STP/GARBAGE Odour Removal

Most of the new sewage treatment plants (STP) are built in Building Basement area. The whole facility is enclosed in a single building. The STP system is a combination of Pre-treatment, primary treatment, secondary (biological) treatment and tertiary treatment. Sewage Treatment Plants produce odor compounds during the treatment process. These compounds are generated by biological processes at different steps within in the plant. Typical areas of odor emissions are the inlet pump station with bar screen chamber, oil & grease trap, biological process, sludge handling, sludge drainage. 

There is a wide spectrum of possible inorganic and organic molecules, which can create unpleasant odors. The most common are ammonia, amines,  aldehydes, ketones, sulphur compounds, hydrogen sulphide and mercaptans. Especially for treatment plants located in or nearby residence/commercial buildings these emissions lead to problems with residents. Therefore regulations are in place to reduce the emissions and set limits for selected parameters/compounds.

When the STP are built in the basement of the building, as per the rules of pollution control boards (in India) it is compulsory to provide exhaust from the STP room and it is mandatory to use ozone in the exhaust for odor destruction. Ozone is a very strong oxidizer and reacts quickly with organic compounds, since there are majorly organic compounds releasing from the STP so ozone reacts with the organic compounds instantly and oxidizes them.

• Hydrogen sulphide and ammonia are two main parameters restricted by regulations. 
• The concentration of H2S found in the exhaust air of Sewage Treatment Plant is in the range of 5 - 15 ppm.
• The emission level for ammonia is typical in the range of 50 to 150 ppm.
• Threshold limit of H2S = 0.002 - 0.15 ppm
• Threshold Limit of NH3 = 5 ppm

Normally for Reduction of Odorous gas requires the dilution with outside air. Due the large capacity of fresh air supply, a duct is required which will dilute the polluted air. Generally 5 – 7 fresh air changes are required for STP Exhaust.
The integration of Air Ozonation System and injection of Ozone into Air Handling System is the latest and most popular technology to reduce H2S and NH3 from enclosed STP Exhaust.

Role of Ozone

• Ozone is a powerful oxidant which rapidly oxidizes odorous gases such as Hydrogen sulphide and ammonia.
• Ozone Reactivity with Hydrogen Sulphide and Ammonia 

                    H2S + O3 → SO2 + H2O
                   2 NH3 + 4 O3 → NH4NO3 + 4 O2 + H2O

Advantages

Ozone is the strongest oxidant available for the treatment of odors - Ozone kills airborne pathogen & viruses - Although ozone is the strongest oxidizing agent and safe to handle - Ozone generators are manufactured in Mild Steel & Stainless Steel are easy to install - Ozone is easily generated onsite with oxygen & electricity (both are readily available) - Easy to control ozone concentration by sensors (Optional) - Compact in design combined with high efficiency - Adjustable ozone sensor (0.02 - 0.1 ppm) (Optional) - Saving Intake of Fresh Air from outside for dilution is greatly reduced up to about 80% - Oxygen for feed gas  gives constant ozone outputs without any Nitrogen compounds like (nitric acid & nitrous oxides by products). 

Salient Features

• Ozone generator system is suitable for achieving reduction in volatile organic compounds, organic odors in indoor environment.
• Ozone Generator system is does not produces any hazardous by‐products.
• Ozone Generator system does not produces NOx (Oxides of Nitrogen) so it will not generate nitric acid, which can damage the AHU Ducts.
• Feed gas to ozone generator is medical grade dry pure oxygen. Oxygen fed gas purity is 90‐93%.
• MOC of Ozone Cell is Stainless with high dissipation design.
• Dielectric Tubes is fabricated of Quartz tube to provide high efficiency dielectric.
• Electrode is air cooled / water cooled.
• The Ozone Generator is suitable for operation on 230V‐ 50Hz Single phase input power.
• Inverter is IGBT based 

Deliverables of Ozonation System 

• Ozone generator is place in STP Plant room & connected to Exhaust duct line through ozone injector.
• Ozone will be injected at entry point of exhaust air duct.
• Ozone will be dosed between 0.5 – 1.5 ppm @ 20 – 25 ACH
• The ozone generator is floor/skid mounted with integrally piped & wired.
• The ozone generator system is designed for continuous operation 
• Cooling System is provided for cooling of ozone cell.