Industrial Wastewater Treatment (10CV835) Presentation Slides - Unit VI (Treatment of Selected Industrial Wastewaters)

Unit VI : Treatment Treatment of Selected Selected Industrial Industrial Waste

Cotton Textile Mill Waste  •

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Introduction: The The fibe fiberrs used used in the the text xtiile ind indust ustry mayb maybe e broadl oadly y clas classi siffied ied into dif differen erentt group oups suc such as cott otton, on, wool ool, synth ynthet etic ic,, etc. etc. The characteristics of the waste from the mill depends on the type of fiber used, as different type of fibers go through different sequences of operations before the woven cloth is sent out of the mill. The pollutants in the wastewater includes the natural impur mpurit itie iess in the the fibe fiberrs used used and and the the proc proces esssing ing chem chemic ical als. s.

Cotton Textile Mill Waste  •

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Introduction: The The fibe fiberrs used used in the the text xtiile ind indust ustry mayb maybe e broadl oadly y clas classi siffied ied into dif differen erentt group oups suc such as cott otton, on, wool ool, synth ynthet etic ic,, etc. etc. The characteristics of the waste from the mill depends on the type of fiber used, as different type of fibers go through different sequences of operations before the woven cloth is sent out of the mill. The pollutants in the wastewater includes the natural impur mpurit itie iess in the the fibe fiberrs used used and and the the proc proces esssing ing chem chemic ical als. s.

Cotton Textile Mill Waste  •

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Manufacturing Process: An integrated cotton cotton textile mill produces its own yarn from the raw cotton. Production of yarn from raw cotton includes steps like opening and cleaning, picking, carding, drawing, spinning, winding and warping. All these sequences are dry operations and as such do not contribute to the liquid waste of the mill. The entire liquid waste from the textile mills comes from the t he following following operation of slashing (sizing), scouring, de-sizing, bleaching, mercerizing, dyeing and finishing.

Cotton Textile Mill Waste 

Manufacturing Process:

Cotton Textile Mill Waste  •

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Wastes produced from the Wet Processes: In Slashing, the yarn is strengthened by loading it with starch or other substances. Wastes originate from this sections due to spills and floor washings. The substitution of low BOD sizes (such as carboxy-methyl cellulose) for the high BOD starches reduces the total BOD of the mill effluent by 40 to 90%. After Slashing, the yarn goes for Weaving.

Cotton Textile Mill Waste  •

Wastes produced from the Wet Processes (Contd.): The prepared cloth now requires scouring and de-sizing to remove natural impurities and the slashing compounds (i.e., starch).

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Enzymes are usually used to hydrolyze the starch.

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Acids may also be used for this purpose.

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Caustic soda, detergents, etc., are also used in this section.

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Replacement of soap use in scouring by low BOD detergents, may reduce the BOD load by 35%. About 50% of the total pollution load of the mill is contributed by this section.

Cotton Textile Mill Waste  •

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Wastes produced from the Wet Processes (Contd.):

Bleaching operations use oxidizing chemicals like peroxides and hyperchlorites to remove natural colouring material. This section contributes about 10% of the total pollution load.

Mecerizing consists of passing the cloth through 20% caustic soda solution. This process includes the strength, elasticity, lustre and dye affinity. Waste from this section is recycled after sodium hydroxide recovery. Negligible waste which may come out of this section contributes little BOD, but a high degree of alkalinity.

Cotton Textile Mill Waste  •

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Wastes produced from the Wet Processes (Contd.):

Dyeing maybe done in various ways, using different types of dyes, which include vat dyes, developing dyes, sulphur dyes, basic dyes, direct dyes, etc. Colour from the dyes vary widely and although these are not usually toxic, they are aesthetically objectionable when they impart colour in the drinking water supplies. Certain chemicals used in dyes, such as chromium are toxic and they are treated separately. Thickened dyes are used for printing and subsequent fixation. After fixation of the prints, the fabric is given a thorough wash to remove the unfixed dyes.

Cotton Textile Mill Waste  •

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Wastes produced from the Wet Processes (Contd.): The Finishing section of the mill imparts various finishes to the fabrics. Various types of chemicals are used for various objectives. These include starches, dextrines, natural and synthetic waxes, synthetic resins, etc. Therefore, a composite waste from an integrated cotton textile mill may include the following organic and inorganic substances: starch, carboxyl methyl cellulose, sodium hydroxide, detergents, peroxides, hyperchloride dyes and pigments, sodium gums, dextrines, waxes, sulphides, soaps, etc.

Cotton Textile Mill Waste  •

Wastes produced from the Wet Processes (Contd.): The characteristics of the mill waste varies widely, but that of a typical cotton textile mill is given below: Sl. No.

Characteristics

Value

1.

pH

9.8 – 11.8

2.

Total Alkalinity

1735 mg/l as CaCO3

3.

Biochemical Oxygen Demand (5-day) or BOD5

760 mg/l

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Chemical Oxygen Demand (COD)

1418 mg/l

5.

Total Solids

6170 mg/l

6.

Total Chromium

12.5 mg/l

Cotton Textile Mill Waste  •

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Effect of Textile Mill Wastes on Receiving Streams/Sewers: If the mill wastewater is discharged into streams, it causes depletion of D.O. to the stream. This is due to the settlement of the suspended substances and subsequent decomposition of the same in anaerobic conditions. The alkalinity and toxic substances like sulphides and chromium affects the aquatic life and also interferes with the biological treatment processes of sewage treatment plants. Some of the dyes are also found to be toxic.

Cotton Textile Mill Waste 

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Effect of Textile Mill Wastes on Receiving Streams/Sewers (Contd.): The colour often renders the water unfit for use for some industrial purposes in the downstream side. The presence of sulphides makes the waste corrosive particularly to the concrete structures.

Cotton Textile Mill Waste 

Treatment of Textile Mill Wastes:

Cotton Textile Mill Waste  •

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Treatment of Textile Mill Wastes (Contd.): All treatment plants should be planned giving consideration for the reduction of waste volume and strength, through the process of chemical substitution, chemical recovery and recycling of water. The pollutional load from a textile mill is dealt with operations like segregation, neutralization, equalization, chemical precipitation, chemical oxidation and biological oxidation. Several chemicals are used to reduce the BOD by chemical coagulation such as alum, ferric sulphate, ferrous sulphate, and ferric chloride. Lime or sulphuric acid is used to adjust pH in the process.

Cotton Textile Mill Waste  •

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Treatment of Textile Mill Wastes (Contd.): The dye waste maybe economically treated by biological methods, with prior equalization, neutralization and chemical oxidation. A composite waste, when free from toxic substances maybe treated as efficiently as domestic sewage, as most of the textile mill wastes contain sufficient nutrients like nitrogen and phosphorus. Trickling filters, Activated Sludge Process (ASP) and stabilization ponds have been effective in treating textile mill wastes. Extended aeration is found to be very effective in treating strong wastes even without equalization and pre-treatment.

Tannery Wastes 

Introduction:

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The tanning industry is one of the oldest industry in India.

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Usually, the tannery wastes are characterized by strong colour, high BOD, high pH and high dissolved solids. The concentrated growth of this industry in certain localities has shown how the waste from this industry can cause irreversible damage to the water environment in the vicinity. In view of its peculiar pollution potential and the increasing demand for good quality water, it has become essential to treat its waste to a certain degree prior to its disposal.

Tannery Wastes 

Manufacturing Process:

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Tanning process consists of 3 basic stages:

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Preparation of hides for tanning.

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Tanning proper

III. Finishing

Tannery Wastes 

Manufacturing Process Flow Diagram:

Tannery Wastes 

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Manufacturing Process: Preparation of hides for tanning: In the first stage, the hides are used to remove dirt and preservative salts used earlier, and then soaked in fresh water containing sodium chloride and preservative chemicals for 1-5 days. The soaked hides are then washed again with sufficient water. The washed hides are then limed with a paste of lime and sodium sulphide limed hides are then mechanically cleaned off hairs and fleshing in wooden vats with running fresh water. The subsequent operations are de-liming and bating.

Tannery Wastes 

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Manufacturing Process: Preparation of hides for tanning (Contd.): Bating prepares the hides for tanning by reducing the swelling and removing the degradation products in it. The de-liming and bating is carried out in vertically rotating grounds in a warm solution of ammonium salts and commercially prepared enzymes. An additional treatment known as “Pickling” is required for preparing the hide for “Chrome Tanning”, which involves the treatment of hides with sodium chloride and acid.

Tannery Wastes 

Manufacturing Process:

II. Tanning Proper: •

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The second stage of leather making, the tanning proper, involves the treatment of hides to make them nonputrescible and soft, even when dried. Depending on the type of product, either vegetable substances containing natural tannings such as extract of  barks, wood, nuts, etc., or inorganic chromium salts are used as tanning agents. The use of synthetic tanning materials is expensive and is not adopted anywhere in India. Vegetable tanning is used for heavy leathers, while chrome tanning is used for light leathers.

Tannery Wastes 

Manufacturing Process:

II. Tanning Proper (Contd.): •

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In the chrome tanning process, the tanning is done in the same vat after one day of picking by adding a solution of   chromium sulphate. After 4 hours of tanning, the leather is bleached with the dilute solution of sodium thiosulphate and sodium carbonate in the same vat. The chrome tanned leather is then pulled out and half of the spent liquor is thrown out and the remaining is reused along with a fresh volume of water. The vegetable tanned leathers are washed after the tanning proper.

Tannery Wastes 

Manufacturing Process:

III. Finishing: •

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The third stage of finishing consists of stuffing and fatliquoring followed by dyeing. Dyeing can be done using synthetic dye stuffs.

Tannery Wastes  •

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Sources and characteristics of wastewater: The wastewater originates from all the operations in the tanning process. The wastes maybe classified as continuous flow waste and intermittent flow waste. Continuous flow wastes consist of wash waters after various processes, and comprises of a large portion of the total waste and are relatively less polluted than the other one. Spent liquors belonging to soaking, liming, bating, pickling, tanning and finishing operations are discharged intermittently. Although small in volume, they are highly polluted and contain varieties of soluble organic and inorganic substances.

Tannery Wastes  •

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Sources and characteristics of wastewater (Contd.): The spent soaked liquor contains soluble proteins of hides, dirt and large amount of common salt where salted hides are processed. This spent liquor undergoes putrefaction very rapidly as it offers a good amount of nutrient and favourable environment for bacterial growth. The growth of pathogenic anthrax bacteria in this waste is also reported. The spent lime liquor contains dissolved and suspended lime, colloidal proteins and their degradation products, sulphides, emulsified fatty matters, and also carry a sludge composed of unreacted lime, calcium sulphide and calcium carbonate.

Tannery Wastes  •

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Sources and characteristics of wastewater (Contd.): As such, the spent lime liquor has a high ammonia nitrogen content. The spent bate liquor contains high amount of organic and ammonia nitrogen due to the presence of soluble skin proteins and ammonia salts used in bating. The vegetable tan extract contains tannins. Tannins are of high COD, but relatively low BOD value, while non-tannins including inorganic salt, organic acids and salts and sugar are of high BOD and COD. The spent vegetable tanning liquor is the strangest individual waste in the vegetable tanneries having the highest BOD and a very strong dirty brown colour.

Tannery Wastes  •

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Sources and characteristics of wastewater (Contd.): The spent pickling and chrome tanning waste comprises of a small volume, having a low BOD and contains traces of proteinic impurities, sodium chloride, mineral acids and chromium salts. Chromium is known to be highly toxic to the living aquatic organisms.

Tannery Wastes  •

Sources and characteristics of wastewater (Contd.): An average composition of combined waste in a typical Indian tannery is as follows: Sl. No.

Characteristics

Combined waste (10 hrs. composite sample)

Hourly maximum of combined waste

1.

Total Alkalinity

8.9

12.3

2.

Alkalinity as CaCO3 (mg/l)

260

700

3.

Acidity as CaCO3 (mg/l)

-

-

4.

Chloride as Cl (mg/l)

4280

10600

5.

Total Solids (mg/l)

10505

23410

6.

Suspended Solids (mg/l)

1080

3310

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COD (mg/l)

3700

6675

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BOD (mg/l)

1725

4000

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Chromium as Cr6+

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2800

Tannery Wastes  •

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Effects of wastes on streams and sewage: Tannery wastes are characterized by high BOD, high suspended solids and strong colour. These wastes when discharged into streams deplete the DO very rapidly due to both chemical and biological oxidation of sulphur and organic compounds. A secondary pollution of streams may occur due to the deposition of solids near the discharge point and its subsequent putrefaction. The gas evolved during the process has got a typical foul odour. Chlorides in excess of 500 mg/l, renders the water unsuitable for future use.

Tannery Wastes  •

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Effects of wastes on streams and sewage (Contd.): The chromium is toxic to aquatic life and inhibits the growth of fish in the stream. Even the lagooning of the untreated tannery waste on open land may adversely affect the groundwater and nearby surface water sources due to the seepage of dissolved solids. This makes the soil unsuitable for cultivation for its high salt content. The tannery waste when discharged into a sewer, not only chokes the sewer due to the deposition of solids, but also reduces the cross section of the sewer arising out of the lime encrustations.

Tannery Wastes  •

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Effects of wastes on streams and sewage (Contd.): Chromium compounds in excess of 10-20 mg disrupts the operation of the trickling filter. Sulphides are also toxic to micro-organisms.

Tannery Wastes 

Treatment of combined waste from a vegetable tannery (flow diagram):

Tannery Wastes  •

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Treatment of combined waste from a vegetable tannery: The method of treatment of tannery wastes maybe classified as physical, chemical and biological. The physical treatment includes screening and sedimentation. Screens are required to remove fleshings, hairs and protein substances. The screenings maybe used in the manufacture of glue, or maybe simply recovered for hairs, fleshings, fat, etc. The continuous flow sedimentation tank is found to be effective in 90% removal of suspended solids. About 98% of chromium can be precipitated in the primary sedimentation tank, and is removed along with the sludge.

Tannery Wastes  •

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Treatment of combined waste from vegetable tannery (Ctd.) : The sludge is dried over sand drying beds and can be used as a good manure. Chemical coagulation (alum, ferric chloride and ferrous sulphate), with or without prior neutralization, followed by biological treatment is necessary for better quality of the effluent. Ferrous sulphate is reported to be the best coagulant for the removal of sulphides and maybe used for the effective removal of colour, chromium, sulphides, BOD and suspended solids from chrome tanning wastes. However, in case of a vegetable tanning waste, alum maybe used with prior neutralization.

Tannery Wastes  •

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Treatment of combined waste from vegetable tannery (Ctd.) : Biological treatment of the tannery waste in Activated Sludge Process (ASP), after mixing with municipal wastewater in a suitable proportion is capable of reducing BOD, COD and tannins to about 90%. Prior chromium reduction is however required in the case of chrome tanning wastes. Trickling filters may also be used for effective removal of BOD, COD and colour. The biological treatment of tannery wastes are not difficult, but are relatively costlier due to their high BOD content and are not within the reach of a small tannery.

Tannery Wastes  •

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Treatment of combined waste from vegetable tannery (Ctd.) : Vegetable tanning waste can also be effectively treated by anaerobic contact filters. The low cost biological methods such as oxidation ponds and anaerobic lagoons are recommended for small and isolated tanneries. Anaerobic lagoons require less land area and nutrient addition comparatively to oxidation ponds. For further improvement of effluent quality, the anaerobic lagoon maybe followed by aerated lagoon. Chloride, particularly sodium chloride is not removed by conventional treatment processes.

Tannery Wastes 

Treatment of combined waste from vegetable tannery (Ctd.) :

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This problem can be tackled by making reuse of spent liquors.

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The same spent liquor maybe reused several times with or without make-up water. water. Use of substances other than salt as a preservative to the raw hides will also reduce the problem of sodium chloride. Recently, Recently, the use of saltless short-term preservatives like neem oil has got several other advantages advantages also. The volume of waste in any tannery can be considerably reduced by direct reuse of the same comparatively comparatively clean wash waters, pickling wash waters and dyeing wash waters. Segregation Segregation of spent chrome tanning liquor and the recovery recovery of chromium from it is often suggested.

Tannery Wastes  •

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Treatment of combined waste from vegetable tannery (Ctd.) : The process involves the chemical precipitation of chromium, in the form of chromium hydroxide, hydroxide, with lime at a pH of 6.6, and subsequent separation or filtration on sand bed filters. The recovered chrome tanning liquor is equally comparable to the freshly prepared liquors, liquors, but needs only adjustment adjustment of pH. The filtrate containing residual chromium maybe sent for further treatment along with other wastes. Although, the cost of recovery of chromium is less than the cost of fresh chrome powder, powder, the margin of profit is not much. However, the practice of recovery will considerably reduce the pollution load of the waste and also some amount am ount of foreign exchange, exchange, as the commercial chromium is imported from abroad.

Sugar Mill Wastes  •

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Introduction: In countries like India, Cuba and Jamaica, the sugar is produced from sugar canes, while in many other places, beetroots are used as raw mat materia rial for the sugar productio tion. In India, most of the sugar mills are situated in the countryside and operate for about 4-8 months just after the harv harves esti ting ng of the the sug sugarc arcanes anes.. A large volume of waste of organic nature is produced during the period of production and normally they are discharged on to land or into the near-by water source, usually small stre stream amss prac practi tica call lly y witho without ut trea treatm tmen ent. t.

Sugar Mill Wastes

Sugar Mill Wastes  •

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Manufacturing Process: The sugarcane is normally harvested manually in India, which eliminates the carriage of soil and trashes to the factory along with the sugarcanes. The sugarcanes are cut into pieces and crushed in a series of  rollers to extract the juice in the mill house. Milk of lime is then added to the juice and heated where in all the colloidal and suspended impurities are coagulated.

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Much of the colour is also removed during lime treatment.

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The coagulated juice is then clarified to remove the sludge.

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The clarifier sludge is filtered through the filter press and then disposed off as a solid waste.

Sugar Mill Wastes  •

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Manufacturing Process (Contd.): The filtrate is recycled to the process and the entire quantity of clarified juice is treated by passing sulphur dioxide gas through it. This process is known as Sulphitation Process. Here, colour of the juice is completely bleached out due to this process. The clarified juice is then pre-heated and concentrated in evaporators and vacuum pans. The partially crystallized syrup from the vacuum pan known as “massecuite” is then transferred to the crystallizers, where complete crystallization of sugar occurs.

Sugar Mill Wastes  •

Manufacturing Process (Contd.): The “massecuite” is then centrifuged to separate the sugar crystals from the mother liquor.

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The spent liquor is discarded as black strap molasses.

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The sugar is then dried and bagged for transport.

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The fibrous residue of the mill house known as “bagasse” maybe burnt in the boilers or maybe used as raw materials for the production of paper product. The black strap molasses maybe used in the distilleries.

Sugar Mill Wastes  •

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Sources and Characteristics of Wastes: Waste from the mill house include the water used as splashes to extract maximum amount of juice and those used to cool the roller bearings. As such the mill house waste contains high BOD, due to the presence of sugar and oil from the machineries. The filter cloths, used for filtering the juice needs occasional cleaning. The wash water thus produced, though small in volume, contains high BOD and suspended solids. A large volume of water is required in the barometer condensors of the evaporators and vacuum pan.

Sugar Mill Wastes  •

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Sources and Characteristics of Wastes (Contd.): The water is usually partially or fully recirculated after cooling through a spray pond. This cooling water gets polluted as it picks up some organic substances from the vapour of the boiling syrup in the evaporator and vacuum pans. This polluted water, instead of being recirculated is discarded as excess condensed water. These discharges contribute substantially to the waste volume and BOD in many sugar mills. Additional waste originates due to the leakages and spillages of juice, syrup and molasses in different sections.

Sugar Mill Wastes  •

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Sources and Characteristics of Wastes (Contd.): The periodical washings of the floor, though small in volume has got very high BOD. The periodic blow-off of the boilers produce another intermittent waste discharge. This waste is high in suspended solid, low in BOD and usually alkaline.

Sugar Mill Wastes 

Sources and Characteristics of Wastes (Contd.): Sl. No.

Characteristics

Combined waste

1.

pH

4.6 - 7.1

2.

COD (mg/l)

600 - 4380

3.

BOD (mg/l)

300 - 2000

4.

Total Solids (mg/l)

870 - 3500

5.

Total Suspended Solids (mg/l)

220 -800

6.

Total Nitrogen (mg/l)

10 - 40

Sugar Mill Wastes  •

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Effects of Wastes on Receiving Waters: The fresh effluent from the sugar mill decomposes rapidly after a few hours of stagnation. It has been found to cause considerable difficulties when this effluent gets an access to the water courses particularly the small and non-perennial streams in the rural areas. The rapid depletion of oxygen due to biological oxidation followed by anaerobic stabilization of the waste causes secondary pollution of offensive odour, black colour and fish mortality.

Sugar Mill Wastes  – Treatment Flow Diagram

Sugar Mill Wastes  •

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Treatment of Wastes: Like any other industry, the pollution load in sugar mills can also be reduced with a better water and material economy practiced in the plant. Judicious use of water in various plant practices and its recycle, wherever practicable, will reduce the volume of  waste to a great extent. Volume of mill house waste can be reduced by recycling the water used for splashing. Dry cleaning of floors or floor washings using controlled quantity of water will also reduce the volume of waste to a certain extent.

Sugar Mill Wastes  •

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Treatment of Wastes (Contd.): The organic load of the waste can only be reduced by a proper control of the operations. Over-loading of the evaporators and the vacuum pans and the extensive boiling of the syrup leads to a loss of sugar through the condenser water and this in turn increases both volume and strength of the waste effluent. Disposal of the effluent on land as irrigation water is practiced in many sugar mills, but it is associated with odour problems. Anaerobic treatment of the effluent using both digesters and lagoons have been found to be very effective and economical.

Sugar Mill Wastes  •

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Treatment of Wastes (Contd.): A BOD reduction of about 70-88% was observed in a pilot plant study with an anaerobic digester, where BOD loading was 0.65-1.79 kg/m3/day with a detention time of 2-2.4 days at a controlled temperature of 370C. The effluents of the anaerobic treatment units are found to contain sufficient nutrients (nitrogen and phosphorus). Therefore, the further reduction of BOD can be accomplished in aerobic and waste stabilization ponds. Where sufficient land is available, a two stage biological treatment with anaerobic lagoons followed by aerobic waste stabilization plants is recommended for Indian conditions.

Sugar Mill Wastes  •

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Treatment of Wastes (Contd.): The mill effluent, however is to be pre-treated primarily in bar screens and grease traps. From the flow-sheet of the complete treatment of the sugar mill waste, it is expected that the BOD reduction in the anaerobic process will be in the order of 60%. However, overall BOD reduction maybe in the order of 90%.

Distillery, Winery & Brewery Wastes  •

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Introduction: While wineries and breweries produce wine and beer respectively, distilleries produce a large number of products. The range of products from distilleries include industrial alcohols, rectified spirit, absolute alcohol, silent spirit, beverage alcohol, etc. But two things are common in all the products mentioned above:

1. All the above products are obtained through the biochemical process of fermentation by yeast using carbohydrates as raw materials, and 2. All the products proportions.

contain

ethyl

alcohol

in

different

Distillery, Winery & Brewery Wastes  •

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Introduction: In all the industries mentioned above, the wastes have high BOD and they present a threat to the environment when discharge into the water sources or onto the land without treatment. Due to their varying polluting potential, all the three industries will be discussed in isolation.

Distillery, Winery & Brewery Wastes Manufacturing Process of Beer 

Distillery, Winery & Brewery Wastes 

Manufacture of Beer:

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Making of beer essentially consists of two stages:

1. Preparation of malt from grains like barley. 2. Brewing the barley. •

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In the malt making, the barley grains are steeped (soaked) to bleach out colour and then made to “sprout” (germinate) under aerobic conditions. The grain malt is then dried and stored after screening the sprouts out. The malt from the malt house is then transported to the brewing section, where the “wort ”, the medium for fermentation is prepared by mixing the course grain malt with hot water and by transferring the starch to sugars boiling in hops.

Distillery, Winery & Brewery Wastes  •

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Manufacture of Beer (Contd.): The “wort” is then filtered and cooled. The filtered “wort ” is then inoculated with a prepared suspension of yeast which converts the sugar to alcohol. When the fermentation is complete, the yeast and malt residue is filtered out and finally the beer is carbonated before packing for sale. As the flavour of the product is of prime importance, selection of raw materials and control of processes is done accordingly.

Distillery, Winery & Brewery Wastes  •

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Origin and Characteristics of Brewery Wastes: Brewery wastes originate during preparation of the malt as well as brewing the barley. The spent water from the steeping process of the malt house is one source. These wastes include the water soluble substances of the grain that are diffused into it. Characteristically, it contains a large amount of organic soluble solids indicated by a high BOD in the order of 400-800 mg/l, and low suspended solids concentration. In the brewery plant, the major pollutant is the fermentation residue or the spent grains.

Distillery, Winery & Brewery Wastes 

Origin and Characteristics of Brewery Wastes (Contd.):

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This contains a high suspended solids and also a high BOD.

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Wastes also originate in the preparation of yeast suspension (i.e., pre-fermentation section), from washing of containers, equipments and floors and in the process of by-product recovery from spent grains. Large volumes of almost unpolluted water also comes up as waste cooling water. While the malt house waste is usually alkaline in nature, the brewing plant is generally acidic.

Distillery, Winery & Brewery Wastes 

Composition of Malt House and Combined Brewery Wastes:

Sl. No.

Item

Malt House Waste

Brewery Waste

1.

pH

6.9 – 9.5

4.0 – 7.0

2.

COD (mg/l)

30 – 180

30 – 1200

3.

BOD5 (mg/l)

20 – 210

70 – 3000

4.

Total Solids (mg/l)

20 – 340

20 – 520

5.

Total Nitrogen (mg/l)

14 – 56

7 – 42

Distillery, Winery & Brewery Wastes Manufacture of Alcohol in Distilleries

Distillery, Winery & Brewery Wastes  •

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Manufacturing Process in Distilleries: Molasses (black strap type) are exclusively used as raw materials in the industrial alcohol industry. In molasses distilleries, a mash is prepared which consists of:

1. Dilution by water to a sugar content of about 15%. 2. pH adjustment to 4.0-4.5 to prohibit bacterial activities. 3. Nutrient addition. •

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The yeast suspension is prepared separately in the laboratory with part of the diluted molasses and then innoculated into the mash for fermentation under controlled conditions. The fermented liquor containing alcohol is then sent to an overhead tank without separation of the solid materials.

Distillery, Winery & Brewery Wastes  •

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Manufacturing Process in Distilleries (Contd.): The same is then de-gasified and the alcohol is stripped (separated) leaving a spent-wash. The crude alcohol is then re-distilled and stored in bags. Some of the alcohols like gin, attain their final form at this stage, some others like whisky require ageing in charred oak wood barrels.

Distillery, Winery & Brewery Wastes  •

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Origin and Characteristics of Distillery Wastes: The “spent-wash” is the major polluting component of the distilleries and it is reported to be 10-15 times the final product in volume.

The other pollutants include yeast sludge, which deposits at the bottom of the fermentation vats. In most of the distilleries in India, this yeast sludge is mixed with the spent-wash and discharged. In addition to these, the major BOD and solids contributing wastes, floor wastes, waste cooling water and wastes from the operations of yeast recovery processes also contribute to the volume of these wastes.

Distillery, Winery & Brewery Wastes 

Characteristics of Combined Waste, Spent Wash and Yeast Sludge from different Indian distilleries:

Sl. No.

Item

Yeast Sludge

Combined Waste

Spent-wash

1.

pH

4.8

3.9 – 4.3

3.5 – 3.65

2.

COD (mg/l)

368,000

27,900 – 73,000

118,000

3.

BOD5 (mg/l)

165,000

12,230 – 40,000

41,380

4.

Total Solids (mg/l)

 –

16,640 – 26,000

99,000

5.

Total Nitrogen (mg/l)

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–

1,135

6.

Colour

 –

–

Dark Brown

Distillery, Winery & Brewery Wastes Manufacture of Wine in Wineries

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Manufacturing Process in Wineries: The wineries utilize the fruit juices as the raw materials. So, the first operation in any winery is the pressing of   fermented juice from the fruits like grape. The waste from this operation resembles that from the canning industry and includes the spent fruits or pomace, wastage of fermentable juice and floor wash wastes. The second stage in any winery consists of fermentation of  this juice. The wine attains its final form at this stage, and requires only decantation, blending and bottling for sale.

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Manufacturing Process in Wineries (Contd.): The waste from this stage comes from fermenting, decanting, spillages, floor washings, etc., and resembles that from a brewery. In the third stage, i.e., the brandy plant, wine of either type or the fermentation residue in the wine making is distilled to obtain brandy.

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Origin and Characteristics of Winery Wastes: Depending upon the source of the brandy, the waste may have low to very high solids concentration, and resembles distillery wastes very much.

Characteristics of combined wastes from brewery, winery and food processing wastes: Sl. No.

Item

Combined Waste

1.

Temperature

20 – 290C

2.

Colour

Brownish yellow

3.

pH

4.0

4.

COD (mg/l)

1800 – 3000

5.

BOD5 (mg/l)

1500 – 2000

6.

Total Dissolved Solids (mg/l)

6800 – 9400

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Effects of Wastes on Receiving Waters: The wastes from these industries are not toxic to the aquatic life of the receiving stream. But, due to their high BOD content, they deplete the DO of  the receiving water. This results in anaerobic decomposition of this organic solids, both settled and suspended, producing a malodorous condition over the fairly long stretch of the stream. The conditions further deteriorate due to the growth of   sewage fungi. The dark colour of the stream renders it unaesthetic.

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Effects of Wastes on Receiving Waters (Contd.): Brewery wastes, which is comparatively of lesser strength maybe discharged in a fresh condition into the sewers to the extent of 3-5% of the domestic sewage. The strong acidic or putrified brewery waste will disrupt the normal biological activities of the waste treatment plants. If brewery waste is to be discharged into public sewers, it must be screened and pre-treated with lime. The very high BOD content of the distillery waste makes it non-amenable to the aerobic biological treatment. Therefore, it cannot be discharged into the municipal sewerage system directly.

Distillery, Winery & Brewery Wastes Treatment of Brewery Wastewaters

Distillery, Winery & Brewery Wastes Treatment of Distillery Wastewaters

Distillery, Winery & Brewery Wastes Treatment of Winery Wastewaters

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Treatment of Wastes: Brewery wastes being comparatively less strong, can be treated by aerobic biological treatment, after screening and neutralization. Usually the biological treatment is accomplished by a twostage process for 90-94% BOD reduction. The brewery waste maybe reused for broad irrigation after neutralization to utilize the fertilizing components of the waste. The yeast sludge from distilleries which contains very high suspended solids and BOD is rich in proteins, carbohydrates. Vitamins maybe treated separately for by-product recovery.

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Treatment of Wastes (Contd.): But in practice, they are mixed and discharged along with the spentwash. The raw spentwash with low pH, high dissolved solids, high temperature, high sulphates and BOD is not amenable to aerobic biological treatment. Physico-chemical methods are also found to be ineffective in the treatment of spent-wash or combined distillery waste. Two-stage biological method of treatment consisting of an anaerobic treatment followed by aerobic treatment of the waste have been widely accepted as the only methods of   treatment of distillery spent-wash.

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Treatment of Wastes (Contd.): Both closed anaerobic digestion and open lagooning have been tried in India.

anaerobic

A single-stage digestor is usually adopted for anaerobic treatment when land available is limited. Production of hydrogen sulphide impairs the anaerobic digestion, as soluble sulphides are toxic to the microorganisms. It has been found that conversion of soluble sulphides to insoluble ferric sulphide by the addition of iron salts improves the condition as the ferric sulphides are not toxic to the micro-organisms.

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Treatment of Wastes (Contd.): Anaerobic lagooning is a low-cost alternative to the digestor when land is available plentily. The only disadvantage of anaerobic lagooning is the evolution from the ponds. This odor nuisance can be eliminated by establishing a proper anaerobic activity in the lagoon. As the high sulphate content and low pH is unfavorable for the methane fermenters, neutralization of the waste helps in establishing a proper condition for their activity. A greater initial dilution and greater amount of acclimatized seed sludge may also help in establishing proper anaerobic activities.

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Treatment of Wastes (Contd.): Effluent of the digesters and the anaerobic lagoons still contains a high BOD, which cannot be discharged into the receiving waters. These effluents are successfully treated either in aerated lagoons or in oxidation ditches. About 90% BOD removal can be accomplished in aerated lagoons. Aerated lagoon effluent requires further treatment in a polishing lagoon of about 24 hrs detention time. Single-stage anaerobic treatment either in lagoon or in digesters is followed by two-stage aerobic treatment is also proposed for distillery wastes.

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By-product Recovery: The yeast sludge from the distilleries contain the degradation product of the dead yeast. Organic debris from the malts contain proteins, fats, vitamins and carbohydrates. On the other hand, the spent-wash contains all the above nutrients plus unfermented sugars, amino acids, caramels, ammonia phosphate, etc. Here, two types of by-products, i.e., the nutrient-rich animal feed and the potassium-rich fertilizers maybe recovered in the distillery.

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By-product Recovery (Contd.): The segregation of yeast sludge for processing the animal feed is practiced in some distilleries which in turn reduces the insoluble BOD load of the waste. Yeast powder of pharmaceutical grade can also be obtained from a yeast sludge and spent-wash mix. The animal feed derived from the waste debris and from the spentwash of grain distilleries is usually considered useful as cattle feed. The repeated soaking of the liquid waste and drying under direct sunlight produces a very good feed for fish.

Distillery, Winery & Brewery Wastes 

By-product Recovery (Contd.):

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The liquid waste is first screened, evaporated and then dried.

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The dried screen wastes are known as dried distillery waste.

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The evaporating and concentration of soluble wastes is accomplished in different types of evaporators. The concentrated waste is then dried on conventional spray and drum driers. This product is known as dried distillery solubles (DDS) which is normally used as an animal feed. The DSS can be further incinerated in hearths (at temperatures not exceeding 7000C) to produce inorganic ash rich in potassium salts.

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By-product Recovery (Contd.): The ash containing potassium salts can further be purified by sequence of operations like leaching, filtration and acidifying by sulphuric acid. It is further concentrated in vacuum evaporators and finally crystallization of potassium chloride and sulphates is done. It maybe noted that the condensing water arising out of the process of evaporation of spent-wash still contains a high BOD and should be treated before its disposal.