TITLE: JAR TEST 1.0 OBJECTIVE: 1. To conduct jar test. 2. To show the effectiveness of chemical treatment in a water treatment facility. 3. To evaluate coagulation efficiency. 4. To determine the most effective dosage of the recommended coagulants and flocculants. 5. To selects the best chemical or best dosage to feed on the basis of clarifies of effluent and minimum cost of chemicals. 6. To gain a ’hands on’ understanding of the treatment process for removing suspended solids from water. 2.0 THEORY: Raw water or wastewater must be treated to remove turbidity, color and bacteria. Colloidal particles are in the size range between dissolved substance and suspended particles. The particles are too small to be removed by sedimentation or by normal filtration processes. Colloidal particles exhibit the Tyndall effect; that is, when light passes through liquid containing colloidal particles, the light is reflected by the particles. The degree to which colloidal suspension reflects light at 90º angle to the entrance beam is measured by turbidity. The unit of measure is a Turbidity Unit (TU) or Nephlometric Turbidity Unit (NTU). It is determined by reference to a chemical mixture that produces a reproducible refraction of light. Turbidities in excess of 5 TU are easily detectable in a glass of water and are usually objectionable for aesthetic reasons. For a given particle size, the higher the turbidity, the higher the concentration of colloidal particles. Color is a useful term that is used to describe a solution state. But it is difficult to distinguish ‘dissolved color’ and ‘colloidal color’. Some color is caused by colloidal iron or manganese complexes. Although, the most common cause of color is from complex organic compounds that originate from the decomposition of organic matter. Most color seems to be between 3.5 and 10μm, which is colloidal. Color is measured by the ability of
the solution to absorb light. Color particles can be removed by the methods discussed for dissolved or colloidal, depending upon the state of the color. Finely dispersed solid (colloids) suspended in wastewater are stabilized by negative electric charges on their surfaces, causing them to repel each other. Since this prevents these charged particles from colliding to form larger masses, called flocs, they do not settle. To assists in the removal of colloidal particles form suspension, chemical coagulations and flocculation are required. These processes, usually done in sequence, are a combination of physical and chemical procedures. Chemicals are mixed with wastewater to promote the aggregation of the suspended solids into particles large enough to settle or be removed. Coagulation is the destabilization of colloids by neutralizing the forces that keep them apart. Cationic coagulants provide positive electric charges to reduce the negative charge of the colloids. As a result, the particles collide to form larger particles (floc). Rapid mixing is required to disperse the coagulant throughout the liquid. The coagulants overdose can cause a complete charge reversal and destabilize the colloid complex. A coagulant is the substance (chemical) that is added to the water to accomplish coagulation. There are three key properties of a coagulant; 1. Trivalent cation: As indicated in the last section, the colloids most commonly found in natural waters are negatively charged; hence a cation is required to neutralize the charge. A trivalent cation is the most efficient cation. 2. Nontoxic: This requirement is obvious for the production of safe water. 3. Insoluble in the neutral pH range. The coagulant that is added must precipitate out of solution so that high concentrations of the ion are not left in the water. Such precipitation greatly assists the colloid removal process. The two most commonly used coagulants are aluminum (Al3+) and ferric iron (Fe3+). Both meet above three requirements. Aluminum can be purchased as either dry or liquid alum [Al2(SO4)3·14H2O]. Commercial alum has an average molecular weight of 594. When alum added to a water containing alkalinity, the following reaction occurs;
Al2(SO4)3·14H2O + 6HCO-3 ↔ 2Al(OH)3(s) + 6CO2 + 14H2O + 3SO42The above reaction shifts the carbonate equilibrium and decreases the pH. When sufficient alkalinity is not present to neutralize the sulfuric acid production, the pH may be greatly reduced; Al2(SO4)3·14H2O ↔ 2Al(OH)3(s) + 3H2SO4 + 8H2O If the second reaction occurs, lime or sodium carbonate may be added to neutralize the acid. The optimal pH range for alum is approximately 5.5 to 6.5 with coagulation possible between pH 5to pH 8 under some conditions. In flocculation process, the flocculating agent is added by slow and gentle mixing to allow for contact between the small flocs and to agglomerate them into larger particles. The newly formed agglomerated particles are quite fragile and can be broken apart by shear forces during mixing. Increasing the dosage will increase the tendency of the floc to float and not settle. Once suspended particles are flocculated into larger particles, they can usually be removed from the liquid by sedimentation, provided that a sufficient density difference exists between the suspended matter and liquid. When a filtering process is used, the addition of a flocculants may not be required since the particles formed by the coagulation reaction may be of sufficient size to allow removal. The flocculation reaction not only increases the size of the floc particles to settle them faster, but also affects the physicals nature of the floc, making these particles less gelatinous and thereby easier to dewater.
3.0 EQUIPMENT AND MATERIAL
1. Jar test apparatus with six rotating paddles
2. Six (6) beaker
3. Thermometer
4. Time / Stopwatch
5. pH meter
6. Turbidity meter
7. pipette 4.0 REAGENT 1. Coagulant e.g. aluminum sulfate (alum), polyaluminum chloride (PAC), ferrous sulfate, ferric chloride, etc. 2. Coagulant aid e.g. pH adjusters (lime or sulfuric acid), activated silica, polyelectrlye (e.g. synthetic polymer such as acrylamide), clays (e.g. bentonite, montmorillonite, etc.) 3. Liquid sample 5.0 PROCEDURES 1. The waste water from the treatment plant was prepared. The sodium was use to stability the PH of the waste water to the neutral. 2. The temperature, pH, color, alkalinity and turbidity of the synthetic water sample were measured. 3. 600ml was filled each of the prepared synthetic water suspension into six different beakers (Plexiglas beakers) 4. The prescribed dose of coagulant was added to each jar by using a pipette. One jar has no coagulant since a control sample was required. 5. If a coagulant aid is required, it is added to each jar (except for control sample) during the last 15 seconds of the rapid mix stage.
6. Start stirring rapidly (60 to 80 rpm) for 3 minute (Rapid mix stage). 7. After the rapid mix stage, reduce the speed to 30 rpm for 20 minutes. 8. Floc formation were record ed by referring to the chart of particle sizes in final 10 minutes. 9. After the stirring period was over, stop the stirrer and the flocs was allowed to settle for about 5 minutes as in scheme (iv) 10. 500mL of settle water was separate out into another beaker. 11. The temperature, pH, color, alkalinity and turbidity of the clarified water were determined. 12. A graph of turbidity versus coagulant dose (mg/L) was plotted. The most effective dose of coagulant (or with the present of coagulant aid) that gives the least turbid results also determined. 13. The qualitative characteristics of floc as bad, moderate, good and very good were recorded. Cloudy samples indicate bad coagulation while good coagulation refers to rapid floc formation resulting in clear water formation on the upper portion of the beaker. 14. The following graph: color versus coagulant dose, pH versus coagulant dose, temperature versus coagulant dose, etc. were plotted. These graphs will assist students in the interpretation of the coagulation-flocculation process. 6.0 RESULT AND DATA ANALYSIS
JAR NO. Initial pH Initial Temperature (oC) Coagulant dose (mg/L) Agigate (minutes) Fast (rpm) Slow (rpm) Settling Depth (mm) Final pH Final Temperature (oC) Final Turbidity (NTU)
1 6.42 26.5 10 23 70 30 10 5.35 23.1 7
2 6.42 26.5 20 23 70 30 8 4.06 23.1 5 Very
Floc Formation Time of floc formation =
fine fine 5 minutes
3 6.42 26.5 30 23 70 30 4 3.60 22.9 4
4 6.42 26.5 40 23 70 30 3 3.25 22.9 17
5 6.42 26.5 50 23 70 30 2 3.22 22.9 32 Very
6 6.42 26.5 control 23 70 30 2 108 Moderately
moderate
Coarse
coarse
fine
Floc sizes for: Very fine
is
0.30mm to 0.75mm
Fine
is
0.50mm to 0.75mm
Moderate fine
is
1.00mm to 1.50mm.
From the graphs we could conclude; The most effective coagulant dose is 10 mg/L, and 20 mg/L The most effective pH is 5.35 The expected temperature was 22.90 at optimum coagulant dose.
DISCUSSION We had successfully done this experiment because the objective of this experiment, to conduct various experiments on chemical coagulation and flocculation and to determine the optimum dose combination of coagulant aid (when used) which will produce the highest removal of turbid water sample has achieved.
Jar tests have been used to evaluate the effectiveness of various coagulants and flocculants under a variety of operating conditions for water treatment. . This procedure allows individual polymers to be compared on such criteria as floc formation, settling characteristics, and clarity. Generally, the best performing products provide fast floc formation, rapid settling rate, and clear supernatant. This test should be performed onsite, since large amounts of water may be required for testing. Turbidity is essentially a measure of the cloudiness of the water which indicates the presence of colloidal particles. The particles should be making sure removed from the water before for the publics use. However these colloids are suspended in solution and can be removed by sedimentation or filtration. Very simply, the particles in the colloid range are too small to settle in a reasonable time period, and too small to be trapped in the pores of a filter. For colloids to remain stable they must remain small. Most colloids are stable because they posses a negative charge that repel other colloidal particles before they collide with one another. The colloids are continually involved in Brownian movement, which is merely random movement. Charges on colloids are measured by placing Dc electrodes in a colloidal dispersion. The particles migrate to the pole of opposite charge at a rate proportional to the potential gradient. Generally, the larger the surface charge, the more stable the suspension. Based on this experiment, the first jar is serving as a control and no coagulant was added. The coagulant doses increased in the containers from no 1to no 6. For this water, as the dose of coagulant increased the residual turbidity improved. It is important to note that the optimum coagulant dose is the dose which meets the specified turbidity required on the regulatory permit. The addition of excess coagulant may reduce turbidity beyond what is required but also could lead to the production of more sludge which would require disposal. The most effective dose of coagulant we get from the Graph turbidity versus coagulant after the experiment is 20 mg/L. The most effective pH is 5.36.
Jar tests are used in these procedures to provide information on the most effective flocculants, optimum dosage, optimum feed concentration, effects of dosage on removal efficiencies, effects of concentration of influent suspension on removal efficiencies, effects of mixing conditions, and effects of settling time. The general approach used in these procedures is as follows: a) Prepare stock suspension of sediment. b) Test a small number (six) of polymers that have performed well on similar dredged material which has 2-grams-per-litre suspensions and is a typical concentration for effluent from a well-designed containment area for freshwater sediments containing clays. If good removals are obtained at low dosages (10 milligrams per liter or less), then select the most cost-effective polymer. If good removals are not obtained, examine the polymer under improved mixing and settling conditions and test the performance of other flocculants c) The effects of settling time on the removal of suspended solids and turbidity from a suspension of average concentration should be exanimate using the selected dosage and likely mixing conditions. d) The effects of the range of possible mixing conditions on the required dosage of flocculants for a typical suspension should be exanimate.
8.0 CONCLUSION As conclusion, this experiment is successfully been done and it is because the objective of this experiment which to conduct various experiments on chemical coagulation and flocculation and to determine the optimum dose combination of coagulant aid (when used) which will produce the highest removal of turbid water sample has achieved.
Jar testing is an experimental method where optimal conditions are determined empirically rather than theoretically. Jar test are meant to mimic the conditions and processes that take place in the clarification portion of water and wastewater treatment plants. The values that are obtained through the experiment are correlated and adjusted in order to account for the actual treatment system. After the experiment, Graph turbidity versus coagulant dose are plot, from the graph we get the most effective dose of coagulant is 60mg/L Base on the data, we conclude that although the turbidity is generally declines as the amount of the alum which added into the water but there is a point where more alum should not be added. This is because alum will make the water more acidic. Therefore, to overcome these problems, buffer should be added with same amount of alum at the same time the alum is added. After this experiment, we realize that a successful Jar Test is very reliant upon the proper preparation of the polymers being tested. Dilution technique ("make down") is especially critical, since it involves compactly coiled large molecules in emulsions, prior to activation. The polymer must be uncoiled to provide maximum contact with the colloidal particles to be flocculated. If the following procedures are not followed, the Jar Test results will be very unreliable. As conclusion, after we analyzed the data, we have decided that the optimum dosage of alum for this experiment is 10 mg/L. we reach this conclusion base on the fact that the turbidity minimum at 7 NTU.
9.0 QUESTIONS Two sets of experimental data obtained from a jar test on water samples with initial turbidity of 15NTU and HCO3 alkalinity of 50mg/L CaCO3 Jar No pH Coagulant dose
1 5.0 10
2 5.5 10
3 6.0 10
4 6.5 10
5 7.0 10
6 7.5 10
(mg/L) Turbidity
11
(NTU)
7
5.5
5.7
8
13
JAR TEST 1 Jar No pH Coagulant dose (mg/L) Turbidity (NTU)
1 6.0
2 6.0
3 6.0
4 6.0
5 6.0
6 6.0
5
7
10
12
15
20
14
9.5
5
4.5
6
13
JAR TEST 2 9.1 Plot a graph of turbidity versus pH and turbidity versus coagulant dose (mg/L). 9.2 State the optimum pH value and optimum alum dose of the coagulation process of the raw water. The optimum pH was chosen as 6.25 and the optimal alum dose was about 12.5mg/L (based on graph 7.1) 9.3 What is the usage of Jag test? The purpose of Jar Testing is to predetermine the amount of chemicals requird to treat and precipitate as sludge the contaminants in a given volume of wastewater. The phrase "Jar Testing" is commonly used in the waste treatment industry. It is used in reference to a method that will determine treatability of a solution or establish a sequence of steps required to achieve treatability. Jar Testing is used as a tool to determine why proper treatment is not being achieved. 9.4 How to reduce dosage of alum in treatment plant? Since the two important factors in coagulant addition are pH and dose. Therefore to reduce the dosage of alum we can add coagulant aids such as pH
adjusters (lime or sulfuric acid), activated silica, clay (bentonite montmorilionite)and polymers . The addition of activated silica and clays is especially useful for treating highly colored, low turbidity waters as it add weight to the floc . 9.5 Name and explain briefly three types of alkalis that are suitable for pH control. Lime Ca(OH)2 ,soda ash (NA2CO3), Sodium Bicarbonate, Sodium Hydroxide Magnesium Hydroxide, Calcium Bicarbonate and others .The alum reacts rapidly with compounds in the water that contain carbonates, bicarbonates and hydroxides to produce a jelly-like substance that absorbs impurities. At the same time, alum, with a positive charge, neutralizes the negative charge common to natural particles, which draws them together. Small particles microfloc are formed. The following equation shows the reaction of alum with alkalinity: Al2(SO4)3 . 14H2O Aluminum Sulfate
+ 3Ca(HCO3)2 Calcium Bicarbonate
2Al(OH)3 + 3CaSO4 + 6CO2 + 14H2O Aluminum Calcium Carbon Water Hydroxide Sulfate Dioxide
9.6 What are the advantages of using coagulant aids? To accelerate settling, minimum the usage of chemical in treatment and adjustd the pH of the water into the optimal range for coagulation. 9.7 What are the effects of alum dosage in treatment criteria? Alum will have the effect of lowering pH so careful monitoring is necessary when applying alum. Alum contains aluminum, which is toxic to fish in acid water, therefore overdose of alum can give negative effect to the environment. Alum use results in sludge of precipitated particles that should either be vacuumed out or removed via a bottom drain . 9.8 Name five differences between alum and ferric coagulants. a.
Ph- The optimum pH range for alum is generally about 5 to 8. The optimum pH range for ferric chloride is 4 to 12.
b.
Dosage - Ferric dosage is typically about half of the dosage required for alum.
c.
Chemical Reaction- Ferric coagulant reacts in water with hydroxide alkalinity to form various hydrolysis products that incorporate Fe(OH)3. These compounds possess high cationic charge which allows them to neutralize the electrostatic charges found on colloidal compounds and also to bind to negatively charged particles, including the ferric hydroxide itself. This ability to bind to itself is the mechanism for the formation of floc aggregates and the basis for ferric chloride’s flocculation abilities. FeCI3 + 3 HCO3 = Fe (OH) 3 + 3CO2 + 3CIIn the case of alum coagulants, these reactions can be represented as follows: Al2(SO4)3 + 3 Ca(HCO3)2 = 2 Al(OH)3 + 3 CaSO4 + 6 CO2 Al2(SO4)3 + 3 Ca(OH)2 = 2 Al(OH)3 + 3 CaSO4 Al2(SO4)3 + 3 Na2CO3 + 3 H2O = 2 Al(OH)3 + 3 Na2SO4 + 3 CO2 The alum reacts rapidly with compounds in the water that contain carbonates, bicarbonates and hydroxides to produce a jelly-like substance that absorbs impurities. At the same time, alum, with a positive charge, neutralizes the negative charge common to natural particles, which draws them together. Small particles microfloc are formed.
d.
Ferric coagulant can be purchased either in sulfate salt (Fe2(SO4)3.xH2O) or chloride salt (FeCl3.xH2O) where as alum only in sulfate salt Al2(SO4)3.
e.
Liquid alum is sold approximately 48.8 percent alum (8.3%Al2O3) and 51.2 percent water.if it is sold as a more concentrated solution, there can be probles with crystallization of the alum during shipment and strorage. While ferric coagulant is available in various dry and liquid forms.
10.0 REFERENCES:
G. J. Schroepfer, M. L. Robins, and R. H. Susag, (1964)“Research Program on the Mississippi River in the Vicinty of Minneapolis and St. Paul,” Advances in Water Pollution Research, vol. 1 L.Davis , I.Cornwell. Introduction to Environmental Engineering. Third Edition. Lab sheet: Enviromental Engineering, Test: JAR Test Website: 4th Feb 2006 (date retrieved) http://www.waterspecialists.biz/html http://www.phippsbird.com/ http://home.alltel.net/mikeric/PretreatMaint/ Hammer, MarkJ. (2001)”Water and Waste water Technology Frouth Edition” New Terzey: Prentice Hall Master, Gelbert M (1998) “Introduction to Environmental Engineering and Science” Black, J.G. (1996). Microbiology. Principles and Applications. Third Edition. Prentice Hall. Upper Saddle River, New Jersey. Tortora, G.J., Funke, B.R., Case, C.L. (1995). Microbiology. An Introduction. Fifth Edition. The Benjamin/Cummings Publishing, Co., Inc., Redwood City, CA. H. A. Thomas,(1998) “Graphical Determination of B. O. D. Curve Constants, “Water and Sewage Works”, McGraw Hill Companies Inc.
