The design team at West Yost Engineers was tasked with finding a better alternative to hypo dosing. Several technologies were explored:

1. Upstream Chemical Treatment: Dosing chemicals like calcium nitrate, sodium hydroxide, or ozone upstream of the wet well. Not viable because EBMUD does not own the upstream sewer system, and setting up new dosing facilities in a residential area was not feasible.
2. On-site Hypochlorite Generation: Required regular salt deliveries and came with hydrogen gas venting risk—a major safety concern. Also, still involved chemical deliveries and increased environmental impact.
3. Ozone (O3) Generation: Ozone is a powerful oxidizing agent with proven odor control effectiveness. On-site ozone generation would introduce ozone into wastewater through a wet well air lift pump. Ozone generation with detection sensors for level monitoring was ultimately chosen, due to its high efficiency.
4. Carbon Adsorption: The team also considered adsorptive media systems like carbon filtration. New carbon canisters were installed to complement the AOP system, providing an additional layer of odor control.

Most promising was the Advanced Oxidation Process (AOP), utilizing ozone generation in conjunction with carbon adsorption for odor control. The AOP system at PSM consists of two Titus Wastewater Solutions ozone generators that produce up to 40 grams of ozone per hour when both are operating. These generators work by creating a corona discharge, which ionizes the air and converts oxygen into ozone, a potent oxidizer that reacts with odor-causing compounds in wastewater.

The ozone generators were housed in stainless steel enclosures with noise-reducing padding, air conditioning, and particulate filters, to maintain an optimal operating environment. A key safety feature of the AOP system is the integration of O3 sensors that automatically shut down the system if ozone levels exceed safe thresholds. This ensures that operators can safely monitor and maintain the system.

In addition to ozone generators, Titus Twister mixing aerators were installed in the wet well to help distribute the ozone throughout the wastewater and improve mixing. These aerators serve multiple purposes:

• Odor Control: Ozone reacts with wastewater contaminants to neutralize odors.
• Wastewater Agitation: The aerators break down fats, oils, and grease (FOG) and prevent mop heads from forming. Mop heads are large balls of personal wipes or rags that form in turbulence at the bottom of the pump station. When ingested into a pump, they can cause significant damage. Individual rags can easily pass through a pump without damaging or clogging it. This ensures better pump performance and reduces maintenance.

The installation of the Twister aerators was straightforward, and they worked in tandem with the ozone generators to enhance the overall odor control system. The aerators can also operate without ozone to provide agitation, further improving wastewater quality and pump performance.

The Bay Area Air Authority limited the amount of ozone that could be injected into the wet well, somewhat limiting the AOP system’s effectiveness. While it neutralized most odors, some remained, which was addressed with the addition of carbon canisters. They were installed downstream of the AOP system to adsorb any remaining hydrogen sulfide (H2S) gas. Each canister is filled with 140 pounds of activated carbon, capturing odor-causing contaminants. As the ozone injected into the wastewater eliminates most of the dissolved sulfides, and thus the H2S gases, the carbon filters should need very little maintenance.