Jar Test procedure and calculation for water treatment process

A Comprehensive Guide to Jar Testing: The selection of right coagulants and coagulant aids is an important step in the process of water treatment. To make this conclusion, water treatment authorities rely on bench-scale tests known as jar tests. As per the plant conditions, the jar test serves as a practical and informative tool to evaluate the effectiveness of chemical coagulation processes. In this comprehensive guide provides knowledge on the jar test, exploring its purpose, procedure, and significance in the water treatment process.

Purpose of the Jar Test:

The primary objective of the jar test is to support water treatment authorities in making decisions regarding coagulation and flocculation dosing processes. The jar test helps several key purposes:

1) Coagulant Selection: It aids in the selection of the most suitable coagulant for a particular water source. Different coagulants, such as aluminum sulfate (alum), ferric chloride, or polymer-based coagulants, exhibit varying amount of the chemicals are compared against each other to find out which chemical and dosage best accomplishes to desired results based on water quality parameters.

2) Optimal Dosage Determination: The jar test helps determine the ideal dosage of coagulants and flocculant aids required to achieve the desired goals in water treatment process, such as turbidity reduction, color removal, or pathogen removal.

3) Treatment Process Optimization: The jar test contributes in optimizing the water treatment process by fine-tuning chemical dosages and understanding the settling characteristics of flocs formed during coagulation and flocculation.

Preparation of stock solution for jar test with example

Stock solution of coagulant and coagulant aids and other chemicals, should be prepared at concentrations such that quantities suitable for use in the jar tests. They serve as concentrated sources of these chemicals that can be accurately and conveniently measured for use in laboratory-scale jar tests.

Normally the stock solution prepared the concentration of 1 gram per liter (1 g/L), which is equivalent to 0.1% weight/volume (w/v). This concentration simplifies dosing, as 1 milliliter (1 mL) of a 1 g/L solution equals 1 milligram (1 mg) per liter (1 mg/L) or 1 part per million (ppm).

Preparing Stock Solutions from Dry Chemicals

If one is dealing with dry chemicals the preparation of these stock solution is straight forward.

For example, to prepare a one gm/l stock solution using dry chemicals with 100% concentration of base chemical. 1 gram of the chemical is made 1000ml with distilled water.  If the base chemical concentration varies the quantity of addition will be calculated accordingly.

If the base chemical’s concentration is less than 100%, adjust the quantity accordingly. For example, if the base chemical has a concentration of 73%, use 1.37 (1*100/73) grams of the chemical to prepare a 1 g/L stock solution in 1000 mL of distilled water.

Preparing Stock Solutions from Concentrated Liquid Solutions

While dealing with the concentrated liquid solutions a dilute step is required. Take into account the specific gravity of the solution when diluting.

48.5% liquid alum solution with a specific gravity of 1.35: To prepare a 1 g/L stock solution, follow these steps:

• • Calculate the mass of alum in 1 ml of the solution: 1 ml contains = 1.35 g (specific gravity) x 48.5% = 0.65 g of alum.
  • Determine the volume of the solution needed to obtain 1 gram of alum

i.e., 1 gram alum = 1 gram / (0.65 gram/ml) = 1.54 ml.

• • Add distilled water to 1.54 ml of the liquid alum to make up the volume to 1000 ml, creating 1 g/L (0.1% w/v) stock solution.

Therefore, add distilled water to 1.54ml liquid alum to makeup 1000ml for a 1g/l (0.1%w/v) stock solution.

Dosing Rate Guidelines as per the flow rate of treatment water:

The following tables gives an idea to determine the mass of the chemical in kgs that will be required to feed at the rate as per the dosing rate.

Procedure of the Jar Test:

The jar test procedure involves the following key steps:

a) Sample Collection: Obtain a representative water sample from the source to be treated. This sample should reflect the water’s natural characteristics and impurities.

b) Prepare Jar Test Apparatus: Fill several identical glass or plastic jars with equal volumes of the water sample. The number of jars used can vary, but typically, a range of coagulant dosages is tested in separate jars.

c) Add Coagulants: In each jar, add a specific coagulant or coagulant combination at various dosages. Stir or agitate the jars to ensure thorough mixing.

d) Flocculation: After adding coagulants, gently stir the contents of each jar to simulate the flocculation process. This involves the formation of flocs, which are larger, aggregated particles that capture impurities.

e) Settling Time: Allow the jars to sit undisturbed for a predetermined settling time. During this period, flocs settle to the bottom of the jars, leaving clearer water above.

f) Observation and Analysis: After settling, carefully examine the jars to assess the effectiveness of coagulation and flocculation. Parameters such as clarity, floc size, and settling characteristics are observed and compared.

g) Determine Optimal Dosage: Based on the jar test results, identify the coagulant dosage that produces the desired water quality improvements. This dosage can then be applied in full-scale treatment processes.

Significance of the Jar Test:

The jar test holds significant importance in the field of water treatment for several reasons:

a) Cost-Effective: The jar test simulates, on a small scale, the activities going on in various sections of the full-scale water treatment process. The jar test allows treatment plants to make informed decisions without the need for wide pilot-scale testing. Hence saving of both time and resources.

b) Customization: The test can be custom-made to specific water sources and treatment objectives, ensuring a customized approach to water and wastewater treatment.

c) Process Optimization: By fine-tuning coagulant dosages and understanding settling characteristics, treatment processes can be optimized for efficiency and effectiveness.

d) Quality Assurance: Regular jar testing helps maintain consistent water quality standards and ensures that treatment goals are consistently met.

In conclusion, the jar test serves as a valuable tool for water treatment professionals, enabling them to make informed decisions about coagulant and flocculant selection, dosage optimization, and overall process enhancement. By replicating plant conditions and evaluating the performance of chemical coagulation, the jar test plays a pivotal role in delivering clean, safe, and potable water to communities around the world.

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