Nataša Uranjek, B.Sc. is the head of technology and management in energy company Velenje, which specializes in drinking water, waste-water and district heating management. Her passion for chemistry and engineering led her to studying chemical engineering, where she combines theory with practical skills. Her work includes a supervision of water treatment and distribution, researching new technologies and consulting. As a member of The Slovenian Association for Water Protection she deals with the protection of water resources.

Nataša: I decided to study Chemical engineering because I was attracted to chemistry, medicine and also pharmacy when I was younger, but it seemed to me that all these things were somehow combined in chemistry. I’m also more of a “practical and curious type of person”, which makes engineering more appealing to me, as it requires a combination of theoretical knowledge and practical experience.

Nataša: My work in recent years mainly consists of supervising the operation and performance of drinking water and wastewater treatment and distribution, studying new technological processes and introducing them in the company, and advising other companies that are experiencing problems in ensuring the proper functioning of their municipal utilities.

I am also involved in the design and supervision of new wastewater treatment plants, as well as water supply plants and systems. In the past, I was also the head of our company’s technology laboratory, which monitors the performance of our equipment and systems.

Nataša: Everything that people pour down sinks and flush down toilet bowls is present in municipal wastewater. Faeces, food and food scraps, cleaning products, cosmetics, even chemicals (solvents, paints, pesticides, medicines…) that people pour down drains. Wastewater is a “super cocktail” of all these, and in addition to the basic compounds that are flushed down the drain, new compounds are formed as a result of reactions between them. Some of it breaks down into simpler components, and some of it is already consumed as food for bacteria on its way to the treatment plant. The more persistent compounds make it all the way to the treatment plant, where treatment processes try to remove as much as possible before the wastewater is released into the watercourse.

Nataša: At our largest treatment plant (50,000 population equivalents (PE for short)), we have on-line meters and analysers for various parameters, the ones that are most important for controlling the treatment process. Thus, we measure electrical conductivity, pH, ammonium nitrogen and orthophosphate at the inlet and, in addition to these measurements, dissolved oxygen, COD and nitrate-nitrogen concentrations at the outlet.

Weekly measurements are carried out on the sludge line, where anaerobic stabilisation of the sludge produces biogas and consequently electricity (bipolar is used as fuel in the cogeneration plant). Every 3 weeks, monitoring is carried out on the entire water line at 5 intake points, where measurements of COD, BOD5, all forms of nitrogen (NO2-N, NO3-N, NH4-N, TN), ortho-phosphate, and total phosphorus are carried out in 24-hour samples, suspended solids and other technological parameters.

Nataša: If any of the statutory values exceed the limit value, the operation of all appliances and equipment that could be the cause of the elevated values shall be checked immediately. On-line measurements and correlations between parameters are checked. Usually, the technologists are consulted to find out what could be the possible cause of such a situation on the device. All disciplines are involved; mechanical, electrical and chemical technologists. When any deviation from normal operation is detected, action is taken in accordance with the technical rules.

Nataša: Unfortunately, we do not yet have, or do not know of, or do not have access to, a device that can analyse all chemicals. The chemical analysis process is not like what you might see on TV, e. g. CSI Miami or a similar series, where they put a sample in a “miracle” machine and get a result immediately. Maybe a research institute has similar facilities, but even there they have to go to a lot of trouble to get the sample right. Also, not all compounds can be analysed using the same procedure.

The concentration of a particular compound in the wastewater is also very important; whether the compound is present in grams per litre, milligrams, nanograms or even less. Typically, we target wastewater samples to look for specific chemicals and analyse them to determine their concentration. For wastewater, we have certain parameters to describe the basic characteristics of wastewater. For example, the COD and BPK5 parameters tell how much organic compound pollution is there in the water, and their ratio tells whether this pollution is biodegradable.

Nataša: These parameters are currently analysed in Slovenia in the framework of various surveys, but are not prescribed in municipal wastewater monitoring. I can tell you that we (our wastewater) have already participated in such a study and, of course, these substances have been proven and measured in our wastewater. However, such analyses are very complex and, in addition to the basic chemicals or drugs, the wastewater is also analysed for metabolic residues, as these are partly metabolised by humans after ingestion of medicines or other substances (e. g. drugs), which are then excreted in the wastewater. However, analyses of microplastics found that around 90% is retained in activated sludge.

Nataša: I definitely use my knowledge in my daily life. I avoid convenience foods, try to eat as much locally grown, seasonal food as possible, and when using cosmetics and other products, I check their ingredients and try to avoid those that contain potentially dangerous substances. My principle is to copy things I know and not to “experiment” too much. But when I decide on a new product, I usually check the ingredients.

Nataša: It is important to remember that most of the microplastics contained in municipal wastewater come from laundry and the use of cosmetics. The current requirements for the treatment of urban wastewater do not yet include the removal of microplastics. As I mentioned earlier, most of it is retained in the activated sludge, and its disposition also completes the pathway of microplastics reaching the wastewater treatment plant.

Of course, some wastewater treatment technologies, such as MBR – membrane technology, which includes membrane filtration in the treatment process, retain virtually all microplastics in the activated sludge. As with most pollutants, the aim with microplastics is to minimise contamination and therefore prevent it from entering the wastewater in the first place. This is already being tried by installing special filters in washing machines, and for cosmetics, microplastics should be replaced by natural materials, which were already used in the past, before we started using plastics.

Nataša: This is a difficult question to answer. The fact is that before microplastics were used in cosmetics, they could not have entered wastewater. Microplastics from washing clothes also came from the use and washing of synthetic clothes. However, the actual measurement and analysis of microplastics in wastewater is not yet systematically carried out, as there have been difficulties in establishing methods for determining microplastics. Only when standardised methods of sampling and analysis or microplastics determination are in place will we be able to successfully compare surveys with each other.

Nataša: Conventional treatment processes for municipal wastewater do not include technology to completely remove all organic compounds. The technology for treating urban wastewater is based on biological treatment, which does not remove all the man-made compounds (medicines, cleaning products, hormone disruptors, microplastics, persistent chemicals, etc. ) that are present in the wastewater.

Of course, there are technologies that can clean even persistent and difficult-to-degrade chemical compounds, but these are expensive technologies that require specific equipment and a lot of energy. The trend is to prevent the introduction of these compounds into waterways, to treat them at source (e. g. the pharmaceutical industry) and to introduce these advanced wastewater treatment processes also in the field of municipal wastewater on a polluter-pays basis.

In wastewater treatment research, all kinds of technologies are being tested, including the two you mentioned, but specific treatment methods are used for specific pollutants. The same cleaning method cannot be used for all pollutants, as the effect of one treatment can vary considerably from pollutant to pollutant.

Nataša: For larger wastewater treatment plants with daily flows of 10,000 m3 (10,000,000 L) and more, 1 litre of such material has no effect as it is highly diluted. However, this can be a problem for smaller wastewater treatment plants, especially for those with a house size (WWTPs < 50 PE), where such an event can have many consequences. One is that the quality of the effluent is already legally inadequate at the time, and it may be that the activated sludge is completely destroyed, which means that the plant is inoperable for an extended period. Some substances may simply overload the treatment plant, resulting in temporarily elevated discharge parameters, while others may kill or poison the activated sludge and “incapacitate” nature for a longer period.

Nataša: Well, in Slovenia, we have much smaller village clean-ups; 100 – 2,000 PE (Population Equivalente – presents the amount of wastewater pollution generated by residents or communities and is used to assess the efficiency or capacity of wastewater treatment plants.) and for us the bigger ones are already at 10,000 PE; we are a small country with a scattered population. As for the difference in treatment efficiency, the legislation requires stricter treatment requirements for larger discharges, which is logical when looking at the issue from the point of view of immissions to water. It’s not just concentration that matters, flow also plays a big role when measuring the mass of material released into a watercourse. So, it is the pollution burden that is key in setting the pollution limit.

Nataša: In any case, the treatment of urban wastewater will need to be raised from the level of removal of carbon compounds and nutrients (nitrogen, phosphorus) to a higher level. The next step will be to use appropriate technology (AOP – advanced oxidation processes) to remove drug residues and hormone disruptors from the wastewater, as well as persistent organic matter. The problem here, as so often, is money. Therefore, the trend (as with all waste) is to prevent the entry of difficult-to-degrade substances into municipal wastewater in the first place, to ensure treatment at source and to gradually increase the level of treatment at municipal wastewater treatment plants.

Nataša: I think that is probably also a question of where it would make sense and be possible to use it.

Nataša: Our drinking water, here in our valley, is of high quality, not least because it is treated in a modern way – ultrafiltration. Our drinking water supply is provided by a karst spring catchment, which means that there is contact between surface and underground water and is therefore sometimes microbiologically contaminated (especially during rainfall). Its chemical composition is good or excellent.

There are no problems with fertiliser or pesticide residues, as the water intakes are located outside agricultural areas, and the geology of the hinterland is not problematic. So, through the process of ultrafiltration, we prepare water for our users from captured spring water by a physical filtration process, without the addition of chemicals.

But the price for treating and distributing water to users is, in my opinion, low and perfectly acceptable. If we compare the fact that a consumer pays practically the same in the shop for 0. 5 litres as he pays for 1 000 litres of tap water at home, I think no further comment is needed.

Nataša: Anything that is used, mixed with water and down the drain can be expected to end up in drinking water sooner or later. Water is a universal solvent, but it is also constantly circulating. Here on Earth, the water cycle is “closed”. What we put in the water will come back out again somewhere. Maybe in another form, maybe it will or can be broken down by living organisms, maybe it will accumulate in living things or in the soil, and maybe we will get these substances into our bodies through the food chain.

Nataša: Drinking water monitoring measures a wide range of parameters. They are basically divided into microbiological and physico-chemical. Extended analyses measure many parameters, both metals and other elements, as well as organic compounds. Occasionally, “scans” are made of all organic compounds, but only their presence can be checked, not their concentration.

If anyone is interested in what is measured in drinking water, they can look at the Drinking Water Monitoring in Slovenia website (http://mpv.si/porocila), where annual reports are also published. However, there is still a strong emphasis on microbiological water quality, as microbiologically contaminated water is an acute problem and a potential source of hydric epidemics. In Slovenia, we generally have good water; and the bigger the water supply system is, the more managed it is.

Nataša: Drinking water quality is monitored at 2 levels. The water supplier is obliged to implement an Internal Drinking Water Quality Control System, which is based on the HACCP principle. This specifies the number of sampling points and frequency of sampling, depending on the size of the system, and a set of parameters in accordance with the Drinking Water Regulations.

The second level of control, i. e. sampling and analysis, is set up by the national Drinking Water Monitoring. This is done independently of the water supply provider. In addition to regular sampling and analysis of drinking water, we have many on-line meters and a 24-hour monitoring system to manage our water supply system. This is how we ensure a safe water supply and drinking water that complies with the Regulations.

Nataša: Yes, that makes sense to me, especially if they use the water for drinking. Our experience shows that the water from most of these wells is microbiologically unsuitable.