Environmental assessment of an Indian municipal wastewater treatment plant in Rajasthan

ABSTRACT

Wastewater treatment plant (WWTP) reduces environmental load by improving the quality of effluent sewage water. A wastewater treatment plant during its operation, consumes energy for circulation and aeration of water, utilise chemicals such as anti-foaming agents, coagulants and flocculants and release gaseous emissions and solid waste (sludge). It is necessary to consider the environmental impacts of all these activities realistically. Life cycle assessment (LCA) is used to calculate the potential environmental impact associated with the operation of WWTP. In this study, LCA was carried out for a WWTP located in Jaipur in the state of Rajasthan, India. CML 2001 method was used for the life cycle impact assessment using GaBi 8.0 software. The objective of this study is to quantify the environmental impact associated with the operation of a WWTP and to identify the environmental hotspots among different processes within the WWTP. The LCA result of the WWTP reveals that the sequencing batch reactor process 1 and 2 have the highest environmental impacts within the WWTP as this process consumes the highest amount of electricity whereas the pretreatment process has the least environmental impact.

KEYWORDS:

• Wastewater treatment plants (WWTPs)
• life cycle assessment (LCA)
• GaBi
• environmental hotspot

1. Introduction

With the rapid growth of world population, industrial, and agriculture activities, countries worldwide face growing global water stress, both in terms of paucity of water and deteriorated quality (Kamble, Singh, and Kharat 2018). Therefore, appropriate steps like the treatment of wastewater generated from day-to-day activity and its reuse will help in solving the problem of water paucity as well as deteriorating water quality of rivers and oceans. The main objective of a wastewater treatment plant (WWTP) is to lower the environmental impact caused by the wastewater on water bodies like rivers and oceans. The lower number of wastewater treatment facilities is one major problem in developing countries. In India, the situation is much worse because of a large gap between the wastewater generation and the availability of treatment facilities. According to a report published in ‘The Hindu,’ a leading English newspaper, present installed capacity for sewage treatment is just 4000 million litres per day (MLD) out of which only 1000 MLD is fully functional. As a result, about 12,000 million litres of untreated sewage is discharged directly every day into the Ganga River across eleven states. (Koshy, 2018). Urban centres and cities in India are rapidly developing.The sanitation facilities currently available are not adequate for such a high population, resulting in the discharge of untreated wastewater directly into the water bodies (Kalbar, Karmakar, and Asolekar 2014). Though WWTP reduces the environmental impact caused by the direct discharge of untreated sewage water into the water bodies, they have an impact on the environment by themselves, as they consume resources for construction and operation (Lopsik 2013; Garfi, Flores, and Ferrer 2017). Across India, a number of new WWTPs are being installed due to the implementation of higher effluent standards for industrial wastewater. Also programs like NamamiGange, monitored by National Mission for Clean Ganga are rapidly improving the water quality in rivers in part due to the better quality of the water discharged into the rivers. Therefore, the need of the hour is to evaluate the environmental impacts caused by these WWTPs. Life Cycle Assessment (LCA) is considered to be a better way to account for the impact of WWTPs. Life Cycle Assessment, as defined by the ISO 14040 (2006a) and ISO 14044 (2006b), is ‘the compiling and evaluation of the inputs and outputs and the potential environmental impacts of a product system during a product’s lifetime.’ LCA has garnered attention as an environmental assessment tool to evaluate the impacts of various inputs and outputs in complex systems. This can be evidenced by an increase in the number of publications and databases on LCA and its implementation (Corominas et al. 2013). It helps in identifying the environmental impacts and develop the most favorable alternative for the existing process (Lopsik 2013). LCA first applied in the field of WWTPs during the 1990s. Recently, Postacchini, Ciarapica, and Bevilacqua (2018) used LCA technique, to evaluate environmental assessment of a landfill of Italian wastewater treatment plant and also assess the performance of various technologies applied to the treatment of municipal landfill leachate. The study shows the relevant environmental impacts generated by the use of polyaluminum chloride (PAC) as a coagulant chemical agent and sodium hydroxide (caustic soda) as a pH control chemical agent. In order to investigate these results, and to discover more eco-friendly alternatives, two LCA comparisons have been carried out, comparing, respectively, the above two agents to analogous and common substitutes: ferric chloride as a coagulant agent and calcium hydroxide (lime) as a pH control agent. Results of These comparisons show the higher environmental impacts of the use of ferric chloride over PAC and of sodium hydroxide over calcium hydroxide. Teodosiu et al. (2016) focuses on the environmental assessment of a municipal wastewater treatment plant (MWWTP) discharges by means of three evaluation methods, i.e., life cycle assessment (LCA), environmental impact quantification (EIQ) and water footprint (WF) with the purpose to understand their (methodological) weak and strong points in capturing the impacts. The results showed that most impacts induced to surface waters due to Iasi MWWTP effluents are given by the nutrients (nitrogen and phosphorous compounds), which could induce an eutrophication impact, and to a lesser extent by pollutants responsible for toxicity impacts (such as heavy metals). Ideally, the decision regarding the installation of a WWTP in a locality relies on economic and technical limitations. However, environmental impacts, energy scarcity, social aspects, and other environmental issues make it an arduous task to decide whether to instal a WWTP or not.

In India, a small number of studies on WWTP are available in which LCA has been applied. The first comprehensive LCA study was carried out in India by Kalbar et al., in (Kalbar, Karmakar, and Asolekar 2014). There is no national database available for conducting LCA in the Indian Context (Kalbar, Karmakar, and Asolekar 2014; Kamble, Singh, and Kharat 2018). It is therefore necessary to develop the life cycle inventory (LCI) datasets and implement the LCA methodology in the Indian context. In this study, an attempt has been made to present the application of LCA methodology of an existing WWTP in India. The objective of this study is to quantify the environmental impacts associated with the operation of WWTP and to identify the environmental hotspots among different processes within WWTP. This research would be helpful for policymakers for their decision-making, and for researchers to strengthen their LCI database.

The organisation structure of this paper is as follows: After the introduction, Section 2 describes the material and methods to be used. This part describes the description of the WWTP, life cycle assessment (LCA) of central park WWTP, goal and scope definition, life cycle inventory analysis (LCI), and life cycle impact assessment (LCIA). Section 3 presents the results and discussion. Section 4 discusses the main conclusions and future scope of the paper.

2. Material and methods

2.1. Description of the WWTP

Many WWTPs are available in Jaipur, such as Jawahar Circle WWTP, Central Park WWTP, and WWTP at Amber road. Out of all WWTPs, Central Park WWTP was considered for the LCA study because of the availability of quality data. It was established in June 2016 by Eco ParyavaranPrivate Limited under the supervision of the Jaipur Development Authority (JDA). Eco Group is the leading provider of Sewage Treatment Plants in India. The CP WWTP treats wastewater from about 20,000 people (residential wastewater) and has a design capacity of 1000 m³/day average flow. Using advanced Sequencing Batch Reactor (SBR) technology, CP WWTP can eliminate 98% of organic matter and suspended solids and about 83%of total nitrogen and 90% of total phosphorus from the wastewater (Table 1), thus meeting the strictest sewage treatment standards prescribed by Central Pollution Control Board (CPCB) India. Data in Table 1 are the daily averages that were recorded by the operators daily. The treated wastewater was used for watering of central park spread in an area of over four square kilo metres.

Table 1. Removal efficiency of Central Park WWTP

	Influent Wastewater	Effluent treated water	Percentage Removal
Units	mg/L	mg/L	%
BOD	230	4.5	98
SS	605	7	98.8
Total N	45	7.6	83
Total P	8.9	0.9	89.9

Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD)

SBR technology differs from activated-sludge plants because they combine all of the treatment steps and processes into a single basin, or tank, whereas conventional facilities rely on multiple basins (Poltak, 2005). The treatment steps of Central Park WWTP is shown below in Figure 1.

2.2. Life Cycle Assessment (LCA) of Central Park WWTP

LCA is a comprehensive, systematic, and standardised procedure for estimating the potential environmental impacts of a product, process, or activity (Garfi, Flores, and Ferrer 2017). The standard methodology, as described by ISO 14040 (2006a) and ISO 14044 (2006b), is adapted for applying LCA to Central Park WWTP. GaBi software has been used for carrying out the LCA study in this paper. According to ISO 14040 (2006a) and ISO (2006b) 14044 standards LCA involves four main steps, namely:

1. Goal and scope definition

2. Life cycle inventory analysis (LCI)

3. Life cycle impact assessment (LCIA)

4. Interpretation of the results

Figure 1. Treatment steps in Central Park WWTP)

2.2.1. Goal and scope definition

According to ISO 14040 (2006a), defining, Goal, and Scope is the first step in the LCA. The definition of goal determines the intended application, purpose, and the intended audience of the LCA study. The goal of this study is to evaluate the potential environmental impact associated with each process of a municipal WWTP (with a treatment capacity of 1 MLD) and to compare the LCA result of WWTP with the no treatment plant in the Indian context. The intended audience of this study are researchers, policymakers, and practitioners of LCA.

The scope of the study includes the function of the system, functional unit, and system boundaries of the system. The function of this system is to treat wastewater. For the functional unit, several options may be taken into account: for example, the quantity of removed pollutants, volume of treated wastewater, or volume of generated sludge. According to the recommendations by past researchers (Suh and Rousseaux 2002; Li et al. 2013; Raghuvanshi et al. 2017), the quantity of inflow water in a certain period appears to be the best choice since it will be based on realistic data. The amount of influent wastewater flow per month (m³/month) was used as the functional unit for this study as this caters to the variation in the inflow of wastewater in different seasons. An average flow rate of wastewater per month from the period of 2018–2019 was taken into consideration in this study. The inflow of wastewater per month equals to 7697.37 m³. However, Renou et al. (2008) argued that this variation in flow rate would not change the conclusions on LCIA methods.

The system boundary explains which process will be included or excluded from the study. The definition of system boundary should be in accordance with the goal of the study (Kalbar, Karmakar, and Asolekar 2014). System boundary considered for the study will have a large impact on the final result and therefore it should be selected carefully (Tillman, Svingby, and Lundström 1998). System boundary for this study has been considered after a thorough literature study, expert advice, and data availability limitations of the processes. The system boundary chosen for this study is shown in Figure 2. Wastewater treatment plant consists of pretreatment process, sequencing batch reactor process, sludge handling process, centrifuge process, chemical treatment process and water storage tank. The incoming wastewater passes through the screening equipment, namely the silencing chamber, the thin-rod screening chamber and the distribution chamber, in which rags, wood chips, plastics and grease are removed. The removed material is washed and suppressed, and then thrown into the garbage dump. Then the filtered wastewater is pumped to the next step: the grit chamber process. In this step, heavy and fine materials such as sand and gravel are removed from the wastewater. Once the screening is completed and the grit is removed, the sewage still contains organic and inorganic substances and other suspended solids. These solids are tiny particles that can be removed from the sewage in the sedimentation tank. When the flow rate through one of the storage tanks decreases, the suspended solids will gradually sink to the bottom, where a large amount of solids are formed. These solids are called untreated primary called sludge. The sludge is usually removed from storage tanks by pumping. The ‘Sludge Handling Process’ separates the sludge into heavy and lighter sediments. The heavy sediments are dried using a fluidised bed drying while the lighter sediments are sent to the ‘Centrifuging stage’. A centrifuge is a machine that spins very quickly, forcing the liquid to separate from the solid. The liquid can then be processed with the wastewater and the solid is used as fertiliser on fields or as landfill. The Sequencing Batch Reactor (SBR) process uses bacteria with different conditions in several tanks to digest pollutants in the water. These tanks have unique environments and contain different amounts of oxygen. When the water passes through the three tanks, phosphorus is removed and ammonia is broken down into nitrate and nitrogen, which is not possible with other bacterial processes. The water spent about 9 hours in the bioreactor before entering the secondary SBR process, where the bacteria-laden sludge settled on the bottom of the tank. After that water pumped for further chemical treatment where bleaching powder is used to kill the additional pollutants and bacteria. Finally, water is sent to storage tank for further supply.

Figure 2. System Boundary of Central Park WWTP

Based on expert opinion and data availability of the processes, the following assumptions were made in choosing the system boundary:

1. The operation phase of the Central Park WWTP was considered in this study. The construction phase and demolition phase contribute only about 1% of total environmental impacts, and hence it can be neglected (Kalbar, Karmakar, and Asolekar 2014; Lopsik 2013; Hospido, Moreira, and Feijoo 2008).

2. Energy utilisation by pump used for pumping the sewage into the WWTP is not considered in this study. The variation in pumping distance may affect the result of the study (Kamble, Singh, and Kharat 2018).

3. All direct greenhouse gas (GHG) emissions, except methane (CH₄), were considered in this study. Suh and Rousseaux (2002), made a similar assumption to avoid further expansion of the system.

4. Transportation of dried sludge into agricultural fields and their application are not considered in this study because of the absence of data.

2.2.2. Life cycle inventory analysis (LCI)

LCI is the second step in the LCA study, which includes the collection and compilation of the data, quantification of inputs, and outputs for each process. LCI is concerned with the collection of data and calculation procedures required to complete the inventory table (Hospido et al. 2004).For this study, LCI has been generated from primary data by several onsite visits to the Central Park WWTP. The energy utilisation of the different processes is calculated by using the rating of the electrical equipment and hours of operation. The electricity used in WWTP is from coal-fired thermal power plants. For all electricity requirements, the Indian electricity grid mix data set was used. Process wise inventory data for average wastewater influent per month is shown in Table 2. For background process data (Electricity Production, Chemical Production, i.e., Polyelectrolyte, Bleaching Powder), was taken fromGaBi Professional version database.

Table 2. Summary of Life Cycle Inventory for inputs and outputs of Central Park WWTP (Values are according to functional unit- average wastewater inflow per month (m³/month))

Pre Treatment Process
Process Input	Unit	Amount
The oil used in hand-operated Valve	kg/month	0.4539
Process Output	Unit	Amount
Waste Water (Outflow)	m^3/month	7697.37
Grit Chamber Process
Process- Input	Unit	Amount
Waste Water (Pretreatment Outflow)	m^3/month	7697.37
Electricity	kWh/month	540
Oil used in pump	kg/month	0.9078
Grease	kg/month	0.51
Process Output	Unit	Amount
Waste Water (Grit Outflow)	m^3/month	7693.68
Sludge -GC	m^3/month	3.69
Sequencing Batch Reactor-1 &2 Process
Process- Input	Unit	Amount
Waste Water (Grit outflow)	m^3/month	7693.68
Waste Water recovered	m^3/month	12.7131
Electricity	kWh/month	16,353
Oil	kg/month	2.9904
Grease	kg/month	4.02
Process Output	Unit	Amount
Partially Treated Water (SBR effluent)	m^3/month	7659.2631
Sludge-SBR	m^3/month	47.13
Nitrogen	kg/month	270.18
Phosphorous	kg/month	60.81
Sulphur	kg/month	4541.46
Sludge Handling Process
Process Input	Unit	Amount
Sludge-GC	m^3/month	3.69
Sludge-SBR	m^3/month	47.13
Wastewater (effluent of centrifuge)	m^3/month	11.79
Electricity	kWh/month	5.55
Process Output	Unit	Amount
Dried Sludge	kg/month	105
Wastewater (Inflow to SBR)	m^3/month	12.7131
Sludge for further Treatment	m^3/month	47.13
Centrifuge Process
Process Output	Unit	Amount
Sludge for further Treatment	m^3/month	47.13
Electricity	kWh/month	87.3
Polyelectrolyte	kg/month	15
freshwater for process	lit/month	2010
Oil	kg/month	0.4539
Grease	kg/month	1.02
Process Output	Unit	Amount
Dried Sludge	kg/month	450
Waste Water (Inflow to sludge handling)	m^3/month	11.79
Chemical Treatment Process
Process Output	Unit	Amount
Partially Treated Water (SBR effluent)	m^3/month	7659.2631
Bleaching Powder	kg/month	30
freshwater for process	L/month	30,000
Process Output	Unit	Amount
Treated Water	m^3/month	7689.2631
Water Storage and Supply
Process Output	Unit	Amount
Treated Water	m^3/month	7689.2631
Electricity	kWh/month	2250
Process Output	Unit	Amount
Treated Water	m^3/month	7689.2631

2.2.3. Life cycle impact assessment (LCIA)

This phase of LCA identifies and evaluates the amount and significance of the potential environmental impacts arising from the LCI. According to ISO 14044 (2006b), standard LCIA involves mandatory elements, namely, selection of Impact categories, classification, and characterisation, as well as optional elements, namely, normalisation, grouping, and weighting. This study does not include optional elements because of the lack of availability of LCA literature in the Indian context (Kamble, Singh, and Kharat 2018). Potential environmental impacts were calculated using standard impact assessment methods of GaBi software. For this study, CML 2001 (January-2016) impact assessment method is used. Centre of Environmental Science (CML), University of Leiden, Netherland, developed CML 2001 methodology. CML 2001 calculates a score for each impact category separately and thus helps in identifying the potential impacts of each category. Following impact categories are considered as per ISO 14044 (2006b): Abiotic Depletion (ADP fossil), Acidification Potential (AP), Eutrophication Potential (EP), Freshwater Aquatic Ecotoxicity Potential (FAETP), Global Warming Potential (GWP), Human Toxicity Potential (HTP), Marine Aquatic Ecotoxicity Potential (MAETP), Ozone Layer Depletion Potential (ODP), Photochemical Ozone Creation Potential (POCP), TerrestrialEcotoxicity Potential (TETP). A detailed description of the different impact categories chosen and their reference in previous literature are shown in Table 3.

Table 3. Description of impact categories and their reference in previous literature

Impact Category	Unit	Definition	References
Abiotic Depletion (ADP fossil)	MJ	ADP fossil implies a reduction of the amount of fossil energy such as metal-containing ores, crude oil, and mineral raw materials	Suh and Rousseaux 2002;Hospido et al. 2004; Lundin et al. 2004; Hospido et al. 2005; Hospido, Moreira, and Feijoo 2008; Renou et al. 2008; Gallego et al. 2008;Pasqualino et al. 2009; Lopsik 2013; Li et al. 2013; Kalbar, Karmakar, and Asolekar 2014; Garfi, Flores, and Ferrer 2017; Raghuvanshi et al. 2017; Shiu, Lee, and Chiueh 2017; Polruang, Sirivithayapakorn, and Talang 2018; Cartes et al., 2018; Kamble, Singh, and Kharat 2018.
Acidification Potential (AP)	kg SO2 equivalent	The emissions that lower the PH value, i.e. increase the acidity of water and soils.	Suh and Rousseaux 2002;Hospido et al. 2004; Lundin et al. 2004; Hospido et al. 2005; Hospido, Moreira, and Feijoo 2008; Renou et al. 2008; Gallego et al. 2008;Wenzel et al. 2008; Hong et al. 2009;Pasqualino et al. 2009; Lopsik 2013; Li et al. 2013; Kalbar, Karmakar, and Asolekar 2014; Garfi, Flores, and Ferrer 2017; Shiu, Lee, and Chiueh 2017; Polruang, Sirivithayapakorn, and Talang 2018;Crates et al., 2018; Kamble, Singh, and Kharat 2018.
Eutrophication Potential (EP)	kg Phosphate equivalent	Eutrophication implies the enrichment of nutrients in aquatic or terrestrial bodies.	Suh and Rousseaux 2002;Hospido et al. 2004; Lundin et al. 2004; Lundie, Peters, and Beavis 2004; Hospido et al. 2005; Hospido, Moreira, and Feijoo 2008; Renou et al. 2008; Gallego et al. 2008;Wenzel et al. 2008; Pasqualino et al. 2009; Rodriguez-Garcia et al. 2011; Kalbar, Karmakar, and Asolekar 2012; Lopsik 2013; Li et al. 2013; Kalbar, Karmakar, and Asolekar 2014; Garfi, Flores, and Ferrer 2017;Raghuvanshi et al. 2017; Shiu, Lee, and Chiueh 2017; Polruang, Sirivithayapakorn, and Talang 2018;Crates et al., 2018; Kamble, Singh, and Kharat 2018.
Freshwater Aquatic Ecotoxicity Potential (FAETP)	kg DCB equivalent	FAETP refers to the impact on freshwater ecosystems, due to emissions of toxic substances to air, water, and soil.	Suh and Rousseaux 2002; Lundie, Peters, and Beavis 2004; Hospido, Moreira, and Feijoo 2008; Wenzel et al. 2008; Pasqualino et al. 2009;Lopsik 2013; Kalbar, Karmakar, and Asolekar 2014; Raghuvanshi et al. 2017; Shiu, Lee, and Chiueh 2017; Kamble, Singh, and Kharat 2018.
Global Warming Potential (GWP)	kg CO2 equivalent	Global warming is caused due to an increase in the concentration of greenhouse gases in the air leading to an increase in average surface temperature.	Suh and Rousseaux 2002;Hospido et al. 2004; Lundie, Peters, and Beavis 2004; Lundin et al. 2004; Hospido et al. 2005; Hospido, Moreira, and Feijoo 2008; Gallego et al. 2008; Wenzel et al. 2008; Hong et al. 2009; Pasqualino et al. 2009;Rodriguez-Garcia et al. 2011; Kalbar, Karmakar, and Asolekar 2012; Lopsik 2013; Li et al. 2013; Kalbar, Karmakar, and Asolekar 2014; Garfi, Flores, and Ferrer 2017;Raghuvanshi et al. 2017; Shiu, Lee, and Chiueh 2017; Crates et al., 2018; Polruang, Sirivithayapakorn, and Talang 2018; Kamble, Singh, and Kharat 2018.
Human Toxicity Potential (HTP)	kg DCB equivalent	HTP calculates the negative impact of toxic substances on human health.	Suh and Rousseaux 2002;Hospido et al. 2004; Lundie, Peters, and Beavis 2004; Hospido et al. 2005; Hospido, Moreira, and Feijoo 2008; Renou et al. 2008; Hong et al. 2009; Lopsik 2013; Kalbar, Karmakar, and Asolekar 2014; Shiu, Lee, and Chiueh 2017; Kamble, Singh, and Kharat 2018.
Marine Aquatic Ecotoxicity Potential (MAETP)	kg DCB equivalent	MAETP refers to the impact on marine ecosystems due to the emission of toxic substances.	Suh and Rousseaux 2002; Lundie, Peters, and Beavis 2004; Hospido, Moreira, and Feijoo 2008; Pasqualino et al. 2009; Lopsik 2013; Kalbar, Karmakar, and Asolekar 2014; Shiu, Lee, and Chiueh 2017; Kamble, Singh, and Kharat 2018.
Ozone Layer Depletion Potential (ODP)	kg CFC11 equivalent	ODP refers to the depletion of the stratospheric ozone layer due to the emission of fluorine-chlorine-hydrocarbons (CFCs) and the nitrogen oxides (NOX)	Hospido et al. 2004; Hospido et al. 2005; Hospido, Moreira, and Feijoo 2008; Gallego et al. 2008; Pasqualino et al. 2009; Lopsik 2013; Garfi, Flores, and Ferrer 2017; Raghuvanshi et al. 2017; Shiu, Lee, and Chiueh 2017; Kamble, Singh, and Kharat 2018.
Photochemical Ozone Creation Potential (POCP)	kg Ethane equivalent	POCP refers to the formation of ozone in the troposphere (Summer smog)	Suh and Rousseaux 2002; Hospido et al. 2004; Lundie, Peters, and Beavis 2004; Hospido et al. 2005; Hospido, Moreira, and Feijoo 2008; Gallego et al. 2008; Pasqualino et al. 2009; Lopsik 2013; Li et al. 2013; Shiu, Lee, and Chiueh 2017; Polruang, Sirivithayapakorn, and Talang 2018; Kamble, Singh, and Kharat 2018.
Terrestrial Ecotoxicity Potential (TETP)	kg DCB equivalent	TETP refers to the impact on marine ecosystems due to the emission of toxic substances.	Suh and Rousseaux 2002; Hospido et al. 2004; Lundie, Peters, and Beavis 2004; Hospido et al. 2005; Hospido, Moreira, and Feijoo 2008; Gallego et al. 2008; Pasqualino et al. 2009; Lopsik 2013; Li et al. 2013; Kalbar, Karmakar, and Asolekar 2014; Raghuvanshi et al. 2017; Kamble, Singh, and Kharat 2018.

3. Result and discussion

Figure 3 shows the environmental impacts associated with each process in Central Park WWTP. The SBR process dominated in all impact categories considered, while pretreatment and chemical treatment processes have almost negligible impacts on the environment. The result of this study is based on actual data collected from the Central Park WWTP. The life cycle impact assessment of WWTP is shown in Table 4. As the data for the foreground processes, and the background processes are collected by the actual observation at the site, the results of this study should be considered as reasonable starting point for future confirmation. This manuscript contribute towards the enhancement of LCA databases in the Indian context. The study depicts that electricity consumption is a dominant contributor to environmental impacts. The central park WWTP currently consumes about 2.5 kWh of electricity for treating of 1 m³ of wastewater. Electricity consumption value for treating the same amount of wastewater is much lower in the previous studies. Ideally, the consumption range of electricity should be 0.58–2.11 kWh/m³ (Shiu, Lee, and Chiueh 2017). This higher amount of consumption is due to inefficient utilisation of blowers, pumps in the gritting chamber, and the supply of treated water with the help of a pump from the water storage tank. Electricity consumption can be reduced by efficient utilisation of blowers, pump in the gritting chamber, and by adapting the gravity flow technique for the supply of treated water from the water storage tank.

Figure 3. Environmental impacts of different processes in central park WWTP. Values are corresponding to the functional unit: 7697.37 m³of wastewater; ADP fossil: Abiotic Depletion of fossil, AP: Acidification Potential, EP: Eutrophication Potential, FAETP: Freshwater Aquatic Ecotoxicity Potential, GWP: Global Warming Potential, HTP: Human Toxicity Potential, MAETP: Marine Aquatic Ecotoxicity Potential, ODP: Ozone Layer Depletion Potential, POCP: Photochemical Ozone Creation Potential, TETP: TerrestrialEcotoxicity Potential

Figure 3. (countinued)

Table 4. LCIA result of central park WWTP

Impact Category	Unit	Central Park WWTP	Centrifuge Process	Chemical Treatment process	Grit Chamber Process	Pre-Treatment Process	Sequencing Batch Reactor Process −1 & 2	Sludge Handling Process	Water Storage & Supply Tank
Abiotic Depletion (ADP fossil)	MJ	2.42E+05	1.40E+03	147	6.83E+03	15.2	2.06E+05	69.7	2.82E+04
Acidification Potential (AP)	kg SO2 equivalent	297	1.4	0.019	8.34	0.000776	252	0.0856	34.7
Eutrophication Potential (EP)	kg Phosphate equivalent	249	0.066	0.00743	0.353	0.000142	197	0.00362	51.9
Freshwater Aquatic Ecotoxicity Potential(FAETP)	kg DCB equivalent	56.9	0.307	0.0542	1.61	0.00475	48.3	0.0164	6.63
Global Warming Potential (GWP)	kg CO2 equivalent	2.39E+04	132	39.9	670	0.473	2.03E+04	6.87	2.79E+03
Human Toxicity Potential (HTP)	kg DCB equivalent	7.85E+03	36.9	0.784	221	0.0364	6.68E+03	2.27	918
Marine Aquatic Ecotoxicity Potential(MAETP)	kg DCB equivalent	3.40E+07	1.56E+05	1.62E+03	9.55E+05	28.5	2.89E+07	9.82E+03	3.98E+06
Ozone Layer Depletion Potential (ODP)	kg CFC11 equivalent	4.24E-09	3.89E-11	3.78E-12	1.19E-10	2.43E-13	3.59E-09	1.22E-12	4.93E-10
Photochemical Ozone Creation Potential (POCP)	kg Ethane equivalent	13.8	0.0672	0.00129	0.388	0.000269	11.7	0.00398	1.61
Terrestrial Ecotoxicity Potential (TETP)	kg DCB equivalent	64.9	0.31	0.0921	1.82	0.000225	55.1	0.0187	7.58

The detailed value of each impact categories considered for this study is shown in the Table 4. Previous studies on WWTPs demonstrated that electricity required for the operation of the plant is the highest contributor in all the environmental impact categories (Gallego et al. 2008). It can be observed that the sequencing batch reactor process1 and 2 is the highest contributor for all the impact categories considered. This is because ofthe sequencing batch reactor process 1 and 2 consumes the highest amount of electricity among all the processes. The details about the contributor for each impact category are explained below.

3.1. ADP fossil

Consumption of coal is the main contributor to the ADP of fossil (Kamble, Singh, and Kharat 2018). Total ADP depletion for central park WWTP is 2.42E+05 MJ. Out of that, SBR process contributes 2.06E+05 MJ, i.e., about 85% of total ADP fossil depletion. This is because the SBR process consumes the highest amount of electricity, and in India, electricity is mainly produced by coal-fired power plants. The pretreatment process is the least contributor to the ADP of fossil.

3.2. AP

Acidification results due to the emission of SO_X and NO_X. These emissions are abundant in the production of electricity due to the burning of coal. Again, due to the highest electricity consumption in the SBR process, it contributes about 85% of the total plant.

3.3. EP

Eutrophication means nutrient enrichment. The main nutrients that are responsible for eutrophication are nitrogen and phosphorous (Kamble, Singh, and Kharat 2018). SBR process has a contribution of about 79% of the total plant towards eutrophication. This high percentage is because of the large amount of nitrogen and phosphorous are getting removed in the SBR process to meet the required effluent standard of treated wastewater. The pretreatment process has almost negligible eutrophication potential.

3.4. Toxicity potentials (FAETP, HTP, MAETP, and TETP)

Ecotoxicity potential is due to the content of nutrients in the effluent (Lopsik 2013).Discharge of nutrients, Phosphorous and Nitrogen are the largest contributors to ecotoxicity (Shiu, Lee, and Chiueh 2017).Further sludge contains heavy metals that contribute to ecotoxicity (Kamble, Singh, and Kharat 2018). It can be seen that the SBR process is the main contributor for all ecotoxicity categories considered (FAETP, HTP, MAETP, and TETP). The water storage and supply tank process follows the SBR process in ecotoxicity categories. As treated water is used for watering purpose in the Central Park, heavy metals are released by treated water, which contributes to ecotoxicity.

3.5. GWP

GWP is a result of coal combustion during electricity production (Kalbar, Karmakar, and Asolekar 2014). Total GWP for central park WWTP is found out to be 2.39E+04 kg CO₂ equivalent. Out of this SBR process contributes about 85% of total GWP. Water storage and supply follows the SBR process and contributes about 12% of total GWP. This result is because of SBR and water storage, the supply process consumes the highest amount of electricity, and the pretreatment process does not consume any electricity within central park WWTP. Further, GWP for the pretreatment process is found to be negligible, i.e. less than 1% of the total impact.

3.6. ODP

The emission of gases that reduce the ozone layer is marginal. The ODP for central park WWTP is meagre, i.e. about 4.24E-09 kg CFC11 equivalent.

3.7. POCP

POCP impact categories have relevance to the water industry (Lundie, Peters, and Beavis 2004). According to Kamble, Singh, and Kharat (2018), about 0.000185 kg ethane equivalent are emitted from the SBR technology plant for a functional unit of 1 m³ of treated water. The values for central park WWTP are higher, i.e. about 0.0018 kg ethane equivalent for the same functional unit.

The study identified emissions associated with electricity production required to operate the WWTPs, chemical usage, emissions to water from treated effluent, and heavy metal emissions from waste sludge applied to land are the major contributors for overall environmental impacts (Kamble, Singh, and Kharat 2018).

4. Conclusion and future scope

Though previous LCA studies on WWTPs (Kamble, Singh, and Kharat 2018; Kalbar, Karmakar, and Asolekar 2014) have been conducted in India, their system boundaries are different from this study, and they have not considered the impact of the production of chemical due unavailability of LCI in the Indian context. In this study, the impact of chemical products on the environment using GaBi 8.0 professional software is considered. These results are slightly higher than that of the Kamble, Singh, and Kharat (2018). The Central Park WWTP in Jaipur, India, is currently powered by an electric grid mix from India, which is generally produced from coal-fired plants. Production of electricity by coal-fired plants have a very high environmental impact. So the process which consumes a higher amount of electricity has higher environmental impacts and vice versa. From Table 4, it is clear that sequencing batch reactor process 1 and 2 have the highest environmental impacts as this process consumes the highest amount of electricity. The pretreatment process has the lowest environmental impacts as this process does not consume any electricity. The results of the study show that though the environmental impacts associated with the Central Park WWTP are high, it produces good reusable quality of effluent. In areas where water is scarce, governments should promote reusing wastewater by providing additional treatment under safe conditions as much as possible with advanced WWTP.WWTPs should use renewable sources of energy such as solar power and wind power as the production of energy by the source proposed will reduce the environmental impacts significantly. More Life cycle inventories and computerised datasets needed to be developed in the Indian context to capture the potential environmental impacts and to improve environmental decision-making. This study considered the environmental impacts associated with only the operation phase of the WWTP. Therefore, it is recommended that further LCAs studies should consider the sludge management process and demolition phase.

Additional information

Notes on contributors

Hitesh Mishra

Mr. Hitesh Mishra received his Master’s degree in Industrial Engineering from Malaviya National Institute of Technology Jaipur, India in 2018. He was graduated in Manufacturing Engineering from Central Institute Plastics Engineering and Technology, Bhubaneswar, India in 2015. His research interests include life cycle assessment and logistics. 

Gaurav Gaurav

Mr. Gaurav Gaurav pursing a Ph.D. degree in the Department of Mechanical Engineering from Malaviya National Institute of Technology Jaipur, India. He obtained a Master’s degree in Manufacturing System Engineering, from the Malaviya National Institute of Technology Jaipur, India, in 2011. He was graduated in Mechanical Engineering from Kurukshetra University Kurukshetra, Haryana, India, in 2008. She has published 05 research articles in leading SCI and Scopus Index journals. His research interests include sustainable machining and life cycle assessment.

Chandni Khandelwal

Dr. Chandni Khandelwal received his Ph.D. (Management Studies) and MBA (Marketing & Finance) from Malaviya National Institute of Technology Jaipur, India in 2020 and 2014 respectively. She received his Bachelor’s degree in Electronics and Communication Engineering from Rajasthan Technical University, Kota, India in 2012. She has published 07 research articles in leading journals, international conference proceedings and books. Her research interests include finance and marketing, financial management, entrepreneurship systems and sustainability.

Govind Sharan Dangayach

Dr. Govind Sharan Dangayach is a Professor in the Department of Mechanical Engineering at Malaviya National Institute of Technology (MNIT), Jaipur. He was graduated in Mechanical Engineering from M.B.M. Engineering College Jodhpur in the year 1985. He obtained a Master’s degree in Production Engineering from Indian Institute of Technology, Delhi. He earned his Doctorate in Industrial Engineering also at Indian Institute of Technology, Delhi. He has published 250 research papers in various International and National Journals. He is a Reviewer of Twenty-Nine International Journals. He has 34 years of Teaching and Industrial Experience. He is a Life member of various International & National professional Societies. He has guided 27 Ph.D. & 60 Master’s thesis.

P. N. Rao

Dr. P. N. Rao currently Manufacturing Engineering Technology Professor in The University of Northern Iowa, Cedar Falls, USA in the Department of Technology. His active areas of teaching and research are Manufacturing Engineering and Design Engineering. He has received the “Distinguished Scholar” award from University of Northern Iowa for the year 2017-2018. He has authored a number of textbooks on Manufacturing Technology, CAD/CAM and Metal Casting, published by McGraw Hill India and American Foundry Society. He has wide interaction with the industry through the process of consultancy work and conducting continuing education programs on various aspects related to modern manufacturing. He has also published over 260 research papers in international conferences and journals. He is on the editorial boards of International Journal of Precision Technology, International Journal of Mechanical Engineering, Efficient Manufacturing, International Journal on Global Research in Science and Technology, and West Indian Journal of Engineering.