ENGINEER-OPERATOR TEAM DEVELOPS A COST-EFFECTIVE SYSTEM WIDE ODOR CONTROL PROGRAM FOR THE EXTREMELY HIGH SULFIDE CONCENTRATIONS IN THE CITY OF BROWNSVILLE, TEXAS

The City of Brownsville Texas is located at the gateway of trade between the USA and the Republic of Mexico. The City is experiencing rapid population growth along with the growth of several new and existing industries. The City of Brownsville is also located in the center of the South Texas “Sulfide Belt” where dissolved sulfide concentrations greater than 80 mg/L are common in main trunk sewers. Atmospheric hydrogen sulfide gas concentrations have been measured at greater than 2,400 ppm in manholes and lift stations and 250 ppm at the wastewater treatment plants.There are several unique features of the Brownsville wastewater which contribute to odor and corrosion problems in the collection system: long wastewater detention times, yearround warm temperatures, flat sewer slopes, many pumping stations and force mains, and high sewage sulfate concentrations. Even one of these contributory factors can present a significant sulfide problem in any municipal wastewater system. The combined factors listed above result in extremely high sulfide concentrations. These concentrations are some of the highest in North America and are two orders of magnitude higher than those measured in most U.S. cities. Because of the flat topography, the wastewater collection system is shallow and includes 137 lift stations. This paper presents the odor control program that the City is following to control its difficult wastewater odor problem.The long-term goal of this project is to eliminate continuous chemical addition to Brownsville wastewater for odor control. The plan is to install low-cost engineered biological control technologies (biofilters & RAS recycle) to replace the odor control effects of the chemical addition and chemical packed bed scrubbers. Specifically, air from lift station wet wells will be collected and vented through biofilters to remove hydrogen sulfide gas, and RAS recycle systems will be installed at the treatment plants to biologically oxidize dissolved sulfide before it can be released as hydrogen sulfide gas.