Primary settling assistance

During settling, the decrease in absorbance on the whole spectrum, especially between 230 and 350 nm where TSS are responsible for a diffuse absorbance, indicates the removal of settleable solids. About 54% of the suspended solids and 29% of the COD are removed by settling (Fig. 11). Actually, settleable solids are also constituted of a part of colloids that can be trapped with larger solids during the settling operation. Their corresponding spectrum represents about 35% of the absorbance due to suspended matter (Fig. 12). 

In order to help the user in the design of a settling tank (to build or to check), a simple experiment can be proposed (Fig. 13). A wastewater sample is introduced into a2-m-high glass column of 100-L capacity, and aliquots are carefully withdrawn for different heights and times. UV spectra are acquired for a quick estimation of the TSS (after a previous 

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