WO2013061057A1 - Méthodes et systèmes de traitement d'eau - Google Patents

Méthodes et systèmes de traitement d'eau Download PDF

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Publication number
WO2013061057A1
WO2013061057A1 PCT/GB2012/052640 GB2012052640W WO2013061057A1 WO 2013061057 A1 WO2013061057 A1 WO 2013061057A1 GB 2012052640 W GB2012052640 W GB 2012052640W WO 2013061057 A1 WO2013061057 A1 WO 2013061057A1
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water
coagulation
membrane
filtration
stage
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PCT/GB2012/052640
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English (en)
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Thomas Meyn
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Norwegian University Of Science And Technology (Ntnu)
Gardiner, Stephen
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Publication of WO2013061057A1 publication Critical patent/WO2013061057A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/66—Treatment of water, waste water, or sewage by neutralisation; pH adjustment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/14—Ultrafiltration; Microfiltration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/14—Ultrafiltration; Microfiltration
    • B01D61/145—Ultrafiltration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/14—Ultrafiltration; Microfiltration
    • B01D61/147—Microfiltration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/14—Ultrafiltration; Microfiltration
    • B01D61/16—Feed pretreatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D65/00—Accessories or auxiliary operations, in general, for separation processes or apparatus using semi-permeable membranes
    • B01D65/08—Prevention of membrane fouling or of concentration polarisation
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/001—Processes for the treatment of water whereby the filtration technique is of importance
    • C02F1/004—Processes for the treatment of water whereby the filtration technique is of importance using large scale industrial sized filters
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • C02F1/444—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by ultrafiltration or microfiltration
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
    • C02F1/5236—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents
    • C02F1/5245—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents using basic salts, e.g. of aluminium and iron
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2311/00—Details relating to membrane separation process operations and control
    • B01D2311/04—Specific process operations in the feed stream; Feed pretreatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2311/00—Details relating to membrane separation process operations and control
    • B01D2311/06—Specific process operations in the permeate stream
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2311/00—Details relating to membrane separation process operations and control
    • B01D2311/12—Addition of chemical agents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2311/00—Details relating to membrane separation process operations and control
    • B01D2311/18—Details relating to membrane separation process operations and control pH control
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2311/00—Details relating to membrane separation process operations and control
    • B01D2311/26—Further operations combined with membrane separation processes
    • B01D2311/2642—Aggregation, sedimentation, flocculation, precipitation or coagulation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2311/00—Details relating to membrane separation process operations and control
    • B01D2311/26—Further operations combined with membrane separation processes
    • B01D2311/2649—Filtration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2321/00—Details relating to membrane cleaning, regeneration, sterilization or to the prevention of fouling
    • B01D2321/16—Use of chemical agents
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F11/00—Treatment of sludge; Devices therefor
    • C02F11/12—Treatment of sludge; Devices therefor by de-watering, drying or thickening
    • C02F11/121—Treatment of sludge; Devices therefor by de-watering, drying or thickening by mechanical de-watering
    • C02F11/127—Treatment of sludge; Devices therefor by de-watering, drying or thickening by mechanical de-watering by centrifugation
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/10—Inorganic compounds
    • C02F2101/20—Heavy metals or heavy metal compounds
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/30—Organic compounds
    • C02F2101/34—Organic compounds containing oxygen
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/30—Organic compounds
    • C02F2101/38—Organic compounds containing nitrogen
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2301/00—General aspects of water treatment
    • C02F2301/02—Fluid flow conditions
    • C02F2301/024—Turbulent
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2303/00—Specific treatment goals
    • C02F2303/04—Disinfection
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2303/00—Specific treatment goals
    • C02F2303/08—Corrosion inhibition
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2303/00—Specific treatment goals
    • C02F2303/16—Regeneration of sorbents, filters
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2303/00—Specific treatment goals
    • C02F2303/20—Prevention of biofouling

Definitions

  • the invention relates to water treatment methods and systems, particularly for the treatment of surface water and/or water from natural sources, most particularly water with a high natural organic matter (NOM) content.
  • NOM natural organic matter
  • NOM is a precursor for disinfection by-product formations that are known to be carcinogenic (e.g. during chlorination or ozonation) and should preferably therefore be removed during drinking water treatment.
  • NOM is also known to bind microorganic pollutants (e.g. pesticides, herbicides, pharmaceuticals etc.) and heavy metals. The removal of NOM in drinking water production is therefore necessary to eliminate these problems.
  • high NOM concentrations may impact subsequent treatment steps, e.g. by increasing chemical demand, sludge production etc. The removal of NOM is therefore an important consideration and requires advanced drinking water treatment.
  • NOM is a complex material and comprises a multitude of different organic substances. Classification and fractionation of these is a difficult task. However, some main properties are commonly used to describe the NOM characteristics. Key fractions are humic and fulvic substances, which are typically very hydrophobic compounds. These substances typically have a high specific UV absorption due to a high content of aromatic carbon. In conventional treatment such waters are recognized as being well treated by coagulation.
  • Coagulation is defined as the process of destabilization of a given suspension or solution.
  • Flocculation is the process whereby destabilized particles or particles created by destabilization, are promoted to come together and make contact, in order to form larger aggregates. These are then readily removed in subsequent processes.
  • Rapid filtration has the advantage of allowing high throughput, but also has disadvantages including the fact that it does not itself filter out bacteria or protozoan parasites thus necessitating further (usually chemical) disinfection steps.
  • the sludge produced in the rapid filtration process also requires extensive processing.
  • Drinking water regulations vary from country to country, but typically require the water to have a pH in the neutral range or a little higher.
  • the water typically has a pH in the neutral range or a little higher.
  • the marble filter serves to increase the pH into a range where the metal solubility is low and the metal species will thus precipitate in the marble filter, reducing the residual metal content of the treated water.
  • This process where coagulation is coupled with rapid filtration, is in many ways an adequate solution. It is ideal for soft and coloured waters. It performs coagulation at low pH (3.5-4.5). Often no pH adjustment is needed and furthermore residual metal is captured in the marble filtration.
  • Membrane filters have a number of advantages for water treatment, including an improved hygienic barrier and a smaller physical footprint, but one major disadvantage is the potential for membrane fouling, i.e. blocking or obstructing the pores of the membrane and thus reducing the membrane's efficiency.
  • the rapid filtration process is not particularly sensitive to clogging / fouling.
  • Membrane fouling can be classified into two categories:
  • Reversible fouling is fouling that can be cleaned from the membrane by regular backwashing techniques without using chemicals.
  • Irreversible fouling cannot be removed by regular backwashing and can only be removed by chemical cleaning. Commonly alkaline or acidic cleaning solutions are used, sometimes oxidizing agents such as chlorine). Fouling results in a gradual degradation of performance over time, typically causing a pressure build up across the membrane. Membrane fouling is a complex phenomenon and can be difficult to predict. Coagulation / flocculation has been used as a technique for membrane fouling mitigation. However, the choice of coagulant and the operating conditions are very important. The wrong choice of coagulant and/or operating conditions can have drastic effects causing severe fouling. The optimal dose and coagulation condition is required to avoid these effects.
  • membrane fouling can increase drastically, with residual metal concentration remaining too high and with low NOM removal. Also low pH increases metal solubility and consequently the increased residual metal. It is also known that changes in pH level can alter fouling rates. Furthermore, the membrane material must also be taken into consideration as many membrane materials are not suitable for low pH operation and general pH adjustment
  • NOM removal technologies “NOM removal technologies - Norwegian experiences" by H. 0degaard et al, Drink. Water Eng. Sci. Discuss., 2, 161-187, 2009 provides a summary of various NOM removal systems and technologies which have been used in Norway. These include direct nanofiltration techniques in which a calcium carbonate filter is used. The purpose of this filter is largely for replacement of divalent ions which are removed by the very small pores of the nanofiltration device. There is no coagulation treatment in this process. The document also describes
  • coagulation/filtration systems Two such systems are described.
  • a non-membrane filtration system is combined with an alkaline filter for corrosion control.
  • membrane filtration is used, but with no alkaline filter.
  • This second system is earlier work by one of the inventors of the present invention and was designed for different operating conditions, in particular different applied pH values.
  • US 6,416,668 B1 describes a filtration system which predominantly relates to the use of "dense” membranes such as spiral wound nanofiltration (NF) and reverse osmosis (RO) membranes. These membranes have very small pore sizes, and essentially remove everything from the influent. NF membranes are still considered porous, meaning they actually have pores, with sizes of roughly 0.001 ⁇ to 0.01 ⁇ . Such membranes can retain organic molecules and divalent ions.
  • RO membranes are non-porous and the separation mechanism is based on the ability of a solute to diffuse through the membrane. Theoretical pore sizes of such membranes are between 0.0001 and 0.001 ⁇ . They can retain monovalent ions, e.g. Na+ and CI-.
  • a method of treating water comprising: a coagulation step in which a coagulant is added to an input water to induce coagulation of natural organic matter particles within the water; a membrane filtration step in which the water output from the coagulation step is passed through a semi-permeable membrane; and an alkaline filtration step in which the water output from the membrane filtration step is passed through an alkaline filter to raise the pH of the water and induce precipitation of residual metals from the water.
  • the combination of the three process stages makes it possible to use membrane filtration as a viable industrial water filtration method. In particular, it is possible to treat soft / unbuffered waters or low pH waters efficiently.
  • the pH may be lowered by addition of chemicals prior to the flocculation stage.
  • the addition of coagulant reduces the pH of the water. This effect is particularly pronounced in the case of soft waters (i.e. with low mineral content) as the water is not well buffered. This means that the addition of acid or alkaline material produces rapid changes on the overall pH of the water. By contrast, in the case of hard waters (i.e. well buffered waters), the high mineral content can react with the additives, thus slowing down the overall pH change of the water. It has been found that in the case of certain soft waters, the addition of an optimal quantity of coagulant will reduce the pH of the raw water input to the optimal pH level for NOM and colour removal.
  • Ferric based coagulants are particularly suitable for this. In these cases there is therefore no need for additional chemical pH adjustment in order for NOM and colour removal to be optimized.
  • the amount of coagulant added is sufficient to reduce the pH of the water to the level which is optimal for NOM removal.
  • the optimum pH for NOM removal may be in the range of 2 to 8, preferably 3 to 6, 4 to 6 or 5 to 6, alternatively 3 to 5, preferably 3.5 to 4.8, or more preferably still in the range of 4.3 to 4.8.
  • the pH of the water is adjusted to within this range prior to or during the coagulation stage.
  • the amount of coagulant is sufficient to reduce the pH to within the range of 2 to 8, preferably 3 to 6, 4 to 6 or 5 to 6, alternatively 3 to 5, preferably 3.5 to 4.8, more preferably still in the range of 4.3 to 4.8.
  • the coagulant is Iron based and the pH is in the range of 3.5 to 4.8, preferably 4.3 to 4.8.
  • the coagulant is Aluminium based and the pH is in the range of 5 to 6.
  • coagulant is added to reach a concentration which is optimal for NOM removal. This will depend on the initial concentration of NOM and its characteristics / properties.
  • the fouling of the membrane (both reversible and irreversible) is still within acceptable limits.
  • a consequence of the low pH of the filtered water is that metal solubility is high and thus residual metal content is high in water after the membrane filtration step.
  • the alkaline filtration stage brings the pH of the filtered water back up to a level which is acceptable for drinking water (e.g. around 7.8 - 8.5).
  • the alkaline filtration step induces precipitation of residual metal from the treated water, and increases the mineral content of the water, thus providing buffering and corrosion control.
  • the result is a high quality treated water.
  • the residual metal concentration is reduced to levels below the legislated maximum allowed concentration, thus producing a treated water well within the drinking water regulations.
  • membrane filtration provides a particular benefit in that, even if the coagulation step should fail for some reason, the effluent water from the water treatment plant still benefits from a certain level of filtration.
  • the membrane filter can exclude bacteria and parasites regardless of the coagulation efficacy. This provides a certain minimum hygienic barrier effect. This is not the case with a conventional coarse media rapid filtration system where a failure of coagulation will result in a failure of the system as a whole, i.e. neither natural organic matter nor parasites would be removed.
  • the present invention is thus able to provide a higher default water quality even in the event of failure.
  • the process of the invention is particularly applicable to treatment of water with low pH, low buffer capacity and high natural organic matter content.
  • the preferred embodiments of the invention are used for treatment of natural fresh water, surface water or ground water, e.g. river bank infiltration.
  • Particularly preferred examples of source water which can be efficiently treated according to the invention are Nordic (The term Nordic refers to the countries Norway, Sweden, Finland, Denmark and Iceland and their associated territories, the Faroe Islands and Greenland) surface and ground waters and Scottish highland waters as well as surface / ground waters in Kenya, North America, Northern Russia and Siberia / Northern Asia.
  • the invention is particularly applicable to surface waters as these tend to be less buffered compared with ground waters which typically have a higher mineral content. Nevertheless, the invention will apply to some ground waters.
  • the invention also applies to surface waters treated by bank filtration (which may sometimes be referred to as ground water).
  • the membrane filtration step may use a variety of different membranes.
  • organic polymer membranes can be manufactured with a large variety of different properties and can be tailored to a particular process in order to achieve optimum efficiency.
  • polymer membranes which can operate efficiently with low pH fluids, these are very specialized and can be costly.
  • Preferred embodiments of the present invention use a ceramic membrane in the membrane filtration step. Ceramic membranes are more costly to produce and therefore require a higher initial investment. However they are hydrophilic and thus can be operated at higher throughputs. Therefore for a given size they can treat larger quantities of water. From an alternative perspective, for a given water treatment rate, plant size can be reduced with the use of ceramic membranes.
  • ceramic membranes are more resilient to chemical cleaning agents and it is therefore easier to clean a fouled ceramic membrane. Due to their high mechanical strength, ceramic membranes are expected to have a longer life time compared to polymeric membranes. For these reasons, cost savings can be made in the long run.
  • Preferred pore sizes of the membrane are in the ultrafiltration/microfiltration
  • Coagulation can take the form of traditional coagulation / flocculation setups.
  • one or more tanks are provided in which the water and coagulant are mixed so as to encourage flocculation. Once floes have achieved a sufficient size they settle out.
  • Conventional arrangements often include successive arranged tanks, starting with a higher mixing rate to ensure good mixing of the coagulant in the water, and successive tanks with a lower mixing rate to allow for better flocculation.
  • a preferred arrangement is to use inline coagulation. In such
  • the coagulant is added into the pipeline ahead of the membrane filtration stage.
  • the residence time and flow rate of the fluid are designed to allow sufficient mixing and flocculation to occur.
  • Such arrangements may involve a wider section of pipe so as to reduce the speed of fluid flow and thus encourage flocculation.
  • Structure such as an obstruction (e.g. static mixers or baffles, constrictions, nozzles, etc.) may be used to introduce turbulence for improved mixing.
  • Typical residence times in the pipeline between the addition of coagulant and the membrane filter are preferably greater than 30 seconds, more preferably 60 seconds or more. It has been found that inline coagulation can provide sufficiently good NOM and colour removal and has the advantage of simplifying the apparatus and reducing the size of the apparatus.
  • Inline coagulation setups are particularly suitable for use with membrane filtration as less flocculation is required for filtration to be effective.
  • the optimum type of coagulant should be selected according to the exact nature (i.e. mineral content, NOM content, colour, turbidity etc.) of the water to be treated, but in preferred cases the coagulant is a metal salt.
  • Preferred metal salts are aluminium salts and iron salts and in the most preferred embodiments the coagulant is an iron salt.
  • the optimum pH range for NOM removal by iron salts is achievable by simple addition of the appropriate amount of coagulant, without any further chemical pH adjustment required.
  • Aluminium salts may also be used, but the addition of Aluminium salts may cause a drop in pH below the optimal range for NOM and colour removal for such coagulants, (which is in the range of 5.5 to 6.0, i.e. higher than for ferric based coagulants). Therefore, additional chemical pH adjustment may be required in order to bring the pH back to the optimal level.
  • An additional issue with Aluminium is that it may have an increased probability of leaking from the alkaline filter, resulting in a lower quality effluent.
  • the alkaline filtration step may use any suitably chosen alkaline material as the filtration medium.
  • An appropriate material will depend on the composition of the water to be treated and the expected pH and residual metal content.
  • suitable alkaline filter materials are: marble, limestone, dolomite, calcite, water glass.
  • Preferred embodiments of the invention use carbonate mineral filters, such as a marble filter.
  • An alkaline filter provides good buffering at the same time as raising pH due to the water absorbing minerals from the filter medium as it passes through the filter.
  • the invention provides a water treatment system, comprising: a coagulation stage comprising a coagulation stage water input, a coagulant input and a coagulation stage water output; a membrane filtration stage comprising a membrane filtration stage water input connected downstream of the coagulation stage water output and which is situated on one side of a semipermeable membrane, and a membrane filtration stage water output on the other side of the semi-permeable membrane; and an alkaline filtration stage comprising an alkaline filtration stage water input connected downstream of the membrane filtration stage water output and which is situated on one side of an alkaline filtration medium, and an alkaline filtration stage water output on the other side of the alkaline filtration medium.
  • the semi-permeable membrane is preferably a ceramic membrane.
  • coagulation stage may comprise one or more sequentially arranged tanks (e.g. with different mixing rates), but is preferably an inline coagulation stage.
  • the alkaline filtration medium is preferably a marble filter. It will be appreciated that, while in some embodiments additional treatment steps may be provided, in many preferred embodiments no further treatment steps are necessary between the coagulation stage and the membrane treatment stage or between the membrane treatment stage and the alkaline filtration stage. In some embodiments there may be pH adjustments made in between these stages, but preferably no further filtration stages are provided (either membrane filtration or granular filtration).
  • the invention also extends to the use of the above-described systems for treatment of natural water and/or treatment of surface water or ground water.
  • Fig. 1 shows a schematic of the proposed treatment system
  • Fig. 2 shows a graph of DOC removal in dependence on pH value
  • Fig. 3 shows a graph of Zeta potential (particle surface charge) in dependence on coagulation pH
  • Fig. 4 shows residual iron concentration in dependence on the coagulation pH
  • Fig. 5 shows irreversible fouling in dependence on pH
  • FIG. 6 shows reversible fouling in dependence on pH.
  • This system provides a tailor made treatment process for surface waters such as Nordic, surface waters (or other waters of similar characteristics as described above) based on membrane filtration technology.
  • a schematic of the proposed treatment concept is shown in Figure 1.
  • Fig. 1 shows a water treatment system 100.
  • a raw water inlet 105 provides the input for raw water (taken from natural, surface water sources such as rivers or lakes, or possibly from ground water sources) into the system.
  • a volume of raw water is held in buffer tank 1 10 to ensure steady flow conditions within the system 100.
  • An optional pH adjustment may take place by chemical addition at 1 15 if conditions require it, but this step is ideally omitted as the optimal pH adjustment can be achieved via the coagulant addition. Therefore in water treatment plants designed for soft, low buffered waters, the system will preferably not have a chemical pH adjustment.
  • a pump 120 feeds water to the membrane 150.
  • Coagulant is added into the system at 125.
  • the coagulant is typically a metal salt, most often either Iron or Aluminium salts.
  • Coagulation and flocculation takes place at 130.
  • the setup shown in Fig. 1 is an inline coagulation arrangement comprising a structure 135 for generating turbulence and mixing and a section of expanded pipe 140 in which the flow rate is reduced and flocculation is encouraged. The residence time in this pipe section
  • the membrane 150 is a low pressure UF/MF membrane module. Filtered water is output from the membrane module 150 at 155 and sludge is output at 160. The sludge is taken away for further treatment and disposal.
  • the sludge may be concentrated in a hydro cyclone, the concentrated part disposed or discharged and the diluted stream fed back to the raw water.
  • the membrane module 150 filters out flocculated NOM and particles as well as bacteria and parasites, thus producing a high quality permeate at its output 155.
  • the permeate at this point in the process is low in pH and thus the solubility of metals is high meaning that the permeate is likely to have a high residual metal content.
  • An optional C0 2 input 157 may be provided. This is used to adjust the amount of marble which dissolves in the marble filter 165. This directly influences alkalinity and pH of the treated water.
  • the permeate is then passed through the marble filter 165 before exiting the system 100 at 170.
  • the marble filter 165 increases the pH of the water, bringing it back to a normal drinking water level (typically around 7.8-8.5).
  • the permeate absorbs minerals from the marble and thus the buffering capability of the water is increased, thus providing corrosion control in the same step as the pH adjustment.
  • Due to the increase in pH dissolved residual metal is precipitated as hydroxide, e.g. iron hydroxide. Since this is a coagulation process, still remaining organic matter may be either incorporated into or adsorbed onto the hydroxide floes and thus separated by the alkaline filter.
  • the treated water output at 170 may be subjected to further disinfection steps if necessary before being distributed as drinking water.
  • the proposed treatment scheme already includes corrosion control and the removal of dissolved residual coagulant/metal in one treatment step.
  • Coagulation / Flocculation • Classic configuration (rapid and slow mixing with HRT of 20 min); and • Inline configuration (static mixing followed by pipe flocculation with HRT of 60s and G of 31 s-1 )
  • HRT is the Hydraulic Retention Time
  • G is the hydraulic gradient
  • the coagulation pH range from 4.3 to 4.8 may be beneficial for the removal of organic matter. However, while this advantage is gained, there is a trade-off of higher dissolved metal concentrations under such conditions (see Figure 4). Iron concentrations of several hundred micrograms were measured after the membrane filtration step. This is significantly higher than the typical limiting value in drinking water guidelines (e.g. 150 ⁇ g Fe/L in Norway). The results further show that low membrane fouling can be achieved at conditions optimal for coagulation of NOM with iron based coagulants. In the pH range where NOM removal is best, i.e. around 4.7 (e.g. 4.6-4.8), low irreversible membrane fouling is also observed (Figure 5). In addition, low membrane fouling was observed for both applied pre-treatment configurations, inline and classic coagulation.
  • Coagulation reduced irreversible membrane fouling, compared to conditions with no pre-treatment.
  • the advantages of the 3-step water purification process described here are that the system can be made simple and compact.
  • the system and method may be customized for several local areas such as, for example, Nordic conditions.
  • the process effectively removes NOM and colour due to the low coagulation pH.

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  • Engineering & Computer Science (AREA)
  • Water Supply & Treatment (AREA)
  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Hydrology & Water Resources (AREA)
  • Environmental & Geological Engineering (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Inorganic Chemistry (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)

Abstract

L'invention concerne des méthodes et systèmes de traitement d'eau comprenant les étapes suivantes : une étape de coagulation (125) dans laquelle on ajoute un coagulant à une source d'eau pour provoquer la coagulation des particules de matières organiques naturelles présentes dans l'eau ; une étape de filtration par membrane (150) dans laquelle l'eau sortant de l'étape de coagulation (125) traverse une membrane semi-perméable (150) ; et une étape de filtration alcaline (165) dans laquelle l'eau sortant de l'étape de filtration par membrane (150) traverse un filtre alcalin (165) afin d'augmenter le pH de l'eau et de provoquer la précipitation des métaux résiduels dans l'eau. L'utilisation d'une technologie de filtration par membrane offre une barrière hygiénique améliorée et facilite la réduction de la taille de la station de traitement. Les membranes en céramique peuvent être utilisées à des pH faibles où l'élimination des matières organiques naturelles et de la couleur sont optimisées et la filtration sur marbre réajuste le pH et constitue un tampon pour la sortie d'eau traitée.
PCT/GB2012/052640 2011-10-24 2012-10-24 Méthodes et systèmes de traitement d'eau WO2013061057A1 (fr)

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Cited By (2)

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CN109074033A (zh) * 2016-04-01 2018-12-21 凯米罗总公司 用于优化水处理过程中的凝聚和/或絮凝的方法和系统
CN110228834A (zh) * 2019-05-31 2019-09-13 苏州英特工业水处理工程有限公司 可反冲洗的自流式水处理系统

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US6416668B1 (en) 1999-09-01 2002-07-09 Riad A. Al-Samadi Water treatment process for membranes

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MEYN, T.: "Department of Hydraulic and Environmental Engineering. Doctoral Thesis", 2011, ORWEGIAN UNIVERSITY OF SCIENCE AND TECHNOLOGY (NTNU, article "NOM Removal in Drinking Water Treatment Using Dead-end Ceramic Microfiltration: Assessment of Coagulation/Flocculation Pretreatment"
THOMAS MEYN: "NOM Removal in Drinking Water Treatment Using Dead- End Ceramic Microfiltration", THESIS FOR THE DEGREE OF PHILOSOPHIAE DOCTOR, 30 April 2011 (2011-04-30), XP055049318, Retrieved from the Internet <URL:http://ntnu.diva-portal.org/smash/get/diva2:452643/FULLTEXT01> [retrieved on 20130111] *

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109074033A (zh) * 2016-04-01 2018-12-21 凯米罗总公司 用于优化水处理过程中的凝聚和/或絮凝的方法和系统
US10988392B2 (en) 2016-04-01 2021-04-27 Kemira Oyj Method and system for optimization of coagulation and/or flocculation in a water treatment process
CN109074033B (zh) * 2016-04-01 2022-04-19 凯米罗总公司 用于优化水处理过程中的凝聚和/或絮凝的方法和系统
CN110228834A (zh) * 2019-05-31 2019-09-13 苏州英特工业水处理工程有限公司 可反冲洗的自流式水处理系统

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