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Sunday, August 30, 2015

Process Flowchart of Effluent Treatment Plant (ETP)

Effluent can be defined as the excess chemical liquor which is discharged after using original operation.
Effluent is defined by the United States Environmental Protection Agency as "wastewater - treated or untreated - that flows out of a treatment plant, sewer, or industrial outfall. Generally refers to wastes discharged into surface waters". The Compact Oxford English Dictionary defines effluent as "liquid waste or sewage discharged into a river or the sea".
Effluent Treatment Plant is a plant which is used to treat the effluent and make it environment friendly. The process flow chart of ETP is shown in the following fig:

Process Flowchart of ETP

Now I’ll briefly discuss the steps of ETP plant –

Screening is the first unit operation in ETP plant. Screen is a perforated device which is used to retain the coarser materials found in waste water. When the solid materials come in contact of the screen they stack and are removed manually or mechanically. This process is called screening.
Flow Equalization
Flow equalization is a system which is used to reduce the operational problems created by flow variations, to accelerate the downstream process. In case of any process failure in the treatment process, it is also used as an emergency tank to equalize the effluent. It ensures the constant or nearly constant flow rate of the effluent.
It takes place in rapid mix basins which is very rapid. The key function of rapid mix basin is to disperse the coagulant so that it contacts all of the effluent.
It is done to form aggregates from the finely divided matter. The flocculation of effluent is done in two ways. One is mechanical and another is agitation. In both mechanical and air agitation systems, it is common practice to taper the energy input so that the aggregates initially formed will not be broken as they leave the flocculation facilities.
Generally, industrial wastewater contains acidic or alkaline components which should be neutralize before discharge or treatment. Especially sulphuric acid, lime etc. are used to neutral the waste water.
Primary Clarifier
Primary clarification is a physical treatment process. In this process, solids are removed before biological process. After basic screening, it is the most cost effective way to remove these solids. When the process water enters the clarifier tank, floatable solids are removed from the surface by skimmers while settleable solids are collected at the bottom by a rack and are removed via a sludge removal system.
Biological Treatment
There are many biological processes that are used for wastewater treatment. The processes can be divided into five major groups: aerobic process, anoxic process, anaerobic process, combined aerobic anoxic and anaerobic process.

Saturday, March 22, 2014

Water Functions in the textile industry

Within the textile industry several sectors can be distinguished. The most important water consuming sector within the textile industry is textile finishing industry, where water can be used on two different ways: as a medium for textile treatment with direct contact with material or as a heating / cooling medium without direct contact. Following figure shows water circuit in textile finishing production.
The figure shows water circuit in textile finishing production.Wet textile finishing processes consists of operations like: per-treatment, dyeing, printing, finishing, washing, coating and laminating where water is essential.
Different textile processes:
Wet textile finishing processes consists of operations like: per-treatment, dyeing, printing, finishing, washing, coating and laminating, carpet back coating, these operations are explained more into detail below -  
The major water demanding processes during textile production are:
         Fabric preparation;
         Special finishing;
         Cooling processes;
         Steam generation;
         Abnormal incidents (e.g. fire protection);
         Cotton (singeing, desizing, scouring, mercerizing, bleaching);
         Wool (carbonizing, washing/scouring, fulling, bleaching);
         Silk (scouring, weighting);
         Synthetic material (washing; extraction of: surfactants, complexing agents, alkali; thermo fixation).
         Cellulose fibres dyeing;
         Wool dyeing;
         Polyamide fibres dyeing;
         PES fibres dyeing;
         Acrylic fibres dyeing.
         Printing with pigments;
         Printing with dyes.
Finishing (functional finishing):
         Easy care treatments;
         Water repellent treatments;
         Softening treatments;
         Flame-retardant treatments;
         Antistatic treatments;
         Mothproofing treatments;
         Bactericidal and fungicidal treatments;
         Anti-felt treatments;
         Oxidizing treatments;
         Treatments with resins.
        Washing with water (in the presence of wetting agent and detergent);
        Dry cleaning (with solvent, usually perchloroethylene).
Coating and laminating:
        The fabric to be coated / laminated is supplied full width on a roll;
       The fabric is fed under careful tension control to a coating or laminating heat     zone after application of the coating auxiliaries, the fabric is passed through an oven to cure the composite and remove volatile solvents before cooling and rolling up.
Carpet back coating:
        Foam coating;
        Textile back-coating;
        Heavy coating;
        Back finish.
Environmental issues:
        COTTON: Water emissions which vary according to a number of factors: the make-up, the sequence adopted, the fact that some treatments are often combined in a single step, etc;
        WOOL: Water emissions, but also specific operations where halogenated solvents are employed;
        SILK: Scouring baths present a high total organic charge; the concentration of nitrogen organic components in particular is high. The environmental issues associated with silk pre-treatment arise from emissions of washing agents to water;
        SYNTHETIC MATERIAL: When material is washed, about 80 % of preparation agents are released to the waste water and the remaining 20 % can be emitted to exhaust air in the subsequent high temperature treatments (drying and thermo fixation).
The main concerns, as regards waste water, arise from the discharge of poorly or non-biodegradable substances such as mineral oils, EO/PO adducts, silicone oils, hard surfactants, etc. Furthermore, biocides, which are normally contained in the aqueous formulations, contribute to aquatic toxicity of the waste water.
        The dyes themselves (toxicity, metals, colour) auxiliaries contained in the dye formulation (dispersants, salts, powder-binding agents, anti-foaming agents, anti-freeze agents, thickening agents, buffer systems);
        Basic chemicals (alkali, salts, reducing and oxidizing agents) and auxiliaries used in dyeing processes;
        Contaminants present on the fibre when it enters the process sequence (residues of pesticides on wool are encountered in loose fibre and yarn dyeing and the same occurs with spin finishes present on synthetic fibres).  
Water and energy consumption in dyeing processes are a function of the dyeing technique, operating practices and the machinery employed.
        Printing paste residues;
        Waste water from wash-off and cleaning operations (unfixed dye, urea, sulphates, polysaharides, polyacrylates, glycerine, polyvinyl alcohol, m-nitrobenzene sulphonate, multiple-substituted aromatic amines, mineral oils);
        Volatile organic compounds from drying and fixing (aliphatic hydrocarbons, methanol, polyglycols, formaldehyde, ammonia, phenylcyclohexene).
Finishing (functional finishing):
        Ethylene urea and melamine derivatives in their “not cross-linked form” (cross-linking agents in easy-care finishes);
        Oregano-phosphorous and polybrominated organic compounds (flame retardant agents);
        Polysiloxanes and derivatives (softening agents);
        Alkyphosphates and alkyletherphosphates (antistatic agents);
        Fluor chemical repellents.
Coating and laminating:
        Coating powders;
        Coating pastes (fatty alcohols, fatty acids, fatty amines from surfactants; glycols from emulsifiers; alkylphenoles from dispersants; glycol, aliphatic hydrocarbons, n- methylpyrrolidone from hydrotropic agents; aliphatic hydrocarbons, fatty acids/salts, ammonia from foaming agents; phthalates, sulphonamides/esters ex softeners / plasticizers; acrylic acid, acrylates, ammonia, aliphatic hydrocarbons from thickeners);
        Polymer dispersions (aqueous formulations: acrylates, monomers);
        Melamine resins;
        Polymer dispersions (organic solvent-based formulations).
Carpet back coating:
        Foaming agents and stabilizers (surfactants);
        Cross-linkers (sulphur, but also peroxides);
        Vulcanization accelerators (mercaptobenzothiazoles, dithiocarbamates);
        Activators (combination of zno and stearic acid);
        Gelling agent (ammonium acetate, silicon fluoride);
        Hydrophobic substances (paraffin dispersions, silicon emulsions) ;
        Complexing agents (edta, polyphosphates);
        Thickeners (organic polymers based on polyacrylates and cellulose).  
        Anionic and non-ionic surfactants;
        Impurities from material.