Electrochemical sulfide removal from synthetic and real domestic wastewater at high current densities

Hydrogen sulfide generation is the key cause of sewer pipe corrosion, one of the major issues in water infrastructure. Current abatement strategies typically involve addition of various types of chemicals to the wastewater, which incurs large operational costs. The transport, storage and application of these chemicals also constitute occupational and safety hazards. In this study, we investigated high rate electrochemical oxidation of sulfide at Ir/Ta mixed metal oxide (MMO) coated titanium electrodes as a means to remove sulfide from wastewater. Both synthetic and real wastewaters were used in the experiments. Electrochemical sulfide oxidation by means of indirect oxidation with in-situ produced oxygen appeared to be the main reaction mechanism at Ir/Ta MMO coated titanium electrodes. The maximum obtained sulfide removal rate was 11.8 +/- 1.7 g S m(-2) projected anode surface h(-1) using domestic wastewater at sulfide concentrations of >= 30 mg L(-1) or higher. The final products of the oxidation were sulfate, thiosulfate and elemental sulfur. Chloride and acetate concentrations did not entail differences in sulfide removal, nor were the latter two components affected by the electrochemical oxidation. Hence, the use of electrodes to generate oxygen in sewer systems may constitute a promising method for reagent-free removal of sulfide from wastewater. (C) 2011 Elsevier Ltd. All rights reserved

High current generation coupled to caustic production using a lamellar bioelectrochemical system

Recently, bioelectrochemical systems (BESs) have emerged as a promising technology for energy and product recovery from wastewaters. To become economically viable, BESs need to (i) reach sufficient turnover rates at scale and (ii) generate a product that offsets the investment costs within a reasonable time frame. Here we used a liter scale, lamellar BES to produce a caustic solution at the cathode. The reactor was operated as a three-electrode system, in which the anode potential was fixed and power was supplied over the reactor to allow spontaneous anodic current generation. In laboratory conditions, with acetate as electron donor in the anode, the system generated up to 1.05 A (at 1.77 V applied cell voltage, 1015 A m(-3) anode volume), and allowed for the production of caustic to 3.4 wt %, at an acetate to caustic efficiency of 61%. The reactor was subsequently operated on a brewery site, directly using effluent from the brewing process. Currents of up to 0.38 A were achieved within a six-week time frame, Considerable fluctuations over weekly periods were observed, due to operational parameter changes. This study is the first to demonstrate effective production of caustic at liter scale, using BESs both in laboratory and field conditions. It also shows that input of power can easily be justified by product value

Bioelectrochemical hydrogen peroxide production – an opportunity for sustainable mitigation of membrane bioreactor fouling

Membranes in membrane bioreactors (MBR) are typically cleaned with sodium hypochlorite. The latter is a strong oxidant and of concern due to the possible formation of chlorinated hydrocarbons. Here, we propose a new concept for chemical membrane cleaning with hydrogen peroxide (H2O2), generated onsite in a bioelectrochemical system. The energy present in the wastewater organics can be used to power the production process. We investigated bioelectrochemical H2O2 production from a synthetic wastewater in an inclinedbed reactor and discuss the possibility of using H2O2 to replace sodium hypochlorite for membrane cleaning. Low current, the use of carbon fiber as opposed to graphite, and low pH in the cathode all benefited H2O2 production. It was also possible to generate H2O2 with a net energy output, i.e. by operating the reactor as a microbial fuel cell. The highest H2O2 concentration produced in this study was 176.3 mg/l, which was obtained at a production rate of 1.26 mg/h and an energy input of 0.32 kWh/kgH2O2. A concentration of 91.6 mg/l, a production rate of 0.54 mg/h and an energy output of 0.18 kWh/kgH2O2 was obtained when the reactor was operated as a microbial fuel cell. For application in a MBR, a relatively small portion (>3.8 mg/l BOD) of the influent organic compounds would have to be converted to current by the electroactive bacteria living on the anode to produce sufficient amount of H2O2 for membrane cleaning. However, the produced H2O2 concentration must likely reach a concentration of 0.2-0.5%

Electrochemical regeneration of sulfur loaded electrodes

Electrochemical oxidation of sulfide is a promising technique for its removal from wastewaters. Generally, the main product of this oxidation reaction is elemental sulfur. The latter deposits as a solid on the electrode and deactivates it. Therefore, an efficient and effective regeneration technique of sulfur loaded electrodes is required for the practical implementation of this technology. Here we demonstrate a method for in situ reduction of electrodeposited sulfur on carbon fibre electrodes to sulfide/polysulfides, at low energy input. The intermediary coulombic efficiency (CE) values strongly depend on pH and buffer capacity of the solution. These values were recorded up to 435 ± 5% due to simultaneous chemical dissolution of sulfur to polysulfides under alkaline conditions. This process demonstrates the potential for continuously removing dissolved sulfide from wastewaters at an anode as sulfur and recovering the deposited sulfur based on regular switching between anodic sulfide oxidation and cathodic sulfur reduction. Keywords: Sulfide, Electrode, Regeneration, Polysulfide, Wastewater treatmen

Long-term field test of an electrochemical method for sulfide removal from sewage

Corrosion caused by hydrogen sulfide leads to significant costs for the rehabilitation or replacement of corroded sewer pipes. Conventional methods to prevent sewer corrosion normally involve the dosing of significant amounts of chemicals with the associated transport and storage costs as well as considerable maintenance and control requirement. Recently, a novel chemical free method for sulfide abatement based on electrochemical sulfide oxidation was shown to be highly effective for the removal of sulfide from synthetic and real sewage. Here, we report on the electrochemical removal of sulfide using Ta/Ir and Pt/Ir coated titanium electrodes under simulated sewer conditions during field trials. The results showed that sulfide can successfully be removed to levels below the normal target value at the end of a simulated rising main (i.e

Principle and perspectives of hydrogen production through biocatalyzed electrolysis

Biocatalyzed electrolysis is a novel biological hydrogen production process with the potential to efficiently convert a wide range of dissolved organic materials in wastewaters. Even substrates formerly regarded to be unsuitable for hydrogen production due to the endothermic nature of the involved conversion reactions can be converted with this technology. Biocatalyzed electrolysis achieves this by utilizing electrochemically active micro-organisms that are capable of generating electrical current from the oxidation of organic matter. When this biological anode is coupled to a proton reducing cathode by means of a power supply, hydrogen is generated. In the biocatalyzed electrolysis experiments presented in this article acetate is used as a model compound. In theory, biocatalyzed electrolysis of acetate requires applied voltages that can be as low as 0.14V, while hydrogen production by means of conventional water electrolysis, in practice, requires applied voltages well above 1.6V. At an applied voltage of 0.5V the biocatalyzed electrolysis setup used in this study, produces approximately 0.02m3 H2/m3 reactor liquid volume/day from acetate at an overall efficiency of 53±3.5%. This performance was mainly limited by the current design of the system, diffusional loss of hydrogen from the cathode to the anode chamber and high overpotentials associated with the cathode reaction. In this article we show that optimization of the process will allow future volumetric hydrogen production rates above 10m3 H2/m3 reactor liquid volume/day at overall efficiencies exceeding 90% and applied voltages as low as 0.3–0.4V. In the future, this will make biocatalyzed electrolysis an attractive technology for hydrogen production from a wide variety of wastewaters.