Life Cycle Assessment (LCA) of Technological Processes in the Wastewater Treatment Using Flocculants Synthesised from Polymer Waste

Abstract

The technological and environmental challenges promoted by the European Commission (EC) follow its objectives to minimise waste, ensure the rational use of resources and energy, use raw materials more efficiently, and increase recovery and recycling. The new hierarchy of handling products and waste has been a key challenge of the circular economy, enhancing the involvement of both businesses and consumers. The life cycle assessment (LCA) is an environmental management technique that makes it possible to assess the environmental impact of a product, a process, an industry, or even an entire sector of the economy. It is used worldwide with great success to study the various stages of technology, ensuring environmental safety. The experience of Polish and foreign research centres confirms the possibility of using the LCA technique to support the environmental risk assessment of technological innovations, therefore the LCA technique has been used to study the environmental impact of potential technologies for producing flocculants from polymer waste. LCA of newly synthesised flocculants has shown that sourcing flocculants from waste phenol–formaldehyde resins is highly beneficial to the environment due to the high toxicity of waste resins that produce phenol when exposed to physical factors.

1. Introduction

One of the key drivers of economic growth is the establishment of a closed circular economy and the assurance of sustainable access to raw materials. The potential for the production of eco-products through technological innovations related to the utilisation of waste and environmental life cycle assessment enables the issue to be included in the thematic area of the closed circular economy.

The current era is witnessing the advent of the fourth industrial revolution, also known as Industry 4.0. This term describes the social, industrial, and technological changes brought about by the digital transformation of industry. The global trend that has enabled the advent of the next revolution is, first and foremost, the increase in available data and computing capabilities. The consequence of this combination is the uninterrupted flow and accessibility of information at each stage of a product’s life cycle. It is possible to manage company resources, plan production, and manage and optimise. In practice, the data collected can be used to assess and subsequently minimise environmental risks [1].

Consequently, it is necessary to develop tools that can be used to study the environmental impacts of industrial technologies. Life cycle assessment (LCA) is one of the methods used to estimate the environmental burden caused by a given product, production process, or activity. This is achieved by identifying the energy, material consumption, and pollutants discharged into the environment; assessing the environmental impacts associated with energy, material consumption, and pollutant emissions; and finally, evaluating the possibility of improving the environmental impact. Life cycle assessment is thus a diagnostic tool that is useful for environmental management. As a consequence of utilising LCA, managers of a manufacturing company are able to identify specific areas that are a source of particular environmental or human health burdens [2,3,4].

In contrast to traditional environmental management methods, LCA allows for the following:

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comparison of alternative products and manufacturing technologies,

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identification of the sites generating the greatest environmental impact throughout the product life cycle,

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establishment of criteria for eco-labels to identify the best environmental products,

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comparison of alternative ways of disposing of waste [5].

Internationally, the environmental life cycle assessment, which is based on the ISO 14040 series of international standards, is one of the techniques that allows the environmental impact of technologies to be assessed [6]. In order to maintain a competitive position in the market, companies must adopt a long-term plan for innovation development. This will lead to an increase in the competitiveness of companies in the long term and enable a smooth adaptation to the dynamically changing current market conditions and customer preferences.

This paper describes the application of life cycle assessment in source identification analysis and environmental impact assessment of the production process of a new generation of flocculants synthesised from post-production phenol–formaldehyde resin waste [7,8,9]. Chemical modification of phenol–formaldehyde resin waste has produced polyelectrolytes with good flocculant properties. Flocculants are employed in a variety of industrial and municipal wastewater treatment processes. However, they can also be utilised in numerous industrial applications, including the flocculation of metal ores following enrichment in the flotation process.

Many scientists around the world have been studying the use of polymeric flocculants in wastewater treatment for many years. However, the use of the LCA method to analyse and evaluate the environmental impact of polymer flocculants is a relatively new field of research [10,11,12,13]. The first research in the area of applying the LCA technique to the production processes and subsequent application of polymeric flocculants from polystyrene waste and phenol–formaldehyde resin waste was carried out by the main author of this article [14,15,16,17]. The preparation for the analysis of the environmental impact of the newly synthesised polymers with flocculant properties using the SimaPro calculation software required the preparation of technological schemes for the production (on a quarter technical scale) of the new generation of polymers, including equipment. On the basis of calculations using the technological schemes, a material and energy balance was prepared for the production of polyelectrolytes based on phenol–formaldehyde resin waste, and also for their use as flocculants in metallurgical wastewater treatment (taking into account the equipment in the wastewater coagulation process). Currently, the study of flocculants synthesised from polymeric waste used in wastewater treatment and, in particular, the application of the LCA to study the environmental impacts of the different stages in the life cycle of flocculants (the production stage and the stage of use as flocculants) represents a gap in the scientific research. When developing new flocculant technologies, it is crucial to consider the environmental impact, given the pursuit of environmentally sustainable development. Through life cycle assessment, it is possible to determine the environmental impact of each stage of production, use, and disposal of new polymer flocculants. The application of life cycle assessment enables the comparison of different production options for polymer flocculants, thereby facilitating the selection of the most environmentally sustainable solution. This, in turn, allows manufacturers to adapt their production processes in a manner that is more environmentally friendly, thus improving the overall environmental performance of the chemical industry.

2. Materials and Methods

A life cycle assessment of new-generation polymers produced from post-production phenol–formaldehyde resin wastes (flocculants) was conducted in accordance with the guidelines and recommendations set out in ISO 14040 [6] and ISO 14044 [18]. The methodology employed involved four steps: the definition of the purpose and scope, the analysis of the set of inputs and outputs, the assessment of life cycle impacts, and the interpretation of the study results. In accordance with the guidelines set forth in ISO 14040 [6], the analysis entailed the calculation of the environmental footprint of various flocculants derived from waste and their utilisation in the treatment of municipal wastewater, metallurgical wastewater, and underground water from coal mines. This process commenced at the extraction of primary raw materials, also known as the cradle-to-cradle approach, and continued through to the transportation of materials and the manufacture of flocculants and their eventual use.

The calculations were conducted for the territorial scope of the analysis, which was limited to Poland. The technological scope of the LCA included the analysis performed on the basis of project data. The production of 1 tonne of a given flocculant was used as the unit in the analysis. The analysis did not include infrastructure and materials related to the maintenance of the installation. Electricity production data were modelled using data from the Ecoinvent database as an average for Poland [19]. The market for low-voltage electricity in Poland was considered. The distance travelled by purchased raw materials was 200 km, with a payload of 20 t. The EURO5 standard was applied.

The study was conducted utilising the software SimaPro Developer v. 9.4.0.2. The SimaPro software is widely recommended for use in European Union resources. A review of the literature on the use of the LCA in the chemical sector and in environmental engineering, both from a holistic and technological perspective, shows its widespread use [20,21]. It is a reliable and credible tool [22]. The characterisation was developed using the method EF 3.0 v.1.03, with a weighting factor of ‘1’ for each impact category. Once the set of inputs and outputs (LCI) analysis was produced, the impact of the environmental footprint was assessed. The analysis was conducted using the EF 3.0 method with SimaPro and its implemented databases, primarily Ecoinvent [19]. The EF 3.0 method is an impact assessment method adopted by the European Commission (EC). It incorporates the normalisation factors and weights published by the EC in November 2019.

Table 1. Environmental footprint impact categories with category indicators and environmental footprint impact assessment models recommended for use for product and organisational environmental footprint studies [23].

No.	Impact Category of the Environmental Footprint	Environmental Footprint Assessment Model	Environmental Impact Category Indicator	Source
1	Climate change	The Bern model—global warming potential over a 100-year timescale	Tonne of carbon dioxide equivalent	[24]
2	Ozone depletion	Environmental Design of Industrial Products (EDIP) model, based on ozone depletion potentials (ODPs) over an indefinite time horizon, developed by the World Meteorological Organisation (WMO)	Kilogram of CFC-11 equivalent	[25]
3	Ionizing radiation HH	Human health impact model	Kilobecquerel U equivalent (air emissions)	[26]
4	Photochemical ozone formation	Model LOTOS-EUROS	Kilogram NMZO equivalent	[27]
5	Particulate matter	PM model	Morbidity	[28]
6	Human toxicity, non-cancer	Model USEtox 2.1	Comparative Human Toxicity Unit (CTU)	[29]
7	Human toxicity, cancer	USEtox model	Comparative toxic unit for humans (CTUh)	[29]
8	Acidification	Accumulated exceedance model	Mol H+ equivalent	[30]
9	Freshwater eutrophication	EUTREND model	Kilogram P equivalent	[31]
10	Marine eutrophication	EUTREND model	Kilogram N equivalent	[31]
11	Terrestrial eutrophication	Cumulative exceedance model	Mol N equivalent	[30]
12	Freshwater ecotoxicity	Model USEtox 2.1	Comparative toxic unit for ecosystems (CTUe)	[29]
13	Land use	Soil quality index based on the LANCA model	Dimensionless volume (pt)	[32]
14	Water resource depletion	Available WAter REmaining (AWARE) model	Equivalent of the quantity of water deprived of the user, in m3	[33]
15	Resource use: fossils	Depletion of abiotic resources—fossil fuels (ADP—fossil raw materials)	MJ	[34]
16	Resource use: minerals and metals	Depletion of abiotic resources (final ADP stocks	kg SB equivalent	[34]

provides a summary of the recommended characterisation models for each impact category, indicating the impact modelling approach that should be employed. The list presented in Table 1 corresponds to the set of impact categories and characterisation models of the EF 3.0 method.

This set includes 16 environmental footprint impact categories, of which four are resource depletion categories: water resources, mineral resources, fossil resources, and land use. These categories pertain to instances where the withdrawal of a resource from the environment results in the creation of an environmental problem. The remaining 11 categories are emission categories, where the release of a compound into the environment triggers an environmental mechanism.

3. Assessment of the Impact of the Product Life Cycle and Interpretation of the Test Results

The synthesis of polyelectrolytes was carried out in accordance with the established method of sulphonation of aromatic compounds [7,8,9]. As anticipated, the study encompassed the modification of waste phenol–formaldehyde resin to yield the sodium salt of a sulfonic derivative of phenol–formaldehyde resin. Once the data from the inventory tables for the flocculant production processes based on post-production phenol–formaldehyde resin waste had been entered, an energy and material balance was developed (

Table 2. Material and energy balance for the production of 100 kg of sodium sulfone derivative of phenol–formaldehyde resin waste *.

Inputs—Demand for Raw Materials and Energy Factors	Unit	Quantity
Sulphuric acid	kg	467.3
Calcium carbonate	kg	368.57
Sodium carbonate	kg	56.51
Phenol–formaldehyde resin waste	kg	67.94
Electricity	kWh	55
Outputs—Emissions
Carbon dioxide	kg	310.8
Steam	kg	30
Water (wastewater)	kg	110

* co-produced calcium sulphate (409.52 kg).

).

Following the collection of inputs and outputs (LCI) analysis, an assessment of the product’s environmental footprint was conducted using all categories and environmental footprint impact models in accordance with the selected methodology.

3.1. Characterised Results of Impact Category Indicators

Figure 1 shows the results of the characterisation step in the 16 impact categories for the flocculant produced. The results in all impact categories are presented as a percentage.

From the data presented, it can be seen that, depending on the impact category, either the use of sulphuric acid and electricity—which represents an environmental burden—and waste phenol–formaldehyde resin (novolac)—which represents an environmental benefit—have a dominant impact. Furthermore, the diagram reveals a discernible impact from disodium carbonate and calcium carbonate, as well as emissions during the production process. These are described as ‘novolac sulfone derivative’. In instances where potential environmental harms and benefits are presented in a single diagram, the score in a category is the sum of these, to be understood as an environmental benefit. The characterisation of the sulphonic derivative production process of post-production novolac waste revealed that the impact of the category of resource consumption through the use of resin waste is positive.

3.2. Results of Weighted Indicators for Impact Categories

Figure 2 shows the results after weighting in the 16 impact categories. The results in all impact categories are expressed in units of mPt (Pt-mile, Pt-point). The environmental impact of the production of 100 kg of phenol–formaldehyde-sulphone derivative resin (novolac) is 15.47 mPt. All “inputs” to the system have an environmental impact of more than 5%: sulphuric acid (21. 2 mPt, 137%), emissions during production (8.1 mPt, 52%), sodium carbonate (4.3 mPt, 27.6%), electricity (4.1 mPt, 26.5%), calcium carbonate (0.9 mPt, 5.7%), and polystyrene waste as an environmental benefit ((−) 23 mPt, (−) 149%)). Flocculant production has the greatest impact on the categories: climate change (39.4%), acidification (36.4%), particulates (25.1%), water use (15.9%), and resource use—minerals and metals (13.9%). There is a significant environmental benefit from the management of novolac waste—(−) 27.6% in the category of resource depletion—fossil raw materials and in the category of human health—carcinogens 7.1%, resulting from the management of novolac waste.

The results after the weighing step can be presented in similar histograms as for the characterisation step or in a ‘process network’ format. The thickness of the arrows is related to the magnitude of the environmental impact, e.g., in the production of the sulphonated derivative from novolac waste, the key potential environmental impact is the use of sulphuric acid (VI), electricity, and disodium carbonate for its production, while the environmental benefit is the use of novolac waste instead of virgin material—the green arrow (and negative value). Sulphuric acid (VI) for flocculant production was used in excess, so the negative environmental impact could be reduced by optimising the production process. Figure 3 shows the process network as a single indicator. Process networks can also be presented as a single indicator for a specific impact category—e.g., climate change (Figure 4), acidification (Figure 5), or resource depletion—fossil raw materials (Figure 6).

As can be seen from the raw material and process tree developed for the assumed production of the sulphonic acid derivative of phenol–formaldehyde resin, the main potential environmental impact is the production of H₂SO₄ acid, which is used in excess, and to a much lesser extent, the use of electricity during the process, which can be clearly seen in Figure 3, Figure 4, Figure 5 and Figure 6.

Based on the research carried out, it was concluded that the LCA is a very good tool for investigating the environmental impact of technological processes. The LCA as an environmental management technique allows the assessment of the performance of polymer waste recycling. For companies, the LCA can be a very good tool to evaluate production technologies where appropriate safety measures are particularly important.

4. Conclusions

The LCA is an extremely valuable tool for assessing the environmental risks associated with the production of new chemical technologies such as polymeric flocculants. The LCA of newly synthesised flocculants has shown that sourcing flocculants from waste phenol–formaldehyde resins is highly beneficial to the environment due to the high toxicity of waste resins that produce phenol when exposed to physical factors. Through the LCA, more informed decisions can be made to minimise negative environmental impacts and improve the sustainability of the chemical industry. LCA conclusions can also be used to inform customers about potential product risks and promote an informed approach to choosing green products. This can help build a positive corporate image and increase consumer confidence. LCA results are not a substitute for the need to carry out, for example, environmental impact assessments or environmental risk assessments, but they are a good technique to support reliable and credible research in these areas. The research was conducted in order to obtain information on the environmental risks caused by the use of flocculants obtained from polymer waste, taking into account the production processes. Comparative analysis of the obtained products—flocculants—makes it possible to select the most environmentally safe product. Studies using the LCA method were conducted for polymer flocculants used in the treatment of metallurgical and coal-mine wastewater. For the future, in-depth analysis of the waste-based polymer compounds obtained when used as flocculants in wastewater treatment processes is planned, extending the LCA studies to electroplating and municipal wastewater treatment plant effluents. This will not only allow for the selection of an effective flocculant, but above all, will allow for the selection of the most environmentally safe flocculant, analysing the environmental footprint using the LCA method.