Richard E. Danielson

Evaluation of Microbial Risk Assessment Techniques and Applications

This investigation reviewed and evaluated methodologies used for microbial risk assessment with respect to their applicability for reclaimed water applications. The investigation was comprised of five primary components: a comprehensive database of articles, reports and books describing microbial risk assessment methodologies was established and reviewed. Risk assessment techniques and models were identified for estimating the public health risk from exposure to microorganisms via reclaimed water applications. Two models were identified for further evaluation: a static (individual based) and a dynamic (population based).In the third component, the two models were evaluated to differentiate between the conditions under which models predict similar and substantially different estimations of risk. Through numerical simulation, exposure/pathogen combinations were identified when it may be appropriate to use the less complex, static model. Case study risk assessment scenarios demonstrated the model selection process for three realistic, yet hypothetical reclaimed water scenarios. The fourth component presents a constraint analysis for existing reuse regulations. The constraint analysis is carried out by documenting the existing reuse regulations. The constraint analysis is carried out by documenting the existing regs in three states for landscape irrigation and uses that comparison as a starting point to identify how microbial risk assessment may be useful within the context of existing and potential future water reuse regulations. The investigation concludes by identifying criteria for a computer interface that would allow regulatory and/or municipal agencies/utilities to take advantage of the analysis discussed in the report. This title belongs to WERF Research Report Series ISBN: 9781780404141 (eBook) ISBN: 9781843396840 (Print)

City of San Diego potable reuse of reclaimed water: Final results

Abstract Water reclamation is becoming a common component of water resource planning. In the past the driving motivation for water reuse was to provide a means of avoiding effluent disposal into surface waters. With continued drought and increased water demand reclaimed wastewater is now considered an important water resource. Nonpotable and potable use of reclaimed water can enable communities to maximize and extend the use of limited water resources. This paper summarizes results from the Health Effects Study (HES) portion of the City of San Diegos Total Resource Recovery Project, which includes study and implementation of an advanced wastewater treatment system. The HES represents the product of a substantial research effort to estimate the potential health risk associated with the reclaimed water relative to an existing raw water supply to the City.

A quantitative microbial risk assessment of wastewater treatment plant blending: case study in San Francisco Bay

An investigation was carried out to evaluate the impacts of blending practices (i.e., a practice used to manage wet weather flows) on the effluent from the East Bay Municipal Utility Districts (EBMUD) wastewater treatment plant in Oakland, California and water quality in the receiving water (San Francisco Bay). A static based quantitative microbial risk assessment (QMRA) was used to estimate the incremental risk to public health from recreational exposure to adenovirus and the protozoan Giardia spp. in San Francisco Bay for wet season (generally between October and March) blending and non-blending events. The mean risks of infection per recreational exposure event during the wet season for all of the modeled scenarios were more than an order-of-magnitude below the USEPAs illness level (36 illnesses per 1000 contact events) associated with recreational water quality. While the QMRA results showed discernible differences in per event estimated risks between blending and non-blending scenarios, the estimated incremental increase in the annual number of infections due to blending (based on median estimates) resulted in an estimated combined increase of less than one infection annually. These estimates are subject to various uncertainties, including the potential for secondary transmission, assumptions on the extent of exposures, and the number of blending days required in the future due to climate change, which are discussed in this paper.