Phosphorus fractionation and protein content control chemical phosphorus removal from corn biorefinery streams

Abstract

The economic viability of corn biorefineries depends heavily on the sale of coproducts as animal feeds, but elevated phosphorus (P) contents can exacerbate manure management issues. Phosphorus removal from light steep water and thin stillage, two concentrated in‐process aqueous streams at wet milling and dry‐grind corn biorefineries, could simultaneously generate concentrated fertilizer and low‐P animal feeds, but little is known regarding how differences in stream composition affect removal. To address this data gap, we show that the solubility of P in light steep filtrate (LSF) and thin stillage filtrate (TSF) exhibits distinct sensitivity to calcium (Ca) and base addition due to differences in P fractionation and protein abundance. In LSF, P was primarily organic, and near‐complete removal of P (96%) was observed at pH 8 and a Ca/total P (TP) ratio of 2. In TSF, TP removal was lower (81%), and there was more equal distribution of organic and orthophosphate, indicating that the Ca requirements of inorganic P precipitation were a limiting factor. The C/H/N ratio, elemental characterization, and crude protein analysis of the precipitated solids indicated that coprecipitation of amorphous solids containing Ca, Mg, and K with soluble proteins facilitated removal of P, particularly in LSF. Although the removal mechanisms and solubility limits differed, these results highlighted the magnitude (40–70 mM) and efficacy (80–96%) of P recovery from two biorefinery streams.

Mapping the National Phosphorus Recovery Potential from Centralized Wastewater and Corn Ethanol Infrastructure

“…P recovery from large WRRFs in the Midwest has a direct influence on the reduction of P discharge, while P recovery from the large corn biorefineries could reduce embedded P in livestock feed. In states like Iowa, Wisconsin, Minnesota, and Missouri with high livestock populations, the reduction of P at biorefineries could also decrease the risk of manure P losses to surface water due to the lower P content in biorefinery coproducts used in animal feeds. − The mismatch of manure N/P with crop N/P needs means that application of manure to meet crop N needs entails excessive application of P and thus aggravated P loss risk to surface waters . Decreasing the manure P content by reducing the amount of P fed to animals thereby stands to mitigate manure-based contributions to non-point source P losses, which in some watersheds of the US Corn Belt are thought to be the major driver …”

“…Although approximately 1.71 Gg of P as the fertilizer is applied annually to US croplands, nearly 0.54 Gg of P enters water bodies due to soluble and erosive losses . Recovery and agricultural reuse of P from wastewater and aqueous food processing streams can both reduce the amount of phosphate rock needed while also reducing the amount of P in livestock feed that would eventually be lost to water bodies from animal waste streams. − Outside of P recovery that is already done (e.g., land application of manure and wastewater sludge), human waste and animal manure present two main untapped pathways for renewable P (rP).…”

“…Animal waste has also been directly land applied as a means of nutrient recycling but is done to primarily meet nitrogen (N) needs, which can lead to overapplication of P. The environmental impacts associated with transportation are also higher for manure than concentrated rP products due to the excess weight of the organic matrix . An alternative to P recovery from manure is to recover P from highly concentrated biorefinery coproduct streams that are sold as animal feeds such as corn (Zea mays) gluten feed and distillers dried grains with solubles (DDGS), especially considering that the magnitude of P in maize and soybean milling coproducts is nearly equivalent to that of P in excess manure . Currently, this animal feed is fed to livestock and excreted as manure which may be overapplied and cause excessive P losses .…”

Phytin recovered from grain distillation can serve as a phosphorus fertilizer for maize and soybean

“…Although the replacement of highly water-soluble phosphate fertilizers such as MAP by organic P-rich (55% of total P) phytin would be expected to entail lower soil extractable inorganic P, exacerbated by greater P demand with an increasing degree of phytin substitution, we did not detect differences in soil Mehlich-3 P (colorimetric) across the phytin substitution gradient (Figure S1). In addition, since there was more inorganic P in thin stillage (dry grind plants) than light steep (wet milling), the blend ratios identified in this study may not reflect phytin recovered from dry grind facilities or wet milling plants that use phytase (Aguiar et al, 2020).…”

“…promote P mineralization or at least mitigate microbial immobilization of P by decreasing the organic C to P ratio of the fertilizer mixture input (Aguiar et al, 2020;Arenberg & Arai, 2019;Zhang et al, 2014). On the other hand, organic P mineralization can be driven by the microbial need for C (Spohn & Kuzyakow, 2013), raising the possibility that P may be biochemically but not biologically mineralized (Condron et al, 2005) from phytate due to microbial C demand.…”