MIAMI DADES HIGH RATE DISINFECTION PILOT IS FILTRATION REALLY NECESSARY

This paper presents results of Miami-Dade Water and Sewer Department's (MDWASD) pilot testing of alternative disinfection technologies at their MDWASD South District Wastewater Treatment Facility (WWTF). The purpose of this disinfection demonstration was to compare high-rate disinfection (HRD) using chlorine dioxide (ClO2) and ultraviolet light (UV) to high-level disinfection (HLD) with chlorine as defined in Chapter 62-600.440(5) of the Florida Administrative Code (FAC). HLD includes deep bed sand filtration followed by conventional chlorination with 35 min contact time.HRD-ClO2 and UV were piloted without preceding filtration using secondary effluent as influent; both were designed to treat 100 gpm. These pilots were operated in parallel to an existing 1-MGD HLD system previously installed at South district WWTF. Equivalency of the HRD, ClO2 and UV to the HLD was based on meeting pathogen guidelines values stipulated by Florida Department of Protection (FDEP) as shown in Table 1.It is important to note that the pathogen guidelines presented in Table 1 are in terms of “viable” protozoan counts per 100 liters and PFU/100L for enterovirus. Through discussions with the US EPA and negotiations with FDEP, consensus was reached on the interpretation and method of analyses of values specific to this demonstration.”Viable” protozoan was interpreted by Miami-Dade as the true viability values. An Alternate Testing Plan (ATP) was developed for testing of viable protozoan for this project. The ATP was reviewed and approved by US EPA. This paper will describe the details of this ATP. Full Scale Pilot The project included two distinct sampling methods for conducting the full-scale pilot demonstration for each of the samples shown in Table 1 namely, conventional water quality (CWQ) sampling and pathogen sampling analyses.The purpose of the pathogen sampling was to determine if the alternative disinfection technologies could meet either FDEP pathogen guideline values (Table 1) or pathogen reduction equivalent to the optimized HLD. Pathogen analyses included Cryptosporidium, Giardia and enterovirus as outlined in the Consent Order (agreement between FDEP and MDWASD) in addition to true viable analyses under the ATP procedures.A description of each sampling location is illustrated in Figure 1.S1 (Common Influent), which served as influent to the HLD, UV and HRD/ClO2 pilotsS2 (Filter Effluent Prior to Chlorination), which served as influent HLD chlorination processS3 (Chlorinated Effluent), which served as the effluent to the HLD systemS4- UV EffluentS5- HRD/ClO2 EffluentFigure 1 provides a schematic of the disinfection demonstration with sampling locations delineated.In addition, a smaller flow, side-stream pilot was used to seed and sample for “viable” Giardia and Cryptosporidium. The full-scale HLD filter effluent was used for the samples for the side-stream pilot while the chlorination process was simulated in the laboratory.Samples were analyzed for “viable” Cryptosporidium oocysts and Giardia cysts using the methods described in the US EPA approved ATP application. A QA/QC program was implemented to identify changes in wastewater quality during the shipping process to specialty laboratory. CWQ and bacteria samples were collected and shipped to respective laboratories. These data were compared to the water quality data collected after transport and disinfection in the specialty laboratory to identify any changes in water quality.Laboratory results will be described in this paper from the full scale and side stream pilots. It will show how each alternative disinfection approach compared to the HLD pathogen guidelines values stipulated by Florida Department of Protection. A discussion on weather filtration is required to meet the FDEP pathogen guidelines will be presented.