There are four common methods of expressing the intensity/concentration of odor within a system. These are the Perceptibility Threshold (ATC: Absolute Threshold Concentration), Odor Number (TON: Threshold Odor Number), Maximum Exposure Concentration (TVL: Threshold Limit Value), and Maximum Allowable Concentration (MAC). A description about each can be found below:Perceptibility Threshold (ATC): ATC is the minimum concentration that is detectable by 100% (some cases only up to 50%) of persons participating in a sense of smell analysis. Imagine 100 people are in a room. The ATC concentration would be the concentration of smell that is detected by all 100 people in the room. This means there is no question as to whether there is an odor.Odor Number (TON): TON is the number of dilutions needed to reduce the current concentration of smell to ATC. This means that the current concentration of odor is more than the ATC and must be diluted to get to the threshold. The amount of dilutions (which is a preset value used in a laboratory) needed to reduce this concentration is the TON.Maximum Exposure Concentration (TLV): TLV is the maximum concentration a person can be exposed to for 8 hours a day, 5 days a week and 50 weeks a year for a work life of 40 years. Maximum Allowable Concentration (MAC): Is a preset concentration that should never be exceeded. This is defined by the agency governing the concentration. Below is a chart showing some common amounts of concentration for the categories above:

Odor control has many factors that come into consideration for design. According to Dr. Giancarlo Riva and Anthony Sacco in their article Sewage and Wastewater Odor Control “ Some significant factors in designing odor control systems are: type of odor, odor concentration, temperature, specific ozone dose, contact chamber retention time, waste water acceptability criteria and type of scrubbing (odor control) system”. In lift station odor control other design factors include: wet well size, storage capacity, and the amount of influent water usually expressed in gallons per minute. It is important to keep in mind they type of odor control and the mechanical and electrical aspects involved in order to run the odor control system to be sure it fits on site. This can be especially important when trying to integrate the odor control system into a control building or shelter. The designer must be sure that the odor control system fits into the site as specified by the client (ie is a chemical odor control tank housed inside or outside of the control building). Romtec Utilities can assist in this design and can ensure all aspects of the lift station design, including odor control, fit within the site and/or control building/shelter.

Most odor control systems can be classified into one of four categories. These categories include Chemical Adsorption, Biological Oxidation, Chemical Scrubbing, and Combined Technologies. Below is a brief description of each category. Further explanation on each type can be found in their corresponding individual FAQs. Adsorption: Adsorption is the adherence of ions/molecules, gas, liquid, or dissolved material to the surface of a solid. It is also the adherence of ions from an aqueous solution to a solid mineral surface. Adsorption is not to be confused with absorption. Some companies providing adsorption odor control include: Megtec, APC Technologies Inc. Biological Oxidization: Biological oxidations is a process where bacteria and other micro-organisms consume dissolved oxygen and organics substances using the energy released to change organic carbon into carbon dioxide and cellular material. There are two main categories of Biological oxidation. These are bio-oxidation using inorganic media (bio-scrubbers/bio-trickling filters) and bio-oxidation using organic media (bio-filters). Some companies providing bio-oxidation odor control include: Megtec, APC Technologies Inc, Zabocs Biological Odor Control. Chemical Scrubbing: This is also known as chemical absorption. It is defined as the “taking of one substance directly into another substance”. Absorption can be a physical or chemical process. Some companies providing bio-oxidation odor control include: Pacific Service & Supply Co., Inc., Lantec, ERG Air Pollution Control. Combination Technologies: This is combining the technologies of the types of odor control technologies above.

Odor control can be broken down into two main categories: 1) Eliminating odor in the air 2) Changing the chemistry of the water to keep the water from going septic. There advantages and disadvantages to both types of odor control. For example, simply treating the air in the system may be more economical for the lift station customer but many treatment plants wont except the septic water without treatment. The treatment plant may not have the capability to treat the influent waste water, especially if many lift stations of this nature are coming to the treatment plant, or they may not want to have the responsibility of treating the water when it is sourced from another owner (i.e. the lift station owner). There are obvious cost to the treatment and the treatment plant may not want the responsibility. Another factor could be the intensity of the smell. The system may have a low odor that doesn’t need chemical treatment and air treatment would be the best option. However, the smell intensity of the waste water may be due to high concentrations and changing the chemistry of the water may be the best/only option for treatment. There are many other factor for choosing one category over the other. Things like distribution of odor control systems in the area, industrial facility requirements, the surrounding environment, community involvement, ect all contribute to the determination of the odor control system. Romtec Utilities can help assist in getting the right kind of odor control that you need.

One example of an odor control system is a chemical feed system which will allow any number of chemicals to feed into the wet well of a pump station. This chemical feed can be a time controlled feed, a manually adjusted drip feed, or an automated rate fed into the force main. This system allows for the usage of a number of chemicals to achieve the desired odor reduction, as well as minimizing the formation of H2S (Hydrogen Sulfide).