In a non-hazardous waste landfill an integrated odour monitoring system comprised with 2 IOMS, 2 H2S continuous analyser and two automatic air samplers has been operating since 2018: automatic air samplers are activated when two consecutive measurements of 20 ppb at 5 min intervals are measured by H2S continuous analyser or when overall odour emission measured by IOMS exceeded 500 ouE/m3 for more than 5 min.
Problems with odour emissions were noticed in May-August 2019 with almost a daily automatic samplers’ activation, often correlated with complaints of population; moreover, monitoring campaigns of biogas from the landfill surface showed significant increase of surface emissions for certain zones, implying that surface and fugitive emissions form landfill biogas (LFG) collecting system could have been responsible for such odour emissions. The LFG wellfield system of is comprised of a network of 301 vertical wells in the landfill, coupled with conveyance piping for the transport of LFG to energy recovery and 3 blowerflare facilities.
Federico Cangialosia,*, Antonio Fornarob, Gabriella De Santisa
aT&A - Tecnologia e Ambiente Srl, S.P. 237 per Noci, 8 – 70017 Putignano (BA), Italy
bLab Service Analytica S.R.L., via Emilia 51/c – 40011 Anzola dell'Emilia (BO), Italy
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. Cangialosi, Antonio Fornaro, Gabriella De Santis. Detection of gas leakage from landfills using optical gasimaging coupled with fence monitoring system of odour by IOMS: A case study, IWA2021 Conference, Bilbao, Spain, www.olores.org.
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Keywords: landfill, biogas.
In a non-hazardous waste landfill an integrated odour monitoring system comprised with 2 IOMS, 2 H2S continuous analyser and two automatic air samplers has been operating since 2018: automatic air samplers are activated when two consecutive measurements of 20 ppb at 5 min intervals are measured by H2S continuous analyser or when overall odour emission measured by IOMS exceeded 500 ouE/m3 for more than 5 min.Problems with odour emissions were noticed in May-August 2019 with almost a daily automatic samplers’ activation, often correlated with complaints of population; moreover, monitoring campaigns of biogas from the landfill surface showed significant increase of surface emissions for certain zones, implying that surface and fugitive emissions form landfill biogas (LFG) collecting system could have been responsible for such odour emissions. The LFG wellfield system of is comprised of a network of 301 vertical wells in the landfill, coupled with conveyance piping for the transport of LFG to energy recovery and 3 blowerflare facilities. In September 2019 a Leak Detection and Repair survey was carried out, based on OGI (Optical Gas Imaging) technology that uses high resolution and sensitivity infrared image acquisition and processing to detect the predominant presence of methane in biogas. Pressure distribution data in the LFG piping network along with data collected by thermographic survey were used to identify sources of significant emissions, due essentially to poor biogas uptake caused by pressure unbalance in the collection system and to fugitive emissions from wellhead and pipes connections. A contingency plan was carried out in order to balance the suction pressures from the critical zones of the landfill, by modifying the position of LFG blower-flares, expanding the biogas capture network with new wells and checking/repairing the valves and connections of wellfield system. The effectiveness of such improvements was monitored in the following months in terms of reduction of surface emissions and odour nuisances, quantitatively measured by IOMS fence monitoring and automatic samplers’ activations.
Critical aspects of landfill activities are related to surface emissions of landfill gas (LFG) and emissions from fresh wastes daily delivered. This situation requires suitable techniques and procedures for continuously measuring odors around sanitary landfills and other facilities. Generally speaking, three techniques for the characterization and quantification of the nuisance of odors have already been studied: Analytical: chemical analysis; Sensory: dynamic olfactometry; Instrumental sense: Instrumental Odour Monitoring system (IOMS). (Gostelow et al. 2001; Capelli et al., 2008; Giuliani et al. 2012; Gębicki et al. 2017; Zarra et al. 2017; Szulczyński et al. 2018). The senso-instrumental approach is the only technique that allows continuous monitoring of odours (Giuliani et al. 2012; Naddeo et al. 2016). In a previous work, a field study was carried out to assess the potentiality and evaluate the performance of a multisensor IOMS and a H2S continuous analyser - combined with dynamic olfactometry (EN 13725, 2004) - to identify odorous compounds emitted from a non-hazardous waste landfill (Cangialosi et al. 2018). As far as the surface LFG emissions are concerned, the use of optical gas imaging (OGI) technologies to identify and repair surface gas leaks (Ravikumar et al. 2016) could be useful to reduce such odour emission sources. This study concerns the application of OGI (Optical Gas Imaging) technology, using high resolution and sensitivity infrared image acquisition, combined with real-time IOMS fence monitoring and H2S continuous analyser, in order to quantify the beneficial use of leak-detection- and-repair (LDAR) approach for landfill on odour emissions reduction. In the following sections the methods for data collecting and analysis for the monitored period (January-December 2019) are shown in “Phase 1” paragraph, whereas the contingency plan and the evaluation of the improvements on odour emissions are described in “Phase 2” paragraph.
2. Instruments and methods
The study was carried out in a landfill in the municipality of Taranto, in the Apulia Region (South Italy), 1000 m far from the first receptors in the town of Statte. The site is a single basin divided into two operating lots with 213.000 m2 surface and capacity of of 6.2 Mm3 of waste. An integrated odour monitoring system, localized on the Northern and Southern border of the plant, has been active since 2018 to control odour impacts on the receptors. This system is comprised of 2 IOMS (MSEM32® by Sensigent, equipped with 32 sensors), 2 H2S continuous analyser (Jerome® J605 by Arizona Instr., AZ) and two automatic air samplers (OdorPrep® by Labservice Analytica). Two consecutive measurements exceeding 20 ppb at 5 min intervals measured by H2S continuous analyser or overall odour emission measured by IOMS exceeding 500 ouE/m3 for more than 5 min, can activate automatic air samplers. When such limits are exceeded (defined as critical events hereinafter), the samplers purged automatically 8 L samples of biogas to be sent for analysis at the dynamic olfactometry laboratory according to the standard method EN 13725:2004. At the same time, also citizens can report a perceived olfactory harassment with a specifically developed App, called “Nosy”. Moreover, monitoring and control plan includes monthly monitoring of surface gas, according to the UK Environment Agency "Guide to monitoring surface gas emissions in landfills" (hereinafter referred to as LFTGN 07), thus providing another tool for evaluating the impact of LFG emissions.
2.1 Phase 1
By analyzing the data from the monitoring system during 2018 and the first months in 2019, it appeared clearly that 99.9% of the critical events were detected in the northern station. A total of 194 critical odour events (i.e. exceeding the limits set for IOMS and H2S analyser) were detected in 2019, all of them correlated with the wind coming from the landfill: 176 events were detected in the first 9 months; moreover, n.44 reports of citizens with App “Nosy” occurred in the same period. As it was hypothesized that such events were mostly caused by LFG emissions from localized zones on landfill surface, or leaks from LFG collection system, during July-August 2019 period a preliminary screening with a thermographic detection technique was carried out. OGI (Optical Gas Imaging) technology uses high resolution and sensitivity infrared image acquisition and processing to detect the predominant presence of methane in biogas on a stretching band C-H bond. An IR EyeCgas model was used with a Minimum Detectable Leak Rate of 0.35 g/h of Methane. Since the technique showed good results, on September 2019 a ‘high spatial resolution survey’ of Leak Detection and Repair (LDAR) was carried out: in the latter case, the investigation with OGI technology was carried out during the campaign for measuring surface biogas emissions from 167 points over a 84570 m2 surface, also involving a careful monitoring of wellhead and pipes junctions of LFG collection system.
2.2 Phase 2
On the basis of the investigation carried out in July-September period, a contingency plan was developed, aimed at reducing LFG emissions, likely responsible for odour emission by the landfill. The plan was implemented in October 2019. The effectiveness of the improvement actions on odour emissions was studied by observing the monitoring data (continuous monitoring by IOMS and H2S analyser, surface emissions, number of events exceeding the set levels) in the months of November and December 2019.
3. Result and discussion
3.1 Phase 1
Monthly data of diffuse biogas emissions were calculated and analyzed: over more than 150 points measured over the landfill surface for each campaign. During July-August, methane surface emissions in the most critical zones exceeded the limit set by LFTGN 07 (0,1 mg/m2 s), although the landfill, as a whole, never exceeded such value.
Figure 1: May-August 2019 trends in IOMS (red) and H2S (blue) data
Figure 1 shows data collected by continuous monitoring system at the northern station in the period May-August 2019. As it can be observed, several spikes up to 100 ppb of H2S were observed, as well as odour concentration, up to 2500 ouE/m3. In such period, 117 out of total yearly 194 critical odour events were detected, with an average of 30 events per month. The LDAR survey on the landfill surface was then designed and carried out, in order to identify the main causes of emissions problems and then reduce them. In Figure 2, an IR image of the ‘high spatial resolution survey’ with OGI technology on September 2019 is showed, where clear fugitive emissions of biogas are visible near the wellhead junctions.
Figure 4: IR Image of biogas fugitive emissions from wellhead junction
The thermographic analysis showed where methane emissions were found nearby each wellheads/pipes junctions, in order to identify the most critical emission zones. Based on such detailed information, fugitive LFG emissions measured with a portable FID were detected and results were grouped into classes by concentration. Relevant emissions were found in well-defined areas of the landfill because of two flaws of the LFG collecting system: a) surface emissions caused by poor biogas capture and b) leaks from wellhead/pipes junctions. Energy recovery of 1000 Nm3/h is carried out by two engines, whereas 3 blower-flare facilities are used to collect biogas exceeding the capacity of the engines. In order to ascertain whether poor biogas capturing was the main cause as compared to valve/fittings fugitive emissions, the barometric pressure of each wellhead was detected: barometric pressure of a properly operating wellhead is slightly negative/zero (around -0.1 mbar), whereas values around 1 mbar indicate an unsuitable suction capacity with likely release of biogas from the surface surrounding the wellhead. Aa strong correlation between barometric pressure and biogas emissions was found, i.e. high emissivity zones (>10000 ppm) were characterized by positive (around 1 mbar) barometric pressure, whereas zones with low emissions showed slightly negative pressure values. Pressure distribution data in the LFG piping network along with data collected by thermographic survey and FID analysis allowed to clarify that poor biogas capture caused by pressure unbalance in the collection system (rather than valve/fittings fugitive emissions) was the cause of high LFG surface emissions, causing, in turn, odour nuisances.
3.2 Phase 2
In October 2019 the following actions were undertaken in order to improve the LFG pipe network and balance the suction pressures from the critical zones of the landfill: 1) drilling new uptake wells; 2) modifying the position of LFG blower-flares in order to optimize the distances between low-efficiency capture zones and blowers. Checking and repairing the valves and connections of wellfield system was also carried out, particularly in the northern landfill sector, close to the northern boundary. All the monitoring data acquired after the contingency plan was effective, are concomitant: data collected by continuous monitoring system at the northern station (Figure 5) showed an average reduction of concentrations and spikes of H2S exceeding 40 ppb are very low, as well as odour concentration exceeding 500 uoE/m3 in the last 3 months.
Figure 5: September-December 2019 trends in IOMS (red) and H2S (blue) data
The 75th percentiles of methane emission form landfill surface dropped from 0,12 mg/m2 s (August) down to 0,04 mg/m2 s in December, with a 66% reduction in three months. Improvements in lowering LFG surface emissions are clearly beneficial for odour emissions: a dramatic decrease in the number of critical events, from an average of 30per-month in May-August period, to 5-per-month during October-December.
A comprehensive study involving continuous odour monitoring system, surface emissions surveys and thermographic analysis of methane emissions from a non-hazardous landfill was carried out. Critical events for H2S and odour measured at the northern boundary of the plant were recurrent during the summer 2019, associated with high values of biogas surface emissions from limited zones close to the monitoring station. Surveys based on OGI (Optical Gas Imaging) technology allowed to identify diffuse emissions from surface and fugitive emissions from wellhead/pipes junctions of biogas collecting system. Pressure distribution data in the LFG piping network along with data collected by thermographic survey allowed to ascertain that poor biogas uptake in certain zones was mainly responsible of biogas emissions, caused by flow and pressure unbalance in biogas collecting system. A contingency plan was undertaken to correct the flow unbalance, by drilling new wells and equilibrating the flow and pressure distributions in the pipe/wellhead network, selectively operating on the zones identified by OGI survey along with field measurements of emissions with FID. After such improvements, a 66% reduction of biogas surface emissions from the most critical zones was achieved, along with remarkable reduction in H2S and odour concentrations monitored at the fence and a dramatic decrease in the number of critical events in terms of odour emissions, from 30per-month to 5-per-month.
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