Declaration
I am here to declare this report is a recorder original work and being submitted to the Ethiopian institute of technology mekelle university department of chemical engineering and also this is in requirement partial fulfillment for the accomplishment of my four months internship semester. This report has not been submitted to any other university or institute for the fulfillment of the requirement of the internship semester.
Acknowledgement
first of all I would like to thank god for helping me to finish my internship Program. In addition to that I would like to express my gratitude to Mr.Girma, my industry advisor who gave me an efficient care and
constrictive recommendation and suggestion regarding to the project I have performed in the company. And also I would like to thank my university advisor Mr.Getu Adana for his helpful advice and suggestion during my
internship period. Executive
summary the main
objectives of this project was to design secondary waste water treatment system for Awassa textile Share Company by determining the volume, diameter of trickling filter and by adjusting the ph. level of effluent and also by BOD measuring and using important laboratory measurements and other treatment procedure. I hope this project will help you to understand how to design waste water treatment for plants.
Chapter one introduction
background of the company brief history
Awassa textile factory is one of the textile factories in Ethiopia that was established in November 1989.the textile mill is order factory located in the southern people regions administration capital city Awassa 275 km south of Addis Ababa.
It is design to produce various kinds of woven fabrics from 100% cotton as well as finish polyester cotton blended and 100% polyester fabrics.
The equipment’s of the factory are automatic bale pluckier and high speed spinning machine,ragier looms, air conditioning system,
finishing machine in the factory and almost all are Italian origin. The factory land holding is 37,000 square meters of this 31,275 is covered by building and 31,000 square meter by an efficient treatment lagan.
The total man power of the company is 970 the work force to operate and maintain the installed machines and equipments.the present monthly wage bill is 1.2 million birr.Awassa textile share company uses cotton as a Raw material to produce fabrics. The main process includes blowing, carding, spinning warping, sizing, weaving,
desizing,blenching,washing,dyeig,printing,calandering and garment . The main inputs are polyester and cotton. But in currently the factory uses cotton as the main input. Because polyester is so much
There are so many type of product the customer need from the company. Those are yarns, fiber, lap sheet, cope windings, abujede, ranger, bed sheet…etc.
They have more customers. Among them Addis Ababa foam factory, federal police force, debreberhan blanket factory and
other local merchants.
Sources of raw materials
THE OVERALL ORGANIZATION AND WORK FLOW The factory divided in to three main parts. These are
2 Caustic soda Zeway caustic factor
3 Sulpharic acid Awash aluminum sulphate
4 Dye staff and chemical -different supplier
5 Salt - affar
Objective of the company
vision-to be competent in the world market to support vision of country and play a role in leading textile industry.
Mission-to builds capacity of factory’s productions, cumulativeness, working culture and potential to export and domestic customers to supply the quality fabrics.
-To be profitable and competent in world market and domestic market to supply our country economy
objectives-to continuously develop modern and scientific methodology work culture and system.
-to create broad and sustainable market by supplying competitive product those fulfill customer’s requirement and meeting the demand at fair price with highest quality.
Weaving Finishing
OVER ALL ORGANIZATION, MANAGEMENT AND MAN POWER OF AWASSA TEXTILE SHARE COMPANY
The overall activities of the company are managed and administrated by the General Manager, who is assigned by and accountable to the Board of Directors. Board members are appointee of the public enterprise supervisory authority with a responsibility of formality and setting policy, resolving policy issues and follow up of development programs etc…
All functional departments and services are lead and supervised by their respective department managers and service managers who are directly reporting and accountable to Deputy General Manager. This does not include the audit service who is directly reporting to the board of directors.
The General Manager is assisted by the deputy general manager, the department managers and service manager in formulating and revision of operational policies, exclusion of day-to-day activities, resolving of operational problems and preparation of operational plan, budget and establishment of medium and long term development programs.
, The overall work force engaged in the different activities of the company is more than 1300 (permanent and temporary) of which 58% are male and 42% are female with a wage bill of more than 400000 Birr monthly.
Flow Chart Organization Structure of ATSC
Overall Process Description
Raw Materials
Board of
Directors
General
Manage
Deputy
General
Administratio n Department
Finance Department
Commercial Department
Production & Technical Department
Quality Control
Service Planning &
Informationservice
Store & Property Administration service
Audit
Cotton is the only raw material of the factory. The cotton is supplied from Gondar and Addis Ababa. The cotton is transported and stored in the store house, then, it is taken to be processed.
Transporting and storing activities affect the quality of the cotton as well as the quality of the product. So care should be taken on transportation and storage activities.
Properties of Cotton
Cotton is a natural fiber and it is harvested from the cotton plant. The properties of cotton are many, it is soft, versatile and strong, to mention a few. These qualities make it ideal for clothing and many other items.
cotton
• Cotton fabrics show good durability and utility. Cotton is a chemically stable material; it stays undamaged even under the continuous exposure of weak acids and alkalis.
• High water-absorbing capacity. In humid atmosphere cotton fabric can absorb 27% of water without getting damp.
• It has low thermal-conductivity; therefore it is an ideal material for both summer and winter clothes: in summer it prevents your skin from heat, and in winter it preserves the warmth of your body.
• Cotton fabrics have very low elasticity characteristics, so they almost don't stretch.
• They are easy washable and can be ironed even at high temperature.
• It is soft
• Looking at the above unique qualities of cotton it is easy to understand why it is the most popular and best-selling fabric in the world.
• The other imputes are
• sizing chemicals (PVA, starch),
• and desizing chemicals (stabilizer, H2O, NOH),
• dyeing chemicals (dye, H2O, NOH),
• printing chemicals (dye, jelly material),
• Diesel thermal oil and water.
Spinning section
Spinning
spinning is the process of converting the fiber to yarn by opening, cleaning, mixing, straightening, drafting and twisting of fibers
• the main parts of spinning section
1.mixing 2.blow room 3.card 4.comber
5.drawing 6.simple 7.ring 8.auto cone 9.conditioning 10.packing
mixing
Blow room
the name blow room indicates that “transfer of fibers from one machine to other blow room machine by air flow”
It’s where preparatory process of opening, cleaning and more mixing is carried out. It’s also removes heavier impurities of cotton. The impurities became less as cotton pass from one blow room to the next.
Card carding is
Comber
combing is the process of extracting the short fiber from cotton for making high quality yarn from longer fibers. The combining process is normally used to produce smoother, finer stronger and more uniform.
Drawing
the process of straightening and paralleling the fibers by stretching {drafting} and leveling {doubling} is known as drawing. The input materials of drawing is carded or combined sliver and the output is drawing sliver
Simplex
Ring
In this process thin strand {roving} is again drafted and twisted on
smaller called ring bobbin
.
Auto cone
the winding process has the basic function of obtaining a larger package from several small ring
bobbins. Further functions
found.
Conditioning
conditioning is the process in which yarn is conditioned {moisturized} for better performance such as strength, luster, and handle etc.is called yarn conditioning.
Packing
packing process involves storage of cones in bags for proper transfer of material without damaging the yarn.
Weaving section
Warping
warping is the process of certain number of yarn with a given length is wound in the wrappers with warping beam. This beams are consists of a large number of threads arranged in parallel orders the objective of warping is to present a continues length of yarns to the succeeding process with all ends
continuously present and the integrity and elasticity of the yarn as wound fully preserved.
Warping machines
Sizing
sizing is carried out to increase the strength and smoothness of the yarn and to reduce yarn breakage by using some chemicals such as PVA, starch, Texel softener, water and other additional chemicals.
Sizing machine
Finishing room
The final chemical treatments of the fabric which are carried out to impart special characteristics e.g. softening, stiffening, crease resisting, flame retarding, soil release effect etc. is known as textile finishing. The aim of the finishing is to improve the outward appearance and the quality of the fabric, and impart its specific properties.
This stage includes the final operations necessary for making the textile presentable and attractive. The finishing process imparts the final aesthetic, chemical and mechanical properties to the fabric as per the end user requirements. Common finishing processes include: pretreatment wet processes (DE-sizing, washing, dyeing printing and calendaring)
DE-sizing:
DE-sizing is done in order to remove the size from the warp yarns of the woven fabrics. Warp yarns are coated with sizing agents prior to weaving in order to reduce their frictional properties, decrease yarn breakages on the loom and improve weaving productivity by increasing weft insertion speeds. The sizing material present on the warp yarns can act as a resist towards dyes and chemicals in textile wet processing. It must, therefore, be removed before any subsequent wet processing of the fabric.
If the fabric is woven from sized yarn, DE-sizing is essential before subjecting it to other treatments. For this, the fabric must be soaked in 0.5% aqueous solution of amylase enzyme for 8 hours ensuring that it is completely immersed in the solution. After the size has been removed, the fabric is subjected to a hot and cold water wash.
DE-sizing, either with acid or enzymes then removes size from the fabric, so that chemical penetration of the fabric in later stages is not inhibited. DE-sizing effluents have very high organic concentrations, contributing 40-50% of the total organic load from the preparatory sequences. Gums and PVA may be removed by a simple hot wash but starch and its derivatives have to be made soluble by soaking with acids, enzymes or oxidants before being removed by a hot wash. The most commonly used DE-sizing chemicals are:
Hydrogen per oxide (H2O): for bleaching and oxidizing,
Stabilizer: to stabilize H2O not to react with NOH.
Sodium hydro oxide: to develop and open the cotton for dyeing.
Scouring:
Scouring is the first process carried out with or without chemicals, at room temperature or at suitable higher temperatures with the addition of suitable wetting agents, alkali and so on. Scouring removes all the waxes, pectin’s and makes the textile material hydrophilic or water absorbent.
Scouring is carried out to remove impurities that are present in cotton, both natural (e.g. waxes, fatty acids, proteins, etc.) and acquired (such as size, dirt and oil picked up during processing). This is usually done at high temperatures (above 100 °C) with sodium hydroxide and produces strongly alkaline effluents (around pH 12.5) with high organic loads. They tend to be dark in color and have high concentrations of Total Dissolved Solids (TDS), oil and grease.
The scouring is normally done either on a Kier, a J Box, or an open width pad roll system, or on open width continuous plant. Common scouring agents include detergents, soaps, and alkalis, antistatic agents, wetting agents and lubricants.
Bleaching
Bleaching is chemical treatment employed for the removal of natural coloring matter from the substrate. The source of natural color is organic compounds with conjugated double bonds , by doing chemical bleaching the discoloration takes place by the breaking the chromospheres , most likely destroying the one or more double bonds with in this conjugated system. The material appears whiter after the bleaching.
Depending on whether the textile is synthetic or natural, one of two bleach types are added to the material. After textile bleaching, optical whiteners are added to enhance the white color and to make the material easier to dye. Scouring is done beforehand to remove some of the textile additives and to make the textile absorbent.
When a textile is grown or made, it encounters many add-ons that make the textile easier to construct or keep insects or fungus from ruining the material. A few of these additives are
fungicides, pesticides, lubricants and worm killers. While these add-ons are considered necessary during the growing or creation phase, they tend to be poisonous and can be harmful to
consumers. While removing the poison, textile bleaching also makes the textile white, rather than the natural brown color of most textiles, and easier to dye.
Fig.bleaching room
Washing
Washing is a process which is taking place following the desizing process and is used to remove impurities from the surface of fibers, yarns and fabrics and to clean the fabric from dust and other wastes. Washing is done with soap and hot water.
Fig washing machine
Important factors in washing are: water characteristics
choice of soaps and detergents
hydro mechanical action
temperature and pH
rinsing stage
Dyeing
Finally, cotton is an absorbent fiber which responds readily to coloration processes. Dyeing, for instance, is commonly carried out with an anionic direct dye by completely immersing the fabric (or yarn) in an aqueous dye bath according to a prescribed procedure. For improved fastness to washing, rubbing and light, other dyes such as vats and reactive are commonly used. These require more complex chemistry during processing and are thus more expensive to apply. The common dyeing chemicals are Sodium bisulphite: to fix the colors, Hydrogen per Oxide (H2O):
to oxidize the colors. Acetic Acid: to neutralize NaOH base.
Printing
Fig. printing machine
Fig. printer Deign
.
Calendaring
Calendaring, a finishing process by which fabric is pressed into sheets and smoothed, glazed, polished, or given a moiré or embossed surface. The material is passed through a series of rollers; the resulting surface depends on the pressure exerted by the rollers, on their temperature, composition, and surface designs, and on the type of coating or glaze previously applied to the material to be calendared.
calendaring machine
. Packing:
After final inspection, the garments are poly-packed, dozen-wise, color wise, size ratio wise, bundled and packed in the cartoon. The cartoon is marked with important information in printed form which is seen from outside the cartoon easily.
Chapter three
3. The Overall Internship Experience
3.1 Overall Benefits gained from the internship includes the following
3.1.1 Improving Practical Skills
The theoretical knowledge that I have learned three years in the past must be fulfilled in advance to develop practical skills through this internship program on different departments of the company at different working machines.
During the time of this internship program, I have developed the following practical skill.
How to treat waste water.
How to check the pH variation in wastewater.
How to measure the BOD level
How to design waste water treatment system
3.1.2 Upgrading of theoretical knowledge
As we know coming before in the previous theoretical awareness or familiarity and actual place could be distinguishable, so the objective reality and theoretical knowledge may be slightly different. The above theoretical learning is upgrading during my internship program by seeing and doing some work. So the internship program is essential for students to up grad theoretical knowledge’s.
3.1.3 Improving interpersonal communication skills
Developing interpersonal communication skill is essential to organic life in today’s work place. Almost all kind of work requires communicating with other persons who shares ideas. But peoples have different behavioral characteristics, some are emotional and others are based on
reason and so on. In this company also have the above situation. So we readily know the behavior of those people.
Each and every person mentioned above has different behaviors to communicate. In my day to day activities I contact with each person. I have developed the idea of communication with each person in the company and also I know what type of word to use to communicate with the person who is the member of the company. In general, I have observed that it is must to create smooth relationship among different workers in order to get social life in addition to improving practical and theoretical knowledge.
3.1.4 Improving team playing skills
Team playing skills are one of the basic requirements for the proper working of a good company, regardless of its size and service. A company with suitably functioning devote to a special task will always have a graph going up words, with different workers working in different departments such as, spinning department, weaving department and finishing department. Team playing is a basic requirement for getting solution for a specific problem and to share experience. During internship I have developed a team playing skills with operator to gate experience, with engineers to grasp knowledge, and so on.
3.1.5 Improving leadership skills
Although leadership has many definitions, I want to talk any contextual meaning related to this project, it is defined as the process of influencing an organized group towards achieving its goal and a leader is a person who has strong principles, courage’s and dedication to a clear vision, developing a powerful vision, building a strong team and bringing out the best, in those our institution leader are key facts to experience success as a leader. This indicates that the leader should accountable and transparent to their follower’s.
Generally, leader and followers should have integrated relations during working time. In my internship program, I get leadership skills in terms of:
How to communicate with workers on working issue.
How to initiates the workers.
How to give service for a person.
How to share knowledge.
How to share experience.
3.1.6 Understanding about work ethics related issues
Actually any people should have ethics not only in the work place but also in the social life. In my understanding work ethics is a set of values on hard work and diligence, it also believes in normal benefit of work and its ability to enhance. However, in this company some people loss their ethics. It may be due to personal case or the company leadership system. Generally, work ethical employee is a key to productivity. This is to near for a factory to be productive; all of the employees have to be disciplined and ethical in their working environment. Generally, work ethics have broad definition.
Not absent without reason (except during special cases, dead of family members, empowered with knowledge and skills to become effective entrepreneur. The state of being an entrepreneurship can be realized when one engages in profitable risks and creates something of value. It is defined by their habit of innovating and redefines market trends and limits. Generally, entrepreneurs who are able to create worthwhile good and services give a greater impact to society; have faithful and often tested with good results. Generally, entrepreneurship can be realized when we engage in profitable system and create something value from theoretical to practical learning. This means a person who is able to develop a new business area and affect the global economic condition.
Chapter four
4. Case Study (project)
4.1. Designing secondary and introducing tertiary water treatment system in to the company
4.1.1 Introduction
Textile wastewater includes a large variety of dyes and chemical additions that make the environmental challenge for textile industry not only as liquid waste but also in its chemical composition. Main pollution in textile wastewater comes from dyeing and finishing processes. Textile dyeing and finishing industries are one of the biggest users of potable water as well as the chemical additives during various steps of textile processing.
Fig effluent waste
In order to reduce this risk I was initiated to do appropriate waste water treatment system
for Awassa textile Share Company.
The treatment system includes
Primary
Secondary (biological)
Tertiary(Advanced waste water system)
4.1.3. Primary wastewater treatment
The first step in modern wastewater treatment, primary treatment removes solids that are suspended in the wastewater. First the waste is screened to remove larger objects, then grit is removed, and finally the rest of the solids are extracted using gravity in large sedimentation tanks.
Screen chamber girt chamber sedimentation tank
4.1.4. Secondary waste treatment system
This treatment method removes dissolved oxygen demanding organic substances by using microorganism to convert degradable organic matter into cell or energy.
We have two type of secondary treatment
Aerobic
Fig. Trickling filter
4.1.5. Tertiary treatment (Advanced waste water treatment)
Tertiary treatment is simply additional treatment beyond secondary. Tertiary treatment can remove more than 99 percent of all the impurities from sewage, producing an effluent of almost drinking-water quality. The related technology can be very expensive, requiring a high level of technical know-how and well trained treatment plant operators, a steady energy supply, and chemicals and specific equipment which may not be readily available. An example of a typical tertiary treatment process is the modification of a conventional secondary treatment plant to remove additional phosphorus and nitrogen.
4.2. Problem of Statement
The factory does not have any secondary and tertiary wastewater treatment system. The wastewater is discharged directly into the surrounding environment with no regard to the BOD, COD and/or heavy metals content of the water.
The waste water discharged to the environment affects the life of aquatic organisms, wild animals, plants, human beings, and it pollutes the whole environment.
So in order to minimize this risk appropriate secondary & tertiary water treatment systems must be done.
4.3. Objective
4.3.1. Genera objective
How to design secondary and introduce tertiary treatment systems in to Awassa
textile share company
4.3.2. Specific objective
To designing trickling filter
To adjust PH level,
To adjust Aluminum Sulfate, and sulfuric acid flow rate.
To measure BOD level.
4.4. Literature review
During the last 20-28 years, the factory has been ever increasing effort to somehow arrange manufacturing processes in such a way that they cause minimal damage to the environment. The textile industry approximately releases 300 liters/minute of liquid waste these shows
300×60 = 18,000 liter/hour
18,000×24 = 432,000 liter/day
432,000×30 = 12,960,000liter/month
As it is known Awassa textile Share Company releases this liquid wastes directly in to the environment almost for 20 years without any treatment
Fig.2.6 liquid waste
• These wastes have great impact on the environment by damages aquatic animals like fish
• Humans and animals around rural area used this contaminated water for drinking and for other consumptions this will be the case for different diseases.
Fig. effect of waste on human’s life
During 2003 through 2005 efforts focused on waste treatment as the method and regulations as the instrument. The company starts to control the waste by end of pipe treatment system.
End-of-pipe treatment is, by definition, not pollution prevention. However, it is an important aspect of pollution control and it sometimes competes financially with pollution prevention options when facilities are developing pollution control strategies. To make informed decisions about implementing pollution prevention alternatives that include consideration of all applicable costs and potential savings requires accurate data.
Wastes from textile industries are;
Sodium Silicate or Organic Stabilizers,
Acetate,
Stearate,
Spent Solvents and Softeners
Treatment mechanisms
4.4.1. Primary treatment
The objective of primary treatment is the removal of settle able organic and inorganic solids by sedimentation, and the removal of materials that will float (scum) by skimming.
Approximately;
30% of the incoming biochemical oxygen demand (BOD5),
60% of the total suspended solids (TSS) and
65% of the oil and grease are removed during primary treatment. Some organic nitrogen, organic phosphorus, and heavy metals associated with solids are also removed during primary sedimentation but colloidal and dissolved constituents are not affected. The effluent from primary sedimentation units is referred to as primary effluent. The raw effluent first inters in to screen which is the first operation in waste water treatment.
Screening- is the first unit operation in waste water treatment system.
It uses physical barriers (screens) as a removal mechanism.
Primary objective of screening is to remove coarse(large ) solids such as
rages, sticks, plastics, etc
It helps to protect pumps and other mechanical equipments from damage
Prevents solids from clogging valves and other accessories in the treatment
plant.
Screen
Grit removal;
Grit chambers are used to remove inert or grit materials in waste water treatment plant.
Girt includes sand, gravel, cinders, and other heavy materials with specific gravity
greater than organic solids.
Specific gravity of girt ranges from 2.4 to 2.65.
Grit chambers are commonly located after screening and before the primary
Grit chamber
Fig. girt chamber
Aeration
An aeration tank is a place where a liquid is held in order to increase the amount of air within it. The most common uses of aeration tanks are in waste water recovery, as the high oxygen levels will increase speed at which the water is cleaned. The increased oxygen promotes the growth of beneficial biological material. In the aeration tank, air diffusers are found and designed to: ensure uniform permeability and produce a flow of fine air bubbles.
Aeration tank
Fig. aeration tank
Sedimentation;
Sedimentation, or clarification, is the process of letting suspended material settles by
gravity.
Suspended material may be particles, such as clay or silts, originally present in the source
water.
More commonly, suspended material or flock is created from material in the water.
Sedimentation is accomplished by decreasing the velocity of the water being treated to a
point below which the particles will no longer remain in suspension. When the velocity no longer supports the transport of the particles, gravity will remove them from the flow.
FACTORS AFFECTING SEDIMENTATION
Several factors affect the separation of settle able solids from water. Some of the more common types of factors to consider are:
Particle size
Water temperature
Current
Several types of water currents may occur in the sedimentation basin.
Density currents caused by the weight of the solids in the tank, the concentration of solids and temperature of the water in the tank.
Eddy currents produced by the flow of the water coming into the tank and leaving the tank.
Fig. sedementation tank
4.5.Methodlogy
By using laboratory measurement the BOD level is determined this value helpes to design trickiling felter we can find it as follows;
Laboratory Measurement of BOD Testing Procedures
emphasis placed on the reason for each step rather than the details. Since the detailed procedures can be as follows:
Step 1. Clean the incubation bottles with a detergent and drain. Invert bottles in a water bath to prevent contamination between cleaning and use.
Step 2. A special 300mL BOD bottle is completely filled with sample water that has been appropriately diluted and incubated with microorganisms. The bottle is then stoppered to exclude air bubbles. Samples require dilution because the only oxygen available to organisms is dissolved in the water. The most oxygen that can dissolve is about 9 mg/L, so the BOD of the diluted sample should be between 2 and 6 mg/L.Samples are diluted with special dilution water that contains all of the trace elements required for bacterial metabolism so that degradation of the organic matter is not limited by lack of bacterial growth. The dilution water also contains inoculums of microorganisms so that all samples tested on a given day contain approximately the same type and number of microorganisms.
The ratio of undiluted to diluted sample is called the sample size, usually expressed as a percentage, while the inverse relationship is called the dilution factor.
Mathematically, these are:
Sample size (%) = [vol.of undiluted sample/vol.of diluted sample] * 100
Dilution factor = vol.of diluted sample/vol.of undiluted sample = 100/sample size
The appropriate sample size to use can be determined by dividing 4 mg/L (the midpoint of the desired range of diluted BOD) by the estimated BOD concentration in the sample being tested. A convenient volume of undiluted sample is then chosen to approximate to this sample size.
Step 3. Blank samples containing only the inoculated dilution water are also placed in BOD bottles and stoppered. Blanks are required to estimate the amount of oxygen consumed by the added inoculums in the absence of the sample.
Step 4. The stoppered BOD bottles containing diluted samples and blanks are incubated in the dark at 20oc for the desired number of days. For most purposes, a standard time of 5-days is used.
To determine the ultimate BOD and the BOD rate constant, additional times are used. The samples are incubated in the dark to prevent photosynthesis from adding oxygen to the water and invalidating the oxygen consumption results. As mentioned earlier, the BOD test is conducted at a standard temperature of 20oc so that the effect the temperature on the BOD rate constant is
eliminated and results from different laboratories can be compared.
Step 5. After the desired numbers of days have elapsed, the samples and blanks are removed from the incubator and the dissolved oxygen concentration in each bottle is measured. The BOD of the undiluted sample is then calculated using the following equation:
BODt = (DOb, t – DOs, t) dilution factor
DOs, t=dissolved oxygen concentration in sample after t days of incubation, mg/L.
Equipments and Reagents
Apparatus or equipments used for BOD test are as follows:
Incubation bottles: Incubation bottles should be made of glass and should
have a volume of 60ml or greater. Preferred bottles have a 300ml capacity having a ground - glass stopper, and a flared mouse.
Air incubator or water bath :(The incubator must be capable of
maintaining a temperature of 20oc and must keep the bottles in complete
darkness).
Oxygen sensitive membrane electrode, with appropriate meter.
Thermometers and dissolved oxygen measurement.
Test reagents or chemicals required are as follows:
Potassium hydroxide (KOH) : to absorb carbon dioxide gas (CO2)
Acid and alkali solutions, 1N of NaOH and HCl, for neutralization of caustic or
acidic wastewater samples.
Phosphate buffer solution: to provide the optimum environment for survival of
bacteria in the incubated sample, it is necessary to buffer the sample such that it maintains a pH of 6.5 to 7.5.
Nitrification inhibitor: to avoid nitrification
Dilution water, use distilled, tap, or natural water for making sample dilutions.
Pipette bulb.
Limitations of BOD test
Despite widespread use of BOD test, it has the following limitations:
BOD test measures only biodegradable organic matters.
Pre-treatment is needed if the sample contains toxic wastes.
The test loses its stoichiometric validity after the soluble organic matter present in the
solution has been used or exhausted.
The test uses an arbitrary long period of time, to obtain results.
By using this procedure the BOD level of the effluent of Awassa textile Share Company
is 220mg/L.
4.5.2. Secondary (biological) waste water treatment system;
Biological wastewater treatment is the use of bacteria to degrade and decompose organic materials during treatment.
The microbial community is the heart of any wastewater treatment facility. If the treatment system is having a problem, it’s critical to target and fix the root cause: A microbial community that isn’t performing well.
compounds, for example—biological wastewater treatment offers major advantages over alternative treatment strategies:
Lower operating costs compared to alternatives
Efficient degradation and removal of organic and inorganic compounds
Improved flexibility to handle a wide range of wastewater characteristics and flows
However, the key to any biological treatment system is ensuring that the existing microbial community has the right conditions to grow.
4.5.2.1. Trickling Filter
Trickling filter is an attached growth process i.e. process in which microorganisms responsible for treatment are attached to an inert packing material. Packing material used in attached growth processes include
And a wide range of plastic and other synthetic materials.
Process Description
The wastewater in trickling filter is distributed over the top area of a vessel containing
non-submerged packing material.
Air circulation in the void space, by either natural draft or blowers, provides oxygen for
the microorganisms growing as an attached biofilm.
During operation, the organic material present in the wastewater is metabolized by the
biomass attached to the medium. The biological slime grows in thickness as the organic matter abstracted from the flowing wastewater is synthesized into new cellular material.
The thickness of the aerobic layer is limited by the depth of penetration of oxygen into
the microbial layer.
The micro-organisms near the medium face enter the endogenous phase as the substrate is
metabolized before it can reach the micro-organisms near the medium face as a result of increased thickness of the slime layer and lose their ability to cling to the media surface. The liquid then washes the slime off the medium and a new slime layer starts to grow. This phenomenon of losing the slime layer is called sloughing.
The sloughed off film and treated wastewater are collected by an under drainage which
Types of Filters
Trickling filters are classified as high rate or low rate, based on the organic and hydraulic loading applied to the unit.
4. Recirculation ratio 0 0.5 - 3.0 (domestic wastewater) up to 8 for strong industrial wastewater.
Table
The hydraulic loading rate is the total flow including recirculation applied on unit area of
the filter in a day, while the organic loading rate is the 5 day 20°C BOD, excluding the BOD of the recirculant, applied per unit volume in a day.
Recirculation is generally not adopted in low rate filters.
A well operated low rate trickling filter in combination with secondary settling tank may
remove 75 to 90% BOD and produce highly nitrified effluent. It is suitable for treatment of low to medium strength domestic wastewaters.
The high rate trickling filter, single stage or two stages are recommended for medium to
relatively high strength domestic and industrial wastewater. The BOD removal efficiency is around 75 to 90% but the effluent is only partially nitrified.
Single stage unit consists of a primary settling tank, filter, secondary settling tank and
facilities for recirculation of the effluent. Two stage filters consist of two filters in series with a primary settling tank, an intermediate settling tank which may be omitted in certain cases and a final settling tank.
Process Design
Generally trickling filter design is based on empirical relationships to find the required filter volume for a designed degree of wastewater treatment. NRC equations (National Research Council of USA)
NRC equations give satisfactory values when there is no re-circulation, the seasonal
NRC equations: These equations are applicable to both low rate and high rate filters. The efficiency of single stage or first stage of two stage filters, E2 is given by
E2= 100
1+0.44(F1.BOD/V1.Rf1)1/2
For the second stage filter, the efficiency E3 is given by
E3= 100
[(1+0.44)/ (1- E2)] (F2.BOD/V2.Rf2)1/2
Where;
E2= % efficiency in BOD removal of single stage or first stage of two-stage filter,
E3=% efficiency of second stage filter,
F1.BOD= BOD loading of settled raw sewage in single stage of the two-stage filter in
kg/d,
F2.BOD= F1.BOD (1- E2) = BOD loading on second-stage filter in kg/d,
V1= volume of first stage filter, m3;
V2= volume of second stage filter, m3;
Rf1= Recirculation factor for first stage,
R1= Recirculation ratio for first stage filter,
Rf2= Recirculation factor for second stage,
R2= Recirculation ratio for second stage filter.
146.725= π D2
Trickling Filter Design to treat the waste of Awassa textile Share Company.
Problem: Design a low rate filter to treat 432,000 liter/day of sewage of BOD of 220 mg/l. The final effluent should be 30 mg/l.
Solution: Assume 30% of BOD load removed in primary sedimentation i.e., = 220 x 0.30 = 66 mg/l. Remaining BOD = 220 - 66 = 154 mg/l.
Percent of BOD removal required(E2) = (154-30) x 100/154 = 80.519%
BOD load applied to the filter(F1,BOD) = Flow rate x conc. of sewage (kg/d) = 432,000
liter/day x 154mg/l/106= 66.528 kg/d
To find out filter volume, using NRC equation
E2= 100
Depth of filter = 1.5 m, Filter area = volume/depth = 220.087/1.5 = 146.725m2, and
The diameter of the filter is 13.671m.
So in order to get 30mg/L BOD we need to construct a trickling filter with 13.671m and 1.5m depth. Tertiary (advanced waste water treatment system)
Primary and secondary treatment removes the majority of BOD and Suspended Solids found in wastewaters. However, in an increasing number of cases this level of treatment has proved to be insufficient to protect the receiving waters or to provide reusable water for industrial and/or domestic recycle.
Scope Limitation
The following things limits me to do farther
Lack of skilled man power,
Lack of technological equipments,
Absence of laboratory class to test important parameters(since it starts 3 days before we
live the hosting company) ,
Absence of library in the hosting company to refer the process in detail
Chapter five
The BOD level of the effluent of Awassa textile Share Company is 220 mg/L and the
environmental regulation puts to release 30mg/L of final effluent. So; in order to make this 13.671m diameter and 1.5 depth of trickling filter is needed.
Advanced waste water treatment are expensive, and are used only when water produced by
convectional secondary treatment.
5.2 RECOMMENDATION
The following points are recommended for the farther work in the company:
1. During the rainy season the flood water directly inters in the collection tanker and overflow will take place so presentation mechanisms must be done, in order to treat the waste properly.
flooding
2). The PH level must be cheeked at least in 15 minute interval to take appropriate action and to crate good environment for microorganisms .
3) From the desizing and bleaching section a lots of chemicals is consumed to remove dusts the chemicals are the case for environmental pollution so; in order to reduce the chemical consumption we need gas senging machine that works by using gas film. But Awassa textile Share Company hasn’t this machine.
Reference used
1) D.G Rao, R. Senthilkumar, S. Feroz; Waste water treatment Advanced process and technology.
2) G.H Karia, R.A Christian; Second edition; Waste water treatment concept and Design . Approach.
3) Davis, Mackenzie; Introduction to Environmental Engineering.
4) David Handricks; Water treatment unit process physical and chemical.
5) Frank R.Spellmon; Hand book of water and waste water Treatment plant operation.
6) Syed R. Qasim; waste water treatment plants planning, designing and operation.
7) Peter J. Huser; Textile dyeing.
8) Mohamil L. Gulrajni; Advances in the dyeing and finishing of technical textile.
Appendix
BOD - Biochemical Oxygen Demand
COD - Chemical Oxygen Demand
DO - Dissolved Oxygen
UIL – University Industrial Linkage
NRC - (National Research Council of USA)
DOB, t-dissolved oxygen concentration in blank after t days of incubation, mg/L
DOs, t-dissolved oxygen concentration in sample after t days of incubation, mg/L.
TSS - the total suspended solids
