Moving bed capacitive bioanodes

Abstract

Chapter 1 1.1. Wastewater treatment technology for removal of organic material Environmental challengeIn modern society, municipalities and industry produce significant volumes of wastewater. Globally, on average 95 m 3 wastewater is produced per capita per year, with in Europe 124 m 3 /capita/year and North America at 231 m 3 /capita/year: a global total of 380×10 9 m 3 per year (2015 data) [1]. Wastewater contains a mixture of several pollutants, such as dissolved organics, and nitrogen and phosphorus compounds, with differing effects on the environment and ecosystems. In nature, the dissolved organics are degraded by aerobic bacteria, resulting in the deoxygenation of the water. This is especially problematic for wastewater discharged into surface waters, which host important ecosystems that rely on oxygen in the water. Nitrogen and phosphorus discharge can result in eutrophication, which in turn leads to reduced biodiversity and possible toxicity due to proliferation of certain algae species [2,3]. At the end of the 19 th century, wastewater treatment -rather than disposal -became more important as these consequences became clear [4]. Wastewater treatment plants (WWTPs) were constructed, connecting in 78% of the population in the EU to primary and secondary treatment (EU-28, status in 2017) [5]. The wastewater treatment process consists of several steps, including but not limited to: primary treatment for the removal of (suspended) solids, secondary for removal of organics, and tertiary for removal of nutrients, minerals, metals, inorganics, taste, color, odor and pathogens [6]. Traditionally, aerobic treatment has been used to remove these organics, but the recovery of energy contained in the organics, has become a goal in itself: firstly, to make the WWTPs less energy intensive and more self-sustainable and secondly to export the energy for use in society. Aerobic treatment and recovery of the energy from organics in wastewater using anaerobic digestion processes and bioelectrochemical systems will be discussed in the following paragraphs [7,8]. Aerobic treatmentAerobic treatment utilizes oxygen for the oxidation of dissolved organics by aerobic bacteria in the controlled environment of WWTPs. Traditional treatment uses large ponds to flow the wastewater through. Oxygen is forced into the water stream at various points in the pools, and the required oxygen is consumed by the growing bacteria while degrading the organic material. The aerobic biomass is collectively called activated sludge. The aeration requires significant amounts of energy. In the last decade, the aeration step consumed between 0.1 and 0.6 kWh/m 3 wastewater in various WWTPs around the world, depending, among others, on climate, size, technology, and chemical oxygen demand (COD) and total nitrogen requirements of influent and effluent [7]. For typical wastewater, 0.5 kgCOD/m 3 [9], the aerobic energy costs are 0.2 to 1.2 kWh/kg COD. The growth of aerobic microorganisms results in a large volume of sludge in suspension in the wastewater stre...