Use of hollow fiber filtration in conjunction with precipitant technologies to reclaim water from complex aqueous waste streams

Abstract

A method of treating aqueous, preferably concentrated, waste streams with a unique combination of steps in a way that is easily scalable and able to be used with batch or continuous flows. The method comprises at least the following steps: Adding at least one precipitating agent to the waste water to produce precipitated solids; and removing the precipitated solids from the waste water using a forward flushable membrane to remove the precipitate solids.

Claims

1. A method to reclaim water from a waste water with dissolved solids comprising the following steps: Adding at least one precipitating agent to the waste water to produce precipitated solids; and removing the precipitated solids from the waste water using a forward flushable membrane to remove the precipitated solids, wherein the step of: Adding at least one precipitating agent to the waste water to produce precipitated solids, includes the at least one precipitating agent having a range of 0.005×10.sup.−3 to 0.10×10.sup.−3 (milliequivalents/Liter/ppm hardness) selected to produce precipitated lime solids.

2. A method to reclaim water from a waste water with dissolved solids comprising the following steps: Adding at least one precipitating agent to the waste water to produce precipitated solids; and removing the precipitated solids from the waste water using a forward flushable membrane to remove the precipitated solids, wherein the step of: Adding at least one precipitating agent to the waste water to produce precipitated solids, includes the at least one precipitating agent having a range of 0.01×10.sup.−3 to 0.04×10.sup.−3 (milliequivalents/Liter/ppm hardness) selected to produce precipitated lime solids.

3. A method to reclaim water from a waste water with dissolved solids comprising the following steps: Adding at least one precipitating agent to the waste water to produce precipitated solids; and removing the precipitated solids from the waste water using a forward flushable membrane to remove the precipitated solids, wherein the step of: Adding at least one precipitating agent to the waste water to produce precipitated solids, includes the at least one precipitating agent having a range of 0.0140×10.sup.−3 to 0.0250×10.sup.−3 (milliequivalents/Liter/ppm hardness) selected to produce precipitated lime solids.

4. A method to reclaim water from a waste water with dissolved solids comprising the following steps: Adding at least one precipitating agent to the waste water to produce precipitated solids; and removing the precipitated solids from the waste water using a forward flushable membrane to remove the precipitated solids, wherein the step of: Adding at least one precipitating agent to the waste water to produce precipitated solids, includes the at least one precipitating agent having a range of 0.0025×10.sup.−3 to 0.037×10.sup.−3 (milliequivalents/Liter/ppm hardness) selected to produce precipitated soda ash solids.

5. A method to reclaim water from a waste water with dissolved solids comprising the following steps: Adding at least one precipitating agent to the waste water to produce precipitated solids; and removing the precipitated solids from the waste water using a forward flushable membrane to remove the precipitated solids, wherein the step of: Adding at least one precipitating agent to the waste water to produce precipitated solids, includes the at least one precipitating agent having a range of 0.0046×10.sup.−3 to 0.0184×10.sup.−3 (milliequivalents/Liter/ppm hardness) selected to produce precipitated soda ash solids.

6. A method to reclaim water from a waste water with dissolved solids comprising the following steps: Adding at least one precipitating agent to the waste water to produce precipitated solids; and removing the precipitated solids from the waste water using a forward flushable membrane to remove the precipitated solids, wherein the step of: Adding at least one precipitating agent to the waste water to produce precipitated solids, includes the at least one precipitating agent having a range of 0.00730×10.sup.−3 to 0.0115×10.sup.−3 (milliequivalents/Liter/ppm hardness) selected to produce precipitated soda ash solids.

7. A method to reclaim water from a waste water with dissolved solids comprising the following steps: Adding at least one precipitating agent to the waste water to produce precipitated solids; and removing the precipitated solids from the waste water using a forward flushable membrane to remove the precipitated solids, wherein the step of: Adding at least one precipitating agent to the waste water to produce precipitated solids, includes the at least one precipitating agent selected to produce precipitated solids from the group consisting of lime solids, soda ash solids and combinations thereof.

8. The method to reclaim water of claim 7, wherein the step of: Adding at least one precipitating agent to the waste water to produce precipitated solids, includes the at least one precipitating agent having a range of 0.0025×10.sup.−3 to 0.037×10.sup.−3 (milliequivalents/Liter/ppm hardness) selected to produce precipitated solids from the group consisting of lime solids, soda ash solids and combinations thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a block diagram of a prior art example an enhanced membrane system.

(2) FIG. 2 is a process flow diagram of one preferred embodiment.

(3) FIG. 3 is a picture of flow channels of a preferred embodiment of a forward flushable membrane for filtering comprising 3 increasing magnifications of a lumen having an inner diameter of 200 microns. Preferably, the lumen diameter is greater than 100 microns and less than 400 microns; additionally the pore size for permeate flow is greater than 2 nanometers and less than 200 nanometers.

(4) FIG. 4 is a diagrammatic representation of a preferred embodiment of a forward flushable membrane for filtering showing flow.

(5) FIG. 5 is a graph of a fouling curve showing flow rate versus volume of a preferred embodiment of a forward flushable membrane and a forward flushable membrane with a larger pore size.

(6) FIG. 6 is a bar chart showing the removal of Ca, Mg, and Silica for various experimental conditions. Experimental conditions include adding various amounts of lime, soda ash and caustic to stirred wastewater solutions. Waste solutions consisted of 500 mL aliquots of either lab-made waste or one of two customer wastes containing hardness, silica and metal ions. Treatments were added as slurries of product in about 5 to about 25 mL aliquots to stirred solutions of waste. Water was allowed to settle and supernate was filtered through a 0.22 micron syringe filter before being analyzed according to standard methods.

(7) FIG. 7 is a process flow diagram of another preferred embodiment.

DESCRIPTION OF THE EMBODIMENTS

(8) A preferred embodiment of the invention is where Process waters, which have been concentrated to the maximum desirable concentration by traditional means (e.g. RO), are collected and forced to quickly precipitate dissolved ions and/or small suspended solids via electrostatic precipitation methods or by the addition of precipitating and/or coagulating agents such as chelants, lime, slaked lime, dolomitic lime, cold lime softening agents, lime-soda softening agents, warm lime softening agents, warm lime-soda softening agents, hot lime softening agents, hot lime-soda softening agents, caustic softening agents, polymeric chemical precipitants, coagulants, flocculants, and sludge conditioners, silica precipitants and co-precipitants, metal salts such as aluminum, iron and the like, pH adjustment by addition of soda ash, caustic, alkalinity sources, acid sources and the like, or other means as appropriate to the individual water stream.

(9) Preferably, precipitating agents include but are not limited to the following: Dry and liquid (solution or emulsion) polymers such as but not limited to: cationic, polyacrylamide copolymers; cationic, polyacrylamide homopolymers; cationic, polyacrylamide copolymer emulsions; cationic, polyacrylamide homopolymer emulsions; anionic, polyacrylamide copolymers; anionic, polyacrylamide copolymer emulsions; linear polyamine coagulants; branched polyamine coagulants; polyDADMAC coagulants; melamine-formaldehyde colloids; nonionic, polyacrylamide homopolymers; nonionic, polyacrylamide homopolymer emulsions; and other similar materials. Inorganic coagulants and blends, such as but not limited to: ferric chloride; ferric chloride blends with polyamine; aluminum chloride; aluminum chloride blends with polyamines; aluminum chloride blends with polyDADMACs; polyaluminum chloride; polyaluminum chloride blends with polyamines; polyaluminum chloride blends with polyDADMACs; polyaluminum sulfosilicates; polyaluminum chlorosulfates; sodium aluminate; ferric chloride/aluminum chloride blends; ferrous sulfates; ferric sulfates; calcium chlorides; cerium chlorides; aluminum chlorohydrate; aluminum chlorohydrate blends with polyamines; aluminum chlorohydrate blends polyDADMACs; aluminum sulfate; aluminum sulfate blends with polyamines; aluminum sulfate blends polyDADMACs; activated silica; quicklime; hydrated lime; dolomitic lime; magnesium hydroxide; chitosan and its derivatives; aminoethylated tannin coagulants; polyethlene oxides and their derivatives; polyethyleneimines and their derivatives; polyferric sulfates; organoclays; bentonite clays; and other similar materials. This treatment may be in-line or, alternately, use a collection tank may be used. Exact configuration will depend on the volume of waste stream to be processed, required time to process, available footprint and other factors. Process additives may be added using dissolvable bags to allow a “one pot” reaction vessel in certain cases. In cases where larger volumes of added reactants are needed, the addition could be accomplished by preparing the chemical additives in a secondary tank and adding the resulting solution in a manner proportional to the flow of the incoming water. The resulting slurry, consisting of precipitated solids, is pushed through a hollow polysulfone fiber ultrafilter with pore sizes between 0.002 and 0.010 microns. An optional pre-filtration step, such as micron sized cartridge filtration and/or filtration through fine mesh screens may be used to remove large size slurry solids and extend the life of the hollow polysulfone fiber ultrafilter. Slurry solids are retained within the inner lumen of the hollow fiber, while purified water is pushed through the lumen to the outside of the hollow fiber. The sample may be collected or alternately sent through a second stage of the hollow fiber filter. Purified water is collected and returned to the head of the plant for further use. Such water is suitable, for example, as RO feedwater. Slurry solids are retained within the inner lumen of the hollow fiber filter until a system flush is initiated. This flush may be manually triggered, triggered via a timer, or, alternatively, it may be set to occur based on the Delta P across the filter or another metric such as time. Once triggered, a short (between 3 and 60 second) flush removes slurry solid retains from the inner lumen and sends it back to the slurry tank, or a separate collection tank for subsequent removal and processing. In this way the filter is kept clean. Periodically, the slurry tank is “blown down” and slurry solids are removed. These solids may be further treated with traditional liquid-solid separation techniques such as filter presses, etc. to dewater the sludge and produce a filter cake that passes the Paint Filter test and is suitable for off-site disposal. The liquid portion from the dewatering step is returned to the slurry tank. In a modification of the above, a prototype invention, which includes removing the precipitated solids via a drainable basket-type filter is envisioned. This variation includes the ability to prefilter particles prior to entering the hollow fiber filter to help extend the life of the hollow fiber filter. Chemical precipitant added and pH adjusted. The invention may also be used without the additional precipitation step and additives in certain cases.

(10) Preferably, the technique is useful for reducing volumes of RO (“reverse osmosis”) brine, softener regeneration brine, cooling tower blow down, boiler blow down, wastewater blow down and other similar streams.

(11) Preferably, the invention has a small footprint and can be scaled to accommodate various size waste streams from small batch to large GPM flow through systems. More preferably, the smallest size currently envisioned is a 2′×3′ cart.

(12) Preferably, the water slurry is directed into inner lumen of the hollow fiber membrane.

(13) Preferably, hollow fiber membrane material having small flow channels in the nanometer range is composed of a common polymer material, such as polysulfone or polyethersulfone. As a preferred example, the S100 filter contains 0.1 micron hollow fiber membrane, and the SSU filter contains 0.005 micron hollow fiber membrane. The S100 filter fouls to cessation of flow much faster, and under a different curve than the SSU filter. The SSU filter fouls more quickly to the .sup.˜60% capacity level, but then filters 3 to 5 times more volume before fouling, as compared to the S100 filter. The curves obviously change based on the particulate size bell curve of the incoming water, but essentially the theory is that the smaller pores have a lower probability of being permanently blocked with a particle lodged inside the nanometer-sized flow channels.

(14) In a preferred example, the following experimental results are shown as a proof of concept. The basic experimental steps included (a) dosing 500 mL aliquots of waste water with a combination of precipitating agents, (b) adjusting pH, (c) stirring on a gang stirring device for various times and (d) analyzing the supernatant fluid after passing it through a 0.22 micron syringe filter. Samples were analyzed before and after passing the treated waste through a benchtop size forward flushable filter prior to analyzing.

(15) Preferably, one embodiment of the process includes: Adding water containing dissolved solids. Specifically dissolved Ca, Mg, Si, Hardness, metals and the like. Adding a precipitating agent/agents in specific ratios Using a forward flushable ultrafiltration membrane to remove the precipitated solids.

(16) This embodiment of the process is greatly improved by adding the following between the reaction tank and the forward flushable filter to protect the forward flushable filter: Adding a floc building aid Sequential filtration through screens and cartridge/depth filters Mesh screen basket sized to be ideally between 74 and 149 micron wire screen. (Note this is surprising because it is not the same as one expects from micron rated cartridge filters!). <74 micron wire screen will not pass normal water (unexpected) 5 micron cartridge filter 1 micron cartridge filter

(17) Additional features which could be added to this embodiment of the process include: physical baffles and/or mechanical settling aids (this is especially needed for continuous operation but not necessary for batch operation) physical scraping devices to keep screens clear post-process pH adjustment to meet customer specifications monitoring components including, but not limited to: flow switches to control incoming water flow rates (preferably slaved to treatment addition pumps to control treatment feeds) pH meters to monitor and control process (caustic feed regulator) multiple treatment tanks to allow semi-continuous operation and switches to select between tanks additional monitoring and/or physical modifications to the basic unit to allow continuous operation monitoring such as total dissolved solids (TDS), turbidity, or ion-specific electrodes to detect breakthrough of solids and signal the need to perform maintenance on the process/equipment. differential pressure monitoring of individual filtration components to signal the need to change out filters timers to start/stop batch processes (based on settling times)

(18) This embodiment of the process surprisingly found settling of precipitated sludge can result in either cloudy or crystal clear supernatant solutions. The crystal clear supernatant solutions were a surprising result. Factors which appear to contribute to clarity include: age of sludge blanket in process (older sludge is more likely to form clear supernatant) dosage of components. While the system is robust and can operate with a range of component dosages, the more closely matched the dose is to the stoichiometric requirement for precipitation, the more clear the supernatant.
Additionally, other surprises include: age of floc building aid does not impact process significantly. Specifically, dilutions of polymers greater than 1 month old perform as well a fresh dilutions Stabilized precipitating lime slurries (which easily remain in suspension) allow much more effective and rapid settling than non-stabilized versions. Stagnant beds work as well as stirred/fluidized beds Final remaining hardness and/or metals consistently below levels predicted based on “simple” lime-soda softening processes. See examples below:
The table below converts the cold lime softening from typical softener effluent analysis (see below table 7-1) to a percentage removal and compares removal results to the invention result.

(19) TABLE-US-00003 TABLE 3 Comparison of current technology with Invention Ca hardness Mg hardness Total hardness Typical 76% 54% 67% Cold Lime Softening Removal Typical 99% 99% 99% Invention Hardness Removal

(20) TABLE-US-00004 TABLE 7-1 Typical softener effluent analyses. Removal of Calcium Lime- Lime- Alkalinity soda soda Lime Raw Cold- Softening Softening Softening Water Lime (Cold) (Hot) (Hot) Total 250 145 81 20 120 Hardness (as CaCO.sub.3), ppm Calcium 150 85 35 15 115 Hardness (as CaCO.sub.3), ppm Magnesium 100 60 46 5 5 Hardness (as CaCO.sub.3), ppm “P” 0 27 37 23 18 Alkalinity (as CaCO.sub.3), ppm “M” 150 44 55 40 28 Alkalinity (as CaCO.sub.3), ppm Silica (as 20 19 18 1-2 1-2 SiO.sub.2), ppm pH 7.5 10.3 10.6 10.5 10.4 See typical Lime-Soda Softening (reference: https://www.suezwatertechnologies.com/handbook/chapter-07-precipitation-softening)