Best Available Technology for P-Recycling from Sewage Sludge—An Overview of Sewage Sludge Composting in Austria

In order to close the phosphorus cycle in the long term, efficient recycling processes are necessary to ensure that this critical nutrient can be returned to arable land. Sewage sludge recycling is of particular importance due to the relatively high phosphorus content of sewage sludge. In this article, the current recycling paths of Austrian sewage sludge are highlighted, focusing on the advantages and limitations of sewage sludge composting. In addition to nutrient contents, pollutant loads were also analyzed in order to also discuss the limitations of this recycling pathway. Therefore, data from Austrian composting plants with focus on sewage sludge are used. The results show that the currently relevant pollutants (heavy metals) are predominantly below the limits prescribed for recycling and spreading on arable land. However, in order to decide on a recycling path at an early stage, a pollutant monitoring system must be in place. Due to pollution, mono-incineration with subsequent phosphorus recovery is also currently being discussed in Austria. Mono-incineration can represent an important component of sewage sludge disposal, because some sewage sludges are not suitable for composting due to potential environmental hazards. Therefore, it is important that evidence-based limit values and measures for the reduction in pollutants for input sources are determined.

Representation of phosphorus cycle in Joint UK Land Environment Simulator (vn5.5_JULES-CNP)

Most Land Surface Models (LSMs), the land components of Earth system models (ESMs), include representation of N limitation on ecosystem productivity. However only few of these models have incorporated phosphorus (P) cycling. In tropical ecosystems, this is likely to be particularly important as N tends to be abundant but the availability of rock-derived elements, such as P, can be very low. Thus, without a representation of P cycling, tropical forest response in areas such as Amazonia to rising atmospheric CO2 conditions remains highly uncertain. In this study, we introduced P dynamics and its interactions with the N and carbon (C) cycles into the Joint UK Land Environment Simulator (JULES). The new model (JULES-CNP) includes the representation of P stocks in vegetation and soil pools, as well as key processes controlling fluxes between these pools. We evaluate JULES-CNP at the Amazon nutrient fertilization experiment (AFEX), a low fertility site, representative of about 60 % of Amazon soils. We apply the model under ambient CO2 and elevated CO2. The model is able to reproduce the observed plant and soil P pools and fluxes under ambient CO2. We estimate P to limit net primary productivity (NPP) by 24 % under current CO2 and by 46 % under elevated CO2. Under elevated CO2, biomass in simulations accounting for CNP increase by 10 % relative to at contemporary CO2, although it is 5 % lower compared with CN and C-only simulations. Our results highlight the potential for high P limitation and therefore lower CO2 fertilization capacity in the Amazon forest with low fertility soils.

Diversity and function of microbial communities in the sand sheath of Agropyron cristatum by metagenomic analysis

The roots of most gramineous plants are surrounded by a variety of microorganisms; however, few studies have focused on the rhizosheath of psammophytes. Therefore, in this study, we used Illumina HiSeq high-throughput sequencing technology to analyse the composition and functional diversity of microbial communities in the rhizosheath of sand-grown Agropyron cristatum (L.) Gaertn. We found that the number of species and functions of microbial communities gradually decreased from the rhizosheath to the bulk soil. Thus, the microbial composition of the rhizosheath was richer and more diverse, and the abundance of bacteria, including Sphingosinicella, Rhizorhabdus, Friedmanniella, Geodermatophilus, Blastococcus, and Oscillatoria, was higher, and the abundance of fungi, such as Mycothermus, was higher. The abundance of CO2 fixation-related genes (acsA, Pcc, and cbbL) in the carbon cycle; NO3–, NO2–, NH2OH, and N2 transformation genes (nrtP, nirS, hao, and nifK) in the nitrogen cycle; soxB/A/C, Sat, and dsrB genes in the sulphur cycle; and 1-phosphate mannitol dehydrogenase (MtlD) gene and polyketide synthase gene (pks) were higher in the rhizosheath than in the bulk soil, as well as genes related to phosphorus uptake in the phosphorus cycle. Our findings showed that the rhizosheath may host the predominant microbial species related to the formation of a rhizosheath.

Sustainable Production of Reduced Phosphorus Compounds: Mechanochemical Hydride Phosphorylation Using Condensed Phosphates as a Route to Phosphite

Phosphorus removal and recovery technologies have been implemented to tackle the anthropogenic eutrophication caused by phosphate runoff into waterways. In pursuit of a better utilization of the phosphates recovered from waste water treatment, we herein report that condensed phosphates can be employed to phosphorylate hydride reagents under solvent-free mechanochemical conditions to furnish phosphite (HPO3)2−, a versatile chemical with phosphorus in the +3 oxidation state. Hydride phosphorylation, as a two-electron one-proton reduction of a main group element oxide, constitutes a direct parallel with CO2 reduction to formate. Using potassium hydride as the hydride source, sodium trimetaphosphate (Na3P3O9 ), triphosphate (Na5P3O10), and pyrophosphate (Na4P2O7) engendered phosphite in 44, 58, and 44% yields based on total P content, respectively, under their optimal conditions. Formation of overreduced products including hypophosphite (H2PO2−) was identified as a competing process, and mechanistic investigation revealed that hydride attack on in situ generated phosphorylated phosphite species is a potent pathway for overreduction. The phosphite generated from our method could be easily isolated in the form of barium phosphite, a useful intermediate for production of phosphorous acid. This method circumvents the need to pass through white phosphorus (P4) as a high energy intermediate and mitigates involvement of environmentally hazardous chemicals. A bioproduced polyphosphate from baker’s yeast was demonstrated to be a viable starting material for the production of phosphite. This example demonstrates the possibility of accessing reduced phosphorus compounds in a more sustainable manner, and more importantly, closing the modern phosphorus cycle.

Litter inputs and phosphatase activity affect the temporal variability of organic phosphorus in a tropical forest soil in the Central Amazon

Purpose The tropical phosphorus cycle and its relation to soil phosphorus (P) availability are a major uncertainty in projections of forest productivity. In highly weathered soils with low P concentrations, plant and microbial communities depend on abiotic and biotic processes to acquire P. We explored the seasonality and relative importance of drivers controlling the fluctuation of common P pools via processes such as litter production and decomposition, and soil phosphatase activity. Methods We analyzed intra-annual variation of tropical soil phosphorus pools using a modified Hedley sequential fractionation scheme. In addition, we measured litterfall, the mobilization of P from litter and soil extracellular phosphatase enzyme activity and tested their relation to fluctuations in P- fractions. Results Our results showed clear patterns of seasonal variability of soil P fractions during the year. We found that modeled P released during litter decomposition was positively related to change in organic P fractions, while net change in organic P fractions was negatively related to phosphatase activities in the top 5 cm. Conclusion We conclude that input of P by litter decomposition and potential soil extracellular phosphatase activity are the two main factors related to seasonal soil P fluctuations, and therefore the P economy in P impoverished soils. Organic soil P followed a clear seasonal pattern, indicating tight cycling of the nutrient, while reinforcing the importance of studying soil P as an integrated dynamic system in a tropical forest context.

A highly active phosphate-insensitive phosphatase is widely distributed in nature

The regeneration of bioavailable phosphate from immobilised organophosphorus represents a key process in the global phosphorus cycle and is facilitated by enzymes known as phosphatases. Most bacteria possess at least one of three major phosphatases, known as PhoA, PhoX and PhoD, whose activity is optimal under alkaline conditions. The production and activity of these three phosphatase families is negatively regulated by phosphate availability and thus these enzymes play a major role in scavenging phosphorus only during times of phosphate scarcity. Here, we reveal a previously overlooked phosphate-insensitive phosphatase, PafA, prevalent in Bacteroidetes, which is highly abundant in nature and represents a major route for the remineralisation of phosphate in the environment. Using Flavobacterium johnsoniae as the model, we reveal PafA is highly active towards phosphomonoesters. Unlike other major phosphatases, PafA is fully functional in the presence of its metabolic product, phosphate, and is essential for growth on phosphorylated carbohydrates as a sole carbon source. PafA, which is constitutively produced under all growth conditions tested, rapidly remineralises phosphomonoesters producing significant quantities of bioavailable phosphate that can cross feed into neighbouring cells. pafA is both abundant and highly expressed in the global ocean and abundant in plant rhizospheres, highlighting a new and important enzyme in the global phosphorus cycle with applied implications for agriculture as well as biogeochemical cycling. We speculate PafA expands the metabolic niche of Bacteroidetes by enabling utilisation of abundant organophosphorus substrates in the presence of excess phosphate, when other microbes are rendered incapable.