Phosphate fertilizer value of heat treated sewage sludge ash

Abstract

This study focuses on the question whether heat treated sewage sludge ashes are more favourable as fertilizers than untreated sewage sludge ashes (USSA) and whether their fertilization effects are comparable with commercial triple superphosphate (TSP). In a pot experiment, maize was fertilized either with one of three heat treated and Na-, Ca- and Si-compounds amended sewage sludge ashes (two glown phosphates, steel mill slag + sewage sludge ash) or USSA or TSP as control. Fertilization with USSA did not increase the biomass yield and the P uptake of maize in comparison to the P0 treatment (7.25 resp. 8.35 g dry matter/pot). Fertilization with heat treated sewage sludge ashes and TSP resulted in significantly higher yields and plant P uptakes which are on average eight times higher than treatment with USSA and P0 control. Biomass yields and P uptake of maize after fertilization with heat treated sewage sludge ashes are not significantly different from those after TSP fertilization. The main P compound in USSA is Ca<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>. By heat treatment and amendment with different sodium, calcium, sulphur and silicon containing additives or steel mill converter slag, Ca<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub> is converted to Ca- and Na-silico-phosphates, which have a higher water solubility than Ca<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>. This increased solubility is responsible for the high plant availability of this phosphates.

Effect of bioeffectors and recycled P-fertiliser products on the growth of spring wheat

“…This result was in line with earlier work, showing that phosphorus in sewage sludge ash is generally not readily taken up by plants [9]. On the other hand, there may be considerable variations between different sewage sludge ashes, depending on the processing of sewage sludge in the water treatment plant [7].…”

“…This was probably related to an increase in soil pH from ~5.6 in the TSP treatment to ~6.5 in the LDS/SSA treatment (Additional file 1: Table S1), since the availability of phosphates in soil is generally highest close to neutrality [59]. Severin et al [9] found that the LDS/SSA product had high efficiency as a P fertiliser [9] in accordance with this study's results, yielding a P-fertilisation effect comparable to TSP. This shows the potential of this technology to produce a highly effective P fertiliser, partly based on sewage sludge devoid of any organic contaminants.…”

“…BOF (basic oxygen furnace) or LD (Linz-Donawitz) slag from steel production may be used as a liming agent in agriculture [8]. It is also possible, however, to use sewage sludge ash as a means to enrich the hot liquid BOF slag with P, resulting in a fertiliser with a markedly higher P availability compared to the feedstock sewage sludge ash, due to a conversion of Ca 3 (PO 4 ) 2 (whitlockite) of low neutral ammonium citrate (nac) solubility into Casilico-phosphates with a higher nac solubility [9]. P contained in animal manures can be used more sustainably if it is up-concentrated, and thereby more easily transported from areas with a P surplus to areas where soils have a P deficit [3].…”

Potential of three microbial bio-effectors to promote maize growth and nutrient acquisition from alternative phosphorous fertilizers in contrasting soils

“…This is in line with the data on water extractable P in the sludges where the level in the Danish sludge was three times higher than in the German sludge (Table 4). Furthermore, the availability of P in sewage sludge ashes can be quite different depending on the processing of the sludge in the water treatment plant [47].The very high fertilizer efficiency recorded for the P-enriched BOF slag has been observed earlier in wheat [45] and maize [42].…”

“…The TSP (20% P) was provided by Landor in Switzerland and RP (12% P) by Herbert Molitor in Germany. The additional P treatments consisted of recycled inorganic fertilizers (sewage sludge ashes and P-enriched BOF (basic oxygen furnace) slags [42]) and organic fertilizers (fresh biogas digestate, mature compost from green wastes, composted cow and horse manures, and sewage sludge). They were characterized by the local laboratories (Table 4) for their dry matter content, total P content, water extractable P, total potassium (K) and N content, and their ammonium N content.…”