Factors influencing ultraviolet disinfection performance part I: Light penetration to wastewater particles

A technique is described for measuring UV absorbance and internal scattering characteristics of wastewater solids. Wastewater solids developed as part of trickling Biter and activated-sludge processes were observed to be strictly absorbing, with light attenuation following the Beer-Lambert law. Absorbance of solids ranged from 3300 to 569 000 cm(-1). Although absorbance was found to vary with treatment process type, even the lowest measured value is sufficient to block transmission of UV light to solid material. It is unlikely that wastewater treatment processes can be tailored to allow light transmission to solid material. Extremely high absorbance observed indicates that UV light can only penetrate particles because of high particle porosity, not by transmission through solid material. Also, regions exist within some particles that completely block applied UV light. Longer wavelength UV light was not observed to penetrate particles better than lower wavelength UV light.