Low-voltage electrochemical treatment to precipitate sulfide during anaerobic digestion of beet sugar wastewater.

ABSTRACT

Sugar beet processing generates a large amount of wastewater with a high chemical oxygen demand (COD). During wastewater storage and treatment, the hydrogen sulfide (H2S) generated from anaerobic digestion (AD) poses unique safety and environmental challenges due to air emissions to the local environment. A new approach of low-voltage electrochemical treatment using low-cost sacrificial anode material was developed in this study to remove sulfide, maintain a proper pH, and produce low-H2S biogas during the AD of beet sugar wastewater. The wastewater collected was categorized as the medium or high strength wastewater depending on the COD content. By using the medium strength wastewater as the test media, the effects of electrochemical and storage conditions, including the applied voltage, immersed electrode area, initial sulfate level, and operating temperature, on the sulfide removal were studied. The effective electrical charge consumption ranged from 6.0 to 14.4 C·mg-1 S2-, and the headspace H2S concentration was reduced by over 96% for most conditions after 204 h treatment. During the 10-week experiment on high strength wastewater, intermittent electrochemical treatment at 0.7 V applied voltage and 1.2 cm2·L-1 electrode area for two weeks reduced the H2S content in the biogas by up to 96%. The cathodic hydroxyl anion generation during the electrochemical treatment significantly increased the pH from 4.61 to 6.95 and led to earlier biogas production than the one without electrochemical treatment. This technique may feasibly be applied in the AD of other sulfur-compound-rich waste streams.