Time-based evaluation of bioavailable phosphorus in a calcareous soil after the application of anaerobically digested sewage sludge

Abstract

Nowadays, phosphorus natural reserves are being depleted, while P fertilizers demand is increasing. Phosphorus is well contained in waste materials such as sewage sludge. Only a small amount (1–3%) of the soil total phosphorus is bioavailable for plant nutrition. More in detail, the present study focuses on the determination of the kinetics of bioavailable phosphorus concentrations in a sandy calcareous soil after the application of sewage sludge. A centrifuged (C) and dried (D) anaerobic digestate from sewage sludges obtained from the same wastewater treatment plan were separately tested to fertilize a calcareous sandy soil. Falcon tubes (50 mL) containing negative control (T) and soil treated with C and D were incubated from 1 to 90 days. Soil phosphorus fractionation was performed with the SMT method and bioavailable-P was extracted through the Olsen method. Phosphorus was spectrophotometrically quantified by the molybdovanadate method. Lastly, kinetics of bioavailable-P on soils were evaluated using four kinetic models. Phosphorus fractions were constant throughout the experiment. Conversely, the bioavailable-P significantly decreased from day 1 to day 90 in C treatment (from 34.9 ± 2.9 to 23.8 ± 1.5 ppm) and T treatment (from 4.2 ± 1.2 to 0.3 ± 0.6 ppm). This decrease might be due to the precipitation of P with calcium; in fact, high concentration of Ca2+ ions and the alkaline soil pH can induce the sequential formation of calcium phosphates, even less soluble over time. Whereas D treatment showed a peak of bioavailable-P concentration on day 14 (26.6 ± 3.0). This trend could be due to organic carbon compounds, competitive sorption and metal bridging. The fitting of experimental data revealed that the Elovich model best described the adsorptive-precipitate process of bioavailable-P in T (r2 = 0.90) and C (r2 = 0.93). Conversely, none of the models satisfactorily described the behavior of bioavailable-P in D samples. This study increases the knowledge on P-related phenomena for designing and optimizing fertilizers and reducing their drawbacks such as eutrophication.

Performance of an Innovative Low-Cost Recycled Filling (LCRF) in Anaerobic Treatment of Dairy Effluent—A Pilot-Scale Study

“…Mineralization is the only process by which N and P are removed under fermentative conditions [ 47 ]. The only way by which anaerobic bacteria can remove nitrogen and phosphorus is by absorbing them into their cells—a time-consuming process, as the microbes themselves are slow to grow [ 48 ].…”

Disposition of Solids from Hydrothermal Liquefaction of Biomass: Current Understanding, Research Gaps, and Opportunities

“…As for the land application of biosolid residuals from anaerobic digestion biosolids for plant fertilizers, bioavailability of the nutrients in HTL solids was found to be lower than that of the sewage sludge feedstock and simultaneously demonstrated that heavy metal content in the solids exceeded the threshold values for use as a fertilizer . However, recovery of low bioavailable phosphorus has also been demonstrated using HTL solids and other residuals to recover between 42 and 92% as struvite. , Struvite, a crystalline mineral of ammonia, magnesium, and phosphate (NH 4 MgPO 4 ·6H 2 O), can be directly used as a slow-release inorganic fertilizer, helping to reduce fertilizer runoff and the consumption of fertilizers.…”

“…The low bioavailability of P and Fe, possibly other elements, in the HTL solids for microalgae growth required sulfuric acid extraction. 37 As for the land application of biosolid residuals from anaerobic digestion biosolids for plant fertilizers, 38 bioavailability of the nutrients in HTL solids was found to be lower than that of the sewage sludge feedstock and simultaneously demonstrated that heavy metal content in the solids exceeded the threshold values for use as a fertilizer. 39 However, recovery of low bioavailable phosphorus has also been demonstrated using HTL solids and other residuals to recover between 42 and 92% as struvite.…”