Environmental Assessment of A Landfill Leachate Treatment Plant - Impacts and Research For More Sustainable Chemical Alternatives
Environmental Assessment of A Landfill Leachate Treatment Plant - Impacts and Research For More Sustainable Chemical Alternatives
Environmental Assessment of A Landfill Leachate Treatment Plant - Impacts and Research For More Sustainable Chemical Alternatives
a r t i c l e i n f o a b s t r a c t
Article history: The aim of this study is to evaluate, from an environmental point of view, the performance of various
Received 29 September 2017 technologies applied to the treatment of municipal landfill leachate. The study has been led in an Italian
Received in revised form wastewater treatment plant and it applies the principles of the Life Cycle Assessment (LCA) technique,
18 February 2018
using ReCiPe as the assessment method. This study shows how the operating stage of a wastewater
Accepted 20 February 2018
treatment plant, that applies chemical and physical treatments, can affect the following four environ-
Available online 21 February 2018
mental impact categories: “Freshwater Eutrophication”, “Freshwater Ecotoxicity”, “Marine Ecotoxicity”
and “Human Toxicity”. Within this operating stage, the study shows the relevant environmental impacts
Keywords:
Life Cycle Assessment
generated by the use of polyaluminum chloride (PAC) as a coagulant chemical agent and sodium hy-
Municipal landfill leachate droxide (caustic soda) as a pH control chemical agent. In order to investigate these results, and to
Polyaluminum chloride discover more eco-friendly alternatives, two LCA comparisons have been carried out, comparing
Ferric chloride respectively the above two agents to analogous and common substitutes: ferric chloride as a coagulant
Sodium hydroxide agent and calcium hydroxide (lime) as a pH control agent. These comparisons demonstrate the higher
Calcium hydroxide environmental impacts of the use of ferric chloride over PAC and of sodium hydroxide over calcium
hydroxide. Ferric chloride has shown to have more than double the environmental impact of PAC in 9
environmental categories out of the 10 considered, while calcium hydroxide has been able to cut down
the negative environmental impacts of the sodium hydroxide of more than 65% in all the environmental
categories. Considering the highly positive environmental results achieved from our study, whenever
possible, a substitution of calcium hydroxide to sodium hydroxide and of PAC to ferric chloride is strongly
recommended.
© 2018 Elsevier Ltd. All rights reserved.
https://doi.org/10.1016/j.jclepro.2018.02.219
0959-6526/© 2018 Elsevier Ltd. All rights reserved.
1022 L. Postacchini et al. / Journal of Cleaner Production 183 (2018) 1021e1033
ISO, 2006b). In the field of wastewater treatment (WWT), LCA has combination with hydrogen peroxide to a wastewater effluent from
been applied since the 1990s. In the pursuit of more environmen- a sewage treatment plant. The results highlighted that wastewater
tally sustainable WWT, Corominas et al. (2013a) stated that LCA is a reuse, after applying any of the tertiary treatments considered,
valuable tool to elucidate the broader environmental impacts of appeared as the best choice from an ecotoxicity perspective.
design and operation decisions. Hospido et al. (2010) used LCA to evaluate the reuse of anaer-
This paper has been organized as follows: after this introduc- obically digested sewage sludge in agricultural land, focusing on
tion, section 2 presents a review of the analyzed literature con- the possible impacts caused by emerging micropollutants. They
cerning LCA and WWTs; section 3 describes the research objectives also analyzed the influence of different operational conditions
and approach; section 4 explains in details the LCA used for this applied during the anaerobic digestion process on the digested
study; section 5 shows the outcomes of the LCA; section 6 reports a sludge quality. They showed that, from an environmental point of
discussion regarding the outcomes, together with the final con- view, the disposal of undigested sludge is the less suitable alter-
siderations of the study. native. Only the results on GWP contradict this fact, due to the
dominance of the indirect emissions associated with the electricity
used by the digesters. The digestion of sewage sludge before
2. Literature review application to agricultural soil is a meaningful activity, not only
because it is a requirement, according to the actual legislation, but
Life Cycle Assessment has been applied to water treatment also because it reduces the environmental impact associated with
systems (water treatment plants, sewer systems, and waste water the pollutants present in the sludge. Corominas et al. (2013b)
treatment plants) since this technique began to develop. Emmerson presented a methodology to evaluate the environmental impacts
et al. (1995) were the first to publish a study about the environ- of enhanced process performance strategies, applied to wastewater
mental impact of small-scale sewage treatment works, using LCA. nutrient removal systems. They used LCA to assess three different
In their analysis of three sewage-treatment works (with different scenarios depending on the limitation of nitrogen (N), phosphorus
process options), they identified and quantified material use, en- (P), or both when evaluating the nutrient enrichment impact in
ergy use and environmental releases during construction, opera- water bodies. According to them, decision-making in controlling
tion and demolition stage of the WWTPs. wastewater nutrient removal systems can be assessed using a
Most of the LCA studies in WWT have been aimed to compare combination of mechanistic process models together with Life
the different wastewater treatment methods and their different Cycle Impact Assessment (LCIA) models. They found out that the
performance characteristics. Vlasopoulos et al. (2006) described use of site-specific conditions, for the nutrient enrichment impact
the implementation of LCA, to investigate the environmental category, is essential to define best environmental performance
impact of 20 technologies suitable for treating wastewater pro- strategies.
duced during the oil and gas extraction processes. Their results Recently, LCA has been adopted to compare WWTP control
were then incorporated into a decision support system which strategies and management scenarios or the effectiveness and
allowed identification and prioritization technology combinations, applicability of a particular WWT in a specific location. Meneses
capable of producing water for different designated industrial and et al. (2015) showed the potential additional insight that results
agricultural end uses. In 2011, a study of Rodriguez-Garcia et al. from adding indicators based on LCA to the evaluation criteria of
(2011) evaluated the performance of 24 WWTPs using a stream- plant performance, in the control strategies of wastewater treat-
lined LCA, with eutrophication potential (EP) and global warming ment plants. The authors combined plant-performance evaluation
potential (GWP) as environmental indicators and operational costs criteria, as effluent quality and operational cost, jointly with a
as economic indicators. They found out that, for organic matter detailed environmental evaluation for impact category provided by
removal, WWTPs were less costly, both in environmental and LCA. In their comparison of the different control strategies, they
economic terms, if the volume was used as the functional unit. On highlighted the importance of the environmental analysis as an
the other hand, more demanding typologies, such as reuse plants, additional source of information for decision makers. A more recent
showed a trade-off between lower EP and higher cost and GWP. study of Lutterbeck et al. (2017) used LCA to investigate the effec-
However, this was overcome if a second functional unit (based on tiveness, applicability, and environmental sustainability of a
EP reduction) was used instead, proving the sustainability of these wastewater treatment system located on a rural property. They
options and that this functional unit better reflected the objectives studied an integrated treatment system, consisting of anaerobic
of a WWTP. In 2016, Postacchini et al. (2016) used LCA to conduct a reactors and constructed wetlands, in a rural area in Brazil. Their
comparative assessment of the environmental impacts of three study showed that the application of LCA can give valuable insights
different methods of treating primary clarifier effluent in a WWTP. for setting the best configurations for a WWT system in rural areas,
They compared two conventional treatment systems, which are by identifying the most critical parameters and by the evaluation of
activated sludge (AS) and trickling filter (TF) system, with a new actions to reduce the environmental impacts.
experimental one named, high rate anaerobic-aerobic digestion Some studies have discussed the limits and the discrepancies of
(HRAAD). Their results showed TF having the smallest environ- the various impact assessment methods applied to WWT field. This
mental impacts and AS the largest, while HRAAD set itself in be- is the case of Renou et al. (2008), who discussed how LCA could be
tween the two but with much reduced impacts compared to AS. applied to wastewater treatment projects, through a case study on a
LCA has also been used in WWT field to study the impact of full-scale plant, evaluating the influence of the selected impact
tertiary treatments, sludge treatment and disposal and nutrient assessment method on the LCA outcome. They compared five LCIA
removal. Mun ~ oz et al. (2009) assessed the life-cycle environmental
methods: CML 2000, Eco Indicator 99, EDIP 96, EPS and Ecopoints
impact of urban wastewater reuse for agricultural purposes, putting 97. They obtained consistent assessment between these methods
special emphasis on the potential toxicity of priority and emerging regarding greenhouse effect, resource depletion, eutrophication
pollutants, present in the effluents to be reused. The study was and acidification. They pointed out that work was needed
based on benchscale experiments, applying ozone and ozone in
L. Postacchini et al. / Journal of Cleaner Production 183 (2018) 1021e1033 1023
concerning human toxicity impact categories, as large discrep- leachate. Using a LCA-model-based software, they modelled four
ancies were noticed between the impact assessment methods. They scenarios and compared the strategies of leachate recirculation
also discussed the relative importance of the WWTP operation (with or without gas management), leachate evaporation and
phase with respect to construction and dismantlement. They found leachate discharge. They found out that direct discharge of leachate
out that construction of a WWTP appears to be the least polluting may result in ecotoxicity and human toxicity via water contami-
phase: construction greenhouse effect represents 11% of the oper- nated by heavy metals in leachate and that leachate recirculation
ating phase, toxicity and eutrophication 1%, acidification 6% and can be considered a cost-effective and environmentally viable so-
resource depletion 13%. They also stated that the end-of-life stage lution for arid regions, together with a proper landfill gas treat-
could be considered as negligible when compared to the operation ment. Finally, Turner et al. (2017) applied a combined mechanistic
phase, reporting also the fact that WWTPs are usually renovated on solute flow model and LCA approach to evaluate the potential im-
site and not fully dismantled. The findings of Renou et al. (2008) pacts of leachate leakage, over a 10 000 year time horizon, for four
confirmed a previous study of Tangsubkul et al. (2005) in which different landfill aftercare scenarios. Their study investigated the
the construction phase was found to be responsible for 25e35% of potential impacts caused by the loss of active environmental con-
the GWP (which is a relative measure of greenhouse gas emission) trol measures and deterioration of engineering systems, during the
associated with a WWTP and the operating phase of the facility was aftercare period of landfill management. The timing and duration of
found far more relevant for the rest of the categories. Analougus active control loss during aftercare was found to be potentially
results and observations, about construction and end-of-life stage, important in terms of the overall impact of landfilling. The authors
could be found in the studies of Emmerson et al. (1995), Zhang highlighted how the use of LCA could aid landfill operators, by
(2000) and Vlasopoulos et al. (2006). A more recent study of identifying opportunities to reduce the environmental impacts of
Teodosiu et al. (2016) discussed the validity and the limits of the their landfill sites.
LCA itself as impact assessment tool for the WWT field, demon-
strating its weak and strong points. They assessed the environ- 3. Research approach
mental impacts of a municipal wastewater treatment plant by using
three different impact assessment instruments: (1) LCA, (2) envi- Having established the importance of the LCA technique in
ronmental impact quantification (EIQ) and (3) grey water footprint WWT field and the environmental benefits of collection and
(GWF). They critically compared these three methodologies from a treatment of landfill leachate, this study contributes to fill a gap in
practical and applicability point of view and pointed out the ne- research, applying the LCA technique to assess the environmental
cessity for improving each method. According to them, widely used impact of a landfill leachate WWTP. It does so, by analyzing an
LCIA methodologies have to be improved to represent water- operative landfill leachate WWTP that uses chemical and physical
related impacts (including waterborne emissions) better and treatments to treat the leachate (specifically chemical oxidation/
could benefit from the other two impact assessment instruments to precipitation, coagulation, flocculation and adsorption technolo-
better represent local conditions. gies). This study aims at quantifying the environmental impacts of a
Although many LCA studies have been carried out in the WWT leachate treatment plant and at discovering which are the main
field, showing a great potential and effectiveness for this technique, factors that contribute the most to these environmental impacts.
the majority of them dealt with municipal wastewater or specific Furthermore, by locating the environmental “hot-spots” of this
industrial wastewater. There is a lack of research when it comes to WWTP, this paper aims at comparing alternative strategies, within
the application of LCA in landfill leachate treatment systems. the same treatment technologies, while treatment performances
Nevertheless, the importance of leachate collection and treatment, being equal (in terms of effluent quality). Therefore, in the second
in reducing the overall environmental impact from a conventional part of this study, LCA has been used to identify the best environ-
landfill, has been proved by a LCA study of Damgaard et al. (2011). mental chemical alternative, to reach analogous treatment results
They modelled different landfills, using a waste LCA model, ranging in a more sustainable way. The validity of these comparison out-
from a simple open dump to highly engineered conventional comes is not case specific, and it can be easily extended to the
landfills with energy recovery. In the case of leachate collection, general wastewater treatment field. This study has been focused
their results showed drastic improvements for most impact cate- exclusively on the operating phase of a WWTP. It has been decided
gories. For the dump landfill, the main impacts were impacts for not to include the construction and end-of-life phase of the WWTP,
spoiled groundwater due to lack of leachate collection, 2.3 popu- in accordance to the findings of Renou et al. (2008).
lation equivalent (PE) down to 0.4 PE when leachate is collected.
However, at the same time, leachate collection caused a slight in- 4. Materials and methods
crease in eco-toxicity and human toxicity via water. This was due to
the fact that, even if the leachate was treated, slight amounts of This study has been carried out using the Life Cycle Assessment
contaminants were released through emissions of treated waste- technique. The following sections have been structured according
water to surface waters. They concluded that the leachate collection to the ISO 14040 technical standards (ISO, 2006a,b). The method
system, though economically expensive, gave large environmental ReCiPe, in its midpoint hierarchist version, has been chosen and
benefits compared to a no collection system. It has also been proved used to assess the environmental impacts. The Life Cycle Assess-
that an accidental release of leachate to the groundwater might ment has been focused on the following environmental issues:
have several risks to human health and to the environment (Klinck climate change; acidification; eutrophication; toxicity; water
et al., 1999). According to Regadío et al. (2012), the potential depletion and fossil fuel depletion. These issues have been linked to
pollution caused by leachates is the result of several factors, 10 ReCiPe midpoints, out of the 18 available in the ReCiPe method,
including the release of ammonia, chlorinated and non-chlorinated as shown in Table 1.
organic compounds and heavy metal ions into the environment, all
of which are toxic to living organisms. 4.1. Goal and scope definition
In the last years, few studies have focused their attention on
landfill leachate treatment and LCA. Xing et al. (2013) investigated The primary goal of this research is to evaluate the environ-
the environmental impacts of leachate recirculation in landfill, in mental impact of a wastewater treatment plant in treating
an arid region where landfill produces a minimal amount of municipal landfill leachate. The first part of this study is focused on
1024 L. Postacchini et al. / Journal of Cleaner Production 183 (2018) 1021e1033
Table 1
Environmental issues and ReCiPe midpoints.
analyzing the different stages in which the leachate treatment 4.3. Description of the system and system boundaries
process can be divided. The second part of this study is focused on
comparing two chemical agent alternatives for the coagulant and The plant is located in the province of Fermo (Italy), and it can
the pH control agent. In this second section, the polyaluminum treat a maximum of 240 m3/day of municipal landfill leachate. It
chloride (PAC), used as the coagulant agent, has been compared to a applies chemical and physical treatment technologies in order to
similar coagulant agent, the ferric chloride (FeCl3), in dosage to produce a final effluent matching the majority (but not the whole
obtain the same COD removal (according to standard reference set) of the quality requirements, set in the European urban
literature and laboratory jar tests). Ferric chloride has been chosen wastewater directive (EEC, 1991) and the Italian legislation, con-
as the alternative coagulant to compare an aluminum-based cerning the discharge in sewage system (D.lgs 152/06). In order to
coagulant (the PAC) with an alternative iron-based coagulant. fully reach these discharge requirements, a further treatment stage
Indeed, commonly used metal coagulants in WWTPs fall into two in the local municipal WWTP (MWWTP) is applied, abling
general categories: those based on aluminum and those based on discharge into river water. The system boundaries of this study
iron. This is due to their effectiveness as coagulants and also to their include the raw leachate arrival at the WWTP and the discharge of
ready availability in forming multi-charged polynuclear complexes the treated effluent. No consideration has been given to upstream
in solution, with enhanced adsorption characteristics (Bratby, infrastructure (e.g. landfill, pumping stations) and consumables
2016). Moreover, in the past of the considered WWTP, ferric chlo- (e.g. oxygen for odour control). The system boundaries include
ride has already been used with no significant differences in first-order processes (e.g. direct atmospheric emissions, effluent
treatment results (in terms of effluent quality) to PAC use. discharges) and second-order processes (e.g. purchased electricity
Analogous comparison operation has been conducted between generation, chemicals manufacture) for the operating phase only.
sodium hydroxide (NaOH), used as a pH control chemical agent, Therefore, this study considers the environmental impact associ-
and calcium hydroxide (Ca(OH)2), in dosage to obtain the same pH ated with the operation of primary and secondary treatments, the
increment. Calcium hydroxide, also known as lime, has been cho- final discharge of the treated effluent as well as the sludge
sen as alternative pH agent because, according to Metcalf et al. treatment.
(2003), it is the most widely used chemical for pH adjustment in Fig. 1 shows the detailed process flow chart of the treatment
WWT. stage. After a first stage of “fine screening”, the raw leachate passes
to the next stage of “mixing and homogenizing”. Here, the leachate
is mixed in an open tank, in order to promote some oxidation re-
actions and it can be mixed with other different leachates (already
4.2. Functional unit
present into the system), in order to reach a homogeneous input
leachate. This tank is also where all the samples for raw leachate
In the first part of this study, the single cubic meter of raw
analysis of this study have been taken. Next, the leachate goes to
leachate (1 m3 in volume, approximately equivalent to 1 metric ton
the “coagulation” stage, where the coagulant chemical agent (pol-
in mass) has been chosen as the functional unit.
yaluminum chloride) and the pH control agent (sodium hydroxide)
In the second part of this study, two different functional units
are added. The coagulation process, indeed, lowers the pH of the
have been used, respectively for the coagulant and the pH agent
liquid solution, thwarting the correct precipitation of some heavy
comparison:
metals, so the pH value has to be constantly kept in a range of
7.6e7.9, by adding a liquid solution of sodium hydroxide. The next
✓ Coagulant comparison: as the functional unit, the specific
stage is the “flocculation into clarifiers”. Here, a cationic poly-
dosage of coagulant (recommended in literature and tested in
electrolyte solution is added, in order to promote flocks agglom-
the laboratory e jar tests) needed to obtain approximately a 50%
eration and makes particles settling down. The next stage for the
removal of COD in 1 L of leachate, has been chosen. The com-
clarified liquid is the “dynamic filtering”. The filter allows the
parison resulted as 3000 mg of Ferric Chloride (FeCl3) and
reduction in the concentration of suspended solids. The solids are
2100 mg of Polyaluminum Chloride (PAC).
separated from the filtering fabric present in the cylinder and
✓ pH agent comparison: as the functional unit, the specific
removed by the rotation of the same, and in turn, discharged into a
dosage of pH agent, calculated in a stoichiometric way, needed
collection tank. The next stage, “activated carbon”, is the adsorption
to obtain a 1 point pH increment into 1 m3 of water solution
stage using granular activated carbons (GAC). The filtered liquid is
(from pH ¼ 7 to pH ¼ 8) has been chosen. The comparison
pumped into a column containing GAC and leaves the column
resulted as 80 mg of dilute Sodium Hydroxide (NaOH, 50% in
through a discharge system. The last stage is the “ion-exchange",
H2O) and 37.05 mg of Calcium Hydroxide (Ca(OH)2).
L. Postacchini et al. / Journal of Cleaner Production 183 (2018) 1021e1033 1025
Table 2
Leachate analysis in input and output of the WWTP.
Chemical Parameter Unit Input Value Output Value Removal Efficiency Discharge Limits (sewage system)
using resins with a polystyrene structure and a functional group - the average value of the chemical parameter in input to the
ReSO3 (“ion-exchange resin”). The sludge, produced by the “floc- plant (raw leachate value);
culation into clarifiers” stage, is sent to a “sedimentation” stage. - the average value of the chemical parameter in output of the
Soon after being mixed and homogenized, it is ultimately sent to plant (effluent value);
the “centrifugation” stage, in order to be dewatered and being - the average percentage of treatment process efficiency;
disposed as “Primary sludge” in a landfill. - discharge limits reported by law, for discharging into the sewage
Table 2 shows the discharge requirements, for each specific system.
chemical parameter reported in the Italian wastewater legislation:
1026 L. Postacchini et al. / Journal of Cleaner Production 183 (2018) 1021e1033
All the data collected and presented in this study refer to a time Treated Leachate
period of three years of WWTP activity (July 2013eJuly 2016). The 1 metric ton
data have been collected monthly, and they have been referred to
Entry Amount Unit
the leachate quantity that has been treated in that relative month.
In the end, a mean over 36 sets of available data has been done, in Resources
Water 4.63E-02 m3
order to obtain average input values for 1 m3 of treated leachate
(output). Appendix A reports all the input data used in this study.
Materials/fuels
The software SimaPro 8.4 has been used for the LCA modeling, and Flocculant 1.02E-01 kg
all the LCI inputs have been taken from the Ecoinvent database pH control agent (Sodium Hydroxide) e NaOH 1.21Eþ00 kg
(version 3.3: Wernet et al., 2016). Any assumption made during this Coagulant (Polyaluminum Chloride) 2.18Eþ00 kg
phase, especially in the case of missing data, has been specifically Hydrochloric acid, 30% in H2O, at plant 3.83E-03 kg
Cationic resin, at plant 1.09E-02 kg
mentioned. The following sections explain how each stage/process Granular Activated Carbon 6.28E-03 kg
has been modelled.
Electricity/heat
Electricity, low voltage, at grid/IT 2.14Eþ00 kWh
4.4.1. Modelling the inputs
In the following section are reported all the inputs used in the
assessments.
- Electricity: “Electricity, low voltage {IT}” has been chosen as the - pH Agent (Calcium Hydroxide): “Lime, hydrated, loose weight”
general electricity input. Included in this input are the electricity has been chosen to model the calcium hydroxide;
production in Italy and from imports, the transmission network - Granular Activated Carbon: “Activated carbon, granular” has
as well as direct SF6-emissions to air. Electricity losses during been chosen to model the granular activated carbon.
low-voltage transmission and transformation from medium- - Ion-Exchange Resin: “Cationic resin” has been chosen as input
voltage are also accounted for. Electricity production according to model resin with a polystyrene structure and a functional
to related technology datasets (see Dones et al., 2007); group ReSO3;
- Water: “Water, well, in ground, IT” has been chosen as general - Hydrochloric acid: “Hydrochloric acid, without water, in 30%
water input. The plant uses well-water for its treatment activity solution state” has been chosen as input to model the hydro-
and this input represents the quantity of water extracted from chloric acid, used for the regeneration of the ion-exchange resin.
the ground. The energy consumption associated with its
pumping out of the ground is calculated and accounted into the Table 4 shows all the inputs that have been used in the treat-
input “Electricity” (so to include the electrical consumption of ment process, and they refer to 1 metric ton of treated leachate
the extraction pumps); (functional unit).
- Coagulant (Polyaluminum Chloride): since there are no LCI data
available for this chemical product, a specific entry has been
created (see Table 3). According to information provided by the
manufacturer, the PAC usually contains at least 18% of Al2O3 and
22% of ion Cl- (usually from HCl).
5. Results
- Coagulant (Ferric Chloride): “Iron (III) chloride, without water,
in 40% solution state” has been chosen to model the ferric
5.1. Life Cycle Assessment of treated leachate
chloride;
- Flocculant: since there are no LCI data available for the cationic
The first part of this study has regarded the environmental
polyelectrolytes solution, used as flocculant, according to Lopez
impact associated with the treatment process of 1 m3 of leachate
et al. (2011), it has been modelled as in Table 3.
(approximately 1 metric ton in mass). Table 5 represents the results
- pH Agent (Sodium Hydroxide): “Sodium hydroxide, without
obtained by using the Characterization mode available in ReCiPe.
water, in 50% solution state” has been chosen to model the so-
This assessment shows the high contributions of coagulant, pH
dium hydroxide;
control agent and electricity in all the 10 characterization cate-
gories. In particular, the coagulant and the pH control agent have
Table 3 been discovered to be responsible for the highest contribution in all
Modelling the inputs. the categories, except for “Marine Eutrophication”, where the
Coagulant (Polyaluminum Chloride) flocculant has the highest contribution score. Table 6 shows the
results of the ReCiPe normalization, for the quantity of 240 metric
(1 kg)
ton of treated leachate. This quantity corresponds to the maximum
Entry Amount Unit daily treating capacity of the WWTP (see section 4.3). The
Materials/fuels normalization has been obtained using the “World ReCiPe H”
Aluminium oxide 0.18 kg method, which means that these results refer to normalization
Hydrochloric acid, without water, in 30% solution state 0.733 kg
factors for a world citizen. These results have allowed to discover
which are the most relevant characterization categories affected by
Flocculant(1 kg)
the WWTP operating stage, i.e.: “Marine Ecotoxicity”, “Freshwater
Entry Amount Unit
Ecotoxicity”, “Human Toxicity” and “Freshwater Eutrophication”.
Materials/fuels For example, in the category “Marine Ecotoxicity”, the impact of
Acrylic acid, at plant 0.5 kg treating 240 metric ton of leachate is equivalent to 5.5 world citi-
Acrylonitrile, at plant 0.5 kg
zens (in a year).
L. Postacchini et al. / Journal of Cleaner Production 183 (2018) 1021e1033 1027
Table 5
Life Cycle Assessment for 1 metric ton of treated leachate: ReCiPe characterization results.
Climate change 4.32Eþ00 kg CO2 eq 6.3% 36.8% 30.7% 0.0% 0.4% 0.5% 25.3%
Terrestrial acidification 2.28E-02 kg SO2 eq 5.1% 35.4% 38.2% 0.1% 0.4% 0.5% 20.4%
Freshwater eutrophication 2.11E-03 kg P eq 1.4% 43.0% 38.3% 0.1% 0.2% 0.4% 16.7%
Marine eutrophication 1.59E-03 kg N eq 36.5% 28.7% 23.3% 0.0% 0.2% 0.2% 11.1%
Human toxicity 2.46Eþ00 kg 1,4-DB eq 1.6% 35.9% 49.6% 0.1% 0.2% 0.2% 12.3%
Terrestrial ecotoxicity 7.88E-04 kg 1,4-DB eq 1.5% 18.8% 66.2% 0.1% 0.1% 0.1% 13.1%
Freshwater ecotoxicity 6.87E-02 kg 1,4-DB eq 1.5% 32.8% 45.1% 0.1% 0.2% 0.2% 20.3%
Marine ecotoxicity 6.91E-02 kg 1,4-DB eq 1.4% 31.2% 48.4% 0.1% 0.2% 0.2% 18.5%
Water depletion 1.43E-01 m3 2.5% 34.2% 19.3% 0.0% 0.2% 0.0% 11.4%
Fossil depletion 1.33Eþ00 kg oil eq 12.1% 30.4% 32.0% 0.1% 0.6% 0.4% 24.4%
Table 8 ferric chloride is highly acidic, and the solution contains free hy-
PH agent comparison: ReCiPe characterization results. drochloric acid. Hence, the solution is highly corrosive to nearly all
Impact category Unit Sodium Hydroxide Calcium normally used metals, including all grades of stainless steel. This
Hydroxide latter fact, together with the greater sludge production, have been
Climate change kg CO2 eq 1.06E-04 3.46E-05 the main reasons for the WWTP management to dismiss the use of
Terrestrial acidification kg SO2 eq 5.36E-07 4.41E-08 ferric chloride in the past.
Freshwater eutrophication kg P eq 6.01E-08 1.01E-09 The second LCA comparison has pointed out the higher envi-
Marine eutrophication kg N eq 3.03E-08 1.36E-09
ronmental impact on the usage of sodium hydroxide over calcium
Human toxicity kg 1,4-DB eq 5.86E-05 1.50E-06
Terrestrial ecotoxicity kg 1,4-DB eq 9.85E-09 1.27E-09 hydroxide. This latter pH control agent has been able to cut down
Freshwater ecotoxicity kg 1,4-DB eq 1.49E-06 3.06E-08 more than 65% of the negative environmental impacts of the so-
Marine ecotoxicity kg 1,4-DB eq 1.43E-06 4.76E-08 dium hydroxide in all the characterization categories. Taking this
Water depletion m3 3.25E-06 4.55E-08
fact into account, Ca(OH)2 has demonstrated to be a considerably
Fossil depletion kg oil eq 2.68E-05 4.06E-06
more eco-friendly pH control agent than NaOH. The validity of
these comparison outcomes can be easily extended to the general
wastewater treatment field. In order to have a better understanding
of this result, it has been taken into account the consumption (for
category, the usage of PAC has allowed saving approximately 70% of the analyzed 36 months) of sodium hydroxide (50% diluted in H2O)
the water consumed by the usage of ferric chloride. Analogous recorded in the studied WWTP. Figs. 2e4 show the LCA comparison
savings have been reached by PAC in the Eutrophication sector between this sodium hydroxide consumption and the hypothetical
(Freshwater and Marine). The usage of PAC has shown to consume related calcium hydroxide consumption, analyzing three important
less water and release fewer nutrients into the aquatic environment impact categories: “Climate Change”, “Water Depletion” and “Fossil
than the usage of ferric chloride. From a technical point of view, PAC Depletion”. The results are expressed in the relative characteriza-
has shown to require lower dosages and to produce less amount of tion unit of measurement.
sludge than ferric chloride. Since the final disposal of the sludge The results of this last comparison show that 102 911 kg of CO2
involves a subsequent dewatering and transport operations, any- eq. emission, 4645 m3 of water and 33 003 kg of oil eq. (which in
thing that can reduce the volume of the sludge contributes to cost ReCiPe method are intended as “kg oil, crude, feedstock, 42 MJ per
savings for the WWTP management. PAC has also shown to affect kg, in ground-eq”) could have been saved, in these 36 months, by
less the pH and alkalinity of the wastewater. It requires less pH using the calcium hydroxide. It is now more evident that the cal-
correction, therefore less amount of pH agent is needed to raise the cium hydroxide is able to cut down the environmental impact of
pH after coagulation. On the negative side, PAC generally tends to the sodium hydroxide considerably. In addition, from a technical
produce smaller flocks than ferric chloride, that are slow to settle point of view, it is also known that calcium hydroxide is able to
down, and its market cost is usually greater than all the other co- carry out a coagulant action on the wastewater which could be used
agulants (ferric chloride included). Regarding the technical per- as a coagulant agent itself, and the use of it may easily decrease the
formance of ferric chloride, when compared to PAC, it has shown to dosage of the other coagulant agent. On the other hand, Ca(OH)2
have a higher sludge settling rate but also to produce the largest has some industrial application problems that have led WWTP
sludge quantities. Ferric chloride has also shown to consume managers to prefer the use of NaOH. First and foremost, it generates
alkalinity more and faster than PAC. Therefore, in order to ensure a considerable amount of residual sludge (primary sludge) that
that the treated water remains stable, pH agent addition is required must be dewatered and disposed. Dewatering the sludge,
in a greater amount than in the PAC coagulation process. Moreover,
transporting and disposing it are generally the most important and years of this study). These costs are representative of the Italian
highest costs in managing a WWTP. The second problem is that it market price of the time during this study and are reported in
has the tendency of easily creating calcifications along the pipelines Table 9.
of the WWTP, resulting in clogged pipes and ruined pumps. Thirdly, Fig. 5 shows the trend of the cumulative costs over the 36
due to its low solubility, it could create a problem in controlling its months considered in this study, for the two different coagulants. In
dosage into the WW. the end, WWTP management spent a total of 52 270 euro for the
In addition to treatment effectiveness, technical considerations use of PAC. If using the ferric chloride, the cost would have been
and environmental effects, economic cost is certainly among the 55 257 euro to obtain the same treatment results, which means
most important factors that must be taken into consideration, in
selecting the most appropriate coagulant and pH agent. Therefore,
a cost analysis has been performed, in order to understand the
Table 9
economic consequences of the chemical agent choice. Since, Coagulants and pH agents cost.
currently, there is not an international nor a European market price
index for the cost of the chemicals used in wastewater, the Product Cost (euro/kg)
following analysis has taken in consideration the costs that the PAC 0,250
WWTP management company has reported as final costs in their Ferric chloride 0,185
Sodium hydroxide 0,260
financial statement of the WWTP activity (for the considered three
Calcium hydroxide 0,115
1030 L. Postacchini et al. / Journal of Cleaner Production 183 (2018) 1021e1033
approximately 3000 euro higher. PAC is more expensive than ferric also considering its technical issues related to its sludge production
chloride per kg of mass unit, however, in this case, requiring lower that must be dewatered and disposed (considerably increasing also
dosages, it has shown to be a more convenient solution than ferric the WWTP management costs).
chloride. PAC has confirmed to be a better coagulant choice in terms In conclusion, considering the positive environmental results of
of technical issues, environmental impacts and cost. the PAC and, at the same time, the technical issues of the ferric
Fig. 6 shows the trend of the cumulative costs over the 36 chloride use in a WWTP, whenever possible, a substitution of PAC to
months considered in this study, for the two different pH agents. In ferric chloride is recommended. Considering also, the impressive
this case, by using calcium hydroxide instead of sodium hydroxide, positive environmental results of the calcium hydroxide and, at the
the WWTP management could have saved approximately 24 000 same time, the technical issues of its use in a WWTP, additional
euro. Calcium hydroxide is less expensive than sodium hydroxide research would be recommended in order to confirm the positive
per kg of mass unit, and it also requires lower dosages. Calcium LCA results and to study new engineering solutions for its use in a
hydroxide has confirmed to be a better pH agent choice in terms of WWTP.
environmental impacts and cost. However, it needs to be assessed
L. Postacchini et al. / Journal of Cleaner Production 183 (2018) 1021e1033 1031
Table A1
the inputs monthly consumption related to the amount of treated landfill leachate.
Coagulant PAC (kg) Sodium Hydroxide (kg) Water (m3) Flocculant (kg) Electricity (kWh)
Table A2
the specific inputs monthly consumption referred to 1 single metric ton of treated leachate.
N. Sampling date Specific consumption referred to 1 metric ton of treated landfill leachate
Coagulant PAC (kg) Sodium Hydroxide (kg) Water (m3) Flocculant (kg) Electricity (kWh)
Table A2 (continued )
N. Sampling date Specific consumption referred to 1 metric ton of treated landfill leachate
Coagulant PAC (kg) Sodium Hydroxide (kg) Water (m3) Flocculant (kg) Electricity (kWh)
Table A3
the average input consumption values, calculated as mean values over the 36 sets of input consumptions presented in Table A2.
Coagulant PAC (kg) Sodium Hydroxide (kg) Water (m3) Flocculant (kg) Electricity (kWh)
Wernet, G., Bauer, C., Steubing, B., Reinhard, J., Moreno-Ruiz, E., Weidema, B., 2016. waste by comparing with evaporation and discharge (EASEWASTE). Waste
The ecoinvent database version 3 (part I): overview and methodology. Int. J. Life Manag. 33, 382e389. https://doi.org/10.1016/j.wasman.2012.10.017.
Cycle Assess. 21, 1218e1230. https://doi.org/10.1007/s11367-016-1087-8. Zhang, Z., 2000. Life-cycle assessment of a sewage-treatment plant in South-East
Xing, W., Lu, W., Zhao, Y., Zhang, X., Deng, W., Christensen, T.H., 2013. Environ- Asia. Water Environ. J. 14, 51e56. https://doi.org/10.1111/j.1747-6593.2000.
mental impact assessment of leachate recirculation in landfill of municipal solid tb00226.x.