Predicting Phosphate Release from Sewage Sludge Ash Using an Ion Sink Assay

Abstract

Thermochemical treatments allow production of sewage sludge ash (SSA) rich in P and low in heavy metals, which could be recycled in agriculture. Our objective was to quantify P release from SSA using ion sink assays and to relate these results to P speciation in SSA and plant P uptake. Anion and cation exchange membranes saturated with different counterions (HCO3, Na, and H) were used to create a gradient in pH, P, or cation concentration between SSA particles and the surrounding solution. Phosphorus speciation in SSA was assessed using X‐ray powder diffraction, and plant P uptake was determined in a pot experiment with an acidic and a neutral soil. Four SSA products were investigated: a SSA thermochemically treated with CaCl2 or MgCl2 (SSA Ca/Mg), a SSA blended with KCl, and a SSA blended with KCl and triple superphosphate (TSP) to obtain a marketable 12–20 P–K fertilizer. The H membranes dissolved all P species present in SSA. Combined HCO3/Na membranes extracted diffusible P and noncrystalline P from SSA Ca/Mg and stanfieldite from SSA Mg. Blending with KCl hardly changed P release from SSA, whereas blending with TSP masked P release. The amount of P extracted from SSA by combined HCO3/Na membranes was correlated to plant P use in the acid soil, whereas the amount of P extracted by HCO3 membranes alone was correlated to P use in the neutral soil. In conclusion, the ion sink assays delivered information on P release that was related to both SSA mineralogy and P use by plants. Core Ideas Ion exchange membranes are proposed to predict P release from sewage sludge ash (SSA) products. Combined HCO3/Na membranes extract diffusible and noncrystalline P from SSA products. Combined HCO3/Na membranes extract P from stanfieldite in MgCl2–treated SSA products. Hydrogen‐saturated membranes solubilized most of the P present in SSA products. Blending CaCl2–treated SSA with KCl does not affect the amounts of extractable P.

Substrate-Driven Phosphorus Bioavailability Dynamics of Novel Inorganic and Organic Fertilizing Products Recovered from Municipal Wastewater—Tests with Ryegrass

“…In addition to the traditional methods, novel ones that test P in the soil solution (anion exchange resins, iron-coated filter papers, iron bag, Rhizon soil moisture sampler, Diffusive Gradients in Thin Films, etc.) for assessing the P availability of secondary P fertilizing products have indicated a good correlation with the concentration of P in plants [43][44][45][46][47][48]. Still, the number of those studies is limited.…”

Superior residual fertiliser value in soil with phosphorus recycled from urine in layered double hydroxides

“…For instance, a large study undertaken by Römer & Steingrobe 35 using sandy and loamy soils showed that maize and winter wheat had a PUE of under 25% when grown on most treated sewage sludge ashes, with only Mg treated sewage sludge having a PUE higher than 50%. Nanzer et al 36 obtained similar results where plants grown on Mg-treated sewage sludge had higher yields and P uptake compared to Ca-treated sewage sludge in an acid soil. The difference is attributed to the higher solubility of Mg phosphate precipitates compared to Ca phosphates.…”