Evaluation of the Ecological Effect of Biodegradable Waste Processing in a Comprehensive Municipal Waste Management System

A properly managed municipal waste management system allows for the processing of all waste streams, including organic waste, which is one of the significant components of the entire stream. This should be done in accordance with the waste management hierarchy provided for in the Waste Framework Directive 2008/98/EC [1] and amended by 2018/851/EC [2]. In accordance with its provisions, Member States should introduce measures to promote the prevention and reduction of food waste, and in particular, by 2030, halve the global amount of food waste per capita in retail and consumption, reduce food losses in the production and distribution process. Member States should aim to achieve the Union indicative target of a 30% reduction of food waste by 2025 and 50% by 2030. In addition, in the light of the provisions of the Landfill Directive(1999/31/EC) [3]. Member States should develop a national strategy to reduce the amount of biodegradable waste going to landfill. The strategy must ensure a certain degree of reduction of the amount of municipal waste in relation to the level of production in 1995. The levels of reduction of biodegradable waste should be ensured in such a way that no later than 15 years after the introduction of the provisions of the Directive, municipal biodegradable waste intended for landfills is reduced to 35% of the total weight of waste produced in 1995 [4–7].

According to the Central Statistical Office, in 2017 a total of 11,97 million Mg of municipal waste was collected in Poland, both selectively collected and mixed. About 7.5% of this value was made up of selectively collected biodegradable waste (895 thousand Mg). Most of the 811 thousand Mg of biodegradable waste collected in 2017 came from households (90.5%). The remaining biodegradable waste came from sources other than households, i.e. municipal services, trade, small business, offices and institutions (in total about 85 thousand Mg). According to the data of the Central Statistical Office (GUS) from 2018, a total of 11 969 thousand Mg of waste was collected in Poland, including 848 thousand Mg of composting or fermentation processes [8].

In 1995, which is the comparative year, 4.381 million Mg of biodegradable municipal waste was produced, with 155 kg per city inhabitant and 47 kg per rural inhabitant. According to EU data from 2010, on average more than 89 000 Mg was produced in Europe, of which more than 34 000 Mg came from industry, more than 37 000 Mg from households and more than 16 000 Mg from other sources [9].

The need to treat organic waste and the ban on landfill results from the need to reduce greenhouse gases to the environment. Organic recovery and recycling must therefore be applied. According to the law, recovery is any process whose main result is that waste serves a useful purpose by replacing other materials which would otherwise be used to fulfil a given function, or by which waste is prepared to fulfil such a function in a given plant or in the economy in general. Recycling, including organic recycling but not including energy recovery and reprocessing into materials to be used as fuels or for backfilling operations, is also one form of recovery. Among the organic recycling methods, it stands out:

The organic waste treatment processes also cause emissions to the environment [14–15]. Therefore, the aim of the paper will be an attempt to compare the emissions arising from various processes of biodegradable waste processing. Life cycle analysis is often used for this kind of assessments. Life Cycle Assessment (LCA) [20–24] – a relatively new environmental management technique, assessing the environmental impact of products, techniques, technologies or activities during the whole life cycle at particular stages; it is based on ecobalances (materials used, raw materials, energy and emissions received) of the assessed products or technologies, which result in environmental assessment in the form of environmental impact categories or so-called areas of damage defined as: system quality, human health and resource consumption [25–28]. The LCA methodology has found its recognition in the environmental management standards ISO 14000 [29–32]. In the field of waste management, specialist softwares were developed, and used to calculate the environmental load. The most important of them include: EASEWASTE (Environmental Assessment of Solid Waste System and Technologies), developed by the Technical University of Denmark [33], IWM (currently IWM – 2) developed by Procter & Gamble, for the assessment of municipal waste management systems [14, 20, 34], WRATE (Waste and Resources Assessment Tool for the Environment) [35], Integrated Waste Model (IWM) site at the University of Waterloo [33].

The aim of this paper is to present the method of analysis and selection of the system of management of the biodegradable household arising as one of the streams. In the justification of taking into account only the ecological factor of the discussed systems, it should be noted that in their design and analysis the most difficult and controversial aspect is this factor. It affects both the economic factor (increasing costs of waste processing and protection of the environment against the influence of the installation) and the social factor (fears of the inhabitants of the environmental impact and health and life). Thus, the following stages can be distinguished in the proposed method:

The Integrated Waste Model (IWM – 2), developed by Procetr&Gamble for the environmental assessment of waste and packaging management systems [24, 28, 31, 35], was used to determine the ecological effects of waste management systems in the region. The model is based on the LCA (Life Cycle Inventory) analysis and uses its first stage: LCI (Life Cycle Inventory), i.e. determination of sets of inputs and outputs from the analysed waste management system (system balance analysis – data inventory). Transparency of the model allows to track changes at each stage of calculations in the scope of both waste stream balancing and emissions not only from the whole system, but also from individual unit processes. The functional unit of this model is a comprehensive system of municipal waste management in a specific geographical region and at a specific time. The result obtained in the form of emissions from the system will constitute a decision-making matrix and a defined decision-making problem.

A multi-criteria analysis was also used to select the most advantageous waste management system in terms of environmental impact. For the analysis, the waste management scenarios described and balanced in detail in the IWM – 2 programme were adopted. Since the decision-making task was to select the variant which would have the least impact on the environment, the assessment criteria are the values of emissions to the environment, recorded in groups:

The distinction between groups of criteria allows for weighting of individual groups of criteria or individual criteria. For multi-criteria analysis the weighted sum method was used. To solve the decision-making task, the compromise programming method was used, using the concept of ordering individual technology variants according to their distance from a fixed ideal point X'(x₁', x₂', …, x_M'), whose all x_M' coordinates are equal to the maximum value of the adopted standardization scale. The mathematical record of the measure of the distance of the tested variant from the ideal point has the form [24, 28]:

and the choice of the most advantageous solution is made according to the principle:

where:

sj – measure of the difference between a given s _n variant and an ideal point

s – the chosen option,

w _m – weighting factor of criterion m,

x _m ' – m – that coordinate of the ideal point,

r _NM ' – standardised value of the assessment criterion,

M – number of criteria,

α– a power factor measuring the deviation of the strategy from the ideal point X', taken in practice as 1, 2 and ∞.

The final solution when using multi-criteria analysis is to rank the variants of waste management system solutions from the most to the least beneficial for the natural environment.

The aim of this task will be to select the most environmentally beneficial solution for organic recycling in a comprehensive waste management system in the selected region. Among the most important assumptions for the calculation one should specify [35]:

On the basis of the adopted assumptions, the program generated the previously described waste management scenarios, presenting them in the form of diagrams showing the functioning of individual systems and flows of individual waste streams. The comprehensive diagram is presented in Figure 1. The figure in the “yellow” boxes shows mass flows of waste expressed in [Mg/year], on the left side “entering the system”, on the right side “leaving” the waste quantity system. In the “black” boxes the descriptions of waste streams flowing through the system are presented, therefore they should be referred to the yellow “boxes”. The “green” windows at the bottom of the diagram show the total waste streams leaving the system: the stream of raw materials (materials) recovered from waste, the level of weight reduction as a result of waste treatment (e.g. moisture loss) and the remaining amount of treated waste that must be directed to landfill. These values are expressed in [Mg] and [% weight].

Figure 1.

The results obtained from the IWM – 2 programme are the emissions to the environment as a result of the operation of individual scenarios. Emissions are presented at individual stages of system operation (as a result of the operation of each installation) and for each environmental component separately: solid waste emissions, emissions to air and emissions to water; additionally, they are broken down into individual chemical compounds. The decision problem is formulated when the assessment criteria are established and their values expressed in the form of a finite set of numbers (measurable values), resulting from the assessment of individual variants of the waste management system in the same municipality, against selected criteria. The total emissions obtained as a result of the operation of particular waste management scenarios listed in the table may constitute a decision matrix for the selection of the most environmentally beneficial system solution. The columns of Table 1 present the values of emissions to the environment calculated from particular variants, compiled in three groups of impact on particular elements of the environment.

The matrix formulated in this way has become a formulated decision problem to be solved using the formula-weighted sum method (1) and (2). The compromise programming method gives complex results due to the possibility for the evaluator to weight individual evaluation criteria and to introduce additional weighting by introducing the coefficient . The results and the final arrangement of individual solutions of the waste management system are presented in Table 2, ranked from the most favourable to the least favourable. The ranking additionally depends on the adopted weights of particular groups of criteria or particular criteria. Table 2 in the first column presents the weights of the criteria proposed by the author of the study. In most cases, these weights were given to the groups of criteria described in Table 1. Thus, in the first row of Table 2, all the criteria were given a weighting of 1, while in the second row, the first group of criteria (waste resulting from the operation of the scenarios) received a weighting of 2, while the remaining two groups received a weighting of 1. In the last row of Table 2, only two evaluation criteria received a weighting higher than the others.

These were the air emissions “CO₂” and “CH₄”. With such weights and values of the assessment criteria, the result presented in Table 2 was obtained.

On the basis of the assumptions and calculations it was found: