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TREATING SMELLS WITH SHELLS
www.bnm-us.com
Bord na Mona Environmental Products U.S. Inc., the American market subsidiary of the State-owned Irish Utility group Bord na Mona, recently launched a range of wastewater treatment solutions and new odor/VOC control technologies in the United States. A large and diverse group, Bord na Mona initiated research into alternative uses for peat over twenty years ago. Key to this program was the utilisation of peat for the treatment of waste water and odor and VOC air emissions.
Bord na Mona Environmental has over twenty years experience in developing and implementing environmental solutions for the treatment of air and water emissions. The company’s shell based technology, MÓNASHELL®, represents a radical and innovative breakthrough in the treatment of odor and VOC emissions. The technology has been employed on over five hundred installations around the world. This highly effective, low cost technology radically broadened the field of applications for biotechnologies due to its capacity to treat high concentrations of difficult compounds. This effectively paves the way for biotechnologies to compete against chemical scrubbers and thermal systems with a low cost sustainable robust alternative with minimum energy and zero chemical inputs.
Biological Treatment Technologies
A number of key parameters need to be identified and characterised prior to discussing in detail the development and relative merits of biological and enhanced biological treatment technologies. A clear understanding of the inter-relationship between containment structures, ventilation rates, appropriate equipment selection, achievement of the necessary efficiencies and most importantly, capital and operational cost is required. Furthermore, to develop successful control strategies an understanding of odor measurement and chemical characterisation of the chemical constituents specifically responsible for affecting odor (the perception of odor is essentially a reaction by the human olfactometric system to specific chemical compounds) is required. An understanding of dispersion modelling to assess the impact to boundary and the nearest sensitive receptor is also useful. These fore mentioned variables are essential for establishing inlet conditions and performance parameters prior to selection of an odor abatement process.
One further point which warrants reinforcement is that the removal of the dominant odorous component from the air stream does not guarantee significant odor removal as other compounds which were previously being masked will now contribute to an overall odor. The requirement for an effective odor removal plant is good removal performance for the full range of compounds, which have low odor threshold values (i.e. those whose odor may be detected at very low concentrations).
Wastewater Applications
In the main, when dealing with municipal wastewater treatment plants, most odors arise where anaerobic conditions (no oxygen) are prevalent allowing sulphur reducing bacteria to flourish. The result is the formation of dissolved sulphides/hydrogen sulphide in the wastewater which will be released to atmosphere where conditions are favourable (typically high liquid/air interface and liquid turbulence). The problem is exacerbated during periods of warm weather, as biological activity increases with temperature (leading to an increased rate of production of odorous compounds).
Reducing septically will significantly reduce odors and it is a valid strategy for effective odor control. However, it will not necessarily provide the degree of performance and reliability required. Where the potential for significant odor emissions exists, such factors as containment, ventilation and treatment need also to be considered. Before discussing biological treatment options in detail it is critical to understand the relationship between (minimising volume and air tight) containment, which will lead to a reduction in the ventilation requirement (leading to reduced air flow duct work and efficient fan power requirements and size of odor control equipment) and the converse effect on concentration (i.e. increased concentration) of contaminants and hence the challenge to the odor control equipment.
Traditionally, the most prevalent abatement technologies employed for odor control on wastewater are as follows:
Adsorbtion Dry impregnated activated media (Carbon/Alumina)
Chemical Scrubbing Generally two or three stage scrubbing and chemical oxidation to remove different groups of odorous compounds.
Biofiltration Traditionally using organic based media such as peat/heather, compost, woodchip as a capture and support substitute for micro-organisms (capture and biological oxidisation).
Bio-Trickling Filters Typically utilising plastic packing as mass transfer and support substance for micro-organisms.
All of the above technologies possess strengths and weaknesses in relation to applications on wastewater treatment. Of note, however, is that very often, to achieve the required performance, the technologies are combined to affect full treatment.
Biofiltration
Originally developed from soil filters where odorous air was passed through a bed of soil, the contaminants are removed and oxidised naturally in the soil by the action of specific bacteria. Early systems suffered problems due to drying out of the soil and the unhomogeneous nature of the material itself leading to channelling uneven distribution and poor treatment.
Significant improvements to the process were achieved through better selection of organic media and products such as peat fibre/heather mixes and granulated products. Bord na Móna’s patented MÓNAFIL product overcame these problems by offering a more homogenous engineered media with high specific surface area, high void volume, good water retention properties and drainage characteristics, and good adsorption properties.
The benefits with the Biofiltration technology are:
• Excellent removal efficiency of broad range of compounds in a single stage.
• More modern filters employing high quality media have low pressure characteristics and hence low running costs.
• No chemical consumables hence very low running costs. Final effluent can also be employed to maintain moisture content.
• Operational simplicity requires minimal maintenance and controls.
• No secondary pollution.
The drawbacks with the Biofiltration technology are:
• pH Control – the limiting factor for conventional biofilters treating sulphur compounds. This can be controlled by washing out with irrigation water however, it is generally felt that for containment levels, above 50 ppm, pre-treatment should be considered.
• Contaminated concentration a limiting factor.
• Selection of poor quality filter media leads to pressure and performance problems often giving the technology a poor reputation.
Biotrickling Filter
Biotrickling filters are constructed similar to a chemical scrubber employing randomly packed plastic packing. In comparison to a chemical scrubber a much larger contact time is employed and a nutrient solution may be added to the recirculated liquid to encourage development of a biofilm on the plastic packing.
The principle benefit of the technology is a reduced footprint when compared to biofiltration phase and an ability to handle higher concentrations by employing organic media.
The drawbacks are:
• Poor removal efficiency (typically 70%) which means this technology can rarely be employed as a stand alone technology.
• Reliance on residual water hardness for removal of sulphur compounds.
• Biofouling – if the supply water or the air stream has a significant organic component the system is prone to blocking with biomass.
• Treatment of low solubility VOC’s and organic sulphate compounds is limited.
Bord na Mona Environmental championed the development of enhanced biological technology through its research efforts to optimise operating conditions and through selection and adaptation of filtration media best suited to a particular application.
Bord na Móna’s patented MÓNASHELL technology is a process which utilises a naturally occurring shell media. The media employed has an adsorption capability (assist in capture), and in addition it has a chemical affinity for sulphur compounds (chemisorption). The physical shape, size and rigidity render it highly effective as a scrubber packing in its own right (absorption mass transfer). In addition, the pH buffing and slow release nature of the media renders it ideal for pH control. Bord na Mona has installed this MÓNASHELL technology on a large range of applications for over ten years resulting in a well established, proven process technology.
The physical and chemical properties of the shell media affects the main advantages associated with adsorption systems, wet chemical scrubbers and biological treatment systems without many of the disadvantages. It is without doubt one of the most versatile/robust technologies available for the treatment of odorous and VOC emissions. The technology is also extremely effective on the more difficult organic sulphur compounds. Bord na Mona has further developed this technology for treatment of high levels of VOC (Volatile Organic Compounds) on industrial applications.
Multi-staging Dynamic
The most recent development in the Bord na Mona suite of technologies is the use of multi-staging with a low contact time (similar retention to once through systems). This dynamic has been employed to achieve high removal efficiencies on highly concentrated air streams (>99.9% removal). The multistaging approach was developed in the field in response to the occurrence of very difficult airstreams, where Bord na Mona endeavoured to supply a solution to the end-user not entailing excessive cost. Multi-staging is now a standard design criteria in Bord na Mona when responding to client with fluctuating and high emissions where polishing is required. In addition, Bord na Mona has undertaken considerable work in-house on the use of various shell species in the MÓNASHELL system with respect to density, void space and calcium content. This has enables Bord na Mona to offer extended media life guarantees to clients which reduces life cycle costs considerably.
The significant process advantages of the Enhanced Biological Filters (MÓNASHELL) over the conventional biological systems are:
• Ability to treat high and variable contaminant levels.
• In built pH control means no addition of chemicals required.
• Ability to treat VOC’s and low solubility compounds.
• Typical efficiency achieved is 98%. Efficiencies in excess of 99.9% can be achieved by multi-staging with low contact times.
• Residual media can be disposed of to non-hazardous landfill.
• Excellent performance on the broad range of odor compounds (nitrogen, sulphur compounds and low solubility VOC’s).
• Proven on a broad range of municipal and industrial applications.
The MÓNASHELL technology has led the way for biological treatment as the odor abatement process of choice for wastewater treatment plants. The efficiency, flexibility, robustness and low capital and operating costs makes it the ideal solution for most odor control applications on wastewater treatment plants.
Cost Comparisons
It is difficult to carry out a meaningful capital cost comparison without recall to detailed specification. In general terms, it can be stated that the capital costs for chemical scrubbers, bioscrubbers and biofilters are broadly similar with activated carbon having a lower capital cost. The most significant difference in relation to operating cost is where very often the costs for twelve months operation can be more than the actual cost of the plant.
Bord na Mona in the US
Bord na Mona Environmental recently launched its Clean Air Solutions range of technologies at the 81st Annual WEFTEC Conference in Chicago. The company’s MÓNASHELL technology suitable for complex low volume, high concentration emissions is complimented by the MÓNAFIL technology which is suitable for high volume, low concentration applications. MÓNAFIL is a patented engineered peat-based organic biofilter media first developed in the early nineties. The media has developed an excellent world wide reputation and has been extensively utilised in large municipal solid waste composting plants. MÓNAFIL is differentiated by its long media life, low energy requirements (low back pressure) and proven process capability. It is one of the few biofilter media’s to meet the strict statuary legal outlet limit in Italy of 300 ou/m3.
Bord na Mona Environmental is currently treating 1,000,000 m3 per hour of air from four of the five large composting installations in Rome (Malagrotto, Viterbo, Albano, and Ama). With hundreds of MÓNASHELL installations worldwide, projects of particular note include: S.I.A.A.P. in Paris which is the largest wastewater treatment plant in Europe, Bransand Northumbrian Water UK, Monza Wastewater Treatment Facility in Italy, and a more recent addition is at Northpoint pumping station in Hong |Kong. (See attached photos)
The first MÓNASHELL installation in the U.S will be at the company’s innovation centre at the Greensboro Municipal Treatment Works where it will be independently monitored and validated by a local university. Bord na Mona Environmental U.S. Inc is looking forward to bringing their considerable expertise and technology to the North American market delivering low cost, highly effective solutions yielding significant benefits in terms of environment, cost, energy and chemical consumption and long term sustainability.
www.bnm-us.com
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