SOLVIA RedoxFlow is a remote electrochemical module for the zonal control of the oxidation-reduction potential. Part of the flow of a zone passes through a chamber, is given the potential required and returns to one strictly defined zone: the cathode loop lowers the potential, the anode loop raises it.
The oxidation-reduction potential shows which conditions prevail in the water, and the zones of a treatment works call for different values of it: hydrolysis and anaerobic stabilisation run under reducing conditions, denitrification under moderately reducing ones, while polishing for sulphides and odours calls for markedly oxidising ones. An ordinary plant sets those conditions indirectly — through air supply, recirculation and reagent dosing — and the potential comes out as a consequence of the process rather than as a quantity set for it.
The purpose of SOLVIA RedoxFlow is to make that parameter settable for each zone separately. The module stands outside the biological zones and works with side streams: part of the liquid is drawn from the zone in question, is given the potential required in an electrochemical chamber and is returned, while the cathode and the anode loop never mix hydraulically. The development suits existing works and new schemes alike, and the configuration of the loops is chosen for the particular site.
The cathode loop forms a stream of lowered potential, the anode loop one of raised potential. The catholyte returns to an anaerobic, anoxic, hydrolysis, sludge or denitrification zone. The anolyte goes only to a zone of polishing, of disinfection, of sulphide or odour removal, or else works in a service loop isolated from the wastewater. Each loop has an address of return of its own, and the two cannot be interchanged.
The separation is set by the construction, not by a setting. The anolyte carries oxidising properties useful in polishing, but in a reducing zone a stream of high potential upsets the work of the microflora, suppresses denitrification and spoils the anaerobic regime. The supply of the anode stream to anaerobic, anoxic and denitrification zones is therefore excluded by the pipework itself, not by a prohibition in the control algorithm.
Here the development differs from the known use of anolyte and catholyte, where the solutions are produced for disinfection or for sanitary treatment. Such solutions are not tied to biological treatment and are not restricted in the zones they return to. The description of the invention names as the common shortcoming of known solutions the absence of a technical means of altering the potential in several functional zones in opposite directions from a single external module.
For an anaerobic zone the target range may run from −300 to −100 mV, and for a hydrolysis or sludge zone from −300 to −120 mV. If the potential rises above that, hydrolysis, fermentation and anaerobic stabilisation may work worse. A side stream from such a zone passes the cathode chamber, takes a lowered potential and returns; this matters on sites with an unsteady load, with shock discharges, odours and old sludge.
The target range of an anoxic zone runs from −100 to +50 mV: at a higher potential the reduction of nitrate slows down, and where readily oxidisable organics are short the operator adds an external carbon source. In a calculated forecast example for an anoxic zone of 100 m³, two cathode modules with a side stream of 15 % give a speeding of denitrification of 20–40 % and a fall in the demand for external carbon of 15–30 %. That is a calculation, not a measurement at a working site.
The anode loop answers the opposite task. It draws a side stream of clarified water after biological treatment, or water from the polishing zone, raises the potential to the target range of +300 to +700 mV and returns the stream once residual oxidants have been checked. The regime is used for the oxidation of sulphides and residual organics, for a fall in odour and colour, for better clarity and for the microbiological polishing of clarified water.
The electrodes are chosen for the task of the site. With a consumable anode of iron or aluminium the anode loop also serves as electrocoagulation: the iron or aluminium compounds formed bind phosphates and colloidal matter. That configuration is written into the claims of the invention, and one module then works both as an instrument of potential control and as a stage of final phosphorus removal.
It is not the whole flow of the plant that passes the electrochemical module but from 1 to 50 % of the flow of the zone, preferably from 5 to 30 %. Treating the whole volume of wastewater would call for too high an energy use, whereas a well chosen side stream alters the conditions in the zone without pumping the whole flow. The fall in specific power consumption owed to treating the side stream alone is stated in the materials of the invention.
The tie-in runs as separate circulation loops to the zones of a scheme already built: the mechanical treatment, the anaerobic, anoxic and aerobic zones, the secondary settling and the polishing. No full reconstruction of the plant is called for, and the main case remains the upgrade of existing works — those with odours, weak denitrification, overloads, old vessels and too little automation.
The module is assembled from a cathode and an anode chamber parted by an ion-conducting membrane, separate pumps for the cathode and the anode loop, sensors of redox potential and pH in the functional zones, a sensor of residual oxidants at the outlet of the anode loop and separate vents for hydrogen and for oxygen. The control unit takes the signals of those sensors and regulates current, voltage, the pulse regime and the circulation flow.
Servicing is built into the pipework rather than into a schedule of shutdowns. Bypass lines of the cathode and the anode loop let the module be taken out for service without stopping the main treatment process, wash loops of the chambers regenerate the electrodes and the membrane, and differential pressure sensors show the fouling of a membrane or a diaphragm before it tells on the work of the loop.
SOLVIA RedoxFlow is SOLVIA's own technological development in the field of biological, physico-chemical and electrochemical treatment of wastewater. The technology holds patent protection in Russia. The design parameters, the control regimes, the types of electrodes, the settings of current and flow and the target redox ranges are chosen for the particular site and are not disclosed in full in open materials.
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