A92-4 page 1 SOURCE REDUCTION OF POLLUTANTS FROM WASTEWATER. Chet Namboudri - Auburn University

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1 A92-4 page 1 TITLE: SOURCE REDUCTION OF POLLUTANTS FROM WASTEWATER CODE: A92-4 PRINCIPAL INVESTIGATORS: John J. Porter - Clemson University William K. Walsh - Auburn University RESEARCH ASSOCIATES: Chet Namboudri - Auburn University GRADUATE STUDENTS: Shuzhong Zhuang - Clemson University Ninsheng (Nelson) Huang - Auburn University GOALS: The goal of this project was to study and evaluate techniques that would reduce the volume or impact of problems associated with textile wastewater. Projects reported on in this report are: PROJECT 1. The Automated Control of the Recycle of Bleaching Rinse Water to Be Used in the Scour Rinsing Operation to Decrease Hot Water Consumption and Wastewater Discharge - Clemson PROJECT 2. Microfiltration of Direct Dye and Electrolyte Solutions to Evaluate the Removal of Soluble Ionic Dyes From Wastewater - Clemson PROJECT 3. The Chemical Oxidation of Dyeing Wastewater Solutions to Remove Color and Facilitate Dyebath Reuse - Auburn ABSTRACT Bleaching wastewater has been recycled directly to the scouring process with no filtration. The control of the rinse water recycling will be accomplished by monitoring a conductance probe inserted in the bleaching rinse water discharge. This will allow the water supply to be based on fabric needs rather than an estimated value. It is estimated that this range will save $200,000 per year on this single recycle operation. A stainless steel microfilter was obtained from DuPont and evaluated on deionized water containing sodium nitrate, Direct Red 2 and Acid Red 1. Data taken from laboratory experiments revealed that the microfilter was rejecting from 5 to 50% salt as measured by conductivity rejection and up to 99% of soluble direct dyes. Similar results were obtained with a ceramic microfilter manufactured by Rhone Poulenc. The data shows a close correlation to Grahame s equation that correlates the maximum distances that charged surfaces reach and influence ions in an adjacent solution. National Textile Center Annual Report: August

2 A92-4 page 2 Decolorizing spent dyebath effluent with ozone gas and UV radiation in the presence of hydrogen peroxide was investigated. Direct, disperse, acid and reactive dyes with known chemical structures were decolorized. The results show that small amounts of hydrogen peroxide dramatically accelerate the decolorization with the low intensity UV radiation. The system was more effective in treating water soluble dyes than the water insoluble dyes. A rough cost comparison of the two methods is given. INTRODUCTION One major problem facing the textile industry is the removal of color from the 100 billion gallons of wastewater discharged per year to wastewater treatment systems. If techniques could be developed to remove undesirable dyes, salts and auxiliary chemicals from the wastewater at the point source, it would allow water (hot in some cases) to be recovered for reuse. This would produce significant savings in energy, water and waste treatment requirements. Approximately 80-90% of the total textile wastestream comes from the dyeing and preparation processes. If one half the wastewater could be recovered from these processes at the source, it could result in a decrease of 40-45% of the total wastewater discharged by the textile industry or billion gallons annually. This would translate into savings in process water cost, wastewater treatment cost, and water heating cost of more than $280 million annually if only M of the wastewater is recycled. A major problem limiting the acceptance of recycling systems by the textile industry is the fear that if the recycling process fails to produce water of suitable quality, fabric quality will be affected or the process must be shut down. If the recycling process is automatically controlled, the process is protected and fresh water is fed automatically to the process when recycle problems occur. The plant can set water quality standards for recycling. If this is not carefully done, the plant will not tolerate a recycling process that causes upsets or downtime. An integral part of these projects is the incorporation of automation into the recycling process so that fresh water can be introduced into the process if problems occur. PROJECT 1. The Automated Control of the Recycling of Bleaching Rinse Water to Be Used in the Scour Rinsing Operation to Decrease Hot Water Consumption and Wastewater Discharge - Clemson The bleaching wastewater on the preparation range, shown in Figure 1, has been recycled directly to the scouring process with no filtration. This has been done occasionally but not automatically. The plant is retrofitting the control valves to adapt to the recycling system. The main delay has been the required shutdown time to install and modify the recycling system as the plant operates twenty-four hours per day. The control of the rinse water recycling will be accomplished by monitoring a conductance probe inserted in the bleaching rinse water discharge. The conductance of the bleaching rinse water is proportional to the level of impurities present in the bleaching rinse water. This is illustrated in Figure 2, using data taken from Table 1. The conductance probe will be attached to the existing control process for the 12 National Textile Center Annual Report: August 1995

3 A92-4 page 3 Figure 1. System for Recycling Bleaching Rinse Water to Scouring Wash Boxes for a Continuous Preparation Range r I Open Width Preparation Range I I-----_ I preparation range. This will allow the water supply to bleaching wash boxes to be optimized and based on fabric needs rather than an estimated value. No problems are anticipated for the recycling process. The automated system should be in operation Table 1. Analyses of Scouring and Bleaching Rinse Water Samples Taken From the WestpointMevens Clemson Plant Source Scouring Rinse Water Bleaching Rinse Water Parameter & Date 9/28/92 3/11/93 6illr93 9/28/92 3llll93 6fllt93 8kY93 PH BOD, ppm 2,860 2,270 2,240 1,985 1,420 1, COD, ppm 11,070 9,920 11,070 5,100 4,630 5,420 5,599 Solids, ppm Total 14,228 28,000 19,730 6,048 4,780 6,155 6,818 Suspended , Hardness, as CaCO, Sp. Ckmd., pmhoskm 36,800 75,000 49,600 6,120 3, National Textile Center Annual Report: August

4 A92-4 page 4 before the end of It is estimated that this range will save $200,000 per year on this single recycle operation, based on $4/106 BTU energy, $2/1000 gallons waste treatment and $l/looo gallons process water cost. Figure 2. Correlation Between Total Solids in Textile Preparation Wastewater and Specific Conductance of Wastewater at 25 C 0 10,000 20,000 Total Solids in Wastewater, ppm PROJECT 2. Microfiltration of Direct Dye and El,ectrolyte Solutions to Evaluate the Removal of Soluble Ionic Dyes from Wastewater - Clemson In the past three years much interest has been directed to the use of microfiltration for the removal of fine particulate from process wastewater. It was desirable to see if this type of filter could be applied to textile waste streams for the removal of suspended solids and if the filtrate obtained would be suitable for recycling in the process. A rnicrofilter was obtained from DuPont and evaluated on deionized water containing sodium nitrate, Direct Red 2 and Acid Red 1. The microfilter was tubular and composed of stainless steel with a fused layer of titanium dioxide ( 0.2 micron pore diameter, 2OOOA > on its filtering surface. Data taken from laboratory experiments with the microfilter, shown in Figure 3 to 5, revealed that much of time microfilter was rejecting from 5 to 50% salt as measured by conductivity rejection and up to 99% of soluble direct dyes (1). The data obtained was suprising considering the filter was intended to remove particulate or fine suspended solids and allow soluble 14 National Textile Center Annual Report: August 1995

5 1750 A92-4 page 5 Figure 3. Filtration Rate for Deionized Water Using a Stainless Steel 81 Ceramic Microfilters at a Flow Velocity of 4.3 Meters / Second I % Conductivity Rejection 100 k 1400, E V9)?i K s 700 L E = ii Tern peratu re, C Pressure = 0.66 M Pa Figure 4. Filtration of Deionized Water and Direct Red 2 Using a DuPont Stainless Steel Module at a Flow Velocity of 4.3 Meters / Second at 30 C Time of Flltratlon in Hours 1 National Textile Center Annual Report: August

6 A92-4 page 6 Figure 5. Filtration of Deionized Water and Direct Red 2 Using a Ceramic Microfilter at a Flow Velocity of 4.3 Meters / Second at 30 C Time of Filtration in Hours ions to pass through. To confirm the results obtained with the stainless steel filter, a ceramic microfilter was obtained from a different manufacturer, Rhone Poulenc, and used in a similar set of experiments. The data obtained with the ceramic filter was presented at the North American Membrane Society meeting on May 22, 1995 in Portland, Oregon. The results thus far are very interesting and additional work is underway to learn the exact nature of the rejection. At present it is believed that very minute trace ionic impurities in the deionized water interact with the membrane surface and account for the unusual rejection properties of both the stainless steel and ceramic membranes. This hypothesis is supported by the close correlation of the experimental data with the Grahame Equation l(2) shown below and used to form one of the curves Debye Length, nanometers = 1 - = 3.04 * ( Sodium Nitrate, equiv.lliter )-Oe5 lc Equation 1 presented in Figure 6. The Grahame equation is a specific case of the Debye equation (3) which correlates the maximum distances that charged surfaces reach and influence 16 National Textile Center Annual Report: August 1995

7 A92-4 page 7 Figure 6. Conductivity Rejection and Debye Length versus Conductivity for a Ceramic Microfilter at a Flow Velocity of 4.3 Meters / Second at 45 C % Cond. Rej. = 980 x ( Cond.) -Debye Length, A = 1150 x ( Cond.) Premure = 0.66 M Pa 0 I +O Concentrate Conductivity, pm has I cm ions in an adjacent solution. It is generally called the Debye Length and expressed in Angstroms or namometers. A comparison of the Debye length to the conductivity of the solution and the conductivity rejection is shown in Figure 6. PROJECT 3. The Chemical Oxidation of Dyeing Wastewater Solutions to Remove Color and Facilitate Dyebath Reuse - Auburn(4) Decolorizing spent dyebath emuent with UV radiation in the presence of hydrogen peroxide was investigated. Direct, disperse, acid and reactive dyes with known chemical structures were decolorized. The dyes at concentration levels typically present in mill wastewater were treated with low intensity UV (germicidal lamp at 1 watt/in.) radiation in the presence of hydrogen peroxide. The results indicate small amounts of hydrogen peroxide dramatically accelerate the decolorization with the low intensity UV radiation. The system was effective in treating water soluble dyes such as reactive, acid and direct dyes in a shorter time period than the water insoluble dyes such as disperse dyes where the reaction rate was slower. The decolorization of the same dyes was studied with ozone gas. As before, the reaction rates with ozone for acid, direct and reactive dyes were faster than the water insoluble disperse dyes. A rough cost comparison of the two methods is shown in Table National Textile Center Annual Report: August

8 A92-4 page 8 2. The UV peroxide system includes total electricity cost and the cost for peroxide and the ozone system includes the cost for producing a pound of ozone. These are the primary costs for these systems. The results shows approximately comparable cost to treat the dyes with the two systems. Table 2. UV/Peroxide vs Ozone: Cost Comparison for Treating Spent Dyebath Dye Class Concentration Ozone Cost UV / Peroxide Cost * gms dye I $ I 1000 gal. $ / pound of $ / 1000 gal. $ I pound of 1000 gal. waste dye waste dye dye waste dye Direct Acid Disperse Reactive based on cost to produce of ozone, $2.25 / lb. * based on $ O.O7/KWH electricity and $0.35 / lb. Peroxide (50%) A detailed kinetic study of hydrogen peroxide on photolytic degradation of reactive dyes in aqueous solution was made to get a better understanding of the mechanisms. The kinetics of color removal was established for a plug-flow continuous reactor designed and built for the study. Variables in the study were dye color, concentration of hydrogen peroxide, intensity of ultraviolet light, ph, and temperature. Each of these variables affected the kinetics of color removal. The mechanism of color removal was shown to involve two separate reactions: 1) direct photolysis of dye molecules by W light and, 2) oxidation of dye by hydroxyl radicals formed by photolytic decomposition of hydrogen peroxide. The kinetic model used the following equation: Equation 2 In (Co/C.) = (k, + k2) = koi t where, Cc = EMuent dye concentration (g/l); C, = Influent dye concentration (g/l); 12, = Overall reaction rate constant; I = Mean of ultraviolet light intensity (uw/cm2>; 18 National Textile Center Annual Report: August 1995

9 A92-4 page 9 t = Retention time (set); and k, 9 k, = reaction rate constants for UV and free radical decolorization reactions, respectively (cm2/pw-set) Table 3 shows the reaction rate constants for the red dye at three ph conditions and three dye concentrations. The decolorization reaction is faster at lower ph in all Table 3. Effect of ph on Reaction Rate Constants for UV and UV/Peroxide* Decolorization of CL Reactive Red 195 I I 1 I I I I I H,O, concentration = 1.5 g / L, UV intensity = 5.72X10 pw / cm2 cases. The reaction rate constant for photo-oxidation decolorization, k,,, increased significantly with lower dye concentration, while free radical decolorization, k,-k,, was almost constant. This indicated that the photo-oxidation reaction was accelerated by better penetration of UV light. The effect on the radical oxidation of better UV light penetration was much less. The relative contribution of the free radical reaction in dye decolorization was greater than that of photo-oxidation at all dye concentrations, and much greater at the higher concentrations. Apparently hydroxyl radicals produced closer to the light source can diffuse to areas farther from the bulb, where UV penetration is more limited. To achieve different light intensities using the same lamp, the distance between the UV lamp and the reactor was changed. The UV light intensity was taken to be the fraction of light emitted by the lamp that struck the reactor tube containing the dye solution. The fractions were calculated from the geometry of the reactor with the lamp at distances 0,7.5, and 21 cm from the reactor tube. The UV intensities at the surface of the reactor tube are shown in Table 4. have: For the first order reaction which follows the decrease in dye concentration, we Equation 3 In (CO/Cc) = k,z t National Textile Center Annual Report: August

10 If the retention time is held constant, A92-4 page 10 Equation 4 In (CO/C,) = Kim Experiments were done at three different W light infstensities holding retention time constant. Linear regressions were done using various values for the exponent, m. The correlation coefficients for m=l were 0.94, 0.98, and 0.94 for the three dye concentrations, respectively. Other values for m gave lower correlation coefficients confirming that, for this small variation in intensity, the reaction is first order with respect to W light intensity. II Table 4. Effect of Lamp Distance from Reactor on Uv Light Intensity II I I I I IC I I 1 II I 2A74 I 3.48 I I I II I I I II 21 I 4.53 I I 1.98 I A much higher intensity W system (300 watts/in compared to the current 1 watt/in) has been obtained from Fusion Systems, Inc. and a pilot size irradiator has been constructed that will accommodate the larger volumes of dye waste required. The question of whether the linearity of the system applies at these higher levels of intensity will be answered with this device. REFERENCES 1. Porter, J. J. and R. S. Porter, Journal of Membrane Science, lql, 1995 p Grahame, D. C. Journal of Chemical Physics, a,1953 p Israelachvili, J. N., In&molectid S.&ace For=, Academic Press, Inc., London p Kinetics of Photolysis of Reactive Dyes in the Presence of Hydrogen Peroxide, Ninsheng Huang (Swift Textiles, Columbus, GA), MS Thesis, April 7, 1994, Auburn University 20 National Textile Center Annual Report: August 1995