water Article Differences in the Composition of Leachate from Active and Non-Operational Municipal Waste Landfills in Poland Aleksandra Wdowczyk * and Agata Szyma ´nska-Pulikowska Faculty of Environmental Engineering and Geodesy, Institute of Environmental Engineering, Wrocław University of Environmental and Life Sciences, pl. Grunwaldzki 24, 50-363 Wrocław, Poland; [email protected] * Correspondence: [email protected]; Tel.: +48-71-320-5544 Received: 27 September 2020; Accepted: 5 November 2020; Published: 8 November 2020 Abstract: Leachate formation is one of the many environmental hazards associated with landfilling. The leachate may migrate from the landfill to surface water and groundwater, posing a potential threat to aquatic ecosystems. Moreover, its harmful effect on human health and life has been proven. Due to the risks that landfill leachates may pose, it is necessary to control the state of the environment in their surroundings. The paper presents an example of the application of selected statistical methods (basic statistics, statistical tests, principal component analysis) to assess the impact of individual pollution indicators on the quality of landfill leachates. The conducted analysis showed the existence of significant differences between the surveyed active (Legnica, Jawor) and non-operational (Wrocław, Bielawa) landfills in Poland. These differences were especially visible in the cases of the following: electric conductivity (EC) (non-operational landfills 1915–5075 µS/cm, active 5093–11,370 µS/cm), concentrations of total Kjeldahl nitrogen (TKN) (non-operational landfills 0.18–294.5 mg N/dm3, active 167.56–907.4 mg N/dm3), chemical oxygen demand (COD), organic nitrogen (ON), ammonium nitrogen (AN), total solids (TS), total dissolved solids (TDS), total suspended solids (TSS), sulfates, chlorides, sodium, potassium, calcium, magnesium and nickel. Selected indicators should help to determine the progress of decomposition processes inside the landfill and the potential impact of leachate on the environment, and should be used in the mandatory monitoring of landfills. Keywords: municipal waste landfills; leachate monitoring; pollution indicators 1. Introduction Leachate formation is one of the many environmental hazards associated with landfilling [1]. A leachate can be defined as a fluid that seeps through a landfill and is discharged from or contained in a landfill [2]. The leachate contains soluble organic and inorganic compounds, suspended particles and heavy metals [3]. As a result of the physical, chemical and microbiological processes taking place inside the landfill, the leachate takes over a number of substances, and as a result it becomes a highly polluted wastewater [4,5]. The composition of the leachate is dynamic and variable in time, depending on, among other things, the nature of the deposited waste and the chemical and biochemical decomposition processes taking place in it [6], the stabilization level of the deposited waste, the collection system, as well as the location of the landfill and hydrological factors [7,8]. As landfill leachate is one of the main pollutants of the soil and water environment, knowledge of its composition is important in determining the long-term environmental impact of landfills [9]. Leachate from municipal landfills usually contains dissolved organic and inorganic compounds, such Water 2020, 12, 3129; doi:10.3390/w12113129 www.mdpi.com/journal/water Water 2020, 12, 3129 2 of 15 as ammonia, calcium, magnesium, sodium, chlorides, iron and heavy metals (cadmium, chromium, copper, lead, nickel and zinc) [5,10–12]. The leachate may migrate from the landfill to surface water and groundwater, posing a potential threat to aquatic ecosystems [10]. Moreover, its harmful effect on human health and life has been proven [3]. Due to the risks that landfill leachates may pose, it is necessary to control the state of the environment in their surroundings [13,14]. Therefore, the European Union has introduced EU-wide regulations aimed at preserving and improving the quality of the natural environment, i.e., Council Directive 1999/31/EC of 26 April 1999 on the landfill of waste [2]. For all EU countries, uniform general tasks for the monitoring of landfills in the operational and after-closure phases have been established. Their aim is to determine the potential impact of landfills on the environment and to select appropriate measures to regulate this impact. One of the most important provisions of the Directive on monitoring the water environment in the vicinity of municipal waste disposal sites is the requirements concerning the frequency of testing the volume and composition of leachate. They oblige member states to regularly monitor the leachate condition. Despite the introduction of these regulations, the scope of the parameters to be monitored is not specified. It is only specifies that the analyzed substances should be selected on the basis of the composition of the deposited waste. Due to such a situation, the scope of seepage water testing varies significantly between EU member states. This can be observed in the example of several selected EU countries. In Luxembourg, landfill leachate monitoring is carried out under the Grand-Ducal Regulation of 24 February 2003 on the landfill of waste [15]. During the operational and after-closure phase, the parameters tested in the seepage water are determined after prior verification, in accordance with the expected composition of the leachate and the quality of groundwater, but not to a lesser extent than indicated in the Regulation. This includes 23 indicators, as follows: pH, electric conductivity, temperature, chlorides, fluorides, sulfates, nitrates, nitrites, sodium, potassium, ammonium nitrogen, free cyanides, chemical oxygen demand, heavy metals (copper, zinc, lead, cadmium, chromium, mercury, arsenic), total organic carbon, phenols and hydrocarbons. In Portugal, the monitoring of seepage water during the operational phase of a landfill site and after its closure involves a total of 36 parameters analyzed at different intervals, as follows: once a month—pH, electric conductivity, chemical oxygen demand, chlorides, ammonium nitrogen; once every 3 months—carbonates/bi-carbonates, cyanides, arsenic, total chromium, chromium (VI), cadmium, mercury, lead, potassium, phenolic index; once every six months—total organic carbon, fluorides, nitrates, nitrites, sulfates, sulfides, aluminum, barium, boron, copper, iron, manganese, zinc, antimony, nickel, selenium, calcium, magnesium, sodium, adsorbed halogenated compounds (AOX), total hydrocarbons [16]. In Hungary, the parameters to be examined within the framework of seepage water monitoring are determined each time on the basis of the decision of an environmental protection authority, taking into account the composition of waste and hydrogeological properties of the landfill site [17]. Similarly, in Ireland, the parameters to be analyzed in landfill leachate are defined individually in the landfill permit. This range depends on the type and composition of the deposited waste [18]. In Poland, the scope, time, frequency, method and conditions of monitoring are specified in the Regulation of the Minister of the Environment of 30 April 2013 on the landfill of waste [19]. On its basis, the state of the water environment in the vicinity of the municipal waste landfill site is assessed at particular stages of its operation. Landfill leachate tests are carried out, covering 10 indicator parameters, i.e., pH, conductivity, sum of polycyclic aromatic hydrocarbons (PAHs), total organic carbon (TOC) and heavy metals content, including copper, zinc, lead, cadmium, chromium (VI) and mercury. Where a municipal landfill is equipped with a leachate treatment system, samples for physicochemical composition testing are taken at each point of leachate discharge from the landfill, in order to control the effectiveness of the treatment process. Water 2020, 12, 3129 3 of 15 The research on the volume and composition of leachate is carried out in both the operational and post-operationalWater 2020, 12, x FOR phase. PEER REVIEW In theoperational phase, the tests are carried out every 3 months, while in3 of the 15 post-operational phase, every 6 months. No studies are required to establish a set of parameters for thefor monitoringthe monitori ofng landfill of landfill leachate. leachate. It is possibleIt is possible to select to select additional additional parameters, parameters, but due but to due the to costs, the landfillcosts, landfill managers managers most often most order often testsorder only tests within only within the binding the binding scope. scope. TheThe aimaim ofof thethe studystudy waswas toto analyzeanalyze thethe didifferencesfferences betweenbetween thethe compositionscompositions ofof leachatesleachates fromfrom activeactive andand non-operationalnon-operational municipalmunicipal landfills.landfills. The indicators selected in this way shouldshould helphelp toto determinedetermine thethe progressprogress ofof decompositiondecomposition processesprocesses insideinside thethe landfilllandfill andand thethe potentialpotential impactimpact ofof leachateleachate onon thethe environment,environment, andand shouldshould bebe usedused inin thethe mandatorymandatory monitoringmonitoring ofof landfills.landfills. 2.2. Materials and MethodsMethods 2.1.2.1. Study Area TheThe researchresearch waswas conductedconducted inin thethe yearsyears 2018–20192018–2019 onon fourfour municipalmunicipal wastewaste landfillslandfills