Jar Testing

Coagulation

Coagulation occurs when a sample is treated with a positive charged chemical that neutralizes the negative charge on solid particles. By neutralizing the charge, the particles can join, or coagulate, and form larger particles that settle more quickly than the smaller, charged particles.

Lime Softening

Lime softening is used to soften hard water to prevent scaling in pipes and tanks. The process raises the pH of a slurry by mixing it with hydrated lime (Ca(OH)₂) to precipitate calcium and magnesium ions. This reduces the hardness and/or alkalinity of the slurry. Raising the pH through lime softening can also precipitate other ions.

Ballasted Floc

Ballasted flocculation is usually needed when the solids in a sample are too fine or light to settle quickly, even with coagulation and flocculation. Adding a fine sand, or some other seed particle, and a flocculant to a feed slurry produces a ballasted floc. Mixing the slurry with coagulants/polymers and the ballasted floc sand causes the smaller particles attached to the sand to produce larger, heavier particles that settle quickly and leave a clearer supernatant.

Solids Contact Clarification Testing

Solids contact clarification is similar to ballasted floc because solids are added to the feed slurry to act as a seed to improve the solids removal and settling. However, instead of a separate source for the seed, a solids contact clarifier recycles the solids in the underflow to seed the slurry feed. We can determine the mass of solids that need to be recycled for the feed slurry, and then size a clarifier with sedimentation testing.

High Density Sludge Testing

High density sludge (HDS) testing is accomplished by mixing hydrated lime with a portion of previously precipitated solids, raising the pH, then mixing this with the acid water to be treated. The key to this is achieving a pH that will precipitate the metal ions present in the acid water. Mixing the previously precipitated solids with hydrated lime creates a seed that precipitating metal ions can form on. This process results in shorter reaction times for metals removal, reduced super saturation, and a slurry with much better thickening and filtration characteristics.

Metals Removal

Through pH adjustment and other chemical treatments, many metals, metalloids, and even a few non-metals can be precipitated and removed from a slurry. Metals such as calcium and magnesium are precipitated through lime softening to reduce the hardness and/or alkalinity of a slurry. Other slurries may have toxic or hazardous levels of some metals such as lead, nickel and zinc, or metalloids such as arsenic or selenium. pH adjustment can precipitate these elements, and filtration or thickening can remove the precipitated solids.