UNIT-VI

                                     IMPORTANT QUESTIONS

1-   Explain the equalization and neutralization methods of industrial wastewater?

 Equalization and neutralization-

Equalization is a method of retaining wastes in a basin so that the effluent discharged is fairly uniform in its characteristics such as pH, color, turbidity, alkalinity, B.O.D. Etc. equalization consists of holding the waste water for some pre determined time in a continuously mixed basin to produce uniform wastewater . Such an arrangement will of course be necessary when the waste water produced by industry varies in characteristics and quantities over the entire day.

Benefits -

• Equalization improves sedimentation efficiency by improving hydraulic retention time .
• The efficiency of biological process can be increased because of uniform characteristics and minimization of the impact of shock loads and toxins during operation.
• Manual and the automated control of flow- rate-dependent operations, such as chemical feeding, disinfection, and sludge pumping are simplified .
• Treatability of the waste water is improved and some BOD reduction and odor removals BENEFITS OF EQUALIZATION provided if aeration is used for mixing in the equalization basin .
• A point of return for recycling concentrated waste stream is provided, thereby mitigating shock loads to primary setters or aeration basin.

Neutralization:

Neutralization means neutralizing the excessive acidity or alkalinity of the particular waste water by adding alkali or acid respectively to the waste water . This may be achieved either in the equalization tank .

• The excessively acidic or alkaline waste should not be discharged without treatment into a receiving stream, sewer, and effluent treatment plant or on land.
• There are many acceptable methods for neutralization of acidic or alkaline waste water and they are as follows:
• Neutralization of acidic waste:
  • Mixing the waste by the waste from other industry.
  • Passing acidic waste through beds of lime stone.
  • Mixing acidic waste with lime slurry
  • Adding proper proportion of caustic soda or soda ash.
  • Neutralization of alkaline waste:
  • Use of waste boiler flue gas
  • CO2CO2 treatment for alkaline waste
  • Producing CO2CO2 in alkaline waste
  • H2SO4H2SO4 treatment
• Acid waste neutralization in industrial process

2-   What are the applications of industrial waste water as per CPCB  norms?

 There are various types of industries in india and which has different effluent characteristics and properties. Some of them are discussed here-

Aquaculture

Fish Hatcheries and Farms

At fish hatcheries and farms, solids can develop in the water from fish waste and uneaten food. In high amounts, these solids negatively impact the growth and survival rates of the fish because they demand oxygen and contaminate the water with ammonia. A Salsnes Filter system can effectively remove these solids (without crushing like a typical drum filter) to maintain a high water quality for the fish.

Pulp & Paper-

Water is used in nearly every step of the manufacturing process for a pulp and paper mill. So, of course these facilities have large volumes of wastewater to treat and sludge to dispose of. To save costs, many facilities would like to recover excess pulp fiber from their wastewater to be reused in the production line.

For those facilities not recovering fibers, our integrated thickening and dewatering processes are effective with fibrous material and can reduce the volume of sludge and associated disposal costs.

Tanneries

Tanning is one of the oldest industries in the world and produces some of the most challenging wastewater to treat and dispose of. Wastewater is highly toxic and can contain proteins, albumins, hair, blood, shavings, fat and grease. Water is used in many production processes creating high volumes of wastewater to manage. The Salsnes Filter system has unlimited design flow capacity, so installation configurations can be designed for high volumes of wastewater, even the chemically aggressive and high-loaded wastewater of a tannery.

Our advantage over other commonly used filters is that the system quickly and continuously removes TSS, COD and BOD in one compact unit without crushing solids into finer particles. No excess water for screen washing, costly chemicals for sludge conditioning or power for additional sludge dewatering equipment is required.

Breweries and Wineries-

The organic composition of brewery and winery wastewater is dominated by dissolved compounds which cause high biochemical and chemical oxygen demand (BOD, COD). But, the wastewater also contains solids, (e.g. Spent grains, spent yeast, fine colloidal solids and filtration aids like diatomic earth) which makes treatment more complicated.

Very often easy-settling solids like diatomic earth can collect on the bottom of anaerobic reactors and block diffusers. The Salsnes Filter system can remove >50% TSS prior to the anaerobic step to avoid this problem and to also avoid the use of additional filters or separators.

3-   Write down various types of sources which are generated from manufacturing process?

 The sources of wastewater can be categorized into various categories

1-textile mill waste-The Fibres used in the Textile Industry may be broadly classified into four groups : cotton, wool, regenerated and synthetics.

There are two types of waste in textile mills-

• Cotton mill waste
• Woolen mill waste

The crude waste, if discharged into the streams, causes rapid depletion of the dissolved oxygen of the streams. The condition aggravates due to the settlement of the suspended substances and subsequent decomposition of the deposited sludges in anaerobic condition. The alkalinity and the toxic substances like sulphides and chromium affect the aquatic life; and also interfere with the biological treatment process; some of the dyes are also found toxic.

2- dairy waste-Waste producing operations are washing of bottles, cases, cans, tanks, cooling equipment, Processing equipment and floors. Dripping, leaks, spillages and overflows due to improper equipment or inefficient operation. Discharges from evaporators. Wasted buttermilk and whey (watery liquid left when milk forms curds). Spoiled raw or treated products.

3- meat packing waste-Meat is the dressed flesh derived from cattle, buffalo, sheep, goat, pigs and poultry. Meat being a highly perishable product, can be kept in a fresh condition only through proper processing and storage. When meat gets spoiled it becomes slimy or sticky, turns dark brown and develops an unpleasant smell and taste. Meat is preserved in a number of ways such as freezing, curing, smoking, dehydration and canning.

Three major sources of wastes of meat industry are from

1. Stockyards

2. Slaughter House and

3. Packing House

4- pulp and paper mill waste-The paper mills use the 'pulp' as the raw material , which is again produced utilizing different cellulosic materials like wood , bamboo,jute, straw mainly of rice and wheat, waste paper, bagasse etc in the pulp mills.

5-metal plating waste-Plating is the application of a plate, or coat, of metal to a surface for decoration, reflection of light, protection against corrosion, or increased wearing quality. Electroplating is the most common method because it permits the control of the thickness of the plating. We offer: Gold, Nickel, Copper, and Chrome plating.Very small concentrations of cyanide , chromic acid and chromates, heavy metal compounds of cadmium , copper , lead , nickel and zinc are toxic to aquatic life . In high concentrations they are toxic to humans also. As they are toxic to microbiological and biological organisms self purification is inhibited. Further, iron and tin impart colour to the receiving stream. The colloidal and other suspended impurities render a bad appearance to the stream. Plating is the application of a plate, or coat, of metal to a surface for decoration, reflection of light, protection against corrosion, or increased wearing quality. Electroplating is the most common method because it permits the control of the thickness of the plating. We offer: Gold, Nickel, Copper, and Chrome plating.

6-oil refineries waste-Crude oils are complex mixtures of hydrocarbons of varying molecular weight and structure. These hydrocarbons range from simply highly volatile substances to complex waxes and asphaltic compounds. The final petroleum products are obtained from the crude oil through a series of operations viz. Topping , thermal cracking , catalytic cracking , catalytic reforming etc. In general , the crude oil is first subjected to fractional distillation in the process known as " topping " . The products obtained are called raw products and include raw gasoline, raw naptha , raw kerosene , gas oil, fuel oil etc. Now these intermediate refinery products are again treated to yield various finished market products as per the requirements. The operations practiced include "catalytic cracking" or "thermal cracking" and further purification processes like "acid treatment" , "sweetening treatment" , "hydrodesulphurization" etc. The decomposition of heavy or high boiling petroleum distillates like gas oil and fuel oil to lighter products like gasoline is called cracking. These operations take place practically at the atmospheric pressure and at a high temperature. In catalytic cracking, however, an acid type solid catalyst (such as synthetic silica alumina) is introduced into the reactor. A residue of heavy black material known as coke, is obtained out of the process of cracking. In the catalytic cracking process, however , the asphaltic or tar-like products get adsorbed on to the surface of the catalysts in the form of coke. When "high octane" fuels are in demand ,much of the naphtha is "catalytically reformed" into high octane gasoline; the process involved is another form of cracking. The wax distillates of the crude oil may be used as raw material for the manufacture of light lubricating oils. The process of their manufacture consists of chilling the distillates and filtering the wax from the oil. The products thus obtained either as final product or as feedstock for further processing may contain certain undesirable constituents which must be either removed or converted into less harmful compounds by further refining processes. Such refining processes include (i) removal of hydrogen sulfide gas and mercaptans by washing with strong caustic soda solution , or (ii) absorption of hydrogen sulfide gas in an alkaline absorber liquid followed by the recovery of the hydrogen sulfide gas , in the process known as regenerative process (iii) conversion of mercaptans to less harmful desulphide, employing solutions like lead oxide in caustic soda together with sulphur, or sodium hypochlorite or copper chloride , in a process known as "sweatening" and (iv) conversion of alkylsulphides and thiophenes and practically all other sulphur compounds into hydrogen sulfide in a catalytic in the process known as "hydrodesulphurization" - hydrogen sulfide thus formed is recovered by the regenerative process.

4-   What are characteristics of effluent obtained from industries such dairy ,sugar ,textile?

 Different industrial waste water have different characteristics-

1-   Physical characteristics

2-   Chemical characteristics

3-   Biological characteristics

1-Physical characteristics-

Odour- industrial waste water may contain odorous compounds or components that produce odor during the process of waste water treatment .

Temperature – it is a very important parameter that affects aquatic life.

Colour : Colour is contributed by textile and paper mills, tanneries, slaughterhouses and other industries, is an indicator of pollution. Colour interferes with the transmission of sunlight into the stream and therefore lessens photosynthetic action. Furthermore, municipal and industrial water plants have great difficulty, and scant success in removing colour from raw water.

2-chemical characteristics-

Inorganic salts: Inorganic salts, which are present in most industrial wastes as well as in nature itself, cause water to be "hard" and make a stream undesirable for industrial, municipal and agricultural usage. Salt laden waters deposit scale on municipal water- distribution pipelines, increasing resistance to flow and lowering the overall capacity of the lines. These are nitrogen phosphorous and sulphur.

Acids and /or Alkalis : Acids and Alkalis discharged by chemical and other industrial plants make a stream undesirable not only recreational uses such as swimming and boating, but also for propagation of fish and other aquatic life. High concentrations of sulfuric acid, sufficient to lower the pH below 7.0 when free chlorine is present, have been reported to cause eye irritation to swimmers. A low ph may cause corrosion in air conditioning equipment and a ph greater than 9.5 enhances laundering.

Organic matter : Organic Matter exhausts the oxygen resources of rivers and creates unpleasant tastes, odours and general septic conditions. It is generally conceded that the critical range for fish survival is 3to 4 mg/l of D.O certain organic chemicals such as phenols, affect the taste of domestic water supplies.

Suspended solids : Suspended solids settle to the bottom or wash up on the banks and decompose, cause sing odours and depleting oxygen in the river water. Fish often die because of a sudden lowering of the oxygen content of a stream. Visible sludge creates unsightly conditions and destroys the use of a river for recreational purposes. These solids also increase the turbidity of the watercourse.

3-biological characteristics-

Microorganisms : A few industries, such as tanneries and slaughterhouses, some times discharge wastes containing bacteria. These bacteria are of two significant types:

i) bacteria which assist in the degradation of the organic matter as the waste moves down stream. This process may aid in "seeding" a stream and in accelerating the occurrence of oxygen sag in water.

Ii) bacteria which are pathogenic, not only to other bacteria but also to humans.

5-   What is the method of treatment obtained from dairy industry and distillery industry?

1-   Dairy industry-

Treatment-As evident from the high BOD/COD ratio, the dairy wastes can be treated efficiently by biological processes.

Aerobic biological treatment either in the form of high rate trickling filters or activated sludge plant will generally sufficient for this industry

Due to the intermittent nature of the waste discharge, it is desirable to provide, Equalization tank with or without aeration before the same is sent for biological treatment. A provision of grease trap is also necessary as a pretreatment to remove fat and other greasy substances from the waste. An aeration for a day not only prevents the formation of lactic acid, but also reduces the BOD by about 50%. Both high rate trickling filters and activated sludge plants can be employed very effectively for a complete treatment of the dairy waste. On the other hand the low cost treatment methods like oxidation ditch, aerated lagoon, waste stabilization pond etc can be employed with simpler type of equipments and less maintenance.

In unwanted locations oxidation ditch or aerated lagoon may also help ensure good disposal.

2-   Distillery industry-

Treatment-brewery wastewater are being less strong and can be generally treated by two stage aerobic biological treatment units like high rate trickling filters after screening and neutralization.

The raw spent wash with low pH, high dissolved solids, high temperature, high sulphates, and high B.O.D is not amenable to aerobic biological; treatment. Two-stage biological methods of treatment consisting of an aerobic treatment have been widely accepted as the only methods of treatment of the wastes from the distilleries.

A single stage digester is usually adopted for the anaerobic treatment when land available is limited. Anaerobic lagooning is a low cost alternative to the digesters when land is available in plenty. The only disadvantage of anaerobic lagoons is the evolution of volatile gases and obnoxious odour from the ponds.

Effluent of the digesters an the anaerobic lagoons still contain a high B.O.D, which cannot be discharged into the receiving streams. These effluents can successfully be treated either in aerated lagoons, or in oxidation ponds.

6-   Explain methods of treatment obtained from sugar industry?

 Treatment- anaerobic treatment using digesters or lagoons is found to be very effective and economical . Biological treatment however needs to be preceded by screens and grease traps.

Where effluent land is available two stage biological treatment with anaerobic lagoon followed by aerobic stabilization pond  gives very good effluents for Indian conditions.

A B.O.D reduction of about 70% was observed in a pilot plant study with an anaerobic digester. The effluents of the anaerobic treatment units are found to contain sufficient nutrients (nitrogen and phosphorous). As such further reduction of B.O.D can be accomplished in aerobic waste stabilization ponds. Where sufficient land is available, a two stage biological treatment, with anaerobic lagoons followed by aerobic waste stabilization ponds, is recommended for Indian conditions. The mill effluent however is to be pretreated primarily in bar screens and grease trap.

It is expected that the B.O.D reduction in the anaerobic process will be in the order of 60%, while overall B.O.D reduction may be in the order of 90%.

7-   Explain methods of disposal of waste which are obtained form dairy, distillery ,sugar industries?

 Disposal methods of all industrial wastes-

(i) Dilution or disposal into water i.e. into sea, lakes or rivers

(ii) Disposal on land or land treatment i.e. sewage farming and irrigation

Dilution

• Dilution is a prominent method of natural disposal, consists of discharging the wastewater into receiving water body (Such as river, sea, lake etc.)

• This is done on the assumption that the sufficient dissolved oxygen is available in the water body so that biochemical oxygen demand is satisfied.

• If however, the diluting water is not sufficient to supply the biological( or biochemical) oxygen demand to oxidise the entire matter present, there will be nuisance of foul odour and unsighty islands of half digested floating, putrefying matter at the surface.

• In addition to this problem, the depletion of oxygen would kill the aquatic life, and if this dilution water is used at the downstream side for drinking purpose, it will cause danger to the public health.

• for disposal by dilution large volumes of natural clean waters are required .

• It is a very simple method and it requires less skilled supervision.
• Dilution method of disposal requires nil or small head pumping.
• Dilution method requires full or at least partial treatment.

Disposal of Wastewater in Sea or Ocean

• sea water normally contains 20% less oxygen than that contained in fresh water of a river stream.

• Due to this reasons, when the sewage is discharged into the sea water, the lighter and warmer sewage will rise up to the surface, resulting in lighter and warmer sewage will rise up to the surface, resulting in spreading of the sewage at the top surface of sea in a thin film or ‘sleek’

• Moreover seawater contains a large amount of dissolved matter which chemically reacts with the sewage solids, resulting in the precipitation of some of the sewage solids, giving a milky appearance to the sea water and resulting in formation of sludge banks and thin milky layer formed at the top of sea water produce offensive hydrogen sulphide gas by reacting with sulphate rich sea water.

• As such the capacity of seawater to absorb sewage solids is not as high as that of fresh water of a river.

• Also the DO content is less. However, since the sea contains large volume of water, most of these deficiencies can be overcome if the sewage is discharged deep into the sea, much away from the coast line, with extreme care.

• Points be kept in mind while discharging sewage into the sea

a-    The sewage should be discharged in deep sea water.

b-   in order to mix sewage properly with the seawater, the sewage should be released at a minimum depth of 3 to 5 m below the water level and taking it sufficiently inside the shore, and thus preventing nuisance to baths and recreation centres on the shore.

c-    To prevent the backing up and spreading of sewage on the sea shore, the sewage should be disposed of only during low tides, large sized tanks may, therefore be constructed to hold the sewage during high tides. Provision of a large sized sewer, grated with non return valve at the end, is also an alternative to hold the sewage during high tides.

Disposal of Sewage on land

• In this method, the sewage effluent is generally disposed of by applying it on land . The percolating water may either join the water table or is collected below by a system of under drains . This method can then be used for irrigating crops.

• The most common forms of land application are irrigation (Sewage farming) and rapid infiltration.

• When raw or partly treated sewage is applied on the land, a part of it evaporates and remaining portion percolates in the soil.

• If proper voids are maintained in the soil , the organic sewage solids are oxidized by the bacteria present in the soil under aerobic condition.

The cost of land in land disposal method is generally very high specially in cities and urban areas which are situated near the rivers. When the cost of land is high in disposal method ,some return may be available due to sewage farming but then good management also required .

This method of disposal requires no pre treatment of sewage .

Land disposal method is generally found to be better in hot areas

8-   Write down the discharge standards as per CPCB norms?

 Discharge standards as per CPCB norms-

9-   explain gardening ,sewage farming  ?

 Gardening –“Wastewater gardening” is a laymans’ term used for systems that utilise wastewater for growing plants. Wastewater gardens normally support different kinds of trees and/or shrubs against the single species planting in constructed wetlands. It may be constructed in a single cell set up for small systems and more compartments in larger applications. More compartments provide better area for planting and therefore obtain better treatment of wastewater. A bedding of gravel can provide adequate surface area where organic compounds, suspended solids and excess nutrients are removed through chemical, biological and physical mechanisms and increase the residence time for the wastewater for better treatment. The roots of the plants will make the bedding medium porous and aerate the system although the main process is stripping off the nutrients to a green or colourful garden. The physical processes such as aeration, sedimentation, adsorption and decomposition combined with other chemical processes convert wastewater to a quality good enough for discharge or reuse.

Sewage farming-Sewage farming allows use for irrigation of water which might otherwise be wasted. Some of the nutrients and organic solids in wastewater can be usefully incorporated into soil and agricultural products rather than fouling natural aquatic environments. Pumping to the point of application may be the only requirement if the village is not at a higher elevation than the sewage farm. In case of sewage farming the stress is laid upon the use of sewage effluents for irrigating crops and increasing the fertility of the soil.

In order to prevent the land from the sickness several preventive measures are adopted-

1-   choice of land- the piece of land used for sewage farming should normally be sandy or loamy .

2-   rotation of crops-for better sewage farming to plant different crops in rotation . This will help in improving fertility of soil.

10-                       Explain recycle and reuse of industrial wastewater?

 Reuse& recycle in industry-

Reuse or treated waste water in various industries is becoming very popular being a cheaper source of water supply where industrial plant can reuse its own waste water through recycling or after treatment it can be used for irrigation.

Several advanced methods of tertiary treatment are used to meet the standard effluent reuse for several purposes.

1-   Filtration

2-   Granular media filter

Industrial water reuse and recycling is the process by which wastewater produced from one source is treated so it can be used in an industrial process. Sometimes the source wastewater may be produced by the same industrial facility that treats it and reuses it.

Industrial waste water can be reuse for various purposes such as-

1-   Irrigation

2-   Cooling

3-   Rinsing

4-   Feed water

The benefits of recycling industrial wastewater are many:

• Reducing fresh water costs
• Increasing operational efficiency
• Reducing wastewater flows
• Improving production capacity due to increase availability of clean water
• Providing good "corporate citizenship" in your community, particularly in regions where seasonal droughts can occur
• Reducing the size of your water footprint

• Impacting the image of your company positively. If negative publicity around a company's water use can adversely impact a company's sales/growth then positive attention for water recycling can be beneficial.
• Industrial water may be reused in many different ways. Before determining how to reuse waters, you should consider where potential water reuse opportunities exist.

It is estimated that water consumption is cut down by at least 50 percent by industrial wastewater reuse and this figure can even go high as 95 percent. While the use of water used in boilers by cooling has been always prevalent, it is now becoming imperative for industries that use a lot of water to consider the reuse of wastewater because of the costs of looking for water sources and to reduce the consumption of it. This has also been vastly influenced by environmental concerns.

Industries that have a very high potential for industrial wastewater reuse are those of glass, steel, cotton textiles, pulp, and paper. There are other industries like food processing, chemicals, fertilizers, dairies, petroleum refining, and distilleries that have a potential also for reuse of industrial wastewater. There are however industries like tanneries, rubber, pesticides, paint manufacturing and aluminum where the potential is very low because of the high concentration of pollutants in the wastewater and inadequate cheap technologies for treating such waste water.