PAC Dosing Recommendations

After selection of a PAC brand, a dose-MIB removal nomograph should be developed. A Dose-MIB removal plot for Norit 20B is shown in Figure 1. yongruida coconut shell activated carbonThe graphs are developed by conducting similar experiments as for the Index value, except for just a single PAC brand and 2 or 3 different MIB initial concentrations (e.g., 30, 50, 70 ng/L). In separate experiments the PAC dose is varied (e.g., 1, 3, 5, 8, 12, 16, 20, 25, 30, 40 mg/L). After the prescribed contact time the samples are syringe-filtered and analyzed for MIB. Data are plotted as C/Co versus PAC dose. For different initial MIB concentration the C/Co versus PAC dose should overlay, since fractional MIB removal is independent of initial concentration. All the data together should be fit with a best-fit equation (e.g., exponential fit – Equation 2). The best-fit equation can be used directly to compute a PAC dose (see below) or used to generate a dose-MIB removal nomograph (Figure 1).

Where the raw (MIBraw) and finished (MIBfinished) water MIB concentrations are in ng/L. For example, if the influent MIB concentration is 30 ng/L and the desired effluent MIB concentration is 10 ng/L, a 20B PAC dose of about 11.9 ng/L would be required. Practical operating curves were generated for future use of Norit 20B by all C.O.P. WTPs (Figure 1). The operating curves are easy to use nomigraphs what can be used in replacement of Equations 2 and 3, although the equations are more accurate than reading from the nomigraph.

Slurry storage of Norit 20B PAC at a full-scale WTP for approximately 6-months did not effect its removal efficiency for MIB in raw water. However, ordering and storage of PAC is critical for effective MIB removal. On-site PAC storage should be based upon maximum PAC feed rates, maximum design WTP flowrate, and deliveries every five to seven days. A schedule of PAC deliveries should be prepared and provided to PAC suppliers at least one month in advance. PAC feed facilities should be designed for 40 to 50 mg/L of PAC. granular carbon

PAC doses should be varied with flowrate and approximately weekly GC/MS analysis of raw and finished water MIB and Geosmin concentrations. Alternatively FPA can be used more frequently to adjust PAC dosages, however, weekly confirmation by GC/MS should be included. Costs for PAC exceed $25,000 per week during series MIB (assuming 15 mg/L, 100 MGD, $0.30/lb PAC). Therefore conducting GC/MS analysis for MIB of raw and finished water to optimize PAC dose (Equation 3) can be extremely cost effective. It is critical that the analytical laboratories know in advance of the MIB/Geosmin sampling and need for rapid (1 day) turnaround on the data. All WTPs within a city should be sampled and analyzed on the same day (e.g., Monday), and PAC doses adjusted accordingly within 2-days (e.g., Wednesday).