Residual Phosphorus Research Articles

High-level expression and characterization of a novel phospholipase C from Thielavia terrestris suitable for oil degumming

A novel phospholipase C gene (TtPLC) from Thielavia terrestris CAU709 was cloned and efficiently expressed in Pichia pastoris. The deduced protein sequence of TtPLC shared the highest identity of 33% with the characterized phospholipase C from Arabidopsis thaliana. The highest phospholipase C yield of 98, 970 U mL−1, with a protein concentration of 4.9 mg mL−1 was obtained by high-cell density fermentation in a 5-L fermentor. The recombinant enzyme (TtPLC) was purified to homogeneity with a recovery yield of 59.1% and a specific activity of 22, 910 U mg−1. TtPLC was most active at pH 6.5 and 55 °C, respectively. It was stable within the pH range of 4.5–8.0 and up to 45 °C. The enzyme exhibited excellent stability in different surfactants and organic solvents, including Tween 20 (147.6%), Tween 40 (180.6%), Tween 60 (205.4%), cyclohexane (160.0%), n-octane (178.2%), n-heptane (180.7%), acetone (187.5%) etc. The application of TtPLC in crude soybean oil degumming process significantly reduced the residual phosphorus content from 135.4 mg kg−1 to 7.9 mg kg−1 under the optimized conditions, which satisfied the requirement of environmental friendly physical refining process for oil refining industry. Therefore, TtPLC should be a good candidate in oil refining industry.

Effect of iron sulphate application on yield, nutrients uptake, phosphorus and iron fractions in soil at harvest of soybean [Glycine max (L.) Merr.] in Vertisols of Karnataka

Afield experiment was conducted during kharif 2014 in Main Agriculture ResearchStation (MARS), University of Agricultural Sciences (UAS), Dharwad in Vertisols to study the effect of iron sulphate application on yield, nutrients uptake, residual nutrient statusin soil, phosphorus and iron fractions in soil at harvest ofsoybean (Glycine max L.). The field experiment laid-out in RCBD design with three replications, comprised of 12 treatments of combinations such as soil application of 0, 10, 20 and 30 kg FeSO4/ha with no foliar spray, one foliar spray at 30 DAS and two foliar sprays at 30 and 45 DAS of 0.5 % FeSO4. Application of iron sulphate at the rate of 20 kg/ha with two iron sulphate (0.5%) foliar sprays at 30 and 45 DAS (T9) resulted in highest seed (15.3 q/ha) and stover yield (25.6 q/ha) and was at par with T8, T10, T11 and T12 with respect to seed yield and T6, T8 and T10 for stover yield. The lowest seed yield (12.5 q/ha) and stover yield (18.4 q/ha) were recorded in control plot (40:80:25 kg NPK/ha + soil application of FYM @ 6 t/ha + ZnSO4. 7H2O @ 12 kg/ha). Nitrogen, potassium, sulphur and iron uptake by the crop and available iron status in soil at harvest were highest in treatment T9.

Pilot-scale anoxic/aerobic biofilter system combined with chemical precipitation for tertiary treatment of wastewater

In this study, a pilot-scale anoxic/aerobic biofilter system combined with chemical precipitation was devised and applied for the tertiary treatment of nitrogen, and post-treatment of phosphorus and residual organics in effluent from existing wastewater treatment facilities. When the system operated under a system hydraulic retention time (HRT) of 5.98 h, nitrified effluent recirculation ratio of 0.5, average methanol-supplement concentration of 23.2 mg/L, and average aluminum-sulfate concentration of 2.37 mg/L, the average concentration of BOD5, COD, SS, TN, and TP in the system effluent were 3.3, 10.4, 4.2, 6.1, and 0.43 mg/L, respectively. Despite the shorter HRT of 1.35 h in the anoxic filter packed with media, noticeable denitrification was achieved rapidly. A perfect nitrification rate was achieved and no clear deterioration in performance by chemical addition was observed. Thus, the system achieved not only outstanding nitrogen-removal performance, but also the additional removal of residual organics and phosphorus.

Ecological Stoichiometry of Microbial Biomass Carbon, Nitrogen and Phosphorus on Bauxite Residue Disposal Areas

Ecological succession by microbial activity on bauxite residue disposal areas (BRDAs) would accumulate nutrients and convert the residue into a soil-like material. However, the role of microorganisms in nutrient cycling remains elusive on BRDAs. Carbon (C), nitrogen (N) and phosphorus (P) ecological stoichiometry is a critical indicator of nutrient cycling in an ecosystem. In order to investigate the changes in nutrients following long-term natural weathering process, the contents of C, N, P, microbial biomass carbon (MBC), nitrogen (MBN), and phosphorus (MBP) were measured in chronological stacks of bauxite residue. Deeply, their ecological stoichiometric characteristics were analyzed. Compared to freshly stacked residue, organic carbon (OC), total nitrogen (TN) and available phosphorus (AP) have increased 89%, 1640%, and 369% after 20 years, respectively. The C/N in 20-year-old residue (BR20) is 12.41, which close to the mean range of soil C/N in China. Bauxite residue C/P and N/P increased significantly with the stacking age increased. MBC/MBN decreased from 6.75 to 4.52 after stacked for 5 years, whilst MBC/MBP increased from 23.74 to 59.16 with stacking age. Data analysis of C, N, P and MBC, MBN, MBP in bauxite residue correlated significantly, indicating that microbial biomass can be used as a biological indicator to evaluate bauxite residue quality. This study revealed that BRDAs ecosystem development reaches homeostasis gradually, whilst CNP and MBCNP substrate ratio can be used as an effective tool to explore the mechanism of nutrient cycling.

Dynamics of residual phosphorus forms under different tillage systems in a Brazilian Oxisol

Phosphorus (P) accumulation in soil, mainly from decades of agricultural use with frequent additions of phosphate fertilizers, results in a large reserve of this nutrient that can be exploited by farmers. However, the dynamics of soil P forms under the residual effect of phosphate fertilization is still little known. In an experiment located at Embrapa Cerrados, in Planaltina, DF, Brazil, corn or soybeans were grown during the summer for 17 years, receiving 35 kg of P ha−1 year−1. The same area was then cultivated with corn for 4 more years without the supply of this nutrient, in order to characterize the behavior of P fractions accumulated in the soil and identify those that contribute most to crop nutrition when phosphate fertilization is interrupted. Changes in total P (Pt), organic P (Po), inorganic P (Pi), and labile P extracted by the Bray-1, Mehlich-1 and Olsen methods (organic and inorganic) and organic carbon (C) were evaluated by means of samples obtained before and after cultivation without P fertilization in different soil layers subject to no-till (NT) or conventional tillage (CT), previously fertilized with reactive rock phosphate (RRP) or triple superphosphate (TSP) which were applied by broadcast spreading or band-applied to the planting row. The superficial layers were most responsible for crop nutrition in NT, especially in the mode of broadcast application, while in CT the relative contribution of each layer was less stratified. There was a drastic reduction in the stock of almost all P fractions, except for Po which showed an increase, notably in soil cultivated under CT (22% in the 0–10 cm layer), although the C content was reduced. This suggests that the little available inorganic fractions, partially replacing the labile fractions, were responsible for the supply of P to crops. This replacement was more effective in NT, since it could sustain greater P offtake by crops, despite the similar reductions in labile P fractions observed in both systems.

Investigating Nutrient Limitation Role on Improvement of Growth and Poly(3-Hydroxybutyrate) Accumulation by Burkholderia sacchari LMG 19450 From Xylose as the Sole Carbon Source.

Burkholderia sacchari LMG19450, a non-model organism and a promising microbial platform, was studied to determine nutrient limitation impact on poly(3-hydroxybutyrate) [P(3HB)] production and bacterial growth from xylose, a major hemicellulosic residue. Nitrogen and phosphorus limitations have been studied in a number of cases to enhance PHA accumulation, but not combining xylose and B. sacchari. Within this strategy, it was sought to understand how to control PHA production and even modulate monomer composition. Nitrogen-limited and phosphorus-limited fed-batch experiments in bioreactors were performed to evaluate each one's influence on cell growth and poly(3-hydroxybutyrate) production. The mineral medium composition was defined based on yields calculated from typical results so that nitrogen was available during phosphorus limitation and residual phosphorus was available when limiting nitrogen. Sets of experiments were performed so as to promote cell growth in the first stage (supplied with initial xylose 15 g/L), followed by an accumulation phase, where N or P was the limiting nutrient when xylose was fed in pulses to avoid concentrations lower than 5 g/L. N-limited fed-batch specific cell growth (around 0.19 1/h) and substrate consumption (around 0.24 1/h) rates were higher when compared to phosphorus-limited ones. Xylose to PHA yield was similar in both conditions [0.37 gP(3HB)/gxyl]. We also described pst gene cluster in B. sacchari, responsible for high-affinity phosphate uptake. Obtained phosphorus to biomass yields might evidence polyphosphate accumulation. Results were compared with studies with B. sacchari and other PHA-producing microorganisms. Since it is the first report of the mentioned kinetic parameters for LMG 19450 growing on xylose solely, our results open exciting perspectives to develop an efficient bioprocess strategy with increased P(3HB) production from xylose or xylose-rich substrates.

Internal loading potential of phosphorus in reservoirs along a semiarid watershed

ABSTRACT Sediments are important to nutrient dynamics, especially due to phosphorus internal loading. Several studies have observed that internal loading could prevent water quality from improving in lakes, even when external phosphorus loading is significantly decreased. Therefore, there is an urgent need to assess the potential release of phosphorus contained in the sediment, and thus, its potential to impact water quality. In this study, the vertical and horizontal distributions of distinct phosphorus forms in the bottom sediments of artificial reservoirs, located at Forquilha watershed (Ceará, Brazil), were investigated through sequential chemical fractionation. The reservoirs Lagoa Cercada (R#1), Riacho do Algodão (R#2), Riacho Verde (R#3), Cachoeira (R#4), Chagas Manu (R#5), Quandu (R#6) and Balanças (R#7) were investigated. Reservoirs R#1 (most downstream reservoir of the watershed) and R#7 (most upstream reservoir of the watershed) had higher concentrations of total phosphorus (PT) and lower pH values, potentially exerting greater influence in phosphorus concentration in the water column. Reservoirs R#3 and R#4 presented a predominance of residual phosphorus (PRe), the least available fractions of phosphorus and thus, presented a lower potential for internal loading. Reservoirs R#5, R#1 and R#2 showed a tendency of decreasing total phosphorus (PT) as the sediment depth increased, probably indicating an increase of allochthonous phosphorus loading along time. Reservoir R#6 showed the predominance of PFeAl and PCa fractions on points A and B, respectively, showing that the characteristics of the sediments may vary in the same reservoir. Mobile (PM) and iron and aluminum-bound phosphorus (PFeAl) were the least and the most abundant fractions in most of the samples analyzed, respectively.

Second-crop cowpea under residual phosphorus doses in the Brazilian Amazon

ABSTRACT The southeastern mesoregion of the Brazilian Pará state is an important soybean producer, and the second-crop system can increase the local agricultural production. However, Latosols with medium to very clayey texture predominate in the region and, despite being suitable for farming, they naturally have low levels of available phosphorus (P). This study aimed to evaluate the yield of second-crop cowpea [Vigna unguiculata (L.) Walp] under doses of residual P in a Yellow-Latosol. Two experiments were installed under field conditions. The experimental design was randomized blocks, with five treatments (residuals of 0, 50, 100, 150 and 200 kg ha-1 of P2O5) and four replications. The first experiment consisted of cultivating second-crop cowpea after the soybean harvest, with phosphate doses provided during the soybean planting, and the second of second-crop cowpea after the rice harvest, with phosphate doses provided during the rice planting. The 1,000-grain weight and production of pods, husks and grains were evaluated. The production of pods and husks were higher in the area with residual P. The highest yield was obtained in the residual dose of 200 kg ha-1 of P2O5, reaching a grain yield of 1,256 kg ha-1 after the soybean harvest and 885 kg ha-1 after the rice harvest.

Rhizoplane Bacteria and Plant Species Co-determine Phosphorus-Mediated Microbial Legacy Effect.

Much effort has been directed toward increasing the availability of soil residual phosphorus (P). However, little information is available for the P fertilization-induced biotic P legacy and its mediation of plant P uptake. We collected microbial inocula from a monoculture maize field site with a 10-year P-fertilization history. A greenhouse experiment was conducted to investigate whether bacterial communities, as a result of different P-fertilization history (nil P, 33 and/or 131 kg P kg ha–1 yr–1), affected the growth of a conspecific (maize) or heterospecific (clover) plant, at two levels of current P application (5 and 30 mg P kg–1 soil; P5 and P30). Deep amplicon sequencing (16S rRNA) was used to determine the maize and clover root-associated bacterial microbiome in different rhizocompartments (rhizoplane, rhizosphere, bulk soil). For both maize and clover, rhizocompartment and host identity were the dominant factors shaping bacterial assemblages, followed by P supply level and the inoculum effect was smallest. Bacterial operational taxonomic unit (OTU) numbers decreased from bulk soil to rhizoplane, whilst specific OTUs were enriched from bulk soil to rhizoplane. A clear hierarchical habitat filtering of bacterial communities was observed in the rhizoplane of the two plant species. The functional prediction of dominant bacterial taxa in the rhizoplane differed between clover and maize, and clover microbiota were more closely associated with P metabolism and maize with carbon cycling. More connected and complex interactions were observed in the clover rhizoplane compared to maize. The microbial legacy effect caused by long-term P fertilization is overridden by host identity and rhizocompartment. Our results highlight the importance of crop diversification in improving P efficiency. The fine-tuning of rhizosphere microbiome in host metabolism indicates that the functions of microbial communities should be integrated into P management to increase P use efficiency and sustainable food production.

Response of Maize to Different Soil Residual Phosphorus Conditions

Large reserves of phosphorus (P) in Brazilian soils can be potentially used by crops. However, it is not well known how different tillage systems and past P fertilizer management strategies affect legacy P utilization. A trial was conducted in an Oxisol (Rhodic Haplustox) at Embrapa Cerrados, Federal District, Brazil to investigate the effects of different soil residual P conditions on maize yield. For 17 yr, annual summer crops were fertilized with 80 kg ha−1 yr−1 P2O5 in a split‐plot design consisting of eight treatments: no‐tillage system (NT) or conventional tillage (CT), fertilized with triple superphosphate (TSP) or reactive rock phosphate (RRP), applied to the crop furrow or broadcast. P fertilization was then discontinued and maize grown for 4 seasons relied on the residual soil P under NT or CT. Residual P use efficiency, calculated as a ratio between grain yield and total residual P in the soil, was greater under NT than CT, as a consequence of higher availability of P determined by Bray‐1, Mehlich‐1 and Olsen methods. Past use of RRP sustained better yields and higher residual P use efficiency, especially in NT, due to its lower solubilizing rate. P placement strategy did not change residual P use efficiency. We recommend assess amount of available P to identify sites in which residual P may sustain crop needs. Finally, the use of RRP, especially under NT, is a recommended management strategy for reducing phosphate fertilizer demand in heavily weathered soils of Central Brazil.Core Ideas No‐tillage system promotes efficient P use, especially after discontinued P supply. Due to slow solubilizing rate, reactive rock phosphate sustains better residual P availability. Fertilizer placement did not influence residual P use efficiency.

Fertilizing Potential of Rye Stillage in A Maize Agroecosystem

The distillery stillage is a major byproduct generated during ethanol production from plant raw materials (e.g., cereals) and molasses. It contains a high percentage of organic matter susceptible to biodegradation and nutrients necessary for plant growth, and therefore, can be used for fertilization purposes. This study evaluated the fertilizing value of rye stillage applied in a grain maize agroecosystem. The field study was carried out in 2017–2018 (two growing seasons) on Luvisol (loamy sand) in Poland. The experiment scheme included four treatments: W0—the control with no stillage treatment, W15—15 m3 of stillage per hectare, W30—30 m3 of stillage per hectare, and W45—45 m3 of stillage per hectare. It was found that application of rye stillage was significant for maize yields. However, it demands supplementary potassium fertilization and regulation of the soil reaction and/or stabilization of the pH of stillage before its application. Moreover, due to its contribution to the build-up of residual available phosphorus in the soil, rye stillage may pose an environmental risk.

Highly Efficient AuPd Catalyst for Synthesizing Polybenzoxazole with Controlled Polymerization

Summary Using nanoparticles (NPs) to catalyze chemical reactions for the formation of functional polymers with controlled polymerization is an important field of chemical research. In this article, we report an AuPd NP system as an active and stable catalyst to catalyze one-pot reaction of formic acid, 1,5-diisopropoxy-2,4-dinitrobenzene, and terephthaldehyde, leading to the controlled polymerization and the formation of polybenzoxazole (PBO) (Mw = 3.6 kDa). The one-pot reaction is AuPd NP size and composition dependent, and 8-nm Au39Pd61 NPs are the best catalyst for the polymerization. The highly pure PBO shows excellent thermal stability up to 600°C and improved chemical and mechanical stability under challenging environmental conditions compared with commercial PBO (Zylon, Mw = 40 kDa). The reported NP-catalyzed one-pot reaction to polymerization is not limited to the formation of PBO but can be extended as a general approach to rigid polymers that are important for ballistic fiber, anti-flame, and smart-textile applications.

Characterization of waxy starches phosphorylated using phytic acid

Waxy maize and waxy rice starches were subjected to dry heating in the presence of phytic acid at 120 °C for 6 or 24 h under alkaline conditions to induce phosphorylation. Dry heating at 120 °C for 24 h with phytic acid increased the residual phosphorus content of waxy maize and waxy rice starches from 11.5 to 92.9 ppm and from 27.5 to 79.3 ppm, respectively. 31P Nuclear magnetic resonance (NMR) analysis revealed the presence of monostarch monophosphate in the treated starches. The pasting viscosity of the starches was substantially changed by the phosphorylation, showing increases in peak viscosity, breakdown, and setback viscosity, but decrease in pasting temperature. Paste clarity and swelling power also increased after phosphorylation. Reduced melting temperature and enthalpy were observed for the phosphorylated starches. Thus, phytic acid is an effective reagent for phosphorylating starch to improve its pasting properties.

Recovery of ammonia nitrogen and magnesium as struvite from wastewaters in coal‐fired power plant

AbstractThis paper describes a cost‐effective method for recovering ammonia nitrogen (NH4+‐N) from regeneration wastewater by using magnesium recovered from flue‐gas desulfurization (FGD) wastewater in the same coal‐fired power plant. Mg2+ was efficiently removed from FGD wastewater at pH of 11, and the settling performance of Mg (OH)2 was evidently improved by adding anionic polyacrylamide and crystal seed. For NH4+‐N removal optimization by response surface methodology, the results indicated that the molar ratio of phosphorus to nitrogen (P/N) was the more dominant parameter, and the optimum conditions were predicted at Mg/N of 1.1 and P/N of 0.7. At the optimum conditions, the predicted data of NH4+‐N removal efficiency (NRE) and residue phosphorus were 71.41% and 21.90 mg/L, and actual experimental data were 72.12% and 19.60 mg/L. The inhibitory effect of NaCl concentration on NRE matches the modified Monod model with half inhibition concentration of 89.01 g/L. Morphologic analysis confirmed that salinity inhibited the formation and growth of struvite crystals.

Fast and Non-Destructive Determination of N, P, and K in Sorghum, Oat, and Corn Residue Using Near-Infrared Spectroscopy

A fast and non-destructive method is reported to nitrogen, phosphorus and potassium quantification in sorghum, oat, and maize residues. The reflectance spectra of 261 litter plant samples using near-infrared spectroscopy were obtained with integrating sphere and sampling rotator. Second derivative spectra and Partial Least Squares were used to develop calibration and validation models. The cross-validation (leave-one-out) technique was used to evaluate the performance of the calibration and validation models, based on analytical parameters, root-mean-square error of estimation, determination coefficient, number of latent variables, residual prediction deviation, root-mean-square error of cross-validation. It was concluded that near-infrared spectroscopy and chemometric tools are a fast and non-destructive alternative to determine nitrogen and phosphorus content in sorghum, oat, and maize residues using calibration and validation models developed according to values obtained from traditional chemical methods. For potassium content, the results indicate the low quality (imprecision) of the calibration and validation models.

Fate and transport processes of phosphorous fractions in selected surface sediments of Cochin Estuary, Southwest Coast of India

Sediment samples were collected from nine stations located along the Cochin estuary through five seasonal sampling campaigns for evaluating the distribution, accumulation and biogeochemical factors governing the concentration of various phosphorous fractions. Concentrations of sedimentary phosphorus fractions followed the order: iron-bound phosphorus > calcium bound inorganic phosphorous > alkali soluble organic phosphorus > acid soluble organic phosphorous > residual organic phosphorus. The enrichment of calcium bound inorganic phosphorous in the estuarine stations was found to exist in the high alkaline pH. Correlation study revealed that texture of the sediment controlled the distribution of iron bound phosphorous in the sediments. Terrestrial runoff carried huge quantities of humic substances to the riverine sediments that resulted in the peak concentration of alkali bound phosphorous at station S9 during monsoon. Increased levels of acid soluble organic phosphorous was recorded at stations with higher salinity (S5 to S8). Majority of the stations exhibited depleted levels of residual organic phosphorus due to the mineralization process. Meanwhile, total phosphorous ranged between 222.92 ± 3.89 µg/g and 4348.66 ± 15.35 µg/g with significant spatio-temporal variability (p < 0.01). Besides river run off resulted in the transport of organic matter derived from terrigenous, industrial, agricultural and aquaculture sources which brought about large scale accumulation of recalcitrant organic phosphorous in the sediments. Silt and clay exhibited remarkable positive correlations with iron-bound phosphorus, calcium bound inorganic phosphorous and alkali soluble organic phosphorus indicating the role of fine grained sediments in their dispersal mechanism. Multivariate statistical analysis revealed that distribution of phosphorous fractions were mainly controlled by salinity, granulometry, adsorption, desorption, precipitation, redox status, and the microbial processes occurring in the sedimentary environment.

Organic Phosphorus Extraction in the Fouling of the Circulating Cooling System.

The organophosphate scale inhibitor (HEDP)-containing C–P bond is an agent widely used in the circulating cooling system to ensure the safe operation. In order to explore the effects of its decomposition and migration transformation in the system on the system security, it is necessary to carry out the quantitative and qualitative analysis of organic phosphorus in fouling. According to the Ivanoff method, with the organic phosphorus extraction rate as an indicator, the types and concentrations of extractants, extraction time, and mass of the extracted scale were optimized. When the mass of the extracted scale was 0.4 g, the extraction rates of active organic phosphorus and moderately active organic phosphorus were, respectively, 46.53 and 47.14%, and there was no inactive organic phosphorus and residual phosphorus. The total extraction rate of organic phosphorus was up to 94.32%. The optimum extraction conditions of various organic phosphorus components were determined as follows: 10 h extraction in 0.5 mol/L KHCO3 for active organic phosphorus and 3 h extraction in 1.0 mol/L HCl solution for moderately active organic phosphorus. The optimized extraction process only involves two steps: acid extraction of active organic phosphorus and acid extraction of moderately active organic phosphorus. The optimized method is characterized by the simple operation and good extraction effect and can be applied in the detection and analysis of organic phosphorus in the fouling of the circulating cooling system.

Combined use of calcium nitrate addition and anion exchange resin capping to control sedimentary phosphorus release and its nitrate‑nitrogen releasing risk

Calcium nitrate (Ca(NO3)2) addition can be used to control the release of phosphorus from sediments, however it can also cause an increase in the concentration of nitrate‑nitrogen (NO3−-N) in the water column. The risk of NO3−-N release from the Ca(NO3)2-injected sediments may be reduced by the placement of the anion exchange resin (AER) capping layer. In this study, the effectiveness of the combined use of Ca(NO3)2 addition and AER capping to prevent the liberation of phosphorus from sediments was investigated, and the reduction of the risk of NO3−-N released from the Ca(NO3)2-injected sediment by the AER capping was also evaluated. The combined application of Ca(NO3)2 addition and AER capping could tremendously reduce the amount of soluble reactive phosphorus (SR-P) in the overlying water, with SR-P reduction rates of 75.9–98.7%. Furthermore, it could cut down the contents of high-resolution diffusive gradients in thin films (DGT)-labile phosphorus in the sediments, resulting in the formation of phosphorus static layer in the upper sediments. The combined treatment using Ca(NO3)2 and AER had a relatively small effect on the contents of mobile phosphorus in the sediments, but it could greatly increase the amount of residual phosphorus in the top 30mm sediments (increased by 27.7–42.9%). The amount of NO3−-N in the overlying water under the action of the combined treatment method using Ca(NO3)2 and AER was much lower than that under the action of the single Ca(NO3)2 treatment during the early stage of sediment remediation. In conclusion, the combined use of Ca(NO3)2 addition and AER capping is a more promising strategy for the control of sedimentary phosphorus release than the single use of Ca(NO3)2 addition from the point of view of both the control efficiency of P release from sediments and the releasing risk of the added nitrate.

Nutrient recovery from source-diverted blackwater: Optimization for enhanced phosphorus recovery and reduced co-precipitation

High residual phosphorus in anaerobically digested source-diverted blackwater allows for increased phosphorus recovery through struvite (NH4MgPO4·6H2O) precipitation. Due to the complex matrix of blackwater, recovered products inevitably contain co-precipitates of other wastewater components that have not been well characterized. The potential hazards present include pathogens, antimicrobial resistance genes (ARGs), organic and inorganic compounds. In this study, several important struvite precipitation conditions (pH, Mg2+:PO43− molar ratio and MgCl2 dosing rate) were tested to determine their impact on phosphorus recovery, while taking into account the co-precipitation of enteric bacteria, ARGs and micro- and macronutrients. Results demonstrate that phosphorus recovery efficiency does not correlate to the degree of metal/microbial co-precipitation. Both PO43− recovery and co-precipitates were affected by the operation conditions examined, and the optimal condition for nutrient recovery from blackwater was at pH 9, a 1.5:1 Mg2+:PO43− molar ratio, and a dosing rate of 24 mM min−1. Although previous struvite recovery studies have identified optimal conditions for phosphorus recovery, limited information is available on the process optimization to minimize the potential risks. Downstream application of recovered struvite inevitably contains co-precipitated hazards that if not assessed can result in undesirable public health outcomes. It is necessary to evaluate struvite application and public health exposure to identify key steps that reduce public health impacts. Hence examination of struvite precipitation parameters on enhanced phosphorus recovery, along with co-precipitates, is necessary when considering the public health risk associated with efficiently recovering residual nutrients.

Spatial variation of phosphorus fractionation in the coral reef sediments of Lakshadweep Archipelago, Indian Ocean

ABSTRACTSurface sediments were collected from the shore and lagoons of Kavaratti, Kadamat and Agatti islands of Lakshadweep Archipelago during May 2015 and analysed for the spatial distribution of the micronutrient element, phosphorus. Phosphorus was separated by sequential extraction procedure into five fractions – exchangeable (Ex-P), iron bound, (Fe-P), calcium bound (Ca-P), organic and residual fractions (OP) and total phosphorus (TP). The average relative contribution of each P species to TP was: OP > Ca –P > Ex – P > Fe – P. The high concentration of organic and residual phosphorus (87–96%) compared to inorganic phosphorus is particularly evident at stations characterised by higher total phosphorus concentrations. Among the three forms of IP in the sediments, Ca-P was dominant at all stations. The OC/OP ratio ranged from 3 to 163 in the sediments, suggesting that the organic matter in sediments had been subjected to degradation. Hence, the major contribution towards organic and residual phosphorus form is from the residual fraction comprising biologically resistant or non-available phosphorus form composed of refractory materials. The concentration of phosphorus reported in the present study is higher than that of the earlier studies in Lakshadweep, indicating a terrestrial and anthropogenic influence on the sediment.