Evolution along the sewer

The variation of wastewater quality is related to the human activities (and thus time dependent as shown before) but also to some physico-chemical factors occurring along the sewer. Fresh organic matter composition can vary from the source (houses, for example) to the treatment plant because of physico-chemical phenomena (solids settling, phase transfer, oxidation, etc.). 

The comparison of differential spectra between the raw and the filtered sample is interesting (Fig. 6). These spectra are related to the characteristics of suspended solids of samples. The TSS concentrations are, respectively, 502 and 669 mg/L, from upstream to the treatment plant, meanwhile the corresponding spectrum seem to be divided twice. The observed increase can be explained, on one hand, by solids input (by incoming water) or formation (related to the biodegradation), and on the other hand, by the aggregation of colloids in suspended solids [6], This is confirmed by the fact that particles of larger size absorb less in the UV region than smaller ones (see Chapter 6). 

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