Techniques for effluent treatment. Lecture 5

Transcription

1 Techniques for effluent treatment Lecture 5

2 Techniques for effluent treatment Dye effluent treatment methods are classified into three main categories: 1. Physical treatment method 2. Chemical treatment method 3. Biological treatment method

3 There are four stages of the treatment process: Preliminary, Primary, Secondary and Tertiary. 1. Preliminary treatment process includes equalization, neutralization and possibly disinfection. 2. Primary stage is mainly physical which includes screening, sedimentation, floatation and flocculation to remove debris, un dissolved chemicals and particular matters. 3. Secondary stage is a combination of physical/chemical separation and biological oxidation to reduce the organic load. 4. Tertiary stages are: to serve as polishing of effluent treatment. The methods are adsorption, ionexchange, chemical oxidation, hyperfiltration (reverse osmosis), electrochemical etc.

4 Chlorine Dioxide Treatment Due to high level of oxidation stage (+4), chlorine dioxide has some unique properties, are as follows: 1. It bleaches cellulosic materials to higher brightness level than hypochlorite and hydrogen peroxide. 2. It has substantial bactericidal properties. 3. Chlorine Dioxide, in gas form, can not be safely compressed or liquefied. 4. Chlorine Dioxide, in solution form, can be safely handled, even at its maximum solubility in water. Chemistry of Chlorine Dioxide and its generation in industry i. Chlorine generation of chlorine dioxide Cl 2 + H 2 O HOCl + HCl HOCl + HCl + 2NaClO 2 2ClO 2 + 2NaCl + H 2 O ii. Hypochlorite generation of chlorine dioxide NaOCl + HCl NaCl + HOCl HCl + HOCl + 2NaClO 2 2ClO 2 + 2NaCl + H 2 O

5 Ozone Treatment Ozone is sometimes used as disinfectant in place of chlorine. Basically air is filtered, cooled, dried and pressurized then subjected to an electrical discharge of approximately 20,000 volts. The Ozone produced is then pumped into a contact chamber where it contact with water for 15 minutes. Ozone is more destructive than chlorine. A major concern with ozone is the rate at which it decomposes spontaneously in water, according to the reaction: 2O 3 3O 2 Some chlorine must be added to maintain disinfectant character throughout the water distribution system. For this purpose, a strong oxidising agent, ferrate, is added to remove heavy metals and phosphate.

6 Hydrogen peroxide treatment Decolorization of dyes belonging to various groups was carried out using novel free radicals generating systems consisting of Cu(II), organic acids and hydrogen peroxide. Among the organic acids tested, succinic acid was the most effective. A 24 h incubation in the presence of 10 mm Cu(II), 200 mm succinic acid, and 100 mm H 2 O 2 resulted in 85 95% decolorization of Remazol Brilliant Blue R (RBBR), Reactive Blue, Poly B 411, Chicago Sky Blue, Evans Blue and Methyl Orange. The replacement of Cu(II) with other transition metals was less effective but 78% decolorization was detected in the case of Co(III) and succinic acid. The decolorization is due to the formation of hydroxyl radicals, formed during the decomposition of H 2 O 2 by the metal ligand complex.

7 Decolorization of dye wastewater by hydrogen peroxide in the presence of basic oxygen furnace slag The basic oxygen furnace waste slag (BOF slag) generated from steel making plants has been used in dye wastewater treatment. It was shown to be effective for the decolorization of a dye chemical (acid black 1) wastewater by using BOF slag with hydrogen peroxide. In an acid solution, BOF slag can be dissociated to produce ferrous ions and react with hydrogen peroxide to generate hydroxyl radicals and oxidize target pollutant acid black 1. All of the factors that affect the decolorization of acid black 1 were studied including: hydrogen peroxide dosage,concentration of BOF slag, initial concentration of acid black 1 and ph value of solution.

8 Decolorization and degradation of H-acid and other dyes using ferrous-hydrogen peroxide system The decolorization and degradation of two commercial dyes viz., Red M5B, Blue MR and H acid, a dye intermediate used in chemical industries for the synthesis of direct, reactive and azo dyes. Effect of Fe 2+, H 2 O 2, ph, and contact time on the degradation of the dyes was studied. Maximum color and COD removal was obtained for Red MSB, H acid and Blue MR at mg/l of Fe 2+ dose and mg/l of H 2 O 2 dose at ph 3.0. Release of chloride and sulfate from the Fenton's treated Red M5B dye and sulfate from H acid and Blue MR indicates that the dye degradation proceeds through cleavage of the substituent group.

9 Decolorization of the azo dye Reactive Black 5 by hydrogen peroxide and UV radiation. The decolorization of C.I. Reactive Black 5 by the combination of hydrogen peroxide and UV radiation was developed based on experimental results and known chemical and photochemical reactions. The observed kinetic reaction coefficient was determined and correlated as a function of hydrogen peroxide concentration and UV intensity. The decolorization rate follows pseudo first order kinetics with respect to dye concentration. The rate increases linearly with UV intensity and nonlinearly with increasing hydrogen peroxide concentration

10 ZINC OXIDE ASSISTED PHOTOCATALYTIC DECOLORIZATION OF REACTIVE RED 2 DYE The photocatalytic decolorizations of aqueous solutions of Reactive Red 2 dye in the presence of ZnO suspension has been investigated with the use of artificial UV A light sources. The effects of various parameters, such as time of irradiation, photocatalyst amount, ph, addition of H2O2 and temperature on photocatalytic degradation were investigated. The rate of decolorization was found to increase significantly with time of irradiation. Under optimal conditions, the extent of decolorization was 100% after 30 minutes of irradiation. Optimum catalyst concentration [Catalyst]Opt was measured and found equal to 2.5 g/l 1 The oxidizing agents such as oxygen and hydrogen peroxide enhance the decolorization rate.