Recycled Products from Municipal Wastewater: Composition and Effects on Phosphorus Mobility in a Sandy Soil

Abstract

Recycled products from wastewater may contain high concentrations of phosphorus (P) and are thus promising alternative fertilizers. However, to better predict their P fertilizer efficiency and potential for P leaching, investigations on P forms and P mobility in soil are essential. In this study, different recycled products-an untreated sewage sludge ash (SSA), an HSO-digested SSA, four thermochemically treated SSAs (two Mg-SSAs and two Ca-SSAs), and struvite-were investigated using a combination of wet chemical methods and P K-edge X-ray absorption near-edge structure (XANES) spectroscopy concerning their composition and their effects on P sorption in a sandy soil in comparison to triple superphosphate. Most of the P in the SSAs was associated with Ca in stable P fractions. The lowest P values in labile fractions (HO-P, NaHCO-P) were found for the untreated SSA and struvite. However, the addition of struvite resulted in an immediate increase in the bioavailable P fractions and the degree of P saturation in soil after only 1 d of incubation. This suggests a high P fertilizer potential for struvite but also a risk of P losses. Among the SSAs, the two Mg-SSAs increased the bioavailable P fractions in soil the most, whereas the lowest values were measured after application of the untreated SSA. Our results demonstrate that chemical analyses of recycled P products may involve the risk of misjudging the fertilizer quality when performed alone, without considering the behavior of these products in soil.

Phosphorus effects of recycled products from municipal wastewater on crops in a field experiment

“…The lower P effect on labile soil P pools of the Al-SSA compared to struvite can be related to its high concentration of amorphous Al (54.2 g/kg) since Al-rich P recycling products reduced the bioavailability of P in the first months after application to acidic soils due to the increase of P sorption capacity (Bøen et al 2013). This effect of the Al-SSA on the P sorption capacity in acidic soil was demonstrated in a previous incubation experiment (Vogel et al 2017). In addition, it is assumed that the nitrification of NH 4 contained in Table 3.…”

“…This might increase the risk of heavy metal accumulation in soil still further, in particular since the SSAs contain higher amounts of heavy metals compared to struvite (Vogel et al 2017). Furthermore, struvite precipitating is already implemented and operating in full scale, while the processes for recovering P from monoincinerated SSA are currently tested in a pilot phase and the whole P recovery process including the mono-incineration and the post-treatment of the SSA is a cost and energy-extensive process (Kabbe et al 2015).…”

“…Application rate, total P (P t ) content and solubility of P (citric acid soluble P, P ca ), total nutrient concentration (K, Mg, Ca, N, Al, Fe) as well as the pH of the recycling products and triple superphosphate (TSP) (Vogel et al 2017 Vol. 63, 2017, No.…”

Options for Improved Phosphorus Cycling and Use in Agriculture at the Field and Regional Scales

“…Several authors noted that the effect of struvite on crops is not well predicted by its chemical characteristics, especially as determined by solubility assessments or sequential fractionation (Cabeza et al, 2011; Horta, 2017; Vogel et al, 2017a; Wollmann et al, 2018). Thus, different approaches to determining the agronomic value of struvite and other sparingly soluble fertilizers are needed.…”

“…For example, as discussed above, increased STP concentration due to soluble P fertilizer application has been linked to a reduction in the colonization of crop roots by AMF. Struvite application is expected to increase water‐extractable P and STP to a lesser degree than soluble fertilizers (Horta, 2017), but may still have an impact on these labile P pools (Vogel et al, 2017a) and thus on AMF proliferation. Soil fauna including nematodes, mites, termites, and earthworms are known to influence P availability in ecosystems; thus, any indirect effects of P additions on these organisms may in turn affect P dynamics in soil and also affect plant uptake (Faucon et al, 2015; Hallama et al, 2018).…”