Case Study Regarding the Variation of the Qualitative Parameters of Wastewater

Romania is making efforts in order to enforce the Directive concerning urban waste water treatment and was left behind by other member states. Starting from the premise that the lack of a proper treatment of wastewater can negatively influence the quality of the emissary in which they are discharged., we proposed that in this paper we analyze the main indicators of wastewater quality, identifying also the causes of water pollution. For this purpose, we followed the variation of five representative indicators of wastewater from Călărași Wastewater Treatment Plan: chemical oxygen consumption, biochemical oxygen consumption, total nitrogen, total phosphorus, suspended solids. The best results in purification were observed regarding the biochemical oxygen consumption (over 95%). The low temperature of wastewater at the entrance to the Wastewater Treatment Plant during winter leads to a difficult exploitation of the biological step and implicitly to the increase of the phosphorus and total nitrogen concentration in the effluent, which means a weak process of eutrophication in the emissary.


1.Introduction
Sustainable development links in a coherent framework the environment, social and economic policies, thus contributing to the enforcement of environment legislation and policies. It is somewhat early to draw solid conclusions about the impact on the rural development and the environment. In many cases, the information about their impact is missing, partly because some countries have adopted these only recently and partly because monitoring is deficient [1]. Ensuring compliance with environment legislation consists in all activities undertaken by public authorities in order to ensure that industries, farmers and other categories fulfill their obligations to protect water, air and nature and manage waste [2]. The municipal wastewater treatment plants of medium and high size have a specific flow of sludge treatment and conditioning [3].
According to the Accession Treaty, the deadline granted to Romania for ensuring the compliance with the Directive was the end of 2018. Taking into consideration the low compliance rates, the Commission decided to initiate an infringement procedure against Romania, based on the interim terms in 2013 and 2015 established in the Accession Treaty, in respect of compliance with collection and treatment requirements for the agglomerations that exceed 10,000 equivalent inhabitants [4]. The required investment to ensure proper collection and treatment of wastewater from the remaining agglomerations is estimated at 12 billion EUR. This figure is still high, despite the significant number of EU-funded projects. Other ongoing studies indicate greater investment needs. According to the latest report, it is estimated that the last projects will be finalized by 2027-2030, well beyond the deadlines of 2015 and 2018, established in the Accession Treaty of Romania [5]. Romania must finalize as soon as possible the projects for agglomerations that breach the obligations stipulated in the directive. In order to comply with the obligations, Romania needs to improve the methodology for setting priorities concerning the proposed water projects for EU funding and to accelerate their elaboration and implementation. Furthermore, revenues generated by water companies should ensure the sustainability of newly built infrastructure [2]. Romania is compelled to implement and comply with the stipulations of Directive 91/271/EEC on wastewater treatment [6].
According to recent reports, only 2.5% of wastewater in Romania have been collected (8 agglomerations) in accordance with the Directive, and 6 agglomerations have fulfilled the conditions for secundary treatment and only 1 agglomeration has fulfilled the conditions for a thorough treatment [7]. To maintain the ecosystems integrity, environment improvement and keeping the water quality is crucial so that the wastewater can be purified and efficiently managed. Through wastewater treatment the loading into organic and inorganic pollutants, as well as into bacteria is reduced, clean water is obtained, in different degrees of purification, as well as a mixture of minimum substances called sludge. Insufficiently treated wastewater that has reached the emissary affects its capacity of self-purification and natural recovery of the biogeochemical balance. Poor treatment of wastewater makes the water that results from insufficient treatment impossible to be used in households, industry or even agriculture.
Wastewater treatment represents the physical, chemical, biological and bacteriological processes assembly, which reduces the loading in organic and inorganic pollutants as well as in bacteria, in order to protect the environment [8]. As a result of these procedures, clean water is obtained, in different degrees of purification, depending on the technologies and equipment used, as well as a mixture of substances called sludge [9]. The countless sources of water pollution and its limited ability to selfpurify have led to the identification of the main pollutants becoming very important [10]. The real sources of pollution to be considered are those created by the activity of human beings.
Wastewater treatment plays a major role in protecting the environment [11], thus becoming a moral responsibility of each of us, and it plays a role in protecting public health, as poor sanitation of water discharged into the emitter is the main cause of surface water contamination, causing different types of diseases [12].
Worldwide, the most common problem related to the water quality is its pollution with nutrients, most often with nitrogen and phosphorus, coming mostly from the agricultural activities, industrial or human waste [13]. Nitrogen and phosphorus are essential nutrients for plants, but when their concentration exceeds a certain limit, they are considered pollutants and lead to excessive growth of aquatic plants, a process called eutrophication [14]. The elimination of phosphorus from wastewater is an environment necessity, as it stimulates the growth of aquatic plants and contributes to the eutrophication process in general [15]. Red mud proved to have positive influence on the removal of the phosphates from wastewater, to reduce the pollution potential [16].
The treatment enhancement post-physicochemical stage leads to the discharging of the biological stage of further loads, which means that the resulting treated water will have the necessary indicators that allow it to be used [17].
According to the Department for Sustainable Development of Romania, the current institutional structure is not suitable for implementing and monitoring of the Sustainable Development Goals (SDGs). A project to create special structures for the implementation of the SDGs must be designed and implemented. Romania national strategy for sustainable development is under review [11]. In 2018, a voluntary national evaluation on the implementation of the SDG was submitted to the UN [18].
The purpose of this paper is to analise the loading of wastewater with pollutants at their discharge into the emissary (Borcea branch) and into the Danube.

2.Materials and methods
The processed data found in this paper were provided by Călărași Environment Protection Agency, which monthly conducts analyzes of wastewater discharged into the emissary and by the Călărași Wastewater Treatment Plant, which daily collects samples and analyzes them in the laboratory. Călărași Wastewater Treatment Plant is an efficient one, upgraded after the implementation of the European project "Extension and rehabilitation of water supply and sewerage systems in Călărași County", from 2012, co-financed through the cohesion fund within the "Sectoral Operational Program" Environment " [19]. The Wastewater Treatment Plant belongs to ECOAQUA S.A. Călărași and includes the following components: mechanical filtration step, biological step, chemical treatment of wastewater, sludge treatment, installations for gas produced in the treatment plant. The published literature and the European https://doi.org/10.37358/RC. 21.2.8414 Commission Reports, the Directives on urban wastewater treatment respectively, Eurostat Reports, but also the locally drawn up Reports by the organizations where the study was conducted were used for description of technical processes, the requirements regarding the influence of environmental factors on the sustainable development, as well as the content of indicators that were determined following the data processing.
The main indicators of interest regarding waste water quality that have been analyzed in this work are: BOD5 (biochemical oxygen consumption in waterdetermined by the electrochemical method, in mgO2/L, according to SR EN 1899-22002), COD (chemical oxygen consumptiondetermined volumetrically, in mgO2/L, according to SR ISO 6060-96), Ntot (total nitrogendetermined by combustion and IR spectroscopy, according to SR EN ISO 13395:2002), Ptot (total phosphorusdetermined spectrophotometrically, according to SR EN 1189-2000), SS (suspended solidsdetermined gravimetrically, according to STAS 6953-81) [19]. They were compared with the maximum allowed value, according to NTPA001 [20].
Knowing the value of biochemical oxygen consumption at 5 days (BOD5), it is extremely important to evaluate the degree of wastewater pollution, expressing the amount of biodegradable organic substances contained in that water. Dissolved oxygen is determined before and after 5 days of incubation at 20°C ± 1°C in complete darkness. A nitrification inhibitor is added [19].
Chemical oxygen consumption COD (potassium dichromate method) represents the mass concentration of oxygen equivalent to the amount of potassium dichromate consumed for the oxidation in acid medium of dissolved and suspended organic materials present in wastewater.
The method for determining the total nitrogen in wastewater is IR analysis -oxidative combustion. The gases in the combustion tube, after passing the detection in IR, for CO2 analysis, are taken and introduced in a chemiluminescence detector, used for nitrogen analysis [19].
Phosphorus compounds are usually part of the composition of detergents and chemical fertilizers; as a result they can appear in wastewater resulting from household consumption, hotels, restaurants, laundries as well as in agricultural waters.
The suspended solids present in the wastewater are determined by filtering a determining volume of water through a fiber glass filter, followed by dissolving the salts present by washing the filter with distilled water. The filter solids are dried at a standard temperature of 100-105°C. The result obtained is the amount of dry material relative to the volume of water initially used [19].

Results and discussions
Although on national level progress has been made concerning the implementation of Directive 91/271/EEC regarding urban wastewater treatment, the increase of collection and treatment level was registered especially in urban areas in 2009-2015, so that the collection level has increased from approx. 51% in 2009 to 63.46% in 2015 and the treatment level has increased from approx. 37.5% in 2009 to 56.71% in 2015, in agglomerations greater than 2,000 equivalent inhabitants. However, in rural areas, the wastewater collection and treatment level is still very low. One of the causes is the low connection level of the population to the sewerage networks, having infrastructure without connected population [21]. In 2016, the population connected to the sewage systems represented 49.2% and the connection rate to the treatment plants was 47.8%, substantially below the level reached by other countries in the same area [7]. During 2009-2015 about 4.14 billion Euro was invested having different sources of financing (national and international) for the construction, rehabilitation and modernization of wastewater collection and treatment systems [18].
Although significant investments have been made regarding the sewerage network and the modernization of Călărași Wastewater Treatment Plant, wastewater is still a threat to public health and natural ecosystems, affecting the emitter capacity for self-purification and natural recovery of the biogeochemical balance [22,23]. The weaknesses of wastewater collection and treatment system in Călărași county are represented by numerous damages in the sewerage system by break of collectors and collapses, and the population benefiting from the wastewater collection service represents 75% of the population of the municipality [19].
The main watercourse of Călărași county is the Danube river, Borcea branch -considered to be a special avifaunistic protection area [22]. The Danube and Borcea branch have now reached in Călărași municipality the limit of natural capacity for restoring the biogeochemical balance, therefore, a control and an efficient treatment of the discharged waters it is necessary. The spillage of wastewater, poorly purified, in surface waters, produces adverse effects on the natural phenomenon of self-purification [19].
For accurate assessment of wastewater discharge impact in Călărași municipality, both the influent of the wastewater and the resulting effluent from Călărași Wastewater Treatment Plant were chemically analyzed. During 2017-2018, the main indicators of wastewater quality and purified water presented the following values [19]. We observe from Table 1 that during the two analyzed years, the efficiency of treatment plant in terms of purifying treatment degree of main indicators is placed between 72.5% (Ptot value in 2017) and 95.24% (BOD5 value in 2017). In both years of study, the lowest level of purification is phosphorus (72.5%, respectively 74.78%), whilst the highest percentage is biochemical oxygen consumption (94.45% and 95.24% respectively).
The BOD5 variation from water discharged into the emissary during 2017-2018 are presented in the Figure 1. According to data in Figure 1, it can be observed that the highest amount of BOD5 effluent was in January 2017 (11.24 mg/L), followed by February 2018 (10.12 mg/L). The variation of the biochemical oxygen consumption from one month to the other was due mainly to the climatic conditions or the recorded influential flow. However, throughout the studied period, we note that the values of the biochemical oxygen consumption of the purified water were much lower than the maximum value allowed by NTPA001, namely 25 mg/L [20].
In case of chemical consumption of effluent oxygen in the emissary (COD), as we observe in Figure  2, during 2017-2018 it`s values fluctuated, the highest value being registered in June 2017, that is 58, 92 mg/L, but this is well below the limit imposed by NTPA001 (125 mg/L) [20]. In Figure 3 we observe that during the studied period, the total nitrogen values discharged in the emissary exceeded the maximum allowed value according to NTPA001 (15 mg/L) [20] in February and March 2018 with 1.45 mg/L (9.66%) respectively 5.13 mg/L (34.2%). This fact is due to the low temperature of the waste water at the entrance to the treatment plant during the winter season (minimum temperature of 4 0 C, average temperature of 7 0 C) leading to a difficult exploitation of the biological step, the decrease of biological processes speed, the decrease of biodegradation efficiency of the organic compounds and implicitly by increasing the concentration of nitrogen and effluent compounds.

Conclusions
Urban environment actvities are sources of pollution for all environment factors, so these activities must be controlled and managed in order to minimize the impact on the environment. The environment factors air, water, soil, flora, fauna continue to suffer under the impact of human activity and important quantitative and qualitative changes.
Based on the analyzes conducted on the main indicators of water quality discharged in the emissary from Călărași Wastewater Treatment Plant, the following can be concluded: In 2017, the actual load of the station influencer is lower than the projected one, as follows: In 2018, the actual load of the station influencer is lower than the projected one, as follows: -BOD5 with 55%; -COD with 28%; -Total nitrogen (Ntot) with 10%; -Total phosphorus (Ptot) by 35%; -Suspended solid substances (SS) with 38%. In winter, the low temperatures lead to the decrease of efficiency of organic compounds biodegradation, meaning an increase in the concentration of nitrogen in the water discharged in Borcea branch.
The difficult exploitation of the biological step during cold periods results in a lower efficiency in removing phosphorus and total nitrogen, this bringing nutrients into the emissary and causing a process of eutrophication, much smaller than the previous period (the quantities reached in the emissary they are big).
From the evolution of the main analyzed indicators, it is observed the decrease of the content of organic substances and of the water eutrophication agents (total phosphorus and total nitrogen), their values being closer and closer to the norms required by the legislation in force.
The quality indicators of wastewater when entering the plant fall within the limits imposed regarding the quality of the wastewater discharged into the sewage network or directly in the treatment plant.
The quality indicators of wastewater discharged into the natural stream fall within the limits imposed by the regulations in force, NTPA 001 -suspensions respectively, BOD5, COD, total phosphorus, total nitrogen.
The efficiency of treatment plant, analyzed for the 5 indicators is good, varying between 72-95%. In order to solve the problems identified within Calarasi Wastewater Treatment Plant, we propose: ensuring optimal operating conditions during cold periods; ensuring the energy needed to raise the water temperature, to be done with the help of heating installations using unconventional energy sources: heat pumps, solar energy.