections to facilitate mixing. The blades or members may also contact particles within the wastewater, breaking said particles into smaller fragments. This has the advantage of increasing the surface area of the particles and so may further facilitate oxidation of the solids within the wastewater.

In a preferred embodiment, the oxidation agent may be ozone. Said ozone may be provided by a conventional ozone generator. In a further embodiment, the ozone may be mixed with other gases prior to injection such as oxygen. The specific mixture of oxygen and ozone may vary. For instance, the ozone may be provided in a concentration in the range of 5 grams per hour to 50 grams per hour. More specifically the ozone may be applied in a concentration within the range of 10 grams per hour to 20 grams per hour for flow rate of 15 - 20 ton/hr.

In a further embodiment, the oxidising agent may be strongly oxidised water. Such oxidised water may be provided by a system such as that disclosed in PCT/SG2005/000228 contents of which are incorporated herewith by reference.

In a further embodiment, the reservoir may include an outlet so as to selectively direct oxidised wastewater to a solidification chamber. Said solidification chamber may be arranged to receive a coagulant so as to coagulate particles within the wastewater.

In a further embodiment, the system may include a solid liquid separator for separating the coagulated solids and liquid.

In a further embodiment, a filter may be included prior to disinfection and polishing of said wastewater prior to final disposal.

Brief Description of Drawings

It will be convenient to further describe the present invention with respect to the accompanying drawings that illustrate possible arrangements of the invention. Other arrangements of the invention are possible and consequently the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention.

Figure 1 is a schematic view of a wastewater treatment process according to one embodiment of the present invention;

Figure 2 is an elevation view of an oxidation chamber according to a further embodiment of the present invention;

Figure 3 is an elevation view of an oxidation chamber according to a further embodiment of the present invention;

Figure 4 is an elevation view of an oxidation chamber according to a still further embodiment of the present invention;

Figure 5 is an elevation view of an oxidation chamber according to a still further embodiment of the present invention.

Detailed Description

Figure 1 shows one embodiment of the wastewater treatment process 5 according to the present invention. It comprises three phases, 10, 15, 20 whereby wastewater 25 enters into containment 30 and mixes with an oxidising agent 40 from a supply of the oxidising agent 35. The oxidised wastewater having a reduced COD is then sent 45 to a solidification chamber whereby a coagulant 55 is added to the oxidised wastewater so as to "clump" particles in suspension. The wastewater with the clumped particles is then sent to a separator 65 whereby the biologically inactive solids are removed 70 and the wastewater sent to a filter 80 and subsequently a disinfection and polishing area 90 should this be required. At the end of the process, it is expected that the COD will be below 30 and so may be disposed of accordingly to natural water waste, the sea or other uses including irrigation.

By providing effective oxidisation at the primary treatment stage, odour, which is a significant disadvantage of conventional systems, may be markedly reduced. Further the process reduces total organic carbon as well as the COD. By management of the concentration of the oxidisation agent, the total organic carbon and COD may be controlled through strategic design of the system.

Because of the oxidisation process, organic components within the wastewater forming less odourless compounds including PO4, SO4, CL2 etc. As a result the process does not produce gases associated with bacterial degradation resulting in said odours. Other embodiments may also lead to a reduction in energy in order to operate the system and may also produce less carbon dioxide by the removal of the bacterial process and subsequently may be beneficial to the environment.

Further, because the COD of the removed solids is low, it may be available for use immediately and potentially for revenue generating applications such as fertilizers.

Further still, gases associated with conventional processes tend to be corrosive such as methane and hydrogen sulphide. As the process according to the present invention reduces or omits these emissions, the life of the system is lengthened due to a reduced corrosive load. Further still, bacterial processes of conventional systems are extremely slow and also require significant area in which to conduct the biological breakdown.

Further as conventional systems require a bacterial process, conditions to promote the bacteria must be optimum in order to achieve an optimum result. The present system which relies on an oxidation agent during the primary treatment stage merely relies upon the concentration applied at that stage to achieve the desired result. Thus an application of the present invention may be less influenced by environmental conditions unlike a conventional process.

Figure 2 shows an oxidisation stage 10 according to one embodiment of the present invention. Here a tank 100 contains a reservoir 105 of oxidised wastewater It will be appreciated that instead of a tank, an underground containment, a pond or other means of containing large volumes of water may be used. The containment will depend upon the volume of water to be treated and so containment facilities used by conventional wastewater treatment systems may also be applicable here. Feeding into the reservoir 105 is a supply of wastewater 106. The supply of wastewater 106 may have come from preliminary treatment whereby large solid inorganic material including paper and plastic may have been removed from the flow using conventional means. Further, preliminary treatment may also remove grit and silt to prevent downstream equipment being damaged. In any event preliminary treatment will follow conventional techniques and do not form part of, nor limit, the present invention. The system according to Figure 2 further includes a feed loop so as to recycle oxidised wastewater 155 with the new inflow of wastewater 106. This is achieved by draining 140 wastewater from the reservoir 105 and passing this through an oxidation generator 150. In this case, the generator 150 may be an ozone generator and/or means to mix ozone generated with oxygen to the flow of oxidised wastewater 140. Thus the flow 110 entering the reservoir may be purely new wastewater 106 or in combination with recycled oxidised wastewater 155. Mixing with the flow of wastewater 110 is an injection inlet for an oxidising agent 115 arranged to mix 120 with the wastewater 110 prior to discharge into the reservoir 105. Thus the last section of pipe acts as a mixing chamber 130 for the oxidising agent 115 and the wastewater 110. In so doing the wastewater may be completely oxidised before exiting 135 the mixing chamber 130.

It will be noted that the oxidised wastewater 135 exiting the mixing chamber 130 does so below the surface 107 of the reservoir 105. Thus a substantial quantity if not in fact all of the mixing 120 of the wastewater and oxidising agent 115 may be immersed within the reservoir and so distinct from air borne oxidation of non-wastewater treatment applications. The volume of wastewater that is involved in, for instance municipal wastewater treatment makes air borne oxidation impossible. Hence, to ensure adequate oxidation occurs various embodiments of the present invention are employed, including the mix/air chamber, mechanical mixing, recycling of oxidised wastewater etc.

It will be appreciated that the oxidising agent 115 may be ozone or a mixture of oxygen and ozone. Further the oxidising agent 115 may be oxidised water. Figure 3 shows an alternative arrangement of the oxidation stage 10 whereby mixing chamber, in the form of the pipe extension 130 of Figure 2 has been replaced by an actual mixing chamber being an enclosed area separated from the reservoir 105 by a housing 165. The wastewater 110 and oxidising agent 115 both exit into the mixing chamber and are permitted to mix 170 within the chamber prior to discharge 175. This arrangement has the advantage of providing a larger volume in which to create turbulent conditions for the efficient mixing of the oxidising agent and wastewater. Such a chamber may also provide for an injection of air (not shown) which may provide bubbles within the mixing chamber 165 and so further facilitate a turbulent environment and so assist in the mixing process.

Figure 4 shows a further embodiment of the present invention whereby the oxidation stage 10 uses a mixing chamber 165 similar to that of Figure 3. However, included within the mixing chamber is a mixing device 180 being an impeller 190 mounted to a motor 185. The impeller 190 rotates 195 within the mixing chamber and provides two distinct benefits. Firstly it acts to increase turbulence within the mixing chamber 165 and thus assisting with the mixing process. Further the rotating blades of the impeller tend to contact particles 200 from the wastewater 110. This contact and possibly the added effect of turbulence within the mixing chamber tends to break the particles up until considerably smaller particles 205. The smaller particles provide a substantially greater surface area within the mixing chamber and thus substantiallv increase the rate of oxidation of the particles. In each of the embodiments of Figures 2, 3 and 4 the oxidised wastewater is subsequently discharged 160 from the reservoir 105 either as a continuous process to facilitate large volume treatment or possibly as a batch process whereby the reservoir 105 is oxidised and then emptied ready for the new batch.

In either case a further embodiment is shown in Figure 5 for further downstream treatment. Here is shown the solids collection phase 15 comprising a solidification system 50 connected to a solid/liquid separator 65.

The solidification system 50 comprises a tank 210 containing a reservoir of oxidised wastewater 215. The invention includes the use of conventional wastewater containment systems to be adapted for use with the present invention. Therefore the tank 210 shown in Figure 5 may be replaced by a pond or other containment system as may be convenient. The tank 110 is fed oxidised wastewater 160 and further includes dosage of a coagulant 220. Such a coagulant may be chitosan however proprietary coagulants used for conventional systems may also be used, such as aluminium based coagulants (including alum) and ferric/ferrous based coagulants (including ferric chloride, ferrous sulphate and ferric sulphate. It will be noted that the oxidation process 10 tends to impart a negative charge to the particles in suspension within the wastewater and thus aid with the coagulation process. A further mixing device 225 is provided whereby rotation mixes and distributes the coagulant 220 throughout the tank facilitating coagulation of the particles held in suspension. The tank 210 further includes a variety of outlets for directing constituents of the reservoir 215 to various stations. For instance outlet 235 placed proximate to the surface of the reservoir will tend to take sludge, scum and other buoyant solids with outlet 230 located at the base of the tank 210 for removing settled sludge at the base of the tank. Both of these outlets feed into the liquid/solid separator 65 and in particular within a tank 245 to achieve this result. The solids are removed and the liquid separated using conventional techniques including drying, pressing and other known processes for separating the sludge from the collected water. The difference in this case is that the sludge carries a significantly lower COD as compared to conventional systems. Thus the removal of the solids 250 involve removing substantially dry and odourless solid waste which may be used for revenue generating applications including fertilizers. The removal of solids at a similar stage using conventional processes would involve handling solid material having a substantially higher biological activity and, therefore, is not readily available for use. The liquid 255 removed from the separator 245 is then directed to a tertiary treatment if required, possibly involving disinfection by, for instance, chlorine. If the liquid is intended for agricultural or human use then it may be filtered and polished or otherwise sent to disposal. Because the COD is substantially lower, for instance less than 30, it may be disposed in the sea or water way without an adverse environment effect. The separated liquid 255 may be combined with water taken directly from the tank 210 through an additional outlet 240.

As mentioned, liquid is collected from the previous process, which is subsequently filtered (coarse and fine). The BOD level achieved may be < 20 and COD <130. In this process, most of the organic compounds are removed by the coagulant 220. After disinfection, the treated water can be reused for cleaning or industrial purposes. Otherwise, water treatment plants using reverse osmosis membrane filter for water treatment can also use this treated water for recycle water applications. As the salt content in treated water is less than 130mg/L which is very much lower than sea water; direct discharge of the treated water into sea is possible after disinfection if not reused. COD can be further reduced to < 30 and in a shorter time by biological process using bacteria, which can be supported by oxidised water.

Experimental Data Experiments were established to measure the benefit gained from a treatment process according to embodiments of the present invention.

In the first range of tests, detailed in Table 1, a series of sample volumes of 120 litres were taken from various locations such as Changi and Toh Tuck WRP in Singapore. As expected the water constituents were different, however both measured COD< 500. Samples were poured into a treatment tank and pH measurements taken before starting the process. The sample pH was in the range 7 - 7.5 and so no pH adjustment was needed.

The initial set point for the ozone dosage on samples was typically at 10 gm/hr.

^■ Flow rate at 70 L/min.

^■ Before treatment, T ₀ samples were taken. o 1st sample was taken after 30 seconds ie before 1 cycle completion. 2 ^nd sample was taken in the subsequent 30 seconds ^■ To samples were taken at a specified tank sample point

The tests were intended to verify odour removal (TOC reduction), and in particular, the effect on the 1 ^st cycle treatment.

Accordingly, before 1 ^st cycle (30 seconds) completion samples were taken and a subjective test of odour taken. After the 1 ^st cycle a further sample was taken with the subjective assessment of odour to determine if there was a substantial reduction in odour following the process. Subsequent cycles (up to 3) were taken to measure any additional effect.

It will be noted that the TO samples were subjected to "Blending" prior to taking the sample, such that the suspended particles had been made smaller through mechanical mixing according to one embodiment of the present invention.

Dosages of 5, 10 & 20 g/hour were applied. Subjective assessment indicated 5 g/hour was insufficient. A dosage of 10 g/hour was highly effective, with no additional benefit found on an increase to 20 g/hour.

Table 1

Table 2 shows results for a second assessment. Here ozone is applied followed by a Chitosan dosage. After sedimentation, filtered by paper towel, the water samples were sent to the labs for testing

Table 2

The tests as shown for Table 2 were intended to show the drop in BOD and COD after the application of the oxidising agent, in this case ozone, followed by sedimentation. The "Before" sample was taken prior to treatment, and is equivalent to the T ₀ sample of Table 2, but without the "Blending" preparation of samples. Accordingly, these samples had a significantly higher COD than that of the samples of Table 1.

Conclusion

As shown in Table 1, the treatment process according to the present invention achieves a significant odour reduction after a first cycle of oxidization.

Table 2 goes further to show that when combined with sedimentation, the samples also undergo a significant drop in both COD and BOD.