Modelling biological and chemically induced precipitation of calcium phosphate in enhanced biological phosphorus removal systems

Investigating the addition of Fe for improving contaminant removal and regulating microbes in a simulated coastal wetland

Contaminants from wastewater of aquaculture are increasing the risks of red tides in coastal areas. Such types of contaminants are difficult to remove by using conventional biological and ecological treatment methods because of the relatively low C/N ratios and the high salinity in coastal water ambience. Fe is considered a key element in natural chemical cycling and promotes the growth of animals and plants as well. The cycling of Fe ion combined with carbon, nitrogen, and phosphorus stimulates bacterial growth. As a result, it acts as a microbial carbon pump in coastal areas, such as natural wetlands, which have been activated and adapted to be salinity resistant and insufficient energy supply. Along these lines, in this work, constructed wetlands (CWs) with high ecological benefits and low cost of maintenance were used to treat aquaculture wastewater. The impact of Fe ion recycling on multiple contaminants was also systematically investigated. The two types of Fe dosage were pure ferrous ions and a mixture of iron powder and ferrous ions. After the application of a 3-day treatment, the dosage of iron powder/ferric ions (1:1 m/m) at a concentration of 15 mg L-1 showed a better effect, where the total nitrogen, total phosphorus, and chemical oxygen demand removal rates were increased by 2.95%, 2.16%, and 9.76%, respectively. From the microbial analysis, it was indicated that Fe ion affected the abundance and functions of the microbial communities in the CWs. The significant enrichment of Proteobacteria promoted the removal of multiple contaminants under saline stress and fixed carbon, and affected the whole microbe distribution and diversity in CWs. The implementation of such an environmentally friendly and economical approach arises as a promising candidate for the efficient removal of multiple contaminants from aquacultural wastewater in coastal zones.

Dynamic modelling the effects of ionic strength and ion complexation on trace metal speciation during anaerobic digestion

Dosing trace metals into anaerobic digestors is proven to improve biogas production rate and yield by stimulating microorganisms involved in the metabolic pathways. Trace metal effects are governed by metal speciation and bioavailability. Though chemical equilibrium speciation models are well-established and widely used to understand metal speciation, the development of kinetic models considering biological and physicochemical processes has recently gained attention. This work proposes a dynamic model for metal speciation during anaerobic digestion which is based on a system of ordinary differential equations aimed to describe the kinetics of biological, precipitation/dissolution, gas transfer processes and, a system of algebraic equations to define fast ion complexation processes. The model also considers ion activity corrections to define effects of ionic strength. Results from this study shows the inaccuracy in predicting trace metal effects on anaerobic digestion by typical metal speciation models and the significance of considering non-ideal aqueous phase chemistry (ionic strength and ion pairing/complexation) to define speciation and metal labile fractions. Model results show a decrease in metal precipitation and increase in metal dissolved fraction and methane production yield with increase in ionic strength. Capability of the model to dynamically predict trace metal effects on anaerobic digestion under different conditions, like changing dosing conditions and initial iron to sulphide ratio, was also tested and verified. Dosing iron increases methane production and decreases hydrogen sulphide production. However, when iron to sulphide ratio is greater than 1, methane production decreases due to increase in dissolved iron which reaches inhibitory concentration levels.

Preparation of Fe/C-MgCO3 micro-electrolysis fillers and mechanism of phosphorus removal

Iron-carbon micro-electrolysis is effective for the removal of phosphorus in wastewater; however, meeting the stringent emission standards required for treatment is difficult. To meet these treatment standards, modified micro-electrolytic fillers were prepared from iron dust, powdered activated carbon, clay, and additives using an elevated temperature roasting process under an inert atmosphere. The results show that among several additives, the modified micro-electrolytic (Fe/C-MgCO₃) fillers using MgCO₃ were the most effective at phosphorus removal. The preparation conditions for the Fe/C-MgCO₃ fillers and their effects on phosphorus removal performance were investigated. Under the optimal preparation conditions (calcination temperature: 800 °C, Fe/C = 4:1, clay content 20%, and 5% MgCO₃), the filler yielded a high compressive strength of 3.5 MPa, 1 h water absorption rate of 25.7%, and specific surface area and apparent density of 154.2 m²/g and 2689.2 kg/m³, respectively. The iron-carbon micro-electrolysis process removed 97% of phosphorus in the wastewater by using the Fe/C-MgCO₃ fillers, which was 14% more than the Fe/C filler. Electrostatic adsorption and surface precipitation were identified as the main phosphorus removal mechanisms, and the surface of the Fe/C-MgCO₃ filler was continuously updated. These results demonstrated that Fe/C-MgCO₃ is a promising filler for phosphorus removal in water treatment.

Enhanced Bio-P removal: Past, present, and future - A comprehensive review

Excess amounts of phosphorus (P) and nitrogen (N) from anthropogenic activities such as population growth, municipal and industrial wastewater discharges, agriculture fertilization and storm water runoffs, have affected surface water chemistry, resulting in episodes of eutrophication. Enhanced biological phosphorus removal (EBPR) based treatment processes are an economical and environmentally friendly solution to address the present environmental impacts caused by excess P present in municipal discharges. EBPR practices have been researched and operated for more than five decades worldwide, with promising results in decreasing orthophosphate to acceptable levels. The advent of molecular tools targeting bacterial genomic deoxyribonucleic acid (DNA) has also helped us reveal the identity of potential polyphosphate-accumulating organisms (PAO) and denitrifying PAO (DPAO) responsible for the success of EBPR. Integration of process engineering and environmental microbiology has provided much-needed confidence to the wastewater community for the successful implementation of EBPR practices around the globe. Despite these successes, the process of EBPR continues to evolve in terms of its microbiology and application in light of other biological processes such as anaerobic ammonia oxidation and on-site carbon capture. This review provides an overview of the history of EBPR, discusses different operational parameters critical for the successful operation of EBPR systems, reviews current knowledge of EBPR microbiology, the influence of PAO/DPAO on the disintegration of microbial communities, stoichiometry, EBPR clades, current practices, and upcoming potential innovations.

Kinetic modeling of autotrophic microalgae mainline processes for sewage treatment in phosphorus-replete and -deplete culture conditions

A kinetic model of autotrophic microalgal growth in sewage was developed to determine the biokinetic processes involved, including carbon-, nitrogen- and phosphorus-limited microalgal growth, dependence on light intensity, temperature and pH, light attenuation and gas exchange to the atmosphere. A new feature was the differentiation between two metabolic pathways of phosphorus consumption according to the availability of extracellular phosphorus. Two scenarios were differentiated: phosphorus-replete and -deplete culture conditions. In the former, the microalgae absorbed phosphorus to grow and store polyphosphate. In the latter the microalgae used the stored polyphosphate as a phosphorus source for growth. Calibration and validation were performed with experimental data from a pilot-scale membrane photobioreactor (MPBR) fed with the permeate obtained from an anaerobic membrane bioreactor (AnMBR) pilot plant fed with real urban wastewater. 12 of the model parameters were calibrated. Despite the dynamics involved in the operating and environmental conditions, the model was able to reproduce the overall process performance with a single set of model parameters values. Four periods of different environmental and operational conditions were accurately simulated. Regarding the former, light and temperature ranged 10-406 μmol·m^-2·s^-1 and 19.7-32.1 °C, respectively. Concerning the later, the photobioreactors widths were 0.25 and 0.10 m, and the biomass and hydraulic retention times ranged 3-4.5 and 1.5-2.5 days, respectively. The validation of the model resulted in an overall correlation coefficient (R²) of 0.9954. The simulation results showed the potential of the model to predict the dynamics of the different components: the relative proportions of microalgae, nitrogen and phosphorus removal, polyphosphate storage and consumption, and soluble organic matter concentration, as well as the influence of environmental parameters on the microalgae's biokinetic processes. The proposed model could provide an effective tool for the industry to predict microalgae production and comply with the discharge limits in areas declared sensitive to eutrophication.

Mathematical modeling of the role of bone turnover in pH regulation in bone interstitial fluid

BACKGROUND AND AIMS

Bone turnover is strongly affected by pH of surrounding fluid, and in turn plays a role in maintaining systemic pH, however the quantitative contribution of bone processes to pH regulation is not known. Our goal was to develop a mathematical model describing pH regulation in the interstitial fluid and to examine the contribution of hydroxyapatite dissolution and precipitation to pH regulation.

MATERIALS AND METHODS

We modeled twelve reversible equilibrium reactions of sixteen calcium, phosphate, hydrogen and carbonate species in the interstitial fluid and examined the buffering capacity and range. The effect of hydroxyapatite dissolution and precipitation was modeled by assuming that the calcium, phosphate and hydroxide contained in the bone volume adjacent to the interstitial fluid is instantaneously added to or removed from the interstitial fluid.

RESULTS

The carbonate buffer was found to dominate electrochemical buffering system of the bone interstitial fluid. Nevertheless, the phosphate added during dissolution of bone hydroxyapatite significantly improved the interstitial fluid buffering capacity. In contrast, hydroxyapatite precipitation had limited effect on the interstitial fluid pH regulation.

CONCLUSION

This study provides mechanistic insights into the physicochemical processes underlying the known role of bone turnover processes in regulation of body pH homeostasis.

Assessment of sludge management strategies in wastewater treatment systems using a plant-wide approach

The objective of this paper is to use plant-wide modeling to assess the net impacts of varying sludge management strategies. Special emphasis is placed on effluent quality, operational cost and potential resource recovery (energy, nutrients). The study is particularly focused on a centralized bio-solids beneficiation facility (BBF), which enables larger, more capital intensive sludge management strategies. Potential barriers include the ability to process reject streams from multiple donor plants in the host plant. Cape Flats (CF) wastewater treatment works (WWTW) (Cape Town, South Africa) was used as a relevant test case since it is currently assessing to process sludge cake from three nearby facilities (Athlone, Mitchells Plain and Wildevoelvlei). A plant-wide model based on the Benchmark Simulation Model no 2 (BSM2) extended with phosphorus transformations was adapted to the CF design / operational conditions. Flow diagram and model parameters were adjusted to reproduce the influent, effluent and process characteristics. Historical data between January 2014 and December 2019 was used to compare full-scale measurements and predictions. Next, different process intensification / mitigation technologies were evaluated using multiple criteria. Simulation values for COD, TSS, VSS/TSS ratio, TN, TP, NH₄⁺/NH₃, H_xPO4^3-x, NO_x alkalinity and pH fall within the interquartile ranges of measured data. The effects of the 2017 severe drought on influent variations and biological phosphorus removal are successfully reproduced for the entire period with dynamic simulations. Indeed, 80% of all dynamically simulated values are included within the plant measurement uncertainty ranges. Sludge management analysis reveals that flow diagrams with thermal hydrolysis pre-treatment (THP) result in a better energy balance in spite of having higher heat demands. The flow diagram with THP is able to i) increase biodegradability/solubility, ii) handle higher sludge loads, iii) change methanogenic microbial population and iv) generate lower solids volumes to dispose by improving sludge dewaterability. The study also reveals the importance of including struvite precipitation and harvesting (SPH) technology, and the effect that pH in the AD and the use of chemicals (NaOH, MgO) may have on phosphorus recovery. Model-based results indicate that the current aerobic volume in the water line (if properly aerated) would be able to handle the returns from the sludge line and the contribution of a granular partial nitritation/Anammox (PN/ANX) reactor on the overall nitrogen removal would be marginal. However autotrophic N denitrification generates a much lower sludge production and therefore increases AD treatment capacity. The study shows for the very first time in Africa how the use of a (calibrated) plant-wide model could assist water utilities to decide between competing plant layouts when upgrading a WWTW.

Long-term simulation of a full-scale EBPR plant with a novel metabolic-ASM model and its use as a diagnostic tool

This study evaluates the predictive capacity of the META-ASM model, a new integrated metabolic activated sludge model, in describing the long-term performance of a full-scale enhanced biological phosphorus removal (EBPR) system that suffers from inconsistent performance. In order to elucidate the causes of EBPR upsets and troubleshoot the process accordingly, the META-ASM model was tested as an operational diagnostic tool in a 1336-day long-term dynamic simulation, while its performance was compared with the ASM-inCTRL model, a version based on the Barker & Dold model. Overall, the predictions obtained with the META-ASM without changing default parameters were more reliable and effective at describing the active biomass of polyphosphate accumulating organisms (PAOs) and the dynamics of their storage polymers. The primary causes of the EBPR upsets were the high aerobic hydraulic retention times (HRTs) and low organic loading rates (OLRs) of the plant, which led to periods of starvation. The impact of these factors on EBPR performance were only identified with the META-ASM model. Furthermore, the first signs of process upsets were predicted by variations in the aerobic PAO maintenance rates, suggesting that the META-ASM model has potential to provide an early warning of process upset. The simulation of a new viable operational strategy indicated that troubleshooting the process could be achieved by reducing the aerated volume by switching off air in the first half of the aeration tank. In this new strategy, the META-ASM model predicted a simultaneous improvement in the biological phosphorus (P) and nitrogen (N) removal due to the enhancement of the hydrolysis and fermentation of the mixed liquor sludge in the new unaerated zone, which increased the availability of volatile fatty acids (VFAs) for PAOs. This study demonstrates that the META-ASM model is a powerful operational diagnostic tool for EBPR systems, capable of predicting and mitigating upsets, optimising performance and evaluating new process designs.

Effects of heavy metals and metal (oxide) nanoparticles on enhanced biological phosphorus removal

With the rapid growth of economics and nanotechnology, a significant portion of the anthropogenic emissions of heavy metals and nanoparticles (NPs) enters wastewater streams and discharges to wastewater treatment plants, thereby potentially posing a risk to the bacteria that facilitate the successful operation of the enhanced biological phosphorus (P) removal (EBPR) process. Although some efforts have been made to obtain detailed insights into the effects of heavy metals and metal (oxide) nanoparticles [Me(O)NPs], many unanswered questions remain. One question is whether the toxicity of Me(O)NPs originates from the released metal ions. This review aims to holistically evaluate the effects of heavy metals and Me(O)NPs. The interactions among extracellular polymeric substances, P, and heavy metals [Me(O)NPs] are presented and discussed for the first time. The potential mechanisms of the toxicity of heavy metals [Me(O)NPs] are summarized. Additionally, mathematical models of the toxicity and removal of P, heavy metals, and Me(O)NPs are overviewed. Finally, knowledge gaps and opportunities for further study are discussed to pave the way for fully understanding the inhibition of heavy metals [Me(O)NPs] and for reducing their inhibitory effect to maximize the reliability of the EBPR process.

Preparation of a New Iron-Carbon-Loaded Constructed Wetland Substrate and Enhanced Phosphorus Removal Performance

Iron-carbon substrates have attracted extensive attention in water treatment due to their excellent processing ability. The traditional iron-carbon substrate suffers from poor removal effects, separation of the cathode and anode, hardening, secondary pollution, etc. In this study, a new type of iron-carbon-loaded substrate (NICLS) was developed to solve the problems of traditional micro-electrolytic substrates. Through experimental research, a preparation method for the NICLS with Fe and C as the core, zeolite as the skeleton, and water-based polyurethane as the binder was proposed. The performance of the NICLS in phosphorus-containing wastewater was analyzed. The results are as follows: The optimal synthesis conditions of the NICLS are 1 g hydroxycellulose, wood activated carbon as the cathode, an activated carbon particle size of 200-60 mesh, and an Fe/C ratio of 1:1. Acidic conditions can promote the degradation of phosphorus by the NICLS. Through the characterization of the NICLS (scanning electron microscope (SEM), X-ray diffractometer (XRD), and energy-dispersive spectrometer (EDS), etc.), it is concluded that the mechanism of the NICLS phosphorus removal is a chemical reaction produced by micro-electrolysis. Using the NICLS to treat phosphorus-containing wastewater has the advantages of high efficiency and durability. Therefore, it can be considered that the NICLS is a promising material to remove phosphorus.

Recovery of phosphorus and metallic nickel along with HCl production from electroless nickel plating effluents: The key role of three-compartment photoelectrocatalytic cell system

A three-compartment photoelectrocatalytic (PEC) cell system combined with ion exchange and chemical precipitation was proposed to recover phosphorus and nickel from electroless nickel plating effluents containing hypophosphite (H₂PO₂^-) and nickel ions (Ni²⁺). Ion exchange was used to concentrate and separate Ni²⁺ and H₂PO₂^-. As a key unit, the established PEC system consisted of TiO₂/Ni-Sb-SnO₂ photoanode and Ti cathode. With 25.8 mM NaH₂PO₂ and 500 mM NiCl₂, 100 % H₂PO₂^- was oxidized to PO₄^3- in the anode cell, 78 % Ni²⁺ was recovered as metallic Ni in the cathode cell, and 900 mM HCl was obtained in the middle cell within 24 h at 3.0 V. Based on quenching experiments and ESR technique, OH radicals were mainly responsible for H₂PO₂^- oxidation. In situ Raman spectroscopy indicated that Ni²⁺ initially reacted with OH^- to form α-Ni(OH)₂, which was gradually reduced to metallic Ni. Fortunately, a slight pH decrease in the cathode cell in the three-compartment cell system was beneficial for Ni²⁺ reduction to Ni°. The obtained PO₄^3- was recovered by chemical precipitation. Finally, recovery of phosphorus and metallic nickel along with HCl production from an actual electroless nickel plating effluents in terms of efficiency, cost-benefit, and stability assessment were demonstrated.

Plant-wide modelling in wastewater treatment: showcasing experiences using the Biological Nutrient Removal Model

Plant-wide modelling can be considered an appropriate approach to represent the current complexity in water resource recovery facilities, reproducing all known phenomena in the different process units. Nonetheless, novel processes and new treatment schemes are still being developed and need to be fully incorporated in these models. This work presents a short chronological overview of some of the most relevant plant-wide models for wastewater treatment, as well as the authors' experience in plant-wide modelling using the general model BNRM (Biological Nutrient Removal Model), illustrating the key role of general models (also known as supermodels) in the field of wastewater treatment, both for engineering and research.

Mathematical modeling of calcium phosphate precipitation in biologically relevant systems: scoping review

Biologically guided precipitation of calcium phosphates is important for the formation of calcified human tissues, such as bone and teeth, and is of practical significance in numerous industrial and agricultural processes, such as wastewater treatment and dairy ultrafiltration. Mineral precipitation is physicochemically complex and becomes even more complex in the presence of biological materials. The theoretical foundation of phase transition in general has been developed and is vital for many applications, such as metallurgy and weather prediction. The goal of this scoping review was to identify and evaluate established mathematical approaches developed to describe the formation of calcium precipitates in biological systems. A scoping review was conducted using MathSciNet, Scopus, and Web of Science databases to retrieve eligible mathematical modeling papers on calcium precipitates in biological systems. From the 2096 studies screened, 115 studies were included. The major biological systems of interest were tissues of the human body (49/115), water research (38/115), and agricultural and earth sciences applications (17/115). The majority of studies described precipitation of calcium phosphate (79/115), followed by calcium carbonate (22/115). Mathematical modeling of calcium precipitation was dominated by classical nucleation (64/115) and kinetic (38/115) theories. Only a minority of studies explicitly modeled chemical reactions in the aqueous phase (33/115). Biological components were explicitly described in 45/115 studies and included as physicochemical limitations in 70/115 studies. The majority of the studies (91/115) attempted to quantitatively compare the model predictions to the experimental data, with 59/115 reporting good to reasonable fit. This scoping review suggests that broad theories, such as classical nucleation and kinetic theories, may be adapted for modeling calcium precipitation in biologically relevant systems; however, detailed mathematical descriptions of biological, chemical, and physicochemical aspects of calcium precipitation are required.

An Adaptive-PSO-Based Self-Organizing RBF Neural Network

In this paper, a self-organizing radial basis function (SORBF) neural network is designed to improve both accuracy and parsimony with the aid of adaptive particle swarm optimization (APSO). In the proposed APSO algorithm, to avoid being trapped into local optimal values, a nonlinear regressive function is developed to adjust the inertia weight. Furthermore, the APSO algorithm can optimize both the network size and the parameters of an RBF neural network simultaneously. As a result, the proposed APSO-SORBF neural network can effectively generate a network model with a compact structure and high accuracy. Moreover, the analysis of convergence is given to guarantee the successful application of the APSO-SORBF neural network. Finally, multiple numerical examples are presented to illustrate the effectiveness of the proposed APSO-SORBF neural network. The results demonstrate that the proposed method is more competitive in solving nonlinear problems than some other existing SORBF neural networks.

Effects of iron and calcium carbonate on contaminant removal efficiencies and microbial communities in integrated wastewater treatment systems

In the paper, we explored the influences of different dosages of iron and calcium carbonate on contaminant removal efficiencies and microbial communities in algal ponds combined with constructed wetlands. After 1-year operation of treatment systems, based on the high-throughput pyrosequencing analysis of microbial communities, the optimal operating conditions were obtained as follows: the ACW10 system with Fe³⁺ (5.6 mg L^-1), iron powder (2.8 mg L^-1), and CaCO₃ powder (0.2 mg L^-1) in influent as the adjusting agents, initial phosphorus source (PO₄^3-) in influent, the ratio of nitrogen to phosphorus (N/P) of 30 in influent, and hydraulic retention time (HRT) of 1 day. Total nitrogen (TN) removal efficiency and total phosphorus (TP) removal efficiency were improved significantly. The hydrolysis of CaCO₃ promoted the physicochemical precipitation in contaminant removal. Meanwhile, Fe³⁺ and iron powder produced Fe²⁺, which improved contaminant removal. Iron ion improved the diversity, distribution, and metabolic functions of microbial communities in integrated treatment systems. In the treatment ACW10, the dominant phylum in the microbial community was PLANCTOMYCETES, which positively promoted nitrogen removal. After 5 consecutive treatments in ACW10, contaminant removal efficiencies for TN and TP respectively reached 80.6% and 57.3% and total iron concentration in effluent was 0.042 mg L^-1.

Electrochemical Induced Calcium Phosphate Precipitation: Importance of Local pH

Phosphorus (P) is an essential nutrient for living organisms and cannot be replaced or substituted. In this paper, we present a simple yet efficient membrane free electrochemical system for P removal and recovery as calcium phosphate (CaP). This method relies on in situ formation of hydroxide ions by electro mediated water reduction at a titanium cathode surface. The in situ raised pH at the cathode provides a local environment where CaP will become highly supersaturated. Therefore, homogeneous and heterogeneous nucleation of CaP occurs near and at the cathode surface. Because of the local high pH, the P removal behavior is not sensitive to bulk solution pH and therefore, efficient P removal was observed in three studied bulk solutions with pH of 4.0 (56.1%), 8.2 (57.4%), and 10.0 (48.4%) after 24 h of reaction time. While P removal efficiencies are not generally affected by bulk solution pH, the chemical-physical properties of CaP solids collected on the cathode are still related to bulk solution pH, as confirmed by structure characterizations. High initial solution pH promotes the formation of more crystalline products with relatively high Ca/P molar ratio. The Ca/P molar ratio increases from 1.30 (pH 4.0) to 1.38 (pH 8.2) and further increases to 1.55 (pH 10.0). The formation of CaP precipitates was a typical crystallization process, with an amorphous phase formed at the initial stage which then transforms to the most stable crystal phase, hydroxyapatite, which is inferred from the increased Ca/P molar ratio from 1.38 (day 1) to the theoretical 1.76 (day 11) and by the formation of needle-like crystals. Finally, we demonstrated the efficiency of this system for real wastewater. This, together with the fact that the electrochemical method can work at low bulk pH, without dosing chemicals and a need for a separation process, highlights the potential application of the electrochemical method for P removal and recovery.

Performance of five plant species in removal of nitrogen and phosphorus from an experimental phytoremediation system in the Ningxia irrigation area

Agricultural non-point source (ANPS) pollution is an important contributor to elevated nitrogen (N) and phosphorus (P) in surface waters, which can cause serious environmental problems. Considerable effort has therefore gone into the development of methods that control the ANPS input of N and P to surface waters. Phytoremediation has been extensively used because it is cost-effective, environmentally friendly, and efficient. The N and P loads from agricultural drainage are a potential threat to the water quality of the Yellow River in Ningxia, China. Yet, phytoremediation has only rarely been applied within the Ningxia irrigation area. In an experimental set-up, five species (Ipomoea aquatica, IA; Lactuca sativa, LS; Oryza sativa, OS; Typha latifolia, TL; Zizania latifolia, ZL) were evaluated for their ability to reduce N and P loads over 62 days and five observation periods. Total N and P concentrations, plant biomass, and nutrient content were measured. The results showed that OS, LS, and IA performed better than ZL and TL in terms of nutrients removal, biomass accumulation, and nutrients storage. The highest overall removal rates of N and P (57.7 and 57.3%, respectively) were achieved by LS treatment. In addition, plant uptake contributed significantly to nutrient removal, causing a 25.9-72.0% reduction in N removal and a 54.3-86.5% reduction in P removal. Thus, this study suggests that OS, LS, and IA would be more suitable than ZL and TL for controlling nutrient loads in the Ningxia irrigation area using phytoremediation.

Plant-wide modelling of phosphorus transformations in wastewater treatment systems: Impacts of control and operational strategies

The objective of this paper is to report the effects that control/operational strategies may have on plant-wide phosphorus (P) transformations in wastewater treatment plants (WWTP). The development of a new set of biological (activated sludge, anaerobic digestion), physico-chemical (aqueous phase, precipitation, mass transfer) process models and model interfaces (between water and sludge line) were required to describe the required tri-phasic (gas, liquid, solid) compound transformations and the close interlinks between the P and the sulfur (S) and iron (Fe) cycles. A modified version of the Benchmark Simulation Model No. 2 (BSM2) (open loop) is used as test platform upon which three different operational alternatives (A₁, A₂, A₃) are evaluated. Rigorous sensor and actuator models are also included in order to reproduce realistic control actions. Model-based analysis shows that the combination of an ammonium ( [Formula: see text] ) and total suspended solids (X_TSS) control strategy (A₁) better adapts the system to influent dynamics, improves phosphate [Formula: see text] accumulation by phosphorus accumulating organisms (X_PAO) (41%), increases nitrification/denitrification efficiency (18%) and reduces aeration energy (E_aeration) (21%). The addition of iron ( [Formula: see text] ) for chemical P removal (A₂) promotes the formation of ferric oxides (X_HFO-H, X_HFO-L), phosphate adsorption (X_HFO-H,P, X_HFO-L,P), co-precipitation (X_HFO-H,P,old, X_HFO-L,P,old) and consequently reduces the P levels in the effluent (from 2.8 to 0.9 g P.m^-3). This also has an impact on the sludge line, with hydrogen sulfide production ( [Formula: see text] ) reduced (36%) due to iron sulfide (X_FeS) precipitation. As a consequence, there is also a slightly higher energy production (E_production) from biogas. Lastly, the inclusion of a stripping and crystallization unit (A₃) for P recovery reduces the quantity of P in the anaerobic digester supernatant returning to the water line and allows potential struvite ( [Formula: see text] ) recovery ranging from 69 to 227 kg.day^-1 depending on: (1) airflow (Q_stripping); and, (2) magnesium ( [Formula: see text] ) addition. All the proposed alternatives are evaluated from an environmental and economical point of view using appropriate performance indices. Finally, some deficiencies and opportunities of the proposed approach when performing (plant-wide) wastewater treatment modelling/engineering projects are discussed.

Effects of cerium oxide nanoparticles on the species and distribution of phosphorus in enhanced phosphorus removal sequencing batch biofilm reactor

The short term (8h) influences of cerium oxide nanoparticles (CeO₂NPs) on the process of phosphorus removal in biofilm were investigated. At concentration of 0.1mg/L, CeO₂ NPs posed no impacts on total phosphorus (TP) removal. While at 20mg/L, TP removal efficiency reduced from 85.16% to 59.62%. Results of P distribution analysis and ³¹P nuclear magnetic resonance spectroscopy implied that the anaerobic degradation of polyphosphate (polyP) and the release of orthophosphate in extracellular polymeric substances (EPS) were inhibited. After aerobic exposure, the average chain length of polyP in microbial cells and EPS was shorter than control, and monoester and diester phosphates in cells were observed to release into EPS. Moreover, the EPS production and its contribution to P removal increased, while the capacity of EPS in P storage declined. X-ray diffraction analysis and saturation index calculation revealed that the formation of inorganic P precipitation in biofilm was inhibited.

Enhanced primary sludge sonication by heat insulation to reclaim carbon source for biological phosphorous removal

Ultrasound pretreatment is a potent step to disintegrate primary sludge (PS). The supernatant of sonicated PS is recycled as an alternative carbon source for biological phosphorus removal. In this study, we investigated the role of temperature on PS disintegration during sonication. We found that a temperature of 60°C yielded a dissolution rate of about 2% soluble chemical oxygen demand (SCOD) as compared to 7% SCOD using sonication at the specific energy (SE) of 7359kJ/kg TS. Using the SE of 6000kJ/kg TS with heat insulation during sonication, the SCOD dissolution rate of PS was similar to the result at the SE of 7051kJ/kg TS without heat insulation. Upon treatment with sonication, the PS released low concentrations of Cu and Zn into the supernatant. The phosphorus-accumulating organisms (PAOs) used the supernatant of sonicated PS as the carbon source. Supplementation with the diluted sonicated PS supernatant (SCOD≈1000mg/L) in anaerobic phase resulted in the release of phosphorus (36mg/L) and the production of polyhydroxyalkanoates (PHAs) (0.36g PHA/g SS). Compared with sodium acetate, higher polyhydroxyvalerate (PHV) faction in the polyhydroxyalkanoates (PHAs) was observed in the biomass when incubated with sonicated PS as the carbon source. This work provides a simple pathway to conserve energy and to enhance efficiencies of ultrasonic pretreatment and the recovery of carbon source from the sludge for improving the phosphorus removal in the ENR system.

Influences of seasons, N/P ratios and chemical compounds on phosphorus removal performance in algal pond combined with constructed wetlands

Nitrogen (N) and phosphorous (P) are main contaminants and P removal was restrained by several factors: season, N/P, and chemical compounds (CCs) in water ecosystems. In this paper, two algal ponds combined with constructed wetlands were built to increase the removal performance. Different hydraulic retention time (HRT), different N/P and chemical compounds were chosen to investigate the influences of the above factors on the contaminant removal performance. The optimum phosphorus removal rate was 69.74% under the nitrogen removal of 92.85% in influent containing PO₄^3- after 3-day HRT in algal pond combined with constructed wetlands. The investigation results indicated that these factors improved the nutrient removal efficiencies. Seasonal influence on the removal performance can be avoided by choosing the optimal HRT length of 3days. The higher N/P at 60 can improve the phosphorus removal and the lower N/P at 15 showed the stronger synergistic effect between phosphorus and nitrogen removals. Compared with PO₃^- and P₂O₇^4- in influent, PO₄^3- affected phosphorus removal more significantly. The better linear fitting between organic phosphorus removal and nitrogen removal in influent contained P₂O₇^4- was found. Algae can absorb nutrients for growth, and oxygen release, microbial activity intensification and microbial carbon replenishment induced by algae will improve the performance. The study suggested that the control of HRTs, N/Ps, CCs, and algae might be an effective way to improve wastewater treatment performance.

Phosphate recovery from anaerobic digester effluents using CaMg(OH)4

Dolomite lime (DL) (CaMg(OH)4) was used as an economical source of Mg(2+) for the removal and recovery of phosphate from an anaerobic digester effluent of a municipal wastewater treatment plant (MWWTP) wastewater. Batch precipitation results determined that phosphate was effectively reduced from 87 to less than 4mg-P/L when the effluent water was mixed with 0.3g/L of DL. The competitive precipitation mechanisms of different solids in the treatment system consisting of Ca(2+)-Mg(2+)-NH4(+)-PO4(3-)CO3(2-) were determined by comparing model predictions with experimental results. Thermodynamic model calculations indicated that hydroxyapatite (Ca10(PO4)6(OH)2), Ca4H(PO4)3∙3H2O, Ca3(PO4)2(beta), and Ca3(PO4)2(am2) were more stable than struvite (MgNH4PO3∙6H2O) and calcite (CaCO3). However, X-ray diffraction (XRD) analysis determined the formation of struvite and calcite minerals in the treated effluent. Kinetic experimental results showed that most of the phosphate was removed from synthetic effluent containing NH4(+) within 2hr, while only 20% of the PO4(3-) was removed in the absence of NH4(+) after 24hr of treatment. The formation of struvite in the DL-treated effluent was due to the rapid precipitation rate of the mineral. The final pH of the DL-treated effluent significantly influenced the mass ratio of struvite to calcite in the precipitates. Because more calcite was formed when the pH increased from 8.4 to 9.6, a pH range of 8.0-8.5 should be used to produce solid with high PO4(3-) content. This study demonstrated that DL could be used for effective removal of phosphate from the effluent and that resultant precipitates contained high content of phosphate and ammonium.

Modelling phosphorus (P), sulfur (S) and iron (Fe) interactions for dynamic simulations of anaerobic digestion processes

This paper proposes a series of extensions to functionally upgrade the IWA Anaerobic Digestion Model No. 1 (ADM1) to allow for plant-wide phosphorus (P) simulation. The close interplay between the P, sulfur (S) and iron (Fe) cycles requires a substantial (and unavoidable) increase in model complexity due to the involved three-phase physico-chemical and biological transformations. The ADM1 version, implemented in the plant-wide context provided by the Benchmark Simulation Model No. 2 (BSM2), is used as the basic platform (A0). Three different model extensions (A1, A2, A3) are implemented, simulated and evaluated. The first extension (A1) considers P transformations by accounting for the kinetic decay of polyphosphates (XPP) and potential uptake of volatile fatty acids (VFA) to produce polyhydroxyalkanoates (XPHA) by phosphorus accumulating organisms (XPAO). Two variant extensions (A2,1/A2,2) describe biological production of sulfides (SIS) by means of sulfate reducing bacteria (XSRB) utilising hydrogen only (autolithotrophically) or hydrogen plus organic acids (heterorganotrophically) as electron sources, respectively. These two approaches also consider a potential hydrogen sulfide ( [Formula: see text] inhibition effect and stripping to the gas phase ( [Formula: see text] ). The third extension (A3) accounts for chemical iron (III) ( [Formula: see text] ) reduction to iron (II) ( [Formula: see text] ) using hydrogen ( [Formula: see text] ) and sulfides (SIS) as electron donors. A set of pre/post interfaces between the Activated Sludge Model No. 2d (ASM2d) and ADM1 are furthermore proposed in order to allow for plant-wide (model-based) analysis and study of the interactions between the water and sludge lines. Simulation (A1 - A3) results show that the ratio between soluble/particulate P compounds strongly depends on the pH and cationic load, which determines the capacity to form (or not) precipitation products. Implementations A1 and A2,1/A2,2 lead to a reduction in the predicted methane/biogas production (and potential energy recovery) compared to reference ADM1 predictions (A0). This reduction is attributed to two factors: (1) loss of electron equivalents due to sulfate [Formula: see text] reduction by XSRB and storage of XPHA by XPAO; and, (2) decrease of acetoclastic and hydrogenotrophic methanogenesis due to [Formula: see text] inhibition. Model A3 shows the potential for iron to remove free SIS (and consequently inhibition) and instead promote iron sulfide (XFeS) precipitation. It also reduces the quantities of struvite ( [Formula: see text] ) and calcium phosphate ( [Formula: see text] ) that are formed due to its higher affinity for phosphate anions. This study provides a detailed analysis of the different model assumptions, the effect that operational/design conditions have on the model predictions and the practical implications of the proposed model extensions in view of plant-wide modelling/development of resource recovery strategies.

Evaluation of aeration energy saving in two modified activated sludge processes

A variety of modified activated sludge processes are widely used in wastewater treatment plants (WWTPs) for removing organics and nutrients (N and P). Since energy consumption in aeration basin accounts for the major part of the overall energy usage in WWTPs, efforts have been made to find ways to reduce aeration energy. In this study, two modified activated sludge processes in a pilot scale designed for nutrient removal were evaluated for the extent of energy saving: (1) ABA(2) process - adjusting air on/off period (i.e., with a temporal change); and (2) MB-A(2)O process - changing volume ratio of aerobic tank to anoxic tank (i.e., with a spatial change). For the 1st process, the air on/off period was fixed at 60min/45min with aerobic fraction being 0.57, while for the 2nd process, the aerobic/anoxic volume ratio was reduced from 0.58 to 0.42. The results demonstrate that the effluent COD, TN, NH4(+) and TP concentrations are acceptable while reduced aeration time/volume certainly saves significant energy consumption. To the best of our knowledge, this is 1st attempt to reduce the aeration period or aeration volume to save the aeration energy in these two modified activated sludge processes. The implication of these observations is further discussed.

A plant-wide aqueous phase chemistry module describing pH variations and ion speciation/pairing in wastewater treatment process models

There is a growing interest within the Wastewater Treatment Plant (WWTP) modelling community to correctly describe physico-chemical processes after many years of mainly focusing on biokinetics. Indeed, future modelling needs, such as a plant-wide phosphorus (P) description, require a major, but unavoidable, additional degree of complexity when representing cationic/anionic behaviour in Activated Sludge (AS)/Anaerobic Digestion (AD) systems. In this paper, a plant-wide aqueous phase chemistry module describing pH variations plus ion speciation/pairing is presented and interfaced with industry standard models. The module accounts for extensive consideration of non-ideality, including ion activities instead of molar concentrations and complex ion pairing. The general equilibria are formulated as a set of Differential Algebraic Equations (DAEs) instead of Ordinary Differential Equations (ODEs) in order to reduce the overall stiffness of the system, thereby enhancing simulation speed. Additionally, a multi-dimensional version of the Newton-Raphson algorithm is applied to handle the existing multiple algebraic inter-dependencies. The latter is reinforced with the Simulated Annealing method to increase the robustness of the solver making the system not so dependent of the initial conditions. Simulation results show pH predictions when describing Biological Nutrient Removal (BNR) by the activated sludge models (ASM) 1, 2d and 3 comparing the performance of a nitrogen removal (WWTP1) and a combined nitrogen and phosphorus removal (WWTP2) treatment plant configuration under different anaerobic/anoxic/aerobic conditions. The same framework is implemented in the Benchmark Simulation Model No. 2 (BSM2) version of the Anaerobic Digestion Model No. 1 (ADM1) (WWTP3) as well, predicting pH values at different cationic/anionic loads. In this way, the general applicability/flexibility of the proposed approach is demonstrated, by implementing the aqueous phase chemistry module in some of the most frequently used WWTP process simulation models. Finally, it is shown how traditional wastewater modelling studies can be complemented with a rigorous description of aqueous phase and ion chemistry (pH, speciation, complexation).

A systematic study of multiple minerals precipitation modelling in wastewater treatment

Mineral solids precipitation is important in wastewater treatment. However approaches to minerals precipitation modelling are varied, often empirical, and mostly focused on single precipitate classes. A common approach, applicable to multi-species precipitates, is needed to integrate into existing wastewater treatment models. The present study systematically tested a semi-mechanistic modelling approach, using various experimental platforms with multiple minerals precipitation. Experiments included dynamic titration with addition of sodium hydroxide to synthetic wastewater, and aeration to progressively increase pH and induce precipitation in real piggery digestate and sewage sludge digestate. The model approach consisted of an equilibrium part for aqueous phase reactions and a kinetic part for minerals precipitation. The model was fitted to dissolved calcium, magnesium, total inorganic carbon and phosphate. Results indicated that precipitation was dominated by the mineral struvite, forming together with varied and minor amounts of calcium phosphate and calcium carbonate. The model approach was noted to have the advantage of requiring a minimal number of fitted parameters, so the model was readily identifiable. Kinetic rate coefficients, which were statistically fitted, were generally in the range 0.35-11.6 h(-1) with confidence intervals of 10-80% relative. Confidence regions for the kinetic rate coefficients were often asymmetric with model-data residuals increasing more gradually with larger coefficient values. This suggests that a large kinetic coefficient could be used when actual measured data is lacking for a particular precipitate-matrix combination. Correlation between the kinetic rate coefficients of different minerals was low, indicating that parameter values for individual minerals could be independently fitted (keeping all other model parameters constant). Implementation was therefore relatively flexible, and would be readily expandable to include other minerals.

Expanded graphite loaded with lanthanum oxide used as a novel adsorbent for phosphate removal from water: performance and mechanism study

A novel adsorbent of expanded graphite (EG) loaded with lanthanum oxide (EG-LaO) was prepared for phosphate removal from water and characterized by scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. The effects of impregnation time, La3+ concentration, activation time, and activation temperature on the phosphate removal performance of the adsorbent were studied for optimization of preparation conditions. Isothermal adsorption studies suggested that the Langmuir model fits the experimental data well. Adsorption kinetics investigation showed that the pseudo-second-order model fits the experimental data quite well, indicating that the adsorption process is mainly a process of chemical adsorption, and chloride ions compete to react with the active sites of the adsorbent but do not prevent phosphate from adsorbing onto EG-LaO. The adsorption mechanism studies were performed by a pH dependence study of the adsorption amount. The results demonstrated that the probable mechanisms of phosphate adsorption on EG-LaO were electrostatic and Lewis acid-base interactions in addition to ion exchange.

Effects of ionic strength and ion pairing on (plant-wide) modelling of anaerobic digestion

Plant-wide models of wastewater treatment (such as the Benchmark Simulation Model No. 2 or BSM2) are gaining popularity for use in holistic virtual studies of treatment plant control and operations. The objective of this study is to show the influence of ionic strength (as activity corrections) and ion pairing on modelling of anaerobic digestion processes in such plant-wide models of wastewater treatment. Using the BSM2 as a case study with a number of model variants and cationic load scenarios, this paper presents the effects of an improved physico-chemical description on model predictions and overall plant performance indicators, namely effluent quality index (EQI) and operational cost index (OCI). The acid-base equilibria implemented in the Anaerobic Digestion Model No. 1 (ADM1) are modified to account for non-ideal aqueous-phase chemistry. The model corrects for ionic strength via the Davies approach to consider chemical activities instead of molar concentrations. A speciation sub-routine based on a multi-dimensional Newton-Raphson (NR) iteration method is developed to address algebraic interdependencies. The model also includes ion pairs that play an important role in wastewater treatment. The paper describes: 1) how the anaerobic digester performance is affected by physico-chemical corrections; 2) the effect on pH and the anaerobic digestion products (CO2, CH4 and H2); and, 3) how these variations are propagated from the sludge treatment to the water line. Results at high ionic strength demonstrate that corrections to account for non-ideal conditions lead to significant differences in predicted process performance (up to 18% for effluent quality and 7% for operational cost) but that for pH prediction, activity corrections are more important than ion pairing effects. Both are likely to be required when precipitation is to be modelled.

Identification of inorganic and organic species of phosphorus and its bio-availability in nitrifying aerobic granular sludge

Phosphorus (P) recovery from sewage sludge is necessary for a sustainable development of the environment and thus the society due to gradual depletion of non-renewable P resources. Aerobic granular sludge is a promising biotechnology for wastewater treatment, which could achieve P-rich granules during simultaneous nitrification and denitrification processes. This study aimed to disclose the changes in inorganic and organic P species and their correlation with P mobility and bio-availability in aerobic granules. Two identical square reactors were used to cultivate aerobic granules, which were operated for 120 days with influent ammonia nitrogen (NH₄-N) of 100 mg/L before day 60 and then increased to 200 mg/L during the subsequent 60 days (chemical oxygen demand (COD) was kept constant at 600 mg/L). The aerobic granules exhibited excellent COD removal and nitrification efficiency. Results showed that inorganic P (IP) was about 61.4-67.7% of total P (TP) and non-apatite inorganic P (NAIP) occupied 61.9-70.2% of IP in the granules. The enrichment amount of NAIP and apatite P (AP) in the granules had strongly positive relationship with the contents of metal ions, i.e. Fe and Ca, respectively accumulated in the granules. X-ray diffraction (XRD) analysis and solution index calculation demonstrated that hydroxyapatite (Ca₅(PO₄)₃(OH)) and iron phosphate (Fe₇(PO₄)₆) were the major P minerals in the granules. Organic P (OP) content maintained around 7.5 mg per gram of biomass in the aerobic granules during the 120 days' operation. Monoester phosphate (21.8% of TP in extract), diester phosphate (1.8%) and phosphonate (0.1%) were identified as OP species by Phosphorus-31 nuclear magnetic resonance (³¹P NMR). The proportion of NAIP + OP to TP was about 80% in the granules, implying high potentially mobile and bio-available P was stored in the nitrifying aerobic granules. The present results provide a new insight into the characteristics of P species in aerobic granules, which could be helpful for developing P removal and recovery techniques through biological wastewater treatment.

Contribution of precipitates formed in fermentation liquor to the enhanced biogasification of ammonia-rich swine manure by wheat-rice-stone addition

This study investigated the effect of wheat-rice-stone (WRS) addition on mesophilic anaerobic fermentation for methane production from swine manure under high ammonia nitrogen level (5145mg-N/L) in addition to exploring its possible mechanisms involved. Results show that addition of WRS could not only effectively increase methane production by 72% from 82.8 (control) to 142.7ml/g-VS but also remarkably shorten the effective biogasification period from 40 (control) to 20days. In addition, WRS addition could promote the degradation of n-HBu and slow down the accumulation of other volatile fatty acids (VFAs) species, achieving much faster VFAs utilization rate and better pH maintaining capability. More specifically, the existing and released ions especially Ca(2+), Mg(2+), and Fe(3+/2+) were supposed to form precipitates (like struvite and Fe-precipitates) with NH4(+) and PO4(3-) rich in the fermentation liquor, probably contributing a lot to the decreased ammonia concentration and enhanced biogasification under WRS addition.

A generalised chemical precipitation modelling approach in wastewater treatment applied to calcite

Process simulation models used across the wastewater industry have inherent limitations due to over-simplistic descriptions of important physico–chemical reactions, especially for mineral solids precipitation. As part of the efforts towards a larger Generalized Physicochemical Modelling Framework, the present study aims to identify a broadly applicable precipitation modelling approach. The study uses two experimental platforms applied to calcite precipitating from synthetic aqueous solutions to identify and validate the model approach. Firstly, dynamic pH titration tests are performed to define the baseline model approach. Constant Composition Method (CCM) experiments are then used to examine influence of environmental factors on the baseline approach. Results show that the baseline model should include precipitation kinetics (not be quasi-equilibrium), should include a 1st order effect of the mineral particulate state (Xcryst) and, for calcite, have a 2nd order dependency (exponent n = 2.05 ± 0.29) on thermodynamic supersaturation (σ). Parameter analysis indicated that the model was more tolerant to a fast kinetic coefficient (kcryst) and so, in general, it is recommended that a large kcryst value be nominally selected where insufficient process data is available. Zero seed (self nucleating) conditions were effectively represented by including arbitrarily small amounts of mineral phase in the initial conditions. Both of these aspects are important for wastewater modelling, where knowledge of kinetic coefficients is usually not available, and it is typically uncertain which precipitates are actually present. The CCM experiments confirmed the baseline model, particularly the dependency on supersaturation. Temperature was also identified as an influential factor that should be corrected for via an Arrhenius-style correction of kcryst. The influence of magnesium (a common and representative added impurity) on kcryst was found to be significant but was considered an optional correction because of a lesser influence as compared to that of temperature. Other variables such as ionic strength and pH were adequately captured by the quasi-equilibrium description of the aqueous-phase and no further kinetic corrections were required. The baseline model is readily expandable to include other precipitation reactions. For simple representations, large values for kcryst with n = 2 (or n = 2 or 3 for other minerals, as appropriate) should be selected without corrections to kcryst. Where accuracy is required (e.g., in mechanistic studies), machine estimation of kcryst should be performed with robust process data and kcryst should at least be corrected for temperature.

Evaluation of different configurations of hybrid membrane bioreactors for treatment of domestic wastewater

Four membrane bioreactors (MBRs) with the same dimensions were studied for 180 days: three hybrid growth membrane bioreactors with biofilm attached in different packing media and a conventional MBR (C-MBR). The four MBRs had an identical membrane module of hollow fiber with a nominal porous diameter of 0.4 μm. The MBRs were: (1) a C-MBR; (2) a moving bed membrane bioreactor (MB-MBR), which was packed with 2 L of carrier Kaldnes-K1, presenting an exposed surface area of 678.90 m²/m³; (3) a non-submerged organic fixed bed (OFB-MBR) packed with 6.5 L of organic packing media composed of a mixture of cylindrical pieces of wood, providing an exposed surface area of 178.05 m²/m³; and (4) an inorganic fixed bed non-submerged membrane bioreactor (IFB-MBR) packed with 6 L of spherical volcanic pumice stone with an exposed surface area of 526.80 m²/m³. The four MBRs were fed at low organic loading (0.51 ± 0.19 kgCOD/m³ d). The results were recorded according to the behavior of the total resistance, transmembrane pressure (TMP), permeability, and removal percentages of the nutrients during the experimental time. The results showed that the MB-MBR presented the better performance on membrane filtration, while the higher nutrient removals were detected in the OFB-MBR and IFB-MBR.

Phosphorus removal from domestic wastewater by Nelumbo nucifera Gaertn. and Cyperus alternifolius L

Domestic wastewater is a source of phosphorus contamination that causes eutrophication when it contaminates aquatic environments. Nelumbo nucifera Gaertn. and Cyperus alternifolius L. were applied for phosphorus removal from domestic wastewater. From the study, phosphorus in domestic wastewater was removed from the initial concentration of 1.038 ± 0.001 mgL(-1) to 0.094 ± 0.001 and 0.048 ± 0.004 mgL(-1) by N. nucifera and C. alternifolius, respectively, within 5 days. In addition, total Kjeldahl nitrogen (TKN) and chemical oxygen demand (COD) also decreased when wetland systems were applied the same as treatment with conventional method (chemical + activated sludge process). However, the plant removed TDS better than the conventional method. During 5 cycles of exposure, the two plants still survived and were healthy. The weight of plants increased after the experiment from 4060 ± 0.05 g to 4820 ± 0.17 g of N. nucifera, and from 4000 ± 0.00 g to 4600 ± 0.14 g of C. alternifolius. Phosphorus content also increased in both plants after the experiment. However, in the wetland system, phosphorus was removed mainly by the soil, followed by the plants, and then microorganisms. The domain group in the microbial community of both wetland systems was Pseudomas sp.

High efficiency removal of phosphate from water by zirconium sulfate-surfactant micelle mesostructure immobilized on polymer matrix

A zirconium sulfate-surfactant micelle mesostructure (ZS) was synthesized to investigate its capacity for phosphate removal from water. Its phosphate adsorption kinetics, the effect of pH and interfering anions, adsorption isotherm, desorption capacity, and reusability were investigated. The adsorption isotherms could be described by the Langmuir model. The ZS was an effective adsorbent for phosphate with a very high adsorption capacity (114 mg P/g ZS). The phosphate adsorption capacity increased with decrease in pH. Although the adsorption of nitrate, chloride and acetate ions was negligible, bicarbonate ions were found to be possible interfering anions. The adsorbed phosphate was desorbed effectively using NaOH solution. Since breakage of ZS particles resulted when using NaOH, ZS was immobilized on a polymer matrix and a 50-cycle adsorption-desorption test was carried out to determine the ZS-immobilized polymer (P-ZS) reusability. The P-ZS retained its functionality and adsorption and desorption capacity over 50 cycles without loss of original capacity. A phosphate solution containing about 10 mg P/L was treated in a column packed with P-ZS. The phosphate could be adsorbed completely onto P-ZS up to 1020 bed volumes. These results indicate clearly that ZS is a highly effective adsorbent for phosphate and enables the removal of phosphate from water.

Control of methionine biosynthesis genes by protein kinase CK2-mediated phosphorylation of Cdc34

Methionine and metabolites such as S-adenosylmethionine (AdoMet) are of vital importance for eukaryotes; AdoMet is the main donor of methyl groups and is involved in expression control of the methionine biosynthesis genes (MET genes). Genome-wide expression profiling of protein kinase CK2 deletion strains of the budding yeast Saccharomyces cerevisiae has indicated a function for CK2 in MET gene control. Deletion of the regulatory CK2 subunits leads to MET gene repression, presumably due to an impaired phosphorylation of the ubiquitin-conjugating enzyme Cdc34, which controls the central MET gene transcription factor Met4. We show that CK2 phosphorylates Cdc34 at two sites and one of these, Ser282, has a significant impact on MET gene expression in vivo, and that high AdoMet levels inhibit CK2. The data provide evidence for a control of MET gene expression by protein kinase CK2-mediated phosphorylation of Cdc34, and appear to suggest a feedback control loop in which high AdoMet-levels are limiting CK2 activity and thus MET gene expression.