Phosphorus recycling potential by synthetic and waste materials enriched with dairy wastewater: A comparative physicochemical study

Abstract

Recovery of the essential macro-nutrient phosphorus (P) from P-rich waste streams is of global interest, with dwindling sources of P fertilizers threatening food security. We present a comparative physicochemical study of potential P adsorbents: two types of synthetic layered double hydroxide (LDH) and two recycled water treatment residuals (WTRs). Adsorbents were mixed with dairy WW, pre-clarified with either nanocomposites or centrifugation. LDHs practically removed all P (and higher N and organic C). In contrast, WTRs removed 50–80% P. WW-treated WTRs, particularly Fe-WTR, displayed substantially higher P lability than WW-treated LDHs, and inorganic P-loaded forms (e.g., 90 vs. 0.5 mg P kg−1). Adsorbent analyses with SEM, PXRD, FTIR, and 31P solid-state NMR contributed structural and chemical insights. Adsorbents mixture with dairy WW led to chemical and structural alterations, including Ca absorption and co-precipitation with P. Yet, high porosity and predominating adsorbed P species indicated rapid surface adsorption reactions onto the LDHs. The WTRs presented multiple sorption pools, including amorphous oxides, calcite and silicate surfaces, and disequilibrium with Ca-P minerals, accounting for weak P sorption. In addition, it appears Fe-based WTR was most sensitive to organic compounds’ impact. Thus, WW-treated WTRs can be employed as labile P sources, while LDH adsorbents can be employed as excellent purifiers for polluted streams.