UV light directly and because iron will adsorb onto suspended solids, bacterial clumps,and other organic compounds.The sorbed iron can prevent the UV light from penetrating the particle and inactivating organisms that may be embedded within the particle.Where iron salts are added in the treatment process, dosage control is extremely important when UV disinfection is to be used.Organic constituents, identified as beingabsorbers of UV light, are compounds with six conjugated carbons or a five- or sixmember conjugated ring.The reduction in transmittance observed during storm eventsis often ascribed to the presence of humic substances from stormwater flows.