Biological Phosphorus Removal Efficiency Research Articles

Redox environment inducing strategy for enhancing biological phosphorus removal in a full-scale municipal wastewater treatment plant

Phosphorus removal from wastewater is crucial for limiting water eutrophication. However, due to improper operating conditions, tremendous phosphorus removal chemicals addition or low C/N ratio in the influent, biological phosphorus removal (BPR) has been regarded as a difficult issue in real full-scale municipal wastewater treatment plants (WWTPs), especially in the membrane bioreactor (MBR) plants with long sludge retention time. Therefore, application of effective enhanced biological phosphorus removal (EBPR) technologies in WWTPs is of great significance to improve the BPR efficiency, reduce chemicals consumption and operating cost. Favorable redox environment, characterized by ORP is important for the growth and enrichment of phosphate-accumulating organisms (PAO), which is mainly responsible for BPR. In this study, a redox environment inducing strategy for EBPR was taken in a real full-scale MBR-WWTP (treatment capacity of 2 × 106 m3/d). The results indicated that the phosphorus release and uptake rate were rather low in the biochemical tank, which reflected the low phosphate-accumulating organisms (PAO) activity and poor BPR efficiency. This problem may be due to inappropriate redox environment, inhibition by phosphorus removal chemicals or low C/N in the influent. After EBPR, the contribution percentage of BPR increased by up to 18% and chemicals dosage reduced by up to 60%. Furthermore, the relative abundance of PAO (Dechloromonas, Thauera and OLB12) was significantly increased in anaerobic tank (4.62, 1.33 and 1.18%), in anoxic tank (4.85, 1.93 and 0.88%) and in oxic tank (5.17, 1.71 and 0.84%) for appropriate redox environment and relieved inhibition by less dosage of phosphorus removal chemicals. In addition, bacteria related to COD degradation and nitrogen removal were also enriched. The simultaneous enhancement of biological phosphorus removal, carbon removal and nitrogen removal was successfully realized in this research, which indicated that the strategy was effective in real large-scale WWTPs.

Effect of fluoxetine on enhanced biological phosphorus removal using a sequencing batch reactor

In this work, the potential impact of emerging pollutant Fluoxetine (FLX) on enhanced biological phosphorus removal (EBPR) was systematically investigated using the sequencing batch reactor. The experimental results showed that even 200 μg/L FLX had no significant effect on EBPR during the short-term exposure. However, in the long-term exposure test, high dosage of FLX inhibited EBPR. 200 μg/L FLX induced biological phosphorus removal efficiency dropped to 71.3 ± 2.1%, significantly lower than that of the blank. The mechanism investigation showed that high concentration of FLX reduced anaerobic phosphorus release and oxic phosphorus absorption, and the consumption of organic matter during the anaerobic period. In addition, FLX decreased the synthesis of intracellular polymer polyhydroxyalkanoates (PHA), but promoted the metabolism of glycogen and polyhydroxyvalerate. FLX reduced the activity of key enzymes in EBPR and the relative abundance of Accumulibacter, but improved the relative abundance of Candidatus Competibacter.

Impact of aerobic availability of readily biodegradable COD on morphological stability of aerobic granular sludge

Operational disturbances in aerobic granular sludge (AGS) systems can result in aerobic availability of readily biodegradable COD (rbCOD). Different from activated sludge, morphological consequences on the short and long term are not well described in literature. This study investigated the effect of incomplete anaerobic uptake of acetate on the morphological and process stability of AGS using a lab-scale reactor. A fraction of the total acetate load was dosed aerobically, which was increased stepwise while monitoring granular morphology. A good granular morphology and an SVI of 40 ml/g were obtained during initial enrichment and maintained for ≤20% aerobic acetate load dosed at 4 mg COD/g VSS/h. Biological phosphorus removal efficiency was initially unaffected, but the aerobic acetate dosage rate did decrease the aerobic phosphate uptake rate. This led to loss of phosphorus removal for >20% aerobic acetate load dosed at 8 mg COD/g VSS/h over the course of 12 days. Subsequently, significant outgrowth formed on the granular surfaces and developed over time into finger-like structures. Under these high aerobic acetate loads the SVI increased to 80 ml/g and resulted in significant biomass washout due to deteriorating settling properties of the sludge. The sludge settleability and biological phosphorus removal recovered 10 days after aerobic feeding of acetate was stopped. Aerobic presence of rbCOD can be tolerated if mostly anaerobic acetate uptake is maintained, thereby ensuring stable granular morphology and good settleability. The high enrichment of phosphate accumulating organisms in the granular sludge through bottom-feeding and selective wasting of flocs makes aerobic granular sludge resilient to morphological deterioration in aerobic presence of rbCOD.

The PHO pathway involved in phosphate metabolism in Yeast for efficient phosphorus removal

Phosphorus is one of the essential elements needed for the growth and reproduction of any organism. To improve the efficiency of biological phosphorus removal in sewage, it is very important to grasp the precise mechanism of biological phosphorus removal. Yeast is a single cell fungus and has a unique advantage in sewage treatment. Recent studies in the different types of yeast have revealed that there is a phosphate-responsive signal transduction (PHO) pathway to regulate phosphate-responsive genes for controlling phosphate absorption. In this review, the metabolic mechanisms and protein-protein interactions associated with the PHO pathway are highlighted firstly, and then several examples about improving the phosphorus removal efficiency of sewage by inducing gene mutation in yeast phosphorus metabolism was introduced. The aim is to provide new ideas for the realization of high-efficiency phosphorus recovery in nature.

Efficiency of Biological Phosphorus Removal by Filamentous Bacteria

Abstract Phosphorus removal in wastewater treatment plant is carried out by chemical precipitation, advanced biological treatment or a combination of both. One of the biggest problems with high concentration of phosphorus in water environment is eutrophication. Activated sludge flocs have a heterogeneous structure, which consist of a variety of microorganisms. Filamentous bacteria are normally present in the activated sludge and have ability to assimilation of phosphorus. In this study phosphorus accumulation by isolated filamentous bacteria from activated sludge foam was present.

Full-scale evaluation of aerobic/extended-idle regime inducing biological phosphorus removal and its integration with intermittent sand filter to treat domestic sewage discharged from highway rest area

Biological phosphorus removal (BPR) has been demonstrated to be successfully achieved in the aerobic/extended-idle (AEI) wastewater treatment regime in previous bench-scale studies. To date, however, its feasibility has never been evaluated by any full-scale investigation. Here we report a first full-scale (180m3/day) evaluation of the AEI process and its integration with intermittent sand filter to treat highway rest area sewage that is often neglected but actually brings significant impacts on receiving water bodies in China. The results showed that 70–99% of influent phosphate was removed in the AEI zone, although the sewage contained 23–37% of carbohydrate that is usually considered to be detrimental for BPR. Batch experimental investigation revealed that the presence of glucose (model compound of carbohydrate) promoted the AEI-inducing BPR efficiency, as opposed to deteriorating the conventional anaerobic/oxic regime-inducing BPR performance. Although the performance of AEI zone was affected by seasonal variation, the efficiencies of contaminant removal were stable and excellent (total nitrogen>86%, others>92%) in the integrated system. This study offers an attractive option for BPR from carbohydrate-rich wastewaters and also provides a prototype for wastewater treatment in remote areas.

Phosphorus removal and recovery from domestic wastewater in a novel process of enhanced biological phosphorus removal coupled with crystallization

A new process of enhanced biological phosphorus removal coupled with crystallization recovery of phosphorus was developed here, where the feasibility of nutrients removal and potential for phosphorus recovery from domestic wastewater was further assessed. Results showed that an excellent nutrients removal and phosphorus recovery performance was achieved, in which the averaged COD, PO43−-P and NO3−-N removal efficiencies were 82.6%, 87.5% and 91.6%, respectively and a total of 59.3% of phosphorus was recovered as hydroxyapatite. What’s more, crystallization recovery of phosphorus greatly enhanced the biological phosphorus removal efficiency. After the incorporation of the phosphorus recovery column via side-stream, the phosphorus concentration of effluent was significantly decreased ranging from 1.24mg/L to 0.85mg/L, 0.52mg/L and 0.41mg/L at the lateral flow ratios of 0, 0.1, 0.2 and 0.3, respectively. The results obtained here would be beneficial to provide a prospective alternative for phosphorus removal and recovery from wastewater.

Effect of dissolved oxygen on biological phosphorus removal induced by aerobic/extended-idle regime

Previous researches have suggested that biological phosphorus removal (BPR) from wastewater could be achieved by the aerobic/extended-idle (A/EI) regime. This study further investigated the effect of dissolved oxygen (DO) concentration on BPR induced by the A/EI regime. The experimental results show that 1mg/L of DO in mixed liquor benefited the BPR performance while a higher DO level of 5mg/L deteriorated BPR. Fluorescent in situ hybridization analysis demonstrated that the improvement at 1mg/L of DO was due to the shift in bacterial population from glycogen accumulating organisms (GAOs) to polyphosphate accumulating organisms (PAOs). The mechanism studies revealed that DO level affected the transformations of polyhydroxyalkanoates and glycogen and the activities of exopolyphosphatase and polyphosphate kinase. In addition, the BPR performances between the A/EI regime and conventional anaerobic/oxic (A/O) process were compared. The results showed that the A/EI regime drove better BPR performance than the A/O process at both low and high DO levels. More PAO and less GAO abundances in the biomass might be the principal reason for the higher BPR efficiency in the A/EI regime. Furthermore, controlling DO at a low level of 0.5mg/L to promote BPR was demonstrated in a real municipal wastewater. The A/EI regime showed an excellent BPR performance at the low DO levels and had a better tolerance to oxygen-limited condition as compared to the A/O regime.

Optimization of a full-scale Unitank wastewater treatment plant for biological phosphorus removal

The Unitank process combines the advantages of traditional continuous-flow activated sludge processes and sequencing batch reactors, and has been extensively employed in many wastewater treatment plants (WWTPs) in China. Biological phosphorus removal (BPR) of a full-scale Unitank WWTP was optimized by increasing anaerobic time from 80 to 120 min in an operation cycle of 360 min and reducing solid retention time (SRT) from 21.3 to 13.1 d. The BPR efficiency of the full-scale Unitank system increased from 63.8% (SRT of 21.3 d) to 83.2% for a SRT of 13.1 d. When the anaerobic time increased from 80 to 120 min, the net anaerobic phosphorus release amount increased from 0.25 to 1.06 mg L−1, and sludge phosphorus content rose from 13.8 to 15.0 mgP·(gSS)−1. During half an operation cycle, the average specific phosphorus release rate increased from 0.097 mgP·(gVSS·h)−1 in 0–40 min to 0.825 mgP·(gVSS·h)−1 in 40–60 min. Reducing SRT and increasing anaerobic time account for 84.6% and 15.4% in the total increment of phosphorus removal of 1.15 mg L−1.

Performance of biological phosphorus removal and characteristics of microbial community in the oxic-settling-anaerobic process by FISH analysis

Performance of biological phosphorus removal in the oxic-settling-anaerobic (OSA) process was investigated. Cell staining and fluorescent in situ hybridization (FISH) were used to analyze characteristics and microbial community of sludge. Experimental results showed that phosphorus removal efficiency was near 60% and the amount of biological phosphorus accumulation in aerobic sludge of the OSA system was up to 26.9 mg/g. Biological phosphorus removal efficiency was partially inhibited by carbon sources in the continuous OSA system. Contrasted to the OSA system, biological phosphorus removal efficiency was enhanced by 14% and the average total phosphorus (TP) contents of aerobic sludge were increased by 0.36 mg/g when sufficient carbon sources were supplied in batch experiments. Staining methods indicated that about 35% of microorganisms had typical characteristics of phosphorus accumulating organisms (PAOs). FISH analysis demonstrated that PAOMIX-binding bacteria were predominant microbial communities in the OSA system, which accounted for around 28% of total bacteria.

Using low intensity ultrasound to improve the efficiency of biological phosphorus removal

Low intensity ultrasound can produce various effects on biological materials, such as stimulating enzyme activity, cell growth, biosynthesis, etc., which may improve the efficiency of enhanced biological phosphorus removal (EBPR). We adopt total phosphorus (TP) and dehydrogenase activity (DHA) as indicators to confirm the feasibility of applying low intensity ultrasound in EBPR. Single-factor experiments and orthogonal test were conducted in batch anaerobic/oxic (A/O) process simulation to study the influence of ultrasonic intensity and exposure time in the EBPR process. The results showed that the optimal ultrasonic parameters were 0.2W/cm2 and 10min under which condition the TP concentration in the effluent was 35–50% lower than that of the control (without ultrasonic irradiation). Changes of sludge activities after ultrasonic irradiation were examined. The improvement of sludge activity by ultrasound took 4h after irradiation to reach the peak level, when an increase above 50% of DHA has been achieved by ultrasonic irradiation, and the enhancing effects induced by ultrasound disappeared in 16h after irradiation. A tentative mechanism of biological phosphorus removal enhancement stimulated by ultrasound was discussed based on these phenomena.

New Biological Phosphorus Removal Concept Successfully Applied in a T-Ditch Process Wastewater Treatment Plant

Luofang Wastewater Treatment Plant adopted a new concept of enhanced biological phosphorus removal in combination with a traditional Triple Ditch (T -Ditch) process to optimize the efficiency of biological phosphorus removal. The new concept included the addition of a thickener and anaerobic cell ahead of the T -Ditch system. Recorded data shows that the modified system is operating successfully with effluent which is much better than most T -Ditch systems. It also shows that it has better treatment efficiency than other complicated biological treatment processes with the same wastewater characteristi cs and same temperature conditions.

Effect of solids retention time and wastewater characteristics on biological phosphorus removal

The paper deals with the effect of wastewater, plant design and operation in relation to biological nitrogen and phosphorus removal and the possibilities to model the processes. Two Bio-P pilot plants were operated for 2.5 years in parallel receiving identical wastewater. The plants had SRT of 4 and 21 days, the latter had nitrification and denitrification. The plant with 4 days SRT had much more variable biomass characteristics, than the one with the high SRT. The internal storage compounds, PHA, were affected significantly by the concentration of fatty acids or other easily degradable organics in the wastewater, and less by the plant lay-out. The phosphorus removal is mainly dependent on availability in the wastewater of fatty acids but also by the suspended solids in the effluent, which is higher in the plant with nitrification-denitrification, probably due to a higher SVI or denitrification in the settler. The addition of glucose to the influent seems to have an effect on the performance of the plants similar to that of acetic acid. In spite of great load variations over time to the pilot plants and the different operational modes, the study of population dynamics showed less significant variations with time which has importance in relation to modelling. The overall conclusion of the comparison between the two plants is that the biological phosphorus removal efficiency under practical operating conditions is affected by the SRT in the plant and the wastewater composition. Thus great care should be taken when extrapolating results from one type of plant to another. Indirectly the experiments confirm that results from lab-experiments with artificial wastewater are difficult to extrapolate through modelling to real life wastewater and conditions. The 2.5 years time series can be valuable in verification of models for Nitrogen and Enhanced Biological Phosphorus Removal.

The use of mathematical modeling and pilot plant testing to develop a new biological phosphorus and nitrogen removal process

A mechanistic mathematical model for carbon oxidation, nitrogen removal, and enhanced biological phosphorus removal was used to develop the Step Bio-P process, a new biological phosphorus and nitrogen removal process with a step-feed configuration. A 9 000-L pilot plant with diurnally varying influent process loading rates was operated to verify the model results and to optimize the Step Bio-P process for application at the Lethbridge, Alberta, Canada, wastewater treatment plant. The pilot plant was operated for 10 months. An automatic on-line data acquisition system with multiple sampling and metering points for dissolved oxygen, mixed liquor suspended solids, ammonia–nitrogen, nitrate–nitrogen, ortho-phosphate, and flow rates was used. A sampling program to obtain off-line data was carried out to verify the information from the on-line system and monitor additional parameters. The on-line and off-line data were used to recalibrate the model, which was used as an experimental design and process optimization tool.The pilot plant results matched and verified the initial mathematical model results. Total phosphorus concentrations were reduced from 14 mg P/L in the biological process influent to less than 1 mg P/L in the secondary effluent. Complete nitrification and 85% nitrogen removal were consistently achieved, and sludge with excellent settling characteristics (sludge volume index values of approximately 80 mL/g) was produced. The step-feed configuration allows an increased bioreactor suspended solids inventory to be maintained while, at the same time, reducing the solids loading rate to the secondary clarifiers. The result is maximum use of existing facilities. The Step Bio-P process is particularly suited for retrofitting conventional activated-sludge plants with limited secondary clarifier capacity to achieve biological nutrient removal (BNR). The combined mathematical modeling and pilot testing program demonstrated that the primary factors affecting the performance of the Step Bio-P process are flow-split percentages, mean cell residence time, dissolved oxygen set points, and short chain volatile fatty acid addition. Process performance is relatively insensitive to anoxic recycle and return activated-sludge flow rates. The growth of excessive quantities of glycogen accumulating organisms occurred when an industrial wastewater with high sugar concentrations was treated. Their growth adversely affected the biological phosphorus removal efficiency of the process. Strategies for controlling growth of these organisms were evaluated and tested.

IMPACT OF EXCESSIVE AERATION ON BIOLOGICAL PHOSPHORUS REMOVAL FROM WASTEWATER

It has been reported that deterioration of biological phosphorus removal (BPR) efficiency at some wastewater treatment plants (WWTPs) regularly occurred after heavy rainfall or weekends. The deterioration has been attributed to low plant loading that took place during such events. However, it is hypothesized in this study that the cause of such deterioration may have been the excessive aeration that took place at some of those plants due to inadequate control of aeration system during weekends and rainfall periods. In order to prove this hypothesis, the influence of excessive aeration (aeration during starvation conditions) on BPR processes was studied using a laboratory anaerobic-aerobic-settling sequencing batch reactor (SBR). It was clearly demonstrated that the phosphorus uptake stops due to a gradual depletion of poly-hydroxy-butyrate (PHB) in an over-aerated process. If organic substrate is introduced to the system, phosphorus release is immediately at its maximal rate. However, the released phosphorus cannot be taken-up fully again because the PHB content limits the uptake rate. Consequently, incomplete phosphorus uptake leads to temporary reduction of BPR efficiency. This causal effect can explain the deterioration of BPR efficiency after heavy rainfall or weekends. Since excessive aeration clearly negatively affects the BPR processes, the aeration should be properly controlled at sewage treatment plants. Some other findings of this study deserve to be mentioned. • • It was confirmed that the presence of acetate under aerobic conditions provokes phosphorus release. This may also contribute to deterioration of the BPR efficiency. • • The aerobic phosphate uptake was found to depend not only on the PHB but also on polyphosphate (poly-P) content of the cells. • • A maximal poly-P (0.18 g-P/g-VSS) and minimal PHB content of the cells (2.11 mg-COD/g-VSS) were observed in the enriched sludge during excessive aeration experiments. • • It was shown that, under aerobic starvation conditions, glycogen can not replace PHB for phosphate uptake and is only used for maintenance. During this period, no oxygen consumption due to decay processes has been observed. © 1998 Elsevier Science Ltd. All rights reserved

Biological Phosphorus Removal: Effect of Low Temperature

Phosphorus is a key nutrient responsible for eutrophication. Conventional activated sludge process (ASP) removes approximately 30 to 40% phosphorus. Additional phosphorus removal has been achieved by incorporating an anaerobic stage before aerobic ASP. The application of technology, however, in cold-region countries is limited. Temperature is an important consideration in the design of any treatment process in cold regions. In this paper, the performance of biological phosphorus removal (BPR) systems at low temperatures has been reviewed. The mechanism of BPR has been considered to analyze the effect of reduced temperature. Chemical coprecipitation of phosphorus, and acetate and/or short chain fatty acid (SCFA) production may affect BPR efficiency. Both these aspects have been reviewed in systems other than BPR.

Biological nutrient removal in high salinity wastewaters

Abstract The effect of a saline wastewater on the performance of a biological nutrient removal system was investigated using a model A2/O activated sludge system. The system was operated at a 13 day sludge age with a salinity level of 4,000 mg/l and compared with a similarly operated system with a salinity level of 200 mg/l. Mass balance calculations and the student t‐test were used for data analysis. It was found that a COD removal efficiency of 90 percent can be achieved when treating wastewater having an influent salinity of 4,000 mg/l. Nitrogen could be removed from the saline wastewater with the same efficiency as for the nonsaline wastewater. Excess biological phosphorus removal efficiency decreased from 82 percent to 25 percent at salinity levels of 200 and 4,000 mg/l, respectively.