The Biological Method For Treating Textile Effluent

THE BIOLOGICAL METHOD FOR TREATING TEXTILE EFFLUENT Nature recovers a lot of pollution from the very beginning of earth. As the energy transfer from one stage to another by means of different action, bacteria are very much essential living being of earth. It helps us a lot to prevent pollution. Actually when wastages can not control by the environment then that wastages are termed as pollutants. In textile wet processing basically organic compounds are used to control process. How ever inorganic compounds are also essential. Mainly two methods are applicable to remove such organic compounds one is by coagulation which is followed by flocculation and to sediment. And another is degradation of organic compound by means of bacteria. Here mainly organic compounds are used to be the food of bacteria nothing else. Here sludge are formed which are sediment by means of gravity. Later the sludge are separated and deposited in sludge tank. But bacteria can not control the pH value and can not reduce the chemical oxygen demand (COD). For this manner some of acid addition is required. If acid is not required to neutralize the effluent it must require for providing acidic medium for bacterial action. In biological treatment COD is controlled by aeration by means of blower. The biological method for effluent treating is discussed below according to the ETP of Comfit Knit Composite Limited.

Screening: Screen is the synonyms of filtration. Here action is nothing but the filtration or separation of suspended solid from the liquor or raw effluent.. Separately three screening chamber is used to filter suspended solid. Drain from two different units has a net of iron having 1 sq. inches of each hole. It separates the different foreign materials like bulk of trees, leaves, polyethylene bag etc. picture will describe better.

Picture: filtration of suspended solid by iron net

To treat 100 cubic meter per hour, here three screening chamber are used. Suspended solid which can pass through the first filter are finally filtered here. The screen has around 250-300 slits per sq inches. This screening system has automatic wiping action with four wipers or brush. Cotton fibers, yarns with the liquor are deposited on the screen and raw effluent passes through the slits. This is a simple filtering method. The screen is curved around 90 degree angle (ie, quarter part of circle). Curved screen provide a strong control of wiping by rotating wiper. Materials deposited here are calculated for a cubic meter effluent load, which is, 76.8 mg. there is a tray just above the screen in which suspended solids are deposited.

Suspended solid Picture: deposition of suspended solid from the screen Wiper is rotating at an interval of 9 minutes for 3 minutes at 1.5 rpm speed. Its rotation speed duration of pause is regulated on the basis suspended solid’s load. The next picture will provide a clear conception.

Tray deposited suspended solid

Screen

Picture: Screening of raw effluent. Raw effluent Wiper After screening of raw effluent raw effluent is stored in storage tank.

Storage tank: Raw effluent is stored after screening in the storage tank. There are two storage tanks. Delivery of raw effluent from storage tank is carried out by means of submergible pump. It has an automatic lifting plan to deliver raw effluent into the next section of ETP. This automation is programmed according to the effluent load in the storage tank which ensures an uniform flow of effluent for every section. The pump gets off automatically after lifting a certain volume of effluent which is varied according to effluent load. In each turn this lifting pump arrangement is allowed to discharge 50 cubic meter of stored effluent. In between two storage tanks there is a bi-pass channel. Through which stored effluent can pass from one store to another. Bi-pass is used when any of the lifting pump is off for maintenance.

Pictures: storage tank 1& 2

Picture: delivery from storage tank.

Equalization chamber:

Pictures: equalization tank The term equalization means to make equity. Here equalization means to form an identical effluent of different characteristics. The effluent comes from storage tank are mixed homogeneously. The effluents from different stages like scouring, dyeing, soaping etc. are mixed homogeneously here. That’s why it is also termed as Homogenizing chamber. The treatment of equalization chamber is basically depending on character of effluent. Here temperature of effluent is decreased. This chamber equalized with respect to its characteristics, homogeneity, flow and a uniform pollution load as well as to make bacteria acclimatized. In this ETP two vertical agitator and flow jet are used homogenize to mix the effluent. These two agitators are not using as they can not carry any advantage for the treatment. Water jet is carrying out the mixing action continuously and it is placed at the bottom of the chamber. If the mixing is not accomplished homogenously then it will hamper the further treatments resulting inefficient treatment. As the temperature of the effluent is higher than the atmospheric temperature it is necessary to be reduced to meet the temperature demand of the bacterial action as well as the environment. The volume of effluent treated is 2000 cubic meter. Here no cooling mechanism is added as this chamber possess 200 sq meter of open area which is directly in contact with air. Again the effluent is treated here for 20 hours which is another reason for the effluent being cooled. So the cooling action for the effluent is carried out naturally. It should be noted that the movement of molecules provide reduction of their internal energy. Due to the flow jet the effluent keeps on flowing which results the reduction of the thermal energy thereby dropping temperature.

Neutralization Chamber:

Neutralization refers to preparing neutral. Here neutralization stands for neutralizing the effluent solutions’ pH value. First of all we are discussing about pH. A term used to express the intensity of the acid or alkalinity source. pH represents the effective concentration (activity) of hydrogen ions (H+) in water. This concentration could be expressed in the same kind of units as other dissolved species, but H+ concentrations are much smaller than other species in most waters. The activity of hydrogen ions can be expressed most conveniently in logarithmic units. pH is defined as the negative logarithm of the activity of H+ ions: pH = -log [H+] Where [H+] is the concentration of H+ ions in moles per liter (a mole is a unit of measurement, equal to 6.022 x 1023 atoms). Because H+ ions associate with water molecules to form hydronium (H3O+) ions, pH is often expressed in terms of the concentration of hydronium ions. In pure water at standard atmospheric temperature, H3O+ and hydroxyl (OH-) ions exist in equal quantities; the concentration of each is 1.0 x 10-7 moles per liter (mol/L). Therefore, pH of pure water = -log (1.0 x 10 -7) = -(-7.00) = 7.00. Because pH is defined as –log [H+], pH decreases as [H+] increases (which will happen if acid is added to the water). Since pH is a log scale based on 10, the pH changes by 1 for every power of 10 changes in [H+]. A solution of pH 3 has an H+ concentration 10 times that of a solution of pH 4. The pH scale ranges from 0 to 14. However, pH values less than 0 and greater than 14 have been observed in very rare concentrated solutions. The U.S. Environmental Protection Agency (U.S. EPA) sets a secondary standard for pH levels in drinking water: the water should be between pH 6.5 and 8.5. But the Department Of Environment (BD) suggests the pH value in between 6- 9.

Very high (greater than 9.5) or very low (less than 4.5) pH values are unsuitable for most aquatic organisms. Young fish and immature stages of aquatic insects are extremely sensitive to pH levels below 5 and may die at these low pH values. High pH levels (9-14) can harm fish by denaturing cellular membranes. Changes in pH can also affect aquatic life indirectly by altering other aspects of water chemistry. Low pH levels accelerate the release of metals from rocks or sediments in the stream. These metals can affect a fish’s metabolism and the fish’s ability to take water in through the gills, and can kill fish fry. In cotton dyeing industry effluent is always alkaline then water in nature. So it is required to reduce the pH value. For reducing, acid dozing is essential according to the pH and effluent character. Here in this ETP no acid dozing is required for neutralizing. As the effluent possesses a standard value of pH ie, 8.2 where as the standard value of pH is 6-9 (Recommended by DOE) for treated effluent. But there is a pipe line for acid dozing. If the pH value rises than the limit 8.9 then automated acid dozing will be started. This automation is controlled at panel board. In panel board there is an alarm to inform operator. However from the beginning of ETP they did not need to apply acid for neutralization. This due to their high liquor ratio at every stage of wet processing and washing water, rinsing water, dyeing water etc. are directly discharged to ETP. It should be informed that they use a lot of water for rinsing purpose. In neutralization tank effluent is kept for 6 minutes and volume of effluent is 10 cubic meter.

Sludge return tank: First of all we are discussing about sludge. The settable solids separated from the effluent during sedimentation (clarification). This is simply the degraded part of polymers.The sludge is very toxic in nature and needs to be dealt with very carefully. Under no circumstances it should be mix with the environment again Sludge return tank is not common among biological effluent treatment plans. How ever it brings profit for a knit dyeing unit. We know that effluent discharging from knit dyeing unit possesses low quantity of food for bacteria. For that manner here developer decided to recycle the sludge. Here not only sludge is returned but also food for bacteria is also provided. And Sulphuric acid is also given here. As for bacterial action pH around …..

Picture: sludge return tank

In sludge return tank sludge, nutrients and acids are given for the bacterial action. It is about 60 cubic meters in volume. And effluent is treated here for 36 minutes. As nutrient urea is provided at 2.706 gm per cubic meter of effluent, TSP at 1.875 gm per cubic meter of effluent and 98% pure sulphuric acid at 72 cc per cubic meter of effluent.

Picture: sludge return tank. Effluent flows from neutralization tank to sludge return tank by means of two pumps. This addition of sludge return is a beneficial step for environment. And quality of treatment results best by means of bacteria. If the sludge does not return then a significant amount of bacteria may die due to food, as a result bacteria can not get when it requires. Sludge returning helps bacteria to run its life cycle. It should be noted that manufacturer demanded that sludge is a poor food for bacteria then the polymeric compounds found in effluent. As knit dyeing process possesses less BOD, that’s why sludge retuning is essential. But bacterial treatment can not degrade dyes totally.

Aeration tank: In aeration tank basically aeration is occurred by means atmospheric air. Air from atmosphere is firstly filtered then blower sucks them and flows air to the aeration tank through 860 diffusers. There are three blowers are used to perform their function. Every blower is running for 16 hours in the set of two. And every blower pauses blowing for 8 hours. Usually two blowers are running all the time to blow 1500 cubic meter of fresh air per hour. 860 diffusers are uniformly distributed around the 470 sq meter area.

air filter blower Picture: blowers for aeration.

Picture: aeration system to tank

Diffusers are kept at bottom of the tank floor. Blower takes air from atmosphere and then it passes though pipe to the diffusers. Then diffusers supply air as well as oxygen to the effluent. These blowers possesses the 25% cost of the plan. Blowers are highly stronger than the normal. These blowers are micro chipped program with the reader JUMO GMBH (it is a dissolve oxygen reader). When the dissolved oxygen comes up to 2.6 mg/L then the inverter of blowers’ motor worked to reduce rpm of blower. These are the description of plan for aeration tank. Now the question how does the function of air. This aeration does nothing but increase the quantity of dissolve oxygen. 4700cubic meter effluent is treated here for 47 hours, it’s a huge time during this time oxidative chemicals are liked to fill up their oxygen demand from the air. That’s why increasing amount of dissolved oxygen is required to meet the demand. Without this the aquatic life in this tank ie, bacteria demands oxygen which is also filled up by this dissolved oxygen. These are all about air at aeration tank. During aeration bacteria is also involved to do degrade effluents. Next chemical reactions will describe better.

The bacterial action: COHNS

+ O2 + Bacteria + TSP & UREA

CO2 + NH3 + Energy + Other end Products

TSP and Urea is used as food for the microorganism COHNS + O2 + Bacteria C5H7NO2 + 5O2 Question to sir?

C5H7NO2 (new bacteria) CO2 + NH3 + 2H2O

Apart from the above basics reaction there are some other reactions that take place in the aeration tanks. During aeration the oxygen reacts with C, S and N which is shown below. C + O2 CO2 S + O2 SO2 N + O2 NO2

Pictures: the aeration tank

Picture: the delivery from aeration tank Aeration tank of this plan play the chief role for treating effluent. Polymers are here polymers are degraded, but only biodegradable polymeric chemical compounds are degraded. Manufacture of this plan may appreciate for this simple technique but for environment dyers must need to use selective chemicals. But it is appreciated for knit dyeing industries as the knit dyeing process possesses almost eco friendly chemicals. But for printing like industries effluent characters can not support this type of effluent treatment plan.

Lamella filtration:

out let of treated effluent Picture: Lamella filtration inlet of effluent (Red line shows the effluent entrance direction & the green shows the treated effluents’ exit direction) This is a special kind of filtration system of sludge from treated effluent. Mainly sludge is denser than the water, which results its sedimentation at the bottom of the chamber. There are eight units for filtration they are separated from each other by thin tin sheets. Inlet is

brick walled and the inlet pipes (8) are at 2 feet depth from the surface of treated effluent. Treated effluent comes out through over flow and the sludge sediment at the bottom of lamella filtration system. Lamella membranes are special kinds here. These are not usual lamella membrane. These are like shits having smooth surface on face side. Water molecule cannot pass through the membrane of these shits. In between two shits .02mm space has kept for the passage of sludge. Water can also pass through this passage. For total filtration system 8 lamella chambers are there. Each chamber there is huge amount of lamella sheets. There number is not possible to count. After every three months lamella sheets are washed by water flow as no sludge may present there. Lamella membranes are inclined at 45 degree or at less. A sketch may describe better.

This 45 degree inclination of membrane brings an advantage to flow treated effluent out of the chamber. Effluent with sludge hits at the membrane and sludge likes to fall down through the space with some liquids and the maximum liquid tends to bounce back perpendicularly with the slope. This action results a over flow of treated effluent. Picture will describe better.