Principal of environmental life cycle assessment for medical waste during COVID-19 outbreak to support sustainable development goals.

Disposal of medical waste (MW) must be considered as a vital need to prevent the spread of pandemics during Coronavirus disease of the pandemic in 2019 (COVID-19) outbreak in the globe. In addition, many concerns have been raised due to the significant increase in the generation of MW in recent years. A structured evaluation is required as a framework for the quantifying of potential environmental impacts of the disposal of MW which ultimately leads to the realization of sustainable development goals (SDG). Life cycle assessment (LCA) is considered as a practical approach to examine environmental impacts of any potential processes during all stages of a product's life, including material mining, manufacturing, and delivery. As a result, LCA is known as a suitable method for evaluating environmental impacts for the disposal of MW. In this research, existing scenarios for MW with a unique approach to emergency scenarios for the management of COVID-19 medical waste (CMW) are investigated. In the next step, LCA and its stages are defined comprehensively with the CMW management approach. Moreover, ReCiPe2016 is the most up-to-date method for computing environmental damages in LCA. Then the application of this method for defined scenarios of CMW is examined, and interpretation of results is explained regarding some examples. In the last step, the process of selecting the best environmental-friendly scenario is illustrated by applying weighting analysis. Finally, it can be concluded that LCA can be considered as an effective method to evaluate the environmental burden of CMW management scenarios in present critical conditions of the world to support SDG.

Introduction

Coronavirus disease of the pandemic in 2019 (COVID-19), a contagious disease with human to human transmission, has had an extraordinary dangerous impact on universal healthcare systems, with a significant influence on human beings. It was initially recognized in December 2019 in Wuhan, located in China (Pakravan-Charvadeh et al., 2021). Since the outbreak of COVID-19, a large amount of medical waste (MW) has been made around the globe. MW manufactured in COVID-19 pandemic (CMW) can be more infectious than typical MW, and its amount is considerably more than the disposal capacity existed in districts that have a significant epidemic. Safe MW disposal is vital protection for preventing the epidemic, and controlling is one of the most critical processes for being successful in overcoming this difficulty (Ma et al., 2020).Today the disposal of MW is initially applied around the globe with the use of 3 primary methods consisting of pyrolysis, chemical disinfection, and steam sterilization technologies and each method has several sub-methods (Windfeld and Brooks, 2015). Each of these methods has its technical advantages and disadvantages, but the important point is their destructive effects on the environment. These effects in the COVID-19 outbreaks can have more devastating effects on public health and pose a significant threat to the quality of global health.

Life cycle assessment (LCA) is recognized as an appropriate method with efficiency for analyzing environmental impacts of any activities, processes, or products in the entire life cycle for designing in an ecologically way, having technology and product development, and policy-making (ISO, 2006).

LCA has been applied for accessing the disposal of MW scenario outlines (Aung et al., 2019). By comparing LCA of burning and depolluting with steam autoclave and waste dump MW regions, consequently, it was indicated that the process of incineration using the recovery of energy was more practical compared with sterilization by steam autoclave (Zhao et al., 2009). According to data collected in the laboratory, three MW disposal scenario outlines (including use of microwave, autoclave, and lime) and then landfilling were assessed. it was verified that the disposal of microwave has the least environmental impact (Soares et al., 2013). After analyzing four disposal systems of MW in Korea (including sterilization with steam, incineration, microwave disinfection, and incineration with recovering of heat), results showed that incinerated waste using the recovery of heat was the most appropriate scenario outline for the removal (Koo and Jeong, 2015). Hong et al. (2018) examined the economic effects, and some influences on the environment for dumping of MW with steam sterilization, chemical disinfection technologies and pyrolysis, and realized that sterilization with steam contained the most influences on the environment based on its considerable energy consumption. The impact of the life cycle for many different products made of plastic such as self-protection and health maintenance materials in the period of COVID-19 crisis outbreak was examined. Although the writing mainly concentrated on concise prior researches and presenting forthcoming works, administrations along with recommendations about environmental policies as well as the management of plastic waste can use them for sustainable management of CMW (Klemeš et al., 2020). All the studies concentrated on applying LCA to assess usual disposal scenario outlines based on normal MW production. Nowadays, the integrated facilities of disposal are usually on a large scale with many problems on moves and installation, In addition to not being flexible enough for adoption to the specific dumping requirements for enormous extremely infected MW made immediately in the period of COVID-19 pandemic.

CWM is one of the cross-cutting issues which can have impacts on different parts of sustainable development for three sustainability sciences, including economy, society, and ecology. The mentioned sciences contain hygiene, community health, access to suitable occupation, life quality, terrestrial, aquatic ecosystems, and also the sustainability in the usage of natural resources, which is calculated by environmental LCA. Therefore, more than 12 SDG out of 17 of them in the 2030 program for Sustainable Development have relevant goals and complete connection with CWM, which were declared by 193 united members in September 2015 (Rodić and Wilson, 2017). Lack of having a high- level SDG can be a threat to reducing CWM ‘visibility’ as a vital policy. However, The United Nations Environment Programe (UNEP)’s recent Global Waste Management Outlook (GWMO) followed the opposite different of opinion, which the cross-cutting nature of CWM and its effect on not only one but also on 12 SDG must mainly focus on the significance and rise in the priority for the policy of CWM (The United Nations Environment Programme (UNEP), 2020).

Accordingly, this study emphasizes on the happening of the COVID-19 pandemic in controlling, removal, and also treatments of CMW. Furthermore, the present work focuses on providing environmental LCA for the current problems and challenges that can be solved in COVID-19 conditions, particularly on the MW processes. The objectives of all steps have been met to supply SDG. Moreover, computation methods with examples are provided for a better understanding. The whole CMW procedures and their outlook are displayed in Fig. 1 .

Fig. 1

Overview of CMW management methods.

CMW generation and challenges

Large amounts of MWs (mainly facemasks, mittens, clothes, needles, sharp-edged materials, etc.) are made in hospitals. These materials have been chiefly known as dangerous elements with carrying agents that cause infection (World Health Organization, 2020). Their inappropriate handling would result in contaminating common municipal waste with the virus and also a rise in the probability of its transmission (European Center for Disease Prevention and Control, 2020). Efficient management of MW has been increased in the COVID-19 crisis by taking specific measurements such as appropriate identification, accumulation, separation, storage, transit, treatment, and ultimate disposal (Ilyas et al., 2020). All around the world, the governments have been educated regarding the treatment of dangerous MW as necessary and also significant issues which can decrease its long-term impacts on the healthiness of people as well as natural surroundings. Hospitals and healthcare centers are not the only roots for infected waste. Some human beings who have mild symptoms and even symptomless people may also generate garbage full of viruses (mainly can be made from facemasks, mittens, and used tissue). It is evaluated that viruses may exist in polymers for about six to eight hours and metals for about five to six hours. Besides, in contaminated personal and protective equipment (PPE), virus existence may continue until seven days and, consequently, the disposal of this garbage can contaminate some of the sanitation laborers who are related to managing waste (Chin et al., 2020). The condition has remained unfit in countries that are in the developing process for operators participating in managing CMW due to lack of being sufficiently equipped with PPE. Therefore, many people, including casual waste collectors, might get infected from waste full of viruses in developing countries. Some vital steps should be followed to control the pandemic situation with proper use of hospitals as well as secure CMW dumping, which can also prevent the spreading (Cutler, 2020).

CMW, including mittens, masks, aprons, and any other materials, are mainly made of polymers. They cannot be recycled easily due to a trace of infectious residues that they might have (International Solid Waste Association, 2020). This can significantly affect the skillful workers in the period of handling, collecting those waste, or at the waste treatment facilities. Because of the requirements for workers' safety, some specific rules have been introduced in current conditions such as regular changes as well as cleaning PPE, mittens and professional clothes, and frequent hand washing. Some of the laborers working in recycling sections are in danger in a lot of countries with different development. Many measures have been taken by governments, such as announcing absolute isolation, social distancing among people in society, voluntary quarantine for people who have infectious agents, and obligatory use of protectives to manage SARS-CoV2 virus transmission. As a result, the condition completely changed the generation of the waste and management plans. Commonly, garbage made was controlled by sanitation laborers, and after that they were carried to waste management centers before the COVID-19. As COVID-19 outbreak occurred, the wastes generated were known dangerous with the risk of having infectious agents, and they needed to be separated by handling, treatment, and disposal facilities (Dharmaraj et al., 2021). Inappropriate disposal of CMW may render it mixed up with garbage which has the danger of transmitting the virus to sanitary handlers and the public. Hence, an unconnected waste management system is an urgent need for secure handling of CMW. There is a requirement for decontaminating technologies or treatments to eradicate infectious agents which can be transported by wastes (The United Nations Environment Programme (UNEP), 2020). An appropriate cycle procedure should be performed at the time of handling CMW. It has been advised by the government to sanitary workers to collect medical and other dangerous waste without risk and take them to treatment facility centers during COVID-19 time. It, consequently, may reduce the negative effects of the infectious agents which can be carried by CMW on the health of the public and well as the environment (Sharma et al., 2020).

Because of the COVID-19 outbreak and its spread among many human beings, there has been a considerable need for using some accessories, including masks, mittens, gels for sanitizing hands, sanitizer sprays, to decrease the probability of the spread of the virus (Barcelo, 2020). It is not accurate to consider medical centers or hospitals as the only roots of infectious waste. Therefore, the virus carriers might be people without any symptoms or those with mild symptoms and facemasks, mittens, tissue papers thrown away by them. Furthermore, it is possible for the virus to exist for more times or days in metals, plastics, and cardboard boxes. These items in the dumping time can be harmful to sanitary workers who are engaged in the collecting of the wastage. The situation will get worse for sanitary works in some underdeveloped or developing countries due to the lack of appropriate equipment or suitable wearing types of PPE at the time of handling CMW. Generating a considerable wastage has made some difficulties for waste health centers and hospitals to manage this situation in COVID- 19 pandemic time (Singh et al., 2020). The management of CMW is known as one significant obstacle in different parts of the process, including the collection, carrying, medication as well as disposal in developing countries. Developing countries have their barriers such as low technology, insufficient scientific knowledge base, and imperfect economic background (Bourouiba, 2020). All factors mentioned above have been increased in the pandemic time, and they have made the countries focus on providing sufficient consideration of waste management procedures as well as their health care centers for CMW.

Chemical disinfection

This method is known as the chemical disinfection technique, which is comprehensively utilized to pre-treat CMW with a practical use of prior mechanical shredding. An absolute and efficient filter is used to protect against the formation of aerosol within the shredding process while exhausting air is passing. Keeping in an unopened system and/or under negative pressure for a specific time, the squashed waste mass would be able to mix better with chemical disinfectants. Natural materials deteriorate, and infectious germs are disabled or destroyed during this process. Utilizing little efficient concentration, strong performance, quick operation, and extensive decontamination range without any hazards remained are known as some of the important benefits of using chemical disinfectants since they successfully destroy germs as well as deactivate spores of bacteria (Wang et al., 2020). CMW chemical treatment can be categorized into chlorine- as well as nonchlorine-based systems. ClO2 or NaOCl is utilized as a sterilizer substance, and the chlorine electronegativity supports the process for oxidizing bonds of peptide and proteins denaturing, which leads to penetrating layers of a cell even in normal pH in a chlorine-based treatment system. NaOCl is known as the primary chemical disinfectant that discharges dioxins, chlorinated aromatic combination, and halo acetic acid. The application of ClO2, known as a powerful destructive, is then made. Yet because of its unsteady character, it must be utilized on-site. Besides, this is modified to become less poisonous with salt products that are not responsive to ammonia/alcohol. H2O2 is often utilized as the sanitizer substance in a treatment with a non‑chlorine-based approach. This can be used for oxidizing, and denaturing proteins as well as lipids and, as a result, it may cause derangement of the membrane because of edema of sodden H+-ions. A chlorinated system has some advantages, such as high reactiveness and lack of toxicity in its application. In addition, isopropanol (>70%), ethyl alcohol (>75%) formaldehyde (>0.7%), and povidone‑iodine (>0.23%) are some of chemical solutions that can deactivate SARS-CoV-2 (Duarte and Santana, 2020).

Physical disinfection techniques

Medium heat microwave

This operates starting from 177 °C up to 540 °C, which contains reverse polymerization using microwaves with great energy beneath a motionless atmosphere, for decomposing organic materials. Electromagnetic wave absorption (including wavelengths of 1 mm up to 1 m in frequencies of hundreds up to three thousand megahertz), as a result of vibration and rubbing of molecules, raises the internal energy. On the other hand, nitrogen creates an inert environment, preventing ignition using oxygen to represent the high temperature sterilization. The main advantages of the microwave technique are known as restricted heat loss, relatively lower energy and operation temperature, and fewer environmental problems, as well as not having any infection remained at the end of the process for disinfection. Particularly designed microwave devices under strict controlling processes can significantly deactivate SARS-CoV-2. This disinfection technique can reach the exponential worth of deteriorating viruses that are hydrophilic based on a report published by the Ministry of Ecology and Environment in china (Wang et al., 2020). It has also been recognized as beneficial in the on-site disinfection of CMW. The on-site disinfection prevents dangers that may pose by CMW transportation as well as saving some time (Resilient Environmental Solutions, 2020). Based on disinfection to CMW, the microwave technique is employed with autoclaving works where sterilization is possible with steam (in heat range starting from 95 up to 180 °C).

Low heat autoclave

It is practical in temperatures starting from 95 °C up to 180 °C, and they are mainly contained in autoclaves. For sterilizing agents, steam is used in the autoclave. For decreasing the autoclaved garbage in mass, there is a must for being shredded. A high-efficiency particulate absolute (HEPA) strainer decoys the infection and also allows air inside the autoclave to pass through it and be disinfected before releasing into the environment. Because chemical and dangerous waste may release toxic matters, it is impossible to use the autoclave technique. However, most CMW can be sterilized using this technique. Indeed beds of hospitals, heat resistant containers, and other massive waste cannot be disinfected using the autoclave technique (Zhang et al., 2016).

Incineration

This has been commonly used for municipal solid waste (MSW) disposal due to its ability to enable large cutting in the bulk of garbage, and energy recovery. Therefore, incineration of MSW has been appreciated in various countries without unlimited landfill space (Yang et al., 2012). Moreover, soil coverage can be available because of ash taken from the incineration process. During incineration, all pathogens are burned to death, and easily spoilt organics, which make harmful gases, are totally oxidized (Li et al., 2015). Site selection is much easier because an incineration power plant requires a smaller area compared with landfill sites (Nabavi-Pelesaraei et al., 2017). However, MW incineration discloses ash into the atmosphere, which contains a considerable amount of metal substances with heavy toxicity, including cadmium, chromium, lead, mercury, zinc, copper, and highly toxic substances such as dioxin, which leads to water, soil, and air pollution as well as acid rain (Shim et al., 2003).

For the incineration of CMW, there are two main types of incinerators, namely rotary kiln incinerator and plasma incineration, which are described below.

Rotary kiln incinerator

It has been extensively employed for treating CMW. It is equipped with a post-combustion chamber as well as a rotating oven. Rotary kiln not only supports waste mixing but also presents effective incineration. The kiln rotates about 2 to 5 times per minute, and it is loaded with wastes on the top (Ma et al., 2011). The temperature of incineration can start from 1200 up to 1600 °C, which can effectively damage dangerous matters which are transported by CMW. All gases in the kiln have to pass through the combustion chamber, where organic matters are ignited and resided for 2 s. An accumulation of the remained ashes occurs in the bottom. The capacities of incineration start from 0.5 up to 3 tons per hour. The specified ones that are known as not non-toxic or safe wastes such as CMW should be managed individually as well as being located in a protected environment. Incinerator of rotary kiln is a sufficient technology to handle cytotoxic wastes, infectious wastes, pharmaceutical and also chemical wastes. However, it is not enough for pressurized containers (can get exploded in the time of the process and can have damage to the incinerator), wastes of radioactive (treatment can spread radiation and cannot affect its properties), and content wastes which contain high heavy metal (emission of some heavy metals that are toxic into the atmosphere during the incineration operation).

Due to the risk for the production of exhaust gases as well as ashes during CMW incineration, some harmful materials may still be transported and, therefore, they must be treated again. Typically, the costs of operation and the equipment are not low because of its high energy consumption. Also, the by-products which may be formed are highly corrosive, which can cause the kiln an often need for getting replaced or repaired (Chen and Yang, 2016).

Plasma incineration

The incineration of plasma is known as one of the effective technologies, which are used for an efficient CMW treatment. Electric power is utilized for the production of plasma, and further to 2710 °C can be made during this operation, which makes a considerable amount of waste to divide them immediately into tiny molecules. There is no intermediate product, and all formed gases are purified and released into the atmosphere. Plasma incineration technology presents higher efficiency due to its higher energy generation, and less ash mass production, compared with other techniques (Messerle et al., 2018). There are also some other disinfection technologies, which may be used for CMW treatment, such as plasma pyrolysis, medium-heat microwave, low-heat autoclave techniques, and high-heat pyrolysis.

Pyrolysis

This is a quick thermochemical operation where waste degradation occurs in a bit of supply or an absolute absence of oxygen in specific temperatures (recognized as the pyrolysis temperature) for a particular time. The conditions provided can be helpful in breaking down complicated hydrocarbon compounds into molecules, which are smaller than before. Some necessary products such as liquids, gases, and solid char are created. Significant commercial products can be formed in the pyrolysis operation according to different factors such as the temperature of pyrolysis, concentrations of the waste, the size of particle and catalyst, and rate of heating (Dharmaraj et al., 2021). Pyrolysis is typically performed in temperatures between 310 and 660 °C. The first decomposition of garbage using activities of pyrolysis shapes creates solid char as well as condensed gases. Furthermore, the gases generated would have another degradation which leads to the noncondensable evolvement of liquids, certain gases (such as H2, CO2,CH4, and CO), and char. Due to the resemblance of liquid product or bio-oil (which forms during pyrolysis activities) to the properties of fossil fuels which are commercial, this is known as the most important item (Al-Salem et al., 2017).

Pyrolysis has been widely categorized into 4 different types, namely 1) Fast, 2) Slow 3) Catalytic and four) Conventional. In the fast pyrolysis process, the vapor residence time (VRT) will be about seconds or milliseconds. However, in the slow pyrolysis, the VRT is about minutes or more. Slow pyrolysis has been more categorized as torrefaction, and carbonization. There are mostly differences between the vapor residence time (VRT) as well as operating temperatures (OT). Fast pyrolysis is sorted into two different types, namely 1) Ultrarapid and 2) Flash, and the critical product made will be gases and bio-oil. The content of the oxygen for the product (bio-oils) made is significantly decreased by adding catalyst, which reduces acidity, raises its steadiness, and increases the density of energy during catalytic pyrolysis (Qureshi et al., 2020).

Emergency scenarios for CMW management

The space of ordinary MW concentrated disposal equipment is nowhere near meeting the current disposal requirements because of a considerable amount of MW produced in the COVID-19 pandemic period. The total space of domestic MW disposal has been considerably improved based on emergency disposal equipment in many countries (Yang et al., 2021). Three mobile disposal scenario outlines, as well as two co-incineration scenario outlines are examined as some examples for CMW emergency management in this study. The comparison in Table 1 is about typical features for the five scenarios of emergency disposal.

Table 1

An example for comparison of common characteristics for five samples of emergency disposal scenarios.

Scenario	Disposal scenarios	Disposal capacity	Treatment temperature and time	Dimension
Sc-1	Incineration disposal vehicle	5.1 t/d MW	Incinerator at 610–820 °C, secondary combustion chamber at 1100–1200 °C	12.70 × 2.66 × 5.5 m
Sc-2	Steam sterilization cabin	3.8 t/d MW	124 °C for 65 min	60 m2
Sc-3	Movable microwave sterilization equipment	10.5 t/d MW	Above 85 °C for 47 min	11.24 × 1.77 × 2.22 m
Sc-4	Co-incineration with hazardous waste	13 t/d MW and 39 t/d combustible hazardous waste	Rotary kiln at 950–1100 °C for 1–2 h	_
Sc-5	Co-incineration with MSW	140.4 t/d MW and 2707.5 t/d MSW	Above 960 °C for 1.5–2 h	_

In the first scenario, MW disposal happens in a burning dumping machine, which is a system with a double room thermic oxidizing and capacity for feeding of 5 tons per day. Besides, the flue gas is released securely by deacidification, dust removal, and quenching. In the second scenario, MW can be divided into the mobile chambers for sterilization of steam, which is mainly made of degradation, and packaging units, steam sterilization units, steam production units, garbage gas filtering as well as unwanted water filtering units. The space of disposal for the room is about 2.8 t/d and also, the working area is just 50 sqm. MW which is sterilized with sterilization of steam, would be delivered to MSW incinerating centers for co-incineration. In the third scenario, MW would be separated into mobile microwave facilities of sterilization, which contain decomposed matters units, sterilization units with microwave, units of coil discharge, as well as hydraulic lifting units, and MW would have sterilization by the radiance of microwave as well as steam-assisted heating (Chen et al., 2013). The residue of disinfected MW would be transported to MSW incinerating centers for dumping after microwave sterilization. In the fourth scenario, the disposal of MW is along with inflammable hazardous debris in a rotary kiln, and the combination of MW with dangerous garbage should be observed. In addition, the proportion for a combination of hazardous waste with MW for incineration would be specified by an establishment according to the complete attention of the production of the regional end and the forthcoming generation of dangerous waste and MW. Burning dangerous industrial waste, MW, biocide packing garbage, and burning hazardous trash in MSW have 52.0 wt%, 25.0 wt%, 2.0 wt%, and 23.2 wt% of the whole bulk, respectively, for the combination of waste. In the fifth scenario, the disposal of MW is in a shaver incinerator for co-incineration with MSW and is about six wt% of the whole bulk of the combined waste. The fulfilled dioxins with hydrogen chloride in the flue gas would be jumped by the considerable plastic content in MW. The burning of the high-level thermal value of MW can make domestic overheating in the incinerator (Wang, 2013). Therefore, MW just may have up to 6 wt% (of the whole bulk of the combined waste) for burning with MSW. For the fourth and fifth scenarios at the time for disposing of MW, dangerous waste, and MSW would also be disposed. If it is set by the functional unit to have one-ton disposal of MW, the environmental impacts of the fifth scenario cannot be compared because there would be a disposal of 3.17 tons for dangerous waste in the fourth scenario as well as 19 tons MSW in the fifth scenarios. The extension of system targets to assess the overall influence of establishing the latest products or functions with comprehensiveness would be beneficial (Meng and McKechnie, 2019).

LCA

LCA is known for its ability to evaluate environmental influences as well as potential effects of certain services or products that are sent to societies (Soheilifard et al., 2020). LCA is practical in managing wastes due to its help for having a comparison of various scenarios as well as treatments to choose the most suitable strategy for waste management (Zhang et al., 2021). MW is also no exception to this rule. Usual instruction of LCA has four principal stages which are noticed by ISO (2006), and are life cycle inventory (LCI) analysis, life cycle impact assessment (LCIA), interpretation as well as goal and scope definition (Kaab et al., 2019; Saber et al., 2020), with their relationships as shown in Fig. 2 .

Fig. 2

Relation between LCA steps.

The definition of scope and goal

Developing a model so that simplicity and distortion do not affect the outcome is a challenge for an LCA specialist. The main or appropriate method to tackle it is to specify the precision and objectives of the LCA investigation. The goals and areas of the considered options, including reasons for the implementing of the LCA, description of the service or product, life span and the system boundaries, etc., are described in (Nabavi-Pelesaraei et al., 2016). MW definition is different across various works. This can mention a step for avoiding pollution from MW, a kind of waste separation procedure, or a way that can include the garbage production until ultimate dumping on a large scale (Zhang et al., 2021). The functional unit (FU) contains a profound definition in LCA, which denotes a comprehensive unit for the inventories information (Nabavi-Pelesaraei et al., 2021; Nabavi-Pelesaraei et al., 2018; Saber et al., 2021). In multidimensional evaluation, different FUs can be used based on the LCA scope. FU can usually be explained based on outputs produced by a system (Khanali et al., 2021). As shown in the section above, five emergency disposal scenarios can be defined for CMW, and their system boundaries are disclosed in Fig. 3 . Moreover, one ton of waste input is usually determined as FU, for all scenarios.

Fig. 3

Graphical concept of system boundaries related to five sample emergency scenarios of CMW management.

LCI

In LCI, the study is on all inputs and outputs of environment comrades to a service or product, like using crude matter and energy, emission of contaminant, and flow dissipation (Haupt et al., 2018; Mostashari-Rad et al., 2020). Amid these steps, LCI analysis produces a life-cycle model that involves inputs and outputs of the process to FU. It then collects all relevant interventions, i.e., the release of environmental loads and resource consumption (Nabavi-Pelesaraei et al., 2019). Generally, two main aspects are in LCI, namely direct and indirect emissions (Mostashari-Rad et al., 2021). Indirect emissions are results of the existing reported processes. However, they occur in the sources of control or possession via other processes. The emissions mentioned are associated with the generation of different materials in different aspects of each scenario. There is a physical quantity requirement for all inputs of emissions; however, emissions of origins that are controlled or possessed with the reported entity are recognized as direct emissions. An example of LCI is tabulated in Table 2 .

Table 2

An example for LCI for five samples of emergency disposal scenarios based on 1 ton CMW.

Item	Unit	Amount
		Sc-1	Sc-2	Sc-3	Sc-4	Sc-5
A. Raw materials
Electricity consumption	kWh	46.87	145.01	404.35	171.74	69.43
Activated carbon	kg	2.56	–	0.14	1.30 × 10^(−3)	0.58
Ammonia	kg	–	–	–	–	3.97
Chlorine dioxide	kg	–	–	–	0.02	–
Diesel	kg	–	65.88	–	51.84	0.59
Disinfection solution	kg	1.07	–	4.59	–	–
Fresh water	kg	2421.81	977.40	356.40	2421.81	2226.63
Generated energy	kWh	–	–	–	–	485.88
Hydrated lime	kg	–	–	–	–	12.74
Hydrochloride	kg	–	–	–	–	0.04
Kerosene	kg	54.00	–	–	–	–
Lime	kg	6.40	–	–	3.02	–
Natural gas	m3	–	–	–	–	–
Net energy generation	kWh	–	–	–	–	416.45
Portland cement	kg	–	–	–	–	–
Sodium hydroxide	kg	2.14	–	–	32.29	0.05
Sodium hypochlorite	kg	–	18.04	–	–	–
Sulfate	kg	–	–	–	–	–
Transportation	t*km	11.47	11.64	10.84	11.76	10.98
Urea	kg	–	–	–	9.43	–
B. Direct air emissions
Ammonia	kg	–	4.40 × 10^(−4)	0.01	0.09	2.18 × 10^(−5)
Arsenic	kg	–	–	–	5.04 × 10^(−4)	–
Cadmium	kg	2.14 × 10^(−3)	–	–	–	–
Carbon monoxide	kg	–	–	–	0.78	–
Dioxins	ug	8.13	–	–	0.94	–
Hydrogen chloride	kg	4.28 × 10^(−3)	–	–	0.14	–
Hydrogen fluoride	kg	4.28 × 10^(−3)	–	–	0.02	–
Hydrogen sulfide	kg	–	5 × 10^(−5)	2.92 × 10^(−5)	–	2.91 × 10^(−6)
Lead	kg	4.32 × 10^(−3)	–	–	4.83 × 10^(−3)	–
Mercury	kg	2.56 × 10^(−5)	–	–	5.04 × 10^(−4)	–
Nickel	kg	9.96 × 10^(−4)	–	–	–	–
Nitrogen oxides	kg	0.73	0.11	–	2.04	0.39
Particulate	kg	0.17	0.003	–	0.03	5.27 × 10^(−5)
Sulfur dioxide	kg	0.05	0.55	–	1.94	0.12
Volatile organic compound	kg	–	0.02	–	–	–
C. Waste water
Ammonia nitrogen	mg	4747.25	–	–	9644.40	–
Arsenic	mg	–	–	–	–	–
Chemical oxygen demand	mg	41,538.46	–	–	96,444	–
Chromium	mg	–	–	–	–	–
Lead	mg	–	–	–	–	–
Mercury	mg	–	–	–	–	–
Phosphorus	mg	–	–	–	–	–
Suspended Solids	mg	–	–	–	–	–
Waste water	t	0.18	0.36	0.41	1.93	0.14
D. Solid waste
Sanitary landfill	t	0.32	–	–	0.31	0.27

LCIA

LCIA defines and evaluates the worthiness and significance of possible emissions occurred by LCI. Outputs, as well as inputs, are categorized into suitable impact classification. Then, their likely impacts will be specified based on characterization agents (Harding, 2013). Certain elements are reported throughout the phases in recognizing the domain of studies (ISO, 2006). Selecting relevant characterization, categorization, and impact classifications are obligatory elements. Normalization, classification, and weighting are possible elements of studies (Lasvaux et al., 2016). There are several methods to evaluate the environmental burdens of MSW and MW. However, in this study, ReCiPe2016 is illustrated as a new and applicable method, for determining environmental damages of CMW management scenarios. The aim of the mentioned assessment is the analysis of inputs as well as outputs under the defined scenarios. Impacts are assessed through different impact classifications, and after that, assessment is computed regarding resource categories, ecosystems, and human health in the inventory (Huijbregts et al., 2017).

Some models are available for various impact classifications, mainly in water use, and land, photochemical ozone formation and particulate generation. In this part, models are chosen, and ReCiPe2016 is utilized for combining different impact classifications (Huijbregts et al., 2017). Three conservation zones, namely ecosystem quality, human health, and resource shortage, were selected in ReCiPe2008 (Goedkoop et al., 2013). The three zones of conservation are retained for the implementation in ReCiPe2016 and endpoints cover three zones of conservation. Disability-adjusted life year (DALY) is relevant to human health. It indicates a specific time (in years) for a person’ disability having an illness or incident or a period lost. The species year explains units for the quality of the ecosystem. The unit for the scarcity of resource is United States dollars for 2013 (USD2013) that shows extra expenses related to the extraction of mineral resource and prospective fossil (Huijbregts et al., 2017). In ReCiPe2016, endpoints, relationships among environmental mechanisms, three regions of conservation, as well as 17 midpoint impact classifications are covered, as demonstrated in Fig. 4 .

Fig. 4

Relationship between endpoints and midpoints according to ReCiPe2016 method of LCA.

Different outcomes of scenarios and uniformity of units of each damage category can render it difficult to select the best scenario. Weighting can aid decision-making in cases where tradeoffs among impact category results do not permit selecting a preferable solution among the feasible options or an improvement over others. The weights to be applied should denote an assessment of the relative significance of impacts, based on specific values of options. Via this approach, outcomes would be aggregated among different impact classifications to attain a single score such as the LCA index (Ghasemi-Mobtaker et al., 2020).

Interpretation of results

This section is the last stage of LCA that is accompanied by the presentation of results and discussion. The results of such studies for each scenario should be as follows:

Presenting a physical value of each environmental damage

Providing the share of each input in the number of emissions of each environmental damage

Providing weighted diagrams of environmental damages to compare them among one another and determine the most influential category

It should be noted that after having presented the results, its interpretation is also critical. The discussion should cover two parts, namely reasons for the obtained results and strategies (early and late return) for improving each scenario.

After performing the mentioned three steps for all scenarios, it is time to compare them based on total weighted damages and finally select the best environmental-friendly scenario based on the lowest total weighted emissions.

In this section, we offer an example with the results, and discussions for five defined scenarios of CMW management, which can be used as a comprehensive pattern for future studies.

Table 3 shows an idea of results of environmental damages for these five scenarios of CMW. Based on the results, the ranges of human health, ecosystems and resources vary between 4.05 × 10^(−3) and 5.46 × 10^(−3) DALY, 4.56 × 10^(−5) and 5.89 × 10^(−5) species.yr, and 1245.70 and 1275.49 USD2013, respectively. In all damages, the lowest rate belongs to Sc-3 and vice versa, while Sc-5 has the highest rate in all of them.

Table 3

An example for damages results for five samples of emergency disposal scenarios based on 1 ton CMW.

Environmental damage	Unit	Amount
		Sc-1	Sc-2	Sc-3	Sc-4	Sc-5
Human health	DALY	4.89 × 10^(−3)	4.61 × 10^(−3)	4.05 × 10^(−3)	5.09 × 10^(−3)	5.46 × 10^(−3)
Ecosystems	Species.yr	5.52 × 10^(−5)	4.61 × 10^(−5)	4.56 × 10^(−5)	5.73 × 10^(−5)	5.89 × 10^(−5)
Resources	USD2013	1255.81	1254.33	1245.70	1267.59	1275.49

Fig. 5 shows an example of different input contributions to form environmental damages in five conditions of CMW emergency scenarios. Fig. 5 consists of 5 parts from (a) to (e), and each alphabet shows one scenario. For explanation of these results, first of all, we need to talk about each scenario separately and then summarize the results. For instance, in Sc-1, kerosene has the highest share in human health and ecosystems; but in resources, electricity has the highest share followed by kerosene. In Sc-3, electricity is the most influential input in all damages. Moreover, results of Sc-2, Sc-4, and Sc-5 reveal that the highest percentages are related to diesel followed by electricity among all inputs. It should be noted the electricity in the all scenarios are generated from fossil fuels in power plants. Results should be obvious and understandable, and only brief explanations should be given in the text to understand better and avoid any ambiguity.

Fig. 5

An example for distribution of environmental damages for five samples of emergency disposal scenarios in CMW management.

As mentioned, different units of measurement in environmental damages render it difficult to compare them among one another and interpret the results strategically. A sample of weighting analysis as presented for five CMW emergency scenarios in Fig. 6 indicates which damage category in each scenario has more emissions than other damages. As shown in Fig. 6, five sections are designed for each scenario. Results reveal that emergency management of CMW is most effective for human health in the first rank. Moreover, their environmental effects can disrupt ecosystems and resources in the next step. It should be noted that this trend is approximately equal for all scenarios. Furthermore, the trend of input shares is similar to Fig. 5 for all categories of five CMW emergency management methods.

Fig. 6

An example for weighting analysis for five samples of emergency disposal scenarios in CMW management.

For the selection of the best environmental-friendly scenario of CMW emergency methods, the total weighted damages should be compared among one another. Fig. 7 shows an example for determining the best environmental-friendly scenario. Based on the results, Sc-3 and Sc-5 are the best and worst scenarios from the environmental point of view, respectively. Sc-3 has the lowest amount of normalized damages with 102.52 Pt, and, on the other hand, the highest amount belongs to Sc-5 with 133.90 Pt. This result can help to decide choosing a technology from environmental aspects considering all conditions.

Fig. 7

An example for comparison among five samples of emergency disposal scenarios in CMW management.

In the discussion section, as mentioned, reasons for results, solutions to improve the systems, and prospects for future studies should be provided. For instance, in five defined scenarios of CMW management, diesel and electricity have the most effects on environmental damages. The following items are the main reasons for obtaining these results:

Utilization of worn incineration implementation

Lack of convenient maintenance of equipment

Lack of timely replaced filters in incinerators

Moreover, the following policies and solutions can help achieve more sustainable technologies for CMW management.

Applying standard incinerator in the scenario

Utilization of optimization techniques to allocate proper CMW for each scenario

Establishment of solar technology as a renewable resource for incinerators

Implementing encouraging policies such as subsidy for environmental-friendly scenarios by government

Finally, presenting the limitations of the study and proposing prospects can lead the CMW management to achieving more sustainability and green management.

Establishment of renewable implement for supplying electric energy requirement

Use of treat waste locally, close to collection points

Applying hydroelectric power to transport collected waste to treatment facilities

CMW management and SDG

The successful effort will be known as the next step for achieving CMW management, the SDG, and more notably, chemical-free products to a society that has an unpolluted environment. About 17 goals were declared with the SDG for improving the sustainability of global waste management with the target for decreasing environmental pollution, impoverishment as well as improving social justice, and urban life. The goal mentioned are; secure, sufficient and economical collection services of solid waste up to 2020, well managed opened and burning and dumping, environmentally sustainable managing of even dangerous waste up to 2030 (Wuana and Okieimen, 2011). Furthermore, minimizing waste (in the process of integrated approach) in different regions/countries may be helpful to reach some parts of objectives for 10 SDG (out of SDG) as recommended by United Nations (in Fig. 8 ) (Pujara et al., 2019).

Fig. 8

Anticipated SDG achievements within management of waste.

Accordingly, this will be beneficial for the entire world as predicted by the United Nations in the period of time for release of 17 SDG. Based on Fig. 8, it is evident that total or partial goals of 10 SDG are appropriately compatible with the attempts of integrated waste management as their attempts can indirectly or directly have some effects on improving the people's circumstances. Unified CWM systems will be better options for many countries to make the value-added products in addition to proper waste management. This contains the decrease of waste materials at the root of their production, division at source, efficient collecting and transportation, energy and compost producing before their dumping in the landfill, and transforming recyclable waste materials (Mohee et al., 2015).Utilizing requirements for the separation of biodegradable wastes from the non-biodegradable wastes, which is included in the CMW management rule, would be efficient. Based on providing amended solid waste management rules, biodegradable wastes must be utilized for the production of bio-fertilizers and/or energy. Furthermore, the wastes materials that could not be reused and have 1500 K/Cal/Kg of calorific value can be employed to produce energy. It was found that waste separation, the production of biogas as well as composting, and waste segregation are the best options for the management of CMW in the globe (Pujara et al., 2019). As Narayana (2009) said, about 80–85% of the wastes are biodegradable in nature can be a property for producing appropriate compost quality in developing countries. Consequently, composting is highly recommended in developing countries as a more acceptable choice of waste management with the production of some products that are valued-added.

Conclusions

The increasing MW during the outbreak of COVID-19 has caused waste management to go beyond its normal state, and emergency scenarios need to be developed and organized. But do these scenarios have separate consequences for the environment? Which scenario could be more environmental-friendly? Doesn't using the wrong scenario hinder the realization of SDG? For this reason, in this research, in addition to explaining the conventional scenarios of MW management, emergency scenarios for the management of CMW are also presented. By combining with the basics of LCA, their environmental assessment is fully explained. The results also show that the use of LCA can be an efficient way to estimate environmental emissions caused by each scenario and finally introduce us to the best environmental-friendly scenario. In this way, the disposal of CMW does not become a new and troublesome problem for human beings and can supply SDG.

CRediT authorship contribution statement

Ashkan Nabavi-Pelesaraei: Conceptualization, Methodology, Project administration, Software, Supervision, Writing-Original draft, Writing-Reviewing and editing.

Naghmeh Mohammadkashi: Visualization, Writing-Reviewing and editing.

Leila Naderloo: Investigation, Validation.

Mahsa Abbasi: Resources.

Kwok-wing Chau: Writing-Reviewing and editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.