Chemists from St Petersburg University are participating in the international OneDrop project. Its goal is to create an environmentally safe and cost effective integrated electrolysis unit, generating liquid sodium ferrate. This is a selective oxidant for a large number of organic pollutants. The innovative development is to revolutionise the current industrial wastewater management and drinking water treatment.

‘Ferrates are high-valent iron compounds that have a very high oxidation potential. They can oxidise most organic pollutants converting them into water and carbon dioxide. Secondly, sodium ferrate acts as a coagulant. It is also essential that the by-product of ferrate oxidation – apart from water and carbon dioxide – is an environmentally friendly insoluble iron (III) hydroxide, which can also be used in water purification processes as an adsorbent. After going through the purification process, iron (III) hydroxide can be utilised in other industries, for example as an additive for metallurgical production,’ explains Sergey Ermakov, the OneDrop project manager from St Petersburg University, Professor in the Department of Analytical Chemistry at St Petersburg University.

However, sodium ferrate is quite unstable and rapidly decomposes to the aforementioned iron (III) hydroxide. This leads to problems with regard to its transporting, handling, and storing. In order to resolve these problems, researchers from Russia and Finland launched an international project to design and develop a mobile water purification plant. The ‘core’ of the plant is an integrated electrolysis unit which generates liquid sodium ferrate. A steel anode, sodium hydroxide solution and a current source are all that is needed. The installation generates sodium ferrate, which can be used in situ: for wastewater treatment and localisation of contaminants at the spill sites.

The OneDrop project brought together scientists, researchers and engineers from: St

Petersburg University; Lappeenranta-Lahti University of Technology (Finland); Peter the Great St Petersburg Polytechnic University; the Russian innovation company NPK Omega, as well as from the Finnish company Lappeenranta Free Zone Ltd. The latter administrates the Lappeenranta’s cargo, passenger, and small boat harbours and harbour traffic and manages their maintenance, development, and marketing. Port of Lappeenranta provides the research team with the pollution data and is to be the end-user of the project outputs. The project is funded by a cross-border cooperation programme ‘The South-East Finland – Russia CBC 2014–2020’ (Grant No KS1648).

‘The main task of the team of St Petersburg University chemists is to develop an analytical quality control system for water treatment processes and determine exactly how much sodium ferrate is generated. We also need to develop a method to ascertain that the oxidising process is complete and no harmful substances appear during the ferrate treatment process. Our research has yielded positive results so far. Currently, the installation is being tested at the Institute of Chemistry at St Petersburg University using specially selected pollutants taken from the Seleznevka River. We have chosen this particular water body, as its basin is shared by Russia and Finland. The analysis occurs in an automated mode using optical and electrochemical sensors. The most difficult analytical part of the work is carried out at the St Petersburg University Research Park,’ explains Sergey Ermakov.

According to Sergey Ermakov, unlike chlorine, sodium ferrate does not produce any harmful by-products. Even if introduced in the water treatment system in excess, ferrates soon form insoluble iron (III) species. Whereas when water is treated with chlorine, the socalled free chlorine is formed. The fact is that free chlorine is very dangerous to human health; therefore, water chlorination must be thoroughly controlled at water utilities.

The oxidation kinetics, that is, the kinetics of the removal of organic pollutants from water, is studied by the scientists from St Petersburg University together with their partners from Finland. Unfortunately, the pandemic caused complications with the exchange of samples, and at present, the chemists are mainly sharing research data.

Another task of the international research team is to determine how effective sodium ferrate is in removing pharmaceutical residues that are commonly found in the world’s water systems. The fact is that the traces of drugs that a person takes are excreted from the body, entering water mains and natural water bodies. Consequently, these pharmaceutical contaminants can accumulate in fish. When water is used in agriculture, the contaminants accumulate in soil and enter the food chain, eventually, becoming a hazard to humans.

Not only are pharmaceutical metabolites dangerous, but their subsequent transformation products as well. For example, as a result of oxidation, carcinogenic or other toxic substances can be formed. In order to ascertain to what extent our installation can help to solve this problem, we have been testing it on water samples contaminated with various pharmaceutical pollutants, such as diclofenac. This widely used anti-inflammatory drug is rather stable and it has been detected in fresh water bodies and fish all over the world. Preliminary results indicate the potential for innovative, cost-effective and environmentally friendly solutions to this pressing problem.

Sergey Ermakov, Professor in the Department of Analytical Chemistry, St Petersburg University

Furthermore, the installation will facilitate solving the problem of alien invasive species in various seas. Today ships use a huge amount of ballast water, which provides stability and manoeuvrability during a voyage and during loading and unloading operations. Ballast water is often taken on in the coastal waters in one region after ships discharge wastewater or unload cargo, and discharged at the next port of call. Ballast water discharge typically contains a variety of biological materials, including the so-called invasive alien species that may adversely affect the invaded habitats and bioregions. ‘This leads to a disruption of marine ecosystems and is recognised as a serious threat to the biological diversity and human health in general. Hence the interest in the new ballast water treatment system, expressed by the port of Lappeenranta,’ says the professor.

According to Sergey Ermakov, very small doses of sodium ferrate are required for water purification. Even a prototype installation, which is no bigger than a microwave oven, can decontaminate up to 150 cubic metres of water per hour in one cycle, with the installation operated in a continuous mode.

‘Indeed, if the water is heavily polluted, more sodium ferrate will have to be generated for water purification. However, the autonomous control system that we are currently working on will allow for these indicators to be taken into account. Ultimately, this will increase the reliability and the ease of use of the novel technology. Unfortunately, the work on the installation has been delayed due to the pandemic. Nonetheless, thanks to the coordinated work of all the participants, we are getting closer to the finishing line. I believe that the project will have been completed by the end of 2021,’ emphasised Sergey Ermakov.