Using toxicity testing to evaluate electrochemical reactor operations

Abstract

In the present study, the Microtox® test was used to track the toxicity of electrochemical effluents to the marine bacteria Vibrio fischeri as a function of reaction time. When electrochemistry was used to degrade aqueous phenol using different reactor configurations, two reaction pathways were identified, chlorine substitution and oxidation, depending on whether the electrolyte contained chloride. For a boron-doped diamond (BDD) anode, electrochemistry using Na₂SO₄ electrolyte produced a significantly more toxic effluent than when using NaCl electrolyte with all other conditions remaining the same. This effect is attributed to the reaction pathway, specifically the production of benzoquinone. Benzoquinone was produced only during electrochemistry using Na₂SO₄ and is the most toxic potential intermediate, having nearly 800 times more toxicity than phenol. Although the use of NaCl produced a lower toxicity effluent than Na₂SO₄, caution should be observed because of the production of chlorinated phenols, which can be of special environmental concern. When comparing graphite rod and BDD plate anodes in terms of toxicity evolution when using Na₂SO₄, BDD was found to produce a lower toxicity effluent; this is a result of the increased oxidizing power of BDD, reducing the formation of benzoquinone. In this comparison, the type of anode material/electrode configuration did not seem to affect which intermediates were detected but did affect the quantity of and rate of production of intermediates.

Electrolyte selection and microbial toxicity for electrochemical oxidative water treatment using a boron-doped diamond anode to support site specific contamination incident response

“…The reaction progressed much more slowly in the presence of NaNO 3 , which is not expected to participate in the reaction or produce reactive chlorine. Therefore, this electrochemical oxidation using a BDD anode, in the presence of the NaCl electrolyte, likely produces large concentrations of active chlorine, which may contribute to the degradation of contaminants, similar to reports with other electrodes (Murugananthan et al, 2011;Saylor et al, 2012). Although not directly measured in this study, the formation of organochlorinated intermediates, as well as chlorate, may present further concerns when using the NaCl electrolyte (Sirés et al, 2014).…”

“…The effluent toxicity was a major concern to the WERF expert workgroup for ultimate disposal of contaminated waters treated in emergency response scenarios (Striano et al, 2011). Limited studies have reported that AOP treatments yield degradation intermediates that can be more toxic than the parent compound (Saylor et al, 2012;Haidar et al, 2013). A variety of microbial toxicity assays demonstrate potential eco-toxicity, as well as toxicity to activated sludge from WWTWs.…”

“…The boron-doped diamond (BDD) anode, in particular, is ideal for EAOP treatment because it is able to attain a higher range of working potentials and is more stable to corrosion than other electrodes, resulting in higher overall performance (Kornienko et al, 2011). Moreover, the BDD anode is non-active, meaning it has an inert surface, reducing concerns about adsorption and deactivation due to fouling (Saylor et al, 2012). In electro-oxidation with BDD anodes, contaminants can be degraded either through direct anodic oxidation, or, more likely, through mediated reactions with adsorbed hydroxyl radicals produced from the electrolysis of water (Eq.…”

Visible‐Light Induced Simultaneous Oxidation of Methyl Orange and Reduction of Cr(VI) with Fe(III)‐Grafted K2Ti6O13 Photocatalyst

“…The improper discharge of industrial effluents containing toxic organic and inorganic pollutants lead to severe water contamination and their coexistence in the aquatic systems is a threat to the regulating authorities all over the world . The current problem has exerted pressure on the scientific community to look for an economical and efficient method that could remove these pollutants from wastewater.…”

Simultaneous photocatalytic Cr(VI) reduction and 2,4,6-TCP oxidation over g-C3N4 under visible light irradiation

“…2,4,6-TCP and chromium are common environmental pollutants, and classified as priority pollutants by the U.S. Environmental Protection Agency (EPA) [5][6][7][8]. The mixture of chlorophenol and chromium can be easily found in many waste streams, for instance tannery effluents.…”