Laboratory Simulation on Phosphorus Releasing near the Water/Sediment Interface in the East China Sea off the Changjiang Estuary

Surface sediment samples taken from the East China Sea off the Changjiang estuary are used as raw materials for phosphorus releasing experiment. It is found that after being thoroughly mixed with seawater for about 10 minutes, phosphorus released from the sediments reaches its maximum value. Adsorption kinetics can be fitted with both Elovich equation and two-constant rate equation. The releasing amount is closely related to the composition of the sediments. Phosphorus release from silty and muddy sediment is higher than from that dominated by sandy composition. For the desorption reaction, iron-phosphorus (Fe-P) is the most active one, with a releasing ratio higher than other phosphorus forms, followed by absorbed-phosphorus (Ad-P) and organic bound phosphorus (OP). All of them can be referred to as bio-available phosphorus. The results demonstrate that phosphorus in sediments can be released into seawater under suitable hydrodynamic conditions, and have a great impact on the nutrition state and primary productivity of marine biosphere.

Phosphorus fractions and its release in the sediments of Haihe River,China

The amounts and forms of phosphorus （P） in surface sediments of Haihe River, Tianjin, North China, were examined using a sequential chemical extraction procedure. Five fractions of sedimentary P, including loosely sorbed P （NH4Cl-P）, redox-sensitive P （BD-P）, metal oxide bound P （NaOH-P）, calcium bound P （HCI-P）, and residual P （Res-P） （organic and refractory P）, were separately quantified. The results indicated that the contents of different P fractions in the sediments varied greatly. The total P （TP） contents ranged from 968 to 2017 mg/kg. Phosphorus contents in NH4Cl-P, BD-P, NaOH-P, and HCl-P ranged from 6.7 to 26.6 mg/kg, 54.5 to 90.2 mg/kg, 185.2 to 382.5 mg/kg, and 252.3 to 425.5 mg/kg, respectively, which represented 1.2%-3.2%, 7.7%-13%, 33.3%-48.9%, and 36.2%-54.2% of the sedimentary inorganic P, respectively. For all the sediment samples, the rank order of P-fractions was Res-P 〉 HCl-P 〉 NaOH-P 〉 BD-P 〉 NH4Cl-P. The highly positive relationship between the amounts of P released from the sediments and those in the NH4Cl-P and BD-P fractions, indicated that NH4Cl-P and BD-P were the main fractions that can release P easily.

Competition for Single Carbon Source Between Denitrification and Phosphorus Release in Sludge under Anoxic Condition

In order to investigate the competition for carbon source between denitrification and phosphorus release processes,simultaneous phosphorus release and denitrification in sludge operated in anoxic,aerobic mode are investigated by varying the ratio of influent COD to nitrogenous compound concentration under anoxic condition using a lab-scale sequencing batch reactor（SBR）.The results show that the nitrate reduction rate is nearly independent of the ratio of influent COD to nitrate under anoxic condition.More NOx^--N in the influent leads to less PO4^3--P release during the feeding period.However, PO4^3--P release proceeds at a low rate simultaneously with denitrification even when the influent NOx^--N concentration is as large as 20 mg·L^-1and its rate is increased obviously when NOx^--N is denitrified to a concentration lower than 0.5 mg·L^-1.The variation of pH during anoxic period gives some information about the biochemical reactions of denitrification and PO4^3--P release.When more nitrate is present in the influent,more acetate uptake in feeding period is used for direct microorganism growth.

Effect of Return Sludge Pre-concentration on Biological Phosphorus Removal in a Novel Oxidation Ditch

A pilot-scale,pre-anoxic-anaerobic oxidation ditch was used in this study to treat municipal wastewater with limited carbon source.A novel return activated sludge(RAS) pre-concentration tank was adopted for improv-ing the phosphorus removal efficiency and the effects of RAS pre-concentration ratio were studied.Under the opti-mal operational condition,the suspended total phosphorus(STP) and the total phosphorus(TP) removal efficiencies were around 58.9% and 63.9% respectively and the effluent-P was lower than 0.8 mg·L-1.The reason is that with the optimal RAS pre-concentration ratio,nitrate is completely removed with endogenous carbon source and the secondary phosphorus release is strictly restrained in the pre-anoxic tank.Therefore,the anaerobic phosphorus release and the carbon source uptake by phosphorus accumulation organisms(PAOs) in the sludge,which are ex-tremely important to the phosphorus removal process,can be fully satisfied.Furthermore,the oxidation-reduction potential is proved to be suitable for controlling the RAS pre-concentration ratio due to influent fluctuation and varied conditions.The novel modified system is also beneficial for PAO accumulation.

Effects of benthic algae on release of soluble reactive phosphorus from sediments: a radioisotope tracing study

To evaluate the effect of benthic algae on soluble reactive phosphorus（SRP） release from sediments in shallow lakes, experiments on SRP release with and without benthic algae in sediment cores and an experiment on SRP uptake by benthic algae were conducted using the radioisotope（32P） tracing method. The dissolved oxygen（DO） concentration in sediment cores was also investigated. The results show that benthic algae effectively reduce the release of SRP from sediments to overlying water. The uptake of SRP by benthic algae, which is the direct way in which benthic algae affect the SRP release from sediments, is low in filtered water and increases with the SRP concentration. However, in the experiment, the increased uptake rate lasted for a short time（in one hour）, and after that it returned to a low rate. Benthic algae make the DO concentration and the oxic layer thickness increased, which can indirectly reduce the SRP release from sediments. These findings indicate that benthic algae can reduce the SRP release from sediments in both direct and indirect ways. It seems that the indirect way also plays an important role in reducing the SRP release from sediments.

Effect of Different Remediators on the Control of Phosphorus Release from Landscape River Sediments

In this paper,different chemicals were added to sediments to control phosphorus release from river sediments by means of different dosing methods,thus reducing the concentration of organic pollutants in overlying water.Two remediators,aluminum sulfate and ferric chloride,were respectively added to six groups of experimental samples in three different covering methods,namely injection,mixing and tiling,and a control group was set up.The results showed that at the initially stationary phase of the experiment,the control effect of phosphorus release from sediments of mixing of aluminum sulfate was the most obvious,followed by tiling and injection into the mud;at the finally stationary phase of the experiment,the control effect of phosphorus release from sediments of injection of aluminum sulfate was the most obvious,followed by mixing and tiling.Under the same coverage,the inhibition effect of aluminum sulfate was more obvious than that of ferric chloride.This paper undertook research into the control effect of phosphorus release from sediments to provide a reference point for the control of water eutrophication in the days to come.

Release Flux Estimation of Sediment Phosphorus in Shiwuli River Estuary of Chao Lake in Summer

[Objective] The study aimed to estimate the release flux of sediment phosphorus in Shiwuli River estuary of Chao Lake in summer. [Method] Under static and dynamic conditions, we analyzed the release characteristics of sediment phosphorus in Shiwuli River estuary of Chao Lake in summer, and estimated the release flux of sediment phosphorus in the studied area in summer. [Result] Disturbance had great effects on the release of sediment phosphorus in Shiwuli River estuary of Chao Lake in summer. When phosphorus concentration in overlying water was 0 mg/L, the amount of released phosphorus under dynamic conditions was 2.3 times as much as that under static conditions; as phosphorus concentration in overlying water was 0.05 mg/L, the amount of released phosphorus under dynamic conditions was 1.3 times as much as that under static condi- tions. In a word, the amount of released phosphorus under dynamic conditions was higher than that under static conditions. In summer, the release flux of sediment phosphorus in Shiwuli River estuary of Chao Lake was very high, namely 0.2 t/km2. Therefore, besides controlling exogenous phosphorus pollution, we should pay more attention to the release of sediment phosphorus. [ Conclusion] The research could provide theoretical ref- erences for dredging sediment and controlling lake eutrophication in future.

Effect of phosphate releasing in activated sludge on phosphorus removal from municipal wastewater

Aluminum and ferric salts are commonly used in municipal wastewater treatment plants（WWPTs） for phosphorus（P） removal. In this study, on-site jar tests were conducted to determine the removal of different P species from the fresh samples in the presence and absence of activated sludge（AS） with different doses of alum, poly-aluminum chloride,and ferric chloride at different p H. The soluble P（SP） concentration in the samples was about 0.63 mg/L. When the mixed liquor containing AS was treated with 8 mg/L of Al, SP could be reduced to 0.13 mg/L, while it was reduced to 0.16 mg/L with only 1 mg/L of Al after sedimentation removal of AS from sample. Chemical analysis determined that AS contained 59.8 mg-P/g-TSS and 43.8 mg-Al/g-TSS and most of the P was associated with the aluminum hydroxide. We discovered that the phosphate in the AS could readily be released from it, which was mainly responsible for ineffective removal of P to low levels in mixed liquor even with very high alum dose. This study provides new insight into the behavior and fate of P in the wastewater treatment plants that use alum to enhance P removal in the final effluent.

A new strategy for obtaining highly concentrated phosphorus recovery solution in biofilm phosphorus recovery process

Recovery of phosphorus(P)from wastewater is of great significance for alleviating the shortage of P resources.At present,the P recovery process is faced with the problem of excessive organic carbon consumption when obtaining a P-concentrated recovery solution.This study proposed a new strategy to obtain a more highly concentrated P recovery solution with minimal carbon consumption by strengthening the P storage capacity of the biofilm.A biofilm sequencing batch reactor(BSBR)process was modified to treat synthetic wastewater.The effect of the dissolved oxygen(DO)concentration on the P storage capacity of the biofilm was investigated at DO concentrations of DO 3.5 mg/L(P_(L))and DO 6.5 mg/L(P_(H)).The results showed a maximum P storage of 101.2 and 149.6 mg-P/g-mixed liquid suspended solids under the two conditions.Strengthening the P storage capacity of the biofilm resulted in a net increase in the P recovery rate,which was as high as 66.96%in a harvesting cycle,and total soluble P>220 mg/L in the P recovery solution was successfully achieved.Meanwhile,the carbon cost of P recovery in the BSBR was reduced to 41.57 g-chemical oxygen demand/gP,and the carbon utilization efficiency was enhanced.To highlight the new strategy,the P recovery performance of the BSBR was given and the relationship between P content and anaerobic P release was discussed.In addition,the changes in the microbial communities under P_(L) and P_(H) conditions were analyzed.

Kinetic analysis of anaerobic phosphorus release during biological phosphorus removal process

Enhanced biological phosphorus removal(EBPR)is a commonly used and sustainable method for phosphorus removal from wastewater.Poly-β-hydroxybutyrate(PHB),polyphosphate,and glycogen are three kinds of intracellular storage polymers in phosphorus accumulation organisms.The variation of these polymers under different conditions has an apparent influence on anaerobic phosphorus release,which is very important for controlling the performance of EBPR.To obtain the mechanism and kinetic character of anaerobic phosphorus release,a series of batch experiments were performed using the excessively aerated sludge from the aerobic unit of the biological phosphorus removal system in this study.The results showed that the volatile suspended solid(VSS)had an increasing trend,while the mixed liquid suspended sludge(MLSS)and ashes were reduced during the anaerobic phosphorus release process.The interruption of anaerobic HAc-uptake and phosphorus-release occurs when the glycogen in the phosphorus-accumulating-organisms is exhausted.Under the condition of lower initial HAc-COD,HAc became the limiting factor after some time for anaerobic HAc uptake.Under the condition of higher initial HAc-COD,HAc uptake was stopped because of the depletion of glyco-gen in the microorganisms.The mean ratio ofΔ_(ρP)/Δ_(ρPHB),Δ_(ρ)GLY/ΔρPHB,Δ_(ρP)/ΔCOD,andΔ_(ρPHB)/ΔCOD was 0.48,0.50,0.44,and 0.92,respectively,which was nearly the same as the theoretical value.The calibrated kinetic parameters of the HAc-uptake and phosphorus-release model were evaluated as follows:QHAc,max was 164 mg/(g·h),QP,max was 69.9 mg/(g·h),Kgly was 0.005,and KCOD was 3 mg/L.An apparently linear correlation was observed between the ratio ofΔ_(ρP)/ΔCOD and pH of the solution,and the equation between them was obtained in this study.Enhanced biological phosphorus removal(EBPR)is a commonly used and sustainable method for phosphorus removal from wastewater.Poly-β-hydroxybutyrate(PHB),polyphosphate,and glycogen are three kinds of intracellular storage polymers in phosphorus accumulation organisms.The variation of these polymers under different conditions has an apparent influence on anaerobic phosphorus release,which is very important for controlling the performance of EBPR.To obtain the mechanism and kinetic character of anaerobic phosphorus release,a series of batch experiments were performed using the excessively aerated sludge from the aerobic unit of the biological phosphorus removal system in this study.

Comparison of biochemical characteristics between PAO and DPAO sludges

A successful enhanced biological phosphorus removal （EBPR） was observed in both anaerobic- aerobic sequencing batch reactor （An-Ox SBR） to induce growth of phosphorus accumulating organism （PAO） and anaerobic-anoxic （An-Ax） SBR to induce growth of denitrifying PAO （DPAO）. Although the EBPR performance of An-Ox SBR was higher by 11.3% than that of An-Ax SBR, specific phosphorus release rates in the An-Ax SBR （22.8 ± 3.5 mg P/（g VSS.hr）） and the An-Ox SBR （22.4 ± 4.8 mg P/（g VSS.hr）） were similar. Specific phosphorus uptake rates under anoxic and aerobic conditions were 26.3 ± 4.8 mg P/（g VSS.hr） （An-Ax SBR） and 25.6 ± 2.8 mg P/（g VSS.hr） （An-Ox SBR）, respectively, which were also similar. In addition, an analysis of relationship of poly-β-hydroxyalkanoates （PHA） synthesized under anaerobic conditions with phosphorous release （Preleased/PHAsynthesized） and of PHA utilized under anoxic and aerobic conditions with phosphorous uptake （Puptaked/PHAutilized） verified that biological activities of EBPR per unit biomass between DPAO and PAO were similar. An analysis of the specific denitrification rate of DPAO showed that NO3-N can be denitrified at a rate that does not substantially differ from that of an ordinary denitrifier without additional consumption of organic carbon when the PHA stored inside the cell under anaerobic conditions is sufficiently secured.