EK Reactor - Electrodialytic Technology as a Pre-treatment for Wastewater Reuse Applications

The present re-designed reactor, EK reactor (Figure 1), proposes to reduce the freshwater consumption on e.g. concrete production, replacing 100% of the water that is used by treated wastewater. NOVA’s technology consists of a suitable electrodialytic extraction reactor for a wide variety of contaminants (such as heavy metals, salts, organic contaminants) and self-produce clean hydrogen.

NOVA’s EK reactor provides control of the pH in different stages of the treatment, depending on the final application target. Thus, in the first stage, the pH will decrease as the aqueous matrices gets acidified. After a few hours of treatment, in a second stage, the pH turns into alkaline conditions, reaching suitable conditions for example for the final matrices to be used in concrete (Figure 2). The findings will increase the possibility of having a high-quality aqueous resource for different purposes. Thus, it is possible to remove from wastewater the positively and negative charged compounds, assessing also differences in the pH (promoted by the influence of electrodes that are directly in contact with the sample to be treated – water electrolysis). This water electrolysis will promote the oxidation of the organic contaminants, promoting as well as the electro-degradation. An optimal combination is achieved:

• Acid media – break complexes between elements (e.g. removal of Ca2+, Zn2+)
• Alkaline media - removing e.g. salts (Cl-), electrodes in contact with the contaminated matrices – degradation of the organic compounds.

Other important component of the reactor are the membranes: cation and anion exchange membranes. The surface will attract dissolved ions with the opposite charge (counter-ions) from the pore water of the membranes. Counter-ions will be transported through the membrane due to electrical current and co ions (with same charge as the membrane’s surface) will be rejected. The membranes allow the regulation of ion fluxes, thus selecting ions that reach the electrode compartments and will keep the contaminants separated from the sample to be treated (.

The re-designed reactor:

• Is flexible on scale and do not add any chemicals during the process
• Uses non-destructive materials
• It can remove a large range of contaminants at the same time, meaning lower costs in the updates of the reactor
• Depending on the effluent source, the material can change (1) in the colour (grey to light brown) or (2) texture (rough to softer)

Tests on final matrix characteristics and materials performance were studied in a bench scale reactor, thus:

Matrix final characteristics:

• Salts content: Chloride 75% removal; sulfates 72% removal, in 2h 62% of the chloride was in the central compartment
• Triclosan and its metabolites and by-products degradation: 92% to bellow the detection limit
• pH in the final matrix to be further use: 9-10
• Law parameters: COD 5 93% removal; COD 52% removal

Materials performance using 100% of electro-treated wastewater:

• Compressive tests: mortars with 7 days of age (39 MPa); mortars with 14 days of age (47 MPa); mortars with 28 days of age (51 MPa)
• Setting times: compared to the reference (made with tap water), either is the same time or is faster by 20 minutes
• Workability: compared to the reference (made with tap water) the slump increased by 25 mm;
• pH of the material = same as the reference
• All the materials parameters in accordance with EN 1015-3, EN-196, EN 206-1 and NBR 15900/2009

Additionally, during the process the self-produced hydrogen had a 60% faster flow rate production when compared to the conventional three compartment reactor and presented an average purity from 70% to 90%, depending on matrix initial characteristics.