Influence of operating conditions and wastewater-specific parameters on the electrochemical bulk disinfection of biologically treated sewage at boron-doped diamond (BDD) electrodes

Abstract

The aim of this study was to investigate an electrochemical process for bulk disinfection of biologically treated sewage. The influence of operating conditions (current density and flow rate) on the electrochemical formation of free chlorine in the sewage was determined. Furthermore, the effect of wastewater-specific parameters on the inactivation of Escherichia coli was studied. The disinfection capacity is primarily influenced by the concentration of electrochemically produced free chlorine. The production rate of free chlorine is independent of the flow rate within the range of 25-125 L h À1 . The investigations have also shown that the electrochemical disinfection of E. coli in secondary effluents with BDD electrodes proceeds effectively at an electric charge input of 0.1-0.15 Ah L À1 corresponding to an energy expenditure of 2.0-2.6 kWh m À3 . The electrochemically generated concentration of free chlorine (c = 0.4-0.6 mg L À1 ) is sufficient for an E. coli reduction of four log levels under the following conditions: after-reaction time of 15-20 min, T > 6˚C, pH < 8.5 and DOC < 22 mg L À1 . The formation of organic by-products (AOX, THMs) was marginal to moderate. The inorganic by-products chlorate (1.2 mg L Àl ) and perchlorate (18 mg L À1 ) were produced in considerable concentrations.

Rapid inactivation of waterborne bacteria using boron-doped diamond electrodes

“…The total energy expenditure in WWTP effluent (2.13 Wh/L) was comparable to the literature data with a total consumption of 2.0-2.6 Wh/L for a log-5 reduction of E. coli using the BDD electrode (Haaken et al 2012). The high energy efficiency of the diamond electrode compared to other AOPs, including treatment with UV/H 2 O 2 , which is currently in use for disinfection in wastewater treatment plants, could be shown before in a comparative study (Ureña de Vivanco et al 2013).…”

“…Generation of AOX is triggered by oxidation of chloride (Haaken et al 2012). A decrease in chloride levels was noted in both water matrices, which probably contributed to the formation of AOX in the wastewater matrix.…”

“…Up to the present, only a relatively small number of studies have been conducted to characterise disinfection with BDD electrodes. The numbers, however, are growing, which indicates the increasing interest in this technique (Tanner et al 2004;Jeong et al 2006;Schmalz et al 2009;Frontistis et al 2011;Haaken et al 2012;Liu et al 2012). However, there is a lack of mechanistic investigations in real water matrices.…”

“…Even though no threshold value exists for AOX in drinking water and the majority of them are non-toxic, a maximum discharge limit of 0.7 mg/L for integrated recovered paper mills has been prescribed in the Integrated Pollution Prevention and Control Directive (Council directive 2008/1/EC of 15 January 2008). The application of the BDD electrode in biologically treated sewage has been reported to generate low amounts of AOX, with a maximum value of 127 lg/L being recorded (Haaken et al 2012). In the current study, AOX concentrations were below the detection limit of 10 lg/L in drinking water, whereas in the WWTP effluent, AOX levels were found to increase from 13.3 lg/L up to 158 lg/ L after electrolysis (Table 2).…”

Electrolytic Oxidation as a Sustainable Method to Transform Urine into Nutrients

“…On the other hand, urine contains, in addition to the organic fraction, chlorides, sulfates, and phosphates. The literature review demonstrates that BDD and DSA are able to oxidize these anions and transform them into strong oxidants offering an additional route to transform the organic fraction into minerals and valuable products that are safely recycled in the ecosystem [53][54][55][56]. A careful analysis of the production of the strong oxidants from chlorides, sulfates and phosphates is mandatory to control the quality of the treated urine because excessive amounts would have negative effects and render the treated urine non-useful as enriched-liquid fertilizer.…”