Volume 13 – No.10 – 2004 REPRINT pp. 1057 – 1060 Short Communication
TREATABILITY OF WATER-BASED PAINT INDUSTRY EFFLUENTS Gulin Kutluay, Fatos Germirli Babuna, Gulen Eremektar and Derin Orhon
Angerstr. 12 85354 Freising - Germany Phone: ++49 – (0) 8161-48420 Fax: ++49 - (0) 8161-484248 Email:
[email protected] www.psp-parlar.de
© by PSP Volume 13 – No 10. 2004
Fresenius Environmental Bulletin
TREATABILITY OF WATER-BASED PAINT INDUSTRY EFFLUENTS Gulin Kutluay, Fatos Germirli Babuna, Gulen Eremektar and Derin Orhon Istanbul Technical University, Civil Engineering Faculty Environmental Engineering Department, 34469, Maslak, Istanbul, Turkey Presented at the 12th International Symposium on Environmental Pollution and its Impact on Life in the Mediterranean Region (MESAEP & SECOTOX), Antalya, Turkey, 04 – 08 Oct. 2003
SUMMARY In this study the wastewaters generated from a waterbased paint industry have been investigated with respect to their chemical treatability. As the industry under consideration currently houses sludge drying beds and a chemical treatment facility that consists of an equalization basin, a rapid mixing tank, a slow mixing tank and a sedimentation unit, the main objective of the study was to find out the optimum sodium bentonite dosage applicable to meet the effluent discharge standards by using the existing treatment plant. A wastewater volume of 0.23 m3 per ton of water-based paint is produced by the process. The achieved pollutant removal efficiencies, sludge characteristics and calculated running costs covering sludge disposal and expenses of chemicals used show the introduction of a bentonite dosage of 500 mg/l at the original pH of the effluent as the optimum treatment alternative. The last part of the study is dedicated to evaluate the effect of optimum bentonite application on COD values of different molecular weight cut-off fractions. The results obtained indicate approximately 62 % of the COD originated from the fraction over 1.2 µm, where highest COD removal efficiency is achieved with sodium bentonite.
KEYWORDS: Coagulation, flocculation, molecular weight cut-off, water-based paint, industrial wastewater treatment.
INTRODUCTION Although a wide spectrum of treatment methods, from membrane filtration to electrochemical oxidation, are addressed in literature for the removal of pollutants from the wastewaters generated in water-based paint industries [1], the application of sodium bentonite is among the most feasible treatment alternatives. On the other hand, a case specific assessment of the optimum treatment conditions should be employed due to the fact that each industrial premise has its own mode of production, which, in turn, exerts variations on the composition of the effluents.
In this context, the study mainly focuses on the treatability of the wastewaters from a water-based paint industry with a daily production capacity of 20 tons of the paint by means of sodium bentonite. Apart from establishing a pollution profile for the plant under investigation, an evaluation in terms of running costs is conducted in order to visualize the most feasible option achievable with the existing chemical treatment facility. The last part of the study is devoted to the determination of the differentiation of various COD fractions of the wastewater according to the molecular weight cut-offs and the effect of treatment on these fractions. For this purpose, COD analyses are conducted on raw and treated wastewater samples that are subjected to a previous ultrafiltration. MATERIALS AND METHODS Apart from COD, all analyses for conventional characterization were performed as defined in Standard Methods [2]. COD measurements were accomplished by ISO 6060 [3] method. Filtrates of samples subjected to vacuum filtration by means of Millipore membrane filters with a pore size of 0.45 µm were defined as soluble fractions. The Millipore AP40 glass fiber filters were used for suspended solids (SS) and volatile suspended solids (VSS) measurements. Absorbance measurements were conducted on samples filtered using 0.45 µm membrane filters, at 3 different wavelengths, namely 436, 525 and 620 nm. Pharmacia LKB Novaspec II model spectrophotometer was used for this purpose. All experiments were conducted at room temperature. pH adjustments were made by NaOH or H2SO4 solutions. Each data point was calculated as the mean of three replicate measurements. Acute toxicity was tested using 24-hour old water flea Daphnia magna at a dilution rate of 50 % as described in Standard Methods [2]. Test animals were grown at 16 hours light (with 1000 lux), 8 hours dark cycle. They were fed with Selenastrum capricornutum (300000 cells per ml), Schizosaccharomyces cerevisiae (200000 cells per ml) and baker’s yeast. Acute toxicity tests were repeated twice
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© by PSP Volume 13 – No 10. 2004
Fresenius Environmental Bulletin
using 20 daphnids in 50 ml test beakers at a pH of 8.0, providing a minimum dissolved oxygen concentration of 6 mg/l and 20 0C constant temperature. Results were expressed as percent death or immobilization out of 20 test daphnids after 24 hours.
from the given conventional pollutants, acute toxicity of the process effluents towards Dapnia magna is also assessed. According to the results obtained the raw wastewater filtered through 0.45 µm Millipore membrane filter does not display any toxicity on Dapnia magna at 50 % dilution.
Coagulation-flocculation tests by using various dosages of sodium bentonite were performed on the wastewaters collected from the equalization tank of the investigated plant. A jar-test cycle of two subsequent 3 min flash mixing and 3 min settling followed by a final 3 min flash mixing and 30 min settling was adopted.
Water Extenders (talc etc.) pH adjusters Antifoam Agents Pigments (titanium dioxide etc.)
Differentiation of various COD fractions in terms of their molecular weight cut-offs was also determined and the effect of applied chemical treatability on these fractions was investigated. Wastewater sample treated with optimum sodium bentonite dosing together with raw effluent were subjected to mass distribution experiments by the use of vacuum and molecular filtration. For COD fractionation, the samples were first subjected to vacuum filtration by glass fiber and membrane filters. After that, molecular filtration was applied in a Millipore stirred ultrafiltration cell having a volumetric capacity of 400 ml (Amicon, Model 8400), operating under positive pressure (0.4-2.5 bar; N2 as the inert gas). In ultrafiltration experiments, the samples were filtered on membrane discs, that have molecular weight cut-off values ranging from 100 to 1 kDa (PL series, Millipore). Aliquots, collected after each filtration step, were subjected to COD measurements.
Other additives
Mixing Reactor Wastewater (0.09 m3/ton product) Filter Wastewater (0.01 m3/ton product) Holding Tank
Filling & Packaging
Wastewater (0.03 m3/ton product)
Wastewater (2.0 m3/ton product)
PROCESS DESCRIPTION AND WASTEWATER SOURCES
Product
The production scheme of the investigated industry manufacturing 20 tons/day of water-based paint with batch-wise operations is given in Figure 1. In the first production stage, all the ingredients are mixed where after a check in terms of viscosity, density and color is employed. When a positive result from the check is obtained the reactor contents are filtered through a fabric filter and transferred to a holding tank. After ensuring the required product quality the paint mixture is sent to the subsequent filling and packaging unit. All the process wastewaters are generated due to cleaning operations of production units. According to the process profile given in Table 1, a wastewater volume of 0.23 m3 per ton of water-based paint (corresponding to 4.60 m3/day-1 of wastewater) is produced by the process.
WASTEWATER CHARACTERIZATION AND TREATMENT REQUIREMENT The conventional pollutant characterization of the investigated process effluent is summarized in Table 2. Apart
FIGURE 1 Schematic flowchart of the production processes.
TABLE 1 - Process profile of the investigated plant. Wastewater Generating Processes Mixing Tank Cleaning Filter Cleaning Holding Tank Cleaning Cleaning of Filling Equipment TOTAL
Wastewater Generation (m3/t product) 0.09 0.01 0.03 0.10 0.23
Wastewater Flowrate (m3/day) 1.80 0.20 0.60 2.0 4.60
The organic content of the effluent is in accordance with the concentrations given in literature for industries manufacturing water-based paint [4]. The main part of the COD in wastewaters is particulate in nature (soluble to total COD ratio of around 32%), dictating the application of chemical settling process as a proper treatment alternative. The total COD of the wastewater must be reduced under 200 mg/l, prior to discharging into receiving waters.
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As all the applied sodium bentonite dosages give satisfactory outcomes in terms of both COD removal efficiencies and sludge characteristics, a rough screening based on running costs had to be performed to find out the optimum conditions. In this respect, the costs associated with the used chemicals and the cost of sludge disposal are calculated as shown in Table 4.
TABLE 2 - Conventional wastewater characterization profile.
TABLE 4 - Running costs.
pH
The investigated industrial premise houses sludge drying beds and a chemical treatment facility that consists of an equalization basin, a rapid mixing tank, a slow mixing tank and a sedimentation unit.
CHEMICAL TREATABILTY WITH SODIUM BENTONITE
10
Absorbance (1/cm)
436 nm
17 19
40 -
96 100
0.018 0.012
0.011 0.010
0.013 0.011
750
190
84
19
-
100
0.063
0.051
0.041
300
118
90
12
60
93
0.013
0.014
0.008
99.6
0.014
0.005
0.003
4.83 3.15 3.95 3.80 2.77 1.73 2.40 2.77 1.84 1.31 1.73
0.75 0.56 0.65 0.61 0.60 0.38 0.52 0.60 0.40 0.29 0.37
135 90 93 78 118 110 85 82 126 152 190
1000
620 nm
100
0.055
0.040
0.033
1000
93
25
-
100
0.026
0.034
0.032
300
135
89
31
70
92
0.029
0.017
0.015
500
90
93
18
-
100
0.008
0.009
0.007
750
93
92
21
-
100
0.080
0.062
0.052
1000
78
28
-
100
0.075
0.056
0.046
94
* original pH; SVI = sludge volume index
Raw Wastewater Treated Wastewater
total
-
toplam-1,2µm
17
1,2µm- 0,45µm
93
0,45µm-0,22µm
85 82
0
100kd-30kd
750
200
0,22µm-100kd
19
400
10kd-3kd
91
600
30kd-10kd
110
4
800
