WO1996041245A1

WO1996041245A1 - On-line continuous monitor to optimize coagulant and flocculent feed in wastewater and paint spray booth systems

Info

Publication number: WO1996041245A1
Application number: PCT/US1996/006862
Authority: WO
Inventors: David Brian Mitchell; Thomas P. Curran; Steven M. Deboo; Gary G. Engstrom; Larry M. Kye; John Richardson
Original assignee: Betzdearborn Inc.
Priority date: 1995-06-07
Filing date: 1996-05-14
Publication date: 1996-12-19
Also published as: AU5747096A

Abstract

An apparatus and method for optimizing coagulant and flocculent chemical feed in a wastefluid treatment system is disclosed which uses two or more contaminant-concentration dependent parametric detectors to measure the detected parameter in chemically-treated wastefluid and chemically-treated, solid-separated wastefluid.

Description

ON-LINE CONTINUOUS MONITOR TO OPTIMIZE COAGULANT AND FLOCCULENT FEED IN WASTEWATER AND PAINT SPRAY BOOTH

SYSTEMS

SPECIFICATION

Field of Invention This invention relates generally to the treat¬ ment of fluid flowing through a wastefluid treatment system. More specifically, the invention relates to an automatic device and method for optimizing the amount of treatment-additive released into a wastefluid treatment system for contaminant removal.

Brief Description of the Prior Art Large quantities of contaminated fluids are generated every day. Such contaminated fluids are a result of manufacturing processes, the propensity of certain fluids to absorb other materials, and the practical necessity of expeditiously moving waste products from one location to another. Examples of contaminated fluids include municipal sewage, water scrub from paint booths, food industry waste water, textile waste fluid, electroplating waste from plating baths and street wash-off.

Treatment additives are substances which interact with contaminants in the contaminated fluid and by means of such interaction cause the contaminant to precipitate, coagulate, flocculate, agglomerate, settle or otherwise to become more amenable to removal from the fluid by solids separators such as filters, clarifiers, hydrocyclones, or dissolved air floatation unit ("DAF") . Treatment additives include coagulating agents (such as aluminum sulfate, polyaluminum hydroxide, dimethylamine epichlorohydrin, dimethyldiallyl ammonium chloride, cat- ionic starches and cationic tannins) , flocculants (such as anionic polyacrylamides, acrylic acid-acrylamide, and cationic polyacrylamides, such as dimethylaminoethy1- acrylate) , as well as numerous other materials, such as demulsifiers. The optimal concentration of treatment-addi¬ tive in a wastefluid treatment system is dependent on a number of factors, but in particular upon the concentra¬ tion of contaminant(s) in the fluid which is to be clarified. Too little treatment-additive will inade- quately remove contaminant from the fluid. Too much treatment-additive will in itself contaminate the fluid.

Since many treatment additives are relatively expensive, the addition of too much treatment-additive may also be costly. Both overdose and underdose of treatment-additive cause poor contaminant removal.

Methods for the clarification of contaminated fluids are well known in the art. One particularly useful method employs addition of a coagulant and/or flocculating agent prior to movement of the liquid into a solid-separator known as a clarifier (a lamella design being very common in industrial waste water treatment) .

Clarifiers may be substituted with a DAF or other solid-separator such as a hydrocyclone or filter. It should be understood, however, that there a numerous other methods known in the art and this general descrip¬ tion is not intended to be limiting in any way.

Due to variability in the generation of con¬ taminants over time and in the rate interaction of the contaminants with the fluid, the concentration of con- taminant in any particular aliquot of contaminated fluid may significantly differ from the concentration of con¬ taminant in a previous or subsequent aliquot. There¬ fore, in order to maximize the clarification of contami- nated fluid, the concentration of contaminant must be monitored over time and the concentration of treatment- additive varied with the concentration of contaminant. Conventionally, the optimum concentration of treatment-additive has been determined by removing an aliquot of the contaminated fluid prior to, and after, the addition of the treatment-additive and analyzing "off-line" a parameter related to the contaminant concentration of each aliquot. Such conventional tech- niques suffer from an inability to continuously monitor fluid contaminant concentrations. That is, adjustments in the amount of treatment-additive released into the treatment system based on samples taken at time X may be inappropriate at time Y. One commonly-used method to overcome the draw¬ back of the conventional sampling technique employs "in¬ line" analysis of a parameter related to contaminant concentratio .

For example, United States Patent No. 3,693,791 ('791 patent) to Topol describes two turbidity meters (turbidity being related to fine particulate concentration) connected in the main flow of the treat¬ ment system. Such meters are positioned to measure the turbidity of a liquid before and after the addition of a treatment-additive prior to the passage of the liquid through a filter structure. The relative signal strengths produced by each meter are used to determine the amount of treatment-additive which should be added to the system. Likewise, United States Patent No. 3,605,775

('775 patent) to Zaander et al. describes an in-line detection apparatus and method used to optimize treat¬ ment-additive feed in liquid purification. In the '775 patent turbidity meters are placed at the influent and effluent ends of a liquid treatment system. The turbidity measurements from each monitor are mathematically contrasted with a pre-determined desired turbidity measurement. The mathematical result is used to determine the amount of a treatment-additive which should be added to the system.

Similarly, United States Patent No. 4,277,343 to Paz ('343 patent) describes an in-line monitoring system for continuously monitoring and controlling alka¬ linity in an aqueous solution. In the '343 patent, a system is shown wherein signals from three pC0₂ probes are used to adjust the amount of an alkalinity-control¬ ling chemical added to the aqueous solution. The three probes are described as being all located prior to the filter.

The described prior art in-line monitoring treatment systems are deficient in a number of respects. Primarily such systems fail to take into account detention of the main flow in detention vessels and clarifiers within the system. Since fluid is not infrequently held in detention vessels or clarifiers for hours, the turbidity, for example, of the flow exiting a detention vessel or clarifier as compared to the non- treated contaminated fluid may be more indicative of the efficacy of the treatment additive for reducing contami¬ nate concentration of the fluid which entered the system hours earlier, rather than upon the contaminant concentration of the fluid which is currently being treated. Further, in-line detectors located immediately after a detention vessel or clarifier may provide inaccurate parametric readings owing to periodic changes in sludge bed depth and clarifier rake speed occurring 6/41245 PC17US96/06862

in such vessels. The latter is especially true in regard to turbidity detectors. Several detectors (including turbidity detectors) require rather constant flow rates to provided optimal performance. The problems associated with in-line monitoring systems are overcome by means of continuously sampling the fluid through pilot lines connected to the main flow. Such a system is described in U.S. Patent No. 3,393,149 to Conley et al. ('149 patent). The "149 patent discloses a system for controlling coagulant feed by monitoring the turbidity of pH-adjusted, coagulant- treated, and filtered effluent from a pilot line. The system comprises a pilot line interconnected with a calcite column for raising the pH of coagulant-treated waste, a plurality of settling tubes, a plurality of multimedia pilot filters and a light-scattering turbimeter.

Prior art pilot line systems also suffer from a number of drawbacks. In particular, prior art systems, such as those described in the '149 patent, call for the system operator to set a range for the parameter measured in which the system will operate without change in the amount of the treatment-additive released into the system. That is, such systems adjust the dose of treatment-additive only if the parametric measurement is outside of a pre-determined range. Since such systems employ only a monitor located at the effluent end of the pilot line, these systems further fail to correlate the quality of the treated, filtered fluid with that of the treated, unfiltered fluid.

Further, systems such as that described in the '149 patent fail to accurately measure turbidity when the flow is first diverted to a settling tank and then the overflow goes to the filter. For an accurate determination of the optimal treatment-additive needed to clarify a particular waste stream, the treatment- additive must be added to the entire waste stream and the turbidity of the latter determined after solids separation.

SUMMARY OF THE PRESENT INVENTION The present invention overcomes many of the disadvantages of prior art wastefluid treatment systems. These disadvantages are overcome by employment of two or more contaminant-concentration dependent detectors positioned in the flow of one or more pilot line(s) emanating at select point(s) along the main fluid conduit. Such detectors include those measuring streaming current, ultraviolet absorption, infrared absorption and specific ions. The select point(s) (is)are chosen such that the detectors are positioned to measure contamination-concentration dependent parameters with respect to treatment-additive treated fluid, and solids-separated (e.g. , filtered) , treatment-additive treated fluid. The signal from the treatment-additive, solids-separated fluid detector is correlated with the signal from the treatment-additive, non-solids-separated fluid detector and the correlative function is used to calculate the optimal concentration of treatment- additive which should be released into the system.

In a preferred embodiment, the parameter which is measured is turbidity. It has been discovered that the turbidity of an non-solids-separated, treatment- additive treated sample and that of a solids-separated, treatment-additive treated sample are reduced to a minimum at approximately the same concentration of treatment-additive. Addition of more treatment-additive to the non-solids-separated, treatment-additive treated sample causes an increase in turbidity, whereas with the solids-separated, treatment-additive treated sample a further increase in the amount of treatment-additive causes no further change in turbidity. The concentration of treatment-additive at which turbidity of both samples is reduced to a minimum has been determined to approximate the optimal concentration of treatment-additive in the system. Since the accuracy of optically-based turbidi¬ ty detectors is diminished by widely differing flow rates to the detectors, the flow to the turbidity detectors is preferably maintained approximately con¬ stant. In the case of the Surface Scatter 6® manufac- tured by HACH Company, optimum flow is approximately between 0.1-1.5 gallons per minute (GPM) . Constant flow rate to the turbidity meter further aids in maintaining a constant shear rate in the treatment system. Variations in shear rate may impact upon the clarifica- tion performance of the treatment-additive. Constant flow rate through the detectors can be accomplished by the conventional means well known to one skilled in the art. For example, a flow monitoring means can be coupled to a pump which can add volume from the main conduit into the pilot line leading to the monitor if a deficit in fluid flow past the detector is detected (or subtract volume from the pilot line if too much fluid flows past the detector) .

In a preferred embodiment, the solids- separator is a filter device. The filter device should withstand considerable solids loading for the waste stream being clarified (e.g. withstanding solids loading of from 100-10,000 ppm total suspended solids in a typical industrial wastewater stream) . The later may be accomplished by means of a bag and/or a continuously unwinding filter, such as an EMCO filter manufactured by EMCO Filtration Company.

BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding of the present invention, reference is made to the following Detailed Description taken in conjunction with the accompanying drawings in which:

Fig. 1 is a side view, with a cutaway portion, showing fluid flow direction and pilot line diversion in an embodiment of the present invention.

Fig. 2 is a side view, with a cutaway portion, of an alternative embodiment of the present invention.

Fig. 3 is a graph of turbidity measurements as a function of detackifier concentration, made on filtered and unfiltered detackified paint sump waste.

Fig. 4 is a graph of turbidity measurements as a function of polymeric coagulant concentration, made on filtered and unfiltered wastewater from a manufacturer of marine motors.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS OF THE PRESENT INVENTION

Referring to Figure 1 of the drawings, there is shown schematically an exemplary monitoring system of the present invention. In such embodiment, contaminated fluid is passed into the monitoring system pilot line from a process pipe 10. Flow from process pipe 10 into the system is controlled by a flow gauge 11, flow being kept as constant as possible. Flow through the monitoring system is aided by a plurality of pumps 12 and 16, such as peristaltic pumps. The contaminated fluid enters by means of an inlet pipe 13, into a first addition pot 14 wherein a first treatment additive 32 (e.g. coagulant) is added to the fluid by means of a feed pump 35. The fluid is detained for approximately 1 minute in the first addition pot 14 while it is mixed with the first treatment additive from source 32. The flow of the additive-treated fluid is subsequently directed through a first static mixer 15 where it is mixed. The fluid is then either led by a by-pass conduit 38 (by manipulation of by-pass conduit valves 20) to the treatment-additive treated, unfiltered fluid turbidity sensor 27 and the treatment-additive treated, filtered fluid turbidity sensor 24, or directed to a pH adjustment detention pot 14 (in which pH adjusting material is added to, and mixed with, the fluid) by means of the by-pass conduit 38 (by manipulation of by¬ pass conduit valves 20) if the pH of the fluid needs to be adjusted for maximum particulate settlement, or directed through a plurality of other second addition pots 17 interconnected to other static mixers 18 disposed in the main conduit wherein further treatment- additive may be added to the fluid (which can be of another type than that added to the fluid entering the first addition pot, e.g. flocculent) . In any case, the fluid is ultimately directed to the treatment-additive treated, filtered fluid turbidity sensor 24 after passage through filter 21, or to the treatment-additive treated, unfiltered fluid turbidity sensor 27. The flow rate to each sensor is monitored by flow meters 23 and 26, the readings of the flow meters being used to correct sensor readings for changes in flow rate by conventional means(not shown) . Fluid exits the pilot line monitoring system through exit port 28.

Figure 1 further illustrates the treatment- additive control system of the present invention. As set forth in the working examples below, the optimum concentration of treatment-additive for the system is ascertained by determining the overlapping concentration range between the concentrations of treatment-additive that produce minimum turbidity readings in turbidity sensor 24 and the concentrations of treatment-additive that produce minimum turbidity readings in turbidity sensor 27. Signals from the detectors are converted to digital signals that are sent to processor 30 by means of lines 29. Processor 30 is programmed to determine the overlapping concentration range between the concentrations of treatment-additive that produce a minimum turbidity reading in turbidity sensor 24 and the concentrations of treatment-additive that produce minimum turbidity readings in turbidity sensor 27 by varying the pump rate of pilot line feed pumps 35, 36, 37 that feed the pilot line monitoring system fluid, storing the concentration of treatment-additive added to the pilot line wastefluid by the pilot line feed pumps in memory storage, and to send signals to the main fluid feed pump(s) 31 which control (s) the amount of a treatment-additive(s) added to the main flow of the wastefluid treatment system, by means of adjusting the pump rate of the main feed pumps 31.

Referring now to Figure 2, where there is shown an alternative embodiment of the present invention. In this embodiment, contaminated fluid is withdrawn from the main conduit after it is treated with treatment-additive. The rate of flow of the treatment- additive treated fluid into the detection system is controlled by pump 112. Part of the treatment-additive treated fluid is directed through flow meter 123 to unfiltered turbidity sensor 124. Another part of the fluid is directed through filter 121, through flow meter 126, and past filtered turbidity sensor 127. As in the embodiment illustrated in Fig. 1, the turbidity measure¬ ments of the sensors is corrected for flow .rate to the meter. The corrected readings are sent to processor 130 which is programmed to determine the overlapping concentration range between the concentrations of treat¬ ment-additive that produce a minimum turbidity reading in turbidity sensor 124 and the concentrations of treatment-additive that produce minimum turbidity readings in turbidity sensor 127 and to send signals to the main feed pump(s) 31 which control the amount of a treatment-additives added to the main flow of the wastefluid treatment system, by means of adjusting the pump rate of the main feed pumps 31.

The following are illustrative examples of invention described herein:

EXAMPLE 1 The present invention was employed to determine its effectiveness in ascertaining the optimum detackifier concentration in the clarification of scrubbing water in a paint booth operation. Detackifier (DT 2438, melamine formaldehyde) was added to paint sump waste. The turbidity of the contaminated fluid was determined after the addition of the detackifier. The detackifier treated fluid was then filtered through a 5 micron fiber filter and the turbidity of the detackified, filtered fluid determined. As shown in Figure 3, the turbidity of the unfiltered samples was at a minimum at approximately the same concentration range of detackifier at which the turbidity of the filtered samples first reached a minimum turbidity. Outside of this range, the turbidity of the 'unfiltered samples increased significantly at the expense of increasing detackifier usage.

EXAMPLE 2 The present invention was further employed to determine its effectiveness in determining the optimum coagulant concentration for use in the clarification of wastewater from a manufacturer of marine motors. The contaminated fluid which was treated contained substantial concentrations of oils (10-500 ppm) and suspended solids (10-lOOppm) . Coagulant (KA 2400, amino methylated tannin) was added to the wastewater. The turbidity of the fluid was determined after the addition of the coagulant. The coagulant-treated fluid was then filtered through a 5 micron fiber filter and the turbidity of the resultant fluid determined. As shown in accompanying Figure 4, the turbidity of the unfil¬ tered samples was at a minimum at approximately the same concentration range of coagulant at which the turbidity of the filtered samples first reached a minimum turbidi¬ ty. Outside of this range, the turbidity of the unfiltered samples increased significantly at the expense of increasing coagulant usage.

While the preferred embodiments of the system and method of the present invention have been described in detail, it will be appreciated that numerous variations and modifications of the present invention will occur to persons skilled in the art. All such variations and modifications shall constitute the present invention as defined by the scope and spirit of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A method to optimize the amount of a treatment-addi¬ tive released into a contaminated fluid flowing in a wastefluid treatment system comprising: a. admixing said treatment-additive into said contaminated fluid to form additive-treated fluid; b. monitoring said additive-treated fluid prior to filtering to sense a property of said additive- treated fluid relevant to the decontamination of said contaminated fluid by said treatment-additive; c. generating a first signal proportional to the magnitude of said sensed property of said additive- treated fluid; d. removing contaminate solids from said addi¬ tive-treated fluid by solids-separator means to form additive-treated, solid-separated fluid; e. monitoring said additive-treated, solid- separated fluid to sense said property of such fluid relevant to the decontamination of said contaminated fluid by said treatment-additive; f. generating a second signal proportional to the magnitude of said sensed property of said additive- treated, solids-separated fluid; g. adjusting the amount of treatment-additive added to the wastefluid treatment system by comparing a plurality of said first signal magnitude to that of said second signal magnitudes.

2. The method of claim 1 wherein said property is tur- bidity.

3. The method of claim 1 wherein said property is particle size. 4. The method of claim 1 wherein said property is streaming current.

5. The method of claim 1 wherein said property is ultraviolet absorption. 6. The method of claim 1 wherein said property is infrared absorption.

7. The method of claim 1 wherein said property is a specific ion.

8. The method of claim 1 wherein said adjustment com- prises: a. determining the range of concentrations of said treatment-additive which reduces the said sensed property of said treatment-additive fluid to a minimum; b. determining the range of concentrations of said treatment-additive which reduces said sensed property of said solids-separated, treatment-additive fluid to a minimum; c. determining the overlapping concentration range with respect to said minimum range concentrations of said treatment-additive fluid and said solids-sepa¬ rated, treatment-additive fluid. d. adjusting the concentration of said treat¬ ment-additive such that the concentration of said treat¬ ment-additive in said wastefluid treatment system is within said overlapping concentration range. . The method of claim 1 wherein the treatment- additive is a detackifier.

10. The method of claim 1 wherein the treatment- additive is a coagulant. 11. The method of claim 1 wherein the treatment- additive is a flocculent.

12. The method of claim 1 wherein the treatment- additive is a demulsifier. 13. The method of claim 1 wherein said contaminated fluid contains paint.

14. The method of claim 1 wherein said contaminated fluid is waste water. 15. The method of claim 1 wherein said solids-separator means is a filter.

16. The method of claim 1 wherein said solids-separator means is a clarifier.

17. The method of claim 1 wherein said solids-separator means is a dissolved air floatation unit.

18. An apparatus for optimizing the amount of treatment additive added to the contaminated main fluid flowing in a wastefluid treatment system having a plurality of main fluid treatment-additive feed pumps, comprising: a. a pilot line monitoring system coupled to said wastefluid treatment sytem; b. a pilot line treatment-additive source and addition means coupled to said pilot line monitoring sytem; c. a processor means coupled to said pilot line addition means for varying the concentration of treatment-additive added to wastefluid flowing into said pilot line monitoring system and storing the concentration of treatment-additive added to the pilot line wastefluid in its memory, said processor having at least a first input and a second input and an output, said output being coupled to said main fluid treatment- additive feed pumps coupled to said wastefluid treatment system; e. a solids-separator means coupled to said pilot line monitoring system; f. a first means positioned at a first location in said pilot line monitoring system for sensing at said first location a sensed property of said contaminated fluid after treatment with a concentration of pilot line treatment-additive and producing a first electrical signal varying with a func- tion of said sensed property; g. a second means positioned at a second loca¬ tion in said pilot line system downstream from said first location for sensing said sensed property of said contaminated fluid after treatment with said treatment- additive and after separating solid contaminants by said solids-separator means and producing a second electrical signal varying with a function of said sensed property; h. means coupling said first and second inputs of said processor means to said first and second sensing means, said processor means capable of determining the optimal concentration of treatment-additive which should be in said waste treatment system main fluid from a plurality of said first and second signal readings, and further capable of adjusting the flow rate of said main fluid treatment-additive feed pumps such that an optimal concentration of treatment-additive is added to said waste treatment system.

19. The apparatus of claim 18 wherein said sensed prop¬ erty is turbidity. 20. The apparatus of claim 18 wherein said first and second sensing means are located outside within the main flow of said wastefluid treatment system.

21. The apparatus of claim 18 wherein said pilot line wastefluid flow is adjusted to keep the flow to said sensing means constant.

22. The apparatus of claim 21 wherein said constant flow is between 0.1-1.5 GPM. 41245 PCΪ7US96/06862

18

23. The apparatus of claim 21 wherein said constant flow is approximately about 0.5 GPM.

24. The apparatus of claim 18 wherein said pilot line wastefluid flow from said main fluid of said wastefluid treatment system is adjusted to ensure constant shear rate throughout said wastefluid treatment system.