Controlling odor problems in sewage collectors and wastewater treatment plants is currently one of the main objectives to reduce and prevent potential problems related to worker safety and minimize the negative social perception that odor problems can generate.
The main sources of odor generation in WWTPs are the phases in anaerobic conditions, where the lack of oxygen favors the development of sulfate-reducing bacteria that use the sulfates present in the system and reduce them to H2S, in collectors and pumping stations.
BIOCONSERVACION recently signed a contract with SIMTEJO (Grupo Águas de Portugal) for the replacement of filter media in several pumping stations located in Lisbon (Portugal).
The objective of the project was to reduce H2S levels below 1 ppmv.
SIMTEJO is a reference company in Portugal whose main strategic objective is to control the pollution of water resources. Therefore, the collection and treatment of pollutants generated in domestic and industrial activities, the protection of water resources and the guarantee that water returns to nature free of pollutants are its main objectives.
SIMTEJO aims to contribute to the well-being of about 1.5 million people in a geographical area of 1000 km2.
Pumping station characteristics
All the pumping stations present a spectrum of pollutants very similar in type and concentration, which are notably increased during the summer season.
- The pumping stations are installed outdoors, with the exception of some that are underground due to their sensitive urban location.
- The purification systems that have been implemented are basically standard upflow reactors. However, in some pumping stations, where higher flows are treated, Split type reactors have been installed in order to achieve better performance.
Characterization of emissions in pumping stations
Emissions generated in pumping stations normally contain a large number of volatile organic compounds (VOCs), H2S concentrations in the range of 10-30 ppmv, as well as other pollutants such as NH3 or mercaptans among others, depending on the nature of the wastewater. Occasionally, H2S concentration peaks of up to 100-200 ppmv can be measured. The objective is to reduce H2S concentration levels below 1 ppmv, as well as the rest of the malodorous contaminants.
Considering the nature of the emissions we are dealing with, BION carb OX was chosen as the most suitable media for the case, due to a number of advantages:
- BION Carb OX consists of a combination of very high quality wood activated carbon and a unique blend of inorganic catalytic phases, which enables an extraordinarily high H2S adsorption capacity to be achieved (80 kg H2S/100 kg BION Carb OX).
- Unlike other products, BION Carb OX does not convert H2S to sulfuric acid (H2SO4), which could lead to corrosion problems in equipment and make it difficult to dispose of the waste generated.
- Instead, the active centers of the metal oxides in BION Carb OX catalytically convert H2S to sulfur (S). The sulfur then migrates and accumulates in the micropores of the activated carbon. Consequently, the metal oxides are again available to oxidize new H2S molecules.
- BION Carb OX also performs very well in the removal of other acid gases such as sulfur dioxide (SO2) or hydrogen chloride (HCl). In addition, it is a remarkably effective means of removing some VOCs that may be present in the gas stream to be treated.
- Unlike in the case of impregnated coals, the presence of high concentrations of CO2 does not affect the H2S absorption capacity.
- Minimization of the risk of fire, due to the very high ignition temperature of the product (420 ºC).
In summary, BION Carb OX is an ideal product for use in wastewater treatment plants due to its high H2S adsorption capacity, as well as its good performance with other malodorous compounds such as methyl mercaptan and some VOCs. Other applications include refineries, paper industry, pumping stations and sludge tanks.
In-service media evaluation
BION continues to work with the end customer after the solution has been implemented and verifies the result. By evaluating the remaining capacity of the media it is possible to re-optimize the process in order to obtain the maximum profitability of the installation.
Moreover, BION tracks the evolution of several key operating parameters by means of versatile sensors that can be easily placed in the reactors. With the data collected, BION is able to re-adapt and re-optimize the process on a facility-specific basis. This strengthens the customer-supplier relationship, which results in technical improvements to the facility itself.