Human Perturbation of the Global Phosphorus Cycle: Changes and Consequences

Conversion of municipal wastewater-derived waste to an adsorbent for phosphorus recovery from secondary effluent

The sustainable management and recirculation of phosphorus resources are essential to our human lives. In this work, phosphorus removal and recovery from secondary effluent were achieved using municipal wastewater-derived materials as adsorbents. Through modification with 0.5 M NaOH for 30 min, iron containing sludge that originated from the coagulation pretreatment of municipal wastewater was successfully converted to phosphorus adsorbent. The maximal adsorption capacity of the prepared adsorbent was estimated to be 22 mg-P/g, and the adsorption performance remained stable in the pH range of 5-8. FeO(OH) was identified as the key adsorption site, and the ligand exchange mediated chemical adsorption was the main mechanism for phosphorus removal by the prepared material. Moreover, a laboratory-scale continuous-flow adsorption column experiment showed that the surplus phosphorus in secondary effluent could be readily reduced to <0.1 mg/L. By pyrolysis of P-laden alkali-treated iron sludge under oxygen limited conditions, the phosphorus was recovered and successfully applied to support wheat growth. This work provides valuable information for both the sustainable management of phosphorus streams in wastewater and cyclic utilization of waste sludge.

Fabrication and evaluation of a regenerable HFO-doped agricultural waste for enhanced adsorption affinity towards phosphate

Chemical modification of agricultural waste biomass has proved to be an economy and effective approach to capture phosphate ions, except for that under acidic conditions and highly competitive ion systems. According to this, a new nanocomposite (HFO@St+) was fabricated by incorporating nano-sized hydrous Fe(III) oxides (HFO) within aminated wheat straw in order to overcome the bottleneck. The optimal pH of phosphate uptake by HFO@St+ was greatly broadened and observed over a wide pH range between 2.0 and 7.0. The binary exchange reaction indicated that phosphate was strongly and preferably adsorbed by HFO@St+ with the separation factor K of phosphate over nitrate increasing from 0.23-1 or 0.20-0.26 to 2.5-38 or 2.5-15 for near neutral or acidic pHs, respectively. The sorption selectivity for HFO@St+ followed the order of phosphate > nitrate > chloride under experimental conditions. The presence of inorganic and organic ligands (SO₄ and HA) showed no significant effect on phosphate adsorption. XPS and FT-IR analyses were performed to explore the underlying mechanism of adsorption. The exhausted material could be regenerated with NaOH-NaCl solution for at least ten cycles, indicating that HFO@St+ can be used as a sustainable biomass product with excellent adsorption affinity for phosphate removal.

Response of phosphorus fractionation in lake sediments to anthropogenic activities in China

In this study, geochemical fractionation is used to establish the relationship between sediment phosphorus (P) pools and anthropogenic activities based on the dated sediment from a suite of lakes in China. Our extraction results showed that the inorganic P fractions, including Ca-P (46% of TP) and Fe/Al-P (24%), constitute most of the P in sediments. Soil erosion dynamics and geographic location are the dominant factors controlling the historical distribution and partitioning of Ca-P in sediments, while over the last few decades, industrial and domestic effluents were the leading factor controlling Fe/Al-P. The organic P (P_o) fractions, NaHCO₃-P_o, HCl-P_o, and Ful-P_o accounted for only 11%, 16% and 12% of P_o on average, respectively, whereas Hum-P_o and Res-P_o made up the dominant P_o fraction (59%) and were the main factors controlling P_o dynamics due to fertilizer and livestock breeding. Thus, the historical fraction of P in the sediment core can be used as an indicator of anthropogenic activities. Ca-P decreased in the top layers of the cores because of the implementation of the Soil and Water Conservation Law in China since 1991. However, Fe/Al-P and P_o continuously increased in the lakes from the economic backward area over the last few decades, which is largely due to enhanced point sources of pollution and an increase in the intensity of agricultural practices. As a potential P source, the massive accumulation of Fe/Al-P and P_o would be released into the overlying water to further facilitate eutrophication via increasing pH and alkaline phosphatase and decreasing in the dissolved oxygen concentration. Therefore, in order to control eutrophication more effectively and efficiently, it is essential that the accumulation of sediment Fe/Al-P and P_o be decreased immediately and domestic wastewater, poultry excreta, and fertilizer loss must be more carefully controlled, especially in economically backward areas.

Molecular Understanding of Humic Acid-Limited Phosphate Precipitation and Transformation

Phosphorus (P) availability is widely assumed to be limited by the formation of metal (Ca, Fe, or Al) phosphate precipitates that are modulated by soil organic matter (SOM), but the SOM-precipitate interactions remain uncertain because of their environmental complexities. Here, we present a model system by quantifying the in situ nanoscale nucleation kinetics of calcium phosphates (Ca-Ps) on mica in environmentally relevant aqueous solutions by liquid-cell atomic force microscopy. We find that Ca-P precipitate formation is slower when humic acid (HA) concentration is higher. High-resolution transmission electron microscopy observations demonstrate that HA strongly stabilizes amorphous calcium phosphate (ACP), delaying its subsequent transformation to thermodynamically more stable phases. Consistent with the formation of molecular organo-mineral bonding, dynamic force spectroscopy measurements display larger binding energies of organic ligands with certain chemical functionalities on HA to the initially formed ACP than to mica that are responsible for stabilization of ACP through stronger HA-ACP interactions. Our results provide direct evidence for the proposed importance of SOM in inhibiting Ca-P precipitation/transformation. We suggest that similar studies of binding strength in SOM-Fe/Al-P may reveal how both organic matter and metal ions control P availability and fate, and thus the eventual P management for agronomical and environmental sustainability.

Speciation Transformation of Phosphorus in Poultry Litter during Pyrolysis: Insights from X-ray Diffraction, Fourier Transform Infrared, and Solid-State NMR Spectroscopy

Converting poultry litter (PL) into biochar by slow pyrolysis is a promising approach for recycling organic waste with enhanced phosphorus (P) utilization efficiency, which needs fundamental knowledge of in situ P speciation transformation for optimizing the biochar conversion conditions. In this study, solid-state NMR spectroscopy was employed to characterize solid-state P and C speciation of raw PL and PL-derived biochars prepared at various pyrolysis temperatures. The NMR analysis indicated that phytates were decomposed while hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) formed during conversion of PL to PL-derived biochar at a pyrolysis temperature above 300 °C. With increasing pyrolysis temperature to above 500 °C, farringtonite (Mg₃(PO₄)₂) formed. The higher pyrolysis temperature also favored the formation of calcite and provided deeper carbonization (i.e., greater dominance of thermally stable aromatic structures) in the biochar products. Water extractable P decreased significantly from 2.9 g/kg in PL to less than 0.3 g/kg in the PL-derived biochars prepared above 300 °C, indicating the inhibition effect of pyrolysis on the P lability mainly through transformation of labile phosphates in PL into less soluble forms. Overall, this study suggested that different pyrolysis temperatures should be considered for selective conversion of PL to biochar products with distinct agricultural and environmental applications that demand special P release patterns.

Characterization of phosphorus accumulation and release using diffusive gradients in thin films (DGT) - linking the watershed to Taihu Lake, China

Taihu Lake is well known internationally due to its algae bloom, and phosphorus fertilization and accumulation in the watershed soil played an important role in the lake eutrophication. To explore the linkage between soil and sediment legacy P, the soils from four representative land uses in the upstream watershed and sediments from typical lake areas were sampled and analyzed for P species. Meanwhile, the DGT technology was used to characterize the labile P in the soil and sediment and its release dynamics. The results indicated that Taihu Lake was the major total phosphorus sink (TP = 481.7 ± 97 mg/kg) and wheat land the major reactive phosphorus stock (RP = 37.3 ± 9 mg/kg) in the watershed. The DGT-P dynamic with the deployment time (t) presented a downward exponential curve (f(t) = a × t^-b, b > 0) and the regression parameters implied the initial P stock (a) and release rate (b) of labile P. Although the result of the extract based method was statistically correlated to the DGT measured P (p < 0.05), the DGT result had advantages over the traditional method due to its in-situ measurement and kinetic characterization of available P. Since the regression parameters reflected combined factors that impact the interaction between solid and solution P, the soil or sediment properties such as pH and organic matters need to be further studied in details, although they presented a significant correlation with DGT-P in this work. Our work provides a new insight in the rapid assessment of the size and resupply capacity of the existing legacy P stocks.

Evaluation of the adsorption of ammonium-nitrogen and phosphate on a granular composite adsorbent derived from zeolite

To remove the extra ammonium-nitrogen (NH₃-N) and phosphorus (P) from contaminated water, a novel granular adsorbent (GAZCA) was fabricated with zeolite powders and Al-Mn binary oxide (AMBO) via the compression method. The SEM-EDS and mapping and XRD results illustrated the microstructure of GAZCA: the homogeneous aggregation of zeolite and AMBO nanoparticles with their crystal integrity and the uniform distribution of Al/Mn/Si/O elements on the adsorbent surface. FTIR and XPS results demonstrated the existence of impregnated sodium cations and hydroxyl groups, which were responsible for the removal of NH₃-N and P, respectively. The results of BET analysis and compression tests exhibited a high surface area (14.4 m²/g) and a satisfactory mechanical strength of GAZCA. Kinetic adsorption results showed a fast adsorption rate for NH₃-N and P, and mutual inference was not observed between the adsorption kinetics of NH₃-N and P in the bi-component system. The adsorption isotherm results demonstrated that the maximum adsorption capacities of NH₃-N and P were calculated as 12.9 mg/g and 9.3 mg/g via the Langmuir model, respectively. In the bi-component system, the adsorption capacities of NH₃-N and P were maintained at low and moderate concentrations and decreased at high concentrations due to the blockage effects of NH₄MnPO₄·H₂O precipitates. The removal efficiency of NH₃-N could be maintained in a wide pH range of 4~10, while P adsorption was inhibited at alkali conditions. The solution of sodium bicarbonate (0.4 M) was used for the regeneration of saturated adsorbents, which permitted GAZCA to keep 98% and 78% of its adsorption capacity for NH₃-N and P even after three regeneration and reuse cycles. Dynamic experiments illustrated that a satisfactory performance was obtained for the in situ treatment of simulated N- and P-contaminated water by using a column reactor packed with GAZCA, thus further confirming its great potential for the control of eutrophication.

Challenges and Approaches in Microbiome Research: From Fundamental to Applied

We face major agricultural challenges that remain a threat for global food security. Soil microbes harbor enormous potentials to provide sustainable and economically favorable solutions that could introduce novel approaches to improve agricultural practices and, hence, crop productivity. In this review we give an overview regarding the current state-of-the-art of microbiome research by discussing new technologies and approaches. We also provide insights into fundamental microbiome research that aim to provide a deeper understanding of the dynamics within microbial communities, as well as their interactions with different plant hosts and the environment. We aim to connect all these approaches with potential applications and reflect how we can use microbial communities in modern agricultural systems to realize a more customized and sustainable use of valuable resources (e.g., soil).