POLLUTION CONTROL IN SMALL AND MEDIUM SCALE INDUSTRIES P.S. PANESAR

As per the new policy document the industrial development in future in all sectors has to be planned in such a way that it is environmentally sustainable. The existing industry has to comply with the requirement of the pollution control regulation with in a time bound programme.

Industries have been classified into red orange or green depending upon the pollution created by them. Unfortunately, some of the small scale industries have fallen into red and orange catagories where control of pollutants to the desired level is a must. Small scale-industry have peculiar problems of their own. Individually they hardly have sufficient finances to provide for MINAS. The actual value of the pollutant may be high on ppm basis but the total load is at times hardly enough to warrant for a serious consideration. • The ecology minded citizen today is very prompt in sending a letter to member secretary about the inconvinience caused to him. He has every right to do so. But unfortunately no pollution/~board has man power to deal with allc

such industries. Therefore, some sort of planning strategy has to be adopted right at the planning state itself so that the pollutants are kept well with in limits.

POLLUTANTS EMITTED:

Despite the diversified processes that are employed for the manufacture of chemicals and allied products, the pollutants fall broadly in a narrow range of selected chemicals species. These are sulfur dioxide, carbon monoxides, hydrogen sulfide, oxides of nitrogen, halides, mercaptant and particulate matter. However, the emission of these pollutants varies considerably with the process technology and the control equipments used by the industry. Most of the state pollution control boards have laid down the limits of pollutants in water and air. These values can be obtained on request from the respective pollution control boards. These limits have to be complied by all sectors of industries. Unfortunately the punishment for violation by marginal amount or by heavy amount is

(Contd... 2/-)

2

the same (closure of industry/non bailable warrents of management). The small and medium scale industry contribute substantially to the national development and hence they have to be quided to incorporate pollution control measures within their available means. The small scale enterpreneurs have to be exposed to the various parameters required for pollution control.

METEOROLOGICAL DATA:

How the local wind velocity varies with time each season decides the dispersion of pollutants in the air. Knowledge of meteorological data is therefore essential before planning an industry at a given site. According 'to the meteorological analysis of the weather data for 1965-69 it is found the pollutability on the eastern coast and southern part of India is one of the lowest. It is only during the winter months when 'inversion' takes place,the acute problem due to stagnation occurs. It is reported by researchers in the India Meteorological Department at Poona, that the frequency of ground inversion over India, south of latitude 18° N is very low as compared to nothern stations. The most frequent thickness of ground inversion is the range of 201-500 metres. The result of acute inversion with high lapse rates, is the formation of stable layers. The purpose of presenting the above data is to provide a scientific basis to assess the effect of meteorological factors in retaining pollutants at ground level in the different parts of India. With the help of other meteorological factors one can arrive at the pollutability of various areas and assign the type of industries that can be located in such areas. As a general rule, the gases leaving the plant stack should be with such velocity that stack height plus plume rise exceeds 200 to 500 metres based on local conditions.

It is important to note here the above observations are of general nature only and for each sit6 there must be a study of micrometeorological conditions in order to determine the effect of emissions from the proposed plants to be located in that area.

So far there are no data available on national basis for the levels of the pollutants at the probable sites for industrial units. However, sufficient meteorological data are available for most of the industrial cities in India to enable a prima facie, analysis of suitability from the environmental view point Pollutability zones of the country based on inversion and stable layer data are given in Fig 1. It is desired that the appropriate

(Contd.... 10/-)

authorities should find out level of various pollutants in each zone and each board in these areas should specify their own limits. STATUTORY STEPS TAKEN BY THE'INDUSTRY, QUASI GOVERNMENT AND CENTRAL GOVERNMNTS It is heartening to note that the industry in India is progressive in adopting the latest technologies that are available to combat pollution hazards. The Indian Chemical Manufacturers Association has created a special cell for this aspect of industrial growth in the country and has recently taken steps to enlighten and educate its memebers in order to take preventive steps.

The B.I.S. has "undertaken the colossal task of setting the emission limits for chemical, metallurgical and allied industries for over last few years. Standards have been finalized and formulated by B.T.S.shall form the basis for the air pollution and water pollution limits which will be applicable in each state. At government level, central as well as state, it is encouraging to note that awareness of controlling air pollution exists at all levels. It is also important to mention here that a pragmatic approach by the authorities concerned has been noticed in the various industrial projects that have been coming up in the recent past. Nevertheless, in order to avoid any unreasenable stand taken up by the State or central authorities on this account, attempt has been made by the industry to furnish maximum available information on this subject.

LOCATION SELECTION OF INDUSTRY -INDICATING A PROJECTION ON POLLUTION LEVEL, METEOROLOGICAL FACTORS, REGIONAL NEEDS: Small scale industry is bound to experience rapid growth in near future if the government policy continues to encourage. With the factors in favour of continued rapid growth the planners must take into cognisance the air and water pollution aspect with the industrialisation. The zones marked in Fig. 1 clearly indicate that nothern India especially near Delhi-Mathura has stable layers persising beyond 24 hours for major part of the year. Stringent emission control measures for chemical units in this zone are required.

The zone covering part of Gujarat, M.P. and U.P. is next area prone to persisting stable layers, especially during winter. The industries in this zone must be equipped with techniques of air pollution control.

(Contd... 4/-)

4

Then comes the zone where pollutability is moderate and diurnal changes of air can disperse the pollutants. Part of this zone is highly industrialized due to other economic factors and hence existing levels of pollutants must be taken into consideration before selecting the site..

The zone south of the latitude 18° N is having lesser frequency of stable layers.

The regional needs arise out of a site which infrastructure-wise is best suited but is either a highly fertile area or near populated city or topographically poor site from pollution point of view.

Similarly one will have to study the pollutability of the waste water receiving system. Unfortunately no models are available to predict the level of pollution acceptable by the Indian rivers. All hopes are pinned on the success of Ganga Action type plans. A MR POLLUTION CONTROL The waste gases are usually emitted continuously from a process, but there are situations .which require disposal of waste gases which are produced intermittently. It is normally not practical to store these gases prior to treatment. Waste gas storage would often require compression and compression to high pressure is often expensive and undesirable. Therefore, the equipment must be able to handle the maximum volume of flow at the discharge of the system on a continuous basis. What particular technique is adopted ;in a situation largely depends upon the quantity and quality of emission with respect to the requirement of local laws and ambient air quality. The type and properties of material being handled and the unit operation and processes involved in the process become guiding factor for selection of available tools for pollution abatement. (a) TYPE QF EMISSION: It is very important to study the type of emission before we take a decision on the type of.control equipment to be selected. The type of emission could be classified as:

(i) Uncontrolled emissions : These are the emission due to faulty operation and maintenance like the leaks from valves and flanges and glands etc. of

(ii) From essential part of the process. It is essential to have complete inventories of polluting components and 100% material balance of uncontrolled emissions accounted for.

fContd 5/-)

5

(b) MEASURES TO BE ADOPTED: We can broadly classify the pollution control methods into the two types. These are : (i) Process modification - Source control or specific

measures. (ii) Provision of additional equipment for removal of a

particular pollutant'. . (C) PROCESS MODIFICATION: Technologists and scientists have been working on the developments of new processejand innovations for manufacture. The approach has lead to emergence of new techniques and processes <or (i) Removal of particulate matter. (ii) Removal of gaseous product. These can each be further divided into control by physical or chemical removal and dillution by addition of air or dispersion. Various equipments for particulate matter removal are gravity settler, centrifugal separation, impingement separator, electrostatic precipitator, filters, wet seperators like cyclone scrubbers packed bed, mobile bed, moving bed or venturi scrubbers etc. The wet scrubbers are also mostly used for simultaneous removal of gaseous and particulate matter. Chemical unit operation like adsorption, absorption and solvent extraction etc. are also being increasingly used. Catalytic or simple incineration is resorted to, when the recovery of combustibles is not economically viable. Odour control is also effectively provided in some of the advanced countries. An efficient design of stack is an essential component of design in which the pollution levels are controlled by efficient dispersion. A general sequence of selection of the available equipment can be followed as under : The waste gas may be pure or contain solids and liquids. If it contains solids, especially those which are noncombustible, separation methods for the removal of solids should be considered. These methods include mechanical separation, electrostatic precipitation or wet scrubbing with water or other liquids.

(Contd.... 10/-)

6

It is possible that the waste gas may contain liquids which can be removed by condensation or by activated carbon solvent extratcion methods. In such cases there are two effluents from the process, one a waste gas and the other a waste solvent or liquid. The solvent or liquid can then be processed seperately . The waste gas can proceed to next treatment step or if it meets air pollution regulation, can be dispersed directly to the atmosphere.

The waste gas may be combustible in nature, for this direct incineration is perhaps the most expedient method. If the calorific value is not high enough, a - waste gas flare may be necessary. After incineration, it is possible that solids will be present in the waste gas, 'which may require mechanical separation or scrubbing to remove the particulate matter. A waste gas which is combustible and contains solids is usually dangerous to process through mechanical separation devices prior to incineration.

The ultimate requirement is to discharge into the atmosphere an effluent free of particulate matter, odourless, colourless and without toxic elements.Occasionally the odour problem in a waste gas which is nontoxic, noncombustible and does not contain any particulate matter can be handled through the unique methods of odour counteraction developed by several companies in the last few years.(This is however, not practiced in India). Often it is not possible to remove completly the toxic elements from a waste gas, but proper dispersion through a stack into the atmosphere can maintain ground level toxicity well below established minimum. This is not the most desirable- method of treating waste gas but may be economically expedient and entirely acceptable to local code's and ordinances. It" should be noted, however, that such local codes and ordinances have the tendency to become more stingent, so that better handling methods soon must be devised. Fig. 2, gives a very comprehensive flow sheet for treatment of waste gases. We may have to choose appropriate combinations in series and parallel to treat the effluent gases to the requirement of codes and laws.

It is going to be very difficult choice for small and medium scale industry. Electrostatic precipitators and vehturi scrubbers are rather difficult choice. But equipments like gravity separators, multiclone, mobile bed contractors may prove to be very handy equipments to reduce the load of particulate matter by 50 to 75% at only nominal additional cost. A re-thinking has to be seriously done on provision of a suitably designed chimney for appropriate dispersion to meet the requirement of ground level concentration.

(Contd.... 10/-)

: 7 : B WASTE LIQUID

The problem of liquid waste treatment is more complex than gas effluent treatment. The waste may contain dissolved gases mixed liquid and suspended solids. The first step is settling, filtration and centrifugation of solids from the system. These materials can further be treated by either concentration to separate dissolved solids, distillation to separate various liquid constituents or solvent extraction to remove important and expensive solvents from the system. These methods are only useful when waste is in concentrated form. Dilute waste should be treated first to bring it to concentrated form.

(a) PRETREATMENT METHODS

Centrifugation and Filtration : Solids suspended in the waste should be first removed in large settling ponds, thickners or through various floatation methods for dilute waste. It is usually more practical to use some common filteration or, centrifugation device often the solid concentration is relatively high and the particle size is suitable for commercially available equipments. The theory of batch and continuous operations is too well known.

(b) EVAPORATION AND CONCENTRATION j_ Concentration of any waste liquid effluent, especially an aqueous effluent is often desirable step in treatment of any waste liquid. Concentration may take the form of settling pond or thickners or tube settlers in which gravity seperation is used to seperate the heavy and light material in the waste for seperate treatment. It may take the form of a decanter, when two or more materials which are immiscible will separate into various layers to be drawn off as concentrated components of the total waste. It may take the from of an evaporator, which will take heat to evaporate the more volatile constituent of the waste having the less volatile in the evaporator for separate treatment or it may take the form of an evaporator crystallizer combined, by which dissolved solids may be removed from liquid by concentration above its solubility point.

In the case of the gravity separation system, all wastes are liquid and either must be reclaimed as pure liquid or pass on to a further treatment step, incineration or direct disposal. In the case of evaporator there may be three products from the system a gas or vapour, a concentrated liquid and possibily a concentrated sludge. The vapour phase may be condensed and once

(Contd 8/-)

inoincidiea, reclaimed or disposed off and the solids may be removed from mother liquor by crystallization and subsequent filtration and centrifugation. All these equipment are also too well known.

(C) DISTILLATION: Distillation like wise is standard chemical engineering unit operation. This is normally used when liquid waste is made up of variety of components of different boiling point, it may be fractionally distilled for separation into various components for ultimate recovery. In most distillation operation, however, there is a final residue not suitable for reclamation, which will require ultimate disposal in some other manner. If the material is combustible, incineration is usually best choice. However, if it is non-combustible then deep well disposal or other dis-persion methods may be used. Distillation is seldom used as a waste disposal tool since it would be more commonly an integral part of processing system for by product recovery if recovery were suitable and possible.

(d) LIQUID - LIQUID EXTRATION: It is used infrequently in waste liquid treatment problems, however it should be mentioned as a possibility for future use. (e) TREATMENT OF DILUTE WASTE WATER: After all effort at recovery and reuse of process waste have been made at the production unit, the remaining dilute waste water is routed through the plant sewage system to control treatment facility. The dilute process waste should be kept segregated from return cooling water to minimize the required size of treatment system. Sanitary sewage can be treated most economically alongwith process waste but some time state regulation require separate treatment facilities. No. attempt therefore, be made for a combined treatment system.

The design of the treatment of system depends on the waste composition, the permissible discharge levels, and the amenabilities of the pollutants of treatment by the multitude of available methods. Common treatement process for dilute waste water include equalization, nutralization, clarification, biological oxidation and recovery of specific components. Proper segregation of various type of liquid waste is specially important. There has bee^i a tendency in the process industry to dump all the liquid waste into a giant container which may take the form of a tankage, a lagoon or settling pond. Such a "brute

(Contd 9/-)

9

force" approach does not always aid the solution of the problem and often complicates it to the point of making a clear solution impossible. While storage vessel for liquid waste provide very little economic incentive to management, a well designed waste tank farm may be most economical first step in the waste treatment system for processing plant. From such a waste storage segregation facility it is possible to isolate individual problmes so that a one step solution is possible. Combination of a large variety of waste into a large settling pond or lagoon may make one step solution impossible. Segregarion of liquid wastes is classified roughly into two areas. The first is predominently aqueous phase with small quantities of organic and inorganic material whose recovery for economic reasons appear to be unfeasible. The antithesis is a highly concentrated organic and inorganic waste which may offer a feasible recovery of some of the components or where solution may be sort 4HNUTI of direct disposal such as incineration. Fig. 3 suggests the solid separation as the first step. While such solid seperation may be effected through filtration or centrifugation where the solid content is high, the liquid waste may have to pass to a concentration step or ultimately settling pond or lagoon for removal of such material the combination of concentration and filteration might remove inorganic salts from waste by evaporating the water to the atmosphere and completely eliminating liquid disposals problem. A combination of organic material with or without water might be fractionally distilled to remove certain desirable components, leaving residue which could be incinerated or handled by another approach. Liquid-Liguid extraction might be used to remove valuable components from a process stream.

Dilute waste water as pointed out earlier may be treated in variety of ways to produce a desirable final effluent. This would include digestion, neutralization, ion-exchange or incineration, depending upon quantity and nature of the contaminents. Ultimately, incineration of combustible and partially combustible residue or on land or river disposal of concentrated wastes which are difficult to handle may be the answer. As in the case of gaseous waste it is possible to dipose the effluent to large volume of water in river, lakes and oceans or waste land areas where such waste will provide safe and efficient dispersion of any toxic elements reaching in the water shed. For this water shed has to be carefully modeled and monitored.

(Contd.... 10/-)

10

C SOLID WASTE DISPOSAL: The last perhaps the most difficult area of waste disposal in a processing plant is that of solid materials. Here again we have the tendency to look at the disposal of most of solids wastes in one of the time tested ways without much thought of segregation of the waste. The so called sanitary land fill method has been used and abused in the country for many years. Many of the materials collected for land fill are completely unsuitable for land fill and in many cases can not be considered-"sanitary.

The first step in solid waste diposal should be segregation of the material into catagories of combustible and non combustible wastes and those that are suitable for land fill and those that are not. If incineration is used, the material which go into the incineration will produce a gaseous effluent which, depending upon its make up,"may be discharged directly to the atmosphere or may require further treatment. A well designed incineration may do an excellent job on boxes, papers and similar wastes. It may, however, produce an unsatisfactory effluent when handling plastic materials such as polythene. It may also deliver gaseous effluent which is a difinite health hazard when handling materials such as polyvinyl chloride or polyurethane. This does not mean that incineration can not be used for such materials, but only that further gas'processing must be incorporated into the system so that the effluent is safe and acceptable. Fig. 4 gives a systematic flowsheets.

Therefore it can be seen that there are three distinct problems, they are quite interrelated in the processing plant and the total system concept must be used in solving them. REFERENCES: 1. N.G. Ashar, Air Pollution and its Control in Indian Chemical

Industry, Paper presented at Chemical Technology. Seminar at Bombay (Jan. 1978)

2. R.D. Ross., Industrial Waste Disposal, Van Nostrand Reinhold Company, 1968.

t\

AMRITSAR

BOMBAY VISHAKKAPATM^M INDEX

COCHIN

TRlVANORUM

[ 1 AREA OF STABLE LAYER PERSISTING BEYOND 24 HRS EXCEPT FOR MONSOON MONTH

VZpi AREA FOR STABLE LAYER PERSISTING BEYOND 24 HRS DURING ALMOST HALF YEAR AREA OF STABLE LAYER PERSISTING BEYOND 24 HRS, PRIMARILY DURING WINTER AREA OF CONTINUOUS AIR CHANGE AT LEAST ONCE A DAY

AREA WHERE FREQUENCY OF STABLE LAYER IS VERY LOW AREA OF MODERATE STABILITY1

ADEQUATE DATA NOT AVA1ABLE AND RAIN IS UNEVEN.

FIG. 1 POLU1TABILITY ZONES BASED ON INVERSION AND STABLE LAYER DATA

FIG. 2. GASEOUS WASTE DISPOSAL - PROCESS FLOW SHEET

, LIQUID WASTE DISPOSAL PROCESS FLOW SHFFT

FIG. 4. SOLID WASTE MANAGEMENT FLOW SHEET