4 common odor removal methods for sewage treatment plants

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1. Odors are generated when nitrogen- and sulfur-containing organic compounds in wastewater undergo biological degradation under anaerobic conditions. The sources of odor in wastewater treatment plants are mainly found in the pretreatment area and the sludge treatment area; the aerobic treatment process in wastewater treatment is not a place where odor occurs, provided it is properly designed and operated. 2. Odor emission standards: The exhaust gas emission standards shall be complied with in accordance with the requirements specified in the \"Emission Standards for Pollutants from Urban Sewage Treatment Plants\" (GB18918—2002). According to this standard, the exhaust gas emission limits for wastewater treatment plants are set in accordance with the second-level standards for the maximum allowable concentration of exhaust gases at the plant boundary (edge of the protection zone). That is: ammonia: 1.5 mg/m3, hydrogen sulfide: 0.06 mg/m3, odor concentration: 20 mg/m3, methane (maximum volume percentage in the plant area): 1 mg/L. The methods used for odor removal have evolved over time; the commonly employed techniques include activated carbon adsorption, biological odor removal, reactive oxygen technologies, and photocatalytic technologies. 1) Activated carbon adsorption method: The activated carbon adsorption method takes advantage of the ability of activated carbon to absorb odor-causing substances in odors, thereby achieving deodorization. To achieve effective deodorization, activated carbons with various properties are typically used. In the adsorption tower, there are activated carbons designed to absorb acidic substances, those designed to absorb alkaline substances, and those designed to absorb neutral substances. After coming into contact with the odors, these activated carbons are then removed from the adsorption tower. The activated carbon adsorption method is commonly used for low-concentration odors and the post-treatment of deodorization units. 2) Biological deodorization: Over the past 30 years, biological deodorization technology has been widely used in Europe, and more recently it has also been applied for deodorization in North America. Biological deodorization relies on microorganisms to remove and oxidize the odor-causing components in gases. As the gas passes through the bioactive filter media, the bacteria present on these media break down the odor-causing substances, producing carbon dioxide and water vapor. Microorganisms parasitize on the moist filter media, forming a thin biofilm; when odor-causing substances pass through the filter media, they are adsorbed and oxidized. Advantages of biological deodorization: Simple operation and management; lower investment costs as well as operating and maintenance expenses compared to other deodorization processes; wide range of applications, including H2S, CS2, ammonia nitrogen, organic sulfides, etc. 3) Reactive oxygen technology utilizes a special pulsed discharge method based on high-frequency, high-voltage electrostatic fields (with reactive oxygen emission tubes releasing hundreds of billions of high-energy ions per second) to generate a high-density supply of high-energy reactive oxygen (a transitional state of oxygen between oxygen molecules and ozone). This reactive oxygen rapidly collides with pollutant molecules, activating them and destroying them directly ； Alternatively, high-energy reactive oxygen species activate oxygen molecules in the air to produce secondary reactive oxygen species, which initiate a series of chain reactions with organic molecules. The energy generated by these reactions is used to sustain the oxidation process, further oxidizing organic substances to produce carbon dioxide, water, and other small molecules; this approach can achieve a very high treatment efficiency in an extremely short time. 4) Photocatalytic technology: Photocatalytic technology is a new type of advanced composite nanotechnology. Its basic principle involves the use of photocatalytic nanoparticles, which, when exposed to ultraviolet light of certain wavelengths, are excited to generate electron-hole pairs. With the participation of oxygen and water, these holes decompose the water adsorbed on the surface of the catalyst, producing highly reactive hydroxyl radicals (•OH). The electron holes then reduce the oxygen surrounding them into active oxygen ions, thereby enabling strong oxidation-reduction reactions. Thanks to this strong oxidizing capacity, various pollutants on the surface of the photocatalytic nanoparticles can be oxidized, and low-concentration chemical pollutants in the air can be broken down into harmless substances, thus achieving the purpose of air purification.