Wastewater treatment plant odor control systems utilize significant resources in terms of electrical energy, water use, and, in some cases, chemical consumption. Odorous air treatment creates a domino effect of energy use through complimentary HVAC systems and their associated fuel use for heating and cooling. Optimizing the design and control of odor systems can produce substantial reductions in energy use and demand from in-plant support systems. Odor control systems are designed to conform to a variety of goals and constraints including: • Prevent fugitive emissions from covered tanks and channels • Achieve effective air treatment to minimize off-site odors and the potential for complaints from neighbors • Maintain safe working conditions in buildings with odor exposure. • Complying with NFPA 820 requirements to maintain adequate ventilation and mitigate fire hazards. These requirements often lead to odor control systems that are very conservatively designed. While the systems may perform well, these designs are often very energy inefficient and result in considerably higher operating costs than is called for. Many systems have no means of system control to operate at less than full capacity. Chemical scrubbers present special problems since they require costly chemicals and chemical solution circulation for effective odorant absorption. Many scrubbers are routinely operated without a good understanding of the correlation between pH, ORP, chlorine concentration, and wasted chlorine residual lost through the scrubber blowdown.