ABSTRACT
One of the main challenges for the implementation of electrocoagulation (EC) in water treatment are fouling and passivation of the electrodes, especially for applications with high contaminant concentrations. For the first time, we investigated in this study the process of fouling mitigation by polarity reversal during the EC treatment of boiler blowdown water from oil-sands produced water, characterized by high silica concentrations (0.5-4 g L-1). This effluent is typically obtained from an evaporative desalination process in oil production industries. Potentiodynamic characterisation was used to study the impact of passivation on the anode dissolution. Although a charge loading of 4,800 C L-1 was found to remove about 98% of silica from a 1 L batch of 4 g L-1 Si solution, fouling reduced the performance significantly to about 40% in consecutive cycles of direct current EC (DC-EC) treatment. Periodic polarity reversal (PR) was found to reduce the amount of electrode fouling. Decreasing the polarity period from 60 to 10 s led to the formation of a soft powdery fouling layer that was easily removed from the electrodes. In contrast, with DC operation, a hard scale deposit was observed. The presence of organics in the field samples did not significantly affect the Si removal, and organics with high levels of oxygen and sulfate groups were preferentially removed. Detailed electrochemical and economic investigations suggest that the process operating at 85 °C achieves 95% silica removal (from an initial concentration of 481 mg L-1) with an electrical energy requirement of 0.52 kWh m-3, based on a charge loading of 1,200 C L-1, an inter-electrode gap of 1.8 cm and a current density of 16 mA cm-2.
Subject(s)
Water Pollutants, Chemical , Water Purification , Aluminum , Electrocoagulation , Electrodes , Silicon DioxideABSTRACT
Cultivating anodic respiring bacteria (ARB) on anodes doped with metal-enhanced biological growth and affected higher electocatalytic activity (ECA). The anode doped with calcium sulfide (CaS) proved more favorable for ARB than the magnetite (Fe3O4) or iron(II) sulfide (FeS). Average anodic current densities of 8.4 Am2- (Fe3O4), 11.1 Am2- (FeS), and 22.0 Am2- (CaS) were achieved as compared to that of nondoped carbon (5.1 A m-2). Thus, CaS-doped graphite represents a promising anode material which is suitable for highly efficient bioelectrochemical systems (BES). Electrochemical evaluation during turnover and starvation using simple cycle voltammetry (CV) and derivative cycle voltammetry (DCV) indicated several extracellular electron transfer (EET) pathways characterized with lower potentials for biofilms. However, despite the high affinity of bacteria to iron, their lower ECA was kinetically attributed to the accumulation of self-produced mediators on iron-doped anodes.
ABSTRACT
A new simple chronoamperometry methodology was developed for the ultrasensitive determination of lead ions using a PEDOT:PSS coated graphite carbon electrode. The polymer was directly coated on a graphite carbon electrode and characterized using simple cycle voltammetric measurements. The presence of lead ions induced a cathodic peak starting at -550 ± 10 mV vs. Ag/AgCl, and an anodic peak starting at -360 ± 10 mV vs. Ag/AgCl. Electroaccumulation of lead ions onto the PEDOT:PSS modified electrode was performed at -650 mV vs. Ag/AgCl for 30s in a pH 2.2 hydrochloric acid solution. Chronoamperometry measurements were carried out at -350 mV vs. Ag/AgCl allowing the oxidation of accumulated lead. Using this method, lead ions were detected for concentrations ranging between 2.0 nmol L(-1) and 0.1 µmol L(-1) (R(2)=0.999). The detection limit was calculated to be 0.19 nmol L(-1) and the quantification limit of 0.63 nmol L(-1). The method was shown to be highly precise and sensitive, negligible interference was detected from other metal ions. The proposed method was successfully applied for the detection of lead ions in vegetables.
