A waste facility in the United Kingdom processes food waste via anaerobic digestion. The site is in a mainly rural location with a number of isolated properties at least 500 m from the site boundary, so odour control is mandatory to protect harmful conditions to the environment and avoid odour nuisances.
The plant was commissioned using an ORGUS® double stage biofilter system with coconut fibre as packing material. The performance of the system was measured in February 2014. Olfactometric samples were undertaken, obtaining an average outlet odour concentration considerably lower than the discharge emission limit stipulated in the contract.
F. Sempere 1*, D. Hidalgo 1, A. Waalkens 1 and C. Gabaldón 2
1. Pure Air Solutions, P.O. Box 135, 8440 AC Heerenveen, The Netherlands.
2. Universitat de València, Avinguda Universitat s/n, 46100 Burjassot, Spain.
Corresponding author: f.sempere@pureairsolutions.nl
Competing interests: The author has declared that no competing interests exist.
Academic editor: Carlos N Díaz.
Content quality: This paper has been peer reviewed by at least two reviewers. See scientific committee here
Citation: F. Sempere, D. Hidalgo, A. Waalkens and C. Gabaldón, 2015, Odour control at a waste-to-energy anaerobic digestion plant by a full scale biofilter, III International Conference of Odours in the Environment, Bilbao, Spain, www.olores.org.
Copyright: 2015 olores.org. Open Content Creative Commons license. It is allowed to download, reuse, reprint, modify, distribute, and/or copy articles in olores.org website, as long as the original authors and source are cited. No permission is required from the authors or the publishers.
ISBN: 978-84-608-2262-2.
Keyword: Biofilter, odours, hydrogen sulphide, VOCs, municipal organic waste facility plant.
Abstract
A waste facility in the United Kingdom processes food waste via anaerobic digestion. The site is in a mainly rural location with a number of isolated properties at least 500 m from the site boundary, so odour control is mandatory to protect harmful conditions to the environment and avoid odour nuisances. The plant was commissioned using an ORGUS® double stage biofilter system (Pure Air Solutions, The Netherlands) with coconut fibre as packing material. The slab footprint of the complete odour control system including a pre-humidifier unit and a 14 m stack is only 495 m2. The ORGUS® treats 60000 m3•h-1 of odorous air coming from the food reception hall, processing plant room, and from all process tanks except the digesters.
Inoculation with activated sludge from a nearby WWTP was done in June 2013 to speed up the start-up period of the ORGUS®, and to date there have been no recorded odour nuisance complaints. The performance of the system was measured during three days in February 2014. Olfactometric samples were undertaken using the lung method, and submitted within 24 hours of collection for analysis at accredited laboratory in accordance with BSEN13725, obtaining an average outlet odour concentration of 373 ouE•m-3, considerably lower than the discharge emission limit of 1500 ouE•m-3 stipulated in the contract. Pollutant concentrations showed a removal efficiency greater than 92% of volatile organic compounds, NH3 concentrations below 0.1 ppm and 1 ppb H2S were obtained in the discharge, demonstrating the suitability of the ORGUS® system to remove odour coming from municipal waste facilities.
1. Introduction
Organic waste is a potential source of energy, worldwide available, and its valorisation offers both generation of clean electric power and environmentally safe waste management and disposal (Iakovou et al., 2010), reducing the dependency of fossil or nuclear fuels. In this sense, anaerobic digestion (AD) of the organic fraction of municipal solid waste (MSW) has experienced an exponential growth since the first plants installed in 1990; treating nowadays almost 8 million ton of organics in 244 plants. This represents about 25% of the biological MSW treatment in Europe; with a great number of composting plants having AD as a primary treatment technology (De Baere and Mattheeuws, 2012).
There are cross-side and environmental effects produced by MSW facilities, related to its production activity such as modification and damage of landscape, increase in traffic load, and particularly emission of pollutants to air or water. In this sense, odour emissions can generate annoyance to residents living nearby; reporting respiratory problems, eye irritation, hoarseness and unusual tiredness among others physical symptoms from people living within 1.5 and 5.0 km from the facility (Aatamila et al., 2011). Therefore, odour emissions must be controlled in order to avoid harmful conditions to people and the environment, besides promoting MSW facilities to be socially accepted.
The European Commission (2003) considered biological treatments as best available techniques for the treatment of waste gases originated from production processes, material handling and product work-up. Nowadays the usage of biofiltration and biotrickling filters to treat odorous waste gases produced by low concentrations of volatile organic compounds (VOCs) and inorganic gases has greatly increased, obtaining high odour removal efficiencies when they are properly designed and operated (Lafita et al., 2012; Frederickson et al., 2013; Fletcher et al. 2014).
The work presented herein is a successful case study using an industrial biofilter system for the abatement of the odorous stream released from an advanced AD plant processing food waste and installed near Bicester (United Kingdom), which has residents living as close as 500 m from the site boundary.
2. Materials and Methods
The ORGUS® biofilter (Figure 1) supplied by the Dutch company Pure Air Solutions treats 60000 m3·h-1 of odorous air coming from the food reception hall, processing plant room, and from all process tanks except the digester buffer feed tanks and digesters that are fed to the gas engines. The system consists of 6 modules, each one with two layers of coconut fibre blended with a mixture of organic and inorganic additives to improve the properties of the media. Each layer of media has an independent spray system to enhance proper water distribution through all the bed, as well as to provide versatility in controlling the moisture content of the whole media. A horizontal quencher integrated in the air duct between the blower and the biofilter modules adequates the physicochemical properties of the air stream, as well as removes dust down to 5 µm particle size. A 14 m stack for the dispersion of the cleaned air completes the system, which has total slab footprint of only 495 m2.
Figure 1. ORGUS® biofilter system (Pure Air Solutions, The Netherland) for odour controlled installed at the MSW facility.
Olfactometry samples from the inlet and outlet streams were simultaneously collected at least by duplicate using the lung method, and submitted within 24 h to a recognised and accredited laboratory in accordance with BSEN13725. H2S concentrations were measured with a Jerome 631 Analyser (Arizona Instruments, USA). Total VOC concentrations were measured using a photoionization detector (PhoCheck, Ion Science, UK). NH3 was measured using detection tubes (Dräger, Germany).
3. Results and Discussion
The ORGUS® modules were transported fully assembled from Pure Air Solutions’ premises, so installation of the biofilters was done in only three days. Commissioning of the ORGUS® system and the AD facility was performed simultaneously in June 2013. Activated sludge from a nearby WWTP was added to the biofilter modules in order to speed up the start-up period and to avoid odour nuisances since the beginning of the process activity of the plant.
After the start-up period, high dust particles were found in the quencher (Figure 2). Samples of the solids were calcined in a muffle furnace at 550ºC during 1 h, being more than 78% related to inorganic compounds. This high inorganic content, as well as the fact that these high dust loads were not repeatedly reported, indicate that dust came from the start-up of the AD facility and/or ductwork, and not from the processed wastes. The good performance of the quencher avoided most of the dust to reach the organic media, as it can be seen from the clean rear side of the demister. Maintenance of the demister was easily done due to the horizontal configuration of the quencher.
Figure 2: High dust loadings collected in the quencher. Left: quencher. Middle: demister front side. Right: demister rear side.
Regarding the odour removal performance, staff from the AD plant reported a subjective good performance since its start-up, which was confirmed in the measurements carried on during three days as per contract specifications in February 2014 (Table 1) by an external company.
Table 1: Pollutant and odour removal performance of the ORGUS®.
|
H2S (ppb) |
TVOC (ppm) |
NH3 (ppm) |
Odour ( ouE·m-3) |
|||||||||
|
Date |
Inlet |
Outlet |
Inlet |
Outlet |
Inlet |
Outlet |
Inlet |
Outlet |
||||
|
04-Feb |
180 |
1 |
1.1 |
ND (<0.1) |
0.2 |
ND (<0.1) |
3121 |
552 |
||||
|
04-Feb |
22 |
ND (<1) |
1.7 |
ND (<0.1) |
0.2 |
ND (<0.1) |
1345 |
643 |
||||
|
05-Feb |
750 |
2 |
3.7 |
0.5 |
ND (<0.1) |
ND (<0.1) |
3427 |
393 |
||||
|
05-Feb |
290 |
ND (<1) |
2.8 |
0.1 |
0.2 |
ND (<0.1) |
1744 |
<158 |
||||
|
05-Feb |
80 |
1 |
3.3 |
0.1 |
0.5 |
ND (<0.1) |
1197 |
365 |
||||
|
06-Feb |
460 |
2 |
3.5 |
0.3 |
0.5 |
ND (<0.1) |
2719 |
368 |
||||
|
06-Feb |
37 |
ND (<1) |
1.9 |
0.1 |
0.5 |
ND (<0.1) |
420 |
<134 |
||||
|
Average |
260 |
1 |
2.6 |
0.2 |
0.3 |
ND (<0.1) |
1996 |
373 |
||||
ND: Not detected.
The ORGUS® average outlet odour concentration was 373 ouE·m-3, considerably lower than the emission limit of 1500 ouE·m-3 imposed by the Environmental Authority. Inlet odour concentrations were expected to be around 10000 ouE·m -3, and since the plant was reported to be working under normal conditions, the lower inlet values could be attributed to winter temperatures. Sironi et al. (2006) reported an average concentration of 7903 ouE·m-3 in the ducts that collect the waste gases from all process steps of 40 waste mechanical and biological treatment of MSW. In that case, waste gases included the emission from the aerobic processes, which is the process with more impact in terms of odour load.
In addition to odour removal, the ORGUS® removed effectively H2S, NH3 and VOC, with average outlet concentration of 1 ppb H2S, 0.2 ppm VOC and NH3 being not detected. VOCs values were also representative of those obtained by Orzi et al. (2010) with slurry samples taken from an industrial AD plant. Authors reported values from 1.7 to 6.0 ppm of VOCs for the non-digested samples and 1.2 to 2.8 ppm of VOCs for the post-digested sample, sulphur compounds only detected at trace levels in some of the samples, and odour concentrations of 15138 ouE·Nm -3 and 5005 ouE·Nm-3 for the non-digested and post-digested samples respectively.
The good performance of the ORGUS® was achieved with low operational costs compared to other physicochemical technologies such as absorption, adsorption or thermal and catalytic oxidation. Operational costs were less than 0.90 € per year per m3·h-1 of air treated, and were basically associated to energy consumption of the extraction blower (installed power of 75 kW), water consumption (~3 m3 per day), and nutrient consumption (13 L per month of 20 gN·L-1 solution). In addition to this, thanks to the double media layer of the system, the AD facility saved at least around 30-50% of footprint compared to the installation of a conventional single layer biofilter.
4. Conclusions
Biofiltration has been proven as a reliable alternative to treat odorous waste gas emissions when is properly designed and operated. In this sense the ORGUS® biofilter system successfully controlled the odorous stream from an AD plant of MSW down to an average value of 373 ouE·m -3; 75% lower than the emission limit of 1500 ouE·m-3 established by contract. This stack discharge value was determined by dispersion modelling to avoid odour nuisances for the residents living nearby the facility, in accordance with the typical indicative odour impact criterion for waste sites of 1.5 ouE·m-3 published by the Environmental Agency. The design of the ORGUS® biofilter also allowed handling unexpected high dust loads without compromising the good performance of the system.
Acknowledgments
The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme FP7/2007-2013/ under REA agreement no. 284949.
References
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