Complex Agent for Phosphate Sequestration from Digested Sludge Liquor: Performances and Economic Cost Analysis

Abstract

Phosphorus (P) management in the “water-energy-resource-nexus” in wastewater treatment plants (WWTPs) remains a longstanding challenge. P adsorption from the P-enriched digested sludge liquor (DSL) is a comparatively more practical and economically viable approach for P recovery in WWTPs. However, high concentrations of impurities in DSL might pose a negative and interferential effect on P adsorption, hindering the application of sorbents or precipitation methods. Given such a situation, highly efficient and cost-effective sorbent towards P reclamation from DSL is highly needed. Therefore, this study aims to develop a novel complex agent containing aluminum coagulant and superparamagnetic nano-sorbent (SNS) that can be used in magnetic seeding coagulation for P recovery. The complex agents with different PACl: SNS ratios showed varied turbidity removal rates and P recovery efficiencies and the optimal ratio was 15 mg PACl: 15 g SNS. PAC and SNS showed significant interaction because PAC could enhance P adsorption by shielding the interferential effect of colloidal impurities. In addition, the complex is highly regenerative, with turbidity and P removal rate stably maintained at 70–80% after 10 adsorption/regeneration cycles. The cost–benefit analysis of the dosing complex agent showed a dosing cost of 0.154 EUR/m3, admittedly much higher than the conventional magnetic seeding coagulation, which could probably be covered by the profit if the expensive and rare P product is reclaimed. This work indicated that the complex agent was superior due to its high adsorption capacity, easy separation, and repeated dosing, and therefore had the potential for P recovery from DSL.

Sludge-Based Superparamagnetic Nano-Sorbent Functionalized by Lanthanum Silicate Nanorods for Phosphorus Adsorption and Fertilization

“…Up to now, a series of nanoparticles consisting of different LDHs and doped with oxides of different transitional elements, like zirconium, cerium, lanthanum (La), and hafnium, have been synthesized and assessed. Among these, the La-doped nano-sorbent seems superior due to its high P adsorption capacity, high selectivity for phosphate, excellent reusability, and minimal generation of secondary pollutants [12,13]. In addition, it is noteworthy that the application of La nanorods to improving plant yields has shown remarkable effectiveness in disease suppression, suggesting that it could serve as an effective and sustainable strategy with which to safeguard crops [14].…”