Bioconservacion has recently been awarded the supply of high capacity odor elimination media for two deodorization systems in a waste water treatment plant (WWTP) located in the Canadian capital of Ottawa.
The Robert O. Pickard Environmental Centre (ROPEC) is located in the city's east end, right next to the Ottawa River. Using an extensive sewer system, all the wastewater coming from urban and industrial areas is collected between Stittsville, Orleans and Manotick.
ROPEC WWTP treats an average of 390 million liters of wastewater per day, generating 39 dry tones of biosolids each day, which are used as agricultural fertilizer.
ROPEC WWTP plant has an important number of carbon adsorption vessels to purify all polluted streams generated in different areas of the plant. All of them are vertical fixed beds, filled with adsorption material supported by a fiber reinforced plastic grating.
Carbon vessels were originally designed for on-site regeneration (using water and caustic solutions). However, regeneration tends to be a messy business and the media tends to lose in average 70% of its initial capacity.
In order to obtain the optimal solution, the City of Ottawa launched a tender for the activated carbon supply and determined a number of criteria (breakthrough capacity, odour removal efficiencies, surface area, pore size distribution, apparent density, etc…) and evaluated and scored each proposal based on these.
After evaluating all tenderers, Chemco Inc., Bioconservacion’s Canadian distributor, was awarded the contract to supply all replacement media for both Screen and Degrit and Biosolid facility.
Waste Water Treatment Plant emissions characterization
Typical WWTP gas emissions comprise a wide number of different volatile organic compounds (VOCs), H2S concentrations in a range between 10-50 ppmv, reduced sulfur compounds and other pollutants such as NH3 or mercaptans among others. Depending on the nature of the sewage and the plant area, pollutants concentration may vary in composition and concentration. The goal of this assignment was to reduce the H2S concentration levels below 1 ppmv as well as the rest of the odorous contaminants.
Carbon vessels in the WWTP can been divided into three main areas, where streams composition are assumed to be similar. Such consideration was carried out assuming a relative humidity content of at least 90% and at an air range temperature between 10 - 30°C. Following are the areas considered and the media requirements:
- Screen and Degrit Facility: media required with high capacity for H2S removal, other reduced sulfurs compounds (mainly DMS, DMDS, MM) and a great variety of volatile organic compounds (VOCs).
- Biosolids Handling Facility: media required with high affinity for H2S, other reduced sulfurs compounds (mainly DMS, DMDS, MM), VOCs and for ammonia/ammines.
After studying the composition and concentration of odorous streams as well as the layout of the existing installations, Bioconservacion suggested the following proposal:
- Screen and Degrit Facility: 100% Bi-On Carb OX.
- Biosolids Handling Facility: 75% Bi-On Carb OX and 25 % Bi-On ACPA.
It is important to highlight that the solution suggested does not require regeneration, which makes operation of the purification systems easier.
- Bi-On ACPA consists on an impregnated carbon with an acidic compound for basic pollutants abatement such as ammonia or amines.
- Bi-On carb OX consists of an extremely high quality activated wood carbon and an exclusive mixture of inorganic catalytic phases which allows an extraordinarily high H2S absorption capacity up to values of 80% w/w (80 kg H2S/100 kg media).
Compared to other products, Bi-On carb Ox does not convert H2S into sulphuric acid (H2SO4), which can cause corrosion problems in equipment. The active centers of metal oxide in Bi-On carb Ox, convert H2S into sulphur (S). Subsequently this sulphur then migrates and is accumulated in the micropores of the active carbon. As a result, metallic oxides are again available to oxidize new H2S molecules.
Bi-On carb OX yields very effective results in the elimination of other acidic gases such as Sulphur dioxide (SO2) and hydrogen chloride (HCI). Moreover, it is a very efficient medium for eliminating VOCs which may be present in the gas stream being treated.
In contrast to impregnated carbons, the exceptionally high sulphur loading is not affected even in the presence of high CO2 levels and has a high ignition temperature (420 ºC), which minimizes the risk of bed fire.
Due to the all these advantages, Bi-On carb OX is ideal for its use in wastewater treatment plants due to its high H2S removal efficiency, as well as its affinity for other typical foul-smelling compounds such as methyl mercaptan and some VOCs. Other applications may include refineries, pulp and paper mills, pumping stations, sludge holding tanks and composting facilities.
Bioconservacion’s prides itself on a personalized service through close relationships the company establishes with our partners and final customers, which continues once the solution has been implemented. Chemco and Bioconservacion has visited the sites and met the team once the contract was awarded both before supply of the media and during change-out in order to witness the installation first-hand and answer any questions for the Municipality.
Bioconservacion has also offered to perform a remaining life analysis halfway through the media life so that the Municipality can plan ahead the next change-out and potentially optimize the mix of media in case the real field conditions have changed from the initial characterization