Tez özetleri Astronomi ve Uzay Bilimleri Anabilim Dalı

Treatability of Electronical Industry Effluents

Water-based paints have been evaluated as alternatives to solvent-based paints. The volatile organic compound (VOC) content of water-based paints is significantly lower than conventional solvent-based paints, thereby reducing VOC emissions. Water-based paints may include such resins as acrylics, vinyls, and epoxies, among others. In addition to the resins, water-based paint is made up of some solvents, pigments, and additives. Due to the varying degree of chemicals used, the wastewater contains appreciable concentrations of BOD, COD, suspended solids, toxic compounds and color. Among various chemical treatment options applicable to highly polluted, toxic and colored effluents, the most commonly used treatment schemes are coagulation-flocculation and Fenton oxidation.

Membrane process has been widely used in both water supply and wastewater treatment application. The application of membrane process has an increasing trend to recover both water and rejected water. Recovery of valuable substances such as detergent, pigment, solvent along with water makes membranes a more attractive process.

The aim of this study is to investigate the facilities of treatment and recycling of extremely polluted water-based paint wastewater from the electronics industry by using coagulation-flocculation, Fenton oxidation and membrane process.

The water-based paint wastewater was collected from the painting unit of an electronics industry which manufactures a various range of color televisions. The characterization of the water-based wastewater is 55.000 to 205.000 mg/L of COD, 9.500 to 32.000 mg/L of SS. The wastewater used in this study was collected four times on different dates and stored at +4ºC. The characterization of the wastewater depends on the painting duration so the COD concentration varies in a wide range. The flow rate of wastewater from the painting unit was 5m3/day and discharged everyday. The water after a suitable treatment is sought after for recycling within the painting unit.

Chemical coagulation flocculation experiments were performed using aluminum sulfate and ferrous sulfate. In order to determine the optimum coagulant dosages and the pH condition, jar-tests were carried out at various reaction conditions (1st wastewater with the concentration of 2500-7500 mg/L aluminum sulfate, 270-10800 mg/L ferrous sulfate and 2nd wastewater with the concentration of aluminum sulfate 600-4000 mg/L, concentration of ferrous sulfate 500-4000 mg/L, and pH 6-10). First, the optimum coagulant dosage at pH 9 was determined. The optimum pH at the optimum coagulant dosage was then obtained. Ca(OH)2 and NaOH were used to adjust pH. Performance of the coagulation was determined by COD removal efficiency and turbidity.

In the Fenton oxidation the constant [Fe+2]=0.02 M and [H2O2]/[Fe+2]=10 were studied. The studies on Fenton’s kinetics was carried out to optimize the reaction time. Performance of the oxidation process was followed by the analysis of COD at various concentrations and different time intervals. All chemical treatment experiments were undertaken in triplicates.

The membranes used in this study were FM UP020, FM UP005 and FM NP010 (Microdyn-Nadir GmbH, Germany). Permeate of the membrane FM UP005 was fed to the membrane FM NP010 to eliminate additional COD.

In the coagulation- flocculation studies, 1st wastewater: 68 % COD removal was achieved at 5000 mg/L of aluminum sulfate dosage at pH 9 and 59 % COD removal was achieved at 2700 mg/L of ferrous sulfate dosage at pH 9. 2nd wastewater: 67 % of COD removal was achieved at 1000 mg/L of aluminum sulfate dosage at pH 7 whereas coagulation with ferrous sulfate obtained 45 % of removal efficiency at 750 mg/L dosage ath pH 8-9. The color and turbidity were removed to acceptable values. Waste sludge produced by coagulation flocculation, hovewer, should consider the disposal of hazardous waste.

Fenton oxidation gave good results for the removals of COD and color. 81 % of COD removal was achieved with [H2O2]/ [Fe+2]=10 at 2 M of [H2O2]. The oxidation time was optimized as 150 min. The color and turbidity were completely removed in all Fenton experiments and waste sludge produced during the Fenton process was less than that of coagulation, but still needs hazardous disposal.

Membrane process presented a more environmentally friendly solution to recover both water and pigments. This study showed that the total flux declines for the ultrafiltration FM UP005 membrane was 73 % and the flux decline by fouling for the membrane was 9 %. 66 % of COD removal efficiency was achieved with this membrane.

The all alternatives applied in this study produced the colorless effluent. Therefore the effluents from the all alternatives can be used in the painting unit for the recycling purpose. Cost analysis involving investment, operation and maintenance, and waste sludge disposal should be made to decide the treatment and/or recycling process.