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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.
在无害废物填埋场中，集成气味监测系统包括2个IOMS，自2018年以来，2台H2S连续分析仪和两台自动空气采样器一直在运行：当H2S连续分析仪每隔5分钟测量两次20 ppb的连续测量值时，或当IOMS测量的总气味排放超过500 ouE/m3超过5分钟时，自动空气采样器启动。
2019年5月至8月，人们注意到气味排放问题，几乎每天都会激活自动采样器，这通常与人口投诉有关；此外，垃圾填埋场表面沼气的监测活动表明，某些区域的表面排放量显著增加，这意味着垃圾填埋场沼气（LFG）收集系统的表面和无组织排放可能是此类气味排放的原因。的LFG井场系统由填埋场中的301口垂直井组成的网络，以及用于将LFG输送至能量回收的输送管道和3个鼓风炉设施。
Abstract
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.
在无害废物填埋场中，集成气味监测系统包括2个IOMS，自2018年以来，2台H2S连续分析仪和两台自动空气采样器一直在运行：当H2S连续分析仪每隔5分钟测量两次20 ppb的连续测量值时，或当IOMS测量的总气味排放超过500 ouE/m3超过5分钟时，自动空气采样器启动自动采样器的激活，通常与人口投诉相关；此外，垃圾填埋场表面沼气的监测活动表明，某些区域的表面排放量显著增加，这意味着垃圾填埋场沼气（LFG）收集系统的表面和无组织排放可能是此类气味排放的原因。的LFG井场系统由填埋场中的301口垂直井组成的网络，以及用于将LFG输送至能量回收的输送管道和3个鼓风炉设施。2019年9月，基于OGI（光学气体成像）技术开展了泄漏检测和修复调查，该技术使用高分辨率和灵敏度的红外图像采集和处理来检测沼气中甲烷的主要存在。LFG管道网络中的压力分布数据以及通过热成像测量收集的数据被用于确定显著排放源，这主要是由于收集系统中的压力不平衡导致的沼气吸收不良以及井口和管道连接处的无组织排放。通过修改LFG鼓风机火炬的位置、用新井扩大沼气捕获网络、检查/维修井场系统的阀门和连接，实施了应急计划，以平衡填埋场关键区域的吸入压力。在接下来的几个月里，通过IOMS围栏监测和自动采样器的激活，对这些改进措施的有效性进行了监测，以减少地表排放和气味滋扰
1. Introduction
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.
垃圾填埋活动的关键方面与垃圾填埋气体（LFG）的表面排放和每天输送的新鲜废物的排放有关。这种情况需要适当的技术和程序来持续测量卫生填埋场和其他设施周围的气味。一般来说，已经研究了三种表征和量化气味危害的技术：分析：化学分析；感官：动态嗅觉；仪表：气味监测系统（IOMS）。（Gostelow等人，2001年；Capelli等人，2008年；Giuliani等人，2012年；Gğbiki等人，2017年；Zarra等人，2017；Szulzyčski等人，2018年）。感官-仪器方法是唯一能够持续监测气味的技术（Giuliani等人，2012；Naddeo等人，2016）。在之前的工作中，进行了一项实地研究，以评估多传感器IOMS和H2S连续分析仪的潜力和性能-结合动态嗅觉（EN 137252004）-以识别非危险废物填埋场排放的有气味化合物（Cangialosi等人，2018）。就地表LFG排放而言，使用光学气体成像（OGI）技术识别和修复地表气体泄漏（Ravikumar等人，2016）可能有助于减少此类气味排放源。本研究涉及OGI（光学气体成像）技术的应用，使用高分辨率和灵敏度的红外图像采集，结合实时IOMS围栏监测和H2S连续分析仪，以量化泄漏检测和修复（LDAR）方法在垃圾填埋场减少气味排放方面的有益用途。在以下章节中，监测期（2019年1月至12月）的数据收集和分析方法见“第1阶段”段落，而应急计划和气味排放改善评估见“第2阶段”段落。
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.
这项研究是在阿普利亚地区（南意大利）塔兰托市的一个垃圾填埋场进行的，距离斯塔特镇的第一个点1000米。该场地是一个单独的水池，分为两个作业区，面积为213.000 m2，废物处理量为6.2 Mm3。位于工厂北部和南部边界的综合气味监测系统自2018年以来一直处于活跃状态，以控制气味对受体的影响。该系统由2台IOMS（Sensitent公司的MSEM32®，配备32个传感器）、2台H2S连续分析仪（亚利桑那州亚利桑那研究所的Jerome®J605）和两台自动空气采样器（Labservice Analytica公司的OdodPrep®）组成。H2S连续分析仪每隔5分钟测量两次超过20 ppb，或IOMS测量的总气味排放超过500 ouE/m3超过5分钟，可激活自动空气采样器。当超过该限值（以下定义为临界事件）时，采样器自动净化8 L沼气样本，并根据标准方法EN 13725:2004送至动态嗅觉实验室进行分析。同时，市民也可以通过专门开发的名为“Nosy”的应用程序报告感知到的嗅觉骚扰。此外，根据英国环境署“垃圾填埋场地表气体排放监测指南”（以下简称LFTGN 07），监测和控制计划包括每月监测地表气体，从而为评估LFG排放的影响提供了另一种工具。
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.
通过分析2018年和2019年前几个月监测系统的数据，很明显，99.9%的关键事件都是在北站检测到的。2019年共检测到194起严重气味事件（即超过IOMS和H2S分析仪的限值），所有这些事件都与来自填埋场的风有关：前9个月检测到176起事件；此外，同一时期还发生了44起公民使用App“Nosy”的报告。由于假设此类事件主要由填埋场表面局部区域的LFG排放或LFG收集系统泄漏引起，因此在2019年7月至8月期间，使用热成像检测技术进行了初步筛查。OGI（光学气体成像）技术使用高分辨率和灵敏度的红外图像采集和处理来检测沼气中甲烷在拉伸带C-H键上的主要存在。使用IR EyeCgas模型，最小可检测泄漏率为0.35g/h甲烷。由于该技术显示出良好的结果，2019年9月，进行了泄漏检测和修复（LDAR）的“高空间分辨率调查”：在后一种情况下，在84570 m2表面上167个点测量地表沼气排放的活动期间，使用OGI技术进行了调查，还包括仔细监测LFG收集系统的井口和管道接头。
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.
根据7月至9月期间进行的调查，制定了一项应急计划，旨在减少垃圾填埋场气味排放的LFG排放。该计划于2019年10月实施。通过观察2019年11月和12月的监测数据（IOMS和H2S分析仪的持续监测、表面排放、超过设定水平的事件数量），研究了气味排放改善措施的有效性。
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.
计算和分析了每月的沼气扩散排放数据：每个活动在填埋场表面测量了150多个点。7月至8月期间，最关键区域的甲烷表面排放量超过了LFTGN 07规定的限值（0.1 mg/m2s），尽管整个填埋场从未超过该值。
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.
图1显示了2019年5月至8月期间北站连续监测系统收集的数据。正如可以观察到的，观察到高达100 ppb的H2S数个峰值，以及高达2500 ouE/m3的气味浓度。在此期间，在每年194起严重气味事件中，检测到117起，平均每月30起。然后设计并执行了填埋场表面的LDAR调查，以确定排放问题的主要原因，然后减少排放问题。在图2中，显示了2019年9月使用OGI技术进行的“高空间分辨率调查”的红外图像，其中在井口接合处附近可以看到沼气的明显无组织排放。
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.
热成像分析显示了在每个井口/管道接头附近发现甲烷排放的位置，以确定最关键的排放区。基于这些详细信息，检测了便携式FID测量的无组织LFG排放，并将结果按浓度分类。由于垃圾填埋场收集系统的两个缺陷，在垃圾填埋场的明确区域发现了相关排放物：a）沼气捕获不良导致的地表排放物；b）井口/管道连接处泄漏。1000 Nm3/h的能量回收由两台发动机进行，而3台鼓风机火炬设施用于收集超过发动机容量的沼气。为了确定与阀门/配件无组织排放相比，沼气捕获不良是否是主要原因，检测了每个井口的气压：正常操作井口的气压略为负/零（约-0.1毫巴），而约1mbar的值表示不合适的抽吸能力，可能会从井口周围的表面释放沼气。发现大气压和沼气排放之间存在强烈的相关性，即高发射率区（>10000 ppm）的特征是正气压（约1毫巴），而低排放区的压力值略为负值。LFG管道网络中的压力分布数据，以及通过热成像测量和FID分析收集的数据，可以澄清收集系统中的压力不平衡（而不是阀门/配件的无组织排放）导致的沼气捕获不良是LFG表面高排放的原因，进而导致气味滋扰。
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.
2019年10月，采取了以下行动，以改善LFG管网并平衡填埋场关键区域的吸入压力：1）钻探新的吸收井；2） 修改LFG鼓风机火炬的位置，以优化低效捕获区和鼓风机之间的距离。还对井场系统的阀门和连接件进行了检查和维修，特别是在靠近北部边界的北部垃圾填埋区。应急计划生效后获得的所有监测数据都是伴随而来的：北部站连续监测系统收集的数据（图5）显示，过去3个月，H2S浓度平均降低，峰值超过40 ppb，且气味浓度超过500 uoE/m3。
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.
填埋场表面甲烷排放的第75个百分位数从0,12 mg/m2 s（8月）下降到12月的0,04 mg/m2 s，三个月内减少了66%。在降低LFG表面排放方面的改进显然有利于气味排放：关键事件的数量大幅减少，从5月-8月期间的平均每月30起，到10月-12月期间的每月5起。
4. Conclusions
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.
进行了一项全面的研究，包括连续气味监测系统、表面排放调查和对无害填埋场甲烷排放的热成像分析。2019年夏季，在工厂北部边界测得的H2S和气味的关键事件反复发生，与监测站附近有限区域的沼气表面排放值高有关。基于OGI（光学气体成像）技术的调查允许识别来自地表的扩散排放和来自沼气收集系统井口/管道连接处的无组织排放。LFG管道网络中的压力分布数据以及通过热成像测量收集的数据，可以确定某些区域的沼气吸收不良是沼气排放的主要原因，这是由沼气收集系统中的流量和压力不平衡造成的。采取了一项应急计划，通过钻探新井、平衡管道/井口网络中的流量和压力分布、在OGI调查确定的区域选择性操作以及使用FID进行的排放现场测量来纠正流量不平衡。经过这些改进后，最关键区域的沼气表面排放量减少了66%，围栏处监测到的H2S和气味浓度显著降低，气味排放方面的关键事件数量大幅减少，从每月30起降至每月5起。
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