The Laboratory Charge Analyzer Model LCA-3 is Chemtrac’s newest model lab unit capable of performing automatic titrations to determine optimum coagulant dosage of a raw water sample. The LCA-3 is also capable of determining the amount of pH adjustment chemical, such as lime or caustic, that is needed to maintain optimum pH conditions for coagulation.
The LCA-3 is equipped with sensors to measure streaming current, pH and temperature, and also includes two titrant pumps: one for feeding coagulant and the other to feed an acid or base to maintain target pH conditions. In this video, a sample of water with high color and low alkalinity is being tested. A 1% aluminum sulfate solution is used as the coagulant (titrant) for determining the ppm dose required for charge neutralization, and a 0.5% caustic solution (NaOH) is used as the pH adjustment titrant.
The pH is very important to successful coagulant dosage determinations using charge measurement and is therefore an essential feature to the LCA. In this demonstration, the pH of the sample starts at 7.66 but quickly drops with the addition of aluminum sulfate. For this test , the target pH for the treatment process has been defined as 6.3. As the pH is seen to drop below the target pH of 6.3, the LCA begins titrating with caustic to raise pH while being careful to not raise it too quickly or to overshoot the target as this could result in needing to feed excess Alum to obtain charge neutralization. The LCA titration is complete once the charge reading has reached zero and the pH has reached its target value of 6.3. The unit then displays the final result showing the parts-per-million dosage of both chemicals. To establish confidence with the LCA test result, it is recommended to perform jar testing to verify optimum reduction of turbidity and organics. Treatment goals may not call for the level of NTU/TOC reduction that is obtained by full charge neutralization of the sample, in which case correlations can be established between the LCA result and the actual dosages that are required to meet the WTP’s target NTU & TOC reduction. With an accurate measurement of charge neutralization, the LCA-3 provides an affordable and efficient way for water treatment plants to quickly determine an optimum dosage of coagulant.