Calcium Carbonate Packed Electrochemical Precipitation Column: New Concept of Phosphate Removal and Recovery

Abstract

Phosphorus (P) is a vital micronutrient element for all life forms. Typically, P can be extracted from phosphate rock. Unfortunately, the phosphate rock is a nonrenewable resource with a limited reserve on the earth. High levels of P discharged to water bodies lead to eutrophication. Therefore, P needs to be removed and is preferably recovered as an additional P source. A possible way to achieve this goal is by electrochemically induced phosphate precipitation with coexisting calcium ions. Here, we report a new concept of phosphate removal and recovery, namely a CaCO3 packed electrochemical precipitation column, which achieved improved removal efficiency, shortened hydraulic retention time, and substantially enhanced stability, compared with our previous electrochemical system. The concept is based on the introduction of CaCO3 particles, which facilitates calcium phosphate precipitation by buffering the formed H+ at the anode, releases Ca2+, acts as seeds, and establishes a high pH environment in the bulk solution in addition to that in the vicinity of the cathode. It was found that the applied current, the CaCO3 particle size, and the feed rate affect the removal of phosphate. Under optimized conditions (particle size, <0.5 mm; feed rate, 0.4 L/d; current, 5 mA), in a continuous flow system, the CaCO3 packed electrochemical precipitation column achieved 90 ± 5% removal of phosphate in 40 days and >50% removal over 125 days with little maintenance. The specific energy consumptions of this system lie between 29 and 61 kWh/kg P. The experimental results demonstrate the promising potential of the CaCO3 packed electrochemical precipitation column for P removal and recovery from P-containing streams.

Electrochemical carbon dioxide capture to close the carbon cycle

“…A pH-swing is also used for other resource recovery applications than CO 2 capture, but the method is not always explicitly referred to as "pH-swing". For instance, pH-swing is employed to recover ammonia electrochemically from urine [50,51] and to remove phosphate from waste water streams [52].…”

Electrochemically mediated precipitation of phosphate minerals for phosphorus removal and recovery: Progress and perspective

“…Moreover, the electrode gap would influence the recombination of cathode-produced OH − with anode-produced H + , affecting the utilization rate of OH − for precipitation. Lei et al (2019c) proposed a simple yet efficient way to deal with the acid-base neutralization issue in electrochemical systems by introducing CaCO 3 particles into the electrochemical cell to fill up the space between the anode and the cathode, as presented in Fig. 7A (Lei et al, 2019c).…”

“…Lei et al (2019c) proposed a simple yet efficient way to deal with the acid-base neutralization issue in electrochemical systems by introducing CaCO 3 particles into the electrochemical cell to fill up the space between the anode and the cathode, as presented in Fig. 7A (Lei et al, 2019c). When H + is produced at the anode, it would firstly react with CaCO 3 instead of neutralizing with OH − , leading to an accumulation of OH − even in the bulk solution and releasing Ca 2+ for the precipitation of Ca-P (Eq.…”

“…Lei et al (2018c) studied the influence of three types of NOM (Suwannee River NOM, Nordic Lake NOM, and Pony Lake NOM) on P removal during electrochemical treatment. Overall, NOM improved Ca-P precipitation on the cathode surface to some extent, mainly via physical co-precipitation with Ca-P after balancing its negative effect on free Ca 2+ availability in the bulk (Lei et al, 2019c). (B) Diagram of scalable column-shaped electrochemical reactor with a tubular stainless-steel cathode (Lei et al, 2021b).…”

“…Moreover, membranes were used in the study of Perera et al (2020), which reduced energy consumption because it can more effectively increase the cathodic pH and lead to better precipitation efficiency. Likewise, similar current density was used in the study of Lei et al (2019c) and Li et al (2021b), yet less energy is consumed compared to the previous two studies, resulting from the relatively high initial P concentration and the presence of CaCO 3 or CaMg(CO 3 ) 2 particles. Additionally, Lei et al (2021b) elucidated that the system's energy consumption increased with the dilution of P-enriched wastewater, pointing out the importance of performing P recovery from raw, undiluted cheese wastewater.…”