Waste Management 34 (2014) 683–691
Contents lists available at ScienceDirect
Waste Management journal homepage: www.elsevier.com/locate/wasman
Landfill aeration in the framework of a reclamation project in Northern Italy Roberto Raga ⇑, Raffaello Cossu DII, Department of Industrial Engineering, University of Padua, via Marzolo, 9-35131 Padova, Italy
a r t i c l e
i n f o
Article history: Received 26 August 2013 Accepted 4 December 2013 Available online 9 January 2014 Keywords: Landfill aeration Waste biological stability Landfill mining Landfill emissions
a b s t r a c t In situ aeration by means of the Airflow technology was proposed for landfill conditioning before landfill mining in the framework of a reclamation project in Northern Italy. A 1-year aeration project was carried out on part of the landfill with the objective of evaluating the effectiveness of the Airflow technology for landfill aerobization, the evolution of waste biological stability during aeration and the effects on leachate and biogas quality and emissions. The main outcomes of the 1-year aeration project are presented in the paper. The beneficial effect of the aeration on waste biological stability was clear (63% reduction of the respiration index); however, the effectiveness of aeration on the lower part of the landfill is questionable, due to the limited potential for air migration into the leachate saturated layers. During the 1-year in situ aeration project approx. 275 MgC were discharged from the landfill body with the extracted gas, corresponding to 4.6 gC/kgDM. However, due to the presence of anaerobic niches in the aerated landfill, approx. 46% of this amount was extracted as CH4, which is higher than reported in other aeration projects. The O2 conversion quota was lower than reported in other similar projects, mainly due to the higher air flow rates applied. The results obtained enabled valuable recommendations to be made for the subsequent application of the Airflow technology to the whole landfill. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction In situ aeration of Municipal Solid Waste (MSW) landfills has become increasingly popular and several projects have been successfully conducted in the last decade worldwide. Thorough reviews on the use of in situ aeration of MSW landfills are available (Rich et al., 2008; Ritzkowski and Stegmann, 2012) providing a summary of existing concepts and listing a number of cases in which different aims were pursued and different techniques applied. With regard to the motivation for the use of landfill aeration, the reported cases can be grouped into two main categories: – acceleration of the biological stabilisation of waste to shorten landfill post-closure care and reduce both current emissions and the residual emission potential; – pre-treatment of the deposited waste before landfill mining. Numerous lab- and full-scale applications of in situ aeration were carried out for the evaluation of the effects of aeration on
⇑ Corresponding author. Tel.: +39 049 827 8987; fax: +39 049 827 8984. E-mail address: [email protected] (R. Raga). 0956-053X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.wasman.2013.12.011
waste biological stability, leachate and biogas emissions (Cossu et al., 2001; Heyer et al., 2005; Prantl et al., 2006; Raga and Cossu, 2013; Ritzkowski et al., 2006). The key issue of the suitability of lab-scale tests to represent what happens in full scale applications has been recently addressed (Hrad et al., 2013); the influence of leachate recirculation and intermittent aeration on leachate quality was investigated on a full scale application by Öncü et al. (2012); crucial matters related to the evaluation of the time needed for landfill bio-stabilization by means of in situ aeration and of the related target values for the relevant waste stability indexes were discussed in a recent paper by Ritzkowski and Stegmann (2013), who propose a methodological approach based on carbon balance including the assessment of the biodegradable organic carbon (BOC), the carbon discharge via leachate and offgas, and the amount of bio-converted oxygen. In situ aeration has proven to be necessary in order to avoid odours and risks connected to the presence of biogas during landfill mining. In this case the aeration time can be shorter as the goal can be reached even for higher values of the stability indexes, provided that proper measures are taken to control biogas migration in the excavation area (Cossu et al., 2003a). However, a prolonged aeration can also result in mining a stable organic fraction, not requiring further treatment for biological stabilization after excavation in case eventual disposal in new landfill sectors is foreseen.
684
R. Raga, R. Cossu / Waste Management 34 (2014) 683–691
In situ aeration is among the recommended measures for the proper management of temporary storage facilities of selected waste streams (Wagner and Bilitewski, 2009). In Italy, in situ aeration has been applied to MSW landfills by means of the Airflow patented technology, developed by the University of Padua and Spinoff srl, a company promoted and participated by the University of Padua, and is based on low pressure air injection and gas extraction, with simultaneous pneumatic extraction of landfill leachate (Cossu et al., 2003a, 2005). A reclamation project was proposed for a MSW landfill in Northern Italy (Landfill C), involving preliminary landfill conditioning by means of the Airflow technology, landfill mining with material and energy recovery, construction of new landfill sectors providing for disposal capacity for two decades, eventual landscaping for the creation of new functionalities by means of the construction of a public park in the landfill area (Cossu, 2003). Comprehensive preliminary investigations were performed on the landfill, involving waste, leachate and biogas sampling and characterization, leachate pumping tests for the assessment of landfill hydraulic characteristics, in situ aeration tests. Subsequently, according to the project, the first stage of the full scale in situ aeration was run for one year, with the objective to evaluate the following: – effectiveness of the Airflow technology for landfill aerobization; – evolution of waste biological stability during the aeration; – effects of the application of the Airflow technology on leachate and biogas quality and emissions. The main outcomes of the 1-year aeration project are presented in the paper.
2. Description of the case study Landfill C started operations in the 1970s, when waste were disposed of in a former clay pit with neither constructed barriers nor drainage layer and leachate extraction systems. The first sectors of the landfill are actually a typical example of uncontrolled waste disposal site, very common in that period in Europe due to the dramatic acceleration of waste generation and the limited environmental awareness. Operations in the uncontrolled sectors ended in 1983; new sectors were then built with bottom liners conforming to the requirements of the new Italian legislation. In the following years a landfill vertical extension was carried out on the old uncontrolled sectors as well and operations continued until 2002. A preliminary risk assessment for the first sectors was carried out (Cossu et al., 2003b), based on the simple evaluation procedure developed in the framework of the European Union Life project ‘‘Evaluation and Preliminary Assessment of old Deposits - EVAPASSOLD’’ (Allgaier and Stegmann, 2005). After the evaluation the site was classified among the ‘‘potentially emitting old deposits (with a low permeable surface cover, and a still high emission potentials, but currently low substance emissions)’’. Subsequently, investigations for the characterization of the old part of the landfill were run, focusing on waste composition (in view of possible material recovery), current and potential emissions (biogas, leachate and waste quality), leachate piezometric levels and landfill hydraulic characteristics by means of leachate pumping tests. In situ aeration tests were carried out for the estimation of the wells’ radius of influence for selected air flow rates and injection pressures. The abovementioned reclamation project was subsequently proposed, with the in situ aeration and excavation designed in or-
der to proceed by stages as sketched in Fig. 1, involving not only the old uncontrolled sectors, but the whole landfill site. At the same time, a 1-year project of in situ aeration with the Airflow system (first stage of the full scale project), was approved by the local authorities and was started in the landfill, to serve as a pilot scale application to be used for proper calibration of the following stages. 2.1. The Airflow system The Airflow system consists of an aeration station with centrifugal blowers for low pressure air injection and gas extraction, pneumatic valves, control devices (flow meters and gas sampling points for the analyses), air injection and gas extraction wells, a control station equipped with gas analyser and a PC-PLC system. The extracted process gas is conveyed to a biofilter system before being released into the atmosphere. Leachate extraction is carried out from every well by means of pneumatic ejectors (model ‘‘Rex’’, currently marketed by ASWM, Inzago, Milan, Italy), designed for the extraction of up to 0.5 m3/h of leachate per well by means of an intermittent pressurized air supply, used to displace the leachate when the accumulation chamber becomes filled. Monitoring points between air injection and gas extraction wells enable the evaluation of leachate and gas quality as well as temperature during the operations. The monitoring points are installed in boreholes based on the concept illustrated in Lofy (1996), in such a way that sampling can be carried out at different depths in the landfill body. A number (in general 3) of HDPE probes of different length are inserted into each borehole, a screened section (1-m long) is present in the lower end of each pipe, each screened section is isolated from the others by means of bentonite clay seals of approx. 30 cm thickness. Leachate pumping is regularly carried out from aeration and gas extraction wells in order to keep the leachate table low inside the landfill and thus increase the volume of unsaturated waste and enhance the air flow in the landfill body. The explosion risk control device is based on a patented system which prevents the generation of explosive mixtures in the blowers by proper monitoring and control of flow rates. This aspect is particularly important at the beginning of each aeration phase, when methane can be present in concentrations within the explosive range in the extracted gas. The distance between the individual wells depends on landfill depth, waste quality and mechanical conditions (compaction, permeability, etc.) and is calculated based on the results of preliminary in situ aeration tests. The plant operation is constantly controlled by monitoring temperature, gas quality, leachate levels and pressures; flow rates are adjusted based on the single well efficiency. 2.2. Airflow plant description and monitoring plan The area selected for the in situ aeration project has a surface of approx. 1 ha and is situated at the northern end of the site, where the older sectors of the landfill are located, with a maximum depth of 12 m. The in situ aeration plant was constructed with maximum air injection as well as gas extraction capacity of 1000 m3/h; 11 gas extraction and 11 air injection wells were installed, all equipped with pneumatic leachate extraction devices. Ten monitoring points (for gas, leachate and temperature), each of them comprising HDPE pipes screened at different depths were positioned between the injection and the extraction wells. In Fig. 2 the layout of the plant is shown. During the operations, a monitoring programme was carried out comprising sampling and analyses of waste, leachate and
685
R. Raga, R. Cossu / Waste Management 34 (2014) 683–691
(a)
(b)
(c)
Fig. 1. First stages of the reclamation project proposed for landfill C. a: old landfill sector where the 1-year in situ aeration project described in the paper was carried out; b and c: planned activities.
Fig. 2. Layout of the in situ aeration plant in the old sector of landfill C.
gas; monitoring of temperature, pressure and leachate level in the landfill body. Monitoring of gas composition was automatically carried out at the blowers; additional monitoring was provided for in the extraction and monitoring wells; the monitoring of temperatures was performed in all of the above and the air injection wells. Samples of leachate were extracted and analyzed every three months from
the monitoring wells and aeration wells. Waste samples were drilled every three months and analyzed for the evaluation of biological stability and moisture content. Respiration index (RI4, mgO2/gDM) was determined by means of Sapromat apparatus (H + P Labortechnik, Germany) according to pertinent German regulations for AT4 (Anonymous, 2001); the same reference was considered for the determination of gas formation (GB21, Nl/kg DM);
686
R. Raga, R. Cossu / Waste Management 34 (2014) 683–691
the fraction
Contents lists available at ScienceDirect
Waste Management journal homepage: www.elsevier.com/locate/wasman
Landfill aeration in the framework of a reclamation project in Northern Italy Roberto Raga ⇑, Raffaello Cossu DII, Department of Industrial Engineering, University of Padua, via Marzolo, 9-35131 Padova, Italy
a r t i c l e
i n f o
Article history: Received 26 August 2013 Accepted 4 December 2013 Available online 9 January 2014 Keywords: Landfill aeration Waste biological stability Landfill mining Landfill emissions
a b s t r a c t In situ aeration by means of the Airflow technology was proposed for landfill conditioning before landfill mining in the framework of a reclamation project in Northern Italy. A 1-year aeration project was carried out on part of the landfill with the objective of evaluating the effectiveness of the Airflow technology for landfill aerobization, the evolution of waste biological stability during aeration and the effects on leachate and biogas quality and emissions. The main outcomes of the 1-year aeration project are presented in the paper. The beneficial effect of the aeration on waste biological stability was clear (63% reduction of the respiration index); however, the effectiveness of aeration on the lower part of the landfill is questionable, due to the limited potential for air migration into the leachate saturated layers. During the 1-year in situ aeration project approx. 275 MgC were discharged from the landfill body with the extracted gas, corresponding to 4.6 gC/kgDM. However, due to the presence of anaerobic niches in the aerated landfill, approx. 46% of this amount was extracted as CH4, which is higher than reported in other aeration projects. The O2 conversion quota was lower than reported in other similar projects, mainly due to the higher air flow rates applied. The results obtained enabled valuable recommendations to be made for the subsequent application of the Airflow technology to the whole landfill. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction In situ aeration of Municipal Solid Waste (MSW) landfills has become increasingly popular and several projects have been successfully conducted in the last decade worldwide. Thorough reviews on the use of in situ aeration of MSW landfills are available (Rich et al., 2008; Ritzkowski and Stegmann, 2012) providing a summary of existing concepts and listing a number of cases in which different aims were pursued and different techniques applied. With regard to the motivation for the use of landfill aeration, the reported cases can be grouped into two main categories: – acceleration of the biological stabilisation of waste to shorten landfill post-closure care and reduce both current emissions and the residual emission potential; – pre-treatment of the deposited waste before landfill mining. Numerous lab- and full-scale applications of in situ aeration were carried out for the evaluation of the effects of aeration on
⇑ Corresponding author. Tel.: +39 049 827 8987; fax: +39 049 827 8984. E-mail address: [email protected] (R. Raga). 0956-053X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.wasman.2013.12.011
waste biological stability, leachate and biogas emissions (Cossu et al., 2001; Heyer et al., 2005; Prantl et al., 2006; Raga and Cossu, 2013; Ritzkowski et al., 2006). The key issue of the suitability of lab-scale tests to represent what happens in full scale applications has been recently addressed (Hrad et al., 2013); the influence of leachate recirculation and intermittent aeration on leachate quality was investigated on a full scale application by Öncü et al. (2012); crucial matters related to the evaluation of the time needed for landfill bio-stabilization by means of in situ aeration and of the related target values for the relevant waste stability indexes were discussed in a recent paper by Ritzkowski and Stegmann (2013), who propose a methodological approach based on carbon balance including the assessment of the biodegradable organic carbon (BOC), the carbon discharge via leachate and offgas, and the amount of bio-converted oxygen. In situ aeration has proven to be necessary in order to avoid odours and risks connected to the presence of biogas during landfill mining. In this case the aeration time can be shorter as the goal can be reached even for higher values of the stability indexes, provided that proper measures are taken to control biogas migration in the excavation area (Cossu et al., 2003a). However, a prolonged aeration can also result in mining a stable organic fraction, not requiring further treatment for biological stabilization after excavation in case eventual disposal in new landfill sectors is foreseen.
684
R. Raga, R. Cossu / Waste Management 34 (2014) 683–691
In situ aeration is among the recommended measures for the proper management of temporary storage facilities of selected waste streams (Wagner and Bilitewski, 2009). In Italy, in situ aeration has been applied to MSW landfills by means of the Airflow patented technology, developed by the University of Padua and Spinoff srl, a company promoted and participated by the University of Padua, and is based on low pressure air injection and gas extraction, with simultaneous pneumatic extraction of landfill leachate (Cossu et al., 2003a, 2005). A reclamation project was proposed for a MSW landfill in Northern Italy (Landfill C), involving preliminary landfill conditioning by means of the Airflow technology, landfill mining with material and energy recovery, construction of new landfill sectors providing for disposal capacity for two decades, eventual landscaping for the creation of new functionalities by means of the construction of a public park in the landfill area (Cossu, 2003). Comprehensive preliminary investigations were performed on the landfill, involving waste, leachate and biogas sampling and characterization, leachate pumping tests for the assessment of landfill hydraulic characteristics, in situ aeration tests. Subsequently, according to the project, the first stage of the full scale in situ aeration was run for one year, with the objective to evaluate the following: – effectiveness of the Airflow technology for landfill aerobization; – evolution of waste biological stability during the aeration; – effects of the application of the Airflow technology on leachate and biogas quality and emissions. The main outcomes of the 1-year aeration project are presented in the paper.
2. Description of the case study Landfill C started operations in the 1970s, when waste were disposed of in a former clay pit with neither constructed barriers nor drainage layer and leachate extraction systems. The first sectors of the landfill are actually a typical example of uncontrolled waste disposal site, very common in that period in Europe due to the dramatic acceleration of waste generation and the limited environmental awareness. Operations in the uncontrolled sectors ended in 1983; new sectors were then built with bottom liners conforming to the requirements of the new Italian legislation. In the following years a landfill vertical extension was carried out on the old uncontrolled sectors as well and operations continued until 2002. A preliminary risk assessment for the first sectors was carried out (Cossu et al., 2003b), based on the simple evaluation procedure developed in the framework of the European Union Life project ‘‘Evaluation and Preliminary Assessment of old Deposits - EVAPASSOLD’’ (Allgaier and Stegmann, 2005). After the evaluation the site was classified among the ‘‘potentially emitting old deposits (with a low permeable surface cover, and a still high emission potentials, but currently low substance emissions)’’. Subsequently, investigations for the characterization of the old part of the landfill were run, focusing on waste composition (in view of possible material recovery), current and potential emissions (biogas, leachate and waste quality), leachate piezometric levels and landfill hydraulic characteristics by means of leachate pumping tests. In situ aeration tests were carried out for the estimation of the wells’ radius of influence for selected air flow rates and injection pressures. The abovementioned reclamation project was subsequently proposed, with the in situ aeration and excavation designed in or-
der to proceed by stages as sketched in Fig. 1, involving not only the old uncontrolled sectors, but the whole landfill site. At the same time, a 1-year project of in situ aeration with the Airflow system (first stage of the full scale project), was approved by the local authorities and was started in the landfill, to serve as a pilot scale application to be used for proper calibration of the following stages. 2.1. The Airflow system The Airflow system consists of an aeration station with centrifugal blowers for low pressure air injection and gas extraction, pneumatic valves, control devices (flow meters and gas sampling points for the analyses), air injection and gas extraction wells, a control station equipped with gas analyser and a PC-PLC system. The extracted process gas is conveyed to a biofilter system before being released into the atmosphere. Leachate extraction is carried out from every well by means of pneumatic ejectors (model ‘‘Rex’’, currently marketed by ASWM, Inzago, Milan, Italy), designed for the extraction of up to 0.5 m3/h of leachate per well by means of an intermittent pressurized air supply, used to displace the leachate when the accumulation chamber becomes filled. Monitoring points between air injection and gas extraction wells enable the evaluation of leachate and gas quality as well as temperature during the operations. The monitoring points are installed in boreholes based on the concept illustrated in Lofy (1996), in such a way that sampling can be carried out at different depths in the landfill body. A number (in general 3) of HDPE probes of different length are inserted into each borehole, a screened section (1-m long) is present in the lower end of each pipe, each screened section is isolated from the others by means of bentonite clay seals of approx. 30 cm thickness. Leachate pumping is regularly carried out from aeration and gas extraction wells in order to keep the leachate table low inside the landfill and thus increase the volume of unsaturated waste and enhance the air flow in the landfill body. The explosion risk control device is based on a patented system which prevents the generation of explosive mixtures in the blowers by proper monitoring and control of flow rates. This aspect is particularly important at the beginning of each aeration phase, when methane can be present in concentrations within the explosive range in the extracted gas. The distance between the individual wells depends on landfill depth, waste quality and mechanical conditions (compaction, permeability, etc.) and is calculated based on the results of preliminary in situ aeration tests. The plant operation is constantly controlled by monitoring temperature, gas quality, leachate levels and pressures; flow rates are adjusted based on the single well efficiency. 2.2. Airflow plant description and monitoring plan The area selected for the in situ aeration project has a surface of approx. 1 ha and is situated at the northern end of the site, where the older sectors of the landfill are located, with a maximum depth of 12 m. The in situ aeration plant was constructed with maximum air injection as well as gas extraction capacity of 1000 m3/h; 11 gas extraction and 11 air injection wells were installed, all equipped with pneumatic leachate extraction devices. Ten monitoring points (for gas, leachate and temperature), each of them comprising HDPE pipes screened at different depths were positioned between the injection and the extraction wells. In Fig. 2 the layout of the plant is shown. During the operations, a monitoring programme was carried out comprising sampling and analyses of waste, leachate and
685
R. Raga, R. Cossu / Waste Management 34 (2014) 683–691
(a)
(b)
(c)
Fig. 1. First stages of the reclamation project proposed for landfill C. a: old landfill sector where the 1-year in situ aeration project described in the paper was carried out; b and c: planned activities.
Fig. 2. Layout of the in situ aeration plant in the old sector of landfill C.
gas; monitoring of temperature, pressure and leachate level in the landfill body. Monitoring of gas composition was automatically carried out at the blowers; additional monitoring was provided for in the extraction and monitoring wells; the monitoring of temperatures was performed in all of the above and the air injection wells. Samples of leachate were extracted and analyzed every three months from
the monitoring wells and aeration wells. Waste samples were drilled every three months and analyzed for the evaluation of biological stability and moisture content. Respiration index (RI4, mgO2/gDM) was determined by means of Sapromat apparatus (H + P Labortechnik, Germany) according to pertinent German regulations for AT4 (Anonymous, 2001); the same reference was considered for the determination of gas formation (GB21, Nl/kg DM);
686
R. Raga, R. Cossu / Waste Management 34 (2014) 683–691
the fraction
