The scum is washed in a counter flow manner to recover sugar contained in the scum collected from the melt clarifier.
High degree of sanitation is important because the scum is very conducive for bacterial activity & the return sweet water can quickly infect the melt liquor. Hence it is very important to carefully design a proper scum de-sweetening system.
This involves three consecutive stages of countercurrent extraction, i.e. scum flow through the process is from 1st to 2nd and to 3rd clarifier, while the hot water flows from 3rd to 2nd and to 1st clarifier.
The scum & water are thoroughly mixed together by a mixing tank agitator to produce a homogeneous solution. This solution then flows by gravity into clarifier. Prior to solution entry into the clarifier, air & flocculants are added. Line saccharate is dosed if required to maintain pH.
The high brix sweet water will be extracted from 1st stage clarifier and flows by gravity to the sweet water tank at melting station. When 3rd stage clarification step is reached, the final desweetened scum is discarded. This system is fully automated, entire 1st Stage VRL.