Alternate: Using Your Nose to Protect Your Assets - Wastewater Odor and Corrosion Control

Wastewater collection and treatment systems play a crucial role in safeguarding public health and environmental integrity. Among the myriad of challenges faced by these facilities, odor issues have traditionally received significant attention due to their negative impact on the community. As customers and community residents complain about odors, utility leaders and local politicians often implement measures to maintain quality of life for those stakeholders. However, since most wastewater odors are related to hydrogen sulfide (H2S) and since H2S is the major contributor to wastewater infrastructure corrosion, the correlation between foul odors and corrosion of critical components within wastewater systems is strong. Measures taken to prevent release of odors don't necessarily address corrosive H2S levels within the infrastructure. However, measures taken to control corrosion almost always simultaneously reduce odors to acceptable levels. Therefore, an odor complaint is an opportunity to identify and protect at-risk infrastructure. This paper discusses the reactions in a collection system that can result in odors and corrosion, reviews mitigation methods for odors and corrosion, and presents a case history of a utility that has observed the benefits of a corrosion-focused mitigation program. Wastewater is a complex and ever-changing medium. The mixture of organic and inorganic substances, along with bacterial populations and debris such as rags, grit, and other materials, creates an environment where chemical and biochemical reactions continually occur. Thus, wastewater that enters a collection system will have a different composition when it arrives downstream at the treatment facility. It is important to recognize collection system water quality changes and address them to minimize adverse impacts. H2S is an odorous and dangerous gas. In addition to causing odor and safety concerns, it also leads to the formation of sulfuric acid which can cause severe corrosion and premature failure of wastewater infrastructure. H2S is rarely contributed to the collection system via collected flows & it is usually formed in the collection system bioreactor. Once formed, H2S presents safety risks for utility personnel, corrosion risk from sulfuric acid production, and odor risk from its distinctive rotten egg smell. There are four main factors that contribute to H2S in wastewater collection systems: wastewater dissolved sulfide concentration, wastewater pH, turbulence, and wastewater temperature. The paper reviews each of these factors in detail. Consideration during design can reduce sulfide generation and enhance the overall sustainability of the collection and treatment system. The paper discusses the following design topics: limit anaerobic conditions, minimize and enforce pretreatment, design for the growth curve, design for a corrosive environment, and targeted ventilation. A case history of Manatee County Utilities (MCU) is presented. MCU's historical approach to collection system design and operation has focused on hydraulics and odor control. The utility has operated a robust odor control program since the 1980s using both chemical dosing and ventilation to achieve odor control objectives. In 2018, MCU expanded the focus of the odor control program to include infrastructure protection via corrosion control. This involved a closer examination of the collection system bioreactions and new control strategies. The paper will discuss the strategies employed by MCU and present the results of the program.