General risk and impact to environment

Textile industry includes a wide number of sub-sectors, from the production of raw material to the finished product, and water management is part of the whole environmental policy for emission minimization. Other issues being air and solid management with the aim of their minimization and or reuse.

The output parameters responsible for degradation of the environment include solids and hazardous wastes, sludges, low grade large measure of heat, wastewater discharges and contaminated atmospheric air and flue gases.

The schematic diagram for resource inputs and final outputs into the surrounding environment for the Textile and allied chemical industries from environment viewpoint is given in Table 1.(1)

Pollution control and minimization

In order to control pollution and reduce its effect on environment, one should consider following measures.

1. Prevention of pollution generation.

2. Treatment of polluted streams close to the source of pollution (start of pipe approach).

3. Treatment of the final effluent (end of pipe approach).

As a very general rule, the pollution prevention actions can normally succeed in all companies, while the start of pipe approach is mostly indicated in medium or big enterprises and the simplicity of the end of pipe approach makes it suitable also in small and medium enterprises.

Pollution prevention techniques have proved to be an effective means to improving process efficiency and to increasing company profits and at the same time to minimizing environmental impact. In each case of implementation of these techniques, the specific conditions must be carefully considered and every option and change must be examined, to understand how it could affect air, land and water pollutant releases. Examples of practical applications of pollution prevention techniques:

Quality control for raw materials

Textile companies can reduce waste emissions by working with suppliers to find out less polluting raw materials. Pre-screening raw materials is a useful practice to determine interactions among processes, substrates, and other chemicals and possibly reduce waste production.

Chemical substitution

Since textile finishing is so chemically intensive, special attention should be dedicated to the selection of textile process chemicals. Opportunities for chemical substitution vary substantially among mills according to the differences in environmental conditions, process conditions, product, and raw materials. The possible actions include the replacement of chemicals as desizing agents, dyes, and auxiliaries with less-polluting ones and/or replacement of chemical treatment in some processes with mechanical or other non-chemical treatments.

Process Modification

Optimization of the processes can be obtained by modifying some operations.

Examples of possible modifications are:

• Substitution of dyeing machines using low liquor ratio, i.e equipment able to substantially reduce bath ratio and allow considerable savings of energy, water, dyes and chemicals.

• Optimization of process conditions, such as temperature and time.

• Combining operations (for instance, combining scouring and bleaching) to save energy and water.

Textile processing industry is characterized by its fairly high specific water consumption and its large amounts of wastewater discharges.

The process water or wastewater situation is characterized by very different conditions of split flows from the different processing steps. Split flows which show an extremely intense colouring or a high organic contamination are residual dyebaths or desizing wastewater.

Split flows which show a comparatively slightly pollution are the big amounts of rinsing waters from different processing steps.

Wastewater: Risk and impact to environment

There are three basic kinds of water pollution:

(i). Modification of water quality due to natural unavoidable reason: for instance storm water, gathering soluble and suspended impurities from the soil at its passage; giving as result a natural pollution, normally within values to allow water to be suitable for almost all purposes, requiring simple treatments.

(ii).  Pollution higher than the previous one, due to unnatural sources, but anyway within the self depuration capacity of the recipient waters: water undergoes biochemical oxidation processes owing to micro-organisms that, using the oxygen dissolved in water, are able to attack organic matter, transforming it into simple mineralized products such as water, CO2, sulphates and so on. In this way, thanks to biodegradation and dilution the pollutant load can be maintained within tolerable levels.

(iii).  The most dangerous pollution level is reached when the pollutant load exceeds the depuration capacity of the reception stream (river) or when toxic substances inhibit the mineralizing action of the river. At this point the water is almost unsuitable: floating matters as oils, foams, suspended matters, colouring substances modify the characteristics of the water, its re-aeration capability, with a chain of consequences destroying the normal river life such as fishes and protozoa and in the meantime there could be a concomitant enormous growing of bacteria, toxic substances, and algae.

Polluting matter

There are four different kinds of pollutants in water, namely floating substances, suspended solids, dissolved substances and biological matter.

The floating substances, such as oils, grease, foam, insoluble matter, which more lighter than water. The suspended solids include insoluble matters with density similar to or heavier than water, in suspension thanks to turbulence: they tend to accumulate on the river bottom, giving putrefaction in case of shortage of oxygen.

In case of dissolved substances, such as acid and basic substances, heavy metals, pesticides, cyanides and other toxic substances, the water becomes undrinkable and aquatic life can be damaged, with evidence of colour, bad smell and bad taste. Lastly, biological matters, such as bacteria, algae and fungi can produce bad smells and destroy vegetal and animal life, but in some conditions they can create an auto depuration process.

Pollutants present in textile wastewater include heat, alkalinity, organic and inorganic matter, heavy metals, sludge, giving a high content of organic matter (COD) and colour problem depending on different forms of dyes, surfactants and textile additives materials used in the process. Textile dyes can be of different kinds, such as; acid, basic, disperse and reactive salts (Several authors have identified as a potential problem the presence of salts in textile dyeing wastewater (EPA, 1996). Many salts are either used as raw materials or produced as by-products of neutralization or other reactions in textile wet processes.

Salt concentrations in effluent from cotton dyeing may reach 2,000 to 3,000 pp and quantities of salts added in dyeing operations range from 20 to 80% of the weight of the goods).

The major part of the waste generated by the textile chain is represented by the wastewater deriving from the wet processing stages. Water and chemicals consumption is rather important and as a consequence large volumes of wastewater are generated.

These streams contain a wide range of contaminant which must be removed from the effluent before their disposal. Organic and inorganic compounds used in the textile processes are discharged in the wastewater at average levels of 80% and 90% respectively. Besides the direct environmental impact of the wastewater, the large consumption of water resource is becoming intolerable in countries subject to real or potential water shortage.

The Table 2 shows potential specific pollutants from textile wet processing operations (Adapted from EPA, 1997 and Correia et al., 1994). (4)

• Wastewater from Bleaching may contain NaOH, H2O2, different kinds of an-ionic stabilizers and detergents;

• Mercerizing effluent may contain spent NaOH as well as some intermediate reaction product of wetting agents and detergents;

• Wastewater from Dyeing & Printing may contain residual of reactive dyes and chemicals used as fixer, binder, thickener, etc.;

• Color Kitchen water may contain urea, Na2CO3, ammonium hydroxide and some other chemicals;

• Boiler generates significant amount of wastewater, which is high in TDS, sludge and chemical residuals;

• Wastewater from the textile units with Screen Development Section and Screen Stripping Area contain high values of chromium, COD and Sulphate;

• Wastewater from the Laboratory is high in BOD5 and COD.

Although it is difficult to predict a realistic range which could represent wastewater quantity generated from textile processing unit, ETPI’s environmental audits of textile industries show that 0.08-0.15 m3 of water is consumed per kg of the finished fabric and 1000-3000 m3 of wastewater is generated per day against a product of 12-20 ton/day. The characteristics of the process wastewater generated by an average textile processing unit in Pakistan is given in table 3.

Discharged wastewater by some industries under uncontrolled and unsuitable condi tions are causing significant environmental problems.

The importance of the pollution control and treatment is undoubtedly the key factor in the human future.

If a textile mill discharges the wastewater into the local environment without any treatment it has a serious impact on natural water bodies and land in the surrounding area.

High values of COD and BOD5, presence of particulate matter and sediments, and oil and grease in the effluent causes depletion of dissolved oxygen, which has an adverse effect on the aquatic ecological system.

Effluent from textile mills also contains chromium, which has a cumulative effect, and higher possibilities for entering into the food chain. Due to usage of dyes and chemicals, effluent are dark in colour, which increases the turbidity of water body. This in turn hampers the photosynthesis process, causing alteration in the habitat. In fact, even if colour is widely considered solely an aesthetic pollutant there are studies currently evaluating aquatic toxicity, photo toxicity, and metal bio-availability for specific dye classes.

Wastewater treatment process

We can identify the following types of treatment:

• Suspended/floating matter separation.

• Insolubilisation followed by separation of dissolved matter.

• Removal of dissolved matter.

• Transformation of biodegradable matter.

• Disinfection.

The most common processes to treat the textile waste products are explained by table 4 given on the next page.(6)

Coming to textile wastewater, textile mills emit pollutants such as BOD, COD, TDS & TSS in very high concentrations and these one can vary a lot from case to case.

Wastewater characteristics & treatment processes

Some data from literature(3) is given in table 5, 6 and 7, which explains the amount of waste generated by wool, cotton, rayon, acetate, acrylic and polyester fibre processing.

Many wastewater treatment processes are available and the wastewater treatment plants can be classified in various ways:

They can be divided according to their sequence and treatment degree:

Pre-treatment: coarse and fine screening, sand removal, de-oiling, pre-aeration, equalization and homogenisation, neutralization. Primary treatment: flotation, sedimentation, physical sedimentation. Secondary treatment: active sludge oxidation, roto-percolator oxidation, lagoon, anaerobic digestion, biological sludge sedimentation, disinfection. Tertiary treatment: nitrification /denitrification, phosphorous precipitation, clariflocculation, filtration, active carbon adsorption, ionic exchange, reverse osmosis, electrodialysis, breakpoint water chlorination, sulphide and ammonia stripping.

Primary treatments remove and decrease suspended and floating matter and are generally less efficient on colloidal and dissolved matter (except those chemically precipitated).

The secondary treatments remove and decrease colloidal, organic suspended and dissolved matter.

Tertiary treatments remove and decrease suspended solids, nutritive matter, organic substances, and dissolved solids with a much high efficiency than the one of the secondary treatments.

They can also be divided according to the kind of process used by the mill.

Mechanical treatment: screening, sand removal, de-oiling, pre-aeration, equalization and homogenisation, flotation, sedimentation, filtration.

Biological treatment: active sludge oxidation, rotopercolator oxidation, lagoon, anaerobic digestion, nitrification /denitrification.

Physical chemical treatment: neutralization, coagulation-flocculation, chemical precipitation of metals, and phosphorous, sulphide and ammonia stripping, disinfection, active carbon adsorption, ionic exchange, reverse osmosis, ultrafiltration, electrodialysis.

Physical chemical treatment

Chemical treatment processes have been used to treat the textile wastewater such as: chemical precipitation, adsorption by activated carbon and some natural absorbents, electrochemical method, ozonation, photocatalytic oxidation and Fenton’s reagent (FR) which is a mixture of hydrogen peroxide (H2O2) and ferrous sulphate (FeSO4) decolourising and reducing the COD.

Coagulation flocculation sedimentation: One of the most used method, specially in the past is Coagulation flocculation sedimentation.

Active on suspended matter, colloidal type of very small size, their electrical charge give a repulsion and prevent their aggregation. Adding in water electrolytic products such as aluminum sulphate, ferric sulphate, ferric chloride, giving hydrolysable metallic ions or organic hydrolysable polymers (polyelectrolyte) can eliminate the surface electrical charges of the colloids. This effect is named coagulation. Normally the colloids bring negative charges, so the coagulants are usually inorganic or organic cationic coagulants (with positive charge in water).

The metallic hydroxides and the organic polymers, beside giving the coagulation, can help the particle aggregation into flocks, increasing so the sedimentation. The combined action of coagulation, flocculation and settling is named clariflocculation.

• Coagulation needs strong stirring.

• Flocculation needs slow stirring.

Settling needs stillness and flow velocity, so these three processes need different reactions tanks. This processes use mechanical separation among heterogeneous matters , while the dissolved matter is not well removed (clariflocculation can eliminate a part of it by absorption into the flocks). The dissolved matter can be better removed by biological or by other physical chemical processes.

Laboratory scale tests of coagulation-flocculation showed good efficiency on sulphur and disperse dyes, while the results obtained with acid, direct, reactive and vat dyes were unsatisfactory (Marmagne & Coste, 1996). Cationic polymers of amides, tested on secondary textile effluent, proved to be more efficient than aluminum polychloride in terms of colour removal (Bravin, 1999) and yielded very good results also in the chemical precipitation of reactive dyes (Wenzel et al., 1997).

Possible drawbacks are: additional chemical load on the effluent stream (which normally increases salt concentration), high sludge production, and uncompleted dye removal.

There are other physical chemical processes besides clariflocculation, some of those are neutralization, oxide reduction, precipitation, stripping, absorption on active carbon, iIonic exchange, electro dialysis, reverse osmosis, ultrafiltration, disinfection, etc. Some of them are given as under in detail:

Chemical processes

Oxidative processes represent a widely used chemical method for the treatment of textile effluent, where decolourisation is the main concern. Among the oxidizing agents, the main chemical is hydrogen peroxide (H2O2), variously activated to form hydroxyl radicals (Robinson et al. 2001), which are among the strongest existing oxidizing agents and are able to decolourise a wide range of dyes.

A first method to activate hydroxyl radical formation from H2O2 is the so called Fenton reaction, where hydrogen peroxide is added to an acidic solution (pH=2-3) containing Fe+2 ions.

Fenton reaction is mainly used as a pre-treatment for wastewater resistant to biological treatment or/and toxic to biomass.

The reaction is exothermic and should take place at temperature higher than ambient. In large scale plants, however, the reaction is commonly carried out at ambient temperature using a large excess of iron as well as hydrogen peroxide. In such conditions iron ions do not act as catalyst and the great amount of total COD removed has to be mainly ascribed to the Fe(OH)3 co-precipitation (Final Report EC contract ENV4–CT95–0064, 1999). The main drawbacks of the method are the significant addition of acid and alkali to reach the required pH, the necessity to abate the residual iron concentration, too high for discharge in final effluent, and the related high sludge production.

Ozonation: It is a very effective and fast decolourising treatment, which can easily break the doublebonds present in most of the dyes. Ozonation can also inhibit or destroy the foaming properties of residual surfactants and it can oxidise a significant portion of COD.

Moreover, it can improve the biodegradability of those effluent which contain a high fraction of nonbiodegradable and toxic components through the conversion (by a limited oxidation) of recalcitrant pollutants into more easily biodegradable intermediates. As a further advantage, the treatment does increase neither the volume of wastewater nor the sludge mass.

Full scale applications are growing in number, mainly as final polishing treatment, generally requiring up-stream treatments such as at least filtration to reduce the suspended solids contents and improve the efficiency of decolourisation.

Sodium hypochloride has been widely used in the past as oxidizing agent. In textile effluent it initiates and accelerates azo-bond cleavage. The negative effect is the release of carcinogenic aromatic amines and otherwise toxic molecules (Robinson et al. 2001) and, therefore, it should not be used.

Adsorption: The high affinity of dyes to several adsorbent materials, such as activated carbon and low cost adsorbents (e.g. peat, fly, ash), makes possible the efficient removal of many dyes and the production of high quality effluent. Decolourisation by adsorption is influenced by many physical-chemical factors, such as dye/adsorbent interaction, adsorbent surface area, particle size, temperature, pH, and contact time.

Activated carbon is the most commonly used adsorbent material and it is very effective towards a wide range of dyes. The performance depends on the type of carbon used and on the characteristics of the wastewater. It can be used either as Granular Activated Carbon (GAC) or as Powdered Activated Carbon (PAC).

Membrane treatment: Membrane processes do not destroy pollutants, they only separate them in a more diluted stream (permeate) and a more concentrated one (retentate or concentrate). By membrane filtration it is possible to clarify, to concentrate and, to separate a diluted dye stream continuously from an effluent. It is therefore possible to recover and recycle some dyes.

Membrane technology has emerged as a reliable and feasible option in the treatment of various textile effluent streams. At present it represents the most widely applied treatment for on-site reuse, allowing the recovery not only of water but also of chemicals and energy.

Attractive features of membranes are also: the low weight and footprint of the equipment, the reduced use of chemicals, a constant quality permeate and the high potential for automated operation. Furthermore, modern membranes present a high resistance to exposure to heat, to acid and basic conditions, to the attack of chemicals and of microorganisms.

The main technical problems to be solved are: potential fouling, vulnerability of the membrane “skin” and disposal of the concentrate.

Laboratory and pilot tests have proved that NF and RO membranes can effectively treat effluent from the reactive dyeing of cotton, from the disperse dyeing of polyester and from combined reactive/disperse dyeing of cotton-polyester mix. The permeate produced by NF can be reused for rinsing, while RO allows the production of permeate suitable for all the technological uses. Furthermore the reuse of hot water allows a significant energy saving (Sojka-Ledakowicz et al. 1998). Rinse water treated by NF or RO was found to have great potential for reuse, irrespective of the dyeing recipe (Wenzel et al., 1998). Another combined biological and physical/chemical process which can be used for textile wastewater treatment is the membrane bioreactor (MBR).

Electro dialysis: Membranes with selected permeability towards anions and cations. By disposition of these membranes, with suitable spacers, like plates of a filter press, alternating the cationic membranes, with the anionic ones and applying continuous electric current, the volumes between the membranes enrich and impoverish alternatively of salts.

Ultrafiltration and RO are based on the selective permeability of some membranes that are selective toward water and dissolved matters: at a pressure higher than the osmotic one water passes through membrane and dissolved matter is retained RO: membrane permeable to water, not to dissolved solids.

Ultrafiltration membrane selectivity is due to a mechanism similar to the filtration: the dissolved matter molecules, of bigger size, don’t pas through the membrane .

In the RO, dissolved matter and water have very different transport velocity through the membrane.

Other physical and chemical methods

Ion exchange allows the removal of cationic and anionic dyes. It represents an alternative to adsorption, the main advantage being the on-site regeneration of the ion exchange beds without any loss of adsorbent material. This process is almost ineffective on disperse dyes (Robinson et al. 2001).

Electrokinetic coagulation allows an excellent removal of direct dyes from effluent but it is poorly effective with acid dyes. The large amounts of ferrous sulphate and ferric chloride to be dosed and the subsequent production of large amounts of sludge are the major drawbacks (Robinson et al. 2001).

Pilot tests on solutions of specific dyes and on real textile effluent have shown the effectiveness of electrolysis with sacrificial iron electrodes (Vandevivere et al. 1998). The main advantages of this process are little chemicals consumption and no sludge production.

Finally, laboratory scale tests have proved that foam flotation can be a simple and effective method for pre-treatment of textile effluent to remove colour and COD (Vandevivere et al. 1998).

Biological treatment

The biological process removes dissolved matter in a way similar to the self depuration but in a further and more efficient way then clariflocculation. The removal efficiency depends upon the ratio between organic load and the bio mass present in the oxidation tank, its temperature, and oxygen concentration.

The bio mass concentration can increase, by aeration the suspension effect but it is important not to reach a mixing energy that can destroy the flocks because it can inhibit the following settling.

Normally the bio mass concentrate ranges between 2500÷4500 mg/l, oxygen about 2 mg/l. With aeration time till 24 hours the oxygen demand can be reduced till 99%.

Nitrification: nitrificant bacteria transform nitrogen from ammonia to nitrate (in the oxidation tank).

While denitrification happens under anossic condition transforming nitrate into nitrogen.

By creating and the beginning of the active sludge treatment an anaerobic phase, where wastewater to be treated enters into contact with the recirculated sludge, it happens the growing of microrganisms that allow the phosphorus removal.

General description of an active sludge treatment

The treatment stages for an active sludge treatment are given as under:

Screening

The aim of this phase is the separation of the solid content, to avoid sedimentation and obstruction in the following process steps.

The wastewater, coming from the textile production, flows to a collecting pit where a pumping system lifts the wastewater to screen, usually automatic self-cleaning type, that separates solids and the textile fibre that fray during the different working phases.

The wastewater flows through the screening surface while the separated solids are automatically taken by the brushes into a collecting hopper. The screened wastewater, flowing through the filter surface, arrives at the equalization and homogenisation tank.

Homogenizing and equalization

This phase of the process is simple but very important, as its aim is to make the feeding in the oxidation phase the most constant possible with reference to polluting parameters and flow.

In this phase air is used in order to move the whole wastewater as well as to avoid the development of anaerobic fermentation areas inside the accumulation unit, which may produce bad smell.

It is necessary to supply air, providing in the meantime the movement of the wastewater. Equipment like mixers and air injectors create a whirling movement and a complete mixture of the wastewater.

Feeding in the biological phase is realized by means of a pump system that transfers the water assuring a constant flow of water during the 24 hours to the oxidation unit. This constant feeding permits to work non-stop in the oxidation unit, thus favoring the metabolic process, as the charge rate BOD/SS remains constant. Moreover, the required average permanence time is respected in such a way as to get efficiency sufficient to grant the respect of the output limits.

Feeding of nutrients salts

It consists of a feeding station of nutrients salts of phosphor and nitrogen, indispensable to the life of microorganisms in the oxidation unit. Feeding is realized by an automatic dosing pump equipped with timer, so that the dose of salts is suited according to the real demand of the plant.

Sedimentation

The aim of this phase is to clarify the effluent coming from the oxidation tank and to allow the settled sludge recirculation.

After biological oxidation phase the mixed liquor arrives by gravity to the final circular sedimentation tank provided with scraping bridge. The biological sludge deposits by gravity at the sedimentation tank bottom and it is conveyed by the bottom blade of the scraping bridge into a central well and from here recirculated by pumps to the head of the oxidation tank. The over-flow sludge, that is the part produced daily, is conveyed to a thickener.

The depurated waters that separate in the upper side of the sedimentation tank are collected in a channel and then discharged by gravity.

Sludge recirculation

The sludge that has separated from the water in the sedimentation unit flows back to the head of the oxidation unit by means of pumps and a piping system that sucks the sludge from the bottom of the sedimentation unit.

The sludge recirculation is an essential phase of the complete depuration cycle avoiding impoverishment of the dry content in the biological unit.

In this way it is possible to control the quantity of biological sludge necessary for a good efficiency of the depuration treatment. At the same time, by using the same pumps, it is possible to eliminate the excess sludge.

Thickening and dehydration of excess sludge

During the sedimentation phase the sludge thickens, but this action does not reach a very high value. Therefore, to have faster feeding, it is necessary to deposit the sludge into an accumulation and thickening unit.

It is possible to add polyelectrolyte to this unit in order to increase dehydration and water separation.These procedures allow greater efficiency in the following dehydration phase performed by a filterpress, centrifuge or drying bed. This permits to get more elevated final dry quantities. The water resulting from the operations of thickening and dehydration is sent again to the initial part of the homogenisation tank.

Sludge

Almost all wastewater treatments produce sludge. In the biological process they arise from the transformation of organic matter into biomass, while in the mechanical and physical chemical process it arise from the separation of suspended matter, from the precipitation of dissolved products and from chemicals addition.

As consequence also sludge has to be handled and disposed in treated in a proper way to avoid environmental diseases. The sludge treatments, whose most important aims are volume reduction, residual organic matter stabilisation and solids reduction, can be classified as follows:

• Dehydration treatments: thickening by gravity or by flotation, dynamic thickening, mechanical dehydration, drying bed .

• Stabilisation treatments: anaerobic or aerobic digestion, chemical stabilisation, lagoon, composting.

• Thermal treatments: drying, incineration.

Sampling, laboratory devices and suggested controls

The sampling techniques used in wastewater survey must ensure that representative samples are obtained because the data from the analysis of the samples will ultimately serve as a basis far designing and / or running of treatment facilities.

There are no universal procedures for sampling: It can be hand made or by automatic devices; sampling programs must be individually tailored to fit each situation.

Special procedures are necessary tohandle problems when sampling wastewater that vary considerably in composition. Thus suitable sampling locations must be selected and the frequency and type of sample to be collected must be determined.

Sampling point:

Where the mixing is enough to guarantee the homogeneity of the water composition, and after screening or de-sanding section to avoid coarse matter. In case of water with floating matter, the container must be positioned at last 10 cm under the water surface.

Normally the sample must be stored at 4 °C max one day for BOD and COD.

It must be paid attention to the degradation of the sample during the whole sampling time (for instance a day).

Remember:

• determination of the sampling point.

• determination of the sampling procedure.

• determination of the sampling conservation.

• determination of the sampling volume.

• sample storage.

Sampling locations

Examination of drawings that show sewers and manholes will help to determine sampling locations where flow conditions encourage a homogeneous mixture.

In sewers and in deep, narrow channels, samples should be taken in the centre, where there is the max speed and the minimal sedimentation and from a point one-third the water depth from the bottom. The collection point in wide channels should be rotated across the channel.

The velocity of flow at the sample point should, at all times, be sufficient to prevent deposition of solids.

When collecting samples, care should be taken to avoid creating excessive turbulence that may liberate dissolved gases and yield an un representative sample.

Sampling intervals

The degree of flowrate variation dictates the time interval for sampling, which must be short enough to provide a true representation of the flow (possibly taken proportionally to the flow rate).

Even when flow-rates vary only slightly, the concentration of waste products may vary widely.

 Frequent sampling (10- or l5-minute uniform intervals) allows estimation of the average concentration during the sampling period.

Sampling type

• Instantaneous.

• Average: homogenisation of several instantaneous samples collected at scheduled.

Volume

Final sample minimum to 2 litres.

Suggested laboratory set

• Scales: analytical type.

• pH-meter.

• Conductivity-meter ( temperature to be reported as it can influence the measure).

• Device for COD measure.

• Oxy-meter.

• Microscope.

• Kit for Ammonia, Nitrite, Nitrate and total Phosphorous.

• Imhoff cone for sludge settling control (Volume of the sludge in a cylinder of 1000 ml after ’30).

Suggested controls of a treatment plant

It is very important to know the running condition of a treatment plant to evaluate its efficiency and its operative cost.

As consequence it is essential to evaluate the inlet and outlet effluent in its physical, chemical biochemical and biological characteristics with setting up a series of procedures and controls, such as sampling collection, conservation and analysis in order to elaborate data useful to understand the plant running.

The methods and modus operandi for each of these operations can vary a lot case by case , depending of the required objective.

Generally it is important to analyze the characteristics of effluent samples collected according to scheduled program, in order to control the efficiency of the whole plant and its operational sections. So, in case of a incorrect functioning it can be possible to find the reason and the suitable remedial solution and verify its effect.

It would be valuable to collect data also by means of experimental tests useful to design eventual modification or improvement of the existing equipment / process / chemicals.

It is advised a joint cooperation and coordination among plant operators, laboratory technicians and production managers with the aim to avoid superfluous or too onerous analytical controls.

Daily controls

• pH.

• Dissolved oxygen.

• Flow-rate.

Every one or two weeks

• Chemical consumption.

• Imhoff cone settling control.

• Microscope control of the biological life: flock structure, size and morphology, microorganisms identification and frequency.

• Inlet COD.

• Outlet COD.

• Ammonium, Nitrate, Nitrite and total phosphorous.

• Every two – three months.

• Inlet and outlet BOD5.

These data, controls and operations must be daily recorded and reported in a register to be carefully stored being the history of the plant life.

Bibliography

• A practical manual for implementing green supply chain management practices, Ahmedabad Textile Industry’s Research Association.(1)

• Responding to the Environmental Challenge. Pakistan's Textile Sector.(2)

• Pollution Prevention and Abatement Handbook. WORLD BANK GROUP Effective July 1998.(3)

• Mattioli D., Malpei F., Bortone G., Rozzi A. (2002). Water minimization and reuse in the textile industry. From "Water Recicling and resource recovery in industry". Editors Lens P., Hulshoff Pol L., Wilderer P., Asano T. – IWA Publishing.(4)

• Abwassertechische Vereinigung: Abwässer der Textilindustrie. Arbeitsbericht der ATVArbeits- gruppe 7.2.23, “Textilveredlungsindustrie”. Korr. Abw. 39 (1989), 1074-1084.(5)

• Roberto Passino, Manuale di conduzione degli impianti di depurazione delle acque, Zanichelli.(6)

•  v Biological Treatment of a Synthetic Dye Water and Industrial Textile Wastewater Containing Azo Dye Compounds. Trevor Haig Wallace.

• EPA/625/R-96/004 September 1996. Best Management Practices for Pollution Prevention in the Textile Industry

• W. Wesley Eckenfelder Jr. Industrial Water Pollution Control Mc Graw-Hill Publishing Company.