Higher PO43 Research Articles

Exploring phosphate impact on arsenate uptake and distribution in freshwater phytoplankton: Insights from single-cell ICP-MS

In this study, we investigated the interaction between arsenate (AsV) and phosphate (PO43−) in freshwater phytoplankton using single-cell inductively coupled plasma mass spectrometry (SC-ICP-MS). This study aimed to elucidate the influence of varying PO43− concentrations on arsenic (As) uptake and distribution at the single-cell level, providing insights into intraspecies diversity. Two species of freshwater phytoplanktons, Scenedesmus acutus and Pediastrum duplex, were cultured under different concentrations of PO43− and AsV in a controlled laboratory environment. Scenedesmus acutus, a species with strong salt tolerance, and Pediastrum duplex, known for its weak salt tolerance, were selected based on their contrasting behaviors in previous studies. SC-ICP-MS revealed non-uniform uptake of As by individual phytoplankton cells, with distinct variations in response to PO43− availability. Arsenic uptake by both species declined with a high PO43− level after 7 days of exposure. However, after 14 days, As uptake increased in S. acutus with higher PO43− concentrations, but decreased in P. duplex. Moreover, our findings revealed differences in cell morphology and membrane integrity between the two species in response to AsV and various PO43− concentrations. S. acutus maintained cell integrity under all experimental culture conditions, whereas P. duplex experienced cell lysis at elevated AsV and PO43− concentrations. This study highlights the varying responses of freshwater phytoplankton to changes in AsV and PO43− levels and underscores the advantages of SC-ICP-MS over conventional ICP-MS in providing detailed, cellular level insights. These findings are crucial for understanding and managing As pollution in aquatic ecosystems.

Modeling of phosphate flux induced by flood resuspension on a macrotidal estuarine mudflat (Seine, France)

Coastal marine sediments can be either major scrubbers or eutrophication contributors to surface waters. Standard methods for direct measurement of nutrient fluxes at the sediment-water interface do not consider hydrodynamic forcing although several ex-situ studies suggest that sediment resuspension can dramatically increase dissolved fluxes. We provide a new model to quantify dissolved phosphate (PO43−) resuspension flux (JR) based on physical representation of its identified components: diffusion stimulation by exposure of deeper sediment layer with higher PO43− concentration in the porewater (JD), pore water mixing with overlying water (JM) and net adsorption/desorption from suspended sediments (JK). This approach was applied to field data from a Seine intertidal mudflat periodically submitted to millimetric erosion. On a tidal scale, the model output reveals a JR of 272.3 ± 360.0 μmol m−2 h−1 (± 52% from parameter uncertainty), well above flux calculated by application of Fick's first law (0.15 ± 0.85 μmol m−2 h−1) or by ex situ core incubation (40.8 μmol m−2 h−1). Iron bound phosphorus within suboxic layers buffers PO43− concentrations in superficial sediments leading to negligible contributions of JD and JM to total fluxes. Conversely, JK appears to be the main exchange pathway, even though improvements in turbidity measurement would allow this term to be defined more precisely. Correction required to enhance and control model robustness are described. These results show the importance of considering the dissolved PO43− resuspension flux in dynamic environments.

Production of N–Mg doped biochars for phosphate adsorption from renewable sources

It is crucial for the environment, the economy, and society to create low-cost adsorbents from renewable resources to remove phosphate from aqueous effluents. Here, two renewablecarbon and nitrogen sources (Douglas fir and Chitosan) were used to produce engineered N-doped biochars modified with Mg for PO43− adsorption. Mg–N doped biochars were prepared using an impregnation-carbonization process. A central composite experimental design was used to select combinations of independent variables to maximize phosphate adsorption capacity. Phosphate adsorption isotherms were fitted with Langmuir and Freundlich isotherms. The biochar produced at 700 °C, 12 wt % MgCl2, and Douglas Fir/Chitosan ratio: 1/1, which has the highest PO43− adsorption capacity, was further studied. Proximate analysis, elemental composition, surface area, pore size distribution, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and Scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDX) were used to characterize this biochar. This biochar has an adsorption capacity of 112.4 mg PO43−/g char. Its phosphate adsorption rate was adjusted to a pseudo-second-order kinetic model. The phosphate adsorption capacity of the biochar produced was comparable with the most effective biochar reported in the literature.

Exploring effects of carbon, nitrogen, and phosphorus on greywater treatment by polyculture microalgae using response surface methodology and machine learning

The microalgae-based wastewater treatment is a promising technique that contribute to achieving sustainable development goals (SDGs), such as SDG-6, “Clean Water and Sanitation”. However, it is strongly influenced by the initial composition of wastewater. In this study, the impact of initial organics and nutrient concentration on the removal of total organic carbon (TOC), total carbon (TC), ammonium (NH4+), total nitrogen (TN), and phosphate (PO43−) from greywater using native polyculture microalgae was explored. Response surface methodology was employed along with two machine learning approaches, AdaBoost and XGBoost, to evaluate the interactions among three main factors: TOC, NH4+, and PO43−, and their effects on treatment efficiency. The C/N ratios for achieving maximum TOC and TC removal efficiency of 99.2% and 97.7% were determined to be 10.3, and 65.4–73.6, respectively. Notably, the N/P ratio did not significantly affect their removal. The highest NH4+ removal efficiency, reaching 96.2%, was attained at C/N ratios of 4.3, 24.0, 38.2, and 212.9, coupled with N/P ratios of 0.3, 2.6, and 23.4. Highest TN removal efficiency of 77.2% was achieved at C/N and N/P ratios of 12.2 and 2.0, respectively. Highest PO43− removal of 78.8% was obtained at N/P ratio 12.8. However, C/N ratio did not affect the removal efficiency. Maintaining these specified C/N and N/P ratios in the influent greywater would ensure that the treated greywater meets the required standards for various reuse applications, including flushing, groundwater recharge, and surface water discharge. The integration of RSM with AdaBoost and XGBoost provided accurate predictions of removal efficiencies. For all the models, XGBoost had the highest R2, and lowest MAE and MSE values. The cross validation of RSM models with AdaBoost and XGBoost further reinforced the reliability of these models in predicting treatment outcomes.

Fine particle pollution during megafires contains potentially toxic elements

Wildfires that raged across Australia during the 2019–2020 ‘Black Summer’ produced an enormous quantity of particulate matter (PM) pollution, with plumes that cloaked many urban centres and ecosystems along the eastern seaboard. This has motivated a need to understand the magnitude and nature of PM exposure, so that its impact on both built and natural environments can be more accurately assessed. Here we present the potentially toxic fingerprint of PM captured by building heating, ventilation, and air conditioning filters in Sydney, Australia during the peak of the Wildfires, and from ambient urban emissions one year later (Reference period). Atmospheric PM and meteorological monitoring data were also assessed to determine the magnitude and source of high PM exposure. The wildfires were a major source of PM pollution in Sydney, exceeding the national standards on 19 % of days between November–February. Wildfire particles were finer and more spherical compared to Reference PM, with count median diameters of 892.1 ± 23.1 versus 1484.8 ± 96.7 nm (mean ± standard error). On an equal-mass basis, differences in potentially toxic elements were predominantly due to higher SO42−-S (median 20.4 vs 4.7 mg g−1) and NO3−-N (2.4 vs 1.2 mg g−1) in Wildfire PM, and higher PO43−-P (10.4 vs 1.4 mg g−1) in Reference PM. Concentrations of remaining elements were similar or lower than Reference PM, except for enrichments to F−, Cl−, dissolved Mn, and particulate Mn, Co and Sb. Fractional solubilities of trace elements were similar or lower than Reference PM, except for enhanced Hg (12.1 vs 1.0 %) and greater variability in Cd, Hg and Mn solubility, which displayed upper quartiles exceeding that of Reference PM. These findings contribute to our understanding of human and ecosystem exposures to the toxic components of mixed smoke plumes, especially in regions downwind of the source.

Adsorptive recovery of phosphate using iron functionalized biochar prepared via co-pyrolysis of wheat straw and sewage sludge

In recent years, the removal and recovery of phosphate (PO43−) from freshwater reservoirs using carbonaceous adsorbents has received much attention to address eutrophication issues and plant phosphate requirements. The viability of FeCl3 impregnated biochar (Fe@CBC) synthesized via co-pyrolysis of wheat straw (WS) and sewage sludge (SS) for phosphate removal from water under systematically designed sorption experiments and its subsequent potential as phosphatic fertilizer for improving plant growth, was thoroughly investigated in this study. The relatively higher PO43− sorption performance of Fe@CBC (5.23 mg/g) compared to FeCl3 impregnated biochars (Fe@WBC: 4.16 mg/g and Fe@SBC: 5.14 mg/g) synthesized via separate pyrolysis of WS and SS were primarily ascribed to the nano porous structure, higher point of zero charge (pHpzc) and enriched iron complexes on its surface (Fe-OH and FeC). Consequently, dominant sorption mechanism of PO43− ions towards Fe@WBC was associated to ligand exchange and chemisorption whereas that of Fe@SBC and Fe@CBC was identified as electrostatic surface complexation coupled with reduction. In comparison to Fe@WBC and Fe@SBC, the surface properties and identified phenomenon allowed Fe@CBC to efficiently recover PO43− ions under optimal water chemistry conditions and coexisting interfering species environment. Additionally, PO43- -sorbed Fe@CBC effectively improved the physical growth (root length: 2 cm, shoot length: 9 cm, fresh weight: 79 mg and dry weight: 8.3 mg) of mustard plants. Economic analysis suggested profit of PO43- removal and recovery by Fe@CBC was $1.5 per kg. Therefore, PO43- -sorbed Fe@CBC could be a promising phosphatic fertilizer for improving plant growth and may have agricultural applications.

Transport and Model Calculation of Microplastics Under the Influence of Ionic Type, Strength, and Iron Oxide

Microplastics (MPs) in soil have attracted extensive attention as an emerging pollutant, and the transport of MPs is affected by their own physical and chemical properties, the chemical composition of soil solutions, and soil minerals. However, in the presence of oxides, the underlying mechanism for the transport of MPs in different ionic types and ionic strengths is still not fully understood. In this study, the effects of ionic type, ionic strength, and iron oxide on the transport of polystyrene microplastics (PSMPs) with different functional groups were investigated through stability experiments and transport experiments. The colloid transport model, CD-MUSIC model, and DLVO theory were used to explore the transport mechanism. The results showed that normalized concentrations (c/c0) of PSMPs were 0.99 in the NaH2PO4 background and 0.94 in the CaCl2 background, respectively, which indicated that the strongest stability of PSMPs was observed in the former and the weakest in the latter. Different ionic types had different effects on the transport of PSMPs. For the cations Na+ and Ca2+, Ca2+ strongly inhibited PSMPs transport in pure quartz sand because of the bridging effect and strong charge neutralization effect; the recovery rate of the PSMPs in the effluent was (43.83±1.71)%, and a first-order retention coefficient on the second kinetic Site-2 (k2a) was 1.54 min-1. The presence of iron oxide enhanced the inhibition, the recovery rate of the PSMPs in the effluent decreased to (6.04±0.40)%, and k2a increased to 5.33 min-1. For the anions Cl- and PO43-, the transport of PSMPs in pure quartz sand was dominated by surface electronegativity of PSMPs, and PSMPs exhibited lower electronegativity under Cl- background and thus showed higher recovery[(92.95±0.63)%] and lower k2a (0.19 min-1). However, in the presence of iron oxides, the Zeta potential of the quartz sand surface was the controlling factor for PSMPs transport. According to results of the CD-MUSIC model, PO43- could be easily adsorbed on the iron oxide surface to form innersphere complexes, which reduced the surface electronegativity of the iron-loaded quartz sand and enhanced the transport of PSMPs, higher recovery[(76.22±1.39)%], and lower k2a (0.66 min-1). Moreover, the species of the formed innersphere complex was controlled by the PO43- concentration, and different species of innersphere complexes had distinct negative surface charges. Higher surface electronegativity of the iron-loaded quartz sand was observed under higher PO43- concentration, which was not conducive to the transport of PSMPs. Further, the transport ability of PSMPs decreased with the increase in ionic strength. Finally, the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was used to calculate the variation in the primary barrier between PSMPs and the collector under the conducted experimental conditions, which helped better elucidate the transport behavior of PSMPs. The variation in the primary barrier was consistent with the transport ability of PSMPs, and a higher primary barrier indicated a larger repulsion between PSMPs and the collector, which was in favor of PSMPs transport.

Adsorption of Phosphate from Aqueous Solution by Calcination of Silicified Coal: Kinetic and Isotherm Studies

Silicified coal (SC) consisting of SiO2 is promising raw material for adsorbent. The present study aimed to utilize the adsorbent of silicified coal bottom ash (SCBA) by calcination of the SC at the temperature of 600, 800 and 1000 oC for 1 hour. The FTIR result showed that the SCBA-600, SCBA-800 and SCBA-1000 had chemical functional groups such as the asymmetric Si-O-Si, the symmetric Si-O-Si and Si-O-Si bond rocking for adsorption of phosphate (PO43−) with the lowest percentage of transmittance of SCBA-1000. The adsorption test showed that a rapid adsorption occurred in the first 10-min of contact time, and it did not change significantly for the rest of contact time until reaching an equilibrium time of 30 min. The PO43− adsorption efficiency and capacity fluctuated over initial PO43− in solution in the range of 60.02–480.29 mg/L. The highest PO43− adsorption efficiency and capacity was at 480.29 mg/L, which was 95.49 % and 45.86 mg/g, respectively using the SCBA-1000. The adsorption kinetic fitted better to pseudo second-order kinetics model (average R2 = 0.999) with the adsorption capacity of 45.454, 45.662 and 45.872 for the SCBA_600, SCBA_800 and SCBA_1000, respectively, and the PO43− adsorption rate was 0.0007, 0.0008 and 0.001 g/mg.min, respectively. The adsorption isotherm followed Langmuir model (average R2 = 0.873) with the adsorption capacity being 2.357, 1.198 and 8.196 mg/g, respectively, and the pore volume being 0.0316, 0.0364 and 0.2103 L/mg, respectively

Adsorption of phosphate in aqueous solution by ash from the fruit peel of Caryocar coriaceum Wittm: adsorption characteristics and behavior.

High phosphate concentrations in natural waters are associated with eutrophication problems that negatively affect the fauna and flora of ecosystems. As an alternative solution to this problem, we evaluated the adsorptive capacity of the fruit peel ash (PPA) of Caryocar coriaceum Wittm and its efficiency in removing phosphate (PO43-) from aqueous solutions. PPA was produced under an oxidative atmosphere and calcinated at 500°C. The XRF and EDS analyses of PPA after contact with an aqueous PO43- solution showed an increase in its PO43- content, thus confirming the adsorption of PO43-. The Elovich and Langmuir models are the ones fitting the kinetics and the equilibrium state of the process, respectively. The highest PO43- adsorption capacity was approximately 79.50mgg-1 at 10°C. PO43- adsorption by PPA is a spontaneous, favorable, and endothermic process involving structural changes. The highest removal efficiency was 97.08% using a 100mg.L-1 PO43- solution. In sight of this, PPA has shown potential as an excellent natural bioadsorbent.

Pyrite and sulfur-coupled autotrophic denitrification system for efficient nitrate and phosphate removal

The inefficiency of nitrogen removal in pyrite autotrophic denitrification (PAD) and the low efficiency of PO43−-P removal in sulfur autotrophic denitrification (SAD) limit their potential for engineering applications. This study examined the use of pyrite and sulfur coupled autotrophic denitrification (PSAD) in batch and column experiments to remove NO3−-N and PO43−-P from sewage. The effluent concentration of NO3−-N was 0.32 ± 0.11 mg/L, with an average Total nitrogen (TN) removal efficiency of 99.14%. The highest PO43−-P removal efficiency was 100% on day 18. There was a significant correlation between pH and the efficiency of PO43−-P removal. Thiobacillus, Thiomonas and Thermomonas were found to be dominant at the bacterial genus level in PSAD. Additionally, the abundance of Thermomonas in the PSAD was greater than that observed in the SAD reactor. This result indirectly indicates that the PSAD system has more advantages in reducing N2O.

Enhancing simultaneous nitrate and phosphate removal in sulfur‑iron (II) autotrophic denitrification biofilters by endogenous magnetic fields: Performance and mechanism

The sulfur‑iron (II) autotrophic denitrification (SIAD) technology can achieve simultaneous nitrogen and phosphorus removal from wastewater with a low C/N ratio without an organic carbon source. However, the low nutrient removal load limits its large-scale application. To enhance N removal load and decrease the effluent SO42− concentration, we propose a novel bioaugmentation technology by adding magnetite to a sulfur‑iron (II) biofilter to generate an endogenous magnetic field (EMF). The treatment characteristics of two biofilters with sulfur‑iron (II) (S1) and sulfur‑iron (II)-magnetite (S2) were comparatively studied in long-term experiments. The maximum nitrate removal load of the S2 system was 1.02 ± 0.04 kg N/(m3·d), 1.27 times higher than that of S1. The S2 system also showed a 40 % higher PO43− removal efficiency compared to S1. The production of SO42− was reduced by >12.34 % in S2 with 5.40 g SO42−/g N. The EMF significantly increased nitrate reductase activity by 3.50 times and enhanced the size of the attached microbial bacterial population by 30 %–50 %. Functional gene prediction indicated that amino acid metabolism, cell activity, N/S metabolism were improved under the EMF, and the genera Ferritrophicum and Thiobacillus were the predominant autotrophic bacteria, forming a symbiotic relationship. Our study demonstrates a novel solution to resolve the limits of high sulfate byproduct and low nutrient removal load in SIAD biofilters, which could promote large-scale application of SIAD process as a highly efficient and low-cost postdenitrification process.

Assessment of Water Quality Using Organic Pollution Index in Some Marshes North of Basra Province

The organic pollution index (OPI) was applied to assess the state of the organic pollution in the southern part of Eastern Hammar marsh, Al-Chebiyesh marsh, and the Euphrates and explain the role of submerged aquatic plants in reducing the level of water pollution. Water samples were collected monthly from two stations for each part (i.e., with and without submerged plants). The OPI depended on three parameters, namely, NO3, PO4, and BOD5. Results show that the highest NO3 was 6.4 mg/L in February in Al Burka, whereas the lowest value was 2.3 mg/L in August in the Euphrates station, which contains submerged plants. The highest PO4 was 0.76 mg/L in February in Al Burka, whereas the lowest value was 0.24 mg/L in August in Saleh River’s station, which contains submerged plants. The highest BOD5 was 3.63 mg/L in August in the Al Burka station, whereas the lowest value was 0.91 mg/L in February in the Euphrates station, which contains submerged plants. The index values indicate the presence of organic pollution in all stations, with discounts varying between (65.9 and 36.2), (49.9 and 35), and (40.1 and 22) in Eastern Hammar, Al-Chebiyesh, and the Euphrates, respectively. The vital role of submerged plants in the consumption of nutrients reduced the OPI annual values to (44.4, 37.8, and 25.3) compared with the values in stations without plants (54.9, 44.6, 36). The annual values varied between the Deteriorated category in the East Hammar marsh, a Poor category in Al-Chebiyesh, and the Medium category in the Euphrates, with yearly values of 49.7, 41.2, and 30.7, respectively.

Pilot-scale phosphate recovery from wastewater to create a fertiliser product: An integrated assessment of adsorbent performance and quality

Eutrophication and the predicted limited future availability of rock phosphate has triggered the increased development of phosphorus (P) recovery technologies, however, for remote regions, recovery solutions are still limited. Here, we report on a novel pilot-scale technology (FILTRAFLOTM-P reactor) to recover phosphate (PO43−) from wastewater effluent through a filtration/adsorption process in a rural setting. This unit employs enhanced gravitational filtration through adsorption media (here, a novel KOH deacetylated crab carapace based chitosan-calcite material (CCM)) with continuous self-backwashing. Trials were designed to assess how the FILTRAFLOTM-P unit would operate under ‘real’ conditions (both at low and high PO43− levels), and to ascertain the effectiveness of the adsorbent to recover phosphate from final effluent. High removal was achieved at low phosphate concentrations, bringing the residual effluent PO43− level below 1 mg/L (EU limit for sensitive water bodies), while phosphate was efficiently harvested (at more than 50%) at higher PO43− levels. Surface microprecipitation and inner-sphere complexation were postulated as the main PO43− adsorption mechanisms through XRD, XPS and EDX elemental mapping. Further, a quality assessment of the P-enriched CCM (which could be used as a potential soil amendment) was undertaken to consider elemental composition, microbiological assessment and quantification of organic micropollutants. Quality analysis indicated ∼2.5% P2O5 present, trace levels (well below legislative limits) of heavy metals and extremely low levels of organic pollutants (e.g., PCBs, pharmaceuticals). No detectable levels of target bacterial pathogens were observed. Pot trials showed that ryegrass cultivated with the addition of the CCM adsorbent achieved higher plant dry matter and P concentration when compared to unfertilised controls, with a slow-release kinetic pattern. This study showed that CCM used with the FILTRAFLOTM-P pilot reactor has high potential to recover phosphate from effluents and encourage resource recovery via bio-based management of waste.

Membrane contactor onsite piloting for nutrient recovery from mesophilic digester reject water: The effect of process conditions and pre-treatment options

Nutrient recovery is an important segment of the circular economy, and it significantly contributes to sustainable development goals. This work reports on the outcomes of a field testing pilot-scale membrane contactor system designed for nitrogen (N) and phosphorous (P) recovery in the form of high purity ammonium salts and high-quality P containing sludge. The pilot testing was conducted at the Viikinmäki WWTP using digester reject water under different treatment conditions. Our system showed a high tolerance for solids (concentration > 500 mg/L). Field test trials showed that the higher the feed flow, the better the ammonia transfer rate. Decreasing the retention time from 4 h to 2 h increased the ammonia mass transfer rate constant by >150 %. Among the tested feed pH levels, a pH of 10 had the highest solids removal, which in turn resulted in the highest ammonia recovery percentage. A high acid concentration lowered the ammonia transfer rate. Strong acids such as HNO3 and H2SO4 had a higher ammonia recovery than that of H3PO4. Pre-treating feedwater with starch resulted in the same ammonia accumulation rate as a poly-aluminum chloride (PAX)/polymer pre-treatment. The highest PO4−3 removal of 99 % was achieved with a PAX/polymer treatment at pH 10, whereas the highest total phosphorous removal of 77 % was achieved with a starch treatment. The produced sludge consists mainly of CaCO3 emanating from the used lime, which can be used as a soil amendment. The produced ammonium salts were of high purity and have a nutrient content comparable to that of commercial fertilizers. This study provides important insights into the selection of process parameters of membrane contactor systems based on the goal of the treatment, whether it be nutrient removal or recovery.

Highly selective recovery of phosphate ions using a novel carbonaceous adsorbent synthesized via co-pyrolysis of spent coffee grounds and steel slags: A potential phosphatic fertilizer

This study rigorously investigated the viability of carbonaceous adsorbents (SS@SCA) prepared through one-step co-pyrolysis of steel slags (SSs) and spent coffee grounds (SCGs) for selectively capturing phosphate (PO43−) ions in aqueous solutions and their subsequent utilizing a phosphatic fertilizer to promote the plant growth. The higher PO43− adsorption capacity (Qe = 23.0 mg/g) and magnetic separability (90.1%) of SS@SCA compared to pristine carbonaceous adsorbents (SCA) prepared through simple pyrolysis of SCGs (Qe = 2.6 mg/g) were mainly attributed to the enriched metal oxides on its surfaces (i.e., CaO, MgO, Fe3O4, Fe2O3, Al2O3). Moreover, the main adsorption mechanism of PO43− ions toward SCA was changed from physisorption (ligand exchange by alcohol functional groups) to chemisorption (electrostatic surface complexation by CaO and MgO) via one-step co-pyrolysis of SCGs and SSs. This phenomenon enabled SS@SCA to selectively capture PO43− ions under the co-existence of Cl−, NO3−, SO42−, and CO32− ions (decreasing rates of Qe: SCA = 38.5–65.4%; SS@SCA = 0.8–8.8%). PO43−-loaded SS@SCA more effectively promoted the seed germination (germination index (GI): 434–467%) and root growth (root length: 4.0–5.1 cm) of garden cress seeds (Lepidium sativum L.) than other liquid and solid matrices, including 20 mg/L PO43−, 100 mg/L PO43−, and SS@SCA (GI: 77–258%; root length: 0.9–3.0 cm). Hence, PO43−-loaded SS@SCA seemed to be potentially applicable to the agricultural field as a phosphatic fertilizer for accelerating the plant growth. Therefore, PO43−-loaded SS@SCA could be practically used as a phosphatic fertilizer to reinforce the plant growth.

Optimization of Microalgae–Bacteria Consortium in the Treatment of Paper Pulp Wastewater

The microalgae–bacteria consortium is a promising and sustainable alternative for industrial wastewater treatment, since it may allow good removal of organic matter and nutrients, as well as the possibility of producing products with added value from the algae biomass. This research investigated the best bacterial and microalgae inoculation ratio for system start-up and evaluation of removing organic matter (as chemical oxygen demand (COD)), ammoniacal nitrogen (NH4+–N), nitrite nitrogen (NO2−–N), nitrate nitrogen (NO3−–N), phosphate phosphorus (PO43−–P) and biomass formation parameters in six photobioreactors with a total volume of 1000 mL. Reactors were operated for 14 days with the following ratios of pulp mill biomass aerobic (BA) and Scenedesmus sp. microalgae (MA): 0:1 (PBR1), 1:0 (PBR2), 1:1 (PBR3), 3:1 (PBR4), 5:1 (PBR5), and 1:3 (PBR6). Results show that COD removal was observed in just two days of operation in PBR4, PBR5, and PBR6, whereas for the other reactors (with a lower rate of initial inoculation) it took five days. The PBR5 and PBR6 performed better in terms of NH4+–N removal, with 86.81% and 77.11%, respectively, which can be attributed to assimilation by microalgae and nitrification by bacteria. PBR6, with the highest concentration of microalgae, had the higher PO43−–P removal (86%), showing the advantage of algae in consortium with bacteria for phosphorus uptake. PBR4 and PBR5, with the highest BA, led to a better biomass production and sedimentability on the second day of operation, with flocculation efficiencies values over 90%. Regarding the formation of extracellular polymeric substances (EPS), protein production was substantially higher in PBR4 and PBR5, with more BA, with average concentrations of 49.90 mg/L and 49.05 mg/L, respectively. The presence of cyanobacteria and Chlorophyceae was identified in all reactors except PBR1 (only MA), which may indicate a good formation and structuring of the microalgae–bacteria consortium. Scanning electron microscopy (SEM) analysis revealed that filamentous microalgae were employed as a foundation for the fixation of bacteria and other algae colonies.

Optimising production of a biochar made from conifer brash and investigation of its potential for phosphate and ammonia removal

As a lignocellulose biomass, waste conifer brash (waste treetops and branches) from felled afforested peatland sites can be converted to biochar through pyrolysis, thus creating a potentially useful product. Here, we propose that brash from ‘forest-to-bog’ peatland restoration sites through conversion to biochar, could be utilised for nutrient (PO43−-P and NH4+-N) removal at such restoration sites, or within the water sector. As a first step, we explore the factors involved in biochar production that will result in high nutrient adsorption efficiency and pyrolysis yield and low production cost (using a Plackett-Burman experimental design (PBD)). Central composite design (CCD) was used for further optimisation of pyrolysis time and temperature as the two most significant factors. Model predictions for an optimised biochar (OB) suggested pyrolysis conditions of 500 °C for 30 min could achieve the highest yield of 34.75 %, the lowest cost of 0.37 £ /kg, and the highest PO43−-P and NH4+-N removal of 9.9 % and 65.2 %, respectively. Additionally, the OB morphology, structure and surface chemistry were characterised using different instrumental techniques which showed typical features for a wood-based biochar. While the OB did remove NH4+-N from solution (due to the presence of negatively charged functional groups), it did not remove significant amounts of PO43--P, indeed it leached PO43--P back into solution. Therefore, an unmodified biochar produced from conifer brash did not fulfil the aim of removing these two key nutrient pollutants for use in improving water quality at restoration sites. To address this challenge, the surface chemistry of the OB could be functionalised to increase its affinity toward both PO43−-P and NH4+-N ions.

Exploring Ocean Biogeochemistry Using a Lab-on-Chip Phosphate Analyser on an Underwater Glider

The ability to make measurements of phosphate (PO43–) concentrations at temporal and spatial scales beyond those offered by shipboard observations offers new opportunities for investigations of the marine phosphorus cycle. We here report the first in situ PO43– dataset from an underwater glider (Kongsberg Seaglider) equipped with a PO43– Lab-on-Chip (LoC) analyser. Over 44 days, a 120 km transect was conducted in the northern North Sea during late summer (August and September). Surface depletion of PO43– (<0.2 μM) was observed above a seasonal thermocline, with elevated, but variable concentrations within the bottom layer (0.30–0.65 μM). Part of the variability in the bottom layer is attributed to the regional circulation and across shelf exchange, with the highest PO43– concentrations being associated with elevated salinities in northernmost regions, consistent with nutrient rich North Atlantic water intruding onto the shelf. Our study represents a significant step forward in autonomous underwater vehicle sensor capabilities and presents new capability to extend research into the marine phosphorous cycle and, when combined with other recent LoC developments, nutrient stoichiometry.

Evaluation of groundwater quality in central Saudi Arabia using hydrogeochemical characteristics and pollution indices.

The groundwater quality and heavy metal (HM) contamination were evaluated in palm farms, central Saudi Arabia, using pollution indices, irrigation quality parameters, and multivariate statistical analyses. Thirty groundwater samples were collected in October 2020 for major anions, cations, and HMs analyses and interpretation. The results showed that the average concentrations of total dissolved solids (TDS), Ca+, Na+, K+, Cl-, SO42-, and F- were greater than the permissible limits of the WHO standards for drinking water. The groundwater facies types were Ca-Na-SO4-Cl (23 samples), Ca-Cl-SO4, (4 samples), and Ca-SO4-Cl type (3 samples). The groundwater quality index indicated that 15 groundwater samples were of good quality and 15 were of poor quality, whereas the metal index and heavy metal pollution index indicated that all samples were categorized as slightly affected and with low pollution, respectively. The variation is attributed to the increasing average concentrations of some ions and decreasing HMs. The dissolution/precipitation of silicates, gypsum, and carbonates and soil leaching were the natural factors affecting groundwater chemistry, whereas higher PO43-, NO3-, F-, Pb, and Zn values in some samples may be attributed to human activities from the extensive use of fertilizers and pesticides on the investigated farms.

Biomass pyrolysis with alkaline-earth-metal additive for co-production of bio-oil and biochar-based soil amendment

The alkaline-earth-metal (AEM) has a good performance on modification of both bio-oil and biochar during biomass pyrolysis. In this work, the pyrolysis of rice husk (RH) in the presence of CaO, CaCO3, MgO and MgCO3 was comparatively studied for selecting an appropriate AEM additive to balance the qualities of pyrolytic products. Pyrolysis of RH with the AEM additives could decrease the acids content and increase the hydrocarbons content in bio-oil. Compared with the Ca-additives (i.e., CaO, CaCO3), the Mg-additives (i.e., MgO, MgCO3) were more beneficial for enhancing the hydrocarbons production. The addition of biochar to soil can significantly enhance the water retention. RHC-MgCO3 had a maximum water retention capacity, while RHC-MgO had a minimum water retention capacity due to its lowest specific surface area. Additionally, the Mg-modified biochar had a much higher nutrient (i.e., K+, PO43−) adsorption capacity. In particular, RHC-MgO with a lowest specific surface area had a highest PO43− adsorption capacity, which was evidenced by the adsorption of PO43− onto biochar mainly controlled by the chemisorption process. PO43− adsorbed in the RHC-MgO released rapidly indicating its low PO43− retention capacity. In general, MgCO3 would be an appropriate candidate that is used in pyrolysis of biomass for co-production of bio-oil and biochar composite with high capacities of water/nutrient adsorption and retention for soil amendment.