BIOLOGICAL TREATMENT OF COLLECTION SYSTEM ODORS IS THE MOST COST EFFECTIVE SOLUTION

The Collier County Wastewater Department currently operates three water reclamation facilities and over six hundred lift stations. Pumping stations located at the extremities of the collection system are often times situated in residential and commercial areas. Due to the flat topography of the service area, the collected wastewater is commonly repumped at several locations before it finally reaches a treatment facility. Long residence times in the collection system, in combination with high temperatures result in the generation of odorous and corrosive gases in the wastewater stream. If no preventive measures are taken these gases are released into the atmosphere at lift stations and manholes and can result in an odor nuisance for neighboring residents and businesses.In 2001 and 2002, the Collier County Public Utilities Department and Camp Dresser & McKee Inc. performed a study to investigate the potential for odor and corrosion build-up in the County's sewer collection system. The primary objectives of this study were to: identify potential problem locations in the collection system; and evaluate several liquid stream and air stream treatment technologies for their applicability at sewer pumping stations. A total of 119 lift stations were sampled for liquid and vapor phase constituents related to the generation of odors in the collection system, most notably dissolved sulfides, pH, and hydrogen sulfide.This paper focuses on the evaluation of different air stream treatment technologies for the prevention of odors and corrosion in sewer collection systems based on the findings from the Collier County Odor and Corrosion Control study. Five different fixed media technologies, including activated carbon, biofilters, bio-trickling filters, iron sponge, and iron sponge followed by activated carbon, were tested in the field for their ability to prevent odor and corrosion in the collection system. Air samples were taken at the inlet and outlet of each air stream treatment device and analyzed for chemical compounds and odors. The different technologies were ranked according to their ability to remove hydrogen sulfide and odors from the treated air. Each of the technologies was then subjected to a twenty year present worth analysis based on the inlet hydrogen sulfide concentration and the airflow. A matrix was developed to identify the lowest cost technology for foul air treatment based on the inlet hydrogen sulfide concentration and the airflow rate.The study concluded that biofiltration achieves the highest odor removal efficiency of all technologies tested. Single-use activated carbon has a distinct cost advantage over all other technologies tested for inlet hydrogen sulfide concentrations of less than 5 ppm. Biofiltration becomes the technology of choice when the average hydrogen sulfide concentration exceeds 5 ppm at airflows equal or greater than 250 cfm.