New insights into the mechanism of phosphate release during particulate organic matter photodegradation based on optical and molecular signatures.

Phosphate release from particulate organic matter (POM) dominates phosphorus (P) cycling in aquatic ecosystems. However, the mechanisms underlying P release from POM remain poorly understood because of complex fractionation and analytical challenges. In this study, the release of dissolved inorganic phosphate (DIP) during POM photodegradation was assessed using excitation-emission matrix (EEM) fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). POM in suspension was significantly photodegraded under light irradiation, concomitantly with the production and release of DIP in the aqueous solution. Chemical sequential extraction revealed that organic phosphorus (OP) in POM participated in photochemical reactions. Moreover, FT-ICR MS analysis revealed that the average molecular weight of P-containing formulas decreased from 374.2 to 340.1 Da. Formulas containing P with a lower oxidation degree and unsaturation were preferentially photodegraded, generating oxygen-enriched and saturated formula compounds, such as protein- and carbohydrate-like P-containing formulas, benefiting further utilization of P by organisms. Reactive oxygen species played an important role in the photodegradation of POM, and excited triplet state chromophoric dissolved organic matter (3CDOM*) was mainly responsible for POM photodegradation. These results provide new insights into the P biogeochemical cycle and POM photodegradation in aquatic ecosystems.

Resin-based iron-manganese binary oxide for phosphate selective removal.

Adsorption technology can effectively remove phosphorus from water and realize phosphorus recovery. Hence, it is used to curb the eutrophication of water and alleviate the crisis caused by the shortage of phosphorus resources. Resin has been attracting increasing interest as an ideal adsorption material; however, its practical application is greatly affected by environmental factors. To solve the competitive adsorption and pore blockage caused by humic acid and coexisting ions during the removal of phosphorus by ion-exchange resin, this study has developed an iron-manganese oxide-modified resin composite adsorbent (Fe/Mn-402) based on the nanoconfinement theory. The structural characterization results of XRD, FT-IR, SEM, and XPS showed that the iron-manganese binary oxide was successfully loaded on the skeleton of the strongly alkaline anion resin and showed good stability under both neutral and alkaline conditions. The batch adsorption experiments showed that the maximum adsorption capacity of Fe/Mn-402 for phosphorus can reach up to 50.97 mg g-1 under the optimal raw material ratio (Fe:Mn = 1:1). In addition, Fe/Mn-402 shows good selectivity for phosphorus removal. Fe/Mn-402 can maintain good adsorption performance for phosphate even under high concentrations of SO42-, HCO3-, and humic acid. The regenerated Fe/Mn-402 can be recycled without any obvious change in its treatment capacity. Hence, it is suitable for stable, long-term usage. In general, this work puts forward a new idea for the development of phosphorus-removal adsorbents for the treatment of wastewater containing coexisting ions and HA.

Comparative study for removal of phosphorus from aqueous solution by natural and activated bentonite.

The novelty of the current article is to investigate the adsorption potential of the Egyptian natural and activated bentonite (Na-bentonite) to inorganic and organic phosphorus (IP, OP) in aqueous media. The natural bentonite (NB) was activated to Na-bentonite (Na-B) by a new facile method within 2 h. NB and Na-B were also characterized using XRD, XRF, BET ESM, and FT-IR. The batch experiment has been employed to select the ideal conditions for the removal of inorganic and organic phosphorus (IP, OP) from aqueous solutions. The findings clearly showed that the Na-bentonite is enriched with sodium in the form of Na-montmorillonite with a higher specific area 138.51 m2/g than the value for the natural bentonite 74.21 m2/g. The batch experiment showed maximum absorption for both IP and OP adsorbents occurred at an equilibrium pH = 6, contact time of 40 to 50 min, 40 °C temperature, and a dose rate of 2 mg/L and 1 mg/L, respectively. The equilibrium data displayed better adjustment to Langmuir than the Freundlich, Temkin, and Dubinin-Radushkevich isotherms and adsorption kinetics followed the pseudo-second-order-type kinetic, and the parameters of thermodynamics reveal that adsorption occurs spontaneously and exothermic nature. Na-bentonite proved to be more efficient in removing target material than natural bentonite. The spent bentonites were easily regenerated by chemical methods.

Spatial optimization of ecological ditches for non-point source pollutants under urban growth scenarios.

Non-point source (NPS) pollution is regarded as the major threat to water quality worldwide, and ecological ditches (EDs) are considered an important and widely used method to collect and move NPS pollutants from fields to downstream water bodies. However, few studies have been conducted to optimize the spatial locations of EDs, particularly when the watershed experiences urbanization and rapid land-use changes. As land-use patterns change the spatial distribution of NPS loads, this study used a cellular automata-Markov method to simulate future land-use changes in a typical agricultural watershed. Three scenarios are included as follows: historical trend, rapid urbanization, and ecological protection scenarios. The spatial distributions of particulate phosphorus loads were simulated using the revised universal soil loss equation and sediment transport distribution model. The results suggested that the total particulate phosphorus (TP) load in the Zhuxi watershed decreased by 10,555.2 kg from 2000 to 2020, primarily because the quality and quantity of forests in Zhuxi County improved over the last 20 years. The TP load in Zhuxi watershed would be 2588.49, 2639.15, and 2553.32 kg in 2040 in historical trend, rapid urbanization, and ecological protection scenarios, respectively, compared with 2308.1 kg in 2020. This indicated that urban expansion increases the TP load, and the faster the expansion rate, the more the TP load. Consequently, the optimal locations of EDs were determined based on the intercepted loads and the period during which they existed during land-use changes. The results suggested that rapid urbanization would consequently reduce the space available for building EDs and also increase the cost of building EDs to control the NPS pollution in the watershed.

The effect of iron oxide types on the photochemical transformation of organic phosphorus in water.

Iron oxides play an important role in the transport and transformation of organic phosphorus in aquatic environments. However, the effect of different types of iron oxide on the environmental fate of organic phosphorus has remained unclear. In this study, the photodegradation of the organic phosphorus compound adenosine triphosphate (ATP) via the activity of crystalline (goethite) and amorphous (ferrihydrite) iron oxides was investigated. It was found that ATP was photodegraded by goethite, resulting in the release of dissolved inorganic phosphate under simulated sunlight irradiation. The concentration of ATP on goethite decreased by 75% after 6 h of simulated sunlight irradiation, while the concentration of ATP on ferrihydrite decreased by only 22%. ATR-FTIR spectroscopy revealed that the intensity of the peaks for the P-O and PO stretching vibrations in the goethite-ATP complex decreased significantly more after simulated sunlight irradiation than did those for the ferrihydrite treatment. Combined with the higher TOC/TOC0 values for the goethite treatment, the results indicate that a more vigorous photochemical reaction took place in the presence of goethite than with ferrihydrite. Reactive oxygen species analysis also showed that hydroxyl and superoxide anion radicals were generated when goethite was exposed to simulated sunlight irradiation, while ferrihydrite did not exhibit this ability. Overall, this study highlights that the type of iron oxide is an important factor in the transformation of organic phosphorus in aquatic environments.

Novel ecological ditch system for nutrient removal from farmland drainage in plain area: Performance and mechanism.

The loading of nitrogen (N) and phosphorus (P) from agricultural drainage as the non-point sources is a worldwide environmental issue for aquatic ecosystem. However, how to remove these nutrients effectively from agricultural drainage remains a big challenge with increasing cemented ditches for better management. Here, we designed a novel ecological ditch system which integrated an earth ditch and a cemented ditch with iron-loaded biochar in the Chengdu Plain to reduce the loss of N and P from farmland. After a two-year monitoring, the removal efficiency of total N and total P reached 24.9% and 36.1% by the earth ditch and 30.7% and 57.8% by the integrated ditch system, respectively. The water quality was evidently improved after passing through the ditch system with the marked decrease in the concentrations of N and P. Dissolved organic N, nitrate, and particulate P became the dominant fractions of N and P loss. Rainfall soon after fertilization increased the concentrations of N and P in the ditch system and markedly affected their removal efficiency. The iron-loaded biochar effectively removed N and P from the drainage, especially at the high concentrations, which was mainly attributed to its high adsorption of the dissolved N and P fractions and the interception of the particulate nutrients. Our results indicate that the designed ecological ditch system has a high potential for alleviating agricultural non-point source pollution in the plain area and can be extended to other lowland agricultural ecosystems.

Molecular insight into the release of phosphate from dissolved organic phosphorus photo-mineralization in shallow lakes based on FT-ICR MS analysis.

Dissolved organic phosphorus (DOP) is a key factor in the water eutrophication process because of its high potential bioavailability and inorganic phosphate (Pi) compensation ability through bio- and photo-mineralization. However, the research on the characterization and transformation of DOP is insufficient owing to their complex composition. This study investigates the release of dissolved Pi from DOP photo-mineralization in Lake Dong based on Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis. The results showed that the photo-release of dissolved Pi is spatially heterogeneous in Lake Dong and is consistent with the distribution of DOP concentration. The FT-ICR MS results showed that the simulated irradiation decreased the relative abundance (RA) of the DOP molecular formulae with higher molecular weight (MW) and higher double bond equivalence values (DBE), while the RA of DOP molecular formulae with lower MW and lower DBE value increased or remained. Besides, the total RA of lipid-like formulae increased from 49.09% to 55.90%, while the oxy-aromatic-like formulae decreased from 50.91% to 44.10%, suggesting that simulated irradiation would influence the potential bioavailability of DOP. As the main photolysis medium during DOP photo-mineralization, the hydroxyl radicals (∙OH) are mainly derived from dissolved organic matter (DOM) compared to the nitrate (NO3-) and iron ion (Fe3+) in Lake Dong. These results are important in understanding the ability and mechanism of DOP photo-mineralization and provide suggestions for cycling phosphorus in eutrophic shallow lakes.

Directed-evolution of translation system for efficient unnatural amino acids incorporation and generalizable synthetic auxotroph construction.

Site-specific incorporation of unnatural amino acids (UAAs) with similar incorporation efficiency to that of natural amino acids (NAAs) and low background activity is extremely valuable for efficient synthesis of proteins with diverse new chemical functions and design of various synthetic auxotrophs. However, such efficient translation systems remain largely unknown in the literature. Here, we describe engineered chimeric phenylalanine systems that dramatically increase the yield of proteins bearing UAAs, through systematic engineering of the aminoacyl-tRNA synthetase and its respective cognate tRNA. These engineered synthetase/tRNA pairs allow single-site and multi-site incorporation of UAAs with efficiencies similar to those of NAAs and high fidelity. In addition, using the evolved chimeric phenylalanine system, we construct a series of E. coli strains whose growth is strictly dependent on exogenously supplied of UAAs. We further show that synthetic auxotrophic cells can grow robustly in living mice when UAAs are supplemented.

Photo-induced phosphate release during sediment resuspension in shallow lakes: A potential positive feedback mechanism of eutrophication.

Dissolved phosphate (Pi) can be released during resuspended sediments exposed to sunlight. However, the significance of this phenomenon in the process of eutrophication is not clear. In this study, the behavior of photo-induced Pi release during sediment resuspension in shallow lakes with the different trophic states was investigated. The amount of photo-induced Pi release in the sediment resuspension from Lake Liangzi, Lake Dong, Lake Tangxun and Lake Longyang in China was 0.013, 0.019, 0.032, and 0.048 mg/L, respectively, and increased as the trophic states of the lakes increased. The results of phosphorus speciation analysis showed that the phosphate monoester in the particulate phosphorus is the organic phosphorus species participated in the photochemical reaction. The steady-state concentration of hydroxyl radical (OH) in the sediment resuspension also increased along with the trophic states of lakes increased and dissolved organic matter (DOM), nitrate, and Fe3+ presented in sediment resuspension were the main photosensitizers for OH production. All these results indicate that the increase of trophic states of lakes leads to the accumulation of organic phosphorus and OH, resulting in more dissolved phosphate photo-released, which accelerate the eutrophication process in a form of positive feedback.

Distribution of organic phosphorus species in sediment profiles of shallow lakes and its effect on photo-release of phosphate during sediment resuspension.

In this work, the distribution of organic phosphorus (Po) species in sediment profiles of five shallow lakes was analyzed and its effect on the photo-release of dissolved phosphate (Pi) was investigated during sediment resuspension under simulated sunlight irradiation. The results show that Po was highly enriched in the surface sediment and gradually decreased as sediment depths increased: 33.10 ±â€¯2.55-96.71 ±â€¯7.60 mg/kg, 33.55 ±â€¯2.34-142.86 ±â€¯5.73 mg/kg, 57.50 ±â€¯3.46-149.68 ±â€¯7.67 mg/kg, 55.18 ±â€¯4.67-168.73 ±â€¯8.31 mg/kg, 98.75 ±â€¯7.56-275.74 ±â€¯10.70 mg/kg for Lake Hou, Lake Tuan, Lake Tangling, Lake Guozheng and Lake Miao, respectively. The photo-release amount of dissolved Pi in the resuspension composed of surface sediments was also higher than that of deep sediment during sediment resuspension under the simulated sunlight irradiation for 9 h. The potential reasons for these results are: (1) difference in morphology and composition of sediments at different depths: the mean particle size of sediment decreased first and then increased as sediment depths increased; (2) difference in composition of Po species with depths in the sediment profiles: more photolytic Po species existed in surface sediments confirmed by sequential extraction and 31P NMR analysis; and (3) more OH production in the resuspension composed of surface sediment under simulated sunlight irradiation, which directly influence the photo-release of dissolved Pi from photodegradation of organic phosphorus. All of these results indicate that the distribution of organic phosphorus species in the sediment profiles plays an important role in P cycle and its photodegradation during sediment resuspension may be one of the potential pathways for phosphate supplement in shallow lakes.

Occurrence and characterization of CaCO3-P coprecipitation on the leaf surface of Potamogeton crispus in water.

In this paper, the characterization of CaCO3-P coprecipitation on the leaf surface of Potamogeton crispus at various temperatures in pot experiments was investigated. White precipitates occurred on the leaf surfaces during the P. crispus growth period, and the chemical analysis demonstrates that the white precipitates contain Ca and P. The primary constituent of the white precipitates on the leaf of P. crispus was octacalcium phosphate (OCP) and hydroxyapatite. XRD characterization showed that the precipitates mostly consisted of crystals formed by calcium carbonate and hydroxyapatite, and the high calcium/phosphorus ratio indicated that the white coprecipitates were CaCO3-P. The scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDX) results confirmed that the precipitates on the surface of P. crispus leaves were carbonate-containing hydroxylapatite. In addition, no significant differences was observed in the structure of CaCO3-P coprecipitation between room temperature and consistent temperature treatments, which means that a little change in the temperature cannot change the process of Ca-P coprecipitation. Finally, coprecipitation of CaCO3-P on the leaf surface of P. crispus was proposed based on the morphology and structure analysis of CaCO3-P coprecipitation.

The role of Fe(III) on phosphate released during the photo-decomposition of organic phosphorus in deionized and natural waters.

The photo-decomposition of organic phosphorus is an important route for the phosphorus cycle by which phosphate is regenerated in the aquatic environment. In this study, the role of Fe3+ as a natural photosensitizer toward the decomposition of organic phosphorus to release phosphate was examined in deionized and natural waters under UV and sunlight irradiation using glyphosate as the organic phosphorus model. The results showed that the concentration of glyphosate decreased with irradiation time in the Fe3+/UV and Fe3+/sunlight systems and TOC gradually decreased, which confirmed that glyphosate was degraded by Fe3+. The amount of phosphate released from the photo-decomposition of glyphosate was higher in the presence of Fe3+ than that of the control experiment under UV and sunlight irradiation conditions, and the generation rate of phosphate also increased with increasing Fe3+concentrations. The formation of hydroxyl radicals (·OH) in the Fe3+/UV and Fe3+/sunlight systems was identified according to the photoluminescence spectra (PL) using coumarin as the trapping molecule, and the steady-state concentrations of ·OH for the Fe3+/UV and Fe3+/sunlight systems were 1.06 × 10-14 M and 0.09 × 10-14 M, respectively. When natural water was spiked with glyphosate and Fe3+, the phosphate that was released in the Fe3+ was higher than that of the control, and the phosphate that was released was inhibited when isopropanol was added to the reaction. All of these results demonstrate that the photochemical activity of Fe3+ has significantly impact in the release of phosphate from the photo-decomposition of organic phosphorus.

Transformation of external sulphate and its effect on phosphorus mobilization in Lake Moshui, Wuhan, China.

Average concentrations of sulphate in lakes continue to increase sharply. The response of phosphorus to sulphate input is of great importance due to the relationship between eutrophication and ecological health. A four-week experiment was conducted under simulated conditions using samples from a heavily polluted lake, Lake Moshui, in Wuhan, China, to examine the influence of external sulphate on phosphorus release and the transformation of sulphate. The results showed that the diffusion of sulphate into the sediments promoted the proliferation of sulphate-reducing bacteria (SRB) and the reduction of sulphate. Acetic acid was consumed due to sulphate reduction. The soluble reactive phosphorus (SRP) and soluble Fe measured with diffusive equilibration in thin-films (DET) probes increased significantly after the input of sulphate. The content of SRP was consistent with the variation in both the SRB number and the S(0) content in the sediments. The maximum SRP concentration of 100.43 mg L(-1) was recorded 3 cm below the sediment-water interface on the 29th d, which was more than twice the value of the control. There was a positive correlation between concentrations of Fe and SRP in the overlying water and the pore water of the sediments.