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DOI : http://dx.doi.org/10.25105/urbanenvirotech.v3i1.5530
Comparison of Global Warming Potential-Impacton the Handling of the Hazardous-Sludge from the Centralized Industrial-Wastewater Treatment Plant
Hakiki, Astuti, Wikaningrum p-ISSN 2579-9150; e-ISSN 2579-9207, Volume 3, Number 1, page 84 - 102, October 2019
Accredited SINTA 2 by Ministry of Research, Technology, and Higher Education of The Republic of Indonesia No. 23/E/KPT/2019 on August 8th, 2019 from
October 1st, 2018 to September 30th, 2023
84
COMPARISON OF GLOBAL WARMING POTENTIAL-IMPACT ON THE HANDLING OF THE HAZARDOUS-SLUDGE FROM THE CENTRALIZED INDUSTRIAL-WASTEWATER TREATMENT PLANT
Rijal Hakiki1*, Maryani Paramita Astuti1,2, Temmy Wikaningrum1 1Department of Environmental Engineering, Faculty of Engineering, President University, Cikarang, Indonesia 2Depatment of Civil and Environmental Engineering, Faculty of Engineering, University of Auckland, Auckland, New Zealand
*Corresponding author: [email protected]
ABSTRACT Aim: This study aimed to compare the secured landfill method and thermally sludge treatment through gasification, in order to determine their environmental impacts. Methodology and Results: The gate-to-gate LCA method was the implementation approach used to determine the, limits and assumptions to the actual condition. The experimental, theoretical mass balance calculation and secondary data of previous researches were used to carry out this study, with open-source openLCA software. In addition, the LCA was made up of four phases which include goal and scope definition, inventory analysis, impact assessment, and data interpretation. The simulation showed that the implementation of the thermal gasification process reduced the emission released to the atmosphere by lowering the hazardous sludge volume which is directly transported to the secured landfill. Conclusion, significance and impact study: Several assumptions and adjustments were made to the simulation results using the openLCA software, in the determined scope of study. Therefore, in conclusion, the thermal (gasification) treatment of hazardous sludge is further studied in connection with its implementation at the treatment plant. This was indicated by the acquisition of global warming potential impact category of 673 kg CO2 eq for direct disposal to secured landfill, which reduced to 424 kg CO2 eq during the implementation of thermal treatment. Conversely, there is a reduction in magnitude of impact by 37%.
MANUSCRIPT HISTORY
Received September 2019
Revised October 2019
Accepted October 2019
Available online October 2019
KEYWORDS Gasification
Gate-to-gate LCA
Hazardous sludge
LCA
OpenLCA
DOI : http://dx.doi.org/10.25105/urbanenvirotech.v3i1.5530
Comparison of Global Warming Potential-Impacton the Handling of the Hazardous-Sludge from the Centralized Industrial-Wastewater Treatment Plant
Hakiki, Astuti, Wikaningrum p-ISSN 2579-9150; e-ISSN 2579-9207, Volume 3, Number 1, page 84 - 102, October 2019
Accredited SINTA 2 by Ministry of Research, Technology, and Higher Education of The Republic of Indonesia No. 23/E/KPT/2019 on August 8th, 2019 from
October 1st, 2018 to September 30th, 2023
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1. INTRODUCTION This paper is a continuation of a previous study that discussed the potential for reducing toxic
and hazardous sludge through the gasification process (Hakiki and Wikaningrum, 2019). Referring
to the list of hazardous waste from the non-specific sources in Table 1, at the Indonesian
government regulation number 101 year 2014, it should be noted that the sludge produced from
the centralized wastewater treatment plant (WWTP) in an industrial estate is classified as toxic
and hazardous waste (Indonesian Government, 2014). From the previous study, it has been
known that the slurry phase produced from the biological treatment contains about 66% of
organic content, as show in Table 1.
Table 1 Slurry characteristics of Jababeka’s centralized WWTP (Hakiki, Wikaningrum, and Kurniawan, 2018)
Component Units Amount
TSS mg/L 7,168.0
MLVSS mg/L 4,732.0
SO4 mg/g 594.0
Ammonia mg/g 14.2
Organic % 66.0
H2O % 43.0
In the existing condition (Figure 1), it can be observed that the hazardous slurry phase from
the secondary settling tank (SST) then conveyed to the belt filter press (BFP) unit to reduce the
water content. The dewatered slurry (the wet sludge) collected in a fabric bag and then dried at
the sludge drying area (SDA) before transported to the sanitary landfill. It should realize that the
dewatering process will only reduce the water but not reducing the organic content significantly.
While the flow of sludge handling through the gasification process provided in Figure 2. As can
be observed in Figure 2, dry sludge from SDA not directly transported to secured landfill, but
experienced a process in gasifier and gas-liquid separator before transported to the landfill. There
is a difference in types of sludge transported to the landfill. For the scenario in Figure 1, all the
dry sludge from the SDA transported to the landfill. While for the scenario in Figure 2, material
transported to the landfill in a form of the fix-carbon residue from gasifier unit and liquid tar
residue from gas-liquid separator unit. The amount of this residue less than the amount of dry
DOI : http://dx.doi.org/10.25105/urbanenvirotech.v3i1.5530
Comparison of Global Warming Potential-Impacton the Handling of the Hazardous-Sludge from the Centralized Industrial-Wastewater Treatment Plant
Hakiki, Astuti, Wikaningrum p-ISSN 2579-9150; e-ISSN 2579-9207, Volume 3, Number 1, page 84 - 102, October 2019
Accredited SINTA 2 by Ministry of Research, Technology, and Higher Education of The Republic of Indonesia No. 23/E/KPT/2019 on August 8th, 2019 from
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sludge produced from SDA unit.
Based on some results of the previous study conducted by Hakiki et al., 2018, it has been
known that the process of hazardous sludge reduction through the gasification method can
reduce the cost of sludge disposal. Gasification which is utilizing thermal energy to decompose
the organic content from the hazardous sludge has been proven, at least at the laboratory scale
to reduce the sludge particle size up to 60% and reduce the sludge mass up to 50% (Hakiki,
Wikaningrum, and Kurniawan, 2018). The reduction of disposal cost can occur because the
reduction of sludge particle size and mass can significantly reduce the total amount of hazardous
sludge transported to the secured landfill. Hypothetically, there will be a reduction in fossil fuel
consumption to transport the sludge from the treatment plant to the secured landfill. The
reduction of sludge transported means the reduction of rotation in transportation, which means,
there will be a reduction of emissions from transportation. So that there will be an amount of
reduction in CO2 emission to the atmosphere.
Figure 1 (a) The industrial wastewater; (b) Mechanical separation of solid particles from wastewater; (c) Dried sludge; (d) The existing flow of wastewater treatment and sludge handling. (Kurniawan, Hakiki, and Sidjabat, 2018)
In addition, green energy produced from the gasification process can also be used as an
alternative energy source (McNamara et al., 2016; Ji et al., 2010). CO2 being an important
constituent in our atmosphere, the changes of concentration in our atmosphere can affect the
global climate (Sun et al., 2015; Anderson, Hawkins, and Jones, 2016; Kusrini et al., 2017; Zhang,
Zhao, and Xu, 2017). Combustion of fossil fuel, in a field of transportation, power generation,
DOI : http://dx.doi.org/10.25105/urbanenvirotech.v3i1.5530
Comparison of Global Warming Potential-Impacton the Handling of the Hazardous-Sludge from the Centralized Industrial-Wastewater Treatment Plant
Hakiki, Astuti, Wikaningrum p-ISSN 2579-9150; e-ISSN 2579-9207, Volume 3, Number 1, page 84 - 102, October 2019
Accredited SINTA 2 by Ministry of Research, Technology, and Higher Education of The Republic of Indonesia No. 23/E/KPT/2019 on August 8th, 2019 from
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domestic activity, manufacturing process and other kinds of human activities are the sources of
CO2. In addition to CO2, there are other gases that are classified as greenhouse gases such as Nox,
Sox, and CH4 which are produced from the combustion process (Rinanti, 2016).
Based on the techno-economic simulation conducted by Hakiki et al., 2018, it is known that
the utilization of green energy produced from the gasification process can reduce the electricity
consumption in a centralized wastewater treatment plant located at the Jababeka industrial
estate up to 3% from the total electricity consumed (R. Hakiki, Wikaningrum, and Kurniawan,
2018). Although the results of the preliminary study appeared to be economically promising,
studies on environmental aspects must be still conducted to find out the prospects for sustainable
development of this technology. Land limitation and the more restrictive regulations for a
secured landfill become the motive behind the idea of utilizing gasification process to reduce the
amount of hazardous sludge (Folgueras, Alonso, and Díaz, 2013; Li et al., 2015; Samolada and
Zabaniotou, 2014).
Figure 2 Another scenario of sludge handling through the thermal-gasification process
However, the impact resulted from the implementation of this process to the environment
becomes an important aspect should be considered in this context. The reduction of CO2 emission
from the transportation side and the CO2 equivalent reduction from the reduction of electricity
consumption are the highlighted-advantages from the utilization of gasification technology to
treat hazardous sludge. Nevertheless, to prove that the reduction of sludge amount and
DOI : http://dx.doi.org/10.25105/urbanenvirotech.v3i1.5530
Comparison of Global Warming Potential-Impacton the Handling of the Hazardous-Sludge from the Centralized Industrial-Wastewater Treatment Plant
Hakiki, Astuti, Wikaningrum p-ISSN 2579-9150; e-ISSN 2579-9207, Volume 3, Number 1, page 84 - 102, October 2019
Accredited SINTA 2 by Ministry of Research, Technology, and Higher Education of The Republic of Indonesia No. 23/E/KPT/2019 on August 8th, 2019 from
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reduction in electricity consumption can also reduce CO2 emission to the atmosphere, it will
require a “technique” to improve the environmental performance of this process, in this context
by calculating the amount of CO2 emitted. Or in other words, this technique can support the
proposed “thermal-gasification” method to handle the sludge.
Refers to ISO 14040:2006 concerning Environmental management-Life cycle assessment-
Principle and framework, stated that life cycle assessment (LCA) is a technique developed to
identify opportunities in terms of improving environmental performance of a product, provide
information to decision-makers, government and non-government organizations in terms of
strategic planning and prioritization, selection of relevant environmental performance indicators
and their relation to branding to increase marketing value (International Organization for
Standardization, 2006). In connection with this, the study tries to compare two kinds of sludge
handling, direct disposal to secured landfill method versus thermally sludge treatment through
gasification before the disposal. This comparison is intended to find out the environmental
impacts that will result from the scope of the sludge handling. Furthermore, the scope will be
limited to the handling of sludge after the SDA until the transport of sludge, without concerning
the impact of a secured landfill. The consideration of this limitation can be observed from Figure
1 and Figure 2, that there is no difference between both processes, it begins from PST > OD > SST,
and for both handling scenario, the residue from the treatment is transported to the landfill. And
the difference can be observed after the SDA Unit and before the transport of the sludge as
illustrated in Figure 3.
Figure 3 Scenario comparison of sludge handling between direct-landfill versus thermal gasification process
DOI : http://dx.doi.org/10.25105/urbanenvirotech.v3i1.5530
Comparison of Global Warming Potential-Impacton the Handling of the Hazardous-Sludge from the Centralized Industrial-Wastewater Treatment Plant
Hakiki, Astuti, Wikaningrum p-ISSN 2579-9150; e-ISSN 2579-9207, Volume 3, Number 1, page 84 - 102, October 2019
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2. RESEARCH METHODOLOGY The study was carried out using the “gate-to-gate LCA method”. Referring to the “AIA Guide to
Building Life Cycle Assessment in Practice”, published by The American Institute of Architects, it
is a partial LCA which only examine value-added process in the entire production chain, for
example by evaluating the environmental impact due to the construction stage of a building
(Bayer et al., 2010). With respect to the possibility to implement the partial analysis of the
environmental impact, in its implementation of this partial LCA, limits, and assumptions have
been determined as an approach to the actual condition. Some of the data used include the
experimental data, theoretical mass balance calculation and secondary data obtained from
previous research. The study was carried out with the Life Cycle Assessment (LCA) method
utilizing openLCA software that is open source (Claudia Di Noi, Ciroth, and Srocka, 2017).
Illustrated in Figure 4, the required data are a combination of primary data and secondary data
that is processed in such a way that the simulation results are expected to be able to approach
the actual process condition. However, the simulation results need to be studied further,
considering the relatively narrow scope of the study area, only limited to the sludge-dewatering
process to the residual-transport of the entire wastewater treatment process from centralized
wastewater treatment in an industrial estate.
Figure 4 Sources of data used in this study using the OpenLCA software
DOI : http://dx.doi.org/10.25105/urbanenvirotech.v3i1.5530
Comparison of Global Warming Potential-Impacton the Handling of the Hazardous-Sludge from the Centralized Industrial-Wastewater Treatment Plant
Hakiki, Astuti, Wikaningrum p-ISSN 2579-9150; e-ISSN 2579-9207, Volume 3, Number 1, page 84 - 102, October 2019
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As can be observed from Figure 4, the data used as the input for inventory data to the
software. It is classified into two major groups of data, the primary data consist of the data
resulted from the laboratory experiments, while the secondary data consist of the mass balance
calculation (theoretically), sludge characteristics and syngas characteristics.
Figure 5 Mass balance data from the lab-scale experiment (Hakiki, Wikaningrum, and Kurniawan, 2018)
Configuration of the lab-scale gasifier illustrated in Figure 5. It can be observed that the
amounts of organic sludge are converted to 40% wet syngas and 60% char, and from the 40% of
wet syngas convey to the gas-liquid separator and results 90% dry syngas and 10% condensate
(from the total 40% of wet syngas resulted in gasifier). The mass balance data is then entered as
inventory data in OpenLCA software. In general, the research stage illustrated in Figure 6.
DOI : http://dx.doi.org/10.25105/urbanenvirotech.v3i1.5530
Comparison of Global Warming Potential-Impacton the Handling of the Hazardous-Sludge from the Centralized Industrial-Wastewater Treatment Plant
Hakiki, Astuti, Wikaningrum p-ISSN 2579-9150; e-ISSN 2579-9207, Volume 3, Number 1, page 84 - 102, October 2019
Accredited SINTA 2 by Ministry of Research, Technology, and Higher Education of The Republic of Indonesia No. 23/E/KPT/2019 on August 8th, 2019 from
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Figure 6 The research stage
2.1 Impact Simulation With OpenLCA The four-phase in the LCA include goal and scope definition, inventory analysis, impact
assessment, and data interpretation (Noor and Soewondo, 2018). The step of simulating the
impact was following the four-phase of the LCA method, utilizing OpenLCA software with CML
Baseline Impact 2000. The functional unit of this study is the mass of sludge treated in ton/month.
2.1.1 Goal and Scope Definition (The Scenario) The goal of this study would be predicting the environmental impacts of both the sludge handling
method, i.e., thermal gasification and direct transport to secure landfill, particularly the potential
of global warming from hazardous sludge treatment. Considering the wide scope of the
wastewater treatment process, this study will be limited only to the solid handling stage from the
sludge dewatering stage to the residual transport process.
DOI : http://dx.doi.org/10.25105/urbanenvirotech.v3i1.5530
Comparison of Global Warming Potential-Impacton the Handling of the Hazardous-Sludge from the Centralized Industrial-Wastewater Treatment Plant
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Figure 7 Direct-secured-landfill scenario
Figure 7 and Figure 8 illustrate the area under this study for direct landfill and thermal process
accordingly. In Figure 1 it can be observed that this study is limited, beginning from the
dewatering process of secondary settling tank (SST) outlet, followed by further drying process at
sludge drying area (SDA) unit, to be transported to a secured landfill. Whereas in Figure 2, a
similar stage is carried out also, beginning with the dewatering process of SST outlet, then
proceed with further drying in the SDA unit.
The difference is the implementation of thermal processes that are equipped with a gas-
liquid separator unit to separate the gas and liquid phase. There are two kinds of waste produced
from this system, in the form of char (from gasifier) and condensate (from separator) which are
then transported to the secured landfill. Char is the residue of the thermal process that does not
convert to the gas phase, but still in solid phase. While the condensate resulted from bottom
product of gas-liquid separator. The separation process in the gas-liquid separator is affected by
the difference in vapor pressure that is owned by each separated fraction.
DOI : http://dx.doi.org/10.25105/urbanenvirotech.v3i1.5530
Comparison of Global Warming Potential-Impacton the Handling of the Hazardous-Sludge from the Centralized Industrial-Wastewater Treatment Plant
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Figure 8 Thermally-hazardous-sludge-treatment scenario
2.1.2 Life Cycle Inventory (LCI) The inventory data was obtained by calculating the mass balance of the process, combined with
the actual data from the plant and from the laboratory experiment results. Therefore, an effort
needs to be made to optimize the energy potential. Carbon compounds in sludge that have been
dewatered, will then be put into the gasifier so that there will be some chemical reactions as can
be observed in Table 2. The equation of chemical reaction is the basis for a stoichiometric
calculation to obtain the required data as input for the simulation process using the openLCA
software.
Only several of the reactions in Table 2 are considered to represent the parameters to
examine in the LCA method. Another information required is regarding GHG which includes the
emission factors for the use of electricity as well as the emission factors for fuel usage. Referring
to the emission factor for electricity usage in the area of Java is 0.84 kg CO2/kWh (Ministry of
Energy and Mineral Resources Republic of Indonesia, 2016). As for the fuel usage emission factor,
referring to the data which is 2.66 kg CO2/L of diesel fuel for land transportation, 0.14 kg CH4/L of
diesel fuel for land transportation and 0.14 kg N2O/L of diesel fuel for land transportation (Boer
et al., 2012). In this study, the units of tonnes per year (t/y) are used as functional units in the
DOI : http://dx.doi.org/10.25105/urbanenvirotech.v3i1.5530
Comparison of Global Warming Potential-Impacton the Handling of the Hazardous-Sludge from the Centralized Industrial-Wastewater Treatment Plant
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calculation of impact assessment (LCIA).
Table 2 Several equations of the chemical reaction as a basis for
stoichiometric calculation (Arena, 2012)
2.1.3 Life Cycle Impact Assessments (LCIA) CML Baseline 2000 impact analysis method is used to process the inventory data, which include
several impact categories: abiotic depletion (kg Sb eq), acidification (kg SO2 eq), eutrophication
(kg PO4 eq), freshwater aquatic ecotoxicity (kg 1.4-DB eq), global warming (GWP 100)
(kg CO2 eq), human toxicity (kg 1.4-DB eq), marine aquatic ecotoxicity (kg 1.4-DB eq), ozone layer
depletion (kg CFC-11 eq), photochemical oxidation (kg C2H4 eq), and terrestrial ecotoxicity
(kg 1.4-DB eq). In each of these categories, it has been compared with the dominant components
that are considered to be representative for further processing in order to obtain the desired
results. The accuracy of the simulation results is determined by several factors, including the
accuracy of the analytical results, the suitability of mass balance calculation and other factors that
are also considered influential in the calculation.
DOI : http://dx.doi.org/10.25105/urbanenvirotech.v3i1.5530
Comparison of Global Warming Potential-Impacton the Handling of the Hazardous-Sludge from the Centralized Industrial-Wastewater Treatment Plant
Hakiki, Astuti, Wikaningrum p-ISSN 2579-9150; e-ISSN 2579-9207, Volume 3, Number 1, page 84 - 102, October 2019
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2.1.4 Interpretation of results Nugraha et al., (2018) stated that the interpretation of results included two important steps, i.e.,
identification of important issues and evaluation (Nugraha, Wiloso, and Yani, 2018). Consistency
of inventory results is needed in identifying important issues that will be discussed, as well as
evaluating the impact caused, referring to the goals and scope that have been determined. The
aspects of completeness, sensitivity, and consistency of the data need to be evaluated so that the
results of the analysis are in line with what is expected.
3. RESULTS AND DISCUSSIONS The model graph generated from the software for both treatments can be observed in Figure 9
and Figure 10. The model for the secured landfill method is simpler than the thermally-sludge-
treatment method. The difference that can be observed is that in Figure 4 there is a part of the
gasifier and gas-liquid- separator, each of which is connected to the residual transport section.
That can be interpreted, that in Figure 3 the sludge generated from the wastewater plant (WWTP)
is directly disposed to a secured landfill.
Figure 9 The model graph generated as a result of input data to the openLCA software for direct-secured-landfill-scenario
Whereas in Figure 4, the sludge generated from WWTP undergoes further treatment in the
gasifier and gas-liquid-separator. Referring to both models, it is known that the input data is in
accordance with the desired scenario. The generated model can function as an initial control to
ensure that the scenario data input into the software is as desired. The incompatibility of the
DOI : http://dx.doi.org/10.25105/urbanenvirotech.v3i1.5530
Comparison of Global Warming Potential-Impacton the Handling of the Hazardous-Sludge from the Centralized Industrial-Wastewater Treatment Plant
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generated model indicates that there is a discrepancy in the data input, which will affect the
assessment results.
Several considerations in this simulation include: a) It is assumed that all process units used
and included in the LCA scope are in good condition and there is no leakage so that emissions
that expose out of the system are actual emissions resulting from the process and not due to
leakage. b) This research is focused on the study of the categories of global warming potential
impacts (kg CO2 eq) because thermal treatment will produce flue gas whose major composition
is classified as greenhouse gas (GHG) compounds. c) It is assumed that other pollutants have been
processed in such a way that they do not cause a negative impact on the environment. d)
Utilization of green energy generated from the thermal process as a power source for dewatering
units, thereby reducing electricity consumption from the power plant (PLN).
Figure 10 The model graph generated as a result of input data to the openlca software for thermally-sludge-treatment- scenario
The use of electrical energy generated from the thermal process is also considered to reduce
the amount of GHG emissions into the atmosphere. This is consistent with what has been studied
by Wiloso et al., (2016), which states that the assumption of the neutrality of biogenic carbon
stored during growth will be released back into the atmosphere in the same number and form,
so it is believed that there is no increase in GHG concentration due to decomposition or
combustion of biogenic carbon compounds (Wiloso et al., 2016). In addition, it should be realized
that utilizing green energy derived from carbon content in sludge will also reduce the
consumption of fossil fuels because it will reduce disturbance to carbon underground reserves.
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Comparison of Global Warming Potential-Impacton the Handling of the Hazardous-Sludge from the Centralized Industrial-Wastewater Treatment Plant
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3.1 Life Cycle Impact Assessment of The Projects Of the several impact categories studied in the CML Baseline 2000 impact analysis method, the
category of global warming potential impact is become a concern. In Table 3, the results of the
impact analysis can be observed for both treatments. However, in addition to the global warming
potential impact category, another observed result is the photochemical oxidation impact
category. It caused by the emission of methane from fossil fuel combustion which not just impacts
global warming potential, but also can produce the photochemical oxidant when it reacted with
other constituents in the atmosphere. Another impact categories which cannot be observed, such
as abiotic depletion, acidification, eutrophication, freshwater aquatic ecotoxicity, human toxicity,
marine aquatic ecotoxicity, ozone layer depletion and terrestrial ecotoxicity caused by the scope
in this study is limited to sludge handling process without calculating wastewater and liquid waste
generated from dewatering, drying, gasification and gas-liquid separation process. In addition, it
can be observed in Figure 1 and Figure 2 that the liquid generated from the dewatering and drying
process directly circulated to the oxidation ditch unit for further treatment so that no liquid-
residual contaminated the water bodies. Whereas, the toxicity impact which may be generated
can also be minimized, because of the solid management specifically in a limited access area of
centralized industrial estate WWTP.
Table 3 shows that the value of global warming potential impact category for the thermal
process is lower than the direct secured landfill treatment. This is due to the greenhouse gases
contained in the top product of gas-liquid separator being the input for green energy. Or in other
words, in the gasification process which is a closed system, there is no exhaust gas emitted into
the atmosphere, except the flue gas produced from the conversion process of syngas into energy.
This is consistent with what has been studied by Wiloso et al., (2016), which states that the
assumption of the neutrality of biogenic carbon stored during growth will be released back into
the atmosphere in the same number and form, so it is believed that there is no increase in GHG
concentration due to decomposition or combustion of biogenic carbon compounds.
DOI : http://dx.doi.org/10.25105/urbanenvirotech.v3i1.5530
Comparison of Global Warming Potential-Impacton the Handling of the Hazardous-Sludge from the Centralized Industrial-Wastewater Treatment Plant
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Table 3 Life cycle impact analysis results for both treatment from openLCA software
Impact category Direct secured
_landfill Thermal_sludge _treatment
Unit
Global warming (GWP100) - CML 2 baseline 2,000
6.73276e+2 4.24385e+2 kg CO2 eq
Photochemical oxidation - CML 2 baseline 2,000
7.68600e-5 4.91904e-5 kg C2H4 eq
3.2 Process Contributions to Global Warming Potential As shown in Figure 11, two stages of the sludge handling process are identified as the major
contributors of GHG production, i.e., residual transport and sludge dewatering. In the residual
transport stage, a considerable amount of GHG is generated from the results of fossil fuel
combustion. Whereas in dewatering stage, GHG has resulted from electricity consumption as the
power source for electric motor which used in belt filter press unit. The amount of GHG identified
is based on the data which stated that the emission factor for electricity usage in the area of Java
is 0.84 kg CO2/kWh (Ministry of Energy and Mineral Resources Republic of Indonesia, 2016). The
emission factor used is the average amount of emitted GHG to the atmosphere and it has been
equalized with the amount of electricity produced by the power plant. Other units are
contributed relatively small amounts of GHG rather than the two major GHG contributors. The
further drying process in the SDA unit only utilizes heat from the radiation of sun, it means there
is no other energy in the form of electricity or fossil fuels used in the process units. Exposure to
solar heat that accumulates on the surface of the sludge, allows the evaporation of volatile carbon
compounds even though the amount is significant when compared to the mass of sludge dried in
the unit.
DOI : http://dx.doi.org/10.25105/urbanenvirotech.v3i1.5530
Comparison of Global Warming Potential-Impacton the Handling of the Hazardous-Sludge from the Centralized Industrial-Wastewater Treatment Plant
Hakiki, Astuti, Wikaningrum p-ISSN 2579-9150; e-ISSN 2579-9207, Volume 3, Number 1, page 84 - 102, October 2019
Accredited SINTA 2 by Ministry of Research, Technology, and Higher Education of The Republic of Indonesia No. 23/E/KPT/2019 on August 8th, 2019 from
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99
Figure 11 Process contributions to global warming potential for both scenario, analysis result for direct-secured-landfill-scenario and thermally-sludge-treatment-scenario
Therefore, in carrying out the calculation it is assumed that there will be 0.25% volatile carbon
that is evaporated into the atmosphere. This value is the estimated value because there is no
measurement data about it. Other units that also do not use electricity or fossil fuel energy are
gas-liquid separator units. So that in ideal conditions, namely in the condition of a vessel without
leakage, there will be no gas emitted into the atmosphere or condensate which pollutes the soil
or waters. Whereas carbon dioxide emissions in the syngas to green energy conversion system
are also assumed to be carbon neutral, according to what has been mentioned earlier, that the
green energy produced will be reused as a source of energy for motor-driven belt filter press unit.
In addition to reducing electricity consumption, it is also considered to be able to offset carbon
emissions released from the results of electricity generation at power plants, without having to
interfere with the availability of underground fossil fuel reserves. Based on the simulation results,
it is known that the amount of carbon emissions generated from the gasifier unit is relatively
large. However, in a closed system, there will be no gas emitted into the atmosphere because the
top product of the gasifier will be flowed to the gas-liquid separator to be further separated
between the gas and liquid phases.
DOI : http://dx.doi.org/10.25105/urbanenvirotech.v3i1.5530
Comparison of Global Warming Potential-Impacton the Handling of the Hazardous-Sludge from the Centralized Industrial-Wastewater Treatment Plant
Hakiki, Astuti, Wikaningrum p-ISSN 2579-9150; e-ISSN 2579-9207, Volume 3, Number 1, page 84 - 102, October 2019
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4. CONCLUSIONS Based on the study of “gate-to-gate” LCA, it can be concluded that the thermal (gasification)
treatment of hazardous sludge can be studied further in connection with its implementation at
the treatment plant. From the actual plant data of 3.2 ton treated-biologically sludge per day,
with 30% water content, it is indicated by the acquisition of global warming potential impact
category of 6.73276e+2 kg CO2 eq (for direct transporting/disposal to secured landfill) reduced
around 4.24385e+2 kg CO2 eq (for the implementation of thermal treatment). In other words,
there is a reduction in the magnitude of the impact to around 37%. This can be achieved if all the
assumptions and conditions required in the simulation process can be met.
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