|Title of Invention||
REMOVAL OF COLOUR IN TEXTILE EFFLUENT USING CHEMICAL REACTANTS
|Abstract||ABSTRACT REMOVAL OF COLOUR IN TEXTILE EFFLUENTS USING CHEMICAL REACTANTS This invention relates to a process for the removal of colour in textile effluent using gaseous chlorine and activated carbon based agents. This process comprises Passing the gaseous chlorine into the reactor where water or effluent containing dyes are allowed to pass. Then the excess free chlorine is brought to the collection tank. Then this free chlorine is mixed well with the rest of effluent in the collection tank. This chlorine is allowed to react with the effluent for several minutes. Then the activated carbon, based agents are dosed in the collection tank for the removal of balance colour. This is mixed well in the effluent. The effluent thus treated is filtered in the filter press for the removal of exhausted activated carbon based agents. The filtrate from this process is free from colour. This invention has the advantage of removing colour without generation of chemical sludge with lesser investment and operating cost.|
|Full Text||REMOVAL OF COLOUR IN TEXTILE EFFLUENTS USING CHEMICAL REACTANTS
The invention relates to removal of colour using chemical reactants from textile effluent thereby making it suitable for reuse or disposal. This invention has a potential to handle effluents from other industries too.
Colour of effluent is due to many factors such as presence of dyes, pigments, soluble organic or inorganic material. Presence of colour indicates presence of one or combination of these materials. These constituents of effluent that attribute colour to effluent can result in high levels of 'Chemical Oxygen Demand' (COD) and 'Bio¬chemical Oxygen Demand' (BOD) making it unfit for disposal to water bodies or irrigation. Therefore, removal of colour is an important aspect of effluent treatment. Textiles industry, paints and coating industry and fermentation industries usually have colour effluents. Removal of colour in coating industry is not very difficult and is easily carried out with chemical reagents. This is possible because, colour is due to pigments that are suspended in the effluent. Removal of suspended solids removes the colour. In other cases, the colour is due to dissolved constituents.
Removal of colour from textile industry effluent is a very arduous process. The common procedure involves removal of colour with help of flocculants and coagulants that remove suspended solids, colloidal solids and well as a part of colour associated with these solids. Dissolved salts are usually not removed in this process. This process also requires certain
amount of 'Alkalinity' to be maintained necessitating addition of lime or caustic. This added alkalinity is consumed by the flocculants for the formation of hydroxides which attracts the solids by surface phenomena. This process ultimately results in formation of 'sludge' which is invariably hazardous due to its chemical nature. Moreover, the dissolved solid content of the treated effluent is increased due to unconsumed alkalinity and the pH is also altered.
More often, it so happens that the colourants require more than one pH for settling. This is so because of different solubilities of the hydroxide / other base that are formed during treatment. Therefore, precipitation will be carried out in several stages. This put in restriction in use of various dyes in manufacture and is also posing problems in effluent treatment.
Disadvantages of the conventional system are summarized below:
1. High capital cost; the conventional system requires separate arrangements for preparation of chemicals, dosing systems, mixing arrangements and clarification of water from sludge.
2. Hazardous waste generation; Resultant sludge of the process is invariably hazardous as defined in 'Hazardous Waste Management and Handling Rules, 1989' vide it's amendment in 2000 and 2002.
3. Inconsistency in the performance: Doses for the flocculation / coagulation chemicals vary with changes in the characteristics of the effluent. Effluent characteristics vary frequently, i.e. more than once a day. The results are also dependent on factors such as quantity of sludge already existing in the clarifier, mixing, and quality of the flocculants used etc. This leads to inconsistency in the performance.
4. High operating cost; Operating cost is quite higher compared to this new process since the former required high amounts of chemicals to be used for precipitation of solids and colour. Moreover, cost associated with sludge treatment and disposal is also quite higher.
5. Skilled supervision: Doses are to be determined for every batch. This is performed using a system called 'Jar Test Apparatus'. This necessitates attention of skilled manpower for every batch that is processed
A schematic of the conventional process is presented in the next page.
The process invented makes use of very efficient oxidizing agents that oxidize the colorants in the textile / industrial effluent along with a part of suspended and colloidal solids. This is then taken to tertiary treatment systems for further beneficial use or disposal. This method effectively avoids primary and secondary stages of effluent treatment plant. Elimination of these stages result in multiple benefits such as easy operations, reduced space requirement and reduction of hazardous sludge.
In this new method, gaseous chlorine is used for oxidising the colourants in a reactor where chlorine is dosed depending on the type of the dyes used, suspended solids content, pH and alkalinity of the effluent and such characteristics. The suspended solids content in the effluent ranges from 350 to 700 ppm , pH ranges from 6.0 to 10.0 and alkalinity upto 953 ppm. The gaseous chlorine is dosed in the reactor between 0.5 to 5.0 bar pressure and the dosage varies from 0.5 Kg to 2.0 Kg per kilo liter of effluent depending on the intensity of the colour and certain other characteristics. The gaseous chlorine thus dosed is allowed to react with the effluent for 30 to 120 minutes. This method effectively removes about 60% to 90% of the colour. Doses, removal efficiency and other operating conditions vary with characteristics of the effluent.
Balance colour is removed using a combination of high efficiency formulated activated carbon based agents. The dosage requirement ranges from 70 ppm to 100 ppm. In this stage, the activated carbon based agents are dosed into the collection tank. With proper control on the residence time, mixing pattern and other conditions in the collection tank,
the carbon adsorbs most of the residual colour. However, this carbon is to be removed to get colour and suspended solids free treated effluent. This is achieved by passing it through a filter press.
The application of the process is further clarified in the following examples.
This system has been installed at Stallion Garments (Dyeing Division), Tirupur and Shri Murugan Process, Erode both situated in the State of Tamilnadu. Results of these two case studies are presented below:
01. Stallion Garments:
Raw effluent colour: >500 hazen units (Not measurable)
Treated effluent colour: Raw effluent COD: 750mg/l
Treated effluent COD: 265 mg/1
02. Shri Murugan Process:
Raw effluent colour: >500 hazen units (Not measurable)
Treated effluent colour: Raw effluent COD: 650 mg/1
Treated effluent COD: 245 mg/1
This treatment makes the effluent suitable for tertiary treatment. In other words, This
treatment scheme eliminates elaborate primary and secondary treatment systems which
are otherwise required for achieving the same results.
1. A process for the removal of colour in textile effluent using gaseous chlorine and activated carbon based agents which comprises passing the gaseous chlorine into the reactor where water or effluent containing dyes are allowed to pass and then the excess free chlorine is brought to the collection tank and this free chlorine is mixed well with the rest of effluent in the collection tank and this chlorine is allowed to react with the effluent for several minutes and then the activated carbon based agents are dosed in the collection tank for the removal of balance colour and this is mixed well in the effluent and the effluent thus treated is filtered in the filter press for the removal of exhausted activated carbon based agents and the filtrate from this process is free from colour.
2. A process as claimed in claim 1 wherein passing of the gaseous chlorine in the reactor where effluent is passed with ambient to 50 C temperature.
3. A process as claimed in claim 1 and claim 2 wherein the effluent is passed to the reactor several times as required till satisfactory removal of colour is assured.
4. A process as claimed in claim 1 to claim 3 wherein usage of activated carbon based agents for the removal of balance colour.
5. A process as claimed in claim 1 to claim 4 wherein removal of exhausted activated carbon based agents using filter press.
6. A process substantially as herein before described in claim 1 to claim 5 with particular reference to the examples given.
|Indian Patent Application Number||43/CHE/2005|
|PG Journal Number||30/2009|
|Date of Filing||19-Jan-2005|
|Name of Patentee||SUDHAKAR MUNISWAMI|
|Applicant Address||NO. 529, MARAI MALAI ADIGAL STREET, GC COLONY, GANDHI NAGAR, VELLORE -632 006|
|PCT International Classification Number||C02F1/00|
|PCT International Application Number||N/A|
|PCT International Filing date|