Mass Balance of Contaminants

Mass Balance of Contaminants

2.2 MASS BALANCE OF CONTAMINANTS: A KEY FOR MODERN LANDFILL DESIGN Raffaello Cossu INTRODUCTION Chapter 2.1 illustrates the range of different landfil...

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2.2 MASS BALANCE OF CONTAMINANTS: A KEY FOR MODERN LANDFILL DESIGN Raffaello Cossu

INTRODUCTION Chapter 2.1 illustrates the range of different landfill barriers available. The waste input barrier and the reactor barrier (i.e., the transformation processes occurring within the landfill mass) represent the basis for the evolution of landfill concepts toward sustainability and long-term repository of contaminants (final sink). The mass balance of a given contaminant can be measured in a landfill by calculating the initial load associated with the waste input, the load collected with gas and leachate, and the load withheld by the lining system. The difference between the initial load, the collected load, and the residual stored amount represents the load released into the environment through the uncontrolled dispersion of leachate and gas.

QUALITY OF WASTE AND MASS BALANCE IN A LANDFILL Substances of particular environmental interest requiring constant monitoring include, among others, carbon and nitrogen, both associated with the organic compounds present in wastes. The quantities and features of wastes vary considerably according to socioeconomic and geographic aspects. As an example, in developing countries putrescible organic compounds may account for up to 80% of waste weight with scarce presence of plastics and paper, whereas in European cities putrescible organic compounds may constitute less than 20%, with a higher presence of other waste fractions. The mean amount of carbon present in a European municipal waste is approximately 20%e25% (Stegmann and Ritzkowski, 2008), distributed among the various organic categories as indicated in Table 2.2.1. With regard to mobility in waste composition, two distinct organic fractions can be identified: • xS ¼ nonmobile concentration of contaminant in the waste and • sS ¼ mobile concentration of contaminant in the waste The mobile fraction of carbon is transferred by means of leaching, biodegradation, or other reactions/conversions from the solid to the liquid (sL ¼ leached fraction) or gas phase (sG ¼ gasified fraction) or is converted, under the existing conditions, into a nonmobile solid form that contributes toward increasing the xS fraction.

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Table 2.2.1 Mean composition of a general European waste expressed as a percentage of total solids (Stegmann and Ritzkowski, 2008; Zeschmar-Lahl, 2003a, 2003b) Component

%

ORGANIC COMPOUNDS Lignin

6

Hemicellulose

7

Proteins

3

Paper additives (organic þ inorganic)

8

Cellulose

16

Hydrocarbons

9

Fats, resins, waxes

2

Plastic

18

INORGANIC COMPOUNDS Plastic additives

3

Minerals

13

Ashes

4

Hazardous substances

1

Metals

10

Mobilization may of course occur with any contaminant, including heavy metals and other nondegradable substances. The conversion processes (leaching, precipitation, complexation, etc.) are dependent on the individual substances. Considering the landfill as black box reactor, the mass balance equation can be summarized as follows: Accumulation ¼ IN  OUT  Reacted

SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann

(1)

The term “IN” refers to the mass of a given contaminant in the deposited waste over a given period of time in a landfill with a volume V. It can be expressed as follows: IN ¼

n X

Qi sSi

(2)

i¼1

where: n, number of waste streams of different typologies “i”; Q i, flow rate of the individual waste typology “i” (t/y); sSi, concentration of mobile fraction of contaminant in waste typology “i” (g/t). The term “OUT ” in Eq. (1) represents the mass released from landfill associated with emission rates of gas (qG, Nm3/year) and leachate (qL, m3/year). Taking carbon as contaminant and denoting the concentrations of carbon present, respectively, in landfill gas (CO2, methane, etc.) and leachate (TOC) as sG (mg/Nm3) and sL (mg/L), the released mass associated with carbon emissions can be calculated as follows: OUT ¼ sL $qL þ sG $qG

(3)

By distinguishing the fractions of landfill gas and leachate collected (qLc and qGc) from the fraction dispersed in an uncontrolled manner through the landfill barrier systems (qLd and qGd), the following applies: qL ¼ qLc þ qLd and qG ¼ qGc þ qGd

(4)

The term “reacted” in Eq. (1) represents the mass of organic substance which is mineralized/ stabilized and can be expressed as follows: Reacted ¼ rV

(5)

where: r, overall reaction rate (mg/m3$year); V, landfill reactive volume (m3). The term “accumulation” expressed as dS/dt represents the variation of the contaminant mass (S) within the landfill versus time (t). According to the previous equations, “accumulation” can be described by the following relationship: n n X X ds ¼ Qi ssi  sL qL  sG qG  rV ¼ Qi ssi  sL qLc  sL qLd  sG qGc  sG qGd  rV dt i¼1 i¼1

(6)

S(t) represents the residual amount of mobile carbon still present in the landfilled waste at a given time and is indicative of the mobile carbon emission potential of the system. For this reason, as long as the emission potential remains high the landfill should be protected, implying that the barrier system comprising impermeable lining and drainage systems should be efficiently active. A graphical representation of the carbon balance terms is given in Fig. 2.2.1.

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Figure 2.2.1 Graphical representation of mass balance terms, considering carbon as a contaminant, in

an municipal solid waste landfill reactor. By moving to the first part of Eq. (6), the terms expressing the uncontrolled emissions of mobile carbon, the following expression is obtained: sL qLd þ sG qGd þ

n X dS ¼ Qi ssi  sL qLc  sG qGc  rV dt i¼1

(7)

The terms comprised in the first part of the equations are those which should be monitored and minimized to prevent adverse environmental impacts both in the short- and the long term. By analyzing Eq. (7) it appears evident that to minimize these terms it is necessary to minimize the positive terms and maximize the negative terms on the right of the equation. From an operational viewpoint this implies the following: • minimizing the mobile carbon mass introduced into the landfill (sSi$Qi), controlling both flow rates (Qi) and quality (sSi) of wastes deposited, as an example by reducing the production of waste, and applying various forms of treatment prior to landfilling; • maximizing the mass of carbon to landfill gas and leachate collected (sL$qLc and sG$qGc), controlling both flow and composition; and • increasing waste stabilization (rV) by enhancing the reaction rate through the aerobization of landfilled waste (forced or natural aeration) or addition of water in the case of water shortage. Although, as a general rule, landfill regulations and practices tend to minimize the generation of leachate by limiting or excluding the infiltration of water into the landfill body, the mass balance equation clearly indicates how water played a key role in controlling negative landfill impacts. Indeed, water controls the reaction rate r as it is a fundamental reagent required by biodegradation processes (Chapter 3.1). Without water the degradation term rV would be nullified, thus resulting in a sort of “mummification” of wastes. Moreover, water controls the transport of contaminants from solid to liquid phase. The more leachate and gas are generated, the more mobile contaminants will be removed from the system, thus preventing their uncontrolled emission into the environment.

SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann

ACCUMULATION OF MASS AND EMISSION BEHAVIOR The accumulation over time of mobile contaminants in the landfilled waste, as described mathematically in Eq. (6), follows the trend illustrated in Fig. 2.2.2. The accumulated mobile contaminant mass, St, represents the emission potential and may be expressed, for instance, in tonne of residual mobile carbon when taking into account organic degradable waste. St reaches a peak during landfill operation and then decreases as a consequence of degradation processes and generation of gas and leachate. Peaks and trends of the accumulation curves will depend on the adopted landfill technologies.

sGqGc

sGqGc

sLqLc

sLqLc

rV

rV

SStt

rV

St barrier

SSt t

Smax

rV damaged barrier

Traditional landfill

S30

Sustainable andfill

Ssust 0 OPERATION

30 AFTERCARE

?

Time (years)

Figure 2.2.2 Curves illustrating accumulation of mobile mass of contaminants (St) throughout the life

span of two different kinds of landfills. The figure also provides a graphical representation of mass balance terms (Eq. 6) at different times. When the barriers lose their efficacy, the lower the St, the lower the potential emissions of contaminant. sL, concentration of mobile carbon (TOC) in leachate, mg/L; qLc, flow rate of collected leachate, m3/year; sG, concentration of mobile carbon in landfill gas (CO2, methane, etc.), mg/Nm3; qGc, flow rate of collected landfill gas, Nm3/year; rV, mass of stabilized contaminant (r, reaction rate, mg/m3$year, V, landfill reactive volume, m3); St, amount of mobile carbon accumulated within the lining system representing the potential of residual emissions, t/year; S30, amount of mobile carbon accumulated within the lining system after 30 years aftercare; Ssust, amount of mobile carbon accumulated within the lining system, representing final storage quality, i.e., accumulation which has reached an equilibrium with the environment.

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A landfill can be deemed stable and aftercare completed once the accumulated mass has reached a value which is sustainable for the environment, Ssust. The values of the term Ssust defines the final storage quality (FSQ) of the landfill. FSQ can be assessed based on a series of different parameters and risk analysis procedures (see Chapter 16.1 and Heyer et al., 2013). Fig. 2.2.2 provides a graphical representation of the way in which individual mass balance termsd expressed by Eq. (6)dchange over time. When the physical barriers lose efficacy due to unavoidable failures in the lining or drainage systemsdsuch as cracking, tears, aging, clogging, etc., (see Chapter 5.1)dthe residual mass of contaminants will no longer be contained and uncontrolled emissions of leachate may occur. The quality of leachate (sL) changes over time, reflecting the trend of residual concentration of contaminants in the waste mass. By using a first-order reaction kinetics (dsL/dt ¼ ksL), the concentration of a contaminant at a given time, sLt, will be as follows: sLt ¼ sL0 ekt where: sL0, initial concentration of contaminant in the leachate; t, observation time; k, reaction rate constant. Studies aimed at predicting the long-term behavior of landfill emissions have enabled calculations to be made for a series of different contaminants in municipal solid waste (MSW) leachate with regard to   _ the time required to reach concentrations which comply with standard limits S L set by national regulations for discharging waste waters in surface water bodies. The results are summarized in Table 2.2.2. For some parameters, such as TKN, a period of several centuries may be necessary. The potential load of mobile contaminants associated with uncontrolled leachate emissions (sL*$qLd) will depend on the adopted landfill technologies and, in particular, the efficiency of the multibarrier system (see Chapter 2.1). The load changes throughout the landfill life span as represented in Fig. 2.2.3. Sustainable conditions are achieved when the accumulation of mobile contaminants, St, reaches FSQ and uncontrolled emissions are below the target values for assessing sustainability (sL*$qLd)sust. In an open dump, uncontrolled emissions reach a peak during landfilling operations and subsequently decrease in the postclosure period. In the case of a traditional contained landfill, uncontrolled emissions will remain below the acceptable threshold values for as long as the physical barrier systems (lining and leachate drainage) remain effective in controlling flow rate of the potential emission (qLd). On loss of barrier efficacy uncontrolled emissions may occur, with environmental impact of the latter being dependent on the concentration of contaminants in the leachate (sL). If the uncontrolled emissions of contaminants at a given time (sL*$qLd)t. exceeds the target value for sustainability (sL*$qLd)sust then adverse environmental impacts may be registered.

SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann

Table 2.2.2 Estimation of the time (TL) required for municipal solid waste leachate parameters to

reach limit concentrations ðb s L Þ established by national regulations for discharging wastewater into surface water bodies in Germany (D) and Switzerland (CH), according to different experiences P

b s L (mg/L)

sL0 (mg/L)

TL (year)

References

COD

Old FRG waste

1800e8400

200 (D)

120e220

Andreas (2013)

COD

Old FRG waste

1800e8400

60 (D)

200e300

Andreas (2013)

COD

Full-scale landfill

22e22500

200 (D)

65e320

Krüempelbeck (2000)

COD

Lysimeter

500e12700

200 (D)

80e360

Heyer (2003)

TKN

Old FRG waste

1100e3600

70 (D)

120e300

Andreas (2013)

TKN

Old FRG waste

1100e3600

5 (CH)

280e580

Andreas (2013)

TKN

Full-scale landfill

1e2530

70 (D)

DecadeseCenturies

Krüempelbeck (2000)

TKN

Lysimeter

200e2100

70 (D)

120e450

Heyer (2003)

Cl

Full-scale landfill

52e8700

100 (D)

25e60

Krüempelbeck (2000)

Cl

Lysimeter

340e2950

100 (D)

90e250

Heyer (2003)

AOX

Full-scale landfill

0.058e6.2

0.5 (D)

40e100

Krüempelbeck (2000)

AOX

Lysimeter

0.39e2.38

0.5 (D)

30e210

Heyer (2003)

sL0 is the concentration of the considered leachate at the start of the simulation time (t ¼ 0). FSL, full-scale landfill; LSR, landfill simulation reactor; O-FRG, old waste from German landfills.

(sLqLd)max

Open dump Traditional landfill Sustainable landfill

(sLqLd)sust 0 OPERATION

30

Time (years)

AFTERCARE

Figure 2.2.3 Curves illustrating contaminant load sL*$qLc associated with uncontrolled emissions of

leachate throughout the life span of an open dump and two different types of landfills, (sL*$qLc)sust, representing the sustainable target for contaminant load. CHAPTER 2 j Mass Balance of Contaminants: A Key for Modern Landfill Design

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Therefore, a poor control of the accumulation of mobile contaminants in traditional landfills (no pretreatment, anaerobic conditions, scarcely permeable top covers) may produce unsustainable situations. On the contrary, a sustainable landfill designed with multibarrier concepts and aimed at optimizing mass balance terms in Eq. (7) and controlling the accumulation term St following loss of efficacy of the barrier system will ideally be characterized by uncontrolled emissions having low contaminant concentrations (sL). Consequently, the mass load of contaminants (sL*$qLd)t could be maintained below sustainability targets. In the light of these considerations it is clear that the expected environmental impacts from landfilling are mainly driven by the technical and administrative requirements established by national regulations. With regard to the aftercare phase, according to the European Directive on Landfilling,1 several national regulations, including Italian law n. 36/2003 (art. 14), have decreed a financial provision to cover aftercare costs over a period of 30 years. However, if at the end of this period the barriers have not maintained their efficacy (see Chapter 7.1) and the residual mobile mass of contaminants (S30)dand consequent emissions (sL*$qLd)30dhave not reached sustainable levels, the financial provision may not cover the costs of eventual remediation. This aspect is critical also in view of the fact that a large majority of national regulations fail to provide for the pretreatment and in situ treatment of waste and, worse still, frequently envisage provisos that may prove detrimental in controlling the accumulation of contaminants, such as the adoption of impervious top covers, prohibition of leachate recirculation, etc. The latter may prove to be particularly onerous for private landfill operators, in view of the liability set by the regulations for the long-term monitoring of landfills.2 The Italian regulations additionally foresee that, in the case of negative environmental effects, the landfill operator shall be called on to comply with the remediation requirements dictated by the Authorities.3 Council Directive 1999/31/EC, Article 10. “Cost of the landfill of waste.” Member States shall take measures to ensure that all of the costs involved in the setting up and operation of a landfill site, including as far as possible the cost of the financial security or its equivalent referred to in Article 8(a) (iv), and the estimated costs of the closure and after-care of the site for a period of at least 30 years shall be covered by the price to be charged by the operator for the disposal of any type of waste in that site. (omissis).

1

Council Directive 1999/31/EC, Article 13. “Closure and after-care procedures”. (omissis). after a landfill has been definitely closed, the operator shall be responsible for its maintenance, monitoring and control in the after-care phase for as long as may be required by the competent authority, taking into account the time during which the landfill could present hazards. The operator shall notify the competent authority of any significant adverse environmental effects revealed by the control procedures and shall follow the decision of the competent authority on the nature and timing of the corrective measures to be taken; .(omissis). for as long as the competent authority considers that a landfill is likely to cause a hazard to the environment and without prejudice to any Community or national legislation as regards liability of the waste holder, the operator of the site shall be responsible for monitoring and analyzing landfill gas and leachate from the site and the groundwater regime in the vicinity of the site. 2

Legislative Decree. 36/2003, art. 13 “Operational and Post-operation management” . (omissis). The management shall, moreover, notify the competent Authority of any significant negative environmental effects detected subsequent to the implementation of monitoring and control procedures, and shall comply with the decision taken by the competent Authority with regard to the nature of corrective actions and the terms of actualization of the same.

3

SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann

To conclude, landfill operators may find themselves in the paradoxical situation whereby on the one hand they are required to comply with technical requirements established by law, although these may at times extend the long-term environmental impact (e.g., sealed top covers), whereas on the other being obliged to accept responsibility for the environmental issues that may arise as a consequence! Moreover, as underlined previously, this situation is further complicated by the total lack of specific definition of standards for environmental acceptability to be applied by the competent Authorities in assigning responsibility. In Chapter 16.1 this issue (Definition and Achievement of Final Quality Targets) is discussed in detail.

MASS BALANCE CONTROL FOR ENVIRONMENTAL SUSTAINABILITY Implementation, from an operational point of view, of mass balance for landfill contaminants may represent the keystone to the calibration of technical interventions aimed, both during the planning, operation, and aftercare phases, at achieving environmental sustainability. As schematically summarized in Table 2.2.3, the different terms of mass balance can be influenced by the use of a series of technologies and management methods, when referring to carbon in organic fractions. Minimization initiatives will undoubtedly influence the quantity of waste to be landfilled. Recycling of biodegradable organics (e.g., composting) may result in a significant reduction of waste quantities and positive variations of waste quality. Waste treatment prior to deposition in a landfill may be undertaken using various types of processes: • physical and physicochemical such as grinding, sieving, compacting, baling, classification, and washing (see Chapter 4.3); • biological (anaerobic and/or anaerobic) usually combined with mechanical unit operation (see Chapter 4.1); and • thermal (see Chapter 4.2). The terms of mass balance may be influenced not only by pretreatment of incoming waste but also by means of in situ interventions and processes both during the operation and aftercare phase. Possible in situ options include the following: • • • • • •

enhanced anaerobic degradation; leachate recirculation (see Chapter 12.1); natural aeration (see Chapter 14.2); forced aeration (see Chapter 16.2); combination of aerobic and anaerobic sequences (hybrid landfill reactors); and flushing (Karnik and Parry, 1997).

Finally, a well-structured physical barrier system (liner þ leachate drainage) is necessary to regulate and control storage of the residual biodegradable fraction of landfilled waste that has not yet been degraded (St).

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Table 2.2.3 Qualitative influence of a range of technical options on mass balance terms in a municipal solid waste landfill (þþþ ¼ high, þþ ¼ medium, þ ¼ fair) Options

sSi

Waste avoidance Separate collection/sorting

Qi

Thermal treatment Leachate recirculation In situ aeration Watering

qLc

sG

qGc

rV

St

DDD D

DD

Mechanical pretreatment Biological pretreatment

sL

D D

D

D

DD

D

D

DD

DDD

DD

DD

DDD

D

D

DD

DD

D

DD

D

D

D

D

DD

D

Physical bottom barrier

DD

SSi, concentration of mobile fraction of contaminant in waste typology “I,” g/kg; Qi, flow rate of the individual waste typology “i,” t/year; SL, concentration of mobile carbon (TOC) in leachate, mg/l; qLc, flow rate of collected leachate, m3/year; SG, concentration of mobile carbon in landfill gas (CO2, methane, etc.), mg/Nm3; qGc, flow rate of collected landfill gas, Nm3/year; rV, mass of stabilized contaminant (r, reaction rate, mg/m3$year; V, landfill reactive volume, m3); St, amount of mobile carbon accumulated within the lining system, t/year.

At variance with the majority of landfill regulations which aim to control waste quality at the gate, the objective of environmental sustainability, as illustrated earlier, may be achieved by means of combined measures, including pretreatment, in situ treatment, and aftercare interventions. Therefore, assessment of sustainability targets should not be based on compliance with a specific parameter of the waste to be landfilled (taking into account only pretreatment methods) but rather by analyzing the landfill matrices (residual landfilled waste, gas, and leachate emissions) after significant periods of time to verify whether they comply with sustainability criteria (see Chapter 16.1). Possible treatment combinations applied with a view to achieving sustainability targets are represented in Fig. 2.2.4. These combinations are strictly linked to the characteristics of the waste. MSW may undergo mechanical treatment (Aa) by means of shredding, sieving, and sorting of recyclables, followed by an anaerobic phase in a landfill bioreactor (Ab) with intense production of gas (e.g., concentrated over an indicative period of 12e15 years) and by a posttreatment phase with forced aeration (see Chapter 14.3). This phase later on could be followed by natural aeration (semiaerobic landfilling). In the latter case, the drainage system should be implemented prior to start-up of landfill operation as the drainage

SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann

a. PRETREATMENT

b. IN SITU OPTIONS

c. AFTERCARE

(A)

MECHANICAL TREATMENT

ANAEROBIC PROCESSING

FORCED AERATION

(B)

MBP

NATURAL AERATION

WATERING

(C)

THERMAL TREATMENT

WATERING

TOP SEALING

(D)

WASHING

CLOSED SYSTEMS

LANDFILL MINING

Figure 2.2.4 Combination of a series of operational alternatives capable of influencing mass balance in a

landfill and promoting sustainability. The proposed combinations are theoretical and indicative, being dependent on the waste characteristics (degradability, combustibility, leachability, etc.) and not reflecting necessarily current practice. system in semiaerobic landfills differs significantly from that adopted in anaerobic landfills (see Chapter 14.2). Further treatment for in situ washing of the waste could fully stabilize the waste allowing a sealing top cover (see Chapter 11.1). Following mechanical pretreatment and sorting of putrescibles (Aa), MSW may alternatively undergo natural aeration (Bb) and then be stored in the medium term before being subjected to landfill mining (Dc) for the recovery of combustible fractions. This option may also be conveniently adopted with plastics, papers, and textiles which have not been, for whatever reason, recycled and when no thermal treatment is available in the area. Subsequent to mechanical biological pretreatment, MSW may undergo either anaerobic landfilling and postcare forced aeration (Ba, Ab-Ac) or natural aeration (Bb) followed by forced aeration in the aftercare phase (Ac). Waste should be pretreated using mechanical biological systems (Ba) to significantly reduce biological activity of the organic compounds. Failure to do so may lead to in situ aeration eliciting the formation of a bacterial biomass in the drainage system capable of obstructing granular drainage beds. Also this kind of landfill may be completed by means of a posttreatment flushing (Bb), with a final sealing top cover (Cc). Another scheme of interest is represented by the line (Ca þ Da þ Bb). Residual waste from thermal treatment undergoes prewashing and natural aeration during landfilling to reduce the leaching potential

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and promote chemical stabilization (carbonation). After assessing the residual leaching potential, the landfill may be closed with a permanent sealing cover (Cc). In the presence of leachable and nonhazardous industrial waste, a convenient treatment solution may comprise the prewashing of waste (Da), which is subsequently landfilled under a roof or any other closed system (Db), with a top seal being applied in the aftercare phase (Cc).

ROLE OF LANDFILL AS A SINK The construction of a sustainable landfill is complementary to the new role that a modern landfill is required to perform in closing the material cycle and, with specific regard to carbon, in acting as a carbon sink. Indeed, taking into account the classification of organic substances used in calculating mass balance, as nonmobile (xS) and mobile fractions (sS, sG, sL), it is clear that an integrated system of pretreatment and in situ treatment (Fig. 2.2.5) should be aimed at progressively converting the mass of degradable organic compounds into leached or gasified carbon and achieving sustainability targets (FSQ). Concurrently, accumulation of the nonmobile fraction of organic compounds (lignin, plastic) originally present in the waste (xS) and the stabilization of biodegradable organics by conversion into nondegradable substances (e.g., insoluble humic substances) effectively describes the role of landfill as a carbon sink. The final quality of landfilled waste, devoid of mobile contaminants, is what is often LANDFILL RAW WASTE

PRETREATMENT

IN SITU TREATMENT

GEOLOGICAL REPOSITORY

AFTERCARE

Sustainability

Sink

BPQ

FSQ

RQ

Gasified carbon Leached carbon Residual mobile carbon in the waste No-mobile carbon in landfilled waste

Figure 2.2.5 Time trend of the organic fractions present in landfilled wastes according to the various

types of waste treatment performed, as indicated in Fig. 2.2.4G. BPQ, best practice quality; FSQ, final storage quality, RQ, rock quality. Modified from Cossu (2012).

SOLID WASTE LANDFILLING j Concepts, Processes, Technologies j R. Cossu, R. Stegmann

referred to as rock quality. When this quality is reached, a landfill can be considered a geological repository (Cossu, 2012). The role of landfill as a sink is also fundamental in closing the material loop in any circular economy strategy as discussed in Box 2.2.1. Box 2.2.1 Back to Earth Sites: from “nasty and unsightly” landfilling to final sink and geological repository Recycling, recovery of resources, urban mining, closing the loop, and zero waste are all terms widely used in waste management to encourage the transformation of waste into resources (Cossu and Williams, 2015). Graphically these concepts are often represented in the form of topedown or bottomedown triangles where different waste management steps are listed in a hierarchical order. Avoidance, material recovery, and recycling are the preferred options “aimed at reducing use of natural resources and controlling contaminant potential, both on a local (water and soil contamination, odour, etc.) and a global scale (emission of greenhouse gases and other air pollutants)” (Cossu, 2009). The amount of waste sent to landfilling should be drastically reduced, with landfilling representing the least preferred option for waste management. Transition from a linear approach (take-make-waste) to a circular approach is commonly described by a perfect cycle in which the different life stages of a product are represented: productionedistributione consumptionereuse/repairerecycling of secondary raw materials to production. The European Union has proposed an Action Plan with the introduction of measures intended to support the whole cycle (EU, 2015). What is completely missing in this strategic vision is the role of landfilling. In the triangular hierarchic representation, landfilling is viewed as a sort of a dustbin in the system, in which to deposit all unavoidable and nonrecyclable wastes, together with residues from previous treatment. In the circular representation, landfilling is simply neglected; the landfill should no longer exist. Accordingly, more and more frequently we witness the issuing of regulations that envisage the elimination of landfills, invariably dictating rather lengthy time frame for achieving goals. As an example, the South African Polokwane Declaration, an official governmental document, sets targets of zero waste to landfills by 2022 and a 50% reduction of the same by the year 2012 (http://soer.deat.gov.za/dm_documents/ polokwane_nmZiT.pdf). These declarations are frequently not based on any technical grounds but merely represent a wish and are seen by politicians currying favor with the populist as the simplest means of dealing with these issues. Other nations and regions boast of waste management systems in which landfills have been eliminated, only to later discover that this has been achieved not by means of comprehensive recycling of all wastes but rather by transferring a portion of the wastes generated elsewhere. In the same way as many of the thorny issues we encounter during a lifetime, everyone builds landfills, but most try to talk about them as little as possible. While Europe promotes a circular economy, the nasty and unsightly landfills continue to meet onethird of the needs for waste disposal, with a particularly high concentration of facilities present in the newest Member States. It should moreover be underlined that while landfills are indicated as the source of a wide range of wellknown environmental problems (e.g., groundwater pollution, odors, greenhouses gases), in almost all industrialized countries national landfill regulations tend to provide for the construction only of “traditional” landfill sites, completely overlooking any accomplishments provided by the impressive scientific and technical developments of sustainable landfilling in recent years. (Continued)

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Taking once again the European situation as an example, the Landfill Directive dates back to 1999 (although technically speaking the document had been under consideration since 1993 but was only published in 1999 due to a difficulty in identifying a common position with the British, who were reluctant to abolish codisposal). All national legislation in European countries is based on this Directive (EU, 1997). These regulations envisage three types of landfill (for hazardous, nonhazardous, and inert waste), the control of biodegradable waste, the implementation of protective measures on the bottom and slopes of the landfill through installation of physical barriers (mineral liners, geomembranes, drainage), and the limitation of water influx. However, nowhere in the entire Directive one can find the magic words “environmental sustainability.” No mention of a word or a sentence that establishes how the long-term impact of a landfill should be exhausted within the span of one generation. On the contrary, the postoperational phase, which follows the closure of a landfill, is addressed only in economic terms (art. 8 and art. 10), defining for landfill managers a financial provision relating to the covering of aftercare costs for a period of at least 30 years. Then stating in art. 13 that “. (c) after a landfill has been definitively closed, the operator shall be responsible for its maintenance, monitoring and control in the after-care phase for as long as may be required by the competent authority, taking into account the time during which the landfill could present hazards.. . (d) for as long as the competent authority considers that a landfill is likely to cause a hazard to the environment and without prejudice to any Community or national legislation as regards liability of the waste holder, the operator of the site shall be responsible for monitoring and analysing landfill gas and leachate from the site and the groundwater regime in the vicinity ..” As no environmental criteria have been established to determine when “a landfill is likely to cause hazard,” the input of data during the planning and design stage relating to how to achieve the aims of FSQ is not envisaged. We all know that the long-term impact of traditional landfilling (the conceptual landfill referred to in the regulation) far exceeds the 30 years covered by the financial provision and, even worse, far exceeds the life span of the physical barriers. As a result, the designing of landfills that comply solely with the European Directive is equivalent to designing contaminated sites. Therefore, although the regulations result in the construction of “nasty and unsightly” landfills, no steps have been taken to improve this situation. Thus, no amended legislation has been made available, no research is supported, and there is no incentive to promote the design of environmentally sustainable landfills. On the contrary, nowadays in Europe the easiest way to have a research proposal rejected is to mention, even in passing, landfills. This leads to perverse environmental outcomes that go against the principles of the circular economy intended to eliminate these issues. During the circular management of waste (Cossu, 2013), the various stages of a product’s life span generate liquid, gaseous, and solid wastes. Although the legal requirements for emission concentrations may be met, the product, because of the volume of emissions, continues to generate a load (expressed in terms of weight/time) that results in an alarming and widespread contamination. The increasing concentration of nondegradable substances in the seas, air, and glaciers at all latitudes represents one of the most pressing environmental problems. We have become so accustomed to referring to concentrations and percentages that we have forgotten that these loads are the real issue. Taking paper as an example, the presence of problematic chemicals (e.g., MOHs (mineral oil hydrocarbons), phenols, phthalates, PCBs, toxic metals) is measurable, with these compounds tending to accumulate throughout the various circulation cycles, reaching relatively high concentrations in both the end product and the residual waste (Pivnenko et al., 2016). The ambitious goal of closing the loop in the circular economy cannot be achieved if the issue of management of residues from production and recycling processes is not properly addressed. The generation of residual waste should not only be reduced but the sustainable management of residues that cannot be avoided should also be pursued.

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By calculating a simple mass balance, starting from the moment the material resources are extracted from the ground, it becomes clear that to close the material loop, a final sink in which the residues can be safely and esthetically deposited needs to be taken into consideration. To avoid environmental issues, the deposited material should be processed to ensure that it will not result in emissions that may negatively affect the quality of the environment. Indeed, the substances present in the final residues returned to the earth should all be in a nonmobile form. This may require specific treatment procedures aimed at eliminating or significantly reducing the mobile waste fraction responsible for generating an environmental impact. The concept of Back to Earth Alternatives (BEA) is thus introduced, implying that the residues, after proper treatment, should be returned to their nonmobile state, as they were before they were extracted from the ground to be used as raw materials (Fig. 1). This would provide the actual closing of material cycles. BEA may include the use of compost in agriculture and use of residues in the production of building materials (e.g., bricks, concrete) and construction of houses, bridges, or roads. Particularly, however, they include what we can call Back to Earth Sites (BES), i.e., permanent waste deposit sites that meet the above-described requirements.

Figure 1 Circular economy conceptual scheme including the sustainable management of the residues to be sent “Back to the Earth” to close the material loop. To implement these concepts, a proactive approach should be taken based on the following objectives: • assessment of quantity and quality of residues in the circular economy; • definition and demonstration of strategies for minimization of residues quantity and quality upgrading; • treatment of the final residues (e.g., washing, mineralizing, stabilization); • definition and demonstration of BEA for the treated residues (e.g., material sink in BES), development of new products and building materials, use in bitumen production, addition to agricultural soil; • economic and environmental (long-term leaching) evaluation for BES and other BEA options; • regulatory and policy framework for BES. The policies frequently adopted to date by national and international authorities on landfilling are largely reminiscent of the three monkeys who do not see, do not hear, and do not speak; we should, however, be fully aware that a circular economy cannot exist in the absence of a sustainable closure of the material loop. In other words, we cannot have a society with no permanent deposit of residues onto or into land. With no landfilling! Raffaello Cossu, 2016. Editorial - adapted from Waste Management, 55, 1-2.

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References Andreas, L., 2013. Long-term behavior of Municipal landfills. Emissions from Old sites in the Eastern part of Germany. In: Cossu, R., van der Sloot, H. (Eds.), Sustainable Landfilling. CISA Publisher, pp. 153e167. ISBN:978-88-6265-005-2. Cossu, R., 2009. From triangles to cycles. Waste Management 29, 2915e2917. Cossu, R., 2012. The environmentally sustainable geological repository: the modern role of landfilling. Waste Management 32, 243e244. Cossu, R., 2013. The urban mining concept. Waste Management 33, 497e498. Cossu, R., Williams, I., 2015. Urban mining: concepts, terminology, challenges. Waste Management 45, 1e3. EU, 1997. Council Directive 1999/31/EC on the Landfill of Waste. EU, 2015. Communication from the Commission to the European Parliament, the Council, the European Economic and Social Committee and the Committee of the Regions. Closing the Loopean EU Action Plan for the Circular Economy, 2015 COM 614. final. Heyer, K.-U., 2003. Emissionsreduzirung in der Deponienachsorge. Hamburger Berichte, band 21, Verlag Abfall aktuell, ISBN:3-9808180-4-7 [cit. in Heyer et al., 2013]. Heyer, K.-U., Hupe, K., Stegmann, R., 2013. Criteria for the completion of landfill aftercare. In: Cossu, R., van der Sloot, H. (Eds.), Sustainable Landfilling. CISA Publisher, pp. 611e622. ISBN:978-88-6265-005-2. Karnik, M., Parry, C., 1997. Cost implication of operating landfills as flushing bioreactors. In: Proceedings Sardinia 97. Sixth International Landfill Symposium, vol. I. CISA, Cagliari, pp. 419e426. Krümpelbeck, I., 2000. Untersuchungen zum Langzeitemissionsgeschehen von Siedllungsabfalldeponien. Dissertation an der Bergischen Universität Gesamthochschule Wuppertal, Bereich Siedlungwasser- und Abfallwirtschaft, Heft 3 [cit. in Heyer, 2003]. Pivnenko, K., Olsson, M.E., Götze, R., Eriksson, E., Astrup, T.F., 2016. Quantification of chemical contaminants in the paper and board fractions of municipal solid waste. Waste Management. Stegmann, R., Ritzkowski, M., May 2008. Landfill Fundamentals. Power Point Presentation. IWWG Training Course on Sanitary Landfilling, Lima, Perù. Zeschmar-Lahl, B., 2003a. Stoffflussanalyse an einer mechanischen Aufbereitungsanlage e Eintrag und Verbleib von Chlor und Metallen. Fachtagung Mechanisch-biologische Abfallbehandlung, Berlin, 2./3.12.2003. In: Thomé-Kozmiensky, K.J. (Ed.), Ersatzbrennstoffe, 3, pp. 231e259 [Cit. in Stegmann and Ritzkowski, 2008]. Zeschmar-Lahl, B., 2003b. Schwermetallentfrachtung am limit. Müllmagazin (4) [Cit. in Stegmann and Ritzkowski, 2008].

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