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Learn about flocculation and jar test in water and wastewater analysis. Discover the analytical procedure, how to evaluate results and the VELP dedicated solutions.
Jar test is a pilot-scale laboratory test that simulates coagulation or flocculation with differing chemical doses. The purpose of this test is to estimate the minimum coagulant dose required to achieve certain water quality goals. In other words, jar test helps to determine the right amount of treatment chemicals: the lowest dose of chemicals that provides satisfactory settling is the dose used to treat the water. 

Jar Test and Flocculation: from the laboratory to the wastewater treatment plant

Jar Test and Flocculation: from the laboratory to the wastewater treatment plant
Jar Test enables the correct choice and dosage of chemical coagulants aimed at removing suspended matter and pollutants in water treated in wastewater treatment plants.

The choice and dosing of the chemical coagulants derive in fact from the results of the laboratory Jar test, which mimics full-scale operation in water treatment plants.

The most used coagulants are Lime (calcium hydroxide), Alum (aluminum sulphate) and Iron salts (ferric or ferrous).

Flocculation or Coagulation is fundamental in every water treatment process and it is a propaedeutic step for sedimentation, filtration and disinfection before distributing water for residential and industrial use.

How it works: Jar Test analytical procedure

How it works: Jar Test analytical procedure

Using a flocculator, the coagulant substance is added to the water sample beakers. The chemical coagulant starts to precipitate trapping all the impurities and forming flocs that will deposit on the bottom of the beaker. 

The sample is continuously stirred so that the formation, development, and settlement of floc can be observed just as it would occur in the full-scale water treatment plant.

The operator then performs a series of tests to compare the effects of different amounts of flocculation agents at different pH values to determine the right size floc.

The most common analytical conditions using a flocculator are:

  • 1000 ml glass beakers (jars), tall form, Ø 105 mm
  • 600 ml wastewater samples + coagulant
  • Height of paddles: middle height of the sample
  • Turbulent stirring: 120 rpm, 120 seconds
  • Slow speed flocculation: 30 rpm, 25 minutes
  • First evaluation of results after 5 minutes of sedimentation

Result evaluation for full-scale application and optimized performance

The results of the Jar Test can be evaluated based on different criteria:
  • Floc dimension evaluation with a numerical degree
  • Time from the addition of chemicals to the first appearance of flocs
  • Evaluation of residual turbidity of supernatant, after a determined sedimentation time, by turbidimeter
  • Measurement of the electro-kinetic potential of suspended particles on a sample taken immediately after the addition and mixing of chemicals
  • Evaluation of filterability of clarified water by standardized membrane filters under pressure. The reduction of water flow is related to the degree of clogging of filters due to residual unsettled suspended matters

VELP dedicated solutions for Flocculation

The Jar Test helps water treatment plant lab operators avoid overfeeding or overdosing, especially with coagulants saving resources and optimizing processes. VELP solutions for Jar Test are robust products with strong resistance to chemical and mechanical corrosion. The illuminated back panel enables simple and clear floc observation and evaluation leading to maximized reproducibility.

VELP Flocculators of the JLT and FCS series with multiple stirrers and reproducible speed guarantee standard conditions, a basic requirement for reliable results according to reference method ASTM D-2035.

VELP flocculators feature independent speed per position or single speed with a digital display and timer, meeting the requirements of every lab. Whenever required, the VELP FP4 is a portable flocculator allowing tests on site.

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