Effects of mixing ratio, contact time, DO, and EPS composition on efficiency of biosorption for primary carbon diversion

Abstract

Wastewater treatment plants are on their way to going from being energy sinks to becoming energy-neutral or even energy-positive utilities. This is possible thanks to improvements in their processes such as primary treatment. Conventional primary wastewater treatment removes a large part of particulate organics but allows the soluble fraction to pass on to secondary treatment. In this paper, the combination of biosorption and solid-liquid separation is tested as an alternative primary treatment method that can remove both particulate and soluble organics. Results show that while the combination of biosorption and fine screens with polymer removes a sizeable amount of particulate (50 to 70 per cent) and soluble (10 to 30 per cent) organic matter, the use of fine screens with polymer without biosorption achieves almost the same removal rates. Further insights were found regarding the isotherm and kinetics of biosorption, oxygen concentration and mixing ratios in the contact tank, and differences between various solid-liquid separation methods. Extracellular polymeric substances make up most of the organic matter in activated sludge, and therefore strongly influence the sludges properties. This paper aims to draw a connection between the make-up of an activated sludge’s extracellular polymeric substances and its ability to conduct biosorption when mixed with raw wastewater. Biosorption is a natural process during which organic matter from a sorbate such as raw wastewater sorbs onto a sorbent such as activated sludge, a process which can be used during primary wastewater treatment. A positive correlation was found between the total concentration of extracellular polymeric substances and the normalized removal of soluble organic matter. It was furthermore postulated that extracellular polymeric substances, specifically proteins, comprised most of the soluble organic matter removed during biosorption. Extraction times of 4 or more hours yielded better identification of extracellular polymeric substances and more consistent ratios between proteins, carbohydrates, humic acids, DNA, and uronic acids than extraction times of 45 minutes.