Treatment of real dairy wastewater by electrolysis and photo-assisted electrolysis in presence of chlorides

Abstract

The efficiency of electrolysis (EC/Cl2) and photo-assisted electrolysis (EC/UV/Cl2) methods, in the presence of chloride, for the abatement of real dairy waste from a producer in the Triangulo Mineiro region of Brazil, was evaluated. A complete 23 factorial design was performed for the variables time, pH and current. After determining the ideal pH, a Central Compound Design (CCD) was performed, where the applied current (533.42 mA) and treatment time (60.45 minutes) were maximized. The effluent was subsequently submitted to prolonged EC/Cl2 and EC/UV/Cl2 treatment in order to evaluate the behaviour of specific environmental parameters over time. The EC/UV/Cl2 method was more efficient than simple EC/Cl2 treatment. The EC/UV/Cl2 method resulted in a reduction of all environmental parameters investigated to levels within legal standards for effluent discharge. A relatively low cost of treatment is obtained with Energy per Order (EEO) values of 0.89 and 1.22 kWh m−3 order−1 for the EC/UV/Cl2 and EC/Cl2 treatments, respectively. The electrochemical production of free chlorine species followed by subsequent photolysis and production of radical species can convert a simple electrochemical process into an advanced oxidation process (AOP).

Experimental design for combined abatement of organic compounds present in urine

“…The initial factorial design was employed in preliminary degradation tests of the organic compounds contained in the artificial urine and to determine the interaction between the different selected factors. The variables and their respective studied levels were selected based on studies previously performed by our research group [15,21,22]. It was possible to observe that when electrochemical methods are combined with ultrasound and UV, the extent of organic removal is increased.…”

“…These materials present high performance towards the chlorine evolution reaction (CER) and the subsequent chlorine-based aqueous equilibrium products [14,21]. In this context the use of electrochemical-based techniques to treat urine is extremely interesting as the dissolved salts are capable of performing the role of the supporting electrolyte and provide electrical conductivity [5,20,22].…”

“…Organic removal efficiency can be improved using chloridecontaining wastewater, due to the electrogeneration of highly oxidizing active chlorine species (Equations 1-4), in a pHdependent process [15,21,23].…”

“…Electrochemical technology and the combination of electrochemical and photochemical methods (photoassisted electrochemistry) and the combination of electrochemical and ultrasonic processes (sonoelectrochemistry) currently offer promising approaches for preventing pollution problems caused by organic contaminants [15, 18, 20, 27]. For example, a number of systems have been treated, such as cosmetics [18], antibiotics [20], pesticides [28], antineoplastics [15], and dairy industry waste [21].…”

Mathematical Modelling for Predicting Pollutant Removal Efficiencies of an Electrolysis System

“…Through optimum conditions, they have achieved a COD removal of 94% and Mn removal of 93%. Sousa et al (2019) investigated effectiveness of electrolysis and photo-assisted electrolysis in the presence of chloride on in removing pollutants (turbidity, conductivity, colour, pH, chlorides, TOC, COD and BOD) from dairy waste. They have achieved more than 90% removals of TOC and COD with only electrolysis (with chloride) and more than 95% removals of TOC and COD with photo-assisted electrolysis (with chloride).…”