Evaluation of Chemical Treatment Alternatives for Odor and Corrosion Control in a Large, Coastal Florida Collection System

Pinellas County is a coastal municipality that is part of the Tampa Bay Area, located on the west coast of Florida. The Pinellas County Utilities Department (PCU) serves more than 80,000 customers of the 300,000 residents that make up the unincorporated population of Pinellas County. Water supplied to PCU customers is a blend composed of groundwater, treated surface water, and desalinated seawater. A number of factors contribute to odor and corrosion control issues within the PCU collection system: warm temperatures, coastal conditions, and hundreds of lift stations manifolded together with a wide range of hydraulic retention times. Without treatment, vapor phase hydrogen sulfide concentrations ranging from 23 ppm to over 1000 ppm have been observed in the collection system.From 2009 through 2013 PCU has used a turnkey service for dosing of magnesium hydroxide suspension at 18 locations in the collection system for odor and corrosion control. This contract was set to expire at the end of 2013. In the summer of 2013, PCU requested that ARCADIS perform an evaluation of various odor and corrosion control treatment chemicals for use in their collection system. Sixteen chemicals were initially identified and researched, and these chemicals were screened down to four for detailed evaluation using the following criteria: performance, cost, service and delivery, and aesthetics.This paper summarizes various liquid phase treatment methods and their modes of operation. The 16 identified odor and corrosion treatment chemicals are presented, and advantages and disadvantaged are discussed, including their applicability to PCU. The four odor and corrosion treatment chemicals identified for further analysis are evaluated in further detail, according to the criteria established by ARCADIS in collaboration with the County. Some initial analysis and recommendations for collection system optimization are also summarized.