Abstract
Inorganic scaling is often an obstacle for implementing electrodialysis systems in general and for nutrient recovery from wastewater specifically. In this work, Donnan dialysis was explored, to prevent scaling and to prolong operation of an electrochemical system for TAN (total ammonia nitrogen) recovery. An electrochemical system was operated with and without an additional Donnan dialysis cell, while being supplied with synthetic influent and real digested black water. For the same Load Ratio (nitrogen load vs applied current) while treating digested black water, the system operated for a period three times longer when combined with a Donnan cell. Furthermore, the amount of nitrogen recovered was higher. System performance was evaluated in terms of both TAN recovery and energy efficiency, at different Load Ratios. At a Load Ratio 1.3 and current density of 10 A m−2, a TAN recovery of 83% was achieved while consuming 9.7 kWh kgN−1.
Highlights
Towards closing the resources cycle for a circular economy, our considered “waste” water has become a source of nutrients and energy. (Cordell et al, 2011; Galloway et al, 2008; Gao et al, 2019; Maurer et al, 2003; Moges et al, 2018; Theregowda et al, 2019) Amongst all the nutrients present in wastewater, phosphorus and nitrogen are of the utmost importance as they play a vital role in plant growth
Up to 2% of the energy produced worldwide is consumed by the Haber-Bosch process. (Kuntke et al, 2017; Kuntke et al, 2018; Shipman and Symes, 2017) Source separation of wastewater has been investigated as a promising concept to allow for energy efficient wastewater treatment and nutrient recovery. (Larsen et al, 2015; Zeeman and Kujawa-Roeleveld, 2011) Phosphorus and nitrogen were recovered from source separated streams such as black water or urine (Kuntke et al, 2018; Ledezma et al, 2015; Tarpeh et al, 2018)
The presence of bivalent ions was previously reported to interfere with electrodialysis process and nutrient recovery, as calcium and magnesium ions are more susceptible to the electric field and changes membranes (CEM) are more selective for divalent ions (Ping et al, 2013; Rijnaarts et al, 2018; Yang et al, 2014)
Summary
Towards closing the resources cycle for a circular economy, our considered “waste” water has become a source of nutrients and energy. (Cordell et al, 2011; Galloway et al, 2008; Gao et al, 2019; Maurer et al, 2003; Moges et al, 2018; Theregowda et al, 2019) Amongst all the nutrients present in wastewater, phosphorus and nitrogen are of the utmost importance as they play a vital role in plant growth. (Larsen et al, 2015; Zeeman and Kujawa-Roeleveld, 2011) Phosphorus and nitrogen were recovered from source separated streams such as black water (combined feces and urine) or urine (Kuntke et al, 2018; Ledezma et al, 2015; Tarpeh et al, 2018). An electrochemical system (ES) has been proposed to recover the remaining ammonia and ammonium (total ammonia ni trogen,TAN), as it does not require chemical dosing and requires less energy than NH3 stripping, chemical precipitation or adsorption (Kuntke et al, 2018; Lei et al, 2007; Rodríguez Arredondo et al, 2015; Wasie lewski et al, 2016). The alkaline pH in the concentrate results in the formation of inorganic scaling on the CEM (e.g. precipitation of insoluble salts such as calcite, gypsum, struvite etc.) (Thompson Brew ster et al, 2017)
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