HYDAURUS is a treatment unit for the surface runoff of an airport, into which de-icing fluids and anti-icing agents find their way over the winter. The runoff is not treated by one process: the glycols are concentrated and oxidised, the potassium salts go to a biological stage.
The unit takes in the winter surface runoff of an airport — meltwater from aprons, runways and taxiways, along with the water from technological washing — and separates it before the treatment proper begins. The separation follows the nature of the pollutant rather than the volumes: the ionic fraction of potassium salts on one side, the neutral glycol organics on the other, and from there each takes a route of its own.
It is meant for airport infrastructure, where the winter treatment of aircraft and pavements is obligatory under the conditions of flight safety, while the runoff that follows cannot be treated as ordinary storm water. The layout is declared modular, and the set of stages — pre-treatment, membrane concentration, EDR, electrochemistry, biological treatment, ultraviolet, sorption, final polishing — follows the runoff composition of the given airport.
Pollutants of different natures are present in the winter runoff of an airport at the same time. The anti-icing agents used on pavements give an ionic fraction: potassium formate, potassium acetate and salts close to them, which under the right process regime break down biologically. The de-icing fluids used on aircraft give the second fraction — ethylene glycol, propylene glycol and organic compounds of similar behaviour are neutral, carry no charge, are poorly retained by ion exchange and pass through many standard barrier stages.
Hence the limit of a common scheme with no separation of the streams. Harsh chemistry, chlorine or aggressive reagents applied to the whole volume suppress the microflora and remove the very possibility of a normal biological breakdown of the salt fraction. The glycols, on the contrary, break down more slowly and call for a different approach: the reliable destruction of such pollutants is tied to hard oxidation, electrochemistry or ozone included. A single way of treating the whole runoff often turns out ineffective.
The order of work in HYDAURUS is the reverse of the habitual one: separate and concentrate first, treat afterwards. Pre-treatment takes out the suspended solids, the heavy organics and the pollutants that would interfere with the membrane and electrochemical processes downstream, and thereby lowers the load on the later stages. The membrane stage then works not as a final barrier but as a means of concentration and separation: instead of a large volume of weakly contaminated water there remain manageable streams.
From there the routes diverge. The glycol fraction is directed to oxidation, and the potassium salts to a biological stage, where they can serve as a biodegradable substrate for the microflora. The membrane stage meanwhile reduces the volume of the problem stream, prepares the concentrate for electrochemical treatment and shields the biological stage from pollutants that do not suit it. The different classes of substance stop competing for one process and part into different process blocks.
Electrochemistry is a strong instrument, but it calls for sensible energetics. Electro-oxidation is applied to concentrated ethylene glycol, by which the anode works at its highest efficiency: the better the stream is prepared and concentrated, the more effectively the oxidation proceeds. To send the whole seasonal volume to high-energy oxidation would make the system too costly, and to send all of it to biology would let the slowly degradable components through under-treated.
The second half of the same logic is to keep the part of the load that breaks down on its own. Potassium salts can reach biological treatment works in unchanged form and be regarded as a biosubstrate balanced in carbon and nitrogen for the microflora. An early treatment with aggressive reagents would destroy the conditions for that stage, so no surplus chemistry and no electricity are spent on the biodegradable part of the runoff.
Treating large volumes of winter runoff should not turn into the constant formation of sludges that have to be hauled away and buried. The scheme is built without coagulants and without sulphuric or hydrochloric acid: there is no aluminium in the final water, and no solid waste for a landfill arises. SnO₂-Sb or BDD anodes work without active chlorine, chlorates and perchlorates, while the ultraviolet stage disinfects the treated water along the way.
The alternative to treatment on site is storage, haulage and handover of the runoff for external disposal, and for a large airport that can turn into a noticeable seasonal expense. The development offers a different approach: the runoff is treated on site as a process stream instead of being carted away as waste. The contamination is at its plainest in winter, yet the declared operating span of the unit is treatment over 12 months a year, on stored and process streams.
HYDAURUS is SOLVIA's own technological development for the treatment of airport wastewater carrying de-icing fluids and anti-icing agents, aimed at modular units with membrane stages, electrochemical blocks and final polishing. A patent application on the method of treating airport wastewater has been filed with Rospatent. The structural solutions, the internal treatment regimes, the design parameters and the particulars of the process scheme are not disclosed in open materials. The technology is stated to be ready for a pilot installation at an airport, and the nearest step of development named is the start-up of a unit on a pilot site.
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