What does the presence of fine alum particles washing over the effluent weirs of the sedimentation basin suggest?

The presence of fine alum particles washing over the effluent weirs of the sedimentation basin indicates that the alum dose may be too high. This observation suggests that there is an excess of coagulant in the water, leading to a situation where fine particles or floc that should be settling properly are instead being carried over with the effluent. Normally, when the coagulation and flocculation processes function correctly, larger, heavier particles settle out, and minimal residual coagulant is present in the effluent.

When the alum dose is appropriate, the formation of flocs occurs effectively, leading to proper sedimentation and minimal alum carryover. If the dose is excessive, it may lead to unstable floc structures that do not settle, causing them to overflow the sedimentation basin. This is particularly important for maintaining water quality and treatment efficiency. In summary, the observation of fine alum particles signifies potential over-addition of coagulant, which can negatively impact the overall treatment process.