Exploration of yellow-emitting phosphors for white LEDs from natural resources

White light-emitting diodes (LEDs) are widely used in various lighting fields as a part of energy-efficient technology. However, some shortcomings of luminescent materials for white LEDs, such as complexity of synthesis, high cost, and harmful impact on the environment, limit their practical applications to a large extent. In this respect, the present work aims to study the ability of using Berberine (BBR) chloride extracted from Rhizoma coptidis and Phellodendron Chinese herbs as yellow phosphor for white LEDs. For this, white LEDs were successfully fabricated by applying 0.006 g of BBR chloride onto the blue LED chips (450 nm). The produced LEDs exhibited good luminescence properties at a voltage of 2.4 V along with eco-friendly characteristics and low cost. The Commission International de l'Eclairage chromaticity, the correlated color temperature, and the color rendering index were determined to be (${x} = {0.32}$, ${y} = {0.33}$), 5934 K, and 74, respectively. Therefore, BBR chloride is a suitable environmentally friendly and easily accessible yellow phosphor for white LEDs.

Potential for Mycorrhizae-Assisted Phytoremediation of Phosphorus for Improved Water Quality

During this 6th Great Extinction, freshwater quality is imperiled by upland terrestrial practices. Phosphorus, a macronutrient critical for life, can be a concerning contaminant when excessively present in waterways due to its stimulation of algal and cyanobacterial blooms, with consequences for ecosystem functioning, water use, and human and animal health. Landscape patterns from residential, industrial and agricultural practices release phosphorus at alarming rates and concentrations threaten watershed communities. In an effort to reconcile the anthropogenic effects of phosphorus pollution, several strategies are available to land managers. These include source reduction, contamination event prevention and interception. A total of 80% of terrestrial plants host mycorrhizae which facilitate increased phosphorus uptake and thus removal from soil and water. This symbiotic relationship between fungi and plants facilitates a several-fold increase in phosphorus uptake. It is surprising how little this relationship has been encouraged to mitigate phosphorus for water quality improvement. This paper explores how facilitating this symbiosis in different landscape and land-use contexts can help reduce the application of fertility amendments, prevent non-point source leaching and erosion, and intercept remineralized phosphorus before it enters surface water ecosystems. This literature survey offers promising insights into how mycorrhizae can aid ecological restoration to reconcile humans' damage to Earth's freshwater. We also identify areas where research is needed.

A new approach to removing and recovering phosphorus from livestock wastewater using dolomite

Recovering phosphorus from livestock wastewater could partly mitigate the global phosphorus resource crisis. Crystallization is a promising method for removing phosphorus from wastewater, but the costs of calcium- and magnesium-containing reagents are increasing. Cheap, available, efficient materials are required to replace conventional calcium and magnesium reagents. Here, we describe a new approach to removing and recovering phosphorus from livestock wastewater of a large pig farm, containing a high phosphorus concentration. The effects of the pH, stirring speed, stirring time, and extract dose (containing calcium and magnesium) on phosphorus removal from livestock wastewater were investigated. The product was characterized by X-ray diffractometry, Fourier-transform infrared spectroscopy, and scanning electron microscopy. Under optimized conditions (pH 9.0, stirring speed 200 r/m, stirring time 600 s, Ca 207.62 mg/L, Mg 122.86 mg/L), 92% of the phosphorus was removed from livestock wastewater. The product was mainly the hydroxyapatite (Ca₅(PO₄)₃OH) precursor amorphous calcium phosphate but also contained 1.65% (by mass) magnesium ammonium phosphate (MgNH₄PO₄·6H₂O) crystals. The cost of dolomite to treat 1 m³ of high-phosphorus wastewater was 0.20 yuan (45.9%, 25.9%, and 75.9% lower than for pure MgCl₂, MgSO₄, and CaCl₂, respectively) in 2019. Using dolomite to provide calcium and magnesium effectively decreases the crystallization process cost and should encourage the use of crystallization to remove phosphorus from wastewater.

Simultaneous denitrification, phosphorus recovery and low sulfate production in a recirculated pyrite-packed biofilter (RPPB)

The simultaneous removal of nitrate (15 mg N-NO₃^- L^-1) and phosphate (12 mg P-PO₄^3- L^-1) from nutrient-polluted synthetic water was investigated in a recirculated pyrite-packed biofilter (RPPB) under hydraulic retention time (HRT) ranging from 2 to 11 h. HRT values ≥ 8 h resulted in nitrate and phosphate average removal efficiency (RE) higher than 90% and 70%, respectively. Decrease of HRT to 2 h significantly reduced the RE of both nitrogen and phosphorus. The RPPB showed high resiliency as reactor performance recovered immediately after HRT increase to 5 h. Solid-phase characterization of pyrite granules and backwashing material collected from the RPPB at the end of the study revealed that iron-phosphate, -hydroxide and -sulfate precipitated in the bioreactor. Thermodynamic modeling predicted the formation of S⁰ during the study. Residence time distribution tests showed semi-complete mixing hydrodynamic flow conditions in the RPPB. The RPPB can be considered an elegant and low-cost technology coupling biological nitrogen removal to the recovery of phosphorus, iron and sulfur via chemical precipitation.

Effects of individual volatile fatty acids (VFAs) on phosphorus recovery by magnesium ammonium phosphate

Volatile fatty acids (VFAs) are a major component of dissolved organic matter in alkaline fermentation supernatants. In this study, effects of different VFAs (acetate, propionate, and butyrate) on phosphorus recovery, as magnesium ammonium phosphate (MgNH₄PO₄·6H₂O, or MAP), were studied. Results showed that optimal pH was 9.5 and MAP purity was ∼70% in VFA-free wastewater. With VFA addition, MAP purities of precipitates were higher, reaching 75%-85%. The crystalline characterization of precipitates suggested that VFAs had a weak complexation ability with Mg²⁺ and NH₄⁺. Further, pH changes during the MAP crystallization process were monitored and results indicated VFAs only contributed to the alkalinity condition, which, in turn, improved the MAP crystallization process. These data provide for a better understanding of P recovery by MAP precipitates from VFA-rich fermented supernatants.

Synthesis and characterization of magnesium oxide nanoparticle-containing biochar composites for efficient phosphorus removal from aqueous solution

The effective removal and recovery of phosphorus from aquatic environments are highly important for successful eutrophication control and phosphorus recycling. Herein, we prepared biochar containing MgO nanoparticles (MgO-biochar) by fast pyrolysis of MgCl₂-impregnated corn stalks, probed its phosphate adsorption performance. Through the fast pyrolysis, the MgCl₂ promoted the formation of micropores and mesoporous, and decomposed into MgO nanoparticles with the size smaller than 100 nm. The adsorption experiments showed that the adsorption property increased with the increase of Mg content, and had a strong correlation with the external surface area. And the phosphate adsorption was well described by the Langmuir-Freundlich model (maximum adsorption capacity was determined as 60.95 mg P/g). Kinetic analysis and characterization analysis of MgO-biochar for different adsorption time indicated that phosphate adsorption onto MgO-biochar was mainly controlled by rapid binding to the external surface (about 75% of the equilibrium adsorption amount), and the uptake rate was limited by the slow diffusion of phosphate into the biochar interior (about 25% of the equilibrium adsorption amount). The results suggested that the synthesized MgO-biochar with enough MgO active site dispersed on a higher external surface can be used as a potential adsorbent for phosphate removal and recovery from aqueous solution.

Understanding the biochemical characteristics of struvite bio-mineralising microorganisms and their future in nutrient recovery

The biochemical properties of selected microorganisms (Bacillus pumilus, Brevibacterium antiquum, Myxococcus xanthus, Halobacterium salinarum and Idiomarina loihiensis), known for their ability to produce struvite through biomineralisation, were investigated. All five microorganisms grew at mesophilic temperature ranges (22-34 °C), produced urease (except I. loihiensis) and used bovine serum albumin as a carbon source. I. loihiensis was characterised as a facultative anaerobe able to use O₂ and NO₃ as an electron acceptor. A growth rate of 0.15 1/h was estimated for I. loihiensis at pH 8.0 and NaCl 3.5% w/v. The growth rates for the other microorganisms tested were 0.14-0.43 1/h at pH 7-7.3 and NaCl ≤1% w/v. All the microorganisms produced struvite, as identified by morphological and X-ray Powder Diffraction (XRD) analysis, under aerobic conditions. The biological struvite yield was between 1.5 and 1.7 g/L of media, the ortho-phosphate removal and recovery were 55-76% and 46-54%, respectively, the Mg²⁺ removal and recovery was 92-98% and 83-95%, respectively. Large crystals (>300 μm) were observed, with coffin-lid and long-bar shapes being the dominant morphology of biological struvite crystals. The characterisation of the biochemical properties of the studied microorganisms is critical for reactor and process design, as well as operational conditions, to promote phosphorus recovery from waste streams.

Startup and stable operation of advanced continuous flow reactor and the changes of microbial communities in aerobic granular sludge

In this study, the granular sludge was operated under low aeration condition in sequencing batch reactor (SBR) and advanced continuous flow reactor (ACFR), respectively. Through increasing the sludge retention time (SRT) from 22 days to 33 days, the ACFR was successful startup in 30 days and achieved long term stable operation. Under SBR operation condition, the aerobic granular sludge (AGS) showed good nitrogen (60%), phosphorus (96%) and COD removal performance. During stable operation of continuous-flow, the nitrogen removal efficiency was increasing to 70%, however, the phosphorus removal efficiency could only be restored to 65%. Meanwhile, the sludge discharge volume from ACFR was about half of that in SBR. Results of high-throughput pyrosequencing illustrated that methanogenic archaea (MA), ammonia oxidizing archaea (AOA), denitrifying bacteria (DNB), denitrifying polyphosphate-accumulating organisms (DPAOs) played an important role in the removal of nutrients in ACFR. This study could have positive effect on the practical application of AGS continuous flow process for simultaneous biological nutrient removal (SBNR).

Diclofenac inhibited the biological phosphorus removal: Performance and mechanism

This work aims to evaluate the effect of new contaminant diclofenac (DCF) in sewage on the performance of Enhanced Biological Phosphorus Removal (EBPR) and its mechanism. The results showed that low-level DCF had no significant effect on EBPR. However, when the concentration of DCF was 2.0 mg/L, the removal efficiencies of chemical oxygen demand (COD), NH₄⁺-N and soluble orthophosphate (SOP) decreased significantly to 71.2 ± 4.2%, 78.6 ± 2.9%, and 64.3 ± 4.2%, respectively. Mechanisms revealed that DCF promoted the ratio of protein to polysaccharide in activated sludge extracellular polymers and inhibited anaerobic phosphorus release and oxic phosphorus uptake. Intracellular polymer analysis showed that when the DCF content was 2.0 mg/L, the maximum content of polyhydroxyalkanoates (PHA) was only 2.5 ± 0.4 mmol-C/g VSS, which was significantly lower than that in the blank. Analysis of key enzyme activities indicated that the presence of DCF reduced the activities of exopolyphosphatase and polyphosphate kinase.

Performance enhancement by adding ferrous to a combined modified University of Cape Town and post-anoxic/aerobic-membrane bioreactor

The removal of nutrients in a combined modified University of Cape Town and post-anoxic/aerobic-membrane bioreactor (UCT-A/MBR) was investigated. Denitrifying phosphorus removal (DPR) and nitrate-dependent anaerobic ferrous oxidation (NAFO) were applied to enhance the nutrient removal performances. The results showed that NAFO with the addition of Fe(II) and DPR could promote nitrogen and phosphorus removal. The total nitrogen removal efficiency gradually increased from 71.05 ± 2.00% to 73.84 ± 1.74% and 75.70 ± 1.47% with no Fe(II) addition, addition to the post-anoxic tank, and addition to the anoxic tank, and the total phosphorus removal efficiency increased from 89.37 ± 1.91% to 95.21 ± 0.85% and 96.01 ± 1.10%, respectively. Gene sequencing was conducted, and Saprospiraceae was determined to be the dominant DPR-related bacteria, with its abundance increasing from 16.31% to 22.45% after Fe(II) addition. Additionally, the proportion of the NAFO-related bacteria Azospira increased from 0.58% to 1.91% after Fe(II) addition. The microbial succession caused by the addition of Fe(II) may have resulted in the enhanced removal performance.

Waste Brick as Constructed Wetland Fillers to Treat the Tail Water of Sewage Treatment Plant

Adopting the concept of "using waste to treat waste", the waste bricks will be used for constructed wetland filling. Integrated vertical-flow constructed wetland (IVCW) studied on the purification effect in influent water under three hydraulic loads (0.15, 0.25, 0.35 m/day). The results show that the waste bricks can be used as the carrier for the growth of the system biofilm, and have positive effects on the removal of pollutants in the influent water. Under three different hydraulic load conditions, the vertical flow of CWs can significantly reduce the load of water intake. In the low hydraulic load condition of 0.15 m/day, the average removal rates of chemical oxygen demand (COD), ammonia nitrogen (NH₃-N), total nitrogen (TN), and total phosphorus (TP) can reach 66.52%, 72.10%, 56.53% and 91.55% in this system, respectively. The influent pool on removal efficiency of pollutants was obviously higher than that of the upper pool, especially in the inlet surface 0-30 cm ranges. This research has achieved the effect of using "waste" to treat wastewater, which has strong practical significance and popularization value.

Bioretention cell incorporating Fe-biochar and saturated zones for enhanced stormwater runoff treatment

Nitrogen (N) and phosphorus (P) removal in conventional bioretention systems is highly variable. Therefore, five novel experimental columns with different media configurations and constituents, and incorporating a saturated zone were developed and assessed to optimize the removal of N, P and other nutrients. Three types of media composed of the conventional mixed sand and soil media (T₁), biochar-amended media (T₂), and iron-coated biochar (ICB)-amended media (T₃) were evaluated. Two of the experimental columns were designed with double-layer configurations, while the other three were of a single-layer structure. Removal efficiencies of nutrients in the experimental columns were evaluated and compared using simulated runoff. Also, the effect of media depth on the retention of P and denitrifying enzyme activity (DEA) in the bioretention columns were evaluated. The experimental column only filled with T₃ showed the best performance for COD, ammonia (NH₄⁺-N) and total phosphorus (TP) removal (94.6%, 98.3% and 93.70%, respectively), whereas columns filled with T₂ performed poorly for TP removal (57.36%). For the removal of nitrate (NO₃^--N) and total nitrogen (TN), the columns using a single-layer and only filled with either T₃ or T₂ exhibited the best performance (93% and 97% TN removal, respectively). Overall, this study demonstrates that our proposed single-layered bioretention cell only filled with T₃ and incorporating a saturated zone effectively improves the runoff quality, and can provide a new bioretention cell configuration for efficient stormwater treatment.

Decolorization and phytotoxicity reduction in an innovative anaerobic/aerobic photobioreactor treating textile wastewater

The potential of a novel anaerobic/aerobic algal-bacterial photobioreactor for the treatment of synthetic textile wastewater (STWW) was here assessed. Algal-bacterial symbiosis supported total organic carbon, nitrogen and phosphorous removal efficiencies of 78 ± 2%, 47 ± 2% and 26 ± 2%, respectively, at a hydraulic retention time (HRT) of 8 days. A decrease in the HRT from 8 to 4 and 2 days resulted in a slight decrease in organic carbon and phosphate removal, but a sharp decrease in nitrogen removal. Moreover, an efficient decolorization of 99 ± 1% and 96 ± 3% for disperse orange-3 and of disperse blue-1, respectively, was recorded. The effective STWW treatment supported by the anaerobic/aerobic algal-bacterial photobioreactor was confirmed by the reduction in wastewater toxicity towards Raphanus sativus seed germination and growth. These results highlighted the potential of this innovative algal-bacterial photobioreactor configuration for the treatment of textile wastewater and water reuse.

Intracellularly stored polysulfur maintains homeostasis of pH and provides bioenergy for phosphorus metabolism in the sulfur-associated enhanced biological phosphorus removal (SEBPR) process

Sulfur-associated enhanced biological phosphorus removal has recently been developed for the removal of biological nutrients. In this new bioprocess, the polymeric sulfur compound (poly-S) is crucial to connecting sulfur conversions and polyphosphate accumulation; however, its mechanisms are still elusive. This study investigated the role of poly-S in maintaining the system stability by operating a lab-scale reactor for 720 d and conducting batch experiments with various initial pH values. The main findings were as follows: i) intracellular poly-S increased from 30 to 95 mg S (g VSS)^-1, whereas polyhydroxyalkanoates increased from 8 to 22 mg C (g VSS)^-1; ii) glycogen increased from 7.5 to 12.5 mg C (g VSS)^-1 during the first 520 d before decreasing; and 3) P removal could be maintained at 8-12.5 mg P (L)^-1. The decrease in glycogen was likely because the accumulation of enough poly-S could replace glycogen to provide reducing power and buffer the inner pH. The results of batch tests confirmed that poly-S could adjust the intracellular protons under anaerobic conditions (pH always returned to neutral or neutral levels at the end of anaerobic phase) and provide cellular bioenergy (adenosine triphosphate, for P uptake, thereby maintaining net P removal). The predominant microbial communities were facultative denitrifying Thauera (11%), sulfide-oxidizing Thiobacillus (8%), and sulfate-reducing Desulfobacter (9%). However, the conventional polyphosphate-accumulating organisms were detected at very low abundance (e.g. Tetrasphaera at only 0.02%). Overall, poly-S could regulate intracellular protons and energy balance and reduce glycogen accumulation, keeping good biological P removal performance.

An influent responsive control strategy with machine learning: Q-learning based optimization method for a biological phosphorus removal system

Biological phosphorus removal (BPR) is an economical and sustainable processes for the removal of phosphorus (P) from wastewater, achieved by recirculating activated sludge through anaerobic and aerobic (An/Ae) processes. However, few studies have systematically analyzed the optimal hydraulic retention times (HRTs) in anaerobic and aerobic reactions, or whether these are the most appropriate control strategies. In this study, a novel optimization methodology using an improved Q-learning (QL) algorithm was developed, to optimize An/Ae HRTs in a BPR system. A framework for QL-based BPR control strategies was established and the improved Q function, Q^t+1(s_t,s_t+1)=Q^t(s_t,s_t+1)+k·[R(s_t,s_t+1)+γ·maxa^tQ^t(s_t,s_t+1)-Q^t(s_t,s_t+1)] was derived. Based on the improved Q function and the state transition matrices obtained under different HRT step-lengths, the optimum combinations of HRTs in An/Ae processes in any BPR system could be obtained, in terms of the ordered pair combinations of the <current state-transition state>. Model verification was performed by applying six different influent chemical oxygen demand (COD) concentrations, varying from 150 to 600 mg L^-1 and influent P concentrations, varying from 12 to 30 mg L^-1. Superior and stable effluent qualities were observed with the optimal control strategies. This indicates that the proposed novel QL-based BPR model performed properly and the derived Q functions successfully realized real-time modelling, with stable optimal control strategies under fluctuant influent loads during wastewater treatment processes.

Thermal pretreatment to enhance biogas production of waste aerobic granular sludge with and without calcium phosphate precipitates

To develop aerobic granules based sustainable wastewater treatment, it is necessary to view wastewater treatment process and excess sludge treatment as a whole to evaluate resource recovery and sustainability. We thus investigated in this study how mineral characteristics of aerobic granules with/without calcium phosphate precipitates for phosphorus removal in treatment process affect the excess sludge digestion for energy recovery. Steam explosion at 170 °C as an effective thermal sludge treatment approach was studied in parallel with normal thermal treatment in an autoclave at 70, 100 and 125 °C, respectively. A liner relationship was found between the thermal treatment temperature in the autoclave and biogas production of aerobic granules. The untreated granules with only 10% mineral content (G1) generated 30% more biogas than the untreated granules with 39% mineral content (G2), but steam explosion is more effective to G2 with high mineral content and relatively poor methane yield potential. In addition, steam explosion improved methane production from G2 more compared with activated sludge although both untreated activated sludge and G2 had comparable methane production, i.e. around 0.235 L CH₄/g VS. Therefore, steam explosion is potential to be used to increase methane production especially when the untreated granular sludge has low methane yield due to high mineral content. This work provides a good basis for a holistic evaluation of resource recovery based on aerobic granular sludge, i.e. combined energy recovery and phosphorus removal and recovery via CaP precipitates, and trade-off between different factors with steam explosion.

Removal of phosphorous and nitrogen from wastewater in Brachiaria-based constructed wetland

Considering the prevalence of eutrophication of water bodies, sustainable treatment technologies like constructed wetlands (CWs) have come up as a promising alternate for nutrient removal and wastewater treatment. The present study was undertaken to investigate the potential of Brachiaria-based constructed wetland for removal of phosphorus and nitrogen in different seasons of a sub-tropical region. The CW cell could efficiently remove phosphate and nitrogen under varying influent concentrations across different seasons. Average removal of total phosphate increased from 55.2% (winter) to 78.5% (spring), 80.7% (autumn), and 85.6% (summer), and maximum removal rate was 384.4 mg/m2-day during the summer season. The soluble/available phosphate was removed on priority owing to its easy bio-availability. The removal efficiency of Brachiaria increased with increasing influent phosphate concentration (5-20 mg/l), if supplemented with nitrogen maintaining the N:P ratio of 5:1. This highlighted the characteristic of Brachiaria to absorb chemical shocks w.r.t. phosphate. The neutral pH (6.2-8.3) and oxidising conditions in rhizosphere ruled out possibility of binding of phosphate with cations (Ca, Fe, and Al) in sediments. Ambient temperature and sunshine hours regulated evapotranspiration and hence nutrient removal. Simultaneous removal of nitrogen (75.6-84.6%) by Brachiaria indicated that it can serve dual purpose of nutrient removal and fodder-production for livestock, thus serving as a sustainable prototype for rural communities in sub-tropical regions.

Achieving deep-level nutrient removal via combined denitrifying phosphorus removal and simultaneous partial nitrification-endogenous denitrification process in a single-sludge sequencing batch reactor

The feasibility of coupling denitrifying phosphorus removal (DPR) with simultaneous partial nitrification-endogenous denitrification (SPNED) was investigated in a single-sludge sequencing batch reactor for deep-level nutrient removal from municipal and nitrate wastewaters. After 160-day operation, the DPR process simultaneously reduced most PO₄^3--P and NO₃^--N anoxically, and the SPNED process achieved further total nitrogen (TN) removal at low dissolved oxygen condition with TN removal efficiency of 90.8%. The effluent NH₄⁺-N, PO₄^3--P and TN concentrations were 1.0, 0.1 and 7.2 mg/L, respectively. Microbial analysis revealed that Dechloromonas (6.7%) dominated DPR process, whereas the gradually enriched Nitrosomonas (4.5%) and Candidatus Competibacter (6.8%) conducted SPNED process accompanied with sharply eliminated Nitrospirae (1.4%). Based on these findings, a novel strategy was proposed to achieve further nutrient removal in conventional treatment through integrating the DPR-SPNED process. As a result, ∼100% of extra carbon and ∼10% of oxygen consumptions would be reduced with satisfactory effluent quality.

Optimization of phosphate recovery as struvite from synthetic distillery wastewater using a chemical equilibrium model

This study investigates the feasibility of recovery of phosphorus via struvite precipitation from a synthetic anaerobically treated distillery spent wash by optimizing the process using a chemical equilibrium model, namely Visual MINTEQ. Process parameters such as Mg²⁺, [Formula: see text], and [Formula: see text] ion concentrations and pH were used as inputs into the model. Increasing the molar ratio of [Formula: see text] from 0.8:1 to 1.6:1 at pH 9 led to an increase in phosphate recovery from 88.2 to 99.5%. The model and experimental results were in good agreement in terms of phosphate recovery, indicating that the Visual MINTEQ model can be used to pre-determine the process parameters for struvite synthesis. Increasing the concentration of calcium ion adversely affected the synthesis and purity of struvite, whereas the presence of melanoidins had no significant impact. This study demonstrates that phosphorus recovery through struvite precipitation is a sustainable approach to reclaim phosphorus from high-strength industrial wastewater.

Treatment of chlorpyrifos manufacturing wastewater by peroxide promoted-catalytic wet air oxidation, struvite precipitation, and biological aerated biofilter

Chlorpyrifos manufacturing wastewater (CMW) is characterized by complex composition, high chemical oxygen demand (COD) concentration, and toxicity. An integrated process comprising of peroxide (H₂O₂) promoted-catalytic wet air oxidation (PP-CWAO), struvite precipitation, and biological aerated filters (BAF) was constructed to treat CMW at a starting COD of 34000-35000 mg/L, total phosphorus (TP) of 5550-5620 mg/L, and total organophosphorus (TOP) of 4700-4840 mg/L. Firstly, PP-CWAO was used to decompose high concentrations of organic components and convert concentrated and recalcitrant TOP to inorganic phosphate. Copper citrate and ferrous citrate were used as the catalysts of PP-CWAO. Under the optimized conditions, 100% TOP was converted to inorganic phosphate with 95.6% COD removal. Then, the PP-CWAO effluent was subjected to struvite precipitation process for recovering phosphorus. At a molar ratio of Mg²⁺:NH₄⁺:PO₄^3- = 1.1:1.0:1.0, phosphate removal and recovery reached 97.2%. The effluent of struvite precipitation was further treated by the BAF system. Total removals of 99.0%, 95.2%, 97.3%, 100%, and 98.3% were obtained for COD, total suspended solids, TP, TOP, and chroma, respectively. This hybrid process has proved to be an efficient approach for organophosphate pesticide wastewater treatment and phosphorus reclamation.

Growth and nutrient removal efficiency of duckweed (lemna minor) from synthetic and dumpsite leachate under artificial and natural conditions

Sustainable management of leachate produced from the dumpsite is one of the major concerns in developing countries Aquatic plants such as duckweed have the potential to remove pollutants from wastewater which can also be cost-effective and feasible options for leachate treatment. Therefore, the objective of our present study was to examine the growth and nutrient removal efficiency of duckweed (Lemna minor) on leachate. Three tests were performed each by growing lemna minor on synthetic leachate under controlled conditions and on dumpsite leachate under natural conditions. During each test, duckweed was grown in 300 ml plastic containers with a surface area of 25.8 cm2. About 60 mg of fresh mass of duckweed was grown on 250 ml leachate at an internal depth of 9.5 cm. Results revealed that, in comparison to synthetic leachate, duckweed removed Chemical Oxygen Demand (COD), nitrogen (N), and phosphorous (P) more efficiently from dumpsite leachate under natural climatic conditions. However, the amounts of N and P absorbed into duckweed body mass were about 16% and 35% respectively more at synthetic leachate under controlled conditions. Maximum growth rate of duckweed (7.03 g m-2 day-1) was also observed for synthetic leachate in comparison to the growth rate of 4.87 g m-2 day-1 at dumpsite leachate. Results of this study provide a useful interpretation of duckweed growth and nutrient removal dynamics from leachate under natural and laboratory conditions.

Adsorption of different forms of phosphorus on modified corn bracts

Excessive phosphorus discharged into the environment could result in the eutrophication, leading to water pollution. Hence, the efficient method for phosphorus removal is urgently in need. In this paper, an agricultural by-product, corn bract, modified by Zr was proposed to remove different forms of phosphorus. A comparison study about the adsorption performance of organic phosphorus (OP) and inorganic phosphorus (IP) was investigated. The results indicated that both the OP and IP reached the maximum adsorption amounts when the initial pH was 2. Compared with IP adsorption, the adsorbent showed higher adsorption rate but lower adsorption capacity for OP. The complexation and the electrostatic attraction were possibly the main adsorption mechanisms. PRACTITIONER POINTS: The agricultural waste, corn bract, was proposed to remove phosphorus. The adsorption performances of OP and IP were compared. The adsorbent showed higher adsorption rate but lower adsorption capacity for OP.

Simultaneous nitrification, denitrification and phosphorus removal in a sequencing batch reactor (SBR) under low temperature

Simultaneous nitrogen and phosphorus removal in winter is one of the great challenges in wastewater treatment processes due to the poor bioactivity of microbial communities. In this study, excellent performance of simultaneous nitrification, denitrification and phosphorus removal (SNDPR) was achieved at low temperature of 10 ^°C and COD/N ratio of 6 in a lab-scale sequencing batch reactor. Total nitrogen (TN) and phosphorus (TP) removal efficiency reached 89.6% and 97.5%, respectively, accompanied with N₂O emission of 7.46% TN due to the primary contribution (70%) of nitrifier denitrification. It was further confirmed that polyphosphate accumulating organisms (PAOs) were dominant in microbial communities revealed by fluorescence in situ hybridization and 16S rRNA amplicon sequencing. Moreover, denitrifying phosphorus removal by PAOs through nitrite pathway was found to be the main reason for the high efficiency of this SNDPR process. Denitrifying PAOs, especially the subgroup PAOII capable of utilizing nitrite to take up phosphorus, played a significant role in highly efficient TN and TP removal at low temperature. Furthermore, genus Propionivibrio was enriched (48.9%) in the bacterial community based on the 16S rRNA analysis, which was proposed to be a crucial member involved in the nitrogen and phosphorus removal simultaneously at low temperature in this system.

Evaluating the potential for sustaining mainstream anammox by endogenous partial denitrification and phosphorus removal for energy-efficient wastewater treatment

This study demonstrated a novel process configuration for sustaining mainstream anammox by integrating the anammox and endogenous partial denitrification-and-phosphorus removal (EPDPR) in two-stage sequencing batch reactors (SBRs). In the EPDPR-SBR, high nitrate-to-nitrite transformation (68.2%) and P removal (99.3%) were achieved by adjusting the anaerobic/anoxic/aerobic durations and influent nitrate concentration, providing a suitable NO₂^--N/NH₄⁺-N (∼1.37) for subsequent anammox reaction. In the Anammox-SBR, ∼95% of TN was removed without external carbon and oxygen demands. Satisfactory effluent quality (∼6 mgTN/L and 0.2 mgP/L) achieved in the integrated EPDPR/anammox opens a new window towards the energy-efficient wastewater treatment. Microbial analysis further revealed that Dechloromonas (1.6-9.6%) and Candidatus Competibacter (6.4-5.8%) respectively conducted P removal and NO₂^--N production (79.2%) from NO₃^--N denitrification in the EPDPR-SBR, whereas Candidatus Kuenenia (7.0-29.7%) dominated NO₂^--N and NH₄⁺-N removal (91.3% and 99.5%) in the Anammox-SBR, with 10 genera identified as denitrifying bacteria (0.6-8.1%) further reduced 18.9% of the produced NO₃^--N.

Biofilm development dynamics and pollutant removal performance of ceramsite made from drinking-water treatment sludge

Alum-sludge ceramsite and denitrifying bacteria (XP-1, XP-2, CL-1, CL-3) were used as substrate and constructed biofilm for enhancing the removal of pollutants from wastewater. The results showed that, due to the large specific surface area, the maximum growth rate was 0.49 mg/(g·day) on the sludge ceramsite, and the mass of biofilm attached onto sludge ceramsite was 5.98 times higher than that when using commercial ceramsite as substrate. Better removal performance could be achieved with the combination of sludge ceramsite and bacteria, viz. 98.6%, 91.0%, and 85.8% reduction in total phosphorus (TP), total nitrogen (TN), and chemical oxygen demand (COD), respectively. Pseudo-first-order kinetics, pseudo-second-order kinetics, Monod kinetics, and multiple Monod kinetics combined with continuous-flow-stirred tank reactor (CFSTR) behavior were used to investigate the dynamics of the pollutant removal processes. The decrease in band brightness for bacteria attached onto sludge ceramsite was 11.5%, while it was more than 35.7% on commercial ceramsite during wastewater treatment according to results from denaturing gradient gel electrophoresis (DGGE). Sludge ceramsite played an important role in maintaining quantities and activities of denitrifying bacteria, and application of sludge ceramsite substrate and denitrifying bacteria was a reliable method to enhance the removals of phosphorus, nitrogen, and COD from domestic wastewater. PRACTITIONER POINTS: Alum-sludge ceramsite was a good substrate for phosphorus adsorption and denitrifying bacterial growth. There was 5.98 times more biofilm on sludge ceramsite than on commercial ceramsite The biofilm of denitrifying bacteria on sludge ceramsite was more stable. High removals of TP (98.6%), TN (90.1%) and COD (85.81%) were achieved.

Comparison of floating-bed wetland and gravel filter amended with limestone and sawdust for sewage treatment

Advancements in the design and technology of constructed wetlands for efficient removal of wastewater contaminants are ever in progress to develop situation-based economical systems. Here, we entrenched two horizontal sub-surface flow constructed wetlands (HSFCW) with either chemical, viz. limestone (HSFCW-LS) or organic, viz. sawdust (HSFCW-SD) substrates, and compared them with biological method, viz. growing of water spinach in floating-bed-constructed wetland (FBCW-WS) to enhance the performance of CWs. Same sewage wastewater was used as influent in each fortified CW replicated thrice. Sewage was replaced weekly, for a total of 12 weeks of experimentation. Sampling of raw sewage from influent was undertaken at the inlet in the beginning, and that of treated effluent from the outlet after a week of treatments. Quality of raw sewage used weekly during experimentation remained almost uniform and near to the wastewater standards. Cumulative data of treated wastewater depicted that the FBCW-WS achieved the highest performance in the removal of total nitrogen (TN), [Formula: see text]-N, and total phosphorus (TP) with average removal efficiencies of 75.9, 90.5, and 94.3%, respectively. Whereas, HSFCW-SD performed better for [Formula: see text]-N, FC, and TSS with corresponding removal efficiency of 77.5, 64.3, and 74.2% while HSFCW-LS showed average performance. This study concludes that performance of biological method of macrophyte cultivation (FBCW-WS) is significantly superior to chemical and organic substrates, so it could be more effective, economical, and sustainable approach for sewage treatment.

Potentials and challenges of phosphorus recovery as vivianite from wastewater: A review

Due to the shortage of phosphorus resources and the limitations of existing phosphorus recovery methods, phosphorus recovery in the form of vivianite has attracted considerable attention with its natural ubiquity, easy accessibility and foreseeable economic value. This review systematically summarizes the chemistry of vivianite, including the characteristics, formation process and influencing factors of the material. Additionally, the potential of phosphorus recovery as vivianite from wastewater has also been comprehensively examined from the prospects of economic value and engineering feasibility. In general, this method is theoretically and practically feasible, and brings some extra benefits in WWTPs. However, the insufficient understanding on vivianite recovery in wastewater/sludge decelerate the development and exploration of such advanced approach. Further researches and cross-field supports would facilitate the improvement of this technique in the future.

Electrochemical acidolysis of magnesite to induce struvite crystallization for recovering phosphorus from aqueous solution

A novel struvite crystallization method induced by electrochemical acidolysis of cheap magnesite was investigated to recover phosphorus from aqueous solution. Magnesite was confirmed to continuously dissolve in the anolyte whose pH stabilized at about 2. Driven by the electrical field force, over 90% of the released Mg²⁺ migrated to the cathode chamber via passing through the cation exchange membrane. The pH of the phosphate-containing aqueous solution in the cathode chamber was elevated to the appropriate pH fit for struvite crystallization. The products were identified as struvite crystals by scanning electron microscopy and X-ray diffraction. Increasing the magnesite dosage from 0.83 to 3.33 g L^-1 promoted the phosphorus recovery efficiency from 2.2% to 78.3% at 3 d, which was attributed to sufficient Mg²⁺ supply. Increasing the applied voltage from 3 to 6 V improved the recovery efficiency from 43.6% to 76.4% at 1 d, since the enhanced current density of the electrochemical system markedly accelerated both the magnesite acidolysis and the catholyte pH elevation. The initial catholyte pH between 3 and 5 was found to benefit the phosphorus recovery due to the final catholyte pH fit for the struvite crystallization.

Comparison of monoculture and mixed culture (Scenedesmus obliquus and wild algae) for C, N, and P removal and lipid production

This study compared the efficiency of nutrient removal and lipid accumulation by a monoculture of Scenedesmus obliquus and mixed cultures of microalgae. The highest removal efficiencies of ammonium (99.2%), phosphate (91.2%), and total organic carbon (83.6%) occurred in the monoculture. All the mixed cultures were dominated by S. quadricauda; in some mixed cultures, the proportions of Chlamydomonas reinhardtii and C. microsphaera reached > 20%. The lipid content and lipid production in the monoculture were 15.9% and 52.3 mg kg^-1, respectively, significantly higher than those in all the mixed cultures of microalgae. In all the mixed cultures, the proportion of palmitic acid was > 50%. The results suggest that the monoculture had advantages over the mixed culture of microalgae in terms of nutrient removal and lipid production.

Enhanced denitrifying phosphorus removal and mass balance in a worm reactor

Phosphorus release is one of the disadvantages during worm predation, which has an adverse effect on wastewater treatment. In order to investigate and reveal the effects and mechanisms of worm predation on phosphorus transformation, batch experiments were conducted on a long-running worm reactor (WR). Denitrifying phosphorus removal (DPR) was observed in WR for the first time owing to the special reactor configuration and operating conditions. After DPR in WR, the concentration of supernatant phosphorus increased to 42.2 ± 1.1 mg L^-1 owing to bacterial phosphorus release and worm predation, which further promoted DPR in the subsequent cycle. DPR rate in the WR was 12.3 times higher than that in the blank reactor (BR). In addition, the synergistic effects of worm predation and bacterial metabolism on sludge reduction and nutrients transformation were analyzed. The sludge reduction of WR was 84.5% higher than that of BR. Bacterial metabolism played an important role in the removal of supernatant nutrients, which consumed 60.2% of total nitrogen and 55.5% of chemical oxygen demand derived from the reduced sludge. The study suggested that under certain conditions, WR could be functionalized as a bacteria selection tank to further improve the wastewater treatment efficiency. Bacterial metabolism was essential for supernatant nutrients removal during worm predation.

The impact of background wastewater constituents on the selectivity and capacity of a hybrid ion exchange resin for phosphorus removal from wastewater

Conventional sorption media are inefficient for phosphorus removal from wastewater due to preference for competing species such as sulphate, nitrate and organics. This work investigates whether the use of hybrid ion exchange resins effectively negates such concerns. Trials were conducted with a hybrid anion exchange (HAIX) media which was preloaded with different background constituents and operated over multiple regeneration cycles to ascertain the likely impacts. The work revealed that whilst the impact of the other constituents was seen in regards to direct competition, the major impact was on reduction of the rate of intraparticle mass transfer through sorption of the constituents onto the base resin thereby reducing the Donnan membrane effect. Comparison of the impact of the background water constituents on the individual components (hybrid resin, base resin, nanoparticles) revealed the importance of the nanoparticle whereby they effectively transform the ion exchange media into a mono component absorber for phosphorus that enables sustained removal even in complex wastewaters.

Effects of different substrates on nitrogen and phosphorus removal in horizontal subsurface flow constructed wetlands

This study aimed to explore the nitrogen and phosphorus removal performance of the horizontal submerged constructed wetland (HSCW) with Ti-bearing blast furnace slag (T). Another two HSCWs, with the converter steelmaking slag (G) and the stone (S) as wetland substrates, respectively, were simultaneously running as control. The results showed that the nitrogen and phosphorus removal capacities of the T-HSCW were generally better than those of another two HSCWs. When the hydraulic retention time (HRT) was 6 days, the effluent concentrations of ammonia nitrogen (NH₄⁺-N) and total nitrogen (TN) were 6.66 mg L^-1 and 14.02 mg L^-1, respectively, and the removal rates of NH₄⁺-N and TN reached 77.54% and 71.07%, respectively. The T-HSCW had better removal efficiency of phosphorus. The effluent concentration of total phosphorus (TP) was lower than 0.3 mg L^-1, and the maximum removal rate could reach 98%. Through the characterization of the three substrates before and after experiments, it was found that the removal of nitrogen and phosphorus by T and G mainly relied on chemical adsorption, while S mainly relied on physical adsorption. Ti could also promote the absorption of nitrogen by plants and increase the nitrogen removal capacity of T-HSCWs.

Improvement of partial nitrification endogenous denitrification and phosphorus removal system: Balancing competition between phosphorus and glycogen accumulating organisms to enhance nitrogen removal without initiating phosphorus removal deterioration

The novel partial nitrification endogenous denitrification and phosphorus removal (PNEDPR) process can achieve deep-level nutrient removal from low carbon/nitrogen municipal wastewater without extra carbons. However, its performance is limited by long hydraulic retention time (HRT) and low specific endogenous denitrification rate (r_NO2). This study aimed at investigating the effects of two improving strategies on PNEDPR. One was decreasing both anaerobic and anoxic reaction time for shortening HRT from 55 h to 17.5 h. The other was temporarily discharging orthophosphate-rich supernatant for balancing the competition between phosphorus and glycogen accumulating organisms to further raise r_NO2 without deterioration of phosphorus removal. Results revealed that, desirable nutrient removal was obtained, as average effluent concentrations of total nitrogen and orthophosphate were 8.4 and 0.5 mg/L with their average removal efficiencies of 86.8% and 90.9%. High-throughput sequencing analysis revealed that, Candidatus_Competibacter conducted nitrogen removal endogenous denitrification and Candidatus_Accumulibacter and Tetrasphaera ensured phosphorus removal.

[Effects of Long-term Poly-P Deficiency on the Metabolic Properties of Accumulibacter in AO-SBR System]

To investigate the changes in microbial community structure and metabolic properties of Accumulibacter under long-term Poly-P deficiency, an activated sludge enriched with Accumulibacter was inoculated into two SBR reactors, where sodium acetate and sodium propionate were used separately as organic carbon sources. The two reactors were operated for 60 days with an influent PO₄^3--P concentration of 2.5 mg·L^-1. The phosphorus removal performance, sludge production, and changes in the microbial community structure of the systems were analyzed. The results indicated that both SBR systems showed good performance of phosphorus and organic matter removal. However, microorganisms in both systems showed glycogen-accumulating metabolism properties under long-term Poly-P deficiency. In the unfavorable environment of long-term Poly-P deficiency, Accumulibacter Ⅰ maintained a high abundance (40%±7%) in the propionate SBR system, indicating that Accumulibacter Ⅰ had higher metabolic activity and its metabolic properties could be independent of Poly-P for survival under Poly-P deficiency for a long period. In comparison, propionate is more conducive to Accumulibacter adaptation to lower phosphorus loads, and Accumulibacter Ⅰ is more competitive than Accumulibacter Ⅱ under lower phosphorus loads.

Direct filtration for the treatment of the coagulated domestic sewage using flat-sheet ceramic membranes

Direct membrane filtration (DMF) is considered as a promising technology for municipal wastewater treatment. We utilized an innovative application of flat-sheet ceramic membranes (FSCM) for DMF for the rapid treatment of domestic sewage. Coagulation was applied before FSCM filtration to increase the pollutant removal and to mitigate membrane fouling. This coagulation-FSCM filtration can significantly reduce the pollutant load on the downstream treatment and concentrate organics and nutrients into sludge to facilitate resource recovery. Using polyaluminum chloride (PACl) based FSCM filtration, approximately 90.0% of the chemical oxygen demand (COD) and 99.0% of the phosphorus (P) were removed from the sewage influent and retained in the concentrated sludge, with less than 25.0 mg/L COD left in the effluent. Long-term operation of the PACl-based FSCM filtration stably maintained a high flux of 41.7 L/m²-h (LMH, or 1.0 m/d). The fouled membranes were cleaned chemically every 3-5 d, and the membrane permeability could almost be completely recovered using chemical backwash for only 10 min with a diluted acidic, alkaline, chlorine or H₂O₂ solution. The novel FSCM process will fundamentally advance wastewater treatment technology. It can be readily modularized and installed as simple add-on units to upgrade and retrofit existing wastewater treatment systems.

A review of bioretention components and nutrient removal under different climates-future directions for tropics

Bioretention systems have been implemented as stormwater best management practices (BMPs) worldwide to treat non-point sources pollution. Due to insufficient research, the design guidelines for bioretention systems in tropical countries are modeled after those of temperate countries. However, climatic factors and stormwater runoff characteristics are the two key factors affecting the capacity of bioretention system. This paper reviews and compares the stormwater runoff characteristics, bioretention components, pollutant removal requirements, and applications of bioretention systems in temperate and tropical countries. Suggestions are given for bioretention components in the tropics, including elimination of mulch layer and submerged zone. More research is required to identify suitable additives for filter media, study tropical shrubs application while avoiding using grass and sedges, explore function of soil faunas, and adopt final discharged pollutants concentration (mg/L) on top of percentage removal (%) in bioretention design guidelines.

Enhanced simultaneous organics and nutrients removal in tidal flow constructed wetland using activated alumina as substrate treating domestic wastewater

A tidal flow constructed wetland (TFCW), a commonly applied system to clean wastewater, contains a substrate to assist pollutants removal, while the choice of substrate affects the formation of bacterial biofilms. Herein, activated alumina-TFCW (A-TFCW) with hydraulic load of 1.35 m³/(m²·d) parallel with shale ceramisite (S-TFCW) was investigated for treating domestic wastewater, aiming to enhance simultaneous long-term removal of organics, nitrogen and phosphorus. A-TFCW achieved significantly higher COD, NH₄⁺-N, TN and TP removal efficiency than S-TFCW, with the removal efficiency of 85.9% COD, 85.4% NH₄⁺-N, 72.8% TN and 96.4% TP respectively. Denitrifying bacteria dominated in both formed biofilms, with higher relative abundance of nitrifying bacteria and denitrifying bacteria in A-TFCW. These results demonstrated that AA substrate was more suitable to be applied in enhancing the removal performance in TFCW for the treatment of domestic wastewater.

Treatment of heavily polluted river water by tidal-operated biofilters with organic/inorganic media: Evaluation of performance and bacterial community

In this study, biofilters (BFs) packed with inorganic (ceramsite and lava rock) and organic (fibrous carrier and biological ball) materials were applied in a tide-flow mode at three flooded/drained (F/D) time ratios (16/8 h, 12/12 h and 8/16 h) to treat heavily polluted river water. The results showed that higher ammonium and phosphorus removals were achieved with BFs filled with ceramsite (95-97% and 76-77%) and lava rock (87-92% and 84-94%), while fibrous carrier-packed BFs obtained better total nitrogen removal (37-44%). Moreover, the F/D time ratio of 16/8 h was slightly preferable for pollutant removal. High-throughput sequencing analysis illustrated that the relative abundance of potential denitrifiers that developed on organic media was much higher than those on inorganic substrates. The results indicated that the combination of inorganic materials and fibrous carriers as substrates could be an effective strategy for enhancing overall pollutant removal in BFs.

Acidogenic phosphorus recovery from the wastewater sludge of the membrane bioreactor systems with different iron-dosing modes

A novel acidogenic phosphorus recovery (APR) process was developed in combination with Fe(III)-based chemical phosphorus removal and a membrane bioreactor (MBR) for enhanced wastewater treatment and effective P recovery. Two different system configurations were evaluated: Fe-dosing MBR (Fe-MBR), with the Fe-dosing into the MBR, and Fe-enhanced primary sedimentation followed by the MBR (FeP-MBR). The results show that both systems performed well for enhanced nutrient (N and P) removals and P recovery, with approximately 50% of the total P recovered from the municipal wastewater in the form of vivianite. Compared to the Fe-MBR system, FeP-MBR achieved more efficient P recovery under low food-waste loading conditions, maintained a higher ratio of biomass in activated sludge and experienced a slower rate of membrane fouling. Important functional bacteria were identified, including Prevotella and Selenomonas, which are active in hydrolysis and acidogenesis of sludge, and Aeromonas and Sulfurospirillum, which are involved in dissimilatory iron reduction.

[Pollutant Removal Performance and Membrane Fouling Characteristics in Marine Aquaculture Wastewater Treatment by a Microalgae Membrane Reactor]

In order to treat mariculture wastewater, the pollutant removal performance and membrane fouling characteristics of a microalgae membrane reactor were investigated using Platymonas helgolandica tsingtaoensis. After 60 days of operation, the total nitrogen (TN) and total phosphorus (TP) removal efficiency of the reactor were 73.6% and 77.9%, respectively, and the removal rates of TN and TP reached 15 g·(m³·d)^-1 and 2.8 g·(m³·d)^-1. The microalgae in the reactor could be enriched rapidly, with a maximum growth rate of 53.3 mg·(L·d)^-1 and a maximum biomass of 1.4 g·L^-1. The microalgae in the reactor were harvested on day 18 and day 36; harvesting did not affect the nitrogen and phosphorus removal efficiency of the reactor. To some extent, the membrane fouling phenomenon was alleviated. The increase in the microalgae biomass would significantly increase the pollutant content of the membrane. The three-dimensional excitation-emission matrix (EEM) spectra results confirmed that tryptophan-like substances and aromatic proteins had a significant effect on membrane fouling.

[Effect of Sludge Retention Time and pH on the Denitrifying Phosphorus Removal Process]

In this work, the effects of the sludge retention time (SRT, 35, 25, or 15 d) and pH (7.5, 8.0, 8.5) on denitrifying phosphorus removal were investigated using denitrifying phosphorus bacteria (DPBs) enriched in a sequencing batch reactor (SBR). The results indicated that shortening the SRT from 35 d to 25 d resulted in a decrease in the mixed liquor volatile suspended solids (MLVSS) from 2821 to 2301 mg·L^-1, while the sludge loading rate (F/M) increased from 0.256 kg·(kg·d)^-1to 0.312 kg·(kg·d)^-1. Although the quantity of net phosphorus release and net phosphorus uptake decreased at this stage, the rates of anaerobic phosphorus release, anoxic phosphorus absorption, and denitrification reached their highest levels with values of 25.07, 15.92, and 9.45 mg·(g·h)^-1, respectively, due to the increased sludge activity. Consequently, the phosphorus content of the sludge increased from 4.78% to 5.33%, and the removal rate of PO₄^3--P was stable at above 95% with an average effluent PO₄^3--P concentration below 0.5 mg·L^-1. When the SRT was further shortened to 15 d, the MLVSS decreased to values as low as 1448 mg·L^-1, and the proportion of DPBs in the phosphorus accumulating organisms (PAOs) decreased from 82.4% to 65.7%, indicating that the DPBs were gradually washed out from the system due to the excessively short SRT. At this stage, the phosphorus content of sludge decreased to 3.43%, while the rates of phosphorus release, phosphorus absorption, and denitrification also decreased to some extent. When the pH was increased (7.5-8.0), the anaerobic phosphorus release rate and the anoxic phosphorus absorption rate also increased, and reached 25.86 mg·(g·h)^-1 and 16.62 mg·(g·h)^-1, respectively, at a pH of 8.0. When the pH exceeded 8.0, the phosphorus removal efficiency dropped rapidly, supposedly due to phosphorus chemical precipitation.

Single-stage denitrifying phosphorus removal biofilter utilizing intracellular carbon source for advanced nutrient removal and phosphorus recovery

Advanced nutrient removal of municipal wastewater has insufficient carbon source, and resource recovery is neglected. In this study, a single-stage biofilter based on denitrifying phosphorus removal (DPR) was proposed for advanced nutrient removal and phosphorus recovery, which was operated under alternating anoxic/anaerobic mode with no extracellular carbon source in anoxic period. The results showed that the biofilter achieved efficient and stable performance with low carbon consumption (C/N ≈ 3.7). The average removal efficiency of NO₃^--N, TN and PO₄^3--P were 74.81%, 71.08% and 91.15%, respectively. DPR primarily occurred in the middle of the filtration bed and nutrient removal was driven by intracellular polymers, which was the main carbon source. High-throughput sequencing indicated that Dechloromonas was enriched and contributed to DPR while Zoogloea was responsible for endogenous denitrification. Denitrifying polyphosphate accumulating organisms and endogenous denitrifiers synergistically enhanced the nutrient removal capacity. The study further provides research perspectives for improving nutrient removal.

Phosphorus release and recovery from Fe-enhanced primary sedimentation sludge via alkaline fermentation

Phosphorus release and recovery from Fe-based chemically enhanced primary sedimentation (CEPS) sludge via alkaline fermentation was investigated. The coagulation results showed that 78% of organic matter and 95% of phosphorus were concentrated from sewage into sludge with the optimum dosages of 25 mg/L FeCl₃. The batch fermentation results revealed that 69.35% of the phosphorus in the Fe-sludge can be released and the maximum phosphorus concentration was 20.57 mg/L at pH 11. In the recovery stage, 90% of the P released in the fermented sludge supernatant was precipitated at a 2:1 ratio of magnesium to phosphorus and pH 11. The result of X-ray diffraction indicated that magnesium ammonium phosphate (MAP) was the major component of the precipitated solids. Thus, the present study provides an alternative option for phosphorus release and recovery as MAP from CEPS sludge via alkaline fermentation.

Improvement of nutrients removal from domestic wastewater by activated-sludge encapsulation with polyvinyl alcohol (PVA)

Conventional activated-sludge (AS) technologies are deficient for nutrient removal because they require specific floc characteristics. Therefore, the encapsulated AS with polyvinyl alcohol (PVA) will favor floc's formation that removes nutrients. The applied method was based on monitoring the removal of organic matter and nutrients (NH₄⁺, NO₃^-, NO₂^-, PO₄^3-) from synthetic domestic wastewater using laboratory-scale AS. The experimental reactors were operated at 8 h as optimized Hydraulic Retention Time (HRT). The sludge characteristics evaluation was carried out through the Sludge Volumetric Index (SVI), Food/Microorganism ratio (F/M), and Mixed Liquor Volatile Suspended Solids (MLVSS). Other specific floc characteristics, such as zeta potential and effective diameter were also evaluated. The results showed that the encapsulated AS with PVA favors nitrogen and phosphorous removal up to 35% but it did not improve organic matter removal. In addition, encapsulated AS with PVA has the characteristics of filamentous sludge (F/M: 0.7 g COD g^-1 MLVSS d^-1) with good settleability conditions (SVI: 43 mL g^-1 MLSVS h^-1) and low zeta potential (ZP: -0.9 mV), which favors its separation from the liquid phase. In conclusion, the encapsulation of AS with PVA improves nutrient removal by improving floc characteristics.

Alleviating Na+ effect on phosphate and potassium recovery from synthetic urine by K-struvite crystallization using different magnesium sources

Human urine is characterized by high concentrations of nitrogen (N), phosphorus (P) and potassium (K), of which the P and K can be recovered as K-struvite crystals. This study first investigated the formation of Na-struvite because of the high Na⁺ present in the urine. From the results, the optimal pH for the Na-struvite crystallization was observed to be 12, and the rise in the Na⁺ concentration distinctly favored the Na-struvite formation. As magnesium needed to be added to induce the K-struvite crystallization, several magnesium sources including MgCl₂, Mg sacrificial electrode and Mg(OH)₂ were applied to recover P and K from synthetic urine. The findings indicated that when MgCl₂ was used as the magnesium source, the K removal could be slightly enhanced by prolonging the reaction time, which would correspondingly decrease the Na concentration in the precipitates; besides, the intermittent addition of MgCl₂ could noticeably improve the removal efficiency of K by 6%, but simultaneously raise the Na content in the precipitates recovered. With respect to the use of the Mg sacrificial electrode, the recovery efficiencies of the P and K from synthetic urine were close to those with the use of MgCl₂. However, when Mg(OH)₂ was used as the magnesium source, the recovery efficiencies of P and K achieved only roughly 50%, which was much lower than those noted when MgCl₂ and the Mg sacrificial electrode were employed. A comprehensive analysis revealed that the MgCl₂ was the best magnesium source for the K-struvite crystallization, followed by the Mg sacrificial electrode and Mg(OH)₂.

[Effect of Influent Ammonia Concentration on a Biological Phosphorus Removal Granules System]

Mature biological phosphorus removal granules were inoculated into a SBR. The effect of the ammonia concentration on biological phosphorus removal granules system was investigated by increasing the concentration of ammonia in the influent. The ability of the system to withstand ammonia loading was determined. The results showed that when the influent ammonia concentration was below 45 mg·L^-1, the biological phosphorus removal granule system showed good performance. The TP removal efficiency was above 96%, the COD removal efficiency was over 89%. The effluent TP concentration and COD concentration were 0.4 mg·L^-1 and 25 mg·L^-1 respectively. The particle size was above 950 μm and the SVI was below 45 mL·g^-1. When the influent ammonia concentration was 60 mg·L^-1, the removal efficiency of TP was more than 95%. The effluent TP concentration was below 0.5 mg·L^-1, the particle size was 760 μm, and the SVI was 56 mL·g^-1. Furthermore, the biological phosphorus removal granules partially disintegrated and the metabolism and growth of PAOs began to be inhibited in the system. When the influent ammonia concentration reached 70 mg·L^-1, the removal efficiency of TP was 70%, the effluent TP concentration was about 3 mg·L^-1, the particle size was 570 μm, the SVI was 75 mL·g^-1, and the value of PN/PS was about 7.50. The biological phosphorus granules severely disintegrated and the metabolism and growth of PAOs was severely inhibited in the system. Moreover, as the influent ammonia concentration increased, the protein increased and polysaccharide decreased from the microbial secretion of biological phosphorus removal granules. Moreover, the value of PN/PS increased, the biological phosphorus removal granules disintegrated, the particle size decreased, the SVI increased, and the structure and function of the biological phosphorus removal granules were destroyed.

Effect of solids residence time on dynamic responses in chemical P removal

The impact of solids residence time (SRT) on the dynamics of phosphorus (P) removal by hydrous ferric oxide (HFO) floc was characterized through experimental and modeling studies. Three abiotic process conditions were considered in systems operated over a range of SRTs (~3 to 27 days): uptake in sequencing batch reactors (SBRs) under (a) constant and (b) dynamic P loading conditions, and (c) uptake in batch sorption tests with preformed HFO solids. P removal under all conditions was characterized by an initial period of fast removal followed by a period of slower removal until pseudo-equilibrium was reached. The initial removal rate increased with increasing P concentrations and was attributed to a larger concentration gradient between soluble- and adsorbed-phase concentrations. A kinetic model was developed and found to describe the dynamic behavior of P adsorption onto HFO floc under all conditions tested. A consistent mass transfer rate coefficient (k) was found to describe mass transfer over a range of SRTs for low initial P concentrations. At elevated SRTs (23-27 days) and elevated influent P concentrations, k values were found to deviate from those estimated at reduced SRTs. Differences in process mixing conditions were reflected in the estimated rate coefficients (k). Integration of the kinetic model with existing equilibrium models in wastewater process simulators will improve the ability to predict P uptake onto HFO floc under dynamic loading conditions in water resource recovery facilities. Models that consider the kinetics of P uptake will be particularly relevant for facilities that are required to achieve ultralow P concentrations. PRACTITIONER POINTS: This work provides a kinetic model that can be integrated with existing equilibrium models in wastewater process simulators to improve the ability to predict P uptake onto HFO floc under dynamic loading conditions. This research can be used to assist WRRFs to achieve ultralow effluent P requirements.

Nutrient removal in an algal membrane photobioreactor: effects of wastewater composition and light/dark cycle

Graesiella emersonii was cultivated in an osmotic membrane photobioreactor (OMPBR) for nutrients removal from synthetic wastewater in continuous mode. At 1.5 days of hydraulic retention time and under continuous illumination, the microalgae removed nitrogen (N) completely at influent NH₄⁺-N concentrations of 4-16 mg/L, with removal rates of 3.03-12.1 mg/L-day. Phosphorus (P) removal in the OMPBR was through biological assimilation as well as membrane rejection, but PO₄^3--P assimilation by microalgae could be improved at higher NH₄⁺-N concentrations. Microalgae biomass composition was affected by N/P ratio in wastewater, and a higher N/P ratio resulted in higher P accumulation in the biomass. The OMPBR accumulated about 0.35 g/L biomass after 12 days of operation under continuous illumination. However, OMPBR operation under 12 h light/12 h dark cycle lowered biomass productivity by 60%, which resulted in 20% decrease in NH₄⁺-N removal and nearly threefold increase in PO₄^3--P accumulation in the OMPBR. Prolonged dark phase also affected carbohydrate accumulation in biomass, although its effects on lipid and protein accumulation were negligible. The microalgae also exhibited high tendency to aggregate and settle, which could be attributed to reduction in cell surface charge and enrichment of soluble algal products in the OMPBR. Due to a relatively shorter operating period, membrane biofouling and salt accumulation did not influence the permeate flux significantly. These results improve the understanding of the effects of N/P ratio and light/dark cycle on biomass accumulation and nutrients removal in the OMPBR.

[Effect of Influent C/N Ratio on the Nutrient Removal Characteristics of SNEDPR Systems]

To determine the performance of nitrogen and phosphorus removal within a simultaneous nitrification endogenous denitrification system (SNEDPR), an extended anaerobic/low aerobic (dissolved oxygen:0.5-2.0 mg·L^-1)-operated sequencing batch reactor (SBR) was fed with simulation wastewater. The SBR was initiated under a constant influent C/N ratio of 10, with the simultaneous enrichment of polyphosphate-accumulating organisms (PAOs). It was then investigated at different influent C/N ratios of 10, 7.5, 5, and 2.5. The experimental results indicated that, when the influent C/N ratio was 10, SNEDPR could be successfully started up. The effluent PO₄^3--P and total nitrogen (TN) concentrations were 0.1 mg·L^-1 and 8.1 mg·L^-1. PO₄^3--P efficiency, TN efficiency, and SNED efficiency were 99.79%, 89.38%, and 58.0%, respectively. When the influent C/N ratio increased from 5 to 10, the nitrogen and phosphorus removal performance of the system improved with PRA, and SNED efficiency increased from 16.0 m·L^-1 and 48.0% to 24.4 mg·L^-1 and 69.2%, respectively. When the C/N ratio was 10, the TN and PO₄^3--P removal efficiencies increased to 94.5% and 100%, respectfully. When the C/N ratio was decreased to 2.5, the nitrogen and phosphorus removal performance of the system decreased. The PRA and SNED efficiencies were only 1.36 mg·L^-1 and 10%, respectively. During the stable phase of the system (C/N ratio were 10, 7.5 and 5), SNED efficiency reached to 85.9%, with the average effluent concentration of NH₄⁺-N, _x^--N, and PO₄^3--P being 0.0, 8.1, and 0.1 mg·L^-1, respectively.