The pollution load of water and wastewater is associated with the presence of floating, coarse, and particulate matters. This type of pollution is important because of its consequences in terms of deposition, clogging, anaerobic degradation, as well as its adsorption potential for metallic or organic compounds, or microorganisms. Colloidal and particulate matters in wastewater have great influence on the performance of wastewater treatment plants: each operation unit, such as settling, biological or chemical treatment, is affected by the phenomena of agglomeration or dispersion of colloids. Wastewater is often a mixture of organic and mineral pollutants. Four families of compounds usually describe the pollution fractions contained in urban wastewater: soluble fraction, colloidal fraction, supracolloidal fraction, and settleable fraction. The measurement of total suspended solids (TSS) includes supracolloids and settleable matter. The colloidal state is an intermediate phase between the solid state and the dissolved phase. UV spectrophotometry integrates different combined optical phenomena such as physical absorption and chemical absorption.