Improving filtration for removal of Cryptosporidium oocysts and particles from drinking water

Cryptosporidium oocyst and polystyrene microsphere removals were evaluated during and after the filter ripening period with pilot-scale conventional and biological filters. Both filter types showed similar oocyst and microsphere removals (roughly 1.7- and 2.1-Log, respectively) during this study, but the biological filters exhibited marginally lower concentrations of oocysts and microspheres in effluent samples containing backwash remnant particles.; The increased passage of particles through granular media filters immediately following backwashing is commonly known as the filter ripening period. A new filter backwashing strategy aimed at eliminating the ripening period, the extended terminal subfluidization wash (ETSW), has been developed and successfully evaluated on both pilot-scale and plant-scale filters. The filter ripening sequence (FRS), or the stages of filtration that occur immediately following backwashing, has been described with new clarity based on the interpretation of experimental results.; Delayed start is an operational procedure aimed at reducing the negative impact of the FRS on filtered water quality that has been evaluated under a variety of conditions to provide insights into the mechanisms behind the FRS. Experiments were conducted at both the pilot and plant scales, and a comparison of these results led to the discovery of the importance of backwash water chemistry on the FRS. Both chlorine and polyphosphates in the backwash water were shown to negatively impact filtered water quality immediately after backwashing. Discoveries were also made that will help explain why delayed start works well for some treatment plants and yet not for others.; Many previous Cryptosporidium removal studies have shown removals ranging from 2- to 6-Log under “optimal” treatment conditions via filtration. The factors influencing which region of this spectrum that results fell had not been determined previously. A series of jar tests were performed to determine optimum coagulation conditions (with several different coagulation schemes) for raw water from Lake Lanier. The previously determined optimum coagulation conditions were utilized in the seeding process of a direct filtration pilot filter to assess polystyrene microsphere removals (as a Cryptosporidium surrogate). Microsphere removals ranged between 2- and 6-Log under these “optimum“' conditions, and the removals were proportional to the coagulant dose.