Chlorination Effluent Treatment Plant
1. Elimination or reduction of colors and odors: Color and odor-producing substances
present in wastewaters are oxidized by chlorine. The oxidizing ability of chlorine is
employed for odor control and color removal in treatment of many industrial effluents
(beet sugar, cannery, dairy, pulp and paper, textiles).
2. Disinfection: Owing to its strong oxidizing capacity, chlorine destroys or inhibits growth of bacteria and alage.
3. BOD reduction: Chlorine accomplishes BOD reduction by oxidation of organic compounds present in wastewaters.
4. Oxidation of metal ions: Metal ions which are in reduced state are oxidized by chlorine (e.g., ferrous to ferric ion and manganous to manganic ions).
5. Destruction of cyanides, phenols and detergents.
6. Control of foams and flies.
7. Aiding scum and grease removal.
Chlorination of wastewater for BOD reduction was practised as long as 1859 in England . A number of studies of BOD reduction by effluent chlorination where it was recognised as such were conducted the 1920s and 1930s . In the USA in the 1920s and 1930s and thereafter the chlorination of Sewage was in use for purposes of protecting water supplies, bathing beaches and shellfish layings situated at the sewer outfalls. Chlorination was reported to reduce Biochemical Oxygen Demand of sewage as well as to control odors. Applications of chlorine in wastewater collection, treatment and disposal are reported in several publications.
In spite of the use of chlorine as disinfacting chemical today, renewed interests have been shown in using chlorine for treating textile dyeing-finishing wastewaters through in-situ generation of chlorine by electrolysis of a chlorine bearing salt in the wastewater. Major achivements reported are: color destruction and significant reduction of COD and BOD. Creative Environmental Consultants have offered technology to treat dyebath effluents with chlorine gasThe textile wastewaters that contain very low dissolved oxygen lack a major component, that is, abundance of oxygen to support dioxin formation. Chlorination of textile wastewater will not produce dioxin.
By using chlorination all the objectives of textile wastewater treatment listed hereunder are achieved. The main objectives of textile wastewater treatment technologies are: color and odor removal
reduction of BOD
reduction of TDS and TSS
maintaining pH of the treated effluent in the range 6.5 – 9.0 And the treated effluent shall meet the limits set in Schedule 12-B of ECR 1997 issued by DoE, Bangladesh.
This is a practical technological option for Bangladesh because of low cost of chlorine gas here, A technology is based on laws of physical sciences and scientific principles which never get old or outdated. On the other hand, an effluent treatment plant (ETP) is basically a chemical process plant consisting of a number of unit operations and unit processes whose performances are governed by underlying principles of thermodynamics, transport processes, reaction kinetics, separation processes etc. These underlying principles do not get old or outdated. The very idea that the ETP of an industry is a chemical process plant is unfamiliar with those who always compare it with a sewage treatment plant.
While planning and designing an ETP for textile wastewater with chlorine gas, advantages of the different functions of chlorination have been employed based on underlying fundamental principles. The resultant ETPs are simple to construct and operate. The so-called and perceived disadvantages of chlorine-based ETPs outweigh the benefits of operating such ETPs with chlorine gas.
Moreover, process engineering assembles technologies of different ages and unrelated areas as long as the designed process plant performs satisfactorily and remains economically viable in a competitive market. It is important to appreciate the sequence in which the various steps in process proceed to completion chemically or physically yielding the desired result. This is how a conscious process engineer can give a simple solution for the so-called difficult problems and the solution may appear to be a common-sense solution.
The Environment Conservation Rules of 1997 (ECR – 1997) have laid down the standards for the effluents from the Integrated Textile Plants and Large Processing Units (with investment more than Taka three crores) as per Schedule 12-B as mentioned below: Standards for Textile Effluents as per ECR-1997 (Schedule 12-B)
|Suspended Solids||100 mg / l|
|Oil and Grease||150 mg / l|
|BOD5*||10 mg / l|
|Total Dissolved Solids||2100 mg / l|
|Wastewater flow||100 mg / l|
|Total Chromium as Cr||2** mg / l|
|Sulfide as S||2** mg / l|
|Phenolic Compounds as C6H2OH||5** mg / l|
|* BOD||150 mg / l|
* * Special parameters based on type of dye used
The Standards for Industrial or Project Effluent set in Schedule-10 of ECR-1997 shall not be applicable for the industries for which separate specific standards have been set (Schedule-12). Please refer to Clause 13 of ECR-1997.
After the gazette notification of ECR-1997 (August 27, 1997), the Department of Environment has not to-date worked out the procedures and methods to be used to measure these parameters. In absence of these procedures which are to be issued through a separate gazette notification by DoE one should use procedures laid down by the US EPA as per CFR-40 or the relevant Indian Standards. Samples are to be analyzed by the accredited Laboratories or Laboratories recognized by the Department of Environment, Bangladesh.