Performance evaluation of first full-scale primary filtration using a fine pore cloth media disk filter.

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 (BOD5 ) 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 on-going 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. 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.

Modeling depth filtration of activated sludge effluent using a compressible medium filter.

A new filter, using 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 medium compression is a significant departure from conventional depth-filtration technology. Unlike conventional filters, it is possible to optimize the performance of the compressible-medium filter (CMF) by adjusting the medium properties (i.e., collector size, porosity, and depth) to respond to the variations in influent quality. Because existing filter models cannot be used to predict the performance of the CMF, a new predictive model has been developed to describe the filtration performance of the CMF and the effect of medium-compression ratio. The model accounts for the fact that the properties of the filter medium change with time and depth. The model, developed for heterodisperse suspensions and variable influent total suspended solids concentrations, can be used to predict all possible phases of filtration (i.e., ripening, constant removal, and breakthrough). A hyperbolic-type, second-order, nonlinear, partial-differential equation was derived to model the CMF. The equation was solved using the finite-difference numerical method. The accuracy of the numerical method was tested by a sensitivity analysis and a convergence test. The model is first-order accurate with respect to medium depth and time. Field data were obtained for the filtration of settled secondary effluent using a CMF with a capacity of 1200 m3/d. Model predictions were compared with observed performance from filter runs conducted at medium-compression ratios between 15 and 40% and filtration rates from 410 to 820 L/m2 min. The difference between the observed and the predicted values was found to be within 0 to 15%.