Adapted Hedley fractionation for the analysis of inorganic phosphate in biogas digestate

Phosphorus bioavailability and recycling potential in various organic Waste: Assessment by enzymatic hydrolysis and 31P NMR

Phosphorus(P) recycling from waste streams is crucial to mitigate the P depletion crisis. P forms and contents in organic waste are critical for determining the recycling method and efficiency. We constructed an approach to characterize P forms in seven organic waste by combining chemical sequential extraction, enzymatic hydrolysis, and nuclear magnetic resonance(NMR). Livestock manure and straw exhibited a higher active P(H2O-P&NaHCO3-P)(70.54%-84.40% and 65.78%-85.26% of total P) than sewage sludge(18.22%) and food waste(43.90%). Enzymatic hydrolysis revealed over 10% P in the so-called active P of corn(11.30%) and rice straw(13.32%) was phytate-like P, which is not bioavailable. These findings indicate the chemical sequential extraction inaccurately gauges bioavailable-P and underscores the need to convert phytate into plant-available P in recycling processes(biogas, composting), especially for crop straws and chicken manure. This work introduces a novel methodological framework for assessing P potential bioavailability in organic waste, providing fundamental knowledge for the P recycling process optimization.

Effects of additives on shifting phosphorus to solid phase during Solid-Liquid separation of digestate in full-scale biogas plant

Phosphorus (P) is critical for plant growth, but global reserves are exhausting within 250-300 years, therefore enhancing phosphate recycling is crucial for the future. Biogas digestate, rich with nutrients is a promising resource for nutrient recovery. Conventional solid-liquid separation shifts approximately 35 % of the total P in the digestate to the solid phase. Separation trials with additive treatment using a screw press with a 0.75 mm sieve were performed at University of Hohenheim's full-scale biogas plant. After 22 h, 67.41 % (kieserite treatment) and 52.35 % (strawflour treatment) of total P shifted to the solid phase. Treatment with kieserite enhanced P shift into the solid phase by forming non-labile fractions through a chemical bond between P and Mg2+ ions. Kieserite treatment for 22 h effectively increases the share of total P in the separated solid phase, it also ensures a sustainable nutrient supply and mitigates the risk of nutrient runoff.

Evaluation of pollution potential in swine manure across growth stages: Impact of dietary nutrients and management strategies

Regulation of dietary nutrient fractions to control the release of labile manure pollutants in swine production remains a challenge. Feeding trials were conducted to assess the impact of dietary nutrient fractions on labile manure composition and pollution potential in pigs at different growth stages. The pigs were selected based on age (weaning = 60 days, feeding = 100 days, and finishing = 160 days), health, and average body weight (23.7 kg, 50.5 kg, and 109.0 kg respectively) and fed with (1) high, (2) medium, and (3) low energy diets twice daily in all three growth stages. Urine and feces were collected for analysis. The study utilized correlation, nutrient balance analysis, and theoretical models to evaluate the dietary impact on nutrient distribution and pollution potential. Results showed higher nutrient retention (N, P, Cu, Zn) with the high-energy diet across all growth stages compared to the other two diet energy levels. Correlation analysis revealed that pigs' weight gain does not reflect dietary efficiency nor indicate lower pollution potential from nutrient retention. However, dietary nutrient fractions played more significant role in labile manure release compare to the total manure component. Overall, the dietary regulatory approach offers a sustainable strategy to mitigate environmental pollution while supporting nutrient recycling using manure with lower pollutant loads.

The phosphorus challenge: biotechnology approaches for a sustainable phosphorus system

Phosphorus (P) is essential for growing crops, but the supply of high-quality phosphate rock reserves used for fertilizer production is finite while losses of P from the food/waste system cause considerable environmental damage. A variety of emerging approaches in biotechnology are reviewed that hold promise for improving the sustainability of P use in the food/water systems. These include improved sensors, cell culture approaches to meat production, bio-based P adsorption and transformation strategies, advancements in understanding of polyphosphate-accumulating organisms, and new approaches involving biomineralization and anaerobic treatment. By advancing these technologies to scale, progress can be made in developing a circular phosphorus economy that improves food security while protecting drinking water and aquatic ecosystems.

Effects of wet-dry alternation on organic phosphorus dynamics and sediment characteristics in the intertidal zone of Nansi Lake

The study of the fractions and distribution characteristics of organic phosphorus in the sediment of the water level fluctuating zone of Nansi Lake is conducive to revealing the transformation of phosphorus in the lake, and has important scientific significance for controlling the eutrophication of Nansi Lake. Based on the sediment of the water level fluctuation zone of Nansi Lake. The improved Hedley continuous grading extraction, ultraviolet-visible spectroscopy and three-dimensional fluorescence spectroscope were used to characterize the structural characteristics and stability of organic molecules in the sediment, and to reflect the differences in the structure and stability of organophosphate in the water level fluctuating zone. Principal component analysis (PCA), Redundancy analysis (RDA) and correlation heat map analysis were used to analyze the correlation between phosphorus and physicochemical index. The results showed that the alternation between wet-dry conditions was more favorable for the release of phosphorus from sediment, compared to continuous inundation conditions. Moreover, the higher the frequency of wet-dry alternations, the greater the release of phosphorus in different forms from the sediment. Wet-dry alternation resulted in a reduction of substituent on the aromatic rings of sediment DOM (dissolved organic matter), and the continuous drying would increase the molecular weight and humidification degree of DOM in the sediment. Correlation analysis showed that NaOH-Po content in sediment was significantly negatively correlated with TP, IP, OP and various organophosphorus forms, indicating a close transformation relationship between phosphorus forms in sediment. The results can provide a scientific basis for controlling the release of endogenous phosphorus and the risk of eutrophication in Nansi Lake.

Phosphorus adsorption characteristics and release risk in saline soils: a case study of Songnen Plain, China

Introduction

The Songnen Plain is one of the three major saline-alkali areas in China, covering a vast area, where drought and overgrazing have exacerbated the salinization trend, and will have great potential for development if utilized rationally. Phosphorus, as one of important soil nutrients, plays a crucial role in plant growth. How to minimize its loss and migration has become a current research hotspot. The objective of the present study was to elucidate the adsorption properties of phosphorus in soils affected by salinization and to establish the correlation between the potential for phosphorus release and soil properties.

Methods

A batch treatment test was conducted in this study using three soils with the various salinization degrees to examine the impact of environmental factors on the adsorption properties and potential release of phosphorus.

Results and discussion

It was found that the maximum phosphorus adsorption by the three salinization soils in 0-360 minutes accounted for 86.8%-90.5% of the total adsorption capacity; the equilibrium adsorption capacity was: HS> MS> LS. In cases where the phosphorus level in the surrounding liquid is low, the three levels of salinized soils exhibited varying levels of phosphorus discharge, with the adsorbent acting as the origin of contaminants. The Pseudo-second-order model kinetics and Langmuir equation can well describe the adsorption process, and the adsorption process is spontaneous heat absorption with entropy increase. Increasing the pH led to an increase in the adsorption of phosphorus from the three salinized soils. Additionally, the adsorption was enhanced by introducing varying concentrations of Na+, Ca2+, and Al3+ to the background solution. The phosphorus eutrophication release risk (ERI) demonstrated a gradual decline as temperature increased. Correlation analysis revealed a noteworthy positive correlation between TN, TP, and ERI, as well as a significant negative correlation between CEC, K+, and ERI. Furthermore, there was a highly significant negative correlation between coarse silt and fine silt. Considering local climatic and environmental factors is crucial for controlling the adsorption capacity of phosphorus in various salinized soils, as it can unveil the mechanism of phosphorus adsorption and impact its migration and release risk.

Comparison of phosphorus species in livestock manure and digestate by different detection techniques

Phosphorus (P) species characterize the effectiveness of the P fertilizer. In this study, the P species and distribution in different manures (pig manure, dairy manure and chicken manure) and their digestate were systematically investigated through combined characterization methods of Hedley fractionation (H₂OP, NaHCO₃-P, NaOH-P, HCl-P, and Residual), X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) techniques. The results from Hedley fractionation showed that >80 % of P in the digestate was inorganic and the HCl-P content in manure increased significantly during anaerobic digestion (AD). XRD manifested that insoluble hydroxyapatite and struvite belonging to HCl-P were presented during AD, which was in agreement with the result of Hedley fractionation. ³¹P NMR spectral analysis revealed that some orthophosphate monoesters were hydrolyzed during AD, meanwhile the orthophosphate diester organic phosphorus like DNA and phospholipids content has increased. After characterizing P species by combining these methods, it was found that chemical sequential extraction could be an effective way to fully understand the P in livestock manure and digestate, with other methods used as auxiliary tool depending on the purpose of studies. Meanwhile, this study provided a basic knowledge of utilizing digestate as P fertilizer and minimizing the risk of P loss from livestock manure. Overall, applying digestates can minimize the risk of P loss from directly applied livestock manure while satisfying plant demands, and is an environmentally friendly P fertilizer.

Synthesis of magnetic adsorbents from titanium gypsum and biomass wastes for enhanced phosphate removal

A novel scheme was proposed to prepare magnetic adsorbents by co-pyrolysis of titanium gypsum (TiG) and agricultural biomass wastes for phosphate (P) recovery. Co-presence of biomass wastes could improve TiG decomposition in inert atmosphere to generate magnetic centers and active sites, and P adsorption correlated well with organic volatiles of biomass wastes. The adsorption process evolved from a biomass-controlled process to a TiG-controlled process when increasing the mass ratio of corncob above 10 %. The optimal adsorbent (i.e. GC₁₀) exhibited higher P adsorption capacity (Q_m 183 mg/g) than many previous adsorbents; moreover, it can be magnetically separated from water after P adsorption. Active sites including CaO, CaS and Fe₃O₄ were deemed as the main factors for P chemisorption and surface precipitation. Most of adsorbed P could be released continuously and slowly by dilute NaHCO₃. These results highlight potential applications of TiG and biomass waste derived adsorbents in P purification and recovery.

Response of phosphorus speciation to organic loading rates and temperatures during anaerobic co-digestion of animal manures and wheat straw

The world is facing huge phosphate (P) shortage and anaerobic digestion (AD) is a recognized technology to promote nutrient (N and P) recycling. The composition of P speciation in the digestate is essential for the fertilizing effect. However, how P speciation in the digestates interacts with the AD process conditions is unknown. Therefore, interaction of P speciation in digestates with AD process conditions was investigated by using a chemical sequential extraction method (Hedley fractionation) and X-ray diffraction; specifically, the effects of organic loading rate (OLR), temperature, and substrate composition were investigated. The results showed that OLR and feedstock affected P speciation in the digestate significantly due to different ion species and ionic strengths. The H₂O-P concentration in chicken manure with straw (CMS) and dairy manure with straw (DMS) digestates decreased by 44.04-48.76% and 48.88-50.49%, respectively, as the OLR increased from 2 to 4 kg VS m^-3 d^-1. Simultaneously, HCl-P increased by 38.02-44.01% in the CMS digestates due to Ca-P and Mg-P formation, indicating that Ca-P and Mg-P formation was positively correlated with OLR, whereas P mobility decreased. Further, thermophilic temperature conditions were more conducive for the formation of insoluble P than mesophilic temperature conditions in the digestates due to the thermodynamic driving force of the reactions. The results would facilitate the understanding of P transformation in the AD process under the influence of feedstock, OLR, and temperature. From the viewpoint of nutrient management, lower OLR and temperature are more beneficial for a fast P availability, whereas higher OLR and temperature are more helpful for storage and export because of P precipitated into solid phase of digestate.

Anaerobic digestion beyond biogas

Anaerobic digestion (AD) is a matured technology for waste (water) remediation/stabilization and bioenergy generation in the form of biogas. AD technology has several inherent benefits ranging from generating renewable energy, remediating waste (water), and reducing greenhouse gas emission to improving health/hygiene and the overall socio-economic status of rural communities in developing nations. In recent years, there has been a paradigm shift in applications of AD technology beyond biogas. This special issue (SI) entitled, "Anaerobic Digestion Beyond Biogas (ADBB-2021)," was conceptualized to incorporate some of the recent advances in AD in which the emphasis is beyond biogas, such as anaerobic biorefinery, chain elongation, treatment of micropollutants, toxicity and system stability, digestate as biofertilizer, bio-electrochemical systems, innovative bioreactors, carbon sequestration, biogas upgrading, microbiomes, waste (water) remediation, residues/waste pre-treatment, promoter addition, and modeling, process control, and automation, among others. This VSI: ADBB-2021 contains 53 manuscripts (14 critical reviews and 39 research). The key findings of each manuscript are briefly summarized here, which can serve as a valuable resource for AD researchers to learn of major advances in AD technology and identify future research directions.