EXPERIEMENT 1.0 JAR TEST
1.1 INTRODUCTION Jar testing is the test conducted to determine the amount of chemical dosage required and pH to remove the small particulate from water and wastewater. Jar testing stimulates the process of coagulation and flocculation at the water treatment plant. This help the operator to observed and determine the suitable amount of chemical and the right pH to remove the suspended solid. In Jar testing, there will be two test conducted. The first test is conducted to determine the optimum pH while the second test conducted to determine the optimum dosage of the chemical. The first test will be conducted by preparing six sample of water with the same amount. Then, then chemical with same amount will be added to the water sample. After that the pH value will be adjust differently for each beaker then it will be stir for some moment. The second test will undergo the same process but the dosage of the chemical added to the water sample will be differently for each beaker while the pH will be constant. According to the David Pask, former National Environmental Service Centre engineer wrote “By performing jar tests, you can try alternative treatment doses and strategies without altering the performance of the full-scale treatment plant and easily compare the results of several different chemical treatments for time of formation, floc size, settlement ability, and, perhaps, filtration characteristics. One cannot make such comparisons with the full plant’s treatment.” Another reason to perform the jar test is this method is cost saving. Suspended solid(particularly colloid) are often removed from water by chemical coagulation and flocculation. Colloidal particles carry a small electrostatic charge that keeps them in suspension. Coagulation is the addition of chemicals to neutralize the effect of colloidal charges and allow aggregation of particles. Following coagulation the suspension is stirred gently to promote particle collision and agglomeration in a process termed flocculation. Colloidal matter in surface water can not settle by itself. Dosing of a coagulant and subsequent flocculation, followed by sedimentation. The result of this treatment is depending on many factors, such as coagulant dose, pH, reaction period and supplied energy of stirring device. A jar test is ideal to assess the influence of these process parameters within a short time.
1.2 OBJECTIVE To determine the optimum alum dose and pH for suspended solids removal from water using water Jar test. 1.3 PROBLEM STATEMENT Treatment of water in the treatment plant will cost high if the amount of alum is highly used. Therefore it is important to determine the optimum dosage of alum and the optimum pH for the optimum coagulation and flocculation process. 1.4 APPARATUS 1. 2. 3. 4. 5. 6. 7. 8.
Beakers. Kaolin clay. Alum solution. Sulphuric acid. Sodium Hydroxide. Stirrer machine. Turbidity reading. Measuring cylinder.
1.5 RESULTS AND ANALYSIS DATA TABULATION
Beaker 1 2 3 4 5 6
1st reading
pH 4.18 5.12 6.07 7.16 8.00 9.08
12.56 0.45 0.10 4.64 5.57 1.15
Turbidity (NTU) 2nd reading 3rd reading 12.16 0.49 0.04 4.89 5.34 0.70
11.85 0.00 0.17 4.97 5.29 1.25
Average Turbidity (NTU) 12.19 0.31 0.10 4.83 5.40 1.03
SAMPLE CALCULATION Turbidity measurement conversion: I FNU = 1 NTU Beaker 1 (pH of 4.18): Average Turbidity value
= ( 12.56 + 12.16 + 11.85 ) / 3 = 12.19 NTU
Beaker 2 (pH 0f 5.12): Average Turbidity value
= ( 0.45 + 0.49 + 0.00 ) / 3 = 0.31 NTU
1.6 DISCUSSION 1. Plot graph of turbidity vs. pH and turbidity vs. alum dose. Get the optimum pH and alum dose.
The graph is plotted and shown as in Figure 1 and 2. For the graph plotted, for the Jar Test for optimum pH (dose constant), it is observed that at pH of 5.9, the turbidity of the solution is at minimum which is 0.1 NTU. Thus, the optimum pH is 5.9. While, for the Jar Test for optimum dosage (pH constant), it is observed that the turbidity is in minimum which is 0 NTU at two times. Firstly when the dosage of Al 2SO4 solution is 60 ml/l and secondly when the dosage of Al2SO4 solution is 100 ml/l. For optimum dosage determination, it is always preferred that the lower dosage of Al2SO4 solution is used in the water and wastewater treatment as due to costing. Thus, in this experiment, the optimum dose for coagulation is 60ml/l. The minimum turbidity value would indicate that the coagulation and flocculation process is happened at best as the solution coagulated and the flocs settled and causing the solution to be in clear state. 2. Name some other chemicals that may be used as coagulants. There are generally two main type of coagulant used in the field. Firstly is the primary coagulant which function to neutralize the negatively charged particle which then causing the particles to clump together to form the colloid. The most common coagulant is such as alum. Secondly is the coagulant aid. Coagulant aid is function to add the density and toughness of the flocs and causing them to settle faster and harder to break during the process of sedimentation or mixing. This coagulant aid is only added for the purpose of time reduction only and not usually required in normal coagulation process. Primary Coagulant: i.
Ferric Chloride - FeCl3.6H2O
ii.
Ferric Sulfate - Fe(SO4)3. 9H2O
iii.
Ferrous Sulfate - FeSO4. 7H2O Coagulant Aid:
i.
Calcium Carbonate - CaCO3
ii.
Sodium Silicate – Na2SiO3
3. In a Jar Test experiment, why does the turbidity increase again after reaching a minimum value? In Jar Test experiment, the objective is to find the optimum value of the pH and dosage of solution for coagulation process. Optimum condition for coagulation is when the turbidity
value is in minimum state. For pH, the minimum turbidity is reached at the pH of 5 to 7. Thus, as the pH of solution is exceeding 7, the turbidity value is starting to increase. This is due to the less absence of positively charged particles that will collide with the negatively charged colloid. The less collision of these particles will increase the cloudiness of solution. For dosage factor, the optimum coagulation is reached as the specific value of dosage of solution is prepared. In jar test experiment, if the dosage of solution is set more than that specific value of dose, the excess coagulant will turn the solution acidic. That condition is negative for pH factor and the excess coagulant will promote the sludge formation and make it difficult for disposal purpose. This sludge formation will increase the turbidity thus increasing the graph value. 4. Briefly discuss the effect of alkalinity on coagulation. Alkalinity is defined as the capacity of water to neutralize the acidic properties which is based on the water’s content of specific chemical compound such as carbonate and hydroxide. In coagulation process, water with high alkalinity is necessary to increase the interaction toward the negatively charged colloids as the more alkalinity property will have more content of positively charged ions. Alkalinity property also will provide anions, which is hydroxide (OH) toward the solution. This property will form an insoluble compounds to precipitate the colloid out. The most significant application of this Jar Test Experiment is in the water and wastewater treatment plant. In the conventional treatment plant, there are tank for process of coagulation, which the solution is being coagulated, mixed, flocculated and settled before the water is flow for the next process. The main purpose of coagulation is to destabilize and causing the non-settled particles to clump together through the neutralization of the electrostatic charges on colloidal particles (R. Parker, 2008) before it flocculate together and let to be settled at lower part of the tank. In the field, it is significant to define the optimum parameters to maximize the coagulation process such as temperature, pH and dosage. Jar Test is a useful tool to determine the pH and dosage parameter under the simulated plant conditions (R. Parker, 2008). The optimum parameter is related to the water qualities and properties, and the treatment costing. An exceeding dose may cause waste in cost term and an unsuitable pH may affected the water properties. 1.7 CONCLUSION Based on the experiment conducted, the graph of turbidity vs alum dosage has been plotted and mark as a Figure 1. It show that the minimum turbidity which is 0 NTU happen two time. Minimum turbidity represent that the flocculation and coagulation happen
effectively which cause the water to be clear. It happen when the amount of 60ml and 100ml of Al2SO4 is added. Due to the costing, it can be concluded that the most suitable dosage of Al2So4 for coagulant is 60ml. The suitable dosage of Al2SO4 is required to remove the suspended solid that contain in the raw water. The jar testing is conducted to stimulate the process of coagulation and flocculation at the treatment plant. By doing this, it help to estimate the suitable dosage and chemical that required for coagulation and flocculation process without undergo the full scale of treatment plant hence it can save the cost.
1.8 REFERENCES Book:
R. Parker, N. Morris, F.N. Fair, S.C. Bhatia. Waste-water Engineering. CBS Publisher. New Delhi (2008)
Internet website:
http://water.me.vccs.edu/concepts/coagulation.html
http://www.wrights-trainingsite.com
http://iaspub.epa.gov
