An innovative filter that uses a synthetic, porous filter media was tested for more than 2 years at the University of California at Davis. The filter is unusual in a number of ways: (I) the synthetic filter media is highly porous (89%), (2) filter media and bed properties can be modified because the media is compressible, (3) the fluid to be filtered flows both around and through the media instead of only flowing around the filtering media (as in granular media filters), (4) the fluid that is filtered is used to backwash the filter, (5) to backwash the filter, filter bed volume is increased mechanically, and (6) the filter operates at high filtration rates (e.g., 410 to 1230 Um 2 'min [10 to 30 gal/min/sq ft]). Performance of the filter, with respect to removal of turbidity and total suspended solids, is similar to the performance of other more conventional filters with the exception that filtration rate is more than 3 to 6 times the rate of other filters. Also, percent backwash water required is significantly less than that used in conventional filtration technologies (typically 2 to 3% versus 6 to 15%). Water Environ. Res., 71,1171 (1999).
A new filter employing a compressible filter medium has been evaluated for the filtration of secondary effluent. The ability to adjust the properties of the filter medium by altering the degree of the bed compression is a significant departure from the conventional depth filtration technology. Unlike conventional filters, it is possible to optimize the performance of the Fuzzy Filter during the filtration cycle by adjusting the medium properties (i.e., collector size, porosity, and depth) to respond to the variations in the influent quality. Because the use of a compressible filter medium is a new development, none of the existing filter models can be used to predict the performance of the Fuzzy Filter. The development of a predictive model that can be used to describe the filtration performance of the Fuzzy Filter is presented and discussed in this paper.A new equation, based on the conservation of mass principle and depth filtration kinetics, was developed taking into account the fact that the properties of the filter medium change with time and depth. The inherent nonlinearity of the problem, caused by the dependency of the concentration, the accumulation of solids within the filter medium, and the medium properties on each other was considered when deriving and solving the new equation. The following hyperbolic type second order nonlinear partial differential equation, which governs the concentration of particulate material as a function of filter medium depth and time, was derived:where C = concentration of particulate material, t = time, x = medium depth in the direction of the flow, v = approach filtration velocity, max σ = maximum mass amount of particulate material that can be accumulated within the medium (usually referred as specific deposit) λ = filter coefficientThe modeling results obtained for different filtration conditions are presented in this paper. The model does not depend on variable empirical coefficients, and can be used to predict the performance of full scale installations.
Over the past 20 years, various new filter technologies have been developed that can be used to (a) enhance the performance of or (b) replace conventional primary treatment facilities. To enhance the performance of a primary sedimentation facility, primary effluent is filtered to further reduce the constituent concentrations discharged to the secondary treatment facilities. This form of primary enhancement is known as primary effluent filtration (PEF). In the second case, where some type of filter technology is used to replace primary sedimentation, the process application is known as primary filtration (PF). The principal focus of this paper is on the performance of the first full-scale PF project using a fine pore cloth media disk filter to maximize the diversion of carbon for the production of energy and to reduce energy usage. Performance data from related pilot-scale cloth disk primary filter (CDPF) systems are included for process verification. The removal performance for total suspended solids (TSS) from the three CDPF installations varied from 83% to 85%, as compared to 55%-60% typically achieved with primary sedimentation. The total overall TSS removal performance achieved with PF is essentially the same as that achieved with PEF, without the need for a primary sedimentation tank. The removal performance for five-day biochemical oxygen demand (BOD 5) from the three CDPF installations varied from 46% to 58%, as compared to 32%-38% BOD removal typically achieved with primary sedimentation. The full-scale CDPF results reported in this paper are from an ongoing research and demonstration project, conducted for the California Energy Commission (CEC), to demonstrate the potential energy savings that can be achieved through the implementation of PF. © 2020 Water Environment Federation • Practitioner points • The performance of the first full-scale primary filtration system using a fine pore cloth disc filter is evaluated in this project. • Design and operational criteria of the primary filtration technology were established in this project to implement in full scale installations. • Primary filtration was demonstrated to increase the diversion of carbon for the production of energy and to reduce energy usage. • Significant decrease in aeration power requirement and increase in digester gas production are possible with primary filtration. • Footprint reduction (both for primary and secondary treatment) are other important attributes of primary filtration.
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