Mechanism Of Phosphorus Removal Research Articles

Synergistic phosphorus removal mechanism of Tetrasphaera enrichment in a micro-pressure swirl reactor

To investigate the effect of Tetrasphaera’s enrichment on phosphorus removal mechanism, three micro-pressure swirl reactor (MPSR) groups were used to experiment on sewage treatment under different SRT (17.2, 50.8, and 68.2 d). Results showed that Tetrasphaera enrichment in the MPSR system was promoted by extending the SRT. After extending the SRT from 17.2 to 68.2 d, the relative abundance of Tetrasphaera increased from 3.1% to 12.1%, and the TP removal efficiency maintained above 92%. The internal circulation results indicated that after extending the SRT, glycogen and polyhydroxybutyrate were co-synthesized during the anaerobic stage, which enhanced the driving force of nutrient removal. Analysis of the microbial composition and functional gene prediction indicated that efficient phosphorus removal can be attributed to the enrichment of Tetrasphaera at long SRT. Overall, the synergistic mechanisms of Tetrasphaera in the organic matter degradation and phosphorus removal processes were integrated into the MPSR.

Resource recovery of water treatment plant sludge and river sediment as phosphorus removal material: feasibility and mechanisms

ABSTRACT Excessive phosphorus is a critical contributor to eutrophication, necessitating the use of substantial amounts of phosphorus removal materials. To address the challenge of managing water treatment plant sludge and river sediment while also supplying mass-produced phosphorus-removing materials for projects targeting phosphorus removal in water bodies, this paper attempted to study the feasibility of preparing phosphorus removal materials by mixing and calcining water treatment plant sludge and river sediment (C-WTPS/RS). The study examined the transformation of phosphorus forms in C-WTPS/RS before and after adsorption. Furthermore, X-ray fluorescence spectrometer, zeta potential, scanning electron microscope, Brunauer–Emmett–Teller equation, Barrett–Joyner–Halenda model, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy were employed to elucidate the phosphorus removal mechanisms. The results showed that C-WTPS/RS was effective in removing phosphorus from water and preventing the release of phosphorus from the sediment. Additionally, C-WTPS/RS had a low risk of releasing phosphorus and metals within the pH range of natural water bodies. These proved that it is feasible to remove phosphorus by C-WTPS/RS. After adsorption, the increased phosphorus in C-WTPS/RS was mainly dominated by the non-apatite inorganic phosphorus within inorganic phosphorus. The main phosphorus removal mechanisms of C-WTPS/RS were physical adsorption, electrostatic adsorption, chemical precipitation, and ligand exchange.

Removal mechanism of phosphorus in water by calcium hydroxide modified copper tailings

With the development of industry and agriculture, eutrophication caused by increasing amounts of phosphorus in the environment has attracted people's attention. On the other hand, copper tailings (CT) is a kind of solid waste with large quantity, large area, and easy to cause groundwater and soil pollution. CT is also a potential resource because of its large specific surface area. CT is intended to be used as an adsorbent for removal phosphate in water, but trace heavy metals and a small amount of phosphate in CT may bring negative effects. Calcium hydroxide (Ca(OH)2) was used to modify CT (CCT), hoping to fix the heavy metals and phosphate in CT at the same time. It was found that the removal capacity of CCT was significantly higher than that of CT. The process of phosphate removal by CCT involves electrostatic sorption and surface precipitation, and there is a synergistic effect between CT and Ca(OH)2. The phosphate removal rate of CCT-0.4 increased with the increase of pH value under alkaline conditions. The XRD patterns of phosphate sorption by CCT mean that Ca3(PO4)2, Ca5(PO4)3(OH) and AlPO4 exist in CCT after phosphate removal, indicating that surface precipitation occurs during the removal process. In summary, the removal mechanism of phosphate by CCT is mainly electrostatic attraction and surface precipitation.

Effect of phosphorus impurities on sulfoaluminate cement-modified gypsum-based self-leveling mortar and improvement method

The preparation of gypsum-based self-leveling mortar (GSLM) from solid waste-derived sulfoaluminate cement-modified hemihydrate gypsum is an effective path to enhance its mechanical properties. However, the phosphorus impurities in phosphogypsum (PG) still pose a challenge to the hemihydrate gypsum & sulfoaluminate cement composite system. To evaluate the impact of phosphorus impurities and develop targeted removal strategies, this study first assessed the effects of different types of phosphorus impurities on the mechanical properties and hydration characteristics of the GSLM. Then, a method of pretreating PG with carbide slag (CS) was proposed, and the removal efficiency and mechanism of phosphorus were examined by ICP-OES and XPS testing. The results indicated that the soluble phosphorus impurities severely inhibit the hydration of both CŜH0.5 and C4A3Ŝ, leading to a most notable reduced mechanical performance. The sequence of inhibitory action was as follows: H3PO4 >> Ca(H2PO4)2·H2O > CaHPO4·2H2O > Ca3(PO4)2. CS could effectively immobilize the soluble phosphorus in PG. The pretreatment by CS notably enhanced the hydration degree of the GSLM by converting soluble phosphorus into Ca3(PO4)2 beforehand. In addition, the alkaline environment provided by CS promoted the ettringite formation. When the CS content approaches 3%, a PG-based GSLM with good performances meeting the G20 standard requirements of GSLM can be prepared.

Harmless disposal of phosphogypsum synergized red mud: Harmful element control and material utilization

Soluble P2O5 and fluorine in phosphogypsum can jeopardize the environment and even human health. The application in building materials is a pathway to consume phosphogypsum on a large scale. However, the presence of soluble phosphorus causes significant retardation that reduces the early strength of building materials containing phosphogypsum. In this study, the mechanism of soluble phosphorus removal from phosphogypsum by red mud were studied. The synergistic effect of phosphogypsum, red mud and blast furnace slag for the preparation of high-sulfur cementitious materials was also investigated. The results demonstrated that the soluble phosphorus was transformed to inert material and was completely stabilized when red mud dosing reached 20 %. The slow setting was significantly improved, causing an increase in 3-d compressive strength. More hydration products were generated to enhance the early strength, indicating that the optimal synergistic effect of phosphogypsum, red mud and blast furnace slag occurred. In addition, the compressive strength reached 21.40 MPa (3 d), 29.60 MPa (7 d), and 48.60 MPa (28 d) when the total admixture of phosphogypsum and red mud was 45 %. The environmental performance research also shows that the material was green and non-polluting. This paper advocates the use of the physicochemical properties of different solid wastes to dispose of hazardous substances in phosphogypsum rather than the use of natural resources.

The feasibility and efficiency of fly ash as an absorbent for phosphate removal

Abstract Phosphorus is an essential nutrient required for the growth and development of plants, animals, and microorganisms. However, excessive phosphorus in wastewater can cause detrimental effects on aquatic ecosystems, leading to eutrophication and harmful algal blooms. Thus, the removal of phosphorus from wastewater is crucial to protect water bodies and maintain environmental sustainability. The removal mechanism of phosphorus by fly ash involves both physical and chemical processes. The high surface area and porosity of fly ash facilitate the adsorption of phosphorus molecules onto its surface, while the presence of calcium and aluminium oxides in fly ash enables the formation of stable precipitates with phosphorus in the solution. Numerous studies have been conducted to investigate the feasibility and efficiency of fly ash as an absorbent for phosphorus removal. These studies have demonstrated that fly ash can effectively remove phosphorus from wastewater, achieving removal efficiencies of up to 90%. The performance of fly ash as an absorbent can be enhanced through various strategies, such as modification with reactive substances or combining it with other materials. Objective of this study is parameters that effect on phosphorus absorption using fly ash as absorbent. The results showed that increasing pH decrease % removal.

Inhibition of phosphorus removal performance in activated sludge by Fe(III) exposure: transitions in dominant metabolic pathways.

Simultaneous chemical phosphorus removal process using iron salts (Fe(III)) has been widely utilized in wastewater treatment to meet increasingly stringent discharge standards. However, the inhibitory effect of Fe(III) on the biological phosphorus removal system remains a topic of debate, with its precise mechanism yet to be fully understood. Batch and long-term exposure experiments were conducted in six sequencing batch reactors (SBRs) operating for 155 days. Synthetic wastewater containing various Fe/P ratios (i.e., Fe/P = 1, 1.2, 1.5, 1.8, and 2) was slowly poured into the SBRs during the experimental period to assess the effects of acute and chronic Fe(III) exposure on polyphosphate-accumulating organism (PAO) growth and phosphorus metabolism. Experimental results revealed that prolonged Fe(III) exposure induced a transition in the dominant phosphorus removal mechanism within activated sludge, resulting in a diminished availability of phosphorus for bio-metabolism. In Fe(III)-treated groups, intracellular phosphorus storage ranged from 3.11 to 7.67 mg/g VSS, representing only 26.01 to 64.13% of the control. Although the abundance of widely reported PAOs (Candidatus Accumulibacter) was 30.15% in the experimental group, phosphorus release and uptake were strongly inhibited by high dosage of Fe(III). Furthermore, the abundance of functional genes associated with key enzymes in the glycogen metabolism pathway increased while those related to the polyphosphate metabolism pathway decreased under chronic Fe(III) stress. These findings collectively suggest that the energy generated from polyhydroxyalkanoates oxidation in PAOs primarily facilitated glycogen metabolism rather than promoting phosphorus uptake. Consequently, the dominant metabolic pathway of communities shifted from polyphosphate-accumulating metabolism to glycogen-accumulating metabolism as the major contributor to the decreased biological phosphorus removal performance.

Modified rare earth waste composite material for simultaneous denitrification and recovery of phosphate in water

Nitrogen and phosphorus discharged into water bodies with sewage are the main causes of water eutrophication.Currently,the adsorption method is a cost-effective and efficient denitrification and phosphorus removal technology. In this study, waste polishing powder, manganese dioxide and sepiolite are used as raw materials, and a novel adsorbent of Sep-pp-MnO2 is prepared through co-precipitation and redox methods for simultaneous removal of ammonia nitrogen and recovery of phosphate in water.The physicochemical properties of the adsorbent are characterised, and the adsorption performances and denitrification and phosphorus removal mechanisms are determined. Results showed that,at a temperature of 25°C and pH of 8, the maximum removal of ammonia nitrogen reaches 11.47 mg/g, while the adsorption capacity for phosphates is 14.93 mg/g. Adsorption mechanisms indicated that the removal mechanism of phosphate is ligand exchange, while the removal mechanism of ammonia nitrogen involves electrostatic attraction and oxidation to nitrogen. Recycling experiments showed that after five desorption cycles, the material could achieve a removal of 4.7 mg/g for ammonia nitrogen, an adsorption capacity of 8.25 mg/g for phosphate and a phosphate recovery rate of 55 % after desorption with 0.1 M NaOH solution. Municipal wastewater validation experiments demonstrated that when the dosage of Sep-pp-MnO2 was 4 g/L,Treated water met the Class B requirements of the comprehensive emission standard for pollutants from urban sewage treatment plants in China (GB18918–2002). This study explores a new method for efficient simultaneous nitrogen and phosphorus removal in water and provides a feasible idea for alleviating the shortage of phosphate rock resources.

Promoting the ecological restoration of black and odorous water by Fe/C internal electrolysis

Three ecological restoration systems vegetated with Vallisneria natans, containing ceramisite (VC), bio-carrier and ceramisite (BVC) or Fe/C filler, bio-carrier and ceramisite (FBVC) as functional substrates were constructed for black and odorous water restoration. The average ammonia nitrogen (NH4+-N) conversion rate of FBVC (90.51 %) was similar to that of BVC (88.49 %) and significantly higher than that of VC (53.35 %). However, the average total nitrogen (TN) removal rate of FBVC (84.93 %) was much higher than that of BVC (73.02 %) and VC (52.06 %). Additionally, the average COD removal efficiencies for VC, BVC and FBVC were 52.54 %, 71.84 % and 80.59 %, respectively; while they were 69.72 %, 74.79 % and 97.38 % for total phosphorus (TP). High-throughput sequencing revealed that the richness and diversity of autotrophic denitrifying bacteria, such as Pseudomonas, Pseudoxanthomonas, Arenimonas and Hydrogenophaga increased significantly in FBVC, while the plant growth-promoting bacterium Rhodobacter was dominant. Overall, this study demonstrated that a Vallisneria natans based ecological restoration system coupled with Fe/C internal electrolysis (Fe/C-IE) effectively improved the quality of black and odorous water. In addition, the mechanism of nitrogen, phosphorus and carbon removal was proposed.

Mechanism of phosphorus removal from Si–Al melt by hydrogen

Phosphorus is a critical impurity in solar cell that deteriorates the photovoltaic convection efficiency of solar cell. Phosphorus removal from metallurgical grade silicon by injecting H2 and Ar-50%H2 mixture during the Al–Si solvent refining was investigated. With gas injecting into the Al–Si melt, the phosphorus concentration in the refined Si decreased with an increase of the injecting time. When the gas injecting time was 2.5 h, the removal fraction of phosphorus increased to 93%, an improvement of 63% compared with 57% without Ar–H2 injection. The effects of H2 proportion, gas refining temperature, and Si proportion in the alloy were investigated. The kinetics of phosphorus removal with Ar–H2 injection were clarified. The mass transfer coefficient of phosphorus was 9.07 × 10−9 m/s during the Ar–H2-assisted solvent refining process. Three mechanisms of phosphorus removal were discussed for this gas-solvent composite refining process. These results demonstrate that H2 or Ar–H2 gas injecting treatment is an effective strategy to further improve the phosphorus removal and reduce the cost during Al–Si solvent refining.

Synergistic Removal of Nitrogen and Phosphorus in Constructed Wetlands Enhanced by Sponge Iron

Insufficient denitrification and limited phosphorus uptake hinder nitrogen and phosphorus removal in constructed wetlands (CWs). Sponge iron is a promising material for the removal of phosphorus and nitrogen because of its strong reducing power, high electronegativity, and inexpensive cost. The influence of factors including initial solution pH, dosage, and the Fe/C ratio was investigated. A vertical flow CW with sponge iron (CW-I) was established, and a traditional gravel bed (CW-G) was used as a control group. The kinetic analysis demonstrated that for both nitrogen and phosphorus, pseudo-second-order kinetics were superior. The theoretical adsorption capacities of sponge iron for nitrate (NO3−-N) and phosphate (PO43−-P) were 1294.5 mg/kg and 583.6 mg/kg, respectively. Under different hydraulic retention times (HRT), CW-I had better total nitrogen (TN) and total phosphorus (TP) removal efficiencies (6.08–15.18% and 5.00–20.67%, respectively) than CW-G. The enhancing effect of sponge iron on nitrogen and phosphorus removal was best when HRT was 48 h. The increase in HRT improved not only the nitrogen and phosphorus removal effects of CWs but also the reduction capacity of iron and the phosphorus removal effect. The main mechanisms of synergistic nitrogen and phosphorus removal were chemical reduction, ion exchange, electrostatic adsorption, and precipitation formation.

Effects of microorganisms on nitrogen and phosphorus removal from wastewater

Nitrogen and phosphorus are key to plant growth. The balance of nitrogen and phosphorus is crucial in nature. Excessive nitrogen and phosphorus content in wastewater has caused great harm to the environment. Traditional nitrogen and phosphorus removal methods can no longer meet the treatment standards for nitrogen and phosphorus. This article introduces the hazards of nitrogen and phosphorus, and points out the harm to nature and human beings if they are not up to standard in wastewater treatment plants. Through the analysis and discussion of several methods, the advantages of microbial nitrogen and phosphorus removal are explained. This article further summarizes several representative new microorganisms and microbial processes through the types and mechanisms of microbial nitrogen and phosphorus removal. Anammox bacteria can accept other electron pools to increase nitrogen removal efficiency. Denitrifying phosphorus-removing bacteria can achieve energy saving and carbon reducing effects through endogenous denitrification. Besides, the enhanced biological phosphorus removal process can allow denitrifying phosphorus accumulating bacteria to absorb phosphorus in an anaerobic, anoxic, aerobic alternating environment. The moving bed biofilm reactor (MBBR) abandons the disadvantages of the traditional biofilm method, while retaining the advantages of the traditional biofilm method such as shock load resistance and low sludge production. These new microorganisms and new microbial processes have become important applications in future nitrogen and phosphorus removal processes due to their advantages of high efficiency, low energy, and no secondary pollution. This article is conducive to the promotion of microbial-based wastewater treatment and can provide suggestions for the sustainable development of wastewater treatment.

Interactions between bacteria and microalgae in microalgal-bacterial symbiotic wastewater treatment systems: mechanisms and influencing factors

Microalgal-bacterial symbiotic wastewater treatment systems (MBSWTSs) have received widespread attention due to their capacity to achieve high pollutant removal efficiency during wastewater treatment, with low energy consumption requirements, efficient carbon sequestration, and wastewater resource utilization. This paper provides an overview of the treatment performance and current research status of MBSWTSs, including a detailed summary of the mechanisms of nitrogen, phosphorus, and carbon removal by MBSWTSs and the interactions between bacteria and microalgae. In particular, this review focuses on the influence of operational parameters on the regulation of the symbiotic system, such as the microalgal:bacterial ratio, N:P ratio, external carbon source, dissolved oxygen concentration, aeration mode, and light availability. Among these factors, the microalgal:bacterial ratio, carbon source, and light availability have an important influence on microalgal-bacterial competition, as well as the trophic mode of the system, biomass production, and the capacity for the process to be practically applied on a large scale. MBSWTSs still have some challenging aspects that have hindered their development and application, such as the unknown mechanism of microalgal-bacterial co-metabolism, limited previous practical applications, algal contamination, and harvesting difficulties. To overcome these challenges, future research requires a multidisciplinary approach, incorporating life sciences, material science, and other disciplines. Comprehensive research should be conducted on the metabolic mechanisms of MBSWTSs, the optimization of process performance and waste resource utilization, providing a theoretical and practical foundation for the practical application of MBSWTSs.

Study on the removal efficacy and mechanism of phosphorus from wastewater by eggshell-modified biochar.

The excessive discharge of phosphorus from rural domestic sewage is a problem that worthy of attention. If the phosphorus in the sewage were recovered, addressing this issue could significantly contribute to mitigating the global phosphorus crisis. In this study, corn straw, a common agricultural waste, was co-pyrolytically modified with eggshells, a type of food waste from university cafeterias. The resulting product, referred to as corn straw eggshell biochar (EGBC) was characterized using SEM, XRD, XPS, XRF, and other methods. Batch adsorption experiments were conducted to determine the optimal preparation conditions of EGBC and to explore its adsorption characteristics. EGBC showed strong adsorption effectiveness within a pH range of 5-12. The adsorption isotherm closely followed the Sips model (R2 > 0.9011), and the adsorption kinetics were more consistent with the pseudo-second-order model (R2 > 0.9899). The process was found to be both spontaneous and endothermic. Under optimal conditions, the phosphorus adsorption capacity of EGBC was measured to be 288.83 mg/g. This demonstrates the high efficiency of EGBC for phosphorus removal and illustrates an effective method of utilizing food waste for environmental remediation. PRACTITIONER POINTS: Biochar prepared from waste eggshell was used to removal and recovery phosphorus in wastewater treatment. EGBC has an impressive adsorption capacity that can reach up to 288.83 mg/g. EGBC has excellent adsorption and filtration capabilities, and there is a sudden increase in concentration at 900 min in the breakthrough curve of EGBC. EGBC has good regeneration performance, with an adsorption effect of 65% and an adsorption capacity of 121 mg/g after four desorption and regeneration cycles.

Phosphorus removal of coal-based bottom ash: Performance evaluation and mechanism exploration

In this paper, the phosphorus removal efficiency and capability and pore structure and composition of coal-based bottom ash before and after phosphorus removal are studied to reveal the phosphorus removal mechanism. The results show that the phosphorus removal rate of bottom ash increases with the increase of pH value; When the pH value is 8, the phosphorus removal rate can reach more than 95%. The highest desorption rate is only 2.42% and the pseudo-second order model can be better fitted with the phosphorus removal process of bottom ash, indicating chemical adsorption is the control mechanism. The maximum phosphorus removal capacity is 5.54 mg/g. After phosphorus removal the fractal dimension and porosity decrease, and the specific surface area increases, indicating that the complexity of the pore structure decreases, and the roughness of the pore wall increases. The characteristic peak of brushite (CaHPO4·2H2O) in the XRD spectrum and HPO42− at 2362 cm−1, 985 cm−1 and 800-650 cm−1 appear, respectively. In the XRF results, P2O5/SiO2 ratio increases from 0.008 to 0.089, but SO3/SiO2 ratio decreases from 0.047 to 0.027. The phosphorus removal mechanism of coal-based bottom ash lies in its complex pore structure and the precipitation reaction between soluble Ca2+ and HPO4− in the sewage.

Spark deposition of lanthanum-carbon composite nanoparticles embedded in a polypropylene membrane for phosphate removal in aqueous solutions

Eutrophication in water, such as rivers or lakes, is becoming increasingly serious. Controlling the phosphate concentration in such waters is the key to solving the eutrophication problem. The use of adsorption methods to limit the level of phosphate in aqueous solutions has the advantages of cost-effectiveness, ease of operation, and selectivity. In this study, a modified polypropylene (PP) membrane was used as the platform for the in-situ deposition of lanthanum-carbon (La-C) composite nanoparticles. Uniform lanthanum (La) and carbon (C) aerosols were deposited on the PP film using spark ablation, and the combined hydrothermal method was used to synthesise the nano-confinement crystal PP-La-C (PLC) for phosphorus removal in an aquatic environment. Because of the nanoconfinement of the PLC, particle agglomeration deactivation was effectively solved, and the doping of C changed the shape of La(OH)3 from particles to ultrafine nano-fibres, which resulted in a larger surface area and more abundant active sites, and the overall adsorption performance was improved. The addition of C reduced the cost, and La proved to be the main active site for phosphate capture. The adsorption test revealed a significant adsorption capability of 194.1 mg⋅P⋅g−1. Three variables, such as reaction time, dose, and original phosphate concentration, were selected and a model for predicting lake water phosphate removal efficiency was developed using the central composite design method. When PLC was used to treat water samples from Lake Qilu (Yunnan, China), the observed removal rate of total phosphorus was 94 %, which is consistent with the model prediction. A series of characterisations established that ligand exchange and multilayer adsorption were the main mechanisms of phosphorus removal.

Mechanisms of total phosphorus removal and reduction of β-lactam antibiotic resistance genes by exogenous fungal combination activated sludge

This study utilized Trichoderma and activated sludge to construct combined activated sludge (TAS). The metagenomic approach was employed to examine the shifts in microbial community structure and function of TAS under amoxicillin stress and investigate the mechanism underlying the reduction of β-lactam antibiotic resistance genes (β-ARGs). The findings demonstrated that the elevated aundance of glpa, glpd, ugpq, glpq, and glpb were primarily responsible for the reduction in total phosphorus (TP) removal by TAS. The increased abundance of Proteobacteria and Verrucomicrobia led to enhanced expression of ugpb, phnd, and phne, thereby improving the TP removal of TAS. Furthermore, antibiotic inactivation has gradually become the primary antibiotic resistance mechanism in TAS. Specifically, an increase in the abundance of OXA-309 in TAS will decrease the probability of amoxicillin accumulation in TAS. A decrease in β-ARGs diversity confirmed this. This study presents a novel approach to reducing antibiotic and ARG accumulation in sludge.

Simultaneous decarbonization and phosphorus removal by Tetrasphaera elongata with glucose as carbon source under aerobic conditions

Previous researches have recognized the vital role of Tetrasphaera elongata in enhanced biological phosphorus removal systems, but the underlying mechanisms remain under-investigated. To address this issue, this study investigated the metabolic characteristics of Tetrasphaera elongata when utilizing glucose as the sole carbon source. Results showed under aerobic conditions, Tetrasphaera elongata exhibited a glucose uptake rate of 136.6 mg/(L·h) and a corresponding phosphorus removal rate of 8.6 mg P/(L·h). Upregulations of genes associated with the glycolytic pathway and oxidative phosphorylation were observed. Noteworthily, the genes encoding the two-component sensor histidine kinase and response regulator transcription factor exhibited a remarkable 28.3 and 27.4-fold increase compared with the group without glucose. Since these genes play a pivotal role in phosphate-specific transport systems, collectively, these findings shed light on a potential mechanism for simultaneous decarbonization and phosphorus removal by Tetrasphaera elongata under aerobic conditions, providing fresh insights into phosphorus removal from wastewaters.

Microalgae biofilm photobioreactor and its combined process for long-term stable treatment of high-saline wastewater achieved high pollutant removal efficiency

High-saline wastewater treatment processes have a high energy demand, while microalgae-driven wastewater biotechnology is both economical and environmentally friendly, and the use of microalgae to treat high-saline wastewater can effectively reduce energy consumption. However, it is unclear whether the performance of microalgae reactor can be stable for a long time. In this study, an open continuous-flow biofilm photobioreactor using Dunaliella salina was innovatively constructed, and operated in combination with a membrane bioreactor (MBR) for high-saline wastewater treatment. The purpose of this study was to investigate the long-term performance of MBR, MBPBR alone and their combined operation for the removal of organic matter, phosphorus and nitrogen, explore the pathway and mechanism of nitrogen and phosphorus removal by MBPBR, and evaluate the feasibility of MBPBR-MBR integrated system for the treatment of saline wastewater. The MBR effectively removed most of the organic matter and converted ammonia nitrogen into nitrate nitrogen, which is a preferred nitrogen source for the growth of Dunaliella salina, thereby providing favorable water quality for Dunaliella salina in the subsequent MBPBR. The MBPBR, with a hydraulic retention time (HRT) of 72 h, achieved a NO3--N removal load of 74.9 g N/(m3∙d) and a removal efficiency of approximately 60 %, and the PO43--P removal load of 8.33 g P/(m3∙d) and removal efficiency of over 80 %. The MBR-MBPBR system demonstrated long-term stability, achieving removal efficiencies of 84.3 %, 81.6 %, and 91.0 % for COD, TN and PO43--P, respectively. Within the MBPBR, the growth of algae and their assimilation contributed 44.9 % and 38.7 % of the nitrogen and phosphorus removal, respectively. The abundance of Dunaliella salina in the MBPBR remained at approximately 90 % for over 40 days of operation, providing an opportunity for Dunaliella salina recovery. These findings provide valuable insights into the utilization of microalgae for the treatment of high-salinity wastewater, while also supporting the practical implementation of microalgae-based treatment methods for such wastewater.

A Study on the Removal Characteristics and Mechanism of Phosphorus from Simulated Wastewater Using a Novel Modified Red-Mud-Based Adsorption Material

In this work, a common third-generation environmentally friendly quaternary ammonium salt disinfectant, dimethyl dioctadecyl ammonium chloride (DDAC), was used as the modifier to achieve one-step rapid preparation of the modified red-mud-based adsorption material under the condition of microwave assistance, and applied it to the adsorption phosphorus in solutions. After the process of this modification, the structure of the red mud (RM) was not changed, and the DDAC modification could provide more adsorption active sites. The adsorption experiments indicated that the novel modified red mud (NMRM) exhibited a good adsorption performance for phosphorus. The adsorption capability of NMRM for phosphorus was significantly enhanced, and was about eight times higher than that of the initial RM. The kinetics model of the pseudo-second-order, which implied that phosphorus was chemically adsorbed on the surface of the NMRM, could accurately represent the adsorption procedure of NMRM. The adsorption equilibrium of NMRM could be better depicted using the isotherm model of Freundlich. It was speculated that the ion exchange might be responsible for the adsorption mechanism of NMRM for phosphorus. Thus, the NMRM is a potential material for the treatment of phosphorus-containing wastewater due to its outstanding adsorption capability.