Energetic Efficiency of Landfill: An Italian Case Study

Available online at www.sciencedirect.com

ScienceDirect Energy Procedia 101 (2016) 66 – 73

71st Conference of the Italian Thermal Machines Engineering Association, ATI2016, 14-16 September 2016, Turin, Italy

Energetic efficiency of landfill: An Italian case study Federico Sisania, Stefano Continia, Francesco Di Mariaa,b, * a

LAR Laboratory- Dipartimento di Ingegneria,via G. Duranti 93, 06125 Perugia 06125, Italy b CIMIS, via G. Duranti 67, 06125, Perugia, Italy

Abstract An energetic analysis of an existing landfill for municipal solid waste was performed concerning the period from 2010 to 2014. The amount of energy recovered, of energy consumed, of waste disposed together with their composition, the amount and the quality of the landfill gas generated were monitored during this period. The amount of waste disposed ranged from about 80,000 tonne/year to about 200,000 tonnes/year. Correspondently the landfill gas collected increased from about 2,000,000 Stm3/year to about 4,000,000 Stm3/year. The amount of energy recovered resulted on average 1.4 kWh/ Stm3 corresponding to an average amount of energy recovered per tonne of waste of about 43 kWh. Among the energetic consumptions a predominant role was played by the leachate treatment. Leachate production resulted characterized by a strong variability with a minimum of about 18.600 m3 for the 2012 and a maximum of about 45,000 m3 for the 2014 requiring from 11.7 kWh to 13.2 kWh of electrical energy per each tonne of waste disposed of. © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2016 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-reviewunder under responsibility of Scientific the Scientific Committee ATI 2016. Peer-review responsibility of the Committee of ATIof 2016. Keywords: Energy recovery, landfill gas, municipal solid waste

1. Introduction Landfill is one of the most diffused solutions for final disposal of waste both in the EU and in other areas [1]. On the other hand landfill represents also an environmental concern due to the pollutant potential of liquid and gaseous emissions generated mainly by the spontaneous degradation of biodegradable components [2-6]. Due to these

* Corresponding author. Tel.: +39-075-5853738; fax: +39-075-5853703. E-mail address: [email protected]

1876-6102 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Scientific Committee of ATI 2016. doi:10.1016/j.egypro.2016.11.009

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aspect landfill has to be managed with the aim of limiting the level of pollutant emissions to values that are considered sustainable by the current legislation [7]. The management of these emission requires materials and energy but can also lead to renewable energy production. In particular the landfill gas (LFG) is one of the most important emissions from landfill. In the EU-15, the contribution of LFG emissions to the whole anthropogenic greenhouse gas (GHG) production is of about 3% [3]. On the other hand LFG is also credited as renewable energy able to substitute fossil fuels. In fact, LFG is a mixture mainly of carbon dioxide and methane in quite similar concentrations [3], along with traces of other gasses such as H2S, H2, N2O and NH3, arising from the degradation of biodegradable materials. These materials are represented mainly by the organic fraction (OF) (i.e. residues of kitchen from household, restaurants and similar activities). Even if big efforts have been performed in the last years for the implementation of a zero waste approach and strategies, a large amount of biodegradable waste will still generated in the next years and disposed of in landfill [8-11]. Some of the component of LFG, such as CH4 and N2O, have a GHG potential significantly higher than the same mass of CO 2. They can reach very high concentrations as the methane (e.g. CH4 >40-45 % v/v) or represent in any case a relevant environmental concern even at low concentration (i.e. N2O). In fact, methane has a GHG potential 28 times higher than CO2, whereas N2O, even at typical concentrations << 1% v/v, gives a relevant contribution to this phenomenon due to its GHG potential of 310 times higher than CO2. On the other hand, due to its origin and its high content in methane, the landfill gas represents also a renewable energetic source able to give a relevant contribution to the achievement of the Europe 2020 and 2030 goals [12,13]. In a previous study [11,14] was detected that an excessive pre-treatment of the waste aimed to reducing its biological reactivity and hence the emissions potential before dispose of in landfills equipped with LFG recovery, can reduce the whole environmental benefits. This result was a consequence of direct and indirect emissions generated by the pre-treatments and by the incidence of the energetic consumption for pretreatments related to the one recovered from the LFG. Other authors investigated the effects of pre-treatment on the amount of LFG generated assessing also the emissions due to its energetic recovery [15-19]. All these results showed that a large part of research activity was focused mainly on the energetic recovery from the landfill gas neglecting other relevant energetic consumptions necessary for the landfill management. In fact, landfill consist of complex and different activities as waste handling by wheeled loaders, climate conditioning of office building, leachate treatment, requiring energy and fuels. In the present study the data concerning the last five years of operation of an existing Italian landfill have been analyzed and presented. The landfill was chosen due to its particular features concerning both energy recovery and emission treatment. In fact, as imposed by National and EU legislation it is equipped with a landfill gas and leachate collection systems. The landfill gas is burned as fuel in a combined heat and power (CHP) plant whereas the leachate is processed in an in-situ treatment facility before being discharged. A given fraction of the heat recovered from the CHP is supplied to the leachate treatment system for increasing the whole energetic efficiency and environmental sustainability of the system. For these reason this landfill represents an innovative and integrated system and hence a relevant case study both from the environmental and energetic point of view. In the following the research was focused on the energetic aspects including all the main activities necessary for the management of the landfill. Nomenclature GHG K LFG LHV MSW

Greenhouse gas Efficiency Landfill Gas Lower Heating Value Municipal Solid Waste

OF Organic fraction V Standard deviation W Power output Subscripts el Electrical

2. Material and methods The landfill analyzed in this study is located in central Italy and has a maximum authorized volume for waste disposal of about 1,500,000 m3 that is a typical value for Italian landfills. The landfill can dispose mainly MSW (Table 1) together with a limited amount of special waste with features similar to MSW. It started operating in the 1995. The LFG collected is currently exploited in an existing combined heat and power (CHP) plant consisting of 6

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internal combustion engines (Table 2, Fig. 1b) with a total max output of about 2,000 kVA. A fraction of the heat recovered from the engines is used for the in-situ leachate treatment plant currently able to process about 15,000 m3/year. As imposed by the current legislation and by the landfill authorization, the company that manage the landfill has to monitor and record several operating and environmental data. Among these the amount of waste disposed, the amount of LFG recovered, the LFG composition (Table 3), the amount of leachate treated in-situ and the amount disposed by other facilities ex-situ represents some of the most relevant ones. Waste handling and compaction is performed by two wheeled loaders and one compactor powered by diesel engines. In the area of the landfill there is also an office building and a weigh station for measuring the amount of waste at landfill inlet. The heat generator used for heating the office building and for the generation of the hot water for workers looking room is fueled by LPG. In the following all the energetic consumptions related to the years from 2010 to 2014 were analyzed with the aim of assessing the global energetic features of the considered landfill. Table 1. Average composition of the MSW (2010-2014). Component

Amount (%w/w)

V

Plastics

11.4

5.0

Paper & Cardboard

19.9

6.7

Others

18.3

18

OF

50.0

13

Table 2. Mean features of the CHP plant. Engine model an n°

IVECO-AIFO 8281 - n°3

IVECO-AIFO 8291 - n°3

Parameter

Value

U.M.

Value

U.M.

Wel

262

kVA

405

kVA

Kel

33.2

%

33.4

%

Displacement

17.2

L

25.8

L

N° of cylinder

8

-

12

-

a)

b)

Fig. 1. Picture of the landfill analyzed (a) and scheme of the engine and relative piping for the CHP plant (b).

3. Results and discussion The amount of waste disposed in the landfill within the year 2009 were 520,000 tonnes. Starting from that date the following amount have been yearly disposed (Fig. 2): 169,800 tonnes in the 2010; 86,160 tonnes in the 2011;

Federico Sisani et al. / Energy Procedia 101 (2016) 66 – 73

79,521 tonnes in the 2012; 198,140 tonnes in the 2013; 156,248 tonnes in the 2014. This leads to a total amount of waste disposed of about 1,200,000 tonnes at the end of the year 2014. Table 3. Component of LFG analyzed and relative methodology. Component

Methodology

U.M.

CH4

ASTM D1964

% v/v

CO2

ASTM D1964

% v/v

O2

ASTM D1964

% v/v

H2S

M.U.634+APHA 4500

mg/m3

LHV

Calculated

kJ/Nm3

1400000 1200000

(tonnes)

1000000 800000

Total disposed waste Yearly disposed waste

600000 400000 200000 0 2010

2011

2012

2013

2014

Year

Fig. 2. Total and yearly amount of waste disposed in the considered landfill from 2010 to 2014.

6000000

(930 kWel) (930 kWel)

5500000

(930 kWel)

(Stm3 - kWhel)

5000000 4500000

(930 kWel) 4000000

(600 kWel)

3500000 3000000

LFG (Stm3) kWhel

2500000 2000000 2010

2011

2012

2013

2014

Year

Fig. 3. Amount of Stm3 of landfill gas (LFG) collected and electrical energy recovered (kWhel) per year from 2010 to 2014. In brackets the average power output of the combined heat and power (CHP) plant. As a consequence of the increased amount of waste disposed in the landfill there was a continuous increase of the amount of LFG collected (Fig. 3) with exception of the year 2013. The decreased amount of LFG collected in this year was a consequence of some works necessary for the construction of new cells for the disposal of the waste. The

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quality of the gas remained in any case quite high with an average concentration of CH 4 not lower than 50 by volume (% v/v) (Fig. 4) even if a slight decrease tendency was detected. The O2 concentration resulted always lower than 0.5 % v/v, on average, whereas the H2S concentration resulted of about 16 mg/m3 and quite constant along the whole period. 60 50 40 30

(% v/v)

20 CH4

10

CO2 O2 H2S

1

0 2010

2011

2012 Year

2013

2014

Fig. 4. Average landfill gas (LFG) composition by volume (%v/v) at the inlet of the combined heat and power (CHP) plant from 2010 to 2014. The slight reduction detected for the CH4 concentration in this period could be mainly a consequence of the quality of the LFG generated by the waste disposed in the recent years. In fact, in these waste the methanogenesis could result not fully implemented being partially inhibited as a consequence of the high concentration of volatile solids [20] causing an accumulation in volatile fatty acids and consequently a decrease in the pH. This inhibits the methanogenesis limiting the amount of methane generated during the anaerobic degradation of the OF of MSW causing an increase in the concentration of CO2. Furthermore this phenomena limits also the overpressure inside the landfill body caused by LFG generation rate allowing the infiltration of ambient air as demonstrated by the trend of the O2 concentration (%v/v) (Fig. 4).These inhibition phenomena could last for several months generating the effect represented in Figure 5. The reduction in CH4 concentration leads also to a reduction of the LHV of the LFG that resulted on average of: 17,118 kJ/Nm3 in the 2010; 16,450 kJ/Nm3 in the 2011; 16,722 kJ/Nm3 in the 2012; 16,155 kJ/Nm3 in the 2013; 15,806 kJ/Nm3 in the 2014. By the way, from the energetic recovery point of view, the positive effect of the increase in the LFG rate was higher than the negative effect of the reduction of the LHV. In fact, with exception of the year 2013, the amount of electrical energy recovered increased with a trend similar to the amount of LFG collected (Fig. 3). In the 2010 the amount of energy recovered was of 3,254 MWh, whereas in the 2014 it resulted of 5,795 MWh. The amount of LFG recovered in the 2010 and in the 2014 resulted of about 2,31 MStm3 and 4,14 MStm3, respectively. This means that the amount of energy recovered per Stm3 of LFG resulted of 1.408 kWh/Stm3 and 1.399 kWh/Stm3, respectively. Similar values were also detected for the other years indicating a quite constant energetic efficiency of the system. On the basis of the data related to the years 2010, 2011 and 2012 per each tonne/year of MSW disposed there was an average landfill gas collection ranging from a minimum 5 Stm3/tonne/year (2011) to a maximum of 7 Stm3/tonne/year (2012). These results were in accordance with those reported by other studies [3,5,11,14]. On the other hand for the management of the landfill and in particular of the leachate are necessary other equipment and facilities that consumes fuels, heat and electricity for their operation. As example, referring to the year 2014, the amount of energy and fuels consumed for the management of the landfill was of 296 Toe (Table 4). About 72% was represented by the electrical energy consumptions (i.e. 1,132,762 kWhel); about 8% was represented by diesel consumption; about 20% was represented by the heat consumption. The latter was completely co-

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generated by the CHP plant. The amount of LPG necessary for heating the office building was practically negligible (i.e. <1%). In particular > 90% of the electrical energy was consumed by the in-situ treatment facility of the leachate that represents the most relevant energetic needs necessary for the management of the landfill. Table 4. Different energy consumption for the management of the landfill (2014). Energy

Amount

Toe

%

Electricity

1,132,762 kWh

211,8

71.5

LPG

0.3 tonnes

0.3

0.10

Heata

602,200 kWh

58

19.6

Diesel

23 tonnes

24

8.11

Total

-

296

100

Legend: a=from CHP plant.

In this facility the leachate enters an evaporator (1, Fig. 5) in which is heated at about 90°C by a thermal resistance. A volumetric pump extracts continuously the vapor maintaining an internal pressure of about 70kPa. The vapor is condensed (2, Fig. 5) and the liquid treated in an reverse osmosis (3, Fig. 5) system before being discharged. The liquid remaining at the bottom of the evaporator is pumped to a second evaporator in which the evaporation heat is supplied by the heat recovered from the water jacket of the engines of the CHP plant. Also in this case the vapor is condensed and treated in the same reverse osmosis system. Standard treatment capacity of this plant is 50 m3/day corresponding to about 15,000 m3/year. The amount of electrical energy consumed by this facility depends mainly on the amount of leachate processed. Figure 6 represents the amount of leachate treated ex-situ, the one treated in-situ and the correspondent electrical energy consumption for the considered period. From these data resulted that the in-situ treatment of 1 tonne of leachate requires from about 70 kWh/tonne to about 75 kWh/tonne. Referring these data to the amount of MSW disposed results that per each tonne of waste disposed there was an electrical energy consumption for the leachate treatment ranging from about 5.5 kWh/tonne to 8.7 kWh/tonne. Even if the amount of leachate generated is not directly dependent from the amount of waste disposed, it is possible to evaluate a net electrical energy generation per each tonne of waste ranging from about 10.5 kWh/tonne to about 57.3 kWh/tonne. These results did not account for the heat cogenerated by the CHP and used by the leachate treatment facility that ranges, per each tonne of waste disposed, from about 3.1 kWh/tonne to about 7.7 kWh/tonne. In general the ex-situ treatment of the leachate is performed by large size existing waste water treatment plant located at about 200 km far from the landfill. As reported by [21] the electrical energy consumed by these plants per kg of chemical oxygen demand (COD) (kgO2/m3) eliminated is of about 1.684 kWh. Considering that the average COD concentration of the leachate generated from 2010 to 2014 was of about 19.720 kgO2/m3 and that, according to national legislation, it has to be decreased to 0.16 kgO 2/m3 the amount of electrical energy consumed per m3 resulted of about 33 kWh. Table 5. Electrical energy recovered from LFG and consumed for in-situ and ex-situ treatment of the leachate from 2010 to 2014.. Energy (MWh) Year

Waste disposed

Recovered

Consumed

Consumed

Net

(tonne)

from LFG

In-situ

Ex-situ

kWh/tonne

2010

169,800

3,254

1,016

967

7.48

2011

86,160

4,502

614

478

39,6

2012

79,521

4,996

693

310

50.2

2013

198,140

3,831

1,083

661

10,5

2014

156,248

5,795

1,060

1,013

23.8

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Including also this figure among the energetic consumption for the management of the landfill it results that the net electrical energy output ranges from a minimum value of 7.48 kWh/tonne for the 2010 to a maximum values of 50.2 kWh/tonne detected for the 2012 (Table 5). In any case the figures reported in Tables 5 highlights the relevance of the leachate treatment, both in-situ and ex-situ, on the energetic efficiency of the whole landfill. The results of this study showed that: 1) the amount of energy recovered is proportional the amount of waste disposed; 2) The amount of leachate generated is not correlated to the amount of waste disposed; 3) The treatment of the leachate represents >90% of the energetic needs for the considered landfill. Furthermore in-situ treatment of the leachate resulted in any case characterized by significantly higher energetic consumptions compared to the ex-situ performed by waste water treatment plants.

Fig. 5. Schematic of the evaporator of the leachate treatment system (Legend: 1-Evaporator; 2-Condenser; 3-Reverse Osmosis). 4. Conclusions Waste disposal represents a relevant environmental, economic and social aspect also in developed countries. Many different techniques are available to reduce the amount of waste produced and its environmental impact. In most cases, sanitary landfills have been and continue to be one of the most diffused solution to dispose urban and industrial wastes. It is well known how landfilling represents an important environmental threat due to gaseous, liquid and solid emission representing a burden for the environment if not correctly managed. From the energetic point of view the management of liquid emissions (e.g. leachate) generated by landfills is the most relevant activity. Globally more than 90% of the energetic needs of the landfill management are represented by this aspect. In general in-situ treatment resulted characterized by an higher specific energetic consumption (kWh/m3) even if costs and fuels consumption due to transport toward ex-situ facilities can be avoided. On the other hand ex-situ treatment, usually performed in existing waste water treatment plants, resulted characterized by a significantly lower energetic consumption (kWh/m3). In this last case the treatment are mainly based on biological processes instead of purely chemical and physical ones of in-situ ones. On the other hand the gaseous emissions generated by landfill (i.e. landfill gas), if properly managed can lead to the production of an important amount of

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renewable energy. Results showed that this energy resulted higher than the energetic needs making the landfill a facility with a surplus of renewable energy available for other uses. 1500

Ex-situ treated leachate (m3) In-situ treated leachate (m3) Electrical energy for in-situ (MWh)

30000

1400 1300 1200 1100

20000

1000

(MWh)

(m3)

25000

900 15000 800 700 10000 600 2010

2011

2012

2013

2014

Year

Fig. 6. Amount of leachate treated and of electricity consumed from the 2010 to the 2014. References [1] ISPRA. 2015. Rapport Rifiuti Urbani. N.230/15. ISPRA, Roma. ISBN978-88-448-0740-5. [2] EEA report, 2011. Greenhouse gas emission trends and projection in Europe 2011. ISSN 1725 9177. [3] Desideri U, Di Maria F, Leonardi D, Proietti S. Sanitary landfill energetic potential analysis: a real case study. Energ Conver Manag 2003;44: 1969-1981. [4] Di Maria F, Micale C, Sordi A, Cirulli G. Leachate purification of mechanically sorted organic fraction waste in a simulated bioreactor landfill. Waste Management & Research 2013;31:1070-1074. [5] De Gioannis G, Muntoni A, Cappai G, Milla S. Landfill gas generation after mechanical biological treatment of municipal solid waste. Estimation of gas generation rate constants. Waste Management 2009;29:1026-1034. [6] Pohland FG, Kim JC. In situ anaerobic treatment of leachate in landfill bioreactor. Water Science Technology 1999;40:203-210. [7] EU, 1999. Counci Directive 99/31/EC of 26 April 1999 on the landfill of waste (landfill Directive). Official Journal L 182, 16/07/1999 pp:119. [8] Glaivc P, Lukman R. Review of sustainability terms and their definition. Journal of Cleaner Production 2007;15:1875-1885. [9] Matete N, Trois C. Towards Zero Waste in emerging countries – A South Africa experience. Waste Management 2008;28:1480-1492. [10] Cossu R, Raga R, Rossetti D. The PAF model: an integrated approach for landfill sustainability. Waste Management 2003;23:37-44. [11] Di Maria F, Sordi A, Micale C. Experimental and life cycle assessment analysis of gas emission from mechanically-biologically pretreated waste in a landfill with energy recovery. Waste Management 2013;33: 2557-2567. [12] EC. EUROPE 2020, A strategy for smart, sustainable and inclusive growth. COM(2010) Brussel, 3.3.2010. [13] EC. A policy framework for climate change and energy in the period from 2020 to 2030. COM(2014) Brussel, 22.12014. [14] Di Maria F, Micale C, Sisani L, Rotondi L. Treatment of mechanically sorted organic waste by bioreactor landfill: Experimental results and preliminary comparative impact assessment with biostabilization and conventional landfill. Waste Management 2016. in press. Doi: 10.1016/j.wasman.2016.03.033. [15] Beylot, A., Villeneuve, J., Bellenfant, G. Life cycle assessment of landfill biogas management: sensitivity to diffuse and combustion air emissions. Waste Management 2013;33: 401–411. [16] Frike K, Santen H, Wallmann R. Comparison of selected aerobic and anaerobic procedures for MSW treatment. Waste Management 2005;25:799-810. [17] Komilis DP, Ham RK, Stegmann R. The effect of municipal solid waste pretreatment on landfill behavior: a literature review. Waste Management & Research 1999;17:10-19. [18] Liekman K, Stegmann R. Influence of mechanical-biological pre-treatment of municipal solid waste on landfill behaviour. Waste Management & Research 1999;17:424-429. [19] Van Praag M, Heerenklage J, Smidt E, Modin H, Stegmann R, Persson KM. Potential emissions from two mechanically-biologically pretreated (MBT) wastes. Waste Management 2009;29:859-868. [20] Di Maria F, Gigliotti G, Sordi A, Micale C, Zadra C, Massaccesi L. Hybrid solid anaerobic digestion batch: biomethane production and mass recovery from the organic fraction of solid waste. Waste Management & Research 2013;31: 869-873. [21] Hernandez-sancho F, Molinos-Senante M., sala-garrido R. energy efficiency in Spanish wastewater treatment plants: A non-radial DEA approach. Science of the Total Environment 2011;409:2693-2699.