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Waste Management xxx (2017) xxx–xxx
Contents lists available at ScienceDirect
Waste Management
journal homepage: www.elsevier.com/locate/wasman
Sustainable mechanical biological treatment of solid waste in urbanized
areas with low recycling rates
Ettore Trulli a, Navarro Ferronato b, Vincenzo Torretta b,⇑, Massimiliano Piscitelli a, Salvatore Masi a,
Ignazio Mancini a
a
b
School of Engineering, University of Basilicata, Viale dell’Ateneo Lucano, 10, I-85100 Potenza, Italy
Department of Theoretical and Applied Sciences, University of Insubria, Via G.B. Vico 46, I-21100 Varese, Italy
a r t i c l e
i n f o
Article history:
Received 30 May 2017
Revised 21 September 2017
Accepted 16 October 2017
Available online xxxx
Keywords:
Low recycling rates
Mechanical biological treatment
Municipal solid waste management
Respirometric analysis
Sanitary landfill
a b s t r a c t
Landfill is still the main technological facility used to treat and dispose municipal solid waste (MSW)
worldwide. In developing countries, final dumping is applied without environmental monitoring and soil
protection since solid waste is mostly sent to open dump sites while, in Europe, landfilling is considered
as the last option since reverse logistic approaches or energy recovery are generally encouraged.
However, many regions within the European Union continue to dispose of MSW to landfill, since modern
facilities have not been introduced owing to unreliable regulations or financial sustainability. In this
paper, final disposal activities and pre-treatment operations in an area in southern Italy are discussed,
where final disposal is still the main option for treating MSW and the recycling rate is still low.
Mechanical biological treatment (MBT) facilities are examined in order to evaluate the organic stabilization practices applied for MSW and the efficiencies in refuse derived fuel production, organic waste stabilization and mass reduction. Implementing MBT before landfilling the environmental impact and waste
mass are reduced, up to 30%, since organic fractions are stabilized resulting an oxygen uptake rate less
than 1600 mgO2 h 1 kgVS1, and inorganic materials are exploited. Based on experimental data, this work
examines MBT application in contexts where recycling and recovery activities have not been fully developed. The evidence of this study led to state that the introduction of MBT facilities is recommended for
developing regions with high putrescible waste production in order to decrease environmental pollution
and enhance human healthy.
Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction
Sanitary landfill is still the main option for treating municipal
solid waste (MSW) worldwide, especially in areas with poor recycling facilities and without reverse logistic policies (Wilson et al.,
2012; Menikpura et al., 2013; Rada et al., 2015; Schneider et al.,
2017; Ferronato et al., 2017). The developing areas, where final disposal is the main solution to solid waste management (SWM)
issues (Bezama et al., 2007; Trois and Simelane, 2010), commonly
have been worsened by the constant increase in population
growth, heavy economic development and high movement of the
population from rural areas into industrial centers (Münnich
et al., 2006; Vaccari et al., 2012; Ragazzi et al., 2014).
Despite regulations and trend changes, also in developed countries landfilling is still one of the most common practices adopted
to reduce the impacts of solid waste. However, environmental
⇑ Corresponding author.
E-mail address: vincenzo.torretta@uninsubria.it (V. Torretta).
pollution is not avoided when high amounts of putrescible waste
are introduced within the disposal site with low technical and
management precautions. Indeed, organic waste is the fraction
that most affects the generation of leachate and landfill gas, involving highly technical issues that need to be solved (Torretta et al.,
2016). Landfill emissions can be successfully handled only by technical plans that are introduced before the development of the disposal site, given that improving the dumping site after waste
storage is an expensive practice, which is also hard to apply in
developed countries as detailed data of waste composition and
underground characteristics are usually limited (Weng et al.,
2015). As a result, in developing countries, where open dumps
are still the main practice to ‘treat’ MSW (Münnich et al., 2006;
Nithikul et al., 2011; Ferronato et al., 2017), environmental and
health issues are common, since no precautions have been introduced and no reliable solutions have been adopted (De Feo et al.,
2014).
Mechanical biological treatments (MBT) can be implemented as
simple practices which can immediately and significantly reduce
https://doi.org/10.1016/j.wasman.2017.10.018
0956-053X/Ó 2017 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Trulli, E., et al. Sustainable mechanical biological treatment of solid waste in urbanized areas with low recycling rates.
Waste Management (2017), https://doi.org/10.1016/j.wasman.2017.10.018
2
E. Trulli et al. / Waste Management xxx (2017) xxx–xxx
the environmental impacts around final disposal sites, since MBT
plants treat unsorted solid waste designated for final disposal
(Bezama et al., 2007; Bayard et al., 2010; Nithikul et al., 2011).
MBT can increase the useful life of the disposal site, reduce the
amount of waste inflow and prevent organic fraction degradation
which is treated before landfilling using biological technologies
(Sánchez et al., 2015). MBT is able to reduce the environmental
impacts due to leachate and landfill gas emissions reducing the
biodegradable organic content of waste: decrease of leachate
chemical oxygen demand (COD) concentrations can be obtained
up to yields of 98%, from 30,000 mg L 1 to 1000 mg L 1, so providing an important solution for reducing the dimension of the leachate treatment plants (Münnich et al., 2006). Furthermore,
implementing MBT processes within MSW management systems
the operating life of the landfill can be optimized and extended
for over 15 years (Robinson et al., 2005; Lornage et al. 2007; de
Araújo Morais et al., 2008; Van Praagh et al., 2009; Tintner et al.,
2010; Heyer et al., 2013; Rada et al., 2014; Trulli and Torretta,
2015).
Thus the application of treatment and sorting plants, before
introducing the waste into the dump sites, is encouraged in areas
where separate collection is not fully applied, for improving environmental sustainability. For instance, the landfill gas and leachate
composition and formation depend on pre-treatment methodologies (Bockreis and Steinberg, 2005) and are considerably reduced
by any MBT (Pan and Voulvoulis, 2007; De Gioannis et al., 2009).
As a result, the significant generation of landfill emissions, among
others, can motivate the implementation of an MBT step at the
final disposal site (Trois and Simelane, 2010).
A large potential to optimize environmental performance may
change the perception of MSW as an ‘energy resource’, thus
increasing the automatization of selection processes and prioritizing biogas-electricity production from MSW organic fraction
(Soyez and Plickert, 2002; Cimpan and Wenzel, 2013; Scaglia
et al., 2013). Even if maximizing energy and material recovery is
not achieved by MBT, it is certainly aimed to a safe disposal.
Alongside incineration and other thermal processes, MBT is an
important management option both in Europe and in developing
countries (Rada et al., 2005; Pan and Voulvoulis, 2007; Baptista
et al., 2011; Di Lonardo et al., 2016; Ranieri et al., 2017). In the Italian case, for instance, MBT has been widely applied as reliable solution for reducing the production of leachate and landfill gas,
especially in final disposal sites without environmental monitoring
and effective leachate treatment plants.
Italy adopted the European Union sanitary landfill regulation
which specifies that solid waste final disposal is only allowed after
a ‘‘pre-treatment” in all cases where limits, fixed by the regulation
and concerning solid waste composition, are not respected. This
regulation matches the principle that final disposal must be sustainable for the environment and human health within the whole
‘‘life cycle”, reducing hazardous waste, pollutant releases and
improving the useful life of the landfill. MBT efficiency is measured
mostly by biological stability tests by means of the oxygen uptake
rate (OUR) (Adani et al., 2006; Bayard et al., 2010; Cesaro et al.,
2016).
This article shows and describes the advantages of the use of an
MBT within regions where recycling systems are inadequate. Biological indexes and waste composition are evaluated while energetic and economic considerations are presented. An
experimental activity was developed at a landfill site in Italy,
which surpassed the recycling rate of 50% although suffered an
unreliable separate collection system in many cities. Data on the
MBT full scale plant have been reported and discussion is related
to several issues of SWM observed in a region where a low recycling rate equal to 25.9% is achieved. Such situation is typical of
developing regions, so the study can be of interest both for decision
makers of low-income regions and stakeholders in high-income
countries.
2. Materials and methods
The survey was implemented at the Giovinazzo (Bari, Southern
Italy) landfill site. The methodology applied for the analysis is
divided in two main parts:
– waste characterization to provide data on waste composition
and about the chemical, physical and biological features of the
inflow waste;
– the analysis of the waste treated by the mechanical-biological
section.
The first analysis was aimed to evaluate the average waste composition generated within the area and inflowing the MBT plant.
The second analysis concerned the respirometric test of the waste
material treated by MBT. Data on the OUR and dynamic respiration
index (DRI) (Adani et al., 2006; UNI/TS, 2006) of the samples after
treatment and the time required for a significant degradation of
the waste were evaluated.
In order to estimate the yields of the examined plant, additional
analysis were carried out such as:
– the waste amounts in the upper sieving system after treatment;
– the weight loss after biological treatment.
Activities have been performed for a period of one year and
were used to collect bio-waste stabilization data, waste inflow
quantities, and the economic and management factors that influenced MBT. Fig. 1 shows the equipment used for the MBT treatment at laboratory/pilot scale.
2.1. The landfill site and the MBT at the full scale plant
The Giovinazzo sanitary landfill serves nine communities for a
total population of 500,000 inhabitants, and is able to treat 320
tons of MSW per day. The landfill was built in 1989 within an
old mine and was initially organized into six operative zones, while
the MBT plant was built in 2003 and has been in operation since
2004. The waterproof under-layer originally consisted of a 1 m clay
layer covered by a 2 mm thick plastic film of HDPE. A biogas collection system consisting of 21 wells and 5 regulation substations was
introduced only in 1995.
In 1996 the landfill gas collected, which is constantly used for
electric energy generation, was composed of 50% methane (while
the other 50% was made of carbon dioxide and non-methane
organic compound), and achieved 1000 Nm3 per hour, whereas in
2007 this decreased to 200 Nm3 per hour due to the anaerobic
activity which stabilized the organic fraction during the years,
according to another study (Torretta et al., 2016).
The mechanical-biological treatment performed before landfilling of selected waste. The process included a unit of bag disruption,
waste selection by sieving and biological treatment of the under
sieve fraction. Afterwards, a second sieving system was considered
by the designers in order to separate the stabilized material for
exploiting the inorganic fraction remaining within the putrescible
matter for energy recovery, since the upper sieve waste can be
used as the refuse derived fuel (RDF). However, this application
is not yet introduced due to the lack of facilities able to exploit
RDF. Indeed, currently, due to the lack of a specific recovery plant,
all of the MSW upper sieving is sent to the landfill (Fig. 2).
The biological treatment is applied by static piles, constructed
with a maximum height of three meters. Within the plant, eight
Please cite this article in press as: Trulli, E., et al. Sustainable mechanical biological treatment of solid waste in urbanized areas with low recycling rates.
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E. Trulli et al. / Waste Management xxx (2017) xxx–xxx
length of the cell
(a)
(b)
(c)
(d)
exhaust air
temperature and oxigen probe
reactor
condensed
water box
air
flow
meter
Pump
leachate drain pipe
(f)
(e)
Fig. 1. Methods for waste mechanical treatment: (a) 20 mm flat sieving screen for manual selection; (b) scheme for sampling of waste in biocell; (c, d) 80 mm drum screen in
‘‘pilot scale”; (e, f) 25 L respirometry.
Please cite this article in press as: Trulli, E., et al. Sustainable mechanical biological treatment of solid waste in urbanized areas with low recycling rates.
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E. Trulli et al. / Waste Management xxx (2017) xxx–xxx
Fig. 2. MBT process and material flow analysis of the MSW in the case study considered.
aerated bio-cells, which are provided by an aeration system that
works through fans with 13.3 kW powered inverters, operate constantly. The volume consists of 4140 m3 (about 500 m3 per biocell) and enables the organic waste to remain within the cells for
28 days in ordinary conditions. Operative conditions are controlled
by measuring the principal parameters:
air flow emitted within the cells, which is about 6000 m3 per
hour (regulated automatically as a function of the temperature
measured within the waste which should not exceed 60 °C);
water content within the mass (monitored and balanced automatically by an internal sprinkler in order to maintain the moisture required for the aerobic process).
laboratory to investigate chemical, physical and biological characteristics. Fig. 3 shows the examined waste.
This procedure was replicated four times in two different
municipalities, three in urbanized areas while the other in the
industrial one. The chemical analysis was applied for only one
sample. The seasonal variation of the waste composition has not
been considered within the study due to the lack of numerous data.
The confidence level (CL) considered for generalising the data
obtained about the composition of the waste was 95%. The sample
of manually mixed raw waste was analysed. Table 1 reports the
average percentages of the waste fractions of the samples and
the confidence interval obtained for each fraction.
2.3. Analysis of the waste
2.2. Characterization of the raw waste
A primary sample of waste, with a mass of one ton, was collected by a collection truck from the street containers around the
study area. To make sure that the sample represents correctly
the waste in the zone of investigation, a specific collection route
was defined on the basis of: urban morphology, housing typology
and presence of industry production plants. The days considered
were in the midweek in order to generalise the results obtained
as example of ordinary condition. Moreover, It was considered a
day with stable weather settings during the spring season, in order
to have stable content of moisture and temperature during the
analysis. The primary sample was reduced in two sub-samples
(200 kg and 15 kg) by manual splitting (quartering methods) to
correctly represent the waste originally gathered. The first subsample (200 kg) was manually sorted to estimate waste composition,
while the second subsample (15 kg) was shipped to the analytical
2.3.1. Chemical and physical composition of the waste
A sample, which contained similar material fractions, was analysed by a chemical, physical and biological investigation in order to
study the waste composition. The data obtained showed high significance comparing the features of samples after treatment and
evaluating the yields of the treatment plant. A 15 kg sample was
transported to a laboratory and prepared for the chemical analysis.
In particular, moisture, percentage of volatile solid (VS), DRI, pH
and ash content were surveyed. At the same time, lower and upper
calorific values, carbon and nitrate content as well as other principal elements were examined at laboratory scale. The obtained
results are reported in Table 2.
The information obtained, in particular regarding the initial DRI,
have been considered for comparison with the main result found
after the respirometric analysis of the waste subsequently biological treatment. Moreover, in order to verify the adaptability of
Please cite this article in press as: Trulli, E., et al. Sustainable mechanical biological treatment of solid waste in urbanized areas with low recycling rates.
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E. Trulli et al. / Waste Management xxx (2017) xxx–xxx
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Fig. 3. Sampling of the waste fraction. (a) raw sample (1 ton); (b) pre-treated waste (about 0.8 tons); (c, d) waste sampling by quartering method.
Table 1
Waste fraction of the material treated.
Waste fraction
Value (%)
Confidence interval at 95%
Putrescible
Paper and cardboard
Plastic
Textile, rubber, wood and leather
Metal
Glass
WEEE
Batteries and drugs
Under sieve (<20 mm)
23.4
21.7
12.1
7.0
3.5
9.6
0.4
0.2
22.0
7.9
2.4
2.2
3.1
1.5
2.8
0.7
0.1
2.9
Table 2
Chemical, physical analysis of the waste inflow into the plant.
Parameter
Unit of measure
Value
Moisture
Dry matter
Volatile solid
Ash
Cl
S
C
H
N
O
C/N
Calorific power (lower/upper)
Raw waste
Suspended solid
%
%
%
%
%
%
%
%
%
%
49.28
50.72
81.77
18.23
0.31
0.08
13.6
5.3
0.66
65
20.6
s.s. = suspended solid; d.w. = dry weight.
fresh waste
fresh waste
s.s.
d.w.
d.w.
d.w.
d.w.
d.w.
d.w.
d.w.
kcal kg
kcal kg
1
1
2666/2803
5238/5507
the material for composting process, the C/N rate was evaluated,
resulting equal to 20.6. In conclusion, the data collected allows
identifying the waste inflow into the MBT as a good material for
the biological treatment.
2.3.2. The respirometric test
The respirometric test took place in a laboratory reactor; a
respirometric equipment produced by Costech International,
3022 model, with a volume equal to 25 L, was used. Twelve analyses were carried out, about one per month, on twelve 10 kg samples collected into the bio-cells. In particular, each analysis was
composed of 16 samples (4 samples from 4 sections) which were
collected from each bio-cell conforming to a pre-defined system.
After pooling and mixing of samples, a large sample was created
and then, by quartering method, the subsample of about 10 kg
was transported to the analytical laboratory. Before testing, density
and moisture of the samples were standardised at values respectively lower than 0.75 kg L 1 and 75% maximum water capacity.
Samples were analysed according to the UNI/TS 11184 methodology (UNI/TS, 2006). The samples were carried out four days long.
Temperature and oxygen concentration in the air inflow and outflow were automatically measured. Mass of hourly consumed oxygen was obtained by data elaboration.
2.3.3. Additional analysis during and after the MBT
Before the respirometric test, another survey was carried out for
estimating the bio-stabilization time required and the efficiency of
this methodology. In particular, a single sample was studied after
7 days treatment and after 28 days handling for studying the yield
of the aerated treatment applied during the time. The analysis of
Please cite this article in press as: Trulli, E., et al. Sustainable mechanical biological treatment of solid waste in urbanized areas with low recycling rates.
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E. Trulli et al. / Waste Management xxx (2017) xxx–xxx
the waste treated was carried out at two different moments of the
biological process: after 7 days and at the final management step,
after 28 days. The samples were gathered from the same cell and
during the same treatment, in order to evaluate the properties of
the waste with the same composition. The moisture, the total volatile and non-volatile solids, DRI and pH were analysed on a 15 kg
sample of waste taken from the cell after 7 days and 28 days of
treatment. The analysis of the total solid and the content of moisture of the sample was performed in an oven at a temperature of
108 °C, and by combustion at 605 °C to estimate the volatile solid.
Secondly, one sample of unsorted waste, after biological treatment, was sieved and the fractions remained in the upper and
under 80 mm sieve were analysed. This research was introduced
in the study in order to quantify the waste fraction available and
so evaluating the feasibility for exploiting the waste as RDF. Finally,
the mass loss after the biological treatment was quantified by measuring of the weight of the MSW sixty times over the year. The
mixed waste introduced in all the bio-cells was weighted before
and after each treatment rounds after 28 days.
3. Results
Before evaluating the DRI after treatment, a single stream process was first analysed in order to evaluate the progress obtainable
during the biological treatment of the studied plant. A value of DRI
equal to 4675 mgO2 kgVS1 h 1 was obtained. The results of both
analysis, after 7 days and after 28 days are reported in Table 3.
The operation applied by the MBT plant can be considered
efficient since already after 7 days the oxygen uptake resulted
Table 3
Characteristic of the waste tested by respirometric analysis.
Parameters
Moisture
Total solids
Volatile solids
Ash
DRI
pH
Unit of measure
% raw waste
% raw waste
% s.s.
% s.s.
mgO2 kgVS1 h
—
1
Treatment time (days)
7 days
28 days
29.71
70.29
57.5
42.5
2339
7.16
41.95
58.05
55.87
44.13
829
7.9
significantly lower than the starting point whereas the sample
resulted well stabilized after 28 days.
According to a study reported in literature (Gea et al., 2004), the
organic fraction of an MSW can be considered stabilized when the
respirometric values are around 1100 mgO2 kgVS1 h 1 while a fresh
sample exceeds 4000 mgO2 kgVS1 h 1. After the preliminary analysis, the respirometric analysis was repeated only after 28 days of
treatment, so to evaluate the MSW stabilization rate obtained treated by biological processing in different period of the year. The
trends of the twelve samples are reported in Fig. 4, expressed in
mgO2 kgVS1 h 1.
The results obtained of the DRI after four days range between
900 and 1600 mgO2 kgVS1 h 1; such values identify a partially stabilized matter which is the result forecasted for a two-stream MBT
plant, where the bio-stabilization process considerably reduces
the DRI of the under sieve, mostly made up of putrescible fractions.
To better illustrate the stability of the waste obtained after 28 days
of biological treatment, the parameter DRI is reported in Fig. 5.
The data shows the mean values obtained during the first 24 h
of analysis as a function of the volatile solid of each sample. Limits
of a stabilized waste are reported according with Adani et al.
(2006). The dashed line divides the stabilized matter and the fractions which are still biologically active. These samples obtained a
DRI which varied between 900 and 2200 mgO2 kgVS1 h 1 which
means a stabilized and a not well-stabilized fraction after 24 h,
respectively. However, the trend is interesting since, after the process, in two cases the low-biodegradable matter obtained was fully
stabilized in the first 24 h of analysis. As a result, the respirometric
test confirmed the importance and the functionality of the MBT
plant concerning the stabilization of the high putrescible fraction
obtained by the sieving system although not every sample can be
considered satisfactory.
Mechanical biological pre-treatment reduces also the volume
and the mass occupied by the waste. For estimating the weight lost
during the treatment, 60 bio-cells were analysed over one year. In
particular, waste was weighted before and after the treatment in
each bio-cell in different periods of the year. The observed results
showed an average weight loss of 30% (Fig. 6).
The conservation of the mass is of great interest as the waste
inflow into the landfill, losing moisture and volatile solids,
decreases in weight, as demonstrated by the conducted study. As
Fig. 4. OUR of the MBT stabilized waste.
Please cite this article in press as: Trulli, E., et al. Sustainable mechanical biological treatment of solid waste in urbanized areas with low recycling rates.
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7
Fig. 5. Average waste oxygen uptake per hour within the first 24 h of analysis as a function of the volatile solid of sample.
Fig. 6. Weight loss during the examined biological treatment.
a result, this guarantees a higher waste density, which within the
site studied and after compaction achieved 1.2–1.3 tons per m3.
Finally, in order to quantify and study the exploitability of the
large fractions produced after a single stream biological pretreatment, the 80 mm sieving process after biological treatment
was applied to quantify the fractions detectable into the material
treated. The largest residues are mainly composed of cardboard,
paper and plastic, which can be separated after the stabilization
of the organic substance (Table 4). As a result, 52.5% of the waste
treated by aerated process (the upper sieve) could be separated
and used as RDF, since it is rich of combustible materials (69.9%
Table 4
Stabilized waste composition after the 80 sieving process.
Waste fraction
Upper sieve [%]
Under sieve [%]
Total percentage obtained
Paper and cardboard
Plastic
Textile, wood and rubber
Metals
Glass and inert
Small fractions (<20 mm)
52.5
47.9
22
14.4
7.1
2.3
6.4
47.5
17.1
6.1
3.1
2.3
10.5
60.9
is plastic and paper), while the rest can be sent to landfill as cover
material.
4. Discussion
Stabilized undersieve waste values measured by respirometric
tests, expressed as a function of the mass of volatile solids of the
examined sample, can vary quite considerably. This is probably
also due to the type of waste feeding and the partly low efficiency
of aeration facilities, which also influence the development of the
biological yield. In order to graphically represent the different
states of waste during the stabilization process and treatment,
the oxygen uptake rate as a function of the VS content was used
(Piscitelli, 2008). Fig. 7 shows a representation of the oxygen
uptake rate and a stability area of MSW.
The MBT plant was an affordable solution adopted to decrease
the MSW inflow to the landfill and thus for reducing the risk of
environmental pollution because, in 2003, there was a low number
of sanitary landfills in order to guarantee a good sanitary service to
the population.
Thus, producing RDF for energy in such a plant within the
framework of a ‘‘circular economy” started in Italy over the last
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Fig. 7. Oxygen uptake rate and ‘‘stability area” of MSW for disposal by landfilling.
few decades, has helped local municipalities to increase the lifespan of landfills and to decrease leachate and methane releases.
Moreover, as stated by Mancini et al. (2009), the DRI of waste
within a 15-years-old landfill in ordinary conditions can be 1108
mgO2 kgVS1 h 1, higher than the technical value of DRI of the MBT
treated waste, which is assumed in this research about 900
mgO2 kgVS1 h 1. This confirms the importance of the MBT in terms
of the stabilization of the organic matter in a single stream treatment plant, which leads to a reduction in biogas production.
Observed data on biogas production was respectively 4.5 m3 t 1
with 98 mgO2 kgVS1 h 1 and 57 m3 t 1 with 1108 mgO2 kgVS1 h 1
(Piscitelli, 2008; Mancini et al., 2009). The loss of 30% in mass of
the waste treated is a good result to save landfill spaces. Similar
results were observed by several authors (Tolvanen and
Hänninen, 2006; Bezama et al., 2007; de Araújo Morais et al.,
2008). Moreover, the MBT plant reduces the waste inflow into
the landfill, facilitating the MSW dumping phase, where there
was a high variability of waste characteristics, including density
and water content which influenced the OUR (Trulli et al., 2007;
Piscitelli, 2008).
In order to develop a more efficient treatment, a post trituration
process could be implemented at the MBT plant, in order to
decrease the additional waste volumes entering the landfill. In
addition, a manual or mechanical removal before the first sieving
process could help remove exploitable materials such as glass,
which decrease the calorific power and increase the recycling rate,
or other exploitable materials. The same practice can be applied
after the second sieving system because, as reported by other
authors, heavy inert reject output from the MBT plant may represent a missed opportunity for the operators who landfill these
materials (Cook et al., 2015).
Many researches reported in literature showed optimal application of MBT, in particular when evidenced high performance of
sorting separation, screening and bio-drying, combined treatment
of putrescible matter as sewage sludge, recycling to reduce environmental impacts and optimize the landfilling (Tolvanen and
Hänninen, 2006; Bezama et al., 2007; Bayard et al., 2010; Trois
and Simelane, 2010; Tintner et al., 2010; Montejo et al., 2013;
Dias et al., 2015; Pantini et al., 2015).
A pre-treatment process, however, affects the cost of the final
disposal of the MSW. The costs estimated within the MBT plant
of Giovinazzo amounts to 30–35 € t 1, while the energy required
for the process is about 45 kWh t 1 for an aerobic treatment of
28 days. This energy consumption can be compared with other
studies, since the average electricity required for the manual and
mechanical operations has been estimated to be about 20–25 kW
h t 1 for a MBT with manual pre-selection and post-composting
(Montejo et al., 2013) or about 30–35 kWh t 1 for short time
MBT (2–4 weeks) and about 50–60 kWh t 1 for long term MBT
(more than 4 weeks) with mechanical pre-sorting (Scaglia et al.,
2013), whereas, a composting process of organic waste from selective collection in aerated and rotating trommels can be considered
of about 53 kWh t 1 (Boldrin et al., 2011). However, the economic
effort can be reduced by the exploitability of the RDF produced and
by the improvement in landfill sustainability concerning leachate
treatment and landfill lifespan. Hence, these costs are also acceptable for countries where landfill construction does not meet
requirements for extensive environmental protection (Münnich
et al., 2006), since investments and operational costs to set up
MBT before landfills could be valued for low-income countries as
8-12 USD t 1 (Trois and Simelane, 2010).
Over the last years, the regional recycling rate in Apulia has
improved considerably, achieving 25.9% (ISPRA, 2015). However,
the program recently introduced by the regional administration
planned to exceed 60% by 2015, thus the reduction of energy and
costs required for MSW final disposal. Hence, MBT was used as a
suitable technology in order to solve an environmental emergency
due to MSW mismanagement (Trulli et al., 2007). In this framework, other public policies concerning material recovery and recycling are necessary and more efforts should be introduced because
the regional goals, in terms of waste recovery, were not achieved.
5. Conclusions
The general targets for the sustainable final disposal of waste
are a generally low environmental impact, low gas emissions,
and a small amount of leachate. These objectives are achievable
by reducing the waste inflow to landfill, applying suitable landfill
construction technologies, recycling exploitable materials and
implementing MBT before final disposal sites.
The analysis shown in this paper has focused on applying MBT
before landfilling in an Italian region with low recycling rates and
where SWM does not provide enough precaution to avoid environmental contaminations. Two analysis were shown: the first for
evaluating the waste inflow into the landfill, and thus into the
MBT plant, while the second regards the waste outflow of the
MBT plant.
The results obtained are significant since the biological treatment reduced the mass of the waste by 30%, resulting in the saving
of landfill space, whereas the DRI values provided information
about a good operation which is able to decrease the OUR up to
900 mgO2 kgVS1 h 1. In addition, waste fraction after treatment
are suited for producing RDF, encouraging the introduction of
waste-to-energy systems.
This case study provides an example of the suitability of this
technology for the treatment of MSW inflow to landfills in order
to decrease environmental pollution and increase the useful life
of final disposal sites when recycling rates are low. Considering
DRI and the mass lost during the process, MBT could also be considered as an appropriate technology for low recycling areas where
take back policies are needed in order to introduce a reverse logistic system. Furthermore, the study provided an indication for the
sustainable development of projects concerning the introduction
of MBT. The improvement of pre-treatment plants is recommended
in regions with unreliable selective collection systems, both in
high-income and low-income countries. The costs and the energy
required are affordable, as environmental and economic benefits
are much higher than the initial investment required.
Globally MBT plants is a reliable solution for waste pretreatment and also represent a good solution for areas in an emergency situation in terms of MSW management as at Giovinazzo
plant. In conclusion, MBT is a first good option for treating MSW,
although integrated efforts are required in order to reduce the
Please cite this article in press as: Trulli, E., et al. Sustainable mechanical biological treatment of solid waste in urbanized areas with low recycling rates.
Waste Management (2017), https://doi.org/10.1016/j.wasman.2017.10.018
E. Trulli et al. / Waste Management xxx (2017) xxx–xxx
environmental impacts and guarantee a sustainable development
following the principle of the circular economy.
Acknowledgment
We would like to thank and say goodbye to Prof. Ettore Trulli,
first author of this paper, who constantly worked in this study
and follows all the steps for producing reliable results and, finally,
this paper. He left us during the month of August. All our best to his
family.
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