Abstract
Nowadays, the industry produces an enormous amount of solid waste that has very negative environmental effects. Owing to waste variety and its scattered sites of production, selecting the most proper solid waste treatment is difficult. Simultaneously, social concern about environmental sustainability rises every day and, as a consequence, improvement on waste treatment systems is being demanded. However, when a waste treatment system is being designed, not only environmental but also technical and economic issues should be considered. This article puts forward a methodology to provide industrial factories with an easy way to identify, evaluate and select the most suitable solid waste treatment.
Keywords
Introduction
The present society demands that the industry is an efficient optimisation of resources and energy, reducing wastes at the same time and contributing to a sustainable development. Such sustainability requires a balance between the environmental protection and the economic and social aspects involved. Industrial solid waste (ISW) comprises a heterogeneous set with managerial problems of all kinds (European Union UE, 2010).
Traditionally, companies considered these residues as an uncomfortable material that increased costs in the production process. Fortunately, the current increased awareness of sustainable development implemented by most industries implies the need to develop integrated treatment systems that meet and exceed the legal requirements, and the technical and economic constraints at the same time.
To consider the safe storage of waste as the only possibility of managing these materials is not enough. Also, their landfill disposal is not considered as the best solution owing to its high costs, and the emissions and concentrated pollutants it generates. The optimal solution would be both to prevent the production of waste and also reintroduce them into the production cycle by recycling its components when there are sustainable solutions from an ecologic and economical point of view. However, in this only a small amount of the materials are found, since, in order to be exploited within the process, they do not even come to be classified as waste material. If there is no possibility of minimisation, recovery, reuse or valorisation of the wastes thereof, then different activities are required to be performed on the different waste streams. An efficient management of such waste should allow the material to be partially or fully exploited, either in their own manufacturing environment, or for an external application, or otherwise its landfill disposal. The cost of these actions varies depending on the nature of the material and the uses they are intended for, also taking into account that the value of these products varies depending on the market. Only part of the materials is subject to be recycled, while the rest should be treated differently or landfilled. The list of recyclable materials, however, increases as new technological advances and production techniques are developed. Moreover, reusing and recycling are affected by the restrictions imposed by the various administrations to the marketing and flow of waste material, for fear of possible mismanagement as uncontrolled dumping, since this market is yet to be consolidated. These restrictions involve different procedures and legal authorisations. The principles of proximity and adequacy usually force producers to manage waste as close to its origin as possible.
Current technology allows, with lower or higher costs and with some exceptions, most waste to be recycled. Moreover, it is a more complex issue when the combination of several techniques is required for optimising the process, thus affecting their viability and, ultimately, their profitability. In turn, each of these processes can be a new waste generator, often with very different characteristics from those at the starting point, entering a complex spiral, which can be approached in many different ways. Therefore, there is no obvious selection of the most sustainable option among the different available management options. New strategies of characterisation, control and monitoring of waste global cycle in the industry are required to improve waste treatment and quality control techniques. That is, the great technological challenge not only focuses on the research, development and application of advanced technologies for the treatment of waste, but also in selecting the most appropriate treatments from the ones available.
As a result, numerous studies have examined what strategies companies can follow and have proposed methods to assess the performance of technologies and treatments used (Coelho et al., 2012) or indexes also to allow the assessment of destination or end use of solid waste (Coelho et al., 2011). The same problem has been addressed in the case of municipal solid waste (MSW) (Consonni et al., 2011; Santiago and Dias, 2012), perhaps with greater intensity owing to the existence of policies that set specific targets for recycling and MSW recovery, for example raised in the European Union (Cucchiella et al., 2012; European Union UE, 2008; Stanic-Maruna and Fellner, 2012). A usual approach is the use of life cycle analysis (LCA) (Buttol et al., 2007; Kirkeby et al., 2007; Massarutto et al., 2011; Song et al., 2013), in order to assess or compare products or processes. However, Vermeulen et al. (2012) show that many of these studies are more oriented to the assessment of the environmental impact rather than sustainability as a whole.
Management methodology of ISW
This article presents a methodology of general application, which allows us to identify the different available treatments for every waste in a determined environment, assessing them according to different criteria with the aim of choosing the most suitable one.
The proposed methodology was structured into four stages.
Waste and environment characterisation: first it is necessary to know all the characteristics of the waste and the environment where it is generated.
Indicators selection: the second stage consists in the selection of a set of specific indicators or measures of different social, economic and environmental parameters in each case of application, starting from a general system of indicators.
Treatment processes identification: the possible solutions to the treatment are identified through a flow chart.
Treatment solution selection: through the set of selected indicators each possible solution will be assessed.
Waste and environment characterisation
The starting point of the developed methodology is the characterisation of waste made by technical staff of the plant through the ‘Waste sheet’, where all information on each waste material is provided.
Identification, origin and legal classification.
Composition and information about its components.
Physical and chemical properties.
Stability and reactivity under certain conditions.
Safety criteria – potential hazardous waste or toxic effects on people or environment.
Other complimentary criteria on management, transportation, etc.
Likewise, an ‘Environmental sheet’ is aimed to collect information regarding conditions of the place where the waste management and treatment system will be located. This will influence each of the stages of such treatment. The following data will be included.
Characteristics of the location where activities are performed.
Weather conditions of environment: temperature, rainfall levels, humidity, etc. Soil environmental conditions: soil composition and nature, depending on the surrounding environment, for example texture, structure, porosity, pH. Habitability conditions, for example if it is an urban, rural, industrial or sheltered environment.
Characteristics of the treatment process or processes that are going to be implemented to the ISW.
Process conditions: once the process sheet is known. How the process characteristics influence their environment.
Characteristics of the final waste that is obtained in the ISW treatment process.
Final waste conditions: they are useful to know the damages waste produces as a result of all the treatment processes in their environment.
Once the waste and its environment are characterised, a set of indicators are defined to be taken into consideration and select the most adequate solution.
Indicators selection
To make a correct selection of environmental indicators, it is essential to identify the significant environmental impacts of the activities of the company, the environmental situation of the environment, social and environmental goals and external requirements. When environmental issues are addressed, it is unrealistic to limit the indicators to a few or to even just one. The main idea is to efficiently meet the relevant categories with a manageable number of concise indicators (IHOBE, 1999).
There are different types of worldwide classification systems for indicators, depending on different uses as, for example, environmental management or corporative social responsibility. Two systems among them have been used as an initial reference.
IHOBE/ISO/EMAS system, according to the three documents that it is based on and which have a common structure.
- The Guide of environmental indicators for the industry from the Basque Government Public Environmental Management Company (IHOBE, 1999). - The ISO14031: Environmental management. Environmental behaviour assessment. General Standards from 1999 (ISO 14031, 1999). - European Commission Recommendation regarding the integration of organisations into the Eco-management European system registered in the 2001 EMAS Regulation (Eco-management and Audit Scheme) (Eco-Management and Audit Scheme (EMAS), 2009), regarding the selection and use of environmental behaviour indicators, published in 2003 by the European Union.
The system coming from the Global Reporting Initiative (GRI), an independent institution that created the first global standard for the elaboration of Sustainability Reports for those companies which wish to assess their economic, environmental and social performance (Global Reporting Initiative GRI, 2002).
After analysing the aforementioned systems, a customised system called the environmental indicators system (EIS) was configured incorporating both environmental and socio-economic factors, which will allow us to measure and quantify information on processing and it is organised in three groups. In the first group, the environmental indicators quantify the material and waste flows, which are generated as a consequence of the production activity and the impact the operations have on the development of these activities in natural systems. They have been organised into three separate sub-groups.
Materials and waste flow: the distribution was organised depending on the input flows (materials, energy, water, support products and services) and the output flows solid wastes, emissions, product and support services wastes, products and energy).
Impact of the activities of the company: they express the effects the production processes have on the environment owing to the development of their activity in relation to transport facilities and land use.
Biodiversity: reflects and quantifies the environmental status of ecosystems owing to pollution (soil, flora and fauna, nature conservation).
The second group, socio-economic indicators, aims to reflect economic and social values associated with environmental issues. Their distribution goes as follows.
Social, divided into the following lines:
- Internships: includes everything related to training workers in environmental issues associated with their health and safety in the workplace. - Society: management of risk appearing as a result of the interaction of companies with the communities in which they operate and the position adopted by companies on public policy (participation in environmental projects). - Responsibility over products: search for environmental compliance in order to achieve the health and safety of the client and the correct labelling of products and services.
Economic, financial support received and investments made to reduce the environmental impact. They are classified as:
- Financial performance. - Investment on environmental management.
Finally, the third group includes indicators of a regulatory type, which are those established by companies to illustrate the environmental performance under the criteria for compliance with the laws, the cost of significant fines and number of sanctions for non-complying with environmental regulations, the number of reported accidents, etc. Also worth noticing is the fact that the compliance with the regulations goes from being an environmental indicator, to having the same hierarchical position as the environmental or social blocks, since all systems must comply with current legislation.
To describe in detail the characteristics of the indicators, an informative sheet has been designed for any indicator. In ‘indicator sheet’ is described as the type of information that the descriptive sheet must provide.
The selection of a system of indicators, and the content of the indicators themselves, must therefore, have a direct relation to the way the company approach the sustainable development issues and a close relationship with its specific activity.
When implementing EISs, which are generally designed to any area of business, waste management is a particular and special case and was configured as a System of Environmental Indicators for Solid Waste Management (SEISWAM). It should be noted that the indicators should be selected not only by the availability of information, but it also must be relevant and consistent with the objectives that the company promotes.
In the solid waste management of any company, first the most significant inputs and outputs must be established and defined.
Inputs:
wastes: solid or sludge;
use of water, energy, electricity and chemical agents for waste treatment.
Outputs:
solid waste transformed as a consequence of their treatment – they will either be removed or valorised;
wastes produced as a consequence of the treatment of the different input wastes.
Therefore, the outcome of this stage must be the selection, by a panel of experts, of a set of indicators from within this general system (SEISWAM). This set of indicators, which must be adapted to any particular case, will be used afterwards as a means of assessment of the possible treatment solutions.
Treatment processes identification
In order to select the proper treatment technology, a thorough selection and assessment must be performed in relation to the possibility of optimisation of the technique. It is, therefore, the type of waste to be used that dictates the guidelines of this process. That is why it is extremely important to define the characteristics of the pollutant – which have been defined before in the ‘waste sheet’ – as well as the adequate treatments to use. Obviously, there are numerous sets of treatments or processes to describe and which must be included in the methodology as part of the system. A division of these sets have been made according to the type of treatment, as well as the type of material to treat, in this case solid waste. Thus, Figure 1 shows some of the most usual techniques that can be found in the existing literature, which can be applied to solid waste management.
ISW treatment techniques.
In order to create the decision support system and be able to make its validation, it is essential to develop waste treatment processes and techniques in a way that can be assessed by the system included in the methodology. The use of this methodology demands a standardisation that permits the diagnostic modules to make an automatic assessment.
Each ‘process sheet’ collects the principal data of interest from each technique and the waste to which it is applied. This data is as follows.
Technique name.
Detail description of the technique regarding its objectives, pre-treatment needs, technique development, equipment used and estimated time of the process.
Waste requirements. Must contain the following information:
name, type and ELW (European List of Waste) code, as well as its origin; description of physical–chemical characteristics of the waste, in terms of its adequacy to be used in the described technique; usage limits.
Water, energy, electricity and chemical agent consumptions. There could be other consumptions expressed in its functional unit.
Process/treatment performance expressed in its functional unit.
Outputs: products, by-products and generated waste. Description and quantification in its functional unit.
Observations related to techniques.
A general diagram representing the inputs and outputs of each treatment process is displayed in Figure 2.
ISW treatment process.
The ‘alternative selection chart’ (Figure 3) developed, presents the necessary process for the treatment of solid waste from its generation to its disposal or reuse. It works as a decision support system, that is, it simplifies the decision making associated with the waste life cycle. It consists of a representation system of the different steps to make to complete a process, organised in a hierarchical way according to its time evolution based on flow lines. An example of use of this diagram on the steel industry is further explained in the case of study.
Decision support diagram for solid waste management.
The chart is organised into five different groups or columns where the decisions, processes, inputs and outputs associated with each one of them are set. Two of these columns belong to the same management process, whereas the three left columns show the inputs and processing results.
Inputs: all inputs to the chart are set in this column, including the waste to be treated and all the supplies, that is, the resources required to achieve any of the processes that waste must undergo.
Unusable product: including waste material that is not possible to transform into by-products or definitive reuse. For its flow disposal, an external agent or a definitive storage is necessary if its deposition or emission into the atmosphere cannot be possible.
Characterization and valorization: it is the first stage of the management process and its objective is to establish waste properties and assess its possible value for reusing or selling as a by-product. In this stage, some decisions are applied, that is, some selections must be made about the waste that modifies or alters its course.
Treatment: second stage in the management process. It includes all the actions to be performed, changing its physical and chemical characteristics, to the conversion of waste into a reusable, eliminable or storable item. Those necessary treatments for its dispatch to an external manager are also included.
Usable product: waste material, which, owing to its initial configuration or future processing, ends its course as a profitable product. It also includes the energy generated that can be profitable in certain processing operations.
This diagram provides a generic methodology for the management of solid waste. To use this diagram it is necessary to follow the flow lines determined by the decisions made according to waste data and processes. Therefore, the final result will be an unspecified number of alternative solutions, each one including one or several treatment processes.
Both the ‘process sheet’ and ‘alternative selection chart’ used in the solid waste management system demand a considerable effort by the technicians working in the plant in the initial implementation stage. Afterwards, a periodic checking upgrading will be required, as well as the upgrading of methods and technology used in waste treatment.
Treatment solution selection
The last stage of the methodology allows the selection of the most appropriate among all possible solutions, which are previously identified and understood as a set of treatments. Each of these alternatives will have some specific costs arising from of the processes used, with a consumption of energy, water, etc., and outputs as by-products and final waste that must be properly reflected in the specific set of selected indicators.
Owing to the great number of criteria to be taken into account, selecting the best option of treatment can be a complex issue that has been previously approached in other studies. Therefore, some authors have used fuzzy logic to manage interrelations between different criteria or their degree of importance (Li and Huang, 2011; Seo et al., 2003).
When selecting the most appropriate assessment method, we evaluate the application of different expert systems, which include the so-called multi-criteria analysis techniques (Khadivi and Fatemi Ghomi, 2012). Between these methods, the analytic hierarchy process (AHP) has been selected as part of the ISW management methodology owing to the following considerations (Saaty and Vargas, 2001).
Its simplicity and flexibility. It is formed by a series of limited alternatives and facilitates the understanding of the issues to perform an adequate decision-making process.
The decision-making problem is modelled establishing a hierarchical method for the criteria, as opposed to other methods in which there is only a global comparison of alternatives.
Qualitative information is only required regarding the assessment of the decision-maker; quantitative information resulting from each of the criteria considered is not necessary.
It is possible to analyse separately the contribution of each of the model components to the general objective.
Individual incoherencies are detected and accepted.
It can be integrated into other multi-criteria methodologies.
This method will allow the industrial waste manager to select more objectively, within assessments made by an expert’s panel, the best treatment solution, having in mind all factors included in the set of indicators previously chosen.
Application in a particular case
Once the methodology is defined, the next step would be to monitor its performance by its application in a particular case. The proposed issue consists of selecting the most suitable treatment for an ISW from steel industry, as is the case of basic oxygen furnace (BOF) sludge (also known as Linz-Donawitz converter or LD), which is generated by the wet treatment of gas from a basic oxygen steelmaking (BOS) process. Such waste is generated in a specific environment, in this case an industrial area in Avilés, northern Spain, characterised by its rainy and damp weather and moderate winds.
According to the proposed methodology, the first step consisted in the collection of the characteristics and properties of the sludge in a sheet (‘waste sheet’). Therefore, when it is selected as input in any process, it makes it easier to determine if those are the adequate characteristics to be used in an input process. Once the physical and chemical characteristics of the sludge are known, the possible treatments must be identified. In the ‘alternative selection chart’ (Figure 3) it is considered that inputs (identified as I in the diagram), the waste itself (I.1) as well as water (I.2), energy (I.3), etc. Then there is a description of the diagram where several matters are discussed, such as: Is it radioactive waste? Is it considered hazardous according to legislation? The answers to these questions or the decisions are taken according to the previous characterisation of the waste material, and are identified with a D in the diagram. In some of the cases, several solutions are possible because the different alternatives are not exclusive, which generates several outputs, such as energy, reusable solids or waste fractions, with other characteristics that would return to the beginning of diagram to repeat the same process.
In this case, six possible alternatives of treatment were obtained.
Alternative 1.a. Ceramisation.
Alternative 1.b. Vitrification.
Alternative 2.1. Hazardous waste external manager.
Alternative 2.2.a. Phytoremediation.
Alternative 2.2.b. Bioremediation.
Alternative 2.2.c. In situ vitrification.
Each of these alternatives is formed by a set of treatments that start once the sludge enters the installation and end with the final product that is obtained. With the aim of identifying them easily, each management alternative was named after the last recovery treatment applied to the BOF sludge.
The first group of alternatives (Alternative 1.a and Alternative 1.b) includes those that aim to valorise the sludge for its use in other industrial processes. The group of alternatives named, starting by number 2, refers to those treatments that do not valorise the sludge since it is destined to be landfilled. In this case, it is possible to apply some kind of previous treatment, which may have different environmental and economic costs.
The next 11 indicators were selected, which include the different environmental impacts (environmental indicators), socioeconomic impacts (financial indicators) and the environment causes in the management process, according to the set of treatments the waste has to endure (return indicators). The selected indicators in this case are:
specific consumption of chemical agents;
specific energy consumption;
specific water consumption;
total share of profitable solids;
volume of liquid effluents;
volume of gas emissions;
operative costs of environmental production;
rainfall in installation area;
wind speed in the area;
proximity to populated areas;
proportion of affected natural resource.
Since we do not have enough data to assess such environmental indicators of an SEISWAM system in a quantitative way, the qualitative assessment of indicators was used as decision criteria of the AHP method.
When applying AHP for the selection of the most sustainable option, different stages were defined.
In the first stage, the decision problem was treated as a hierarchy. The aim or objective was to select the most sustainable process. The 11 indicators previously selected were placed in the second level and the six alternatives of the treatment.
In the second stage, the importance that the decisive unit assigned to each of the selected criteria was assessed. In a side-by-side comparison between each of the indicators or criteria, we obtain the pairwise comparison matrix, which in this case was an 11 × 11 matrix (Table 1), owing to its 11 indicators. The preference of an indicator over another is established by the decision maker, giving marks according to the measurement scales provided by Thomas Saaty (Saaty, 1987), where matrix A is obtained (Table 1). To ensure that such a matrix is representative of the decision process and, therefore, valid and coherent for the analysis, a consistency analysis is performed. To this purpose, the priority vector is calculated (W) and from here, the consistency ratio (CR). For the analysis to be consistent, the method establishes that CR ≤10%. In this case, CR = 5.88% (~0.06), therefore the criteria was met.
In the third stage, the local priorities of the alternatives, where the comparative judgments matrix are paired between them (R), are calculated. This was performed for each of the 11 criteria or indicators. Table 2 shows the matrix A for the first indicator (specific consumption of chemical agents). Each matrix A for each of the 11 indicators was obtained and a corresponding consistent analysis was also obtained.
Matrix A of pairwise comparisons.
R judgments matrix by pairwise comparison between alternatives.
Once the priority vector was calculated, a consistent matrix was obtained, with CR = 3.33. Then, once local priorities were obtained, the total priority matrix and vector were calculated, which present the importance of alternatives with respect to the goal, identifying them in order (Table 3), the one that was best adapted to the final goal being the highest value.
AHP solution.
In this case, where the installation is situated in Avilés, the best management alternative obtained was Alternative 1.a Ceramisation, with a punctuation of 0.2635 according to Table 3, in which the waste material goes through two cycles in the selection chart (Figure 3).
A first stage of drying and another of magnetic separation, in which a profitable solid is obtained (iron), which has a common output for all management options.
A second stage, where dust, with a high content of metal that has not been previously separated by magnetic current, goes into the final recovery treatment stage, which can be vitrification or ceramisation.
The result is consistent, not only because the value of CR is within the required limits, but also because the following characteristics are met.
Less energy is consumed in 1.b Vitrification or 2.2.c In situ vitrification cases than in the rest of options, and water consumption is not very high, though slightly higher than in 1.b Vitrification case.
Since clay is used as a chemical agent in this technique, ceramisation shows a higher level of preference than other alternatives that use toxic or hazardous chemical agents.
Liquid effluents are not generated, since they evaporate in the drying process, there is no water involved in the magnetic separation and neither is there in the ceramisation final stage, whereas alternatives 2.2.b and 2.2.b Phytoremediation.
Two profitable solids are generated, one the iron resulting from the magnetic separation and another the ceramic solid.
The operative costs of environmental production are high, since in the drying process as well as in the valorisation process, techniques for recovering effluents or treating emissions are used; therefore, it represents a positive cost, higher than that produced when waste is landfilled or dispatched.
As for the environmental conditions where management occurs, the high wind speed in this area is a negative factor when weighing up, since if there are fierce winds, it moves gas emissions to other nearby places, such as major populated centres close to industrial areas, as is the case of Aviles. The rainy weather does not influence much in this case, since all processes take place in an enclosed facility, however this does not apply in cases in which they have landfill treatment (bioremediation or phytoremediation) for leachate generation described above.
The proposed methodology has allowed us, in this case, to identify six possible waste management alternatives and to determine, by the AHP method, which one of them is the most suitable according to a set of environmental criteria.
Conclusions
Industrial waste management is currently a major concern, not only for industrial facilities, but also for the governments and society at large because of its great impact on the environment.
In this article, we have presented a complete methodology for managing the ISWs, which includes the following elements.
A set of ‘sheets’ – waste, process and environmental sheets – which make it easier to identify the alternatives and upgrade the available treatment techniques.
A system of general applicability indicators adapted, in this case, to the management of all kinds of industrial waste and which later will serve for the analysis and assessment of the different treatment alternatives.
A general scheme of assessment of alternatives or treatment solutions according to the characteristics of every ISW and treatment technique currently available.
As Morrissey and Browne (2004) indicate, most published studies are focused on the adequacy of the technique used in the proposed model (cost benefit analysis models, life cycle inventory models and multi-criteria models) or on comparing different treatment alternatives (recycling, incineration and disposal). Also, they are mostly centred on MSW treatment. On the contrary, in this article, companies and mainly their waste managers are provided with a methodology to create their own management model and establish mechanisms of waste characterisation, define indicators and select criteria to identify the possible solutions or set of treatments to, eventually, evaluate the different alternatives.
In conclusion, it can be said that this proposed methodology:
provides general applicability;
ensures a more objective analysis or selection of solutions of treatment for waste management, based on the analysis of different aspects and characteristics;
facilitates the repeatability of the analysis and its application to any type of ISW regardless of its origin;
supports without difficulty the incorporation of changes arising from the evolution of technology in social or economic conditions.
Among the possible future lines of research in this study, is the generalisation of the methodology by extending its applicability to other types of waste, which allows us to personalise the system of general indicators and develop an alternative selection diagram similar to that exposed.
This procedure allows the analysis to occur in a more objective way, based on the analysis of different aspects or criteria. It also facilitates the analysis repeatability to be applied to any type of ISW regardless of its origin. The changes resulting from the evolution of technology and social or economic conditions can be easily incorporated into the proposed methodology.
Footnotes
Declaration of conflicting interests
The authors declare that there is no conflict of interest.
Funding
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.