An equation was derived for describing the measured inactivation of particle-associated coliform bacteria in wastewater secondary effluent exposed to UV light disinfection. Parameters of importance are the inactivation rate coefficient and the total number of particles that contain coliform bacteria. Prediction of coliform bacteria dose-response is possible to within the error associated with the multiple-tube fermentation test. The theoretically derived modeling equation can be used with other design approaches that have specific strengths (e.g., incorporation of regulatory permit limitations or hydraulic characteristics). A minimum particle size seems to govern the ability of a particle to shield coliform bacteria from UV light. Particles smaller than that size do not contain regions shielded from UV light. At sizes greater than the critical particle size, size is not significant in determining shielding of coliform bacteria. Coliform bacteria are not typically located in the most shielded regions within particles, and therefore the inactivation of coliform bacteria within a particle does not indicate the application of UV light throughout that particle. Water Environ. Res., 72, 432 (2000).

A technique is described for quantifying the number of particles with embedded coliform bacteria in wastewater samples. This technique was applied to eight different wastewater samples collected from cight significantly different treatment processes (five variations of the activated-sludge process, a trickling filter, an aerated lagoon, and a facultative lagoon). For all treatment process types that did not usc chemical coagulants, total number of particles with embedded coliform bacteria correlated linearly with number of residual coliform bacteria following high doses of UV light. Lagoon treatment processes led to the formation of fewer bacteria-associated particles than either the activatedsludge or trickling-filter processes. Chemical coagulants showed a potential to significantly reduce the inactivation fraction of coliform bacteria associated with particles. Water Environ. Res., 71, 1178 (1999). of UV disinfection systems in all types of wastewater effluents. The model, once calibrated for a particular site, can and has been used to develop designs and cost estimates of full-scale UV disinfection systems (Chinniah and Kwan, 1996; Darby et aI., 1995; James et aI., 1996; Kwan et aI., ]996; Le et aI. and Stafford and Kwan, 1996). Calibrations for different effluents can both change the statistical significance of the parameters and yield radically different coefficient values. For instance, the model was developed and calibrated with data collected using a 1900 m 3 /d (0.5 mgd) UV system operated at two northern California activated-sludge wastewater treatment plants (WWTPs). The resulting model coefficients were A = 1.4 X 1011, a = 0.98, b = -4.1, C = 0, and II = -1.9.High statistical significance was found for 55, UFT, and UV dose. The influent coliform bacteria number concentration (No) was found to be statistically insignificant. The model was later calibrated with data collected during a 4500 m 3 /d (1.2 mgd) UV pilot test at a high-purity oxygen activated-sludge plant (Loge et aI., I996b). The resulting model coefficients were A = 610, a = 1.9, b = 0, C = 0.33, and n = -2.4.High statistical significance was found for No, 55, and UV dose.

A technique is described for measuring UV absorbance and internal scattering characteristics of wastewater solids. Wastewater solids developed as part of trickling filter 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 569000 cm-I .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 obscrved to penetrate particles better than lower wavelength UV light. Water Environ. Res., 71, 377 (1999).

any uncertainty associated with a disinfection model should be accounted for when the model is used in design.The specific objectives of this research were to: (1) develop and test an empirical UV disinfection model for predicting total coliform inactivation in unfiltered activated sludge effluents; (2) to develop a method of accounting for the uncertainty in the empirical model predictions; and (3) to develop a protocol for using the empirical model in the design and sizing of UV disinfection facilities.

A fluorescent 16S rRNA oligonucleotide probe was developed specific to the family Enterobacteriaceae.The l6S oligonucleotide target sequence is 5'-CUCGCGAGAGCAAGCGG-3', corresponding to positions 1273 to 1289 on the Escherichia coli 16S rRNA. Specificity of the oligonucleotide probe to the family Enterobacteriaceae was confirmed using representative members of the 20 genera comprising the family and other selected bacteria. Successful application of the probe to an environmental habitat was demonstrated using wastewater samples collected from primary and secondary effluent of a wastewater treatment plant (WWTP). DAPT and EUB338, an oligonucleotide probe specific to thc domain Bacteria, were used to enumerate total and prokaryotic cells, respectively, in wastewater samples collected from primary and secondary effluent. The probing efficiency, defined as the number of bacteria enumerated with EUB338 divided by the total number of organisms enumerated with DAPI, in both samples was approximately 94%. The relatively high probing efficiency indicates the rRNA copy number is sufficiently high within bacteria in primary and secondary effluent to ensure a detectable fluorescent image. The oligonucleotide probe can potentially be used in the environmental engineering profession as an alternative to the standard coliform test and as a tool to evaluate the effect of upstream processes at a WWTP on disinfection performance. Water Environ. Res .• 71,75 (1999). KEYWORDS: 16S oligonucleotide probe, in situ hybridization, enteric bacteria.