Screening of Polyphosphate Accumulating Organisms and Their Phosphorus Removal Performance

[Objectives]To study the phosphorus removal performance of phosphate accumulating organisms(PAOs).[Methods]Activated sludge from domestic sewage treatment plant was used as the strain source,and phosphate accumulating organisms were screened by plate streaking method and dilution coating plate method.Six kinds of excellent phosphate accumulating organisms were obtained by metachromatic granule staining experiment,total phosphorus experiment and simulated sewage phosphorus removal experiment to assist the observation of bac-terial morphology and experiment of phosphorus removal capacity.In addition,the influencing factors of phosphorus removal capacity(nitrogen source,trace metal ions)were analyzed.[Results]In the case of simulated sewage,the phosphorus removal rate of strain b was the highest,reaching 66.25%,while the phosphorus removal rate of strain e and f was about 10%lower than that of the phosphorus uptake experiment.[Conclusions]This study is expected to provide a theoretical reference for the gradual optimization of the screening method of phosphorus re-moval bacteria in domestic sewage treatment.

Temporal Dynamics and Performance Association of the Tetrasphaera-Enriched Microbiome for Enhanced Biological Phosphorus Removal

Tetrasphaera have been recently identified based on the 16S ribosomal RNA(rRNA)gene as among the most abundant polyphosphate-accumulating organisms(PAOs)in global full-scale wastewater treatment plants(WWTPs)with enhanced biological phosphorus removal(EBPR).However,it is unclear how Tetrasphaera PAOs are selectively enriched in the context of the EBPR microbiome.In this study,an EBPR microbiome enriched with Tetrasphaera(accounting for 40%of 16S sequences on day 113)was built using a top-down design approach featuring multicarbon sources and a low dosage of allylthiourea.The microbiome showed enhanced nutrient removal(phosphorus removal~85%and nitrogen removal~80%)and increased phosphorus recovery(up to 23.2 times)compared with the seeding activated sludge from a local full-scale WWTP.The supply of 1 mg·L^(-1)allylthiourea promoted the coselection of Tetrasphaera PAOs and Microlunatus PAOs and sharply reduced the relative abundance of both ammonia oxidizer Nitrosomonas and putative competitors Brevundimonas and Paracoccus,facilitating the establishment of the EBPR microbiome.Based on 16S rRNA gene analysis,a putative novel PAO species,EBPR-ASV0001,was identified with Tetrasphaera japonica as its closest relative.This study provides new knowledge on the establishment of a Tetrasphaera-enriched microbiome facilitated by allylthiourea,which can be further exploited to guide future process upgrading and optimization to achieve and/or enhance simultaneous biological phosphorus and nitrogen removal from high-strength wastewater.

Nitrogen and phosphorus removal in pilot-scale anaerobic-anoxic oxidation ditch system

To achieve high efficiency of nitrogen and phosphorus removal and to investigate the rule of simultaneous nitrification and denitrification phosphorus removal （SNDPR）, a whole course of SNDPR damage and recovery was studied in a pilot-scale, anaerobicanoxic oxidation ditch （OD）, where the volumes of anaerobic zone, anoxic zone, and ditches zone of the OD system were 7, 21, and 280 L, respectively. The reactor was fed with municipal wastewater with a flow rate of 336 L/d. The concept of simultaneous nitrification and denitrification （SND） rate （rSND） was put forward to quantify SND. The results indicate that： （1） high nitrogen and phosphorus removal efficiencies were achieved during the stable SND phase, total nitrogen （TN） and total phosphate （TP） removal rates were 80% and 85%, respectively; （2） when the system was aerated excessively, the stability of SND was damaged, and rSND dropped from 80% to 20% or less; （3） the natural logarithm of the ratio of NOx to NH4^＋ in the effluent had a linear correlation to oxidation-reduction potential （ORP）; （4） when NO3^- was less than 6 mg/L, high phosphorus removal efficiency could be achieved; （5） denitrifying phosphorus removal （DNPR） could take place in the anaerobic-anoxic OD system. The major innovation was that the SND rate was devised and quantified.

Removal of nitrogen and phosphorus in a combined A^2/O-BAF system with a short aerobic SRT

A bench-scale anaerobic/anoxic/aerobic process-biological aerated filter （A^2/O-BAF） combined system was carded out to treat wastewater with lower C/N and C/P ratios. The A^2/O process was operated in a short aerobic sludge retention time （SRT） for organic pollutants and phosphorus removal, and denitrification. The subsequent BAF process was mainly used for nitrification. The BAF effluent was partially returned to anoxic zone of the A^2/O process to provide electron acceptors for denitrification and anoxic P uptake. This unique system formed an environment for reproducing the denitdfying phosphate-accumulating organisms （DPAOs）. The ratio of DPAOs to phosphorus accumulating organisms （PAOs） could be maintained at 28% by optimizing the organic loads in the anaerobic zone and the nitrate loads into the anoxic zone in the A^2/O process. The aerobic phosphorus over-uptake and discharge of excess activated sludge was the main mechanism of phosphorus removal in the combined system. The aerobic SRT of the A^2/O process should meet the demands for the development of aerobic PAOs and the restraint on the nitrifiers growth, and the contact time in the aerobic zone of the A^2/O process should be longer than 30 min, which ensured efficient phosphorus removal in the combined system. The adequate BAF effluent return rates should be controlled with 1--4 mg/L nitrate nitrogen in the anoxic zone effluent of A^2/O process to achieve the optimal nitrogen and phosphorus removal efficiencies.

Simultaneous phosphorus and nitrogen removal in a continuous-flow two-sludge system

The ability of simultaneous biological phosphorus and nitrogen removal was investigated in a lab-scale continuous-flow two-sludge system. Alternating anaerobic and anoxic conditions were combined with contact oxidation stage for treating raw municipal wastewater. Long-term experiments showed that the contradiction of competing for the organic substrate between denitrifying bacteria and PAOs （phosphorus accumulating organisms） in traditional phosphorus and nitrogen removal system has been resolved. The system can adapt to low influent COD/TN ratio （C/N）. Furthermore the SRT （sludge retention time） of nitrifying sludge and denitrifying phosphorus removal sludge can be controlled at optimal conditions respectively. The removal efficiency of COD, TP, TN, and NH4-N was 81.78%, 92.51%, 75.75%, and 84.47% respectively. It was also found that the appropriate influent C/N should be controlled at the range of 3.8-6, while the optimal C/N to the system ranged between 4-5, and the BFR （bypass sludge flow rate） should be controlled at 0.35 around.

Addition of anaerobic tanks to an oxidation ditch system to enhance removal of phosphorus from wastewater

The oxidation ditch has been used for many years all over the world as an economic and efficient wastewater treatment technology. It can remove COD, nitrogen and a part of phosphorus efficiently. In the experiment described, a pilot scale Pasveer oxidation ditch system has been tested to investigate the removal of phosphorus from wastewater. The experimental results showed that influent total phosphorus(TP) was removed for 35%-50%. After this, two anaerobic tanks with total volume of 11 m 3 were added to the system to release phosphorus. As a result, the TP removal efficiency increased by about 20%. At an anaerobic HRT of about 6 hours, a TP removal efficiency of 71% was achieved.

Optimum operation conditions of nitrogen and phosphorus removal by a biofilm-activated-sludge system

In the biofilm and activated sludge combined system, denitrifying bacteria attached on the fibrous carriers in the anoxic tank, while the sludge containing nitrifying and phosphorus removal bacteria was only recirculated between the aerobic and anaerobic tanks. Therefore, the factors affected and restricted nitrification, denitrification and phosphorus removal in a traditional A/A/O process were resolved. This paper describes the optimum operation conditions for nitrogen and phosphorus removal using this system.

Characterization of phosphorus removal bacteria in （AO）^2 SBR system by using different electron acceptors

Characteristics of phosphorus removal bacteria were investigated by using three different types of electron acceptors, as well as the positive role of nitrite in phosphorus removal process. An （AO）^2 SBR （anaerobic-aerobic-anoxic-aerobic sequencing batch reactor） was thereby employed to enrich denitrifying phosphorus removal bacteria for simultaneously removing phosphorus and nitrogen via auoxic phosphorus uptake, Ammonium oxidation was controlled at the first phase of the nitrification process. Nitrite-inhibition batch tests illustrated that nitrite was not an inhibitor to phosphorus uptake process, but served as an alternative electron acceptor to nitrate and oxygen if the concentration was under the inhibition level of 40mg NO2 - N·L^- 1. It implied that in addition to the two well-accepted groups of phosphorus removal bacterium （ one can only utilize oxygen as electron acceptor, P1, while the other can use both oxygen and nitrate as electron acceptor, P2 ）, a new group of phosphorus removal bacterium P3, which could use oxygen, nitrate and nitrite as electron acceptor to take up phosphorus were identified in the test system. To understand （AO）^2 SBR sludge better, the relative population of the different bacteria in this system, plus another A/O SBR sludge （ seed sludge） were respectively estimated by the phosphorus uptake batch tests with either oxygen or nitrate or nitrite as electron acceptor. The results demonstrated that phosphorus removal capability of （AO）^2 SBR sludge had a little degradation after A/O sludge was cultivated in the （AO）^2 mode over a long period of time. However, deuitrifying phosphorus removal bacteria （ P2 and P3 ） was significantly enriched showed by the relative population of the three types of bacteria, which implied that energy for aeration and COD consumption could be reduced in theory.

Influence Factors of Phosphorus Removal by Chemical Method in Sewage Treatment System

[Objective] The research aimed to study influence factors of phosphorus removal by chemical method in sewage treatment system. [ Method] In different reaction systems, removal effect of the phosphorus in sewage by dosing lime and influence of the constraint factor were stud- ied. [ Result] Lime precipitation method treating high-concentration phosphorus wastewater could not only decline cost of phosphorus removal by chemical method, but also reach better treatment effect under suitable stirring and precipitation conditions by controlling alkalinity and pH. Phosphor- us content of chemical sludge after treatment could reach 9% -12%, with higher recyclable value. E Conclusion] Lime method treating phosphorus- rich sewage was more economic than low-concentration phosphorus sewage, and had very great potential for recycling phosphorus.

A Floating Island Treatment System for the Removal of Phosphorus from Surface Waters

The goal of this project was to design, build, and test a pilot-scale floating modular treatment system for total phosphorus （TP） removal from nutrient-impaired lakes in central Florida, USA. The treatment sys-tem consisted of biological and physical-chemical treatment modules. First, investigations of prospective biological and physical-chemical treatment processes in mesocosms and in bench-scale experiments were conducted. Thirteen different mesocosms were constructed with a variety of substrates and combi-nations of macrophytes and tested for TP and orthophosphate （PO4-^3） removal efficiencies and potential areal removal rates. Bench-scale jar tests and column tests of seven types of absorptive media in addition to three commercial resins were conducted in order to test absorptive capacity. Once isolated process testing was complete, a floating island treatment system （FITS） was designed and deployed for eight months in a lake in central Florida. Phosphorus removal efficiencies of the mesocosm systems averaged about 40%-50%, providing an average uptake of 5.0 g.m ^2.a ^1 across all mesocosms. The best-performing mesocosms were a submerged aquatic vegetation （SAV） mesocosm and an algae scrubber （AGS）, which removed 20 and 50 mg.m ^2.d ^1, respectively, for an average removal of 5.5 and 12.0 g.m ^2.a ^1 for the SAV and AGS systems, Of the absorptive media, the best performance was alum residual （AR）, which reduced PO4-^3 concentrations by about 75% after 5 min of contact time. Of the commercial resins tested, the PhosX resin was superior to the others, removing about 40% of phosphorus after 30 rain and 60% after 60min. Under baseline operation conditions during deployment, the FITS exhibited mean PO4-^3 removal efficiencies of 53%; using the 50th and 90th percentile of PO4-^3 removal during deployment, and the footprint of the FITS system, yielded efficiencies for the combined FITS system of 56% and 86%, respectively, and areal phosphorus removal rates between 8.9 and 16.5 g.m ^2.a ^1

Salt effect on MUCT system performance of nitrogen and phosphorus removal

The effect of salinity on biological nitrogen and denitrifying phosphorus removal was investigated in a Modified University of Cape Town(MUCT)system.Removal rates of COD,NH_(4)^(+)-N,NO_(3)^(-)-N,NO_(2)^(-)-N,phosphorus and the sludge characteristics at salt concentrations(0.0,3.2,6.4,11.2 and 16.0 g L^(-1))were analyzed.With the salt concentration increasing,all the COD,NH_(4)^(+)-N,TN and TP removal rates exhibited a trend of decline,and exhibited an initial reduction and subsequent increase at every stage of salt concentration.NH_(4)^(+)-N,TN and TP removal rates were 92.7%,51.5%and 67.2%in 16 g L^(-1) salt concentration,respectively.And they were outperformed the literature reported and acceptable in practical applications.When the salinity of wastewater changed from 0.0 to 16.0 g L^(-1),the biomass yield coefficients increased from 0.0794 to 0.126 g VSS/g COD.Increased salinity had a detrimental effect on phosphorus-accumulating organisms(PAOs)and denitrifying PAOs(DPAOs)(especially DPAOs).Therefore,phosphorus removal gradually depended on PAO.The simultaneous nitrification and denitrification(SND)rate and nitrogen removal rate(including nitrification rate,denitrification rate,and total nitrogen removal rate)gradually decreased with the increased salinity.

Mechanism of phosphorus removal in beneficiation of high phosphorous oolitic hematite by direct reduction roasting with dephosphorization agent

High phosphorous oolitic hematite ore is one of typical intractable iron ores in China, and the conventional beneficiation methods are found to be impracticable to , remove phosphorus from the ore effectively. Better beneficiation index were gotten by direct reduction roasting with dephosphorization agent followed by two stages of grinding and magnetic separation. P content decreases from 0.82% in the raw ore to 0.06% in the magnetic concentrate, and the total iron grade increases from 43.65% to 90.23%, the recovery of iron can reach 87%. Mechanisms of phosphorus removal in the beneficiation of high phosphorous oolitic hematite ore by direct reduction roasting with dephosphorization agent were studied using XRD, SEM and EPMA. The results showed that about 20% of the apatite in the raw ore transferred into phosphorus and volatilized with the gas in the process of reduction roasting, while the rest 80% apatite was not involved in the reaction of generation of phosphorus, and remained as apatite in the roasted products, which was removed to tailings by grinding and magnetic separation. A small amount of phosphorus existed in the magnetic concentrate as apatite. The oolitic texture of raw ore was partly changed during roasting, resulting in the formation of nepheline in the reaction between the dephosphorization agent, SiO2 and Al2O3 in the raw ore, which greatly improved the liberation degree of minerals in the roasted products, and it was beneficial to the subsequent grinding and magnetic separation.

Thermodynamic study on phosphorus removal from tungstate solution via magnesium salt precipitation method

The thermodynamic equilibrium diagrams of Mg2＋- 3-4PO - ＋4NH -H2O system at 298 K were established based on the thermodynamic calculation. From the diagram, the thermodynamic conditions for removing phosphorus from the tungstate solution by magnesium salt precipitation were obtained. The results show that when the concentration of total magnesium increases from 0.01 mol/L to 1.0 mol/L, the optimal pH for the phosphorus removal by magnesium phosphate decreases from 9.8 to 8.8. The residual concentration of total phosphorus almost keeps the level of 4.0×10-6 mol/L in the system. MgHPO4, Mg3（PO4）2 and the mixture of Mg3（PO4）2 and Mg（OH）2 are stabilized in these system, respectively. However, increasing the total concentration of magnesium has little effect on phosphorus removal by magnesium ammonium phosphate, while it is helpful for phosphorus removal by increasing the total ammonia concentration. The calculated results demonstrate that the residual concentration of total phosphorus can decrease to 5.0×10-7 mol/L as the total concentration of ammonia reaches 5.0 mol/L and the optimal pH value is 9-10. Finally, verification experiments were conducted with home-made ammonium tungstate solution containing 50 g/L WO3 and 13 g/L P. The results show that when the dosage of MgCl2 is 1.1 times of the theoretical amount, the optimum pH for removing phosphorus is 9.5, which matches with the results of the theoretical calculation exactly.

Denitrifying phosphorus removal in a step-feed CAST with alternating anoxic-oxic operational strategy

A bench-scale cyclic activated sludge technology （CAST） was operated to study the biological phosphorus removal performance and a series of batch tests was carried out to demonstrate the accumulation of denitrifying polyphosphate-accumulating organisms （DNPAOs） in CAST system. Under all operating conditions, step-feed CAST with enough carbon sources in influent had the highest nitrogen and phosphorus removal efficiency as well as good sludge settling performance. The average removal rate of COD, NH4^＋-N, PO4^3--P and total nitrogen （TN） was 88.2%, 98.7%, 97.5% and 92.1%, respectively. The average sludge volume index （SVI） was 133 mL/g. The optimum anaerobic/aerobic/anoxic （AOA） conditions for the cultivation of DNPAOs could be achieved by alternating anoxic/oxic operational strategy, thus a significant denitrifying phosphorus removal occurred in step-feed CAST. The denitrification of NO^x--N completed quickly due to step-feed operation and enough carbon sources, which could enhance phosphorus release and further phosphorus uptake capability of the system. Batch tests also proved that polyphosphate-accumulating organisms （PAOs） in the step-feed process had strong denitrifying phosphorus removal capacity. Both nitrate and nitrite could be used as electron acceptors in denitrifying phosphorus removal. Low COD supply with step-feed operation strategy would favor DNPAOs accumulation.

Influence of pH on short-cut denitrifying phosphorus removal

Through a series of experiments using denitrifying phosphorus-accumulating sludge in sequencing batch reactors （SBRs）, the variations of the intracellular polymers during the anaerobic phosphorus release process at different pH values were compared, the probable reasons for different performances of phosphorus removal were examined, and system operations in a typical cycle were investigated. The results show that the phosphorus removal rate was positively correlated with pH values in a range of 6.5-8.5. When the pH value was 8.0, the anaerobic phosphorus release rate and anoxic phosphorus uptake rate of the activated sludge were 20.95 mg/（g, h） and 23.29 mg/（g, h）, respectively; the mass fraction of poly-13-hydroxybutyrate （PHB） increased to 62.87 mg/g under anaerobic conditions; the mass fraction of polyphosphate was 92.67 mg/g under anoxic conditions; and the effluent concentration of total phosphorus （TP） was 1.47 mg/L. With the increase of pH, the mass fraction of acetic acid and PHB also increased, and the absorption rate of acetic acid was equal to the disintegration rate of polyphosphate. When the pH value was above 8.0, biological phosphorus removal was achieved by chemical phosphorus precipitation, and the phosphorus removal rate decreased.

Effect of carbon source and nitrate concentration on denitrifying phosphorus removal by DPB sludge

Effect of added carbon source and nitrate concentration on the denitrifying phosphorus removal by DPB sludge was systematically studied using batch experiments, at the same time the variation of ORP was investigated. Results showed that the denitrifying and phosphorus uptake rate in anoxic phase increased with the high initial anaerobic carbon source addition. However once the initial COD concentration reached a certain level, which was in excess to the PHB saturation of poly-P bacteria, residual COD carried over to anoxic phase inhibited the subsequent denitrifying phosphorus uptake. Simultaneously, phosphate uptake continued until all nitrate was removed, following a slow endogenous release of phosphate. High nitrate concentration in anoxic phase increased the initial denitrifying phosphorus rate. Once the nitrate was exhausted, phosphate uptake changed to release. Moreover, the time of this turning point occurred later with the higher nitrate addition. On the other hand, through on-line monitoring the variation of the ORP with different initial COD concentration, it was found ORP could be used as a control parameter for phosphorus release, but it is impossible to utilize ORP for controlling the denitrificaion and anoxic phosphorus uptake operations.

Enhanced Biological Phosphorus Removal with Pseudomonas putida GM6 from Activated Sludge

The enhanced biological phosphorus removal （EBPR） method is widely adopted for phosphorus removal from wastewater, yet little is known about its microbiological and molecular mechanisms. Therefore, it is difficult to predict and control the deterioration of the EBPR process in a large-scale municipal sewage treatment plant. This study used a novel strain isolated in the laboratory, Pseudomonas putida GM6, which had a high phosphate accumulating ability and could recover rapidly from the deteriorated system and enhance the capability of phosphorus removal in activated sludge. Strain GM6 marked with gfp gene, which was called GMTR, was delivered into a bench-scale sequencing batch reactor （SBR） of low efficiency, to investigate the colonization of GMTR and removal of phosphorus. After 21 days, the proportion of GMTR in the total bacteria of the sludge reached 9.2%, whereas the phosphorus removal rate was 96%, with an effluent concentration of about 0.2 mg L^-1. In the reactor with the addition of GMTR, phosphorus was removed quickly, in 1 h under anaerobic conditions, and in 2 h under aerobic conditions. These evidences were characteristic of EBPR processes. Field testing was conducted at a hospital sewage treatment facility with low phosphorus removal capability. Twentyone days after Pseudomonas putida GM6 was added, effluent phosphorus concentration remained around 0.3 mg L^-1, corresponding to a removal rate of 96.8%. It was therefore demonstrated that Pseudomonas putida GM6 could be used for a quick startup and enhancement of wastewater biological phosphorus removal, which provided a scientific basis for potential large-scale engineering application.

Evaluation of phosphorus removal from wastewater by soils in rural areas in China

Low-cost, easy-maintenance and high-efficiency decentralized wastewater treatment technologies are urgently needed in rural areas of China. Processes with high potential for phosphorus removal are of great interest. However, commonly used treatment methods often do not meet the strict criteria for removing phosphorus from rural wastewater. In order to search an economic and simple technology for phosphorus removal from the common bit-technologies effluent, seven soil types collected from different rural areas in China were investigated for their ability to remove phosphorus. X-ray diffraction （XRD） was used to analyse the mineral structure, and inductively coupled plasma optical emission spectrometer （ICP-OES） was used to analyse the geochemical composition of the soil samples. Three primary minerals - quartz, albite and montmorillonite - were clearly detected. The samples were divided into two soil types, acidic soils and alkaline soils, based on their pH values. The geochemical composition study indicated that a higher percentage of Ca and Mg occurred in alkaline soils （pH 〉 8） than in acidic soils （pH 〈 6.5）. Adsorption isotherms from batch experiments fitted the Langmuir and Freundlich models well, the maximum P adsorption capacities ranged from 0.256 to 1.598 mg P/g, indicating a high phosphorus removal potential for all of these soils. The P fractions extracted revealed that the sum of NaOH-extracted inorganic P （NaOH-Pi） was the major P component in the acidic soils, and CaCO3-bound phosphorus （Ca-P） in the alkaline soils. Dynamic adsorption simulation showed that these soils have the ability to remove phosphorus from wastewater.

Effect of Ferric Chloride on the Properties of Biological Sludge in Co-precipitation Phosphorus Removal Process

This paper studied the effect of ferric chloride on waste sludge digestion,dewatering and sedimentation under the optimized doses in co-precipitation phosphorus removal process.The experimental results showed that the concentration of mixed liquid suspended solid(MLSS) was 2436 mg.L-1 and 2385 mg.L-1 in co-precipitation phosphorus removal process(CPR) and biological phosphorous removal process(BPR),respectively.The sludge reduction ratio for each process was 22.6% and 24.6% in aerobic digestion,and 27.6% and 29.9% in anaerobic digestion,respectively.Due to the addition of chemical to the end of aeration tank,the sludge content of CPR was slightly higher than that of BPR,but the sludge reduction rate for both processes had no distinct difference.The sludge volume index(SVI) and sludge specific resistance of BPR were 126 ml.g-1 and 11.7×1012 m.kg-1,respectively,while those of CPR were only 98 ml.g-1 and 7.1×1012 m.kg-1,indicating that CPR chemical could improve sludge settling and dewatering.

PHOSPHORUS REMOVAL USING STEEL SLAG

Steel slag is a byproduct produced in large amounts in the steel-making process. It is an important resource that can be effectively utilized. An experiment was described in which steel slag was tested as an adsorbent for the removal of phosphorus from waste water. Phosphorus removal depended on the amount of steel slag added, the pH value, the contact time, and the initial concentration. Under laboratory conditions when the added slag was 7.5g/L, the contact time 2h, and the pH value was equivalent to 6.5, over 99% of the phosphorus was removed; the experimental data on steel slag adsorption of phosphorus in the water fitted the Freundlich isotherm model. Steel slag was found to be very effective in adsorbing phosphorus.