Deodorization project: ROPEC WWTP (Ottawa)
Project Description
BION has recently been awarded the supply of high capacity odour removal filter media for two deodorization systems at a wastewater treatment plant (WWTP) located in the Canadian capital, Ottawa.
The Robert O. Pickard Environmental Centre (ROPEC) is located in the east end of the city, right next to the Ottawa River. Using an extensive sewer network, it collects all wastewater from urban and industrial areas between Stittsville, Orleans and Manotick.
The ROPEC WWTP treats an average of 390 million liters of wastewater per day, generating 39 tons of dry biosolids per day, which are used as agricultural fertilizer.
The ROPEC treatment plant has a significant number of carbon-packed tanks to purify all the polluted streams generated in different areas of the plant. They are all vertical fixed beds, packed with filtering granules supported on fiber-reinforced plastic grids (Figure 1).
The media tanks were originally designed for in situ regeneration (using water and caustic solutions). However, regeneration is an arduous process and the filter media tended to lose, on average, 70% of its initial capacity.
In order to obtain an optimal solution, the City of Ottawa launched a tender for the supply of activated carbon, determining a number of criteria (capacity, odor removal efficiency, surface area, pore size distribution, bulk density, etc...).
After evaluating all the bidders, Chemco Inc, Bioconservacion's Canadian distributor, was awarded the contract to supply the replacement filter granules for the deodorization of the Pretreatment zone (grids) and Biosolids.
Characterization of Wastewater Treatment Plant Emissions
Typical gaseous emissions at a WWTP include a large number of volatile organic compounds (VOCs), H2S at concentrations between 10 - 50 ppmv, reduced sulfur compounds and other pollutants such as NH3 or mercaptans among others. Depending on the nature of the wastewater and the area of the plant, the concentration of the contaminants can vary in composition and concentration.
The objective of this project was to reduce H2S concentration levels to concentrations below 1 ppmv, as well as decreasing concentrations of the other odorous pollutants.
The ROPEC WWTP deodorization tanks can be divided into three main areas, where the composition of the streams is assumed to be similar. This consideration was carried out assuming a relative humidity of at least 90% and a temperature between 10 - 30 ° C. The areas considered and the requirements of the granulates without the following:
Pretreatment Zones: require granulates with high capacity for the removal of H2S, reduced sulfur compounds (mainly DMS, DMDS, MM) and a wide variety of volatile organic compounds (VOCs).
Biosolids Zone: requires granulates with high affinity for H2S, reduced sulfur compounds (mainly DMS, DMDS, MM), volatile organic compounds (VOCs) and ammonia / amines.
Solution
After studying the composition and concentration of the flows to be treated, as well as the design of existing facilities, Bioconservacion proposes the following solution:
- Pretreatment zones: 100% BION Carb OX.
- Biosolids Zone: 75% BION Carb OX and 25% BION ACPA.
It is important to note that the proposed solution does not require any regeneration, which simplifies the operation of the purification systems.
Description of the filtering granulates:
BION ACPA consists of a carbon impregnated with an acidic compound for the reduction of basic contaminants, such as ammonia or amines.
BION carb OX consists of a high quality wood activated carbon and a unique blend of inorganic catalytic phases, which allows an extraordinarily high H2S adsorption capacity up to values of 80% w/w (80 kg H2S/half kg 100).
Compared to other products, BION carb Ox does not convert H2S into sulfuric acid (H2SO4), which could cause corrosion problems in equipment. The active metal oxide centers of BION Carb OX convert H2S into sulfur (S). This sulfur subsequently migrates and accumulates in the micropores of the activated carbon. As a result, the metal oxides are again available to oxidize new H2S molecules.
BION carb OX achieves very effective results in the removal of other acid gases such as sulfur dioxide (SO2) and hydrogen chloride (HCl). In addition, it is a very effective granulate for the removal of volatile organic compounds, which are most likely to be found in the gas stream to be treated.
Unlike other impregnated carbons, the high H2S adsorption capacity is not affected, even in the presence of high CO2 levels. In addition, it has a high ignition temperature (420 ºC), which minimizes the risk of bed fire.
Thanks to these advantages, BION carb OX filter granules are ideal for use in wastewater treatment plants due to their high H2S removal efficiency, as well as their affinity for other typical malodorous compounds such as mercaptans and a wide range of volatile organic compounds. Other applications where this granulate can be used are: refineries, pulp and paper mills, pumping stations, sludge storage tanks, composting facilities, etc.
Performance evaluation
BION offers a customized service through a close relationship with our partners and end customers, which continues once the solution has been implemented.
Chemco and Bioconservacion visit this plant once the contract has been awarded, before the supply of the filter granulates and during the changeover, in order to witness the installation and answer any questions that may arise.
BION also offers the service of performing a remaining life analysis of the filtering granulates, halfway through their estimated life, in order to optimize the replacement of the granulate mix, in the event that the actual working conditions differ from the initial ones taken into account in the characterization.
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