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Optimizing Filtration And Disinfection Systems With A Risk-based Approach
Treated wastewater effluents contain high concentrations of particles; many of these particles are large (with diameters greater than 100 m) and consist of densely-packed bacterial cells. Microorganisms occluded in wastewater particles can be difficult to inactivate in chlorine disinfection systems, as the chlorine must first diffuse through the macro- and microscopic pore spaces prior to inactivating the occluded microorganisms. The impact of microorganisms occluded in particles is evident in disinfection, where reduced inactivation rates occur even with increasing doses of the disinfectant. Reduction of occluded microorganisms in plant effluents can be accomplished using filtration to remove the total number of particles, and disinfection to ensure that intra-particle chlorine concentrations are sufficient to inactivate the occluded microorganisms.
In addition to addressing inactivation of dispersed microorganisms, treatment systems design and operation should include consideration of the removal of microorganisms in wastewater particles that may pose a health risk in post-treated waters. In this project, a systematic approach was developed to co-optimize filtration and chemical disinfection systems to collectively reduce the concentration of occluded viable microorganisms in treated effluents to acceptable levels. The optimization process was successfully applied to wastewater samples collected from seven facilities, each with different treatment trains. A range of operating conditions was identified that resulted in acceptable treatment based on particle guidelines developed using the existent regulatory framework for indicator organisms. Extension of the current approach to a pathogen basis was considered, but current data are insufficient to adopt such a procedure although preliminary results suggest that intra-particle chlorine concentrations that are sufficient to inactivate indicator organisms may not be adequate to sufficiently reduce concentrations of occluded pathogens.
Biofiltration For Air Pollution Control
The number-one environmental threat to public health, air pollution remains a pressing problem-made even more complicated by the massive quantity and diversity of air pollution sources.
Biofiltration technology (using micro-organisms growing on porous media) is being recognized as one of the most advantageous means to convert pollutants to harmless products. Done properly, biofiltration works at a reasonable cost-utilizing inexpensive components, without requiring fuel or generating hazardous by-products.
Firmly established in Europe, biofiltration techniques are being increasingly applied in North America: Biofiltration for Air Pollution Control offers the necessary knowledge to "do it right."
The objective of this research was to investigate the clogging process in riverbank filtration (RBF) systems and identify factors significant to yield. Specific objectives included the following:
High-capacity RBF systems have been constructed in a wide range of hydrogeologic settings, and data from these sites provide insight to capacity-limiting factors in RBF systems. Field data for temperature, head, and riverbed flux rates into the riverbed were collected at Louisville, allowing estimates of riverbed hydraulic conductivity to be calculated as a function of distance from the well. These data indicated variations in riverbed hydraulic conductivity resulting from riverbed clogging and the development of unsaturated conditions. The impact of temperature on specific capacity was evaluated at four sites where adequate operating data were available. Wide variations in water viscosity associated with temperature resulted in the doubling of specific capacity from winter to summer, indicating that the rated capacity of RBF systems should be considered as a range between coldest and warmest water conditions. Information from this project was summarized into a set of recommendations for utilities considering the design of an RBF system for future water supply.
- Evaluate commonly available stream and aquifer characteristics from RBF systems with regards to system yield
- Collect data from the RBF system in Louisville and apply the information to clogging theory
- Provide recommendations regarding the design of future RBF systems with regards to riverbed clogging
- Data from the participating sites were compiled to allow easy comparison to future RBF sites.
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