Evaluating the Struvite Recovered from Anaerobic Digestate in a Farm Bio-Refinery as a Slow-Release Fertiliser

Abstract

Biogas production in agricultural biogas plants generates digestate—liquid waste containing organic matter and mineral nutrients. Utilisation of the digestate on farm fields adjacent to the biogas plants is limited. Therefore, bio-refineries implement advanced forms of digestate processing, including precipitation of struvite (MgNH4PO4.6H2O). Struvite can be transported over long distances and dosed precisely to meet the nutritional needs of the plants. Divergent opinions on the fertilising value of struvite and its function over time call for further research on its effects on crop yields in the first and subsequent years after application. This study investigates the effects of struvite (STR), struvite with ammonium sulphate (STR + N), and commercial ammonium phosphate (AP) on the yields, nutrient concentration in the crops, nutrient uptake by the crops, and soil N, P, and Mg content in the second growing period after the application of fertilisers to silty loam (SL) and loamy sand (LS) soils under grass cultivation. Struvite was recovered from the liquid fraction of digestate obtained from a bio-refinery on the De Marke farm (Netherlands). The soils investigated in the pot experiment originated from Obory (SL) and Skierniewice (LS) (Central Poland). The results obtained over the first growing period following fertilisation were published earlier. In our prior work, we showed that the majority of the struvite phosphorus remains in the soil. We hypothesised that, in the second year, the yield potential of the struvite might be higher than that of commercial P fertiliser. Currently, we have demonstrated that, in the second growing period following the application, struvite causes an increase in grass yield, nutrient uptake by the crops, and P and Mg content in the soil. On SL and LS soils, the yields of the four grass harvests from the STR and STR + N treatments were higher than those from AP by approximately 8% and 16.5%, respectively. Our results confirm that struvite is more effective as a fertiliser compared to commercial ammonium phosphate. Struvite can be, therefore, recommended for fertilising grasslands at higher doses once every two years.

Valorisation of Agricultural Digestate for the Ammonium Sulfate Recovery and Soil Improvers Production

“…8B). Similar considerations have been made in the case struvite [40][41][42]. In addition, Grigatti et al [43] showed that the solid fraction of AD of maize had the highest potential P availability (Olsen-P) in comparison to inorganic P source (Ca(H 2 PO4) 2* H 2 O), in line with our results.…”

Effect of Various Rates of P from Alternative and Traditional Sources on Butterhead Lettuce (Lactuca sativa L.) Grown on Peat Substrate

“…Traditional P fertilizers come from rock phosphate, which nowadays is a limited resource and will be depleted within the next 150-250 years [7,8] and thus P is subject to special attention [9]. Recovery of P is limited to the agriculture sector because this sector is mostly based on P and materials rich in this element can be found [10][11][12]. Therefore, as a result, there is growing interest in the efficient recovery of nutrients from waste.…”

“…An interesting source of P supply for farms is STR (magnesium ammonium phosphate) [15]. It is an alternative P fertilizer with valuable properties containing macro elements needed by plants [10,16,17]. This fertilizer is still not implemented as a mineral fertilizer under general EU regulations, but these are currently being revised to recommend the allowance of STR into the EU fertilizer market [18,19].…”

A National Framework for Establishing a Circular Economy for Phosphorus

“…In this system, natural recycling of P is prevented by excessive anthropogenic input and waste and most P applied in agriculture is not utilized, with only 15-20% of the P in PR reaching the food consumed globally (Sutton et al 2013). Underutilized P accumulates in soil and 39.5% of P is lost through erosion and run-off (Lun et al 2018), exacerbating eutrophication, triggering harmful algal blooms (HABs) and creating hypoxic dead zones in water bodies (CRS 2020; US EPA 2021) (Carpenter et al 1998;Szymańska et al 2020). The economic cost of eutrophication in the US was estimated to be over $2.2 billion annually in 2008 (Dodds et al 2008) and is expected to be much higher today.…”