Journal of Scientific & Industrial Research Vol.59, June 2000, pp 446-454

Impact of Industrial Effluents on Soil Health and Agriculture -Indian Experience:

Part II-Tannery and Textile Industrial Effiuents

· P.K. Chhonkar1*, S.P. Datta 1, H.C. JoshF and H. Pathak2

•

1Division of Soil Science and Agricultural Chemistry, 2Division of Environmental Sciences

Indian Agricultural Research Institute, New Delhi II 0012, India

A huge amount of effluents generated from tanning and textile industries is being discharged on land or into water courses. These effluents are characterized by high BOD, COD, Na and total dissolved solids. These eftluents also contain several major primary and secondary plant nutrients (N, P, K, S, Mg, Ca, etc.) as well as micronutrients and heavy metals. Addition of tannery effluents is reported to cause deflocculation of soil particles and increase in theN, P and K levels of soils. Similarly, deleterious effects, such as increase in pH, sodicity and EC in soils due to the use of textile eftluents are reported. However, it is pointed out that the adverse effects of these effluents get progressively reduced with dilution of eftluents. But database is not adequate to indicate the effect of long-term use of these effluents on soil health. The impact of the use of these effluents on various crops, trees and shrubs as well as water bodies is discussed. Salinisation and alkalisation of ground water due to application of these eftluents are also reported. The physicochemical characteristics of these effluents do not permit its disposal directly into inland water or on land for irrigation, hence, several methods of treating these effluents for safe disposal are discussed.

Introduction Due to rapid industrial development during the last

two decades in India, the disposal of industrial effluents has become a serious problem. The tannery and textile are two important industries in the counry. These two industries consume huge amount of water and consequently generate large volume of waste water which contains various organic and inorganic materials as well as toxic trace elements . These effluents are usually discharged to nearby river courses. The application of these industrial effluents to land has also been started during recent years as an alternative means of treatment and disposal. This supplies not only water but also manurial ingradients and plant nutrients likeN, P, K, S and Ca, etc . If these effluents are treated properly and reusedjudiciuosly in agriculture, it may serve as a source of irrigation and plant nutrients. Therefore, in the present communication (Part II) · , the impact of effluents of tannery and textile factory on soil, plant and water courses are discussed, along with the production potential and characteristics of these effluents in Indian context. Management of these effluents for their safe disposal is also reviewed.

' Author for correspondence · Paper I pertains to Distillery and Paper Mill Effluents, J Sci lnd

Res, 59 (No 5) (2000) pp.350-361

Quantity and Characteristics of Eflluents

Tannery Effluents There are about 3000 tanneries in India1 mostly spread

over Tamil Nadu, West Bengal, Uttar Pradesh, Maharashtra, Karnataka, Punjab and Rajasthan. Annually, about 80 million pieces of hides and 130 million pieces of skins are processed by the tanning industry of the country for manufacturing semifinished and finished leather2

. There are about 680 leather finishing units in our country producing about 1000 million square metre of finished leather per annum3. The quantity of effluents discharged amounts to about 30 to 40 litres per kg of skin/hide processed and in the case of finishing units, the quantity is about 50 litre per kg of raw skin/hide2

• A large number of tanneries (about 433) are located in Tamil Nadu and their contribution is about 70 per cent in the total export of leather and leather products from the country. The distribution of tanneries in Tamil Nadu is reported by Sastry4

. AgarwaF delineated the distribution of tanneries in detail for Uttar Pradesh, Rajasthan, Maharashtra, Gujarat, Karnataka, Andhra Pradesh, West Bengal and Bihar.

Two types of tanning processes are mainly followed in India, viz. vegetable tanning and chrome tanning.

CHHONKAR et al.: IMPACf OF TANNERY & TEXTILE INDUSTRIES EFFLUENTS ON AGRICULTURE 447

Consequently, two types of effluents are discharged during the skin processing, i.e. vegetable tannin which does not contain chromium and chrome tannin which contains appreciable amounts of chrornium5

. The leather processing requires large quantities of chemicals like sodium chloride, chromium sulphate, calcium salts, ammonium salts, sodium sulphide, acids, alkalies, fat liquor and organic dyes6

• The tannery effluents are ranked as the highest pollutants among all the industrial wastes 7 .

The effluents (vegetable tannin) emanating from tanning industry near Dindigul, Tamil Nadu, showed that these were highly complex, slightly acidic (pH 6.0) with a variety of dissolved cations and suspended particles (57 mg L-1)x. Tannin (127 mg L- 1) , Na (5380 mg L- 1), Mg (1543 mg L- 1

), K (638 mg L- 1), BOD (7678 mg L-1

) and COD (9589 mg L-1

) were high, whereas Zn (2.56 mg L-1

), Ca (4 mg L-1), Mn (0.67 mg L-1

) and Pb (0.23 mg L- 1

) concentrations were low while Cu and Fe were not detected. However, Singaram6 had reported much higher concentrations of Na, Ca, Mg, BOD, COD etc. in the effluents emanating from tanneries located on the banks of river Palar in North Arcot, Tamil Nadu. There was a lot of difference in respect to pollution load between effluents generated from vegetable tanning and chrome tanning processes9

• The effluents from chrome tanning generally contain much higher concentrations of total dissolved salts, suspended solids, chlorides, etc . as compared to those from vegetable tanning. However, sulphate was not present in chrome tanned effluents. Similarly, chemical analysis of effluents sample collected from Unnao, Uttar Pradesh revealed alkaline nature (pH 8.67) of effluent having low dissolved oxygen (2 mg L-1

)10

• Effluents also contain 0 .705 mg L-1

chromium having high BOD (980 mg L- 1), COD (2080

mg L-1 ) and total dissolved solids (835 mg L-1

).

Farooque 11 analysed the tannery effluents collected from 'fi ll and draw tank ' inside the tannery industry premises, Lucknow, and reported that these effluents contained considerable quantities of chlorides (2148 mg L-1

), nitrogen (56 mg L-1), phosphate (15 mg L- 1

) and sulphide ( 4.7 mg L-1

) along with excess of water soluble salts, BOD, COD and sodium. However, Gupta and Sujatha 12 reported much higher concentrations of total nitrogen (216 mg L-1

) in effluents collected from small tannery industries of Madras. Similarly, several workersl. 13

•14

•15 have also reported high concentration of

total dissolved salts, BOD, COD, chromium etc. in the tannery effluents.

Textile Industry Effluents In India, major textile mills are located at Ahmedabad,

Bombay, Coimbatore and Chennai. However, medium and small units are distributed throughout the country. In Thar desert of western Rajasthan where the water resources are limited, textile hand processing industries operate in Pali, Jodhpur and Barmer (Balotra) districts. There are about 760 hand processing textile units in Pali city alone which discharge about 18 million litres of effluents per day 16

• In Jodhpur a large volume of effluents i.e. 7 million litres per day is being produced from about 650 textile hand processing units and some metal rolling industries 17

• An idea of the quantity of effluents generated from textile industry can be obtained from the fact that the Buckingham and Carnatic textile mill in Tamil Nadu produces about 20000 m3 waste water per day2

.

In the textile industry chemicals such as sodium carbonate, sodium hydroxide, sodium chloride, sodium peroxide, sodium sulphite, sodium nitrite, sodium silicate, sodium oxychloride, sodium sulphide, sulphuric acid, hydrogen peroxide, bleaching powder, acetic acid, tannic acid, detergents, malt or enzymes, dyes, mordants, starch, gum etc. are used 16

• The effluents emanating from hand processing units of Pali (Rajasthan) were characterized with high salinity (SAR 82), BOD (400-800 mg L-1

) and COD (900-1500 mg L-1); excessive concentration of sodium and carbonate ions (RSC 42 meq L-1

); high alkalinity (pH 10-11.5); and unduly low concentration of calcium 16

• The total chromium and phenolic compounds in the effluents of Pali have been found as 0.18 and 0.24 mg L-1

, respectively. Whereas, the mixed industrial effluents (mainly textile) reported17

to have pH range 9.0-1 0.0, EC 5-10 dS m-1 , RSC 10-40 meq L-1 and SAR 60-150. The lack of calcium ions in appreciable amount, occurrence of magnesium ions in concentration of lesser than 2 meq L-1, and excess of carbonate ions ( as high as 30 meq L-1

) have also been observed in these effluents.

The effluents collected from Modi Textile Factory Ltd., Modinagar, Uttar Pradesh was alkaline and reddish brown in colour, deficient in dissolved oxygen, contained large amounts of solids (dissolved, suspended and volatile) and had high values of BOD and COD 1x.

Besides, these effluents were found to contain considerable amounts ofNH

4 -N (32 mg L-1), phosphorus

( 17.0 mg L-1 ), chlorides (780 mg L-1), sulphates ( 400 mg

L-1), sodium (195.4 mg L- 1

) , calcium (280 mg L-1) and magnesium (140 mg L-1

). Several other workers have also reported similar findings 19

•20

•2 1

·22

•

448 J SCI IND RES VOL 59 JUNE 2000

Table !-Effect of tanliquor and tannin on nutrient status of soils26

Parameters Control pH 7.7 EC (dS m·') 0.1

Available Macronutrients (kg ha-1)

N 180.3 p 12.3 K 79.0

Available Micronutrients (mg kg-1)

Cu 1.0 Fe 9.5 Mn 9.1 Zn 1.5

The composition of waste water varies among individual sections of textile factory. For example, effluents emanating from Buckingham and Carnetic Textile Mill were alkaline, except that from sizing and fancy dyeing section which were acidic in reaction23

• The effluents from sizing section had high BOD and COD, while the effluent from yarn dyeing section had low BOD. The effluents from de-sizing had higher BOD, COD and low suspended solids. Waste water from Khaki dyeing had high total dissolved solids in addition to 860 mg L-1 of chromium. Pollution load was high from sizing, de-sizing and fancy dyeing sections .

Current Mode of Disposal of Effluents

Tannery Effluents Tannery is one of the major industries responsible for

water pollution problems of high magnitude. According to Srinivas et aU, the effluents arising from tanneries of North Arcot district of Tamil Nadu are generally discharged into neighbouring fields and hitherto irrigation tanks in untreated form. These effluents finally reach the Palar river and from there, these infiltrate into the earth. The wells and borewells in the area thus tap the contaminated water. Periyar district (Erode) in this state also has a large number of tanneries which discharge their effluents into an irrigation canal (Kalingarayan) as well as the river Cauvery24

• Similarly, chemical pollution problems arising from the discharge of untreated effluents of about 9000 cubic metre per day from Jajmau tanneries near Kanpur directly into the river Ganga with high chromium content and generation of about 400 tons of solid wastes have become a matter of serious concern25

.

Tanliquor Control Tannin 7.4 7.0 6.6 0.1 0.7 0.7

172.9 207.4 244.5 58.8 16.5 21.4 101.2 269.2 503.8

1.1 5.8 0.1 10.5 2.5 0.1 27.9 24.7 238.5 0.4 103.6 112.4

Textile Industry Effluents In Thar desert of western Rajasthan, where the water

resources are highly limited, textile hand processing industries in Pali, Jodhpur and Barmer districts, discharge directly large quantities of effluents in nearby seasonal rivers, viz. Bundi, Jojri and Luni, respectively, causing serious geo-environmental pollution and anthropogenic hazards 16

• Consequently, Pali has been identified as one of the most polluted cities in India where the environmental pollution has acquired serious dimensions. A similar effect is reported of the textile effluents from Jodhpur city 17

•

Impact of Effluents on Soil Health

Tannery Effluents The addition of tannery effluents is reported to have

undesirable effect on soil properties. The total porosity and hydraulic conductivity of soil decrease as a result of addition of these effluents, while bulk density of soil gets increased6

• This may be attributed to the twin effect of direct accumulation of large quantities of inorganic and organic materials as well as the interaction of Na with exchange complex which causes the deflocculation of soil particles. These adverse effects on soil properties, however, get progressively reduced with dilution of added effluents. The untreated tannery effluents , containing mainly tannins, deplete oxygen level and exert high BOD and COD. Sivaswamy26 has studied the effect of tannery effluents (Chennai) and tannin on nutrient status of soil (Table 1 ). In tanliquor treated soils, nitrogen level was found to decline, whereas status of phosphorus and potassium improved markedly. But, in tannin treatment, macroelements get increased appreciably.

CHHONKAR eta/.: IMPACT OF TANNERY & TEXTILE INDUSTRIES EFFLUENTS ON AGRICULTURE 449

There was a tenfold increase in Mn level in tannin-treated soils. In a similar study, the available P and K status of soil was reported to be increased, whereas application of tannin resulted in increase in available N, P and K level of soils27• Karunyal et af.X have also studied the effect of vegetable tannin on the elemental status of garden soil and reported that the soil treated with tannery effluents was rich in Mg, Mn, Fe, Na and K. However, the information pertaining to the effect of tannery effluents on soil health on long-term basis is not available in literature.

Textile Industry Effluents A study on the effect of textile industry effluents by

Nema et al. 2x on soils collected from the agricultural fields adjoining the textile effluents outlet in Jogari river at Salavas (Jodhpur) revealed high build-up ofNa (289.5 mg/ 100 g), medium in available P (35.8 kg ha·1

) and high in available K (308.2 kg ha·1

). The clogging of fields, which sometimes tum the land barren , has also been noticed. Similarly, Ajmal and Khan 1x have reported that the addition of textile effluents (Modi Textile Factory Ltd., Modinagar) to soil even on short-term basis (pot experiment) results into increase in water soluble salts, organic matter, Na, Ca, Mg, K, NH

4-N, P content of soil

as compared to normal water irrigated soil. Some short term field trials29 have too revealed deleterious effects of textile effluents on soil health.

Impact of Effluents on Crops

Tannery Effluents

Thangapandian et al. 24 have studied the cytological effect of tannery effluents emanating from Periyar district of Tamil Nadu on Allium cepa (a useful plant in screening of mutagen30

) and have reported that the mitotic process was severely affected (48%) by the tannery effluents collected directly from effluent canal. The increase in inhibition corresponded with increase in effluents concentration. Anaphase was much affected (54%) followed by the seggregation stage, the telophase (44%); the least effect was on prophase (13 %); and the induction of mitotic abberation was 8.8 per cent. It is also observed that the directly collected effluents were more toxic than the ones collected from the point of mixing with irrigation canal (Kalingarayan) . Even effluents collected from downstream canal about I km away from the point of mixing, showed moderate toxicity indicating that recovery was not achieved . The mitotoxicity of tannery effluents might be attributed to

the presence of various organic and inorganic substances. Since the downstream sample had mitotoxic effects, effluents may have chronic impacts on the crops and other biota in the agroecosystem.

Among the growth processes, seed germination and early seedling growth have been considered critical for raising a successful agricultural crops. Saxena et a/. 31

have studied the impact of untreated tannery effluents of Agra city on germination and seedling growth of four important pulse crops oflndia, extensively cultivated for domestic consumption and marketing. The maximum retardation of seed germination was observed in pea (33.6%) followed by gram (23.2%), blackgram (15.4%) and greengram (8.2%) and subsequent growth of seedlings was also adversely affected by tannery effluents. It has also been reported that tannins were toxic to groundnut (Arachis hypogaea) which are capable of inhibiting and delaying the germination32

. In the case of paddy, Leucaena and Acacia, the germination of seeds was reported to be completely prevented when 100 per cent tannery effluents were usedx. However, at lower concentrations of tannery effluents (1 0% ), the inhibitory effect of effluents on seed germination followed the order: Leucarna > Acacia > Paddy.

Attempts have also been made to compare the effect of tannery effluents on the growth of pulses and cereal crops . There was gradual increase in per cent germination, root and shoot lengths, chlorophyl content and phytomass of pulse and cereal crops seedlings with corresponding increase of effluents up to 7.5 and 5.0 per cent concentrations, respectively (Table 2). The overall pulse seedling growth was better up to 15 per cent of effluent concentration over control, whereas it was up to 7 per cent for cereals, then the adverse effect was observed with corresponding increase in effluent concentrations. The retardation of germination and overall seedling growth of crops can be attributed to high salinity and other ingredients of effluents like sodium chloride, tannin chromium, etc. Karunyal et afK have reported that N a-content of the leaves of tannery effluents treated plants have shown an increase which was highest in black gram followed by tomato, Vigna and cotton. However, the biomass and chlorophyll contents of these plants increased when treated with 25 per cent effluents in pots over control. Similarly, vegetative and reproductive growth as well as yield of lentil (Lens culinaris Medic .) have been seen promoted as a result of the use of 25 per cent tannery effluents 11•

450 1 SCI IND RES VOL 59 JUNE 2000

Table 2-Effect of tannery effluents on germination, root and shoot lengths (em) of crops 15

Effluent(%) Crops

Vigna radiata Cajanus cajan Sorghum bicolor

A B c A B c A B c Control 99.00 -8.62 10.37 99.02 6.12 4.50 99.15 10.27 9.54 2.5 99.08 8.75 10.68 99.10 6.27 4.69 99.15 10.44 9.81 5.0 99.35 8.83 11.85 99.25 6.51 4.97 99.50 11.66 10.74 7.5 99.50 9.03 11.01 99.6 56.75 5.52 99.25 10.33 9.69 10.0 99.75 9.41 11.7 1 99.90 7.01 6.06 96.25 9.83 8.70 15.0 99.00 8.69 10.46 99.51 6.17 4.59 87.83 8.62 7.78 25.0 99.33 8.19 9.35 84.33 5.84 3.81 83.67 7.44 6.17 50.0 72.17 6.08 7.29 62.41 4.53 3.33 55.00 5.77 4.08 75.0 46.00 4.61 4.92 38.17 3.09 2.38 34.33 3.76 2.03

A, B and C denote per cent germination, root length and shoot length, respectively

Beside the field crops, the effect of tannery waste water on trees and shrubs has also been evaluated33

•

Babul (Acacia nilotica), arjun (Termilania arjuna), pipal (Ficus religiosa), kunji (Pongamia pinnata) and awaram (Cassia auriculata) performed better as far as tolerance and growth of these species of trees and shrubs are concerned, as compared to lisora (Cordia dichotoma) , kathsagon (Haplophragina adenophyllum), neem (Azadirachta indica), jamun (Syzygium cumini), bargad (Ficus bengalensis), arusa (Adhatoda vasica) and chir (Pinus roxburghii), when irrigated with tannery waste waters. It is interesting to note that the barks of babul, arjun and awaram are important vegetable tannin materials for the leather industry.

Textile Industry Effluents The germination of kidney bean and lady's finger

seeds has been found to be affected adversely when 75 and 100 per cent concentrations of effluent (Modi Textile Factory Ltd ., Modinagar, Uttar Pradesh) were used as compared to control, while there was no effect up to the concentrations of 50 per cent1x. As far as biomass of both the crops is concerned, the use of effluents up to 50 per cent concentrations was found beneficial. A gradual increase in the sodium content of both the crops was observed with increase in the effluent concentrations. The maximum increase in concentrations of potassium, calcium and magnesium was recorded in both the crops grown on 50 per cent effluent irrigated soils, followed by 25, 75 and 100 per cent effluents 1x. It is interesting to note that unlike other crops, diluted textile effluents (50%) increased seed germination percentage of

groundnut as compared to pure water 1• Other growth

parameters and total biomass have also been found to be stimulated as a result of application of diluted textile effluents up to 50 per cent concentration. The biochemical parameters (starch, total sugar, reducing sugar, etc.) and chlorophy ll content of groundnut seedlings were too influenced favourably when effluents from a dying factory were used in concentrations up to 50 per cent. On the other hand, germination of Cicer arietinum (Bengal gram) seed was reported to be adversely affected even when as low as 5 per cent textile effluent was applied34

. A similar inhibitory effect of diluted effluents (as low as 5%) has been observed on growth and development of nodules of Bengal gram.

Impact of Effluents on Water Bodies

Tannery Effluents Serious deterioration in the quality of groundwater

occurs as a result of the effluents discharged from the tanneries in North Arcot district. Chemical analysis data of water samples from wells located in the tannery affected zones has revealed that pH and electrical conductivity ranged from 2.4 to 8.8 and 1.5 to 10.0 mm hos cm-1

, respectively whereas, carbonate, bicarbonate, sulphate, chloride, sodium and SAR varied from 30 to 150, 122 to 1159, 8.64 to 103.7, 318.6 to 3115 .2, 207 .0 to 1430.6 and 1.52 to 16.87 mg L-1

,

respectively9. The electrical conductivity of analysed

samples are above 3 mmhos cm·1, in most of the places

falling in the severe problem range. Consequently, the agricultural production in the Palar bas in was reported to reduce to one-fourth within a span of 12 to 15 years,

CHHONKAR et al. : IMPACT OF TANNERY & TEXTILE INDUSTRIES EFFLUENTS ON AGRICULTURE 451

Table 3-Effect of textile effluents on quality of water of the riverine wells, located on the bank of the effluent carrying river Bundi 1 ~

Parameter Raw effluents Polluted well Unpolluted wells ( near river) (away from river)

EC (dSm1) 8.5- 13 .9 5.2- 12.5 2.4- 7.4

Sodium 73.0- 124.0 38.0- 112.0 12.0-47.0

Ca+Mg 0.5- 2.0 0.3 - 1.2 4.8-17.0

Carbonate 4.0- 16.0 2.0-6.0 0.0

Bicarbonate 14.0- 40.0 28.0- 38.0 4.0- 16.5

Sulphate 9.0- 15.0 9.8- 15.4 2.6- 16.5

Chloride 75-112 40-90 20-60

SAR 60-100 39.7- 200 4 2-23 .9

RSC 30-43 8.0- 47.7 0.0

All parameters are expressed in (meq L·1) except EC.

with as large as 40,000 acres of fertile land becoming unproductive due to sodium hazard9

•

Textile Industry Effluents The extent of salinisation and alkalisation of

groundwater due to textile hand processing industries of Pali, Rajasthan have been studied by Gupta and Jain 16

•

To evaluate the effect of effluents on groundwater quality, the water samples from theriverine wells i.e. located on the bank of the effluent carrying river Bundi, at Punaita, Jevolia, Kerala and Godhwada villages running up to 30 km down stream from the source of origin, have been analysed (Table 3). A substantial increase in the sodium, carbonate and bicarbonate contents as well as SAR and RSC values has been found in water of polluted wells as compared to that of unpolluted wells. Prior to the advent of industrialization, the analysis of 84 groundwater samples collected from all over Pali block indicated the values of EC, SAR and RSC as 0.9 to 26 .0 dSm·1 (mean 10), 2.2 to 49.6 (mean 21.6) and 3.0 to 26.6 meq L·1 (mean 2.1), respectively. But 20 per cent of water samples mostly representing the riverine wells, had EC lesser than 5 dS m 1 and SAR Jess than 18. Studies conducted by the Groundwater Department have revealed that average values of EC, SAR and RSC of polluted wells were 13.5 dSm 1, 29.7 and 2.2 meq L· 1 compared to corresponding values of 15.5 dS m 1

, 14.3 and 1.9 meq L·1 in the case of non-polluted wells35

•

Quality Standard for Disposal of Tannery and Textile Industry Effluents

Although pH of effluents of different tanning processes varies considerably being highest at liming and lowest at chrome tanning process, the pH of composite tannery effluents mostly falls within the tolerance limits for tannery effluents to be discharged into inland surface water or on land for irrigation (Table 4). The suspended solids and BOD of tannery effluents often exceed the tolerance limits. The effluents contain fairly good amount of Ca and Mg because lime is used for loosening the hair which counteracts the hazardous effect ofNa to some extent, however, higher concentration of Na severely affects the crop growth right from the germination stage. The effluents particularly emanating from chrome tanning process contain much higher concentration of Cr in comparison with tolerance limit (2 mg L·1) which is likely to affect the metabolic processes of plants. Generally, CI· in low concentrations is not harmful but fruit trees are reported to be adversely affected due to thechloride toxicity. Sulphur being an essential element is helpful in low concentration for normal growth and development of plants, however, excess quantity of S, as present in tannery effluents may induce the deficiency of cationic micronutrients, viz. Zn, Cu, Fe and Mn. Thus, ·if the effluent is treated or diluted properly and excess Cr and Na salts are removed, it can be used for irrigation to raise crops successfully.

452 J SCI IND RES VOL 59 JUNE 2000

Table 4-Tolerance limits for disposal of tannery eftluents1"

Parameters Eftluents to be discharged

Into inland surface water On land for irrigation

pH 6.0-9.0 6.0-9.0

BOD 30 100

Suspended solids 100 200

Chloride (as Cl) 1000 200

Chromium (as Cr) 2.0 2.0

Sulphides (asS) 2.0

Sodium(%) 60

Oil and grease 10 10

All parameters except pl-1 are expressed in mg L·1 or otherwise stated

To qualify for safe disposaP6, the effluents emanating

from cotton textile industry should have pH as 5.5-9.0, suspended solids as 100 mg L·' , BOD as 150 mg L 1

, oil and grease as 10 mg L" 1

, chromium 2 mg L·1, sulphide

(asS) 2 mg L·' and phenolic compounds (as C4HpH)

5 mg L·'. By and large, all these parameters of untreated textile effluents exceed the tolerance limits for disposal into inland surface water or on land for irrigation. However, in most cases, the textile effluents contain total Cr and phenolic compounds within the tolerance limits. High values of SAR and RSC and unduly low concentration of Ca disqualify these effluents for discharge into inland surface water or on land for irrigation. But CPCB36 has not set any limit for SAR and RSC for textile effluents to be discharged into inland surface water, although these are the most important factors which determine the suitability of itTigation water.

Treatment of Tannery and Textile Industry Effluents Since the physicochemical characteristics of tannery

and textile effluents do not permit its direct disposal either into inland surface water or land for irrigation, these effluents require some treatment. The growth requirement of water hyacinth associated with fast growth rate makes it suitable for removal of various pollutants from waste water 12

·37Jx _ It has been reported

that water hyacinth is effective in reducing the BOD, COD and total chromium contents in tannery effluents to the extent of 43.8 , 65.2 and 55.4 per cent, respectively after a period of 14 days 12

• A 74.6 per cent reduction in total nitrogen and and 66.6 per cent in phosphate content

of tannery effluents treated with water hyacinth has been observed. In a similar study39 70 per cent COD removal was observed within 8 days of detention with initial COD value of 760 mg L·'. These studies clearly established the effectiveness of the water hyacinth in treating effluents in stabilizing lagoons. In some cases, more than one lagoon may be required with arrangement of frequent replacement of the wilted hyacinth by fresh batches.

Similarly, some aquatic macrophytes like Hydrilla verticillata, Bacopa monnieri and Nymphaea alba have been found to be effective in reducing the chromium concentration in the tannery effluent under monoculture system by more than 50 per cent10

• The mixed cultures of S. polyrrhiza and H. verticillata could remove 40.2, 43.0 and 45.0 per cent Cr from 75, 50, 25 per cent diluted tannery effluents, respectively after 14 days 10

• But in absolute terms, the maximum amount of Cr was removed from undiluted effluents . The outcome of these studies is quite convincing for bioremediation of Cr rich tannery effluents by species mixed cultures of many aquatic macrophytes combinations. However, safe disposal of Cr-contaminated plants will have to be worked out for a practical solution to the Cr-pollution.

A huge quantity of chromium sulphate is lost through the waste water of chrome tanning industries which can be purposefully removed and -reused for tannin g. According to Duqhota et al. 40

, removal of chromium from tannery effluents in the form of hydroxide using an alkali appears to be an economical method. AgarwaF opined that the supernatant liquid (65 %) could be drained above

CHHONKAR et al.: IMPACT OF TANNERY & TEXTILE INDUSTRIES EFFLUENTS ON AGRICULTURE 453

the sludge after a period of 12 h. The residual chromium 92 mg L-1 was less than 2% of original concentration as Cr3+. This can be safely disposed off in nearby water course after mixing with various other wastes from tanning industries. The sludge can be removed and treated with concentrated sulphuric acid and filtered . About 200 mL of concentrated sulphuric acid is used for each litre of concentrated sludge to obtain the maximum recovery of chrome liquor solution at the minimum cost. Kaul et af.3 evaluated the performance of full scale waste water treatment facility for fini shed leather industry and reported that it has been possible to achieve an effluent BOD level of about 135 mg L-1 with an influent BOD of about 1260 mg L-1

• Phenols and chromium have been brought to manageable level of about 0.3 and 0.2 mg L-1

•

Laboratory studies on chemical treatment of synthetic textile mill waste water by precipitating some of the constituents using alum and ferrous sulphate indicate that the reduCtion in COD could be achieved in_ the range of 34-64 per cent in the case of alum and I 0-64 per cent in the case of ferrous sulphate22

. Their studies on biological treatment of waste water by activated sludge and aerated lagoon has shown that removal of 85 and 80-90 per cent of BOD were achieved in the case of activated sludge and aerated lagoon system, respectively.

One model treatment plant has been installed at Pali, Rajasthan which treats only 1 Mgd (45lac litres per day) of textile effluents. The plant consists of five processes, viz. filteration , equalisation, acid treatment, sedimentation and aeration . Sulphuric ac id (4-5 tonnes per day) is being mixed after filtering the raw effluent and making it homogenous. After treatment, pH of the effluent is reported 16 to be reduced from 11 .5 to 8.5, TDS from 7000 to 6700 mg L-1

, TSS from 500 mg L-1 to nil, and COD from 1500 to 180 mg L-1

• Though acid treatment, and other processes are quite efficient in reducing pH, TSS and COD, etc. SAR and RSC values still remain very high as SAR i$ reduced from 82 to 55 and RSC is reduced from 42 to 21 meq L- 1

• Therefore, if such a effluent treatment plant has provision for additional treatment with gypsum to take care of alkalinity (RSC) and sodicity (SAR) hazards1

6.4 1.42, it could prove more efficient.

Conclusion The studies reveal that tannery and textile effluents

contain much higher concentrations of BOD, COD, total dissolved solids, Na, Cr etc. which adversely affect soil,

water courses as well as plant growth. These effluents also contain appreciable amount of plant nutrients, viz. N, P, K, Ca, Mg, S, etc. These studies have highlighted the possible usage of these effluents as a plant growth adjuvent either after proper treatment or at a diluted concentration when availability of water required for dilution is not limiting. It is also pertinent to mention

· that the usage of these effluents is suggested more for growth promotion of plants than for the disposal of the effluents, although some effluents would be disposed off by the irrigation .

Acknowledgement The authors thank Prof. R.B . Singh, formerly Director,

IARI, New Delhi, and presently, Assistant Director General, FAO, Bangkok, for his suggestion to take up this project and advice during the preparation of the manuscript.

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