Denitrifying Phosphorus Removing Bacteria Research Articles

Characteristics of anoxic phosphors removal in sequence batch reactor

The characteristics of anaerobic phosphorus release and anoxic phosphorus uptake were investigated in sequencing batch reactors using denitrifying phosphorus removing bacteria (DPB) sludge. The lab-scale experiments were accomplished under conditions of various nitrite concentrations (5.5, 9.5, and 15 mg/L) and mixed liquor suspended solids (MLSS) (1844, 3231, and 6730 mg/L). The results obtained confirmed that nitrite, MLSS, and pH were key factors, which had a significant impact on anaerobic phosphorus release and anoxic phosphorus uptake in the biological phosphorous removal process. The nitrites were able to successfully act as electron acceptors for phosphorous uptake at a limited concentration between 5.5 and 9.5 mg/L. The denitrification and dephosphorous were inhibited when the nitrite concentration reached 15 mg/L. This observation indicated that the nitrite would not inhibit phosphorus uptake before it exceeded a threshold concentration. It was assumed that an increase of MLSS concentration from 1844 mg/L to 6730 mg/L led to the increase of denitrification and anoxic P-uptake rate. On the contrary, the average P-uptake/N denitrifying reduced from 2.10 to 1.57 mg PO 4 3−-P/mg NO 3 −-N. Therefore, it could be concluded that increasing MLSS of the DEPHANOX system might shorten the reaction time of phosphorus release and anoxic phosphorus uptake. However, excessive MLSS might reduce the specific denitrifying rate. Meanwhile, a rapid pH increase occurred at the beginning of the anoxic conditions as a result of denitrification and anoxic phosphate uptake. Anaerobic P release rate increased with an increase in pH. Moreover, when pH exceeded a relatively high value of 8.0, the dissolved P concentration decreased in the liquid phase, because of chemical precipitation. This observation suggested that pH should be strictly controlled below 8.0 to avoid chemical precipitation if the biological denitrifying phosphorus removal capability is to be studied accurately.

PHOSPHORUS RELEASE AND UPTAKE ACCORDING TO NITRATE LOADING IN ANOXIC REACTOR OF BNR PROCESS

A batch and a continuous type experiments were conducted to test the conditions for simultaneous phosphorus release and uptake, and denitrification, taking place in one process. The bacteria able to denitrify as well as to remove phosphorus were evaluated for the application to biological nutrient removal(BNR) process. In the batch-type experiment, simultaneous reactions of phosphorus release and uptake, and also denitrification were observed under anoxic condition with high organic and nitrate loading. However the rate and the degree of P release were lower than that occurred under anaerobic condition. BNR processes composed of anaerobic-anoxic-oxic(AXO), anoxic-anaerobic-oxic(XAO) and anoxic-oxic(XO) were operated in continuous condition. The anoxic reactors in each process received nitrate loading. In the AXO process, P release in anaerobic reactor and the luxury uptake in oxic reactor proceeded actively regardless to nitrate loading. However in XAO and XO processes, P release and luxury uptake occurred only with the nitrate loading less than /kgMLSS-d. With higher nitrate load, P release increased and the luxury uptake decreased. Therefore, it appeared that the application of denitrifying phosphorus-removing bacteria (DPB) to BNR process must first resolve the problem with decrease of luxury uptake of phosphorus in oxic reactor.

Influence of ORP variation, carbon source and nitrate concentration on denitrifying phosphorus removal by DPB sludge from dephanox process

The effect of added carbon source and nitrate concentration on the denitrifying phosphorus removal by denitrifying phosphorus removal bacteria 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 the 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 of the PHB saturation of Poly-p bacteria, residual COD carried over to the anoxic phase inhibited the subsequent denitrifying phosphorus uptake. This was equal to supplementing the external carbon source to the anoxic phase, furthermore the higher the external carbon source concentration the more powerful the inhibition caused. High nitrate concentration in the anoxic phase increased the initial denitrifying phosphorus rate. Oncethe nitrate was exhausted, phosphate uptake changed to phosphate 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 that ORP could be used as a control parameter for phosphorus release, but it is impossible to utilize ORP for controlling the dinitrification and anoxic phosphorus uptake operations.

Improvement of denitrification by denitrifying phosphorus removing bacteria using sequentially combined carbon

The effects of sequentially combined carbon (SCC) using a symbiotic relationship of methanol and acetic acid on biological nutrient removal were investigated in both the continuous bench scale process consisting of an anoxic, an aerobic and a final settling tank and intensive batch tests. Compared to the use of respective sole carbon sources, methanol and acetic acid, the use of SCC showed superior removal efficiency of nitrogen (98.3%) and phosphorus (approximately 100%). Furthermore, the use of SCC enhanced simultaneous denitrification and phosphorus uptake by denitrifying phosphorus removal bacteria (DPB), resulting in the highest specific denitrification rate (SDNR) of 0.252 g NO3-N/g VSS/d achieved from the first anoxic zone with methanol of 30 mg COD/I. From batch tests performed under carbon limited anoxic conditions, 1 g of nitrate was used by DPB for P-uptake of 1.19 g. According to this result, 0.205 g NO3-N/g VSS/d was accomplished by normal denitrifiers using methanol, and 0.047 g NO3-N/g VSS/d was achieved by DPB. This research also demonstrated that the increase of poly-beta-hydroxybutyrate (PHB) stored by phosphorus accumulating organisms (PAOs) could be of importance in improving aerobic denitrification. The use of SCC produced the highest P-release in the anoxic zone, indicating the amount of PHB would be higher compared to the use of other sole carbons. Therefore, the SCC could be a very effective carbon source for the enhancement of aerobic denitrification as well.

A new method for characterizing denitrifying phosphorus removal bacteria by using three different types of electron acceptors

This study investigated the characteristics of denitrifying phosphorus removal bacteria by using three different types of electron acceptors as well as the positive role of nitrite in phosphorus removal process. Denitrifying phosphorous removal bacteria was enriched under anaerobic–anoxic (A/A) condition. To understand A/A sludge better, sludge from two other sources were also studied. These include sludges obtained from a lab-scale anaerobic–anoxic–aerobic (A/A/O) system and a local sewage treatment plant. Three types of possible electron acceptors (oxygen, nitrate and nitrite) were examined for their roles in phosphorus uptake. The results obtained indicated that oxygen, nitrate and nitrite were able to act as electron acceptors successfully. This observation suggested that in addition to the two well-accepted groups of phosphorus removal bacteria (one can only utilize oxygen to take up phosphorus, P O, while the other can use both oxygen and nitrate, P ON), a new group of phosphorus removal bacteria, P ONn, which could use oxygen, nitrate or nitrite to take up phosphorus was identified. The relative population of these three types of bacteria could be calculated from results obtainable from phosphorus uptake batch experiments with either oxygen or nitrate or nitrite as electron acceptor. The results obtained in this study showed that A/A sludge had similar phosphorus removal performance as the A/A/O sludge. However, it has better denitrifying phosphorus removal capability, which was demonstrated by the relative population of the three groups of bacteria. The results also suggested that nitrite was not an inhibitor to phosphorus removal process. Instead, it is an alternative electron acceptor to oxygen or nitrate.

Biological dephosphatation by activated sludge under denitrifying conditions: pH influence and occurrence of denitrifying dephosphatation in a full-scale waste water treatment plant

The effect of pH on phosphorus release under anaerobic conditions was examined for denitrifying phosphorus removing bacteria (DPB) cultivated in an anaerobic-anoxic sequencing batch reactor. Also batch tests were conducted with activated sludge from a full-scale waste water treatment plant (WWTP) in order to investigate occurrence and contribution of DPB in phosphorus removal processes. In the experiments for the pH effect, enriched DPB sludge was maintained under anaerobic conditions with acetic acid (HAc) present at 5 different pH conditions (6.0∼8.0), and released phosphorus and consumed HAc concentrations were measured. When the biomass concentration was around 2.7 g-VSS/l, the observed P/C (released-P/consumed-HAc) ratios were 0.7, 1.1 and 1.2 g-P/g-C at pH=6, 7 and 8. At 4.2 g-VSS/l, the observed P/C ratios were 0.9, 1.3 and 1.2 g-P/g-C, respectively. The difference between the two experiments resulted from the endogenous phosphorus release. The same pH effect as observed for conventional anaerobic-aerobic SBR sludge, was obtained for the DPB sludge in the range of pH=6.0∼7.5. However due to precipitates formation at pH=8.0, the apparent P/C ratio was approximately 20% less than the ratio calculated from the biological released phosphorus concentration by DPB. From the results of the batch tests with activated sludge and observations on the full-scale WWTP, it was also shown that clearly denitrifying dephosphatation occurs and approximately 50% of the phosphorus removal occurs via denitrifying activities in the WWTP.

Occurrence of denitrifying phosphorus removing bacteria in modified UCT-type wastewater treatment plants

The occurrence of denitrifying phosphorus removing bacteria (DPB) and the contribution of DPB to phosphorus removal in full-scale wastewater treatment plants (WWTPs) has been investigated by batch tests with the activated sludge from two WWTPs (WWTP-Genemuiden and -Holten). Both WWTPs are operated as UCT-type processes. Batch tests to evaluate the biomass composition of the sludges were developed. These batch tests showed a clear difference of denitrifying dephosphatation activity between the WWTP-Genemuiden and -Holten sludge. In the sludge of the WWTP-Genemuiden the (denitrifying) dephosphatation activity was rather low, whereas a high activity was formed in the WWTP-Holten sludge. The following possible reasons for the lower proportion of (denitrifying) dephosphatation activity in the WWTP-Genemuiden sludge in comparison with the WWTP-Holten sludge, were suggested; (a) nitrate/oxygen transfer to the anaerobic/anoxic zone due to the internal recirculation inside the treatment plant, (b) lower amounts of fatty acids in the influent due to shorter retention time of waste water in sewer lines, and (c) lower amount of nitrate recycled to the anoxic zone.

Biological dephosphatation by activated sludge under denitrifying conditions pH influence and occurrence of denitrifying dephosphatation in a full-scale waste water treatment plant

The effect of pH on phosphorus release under anaerobic conditions was examined for denitrifying phosphorus removing bacteria (DPB) cultivated in an anaerobic-anoxic sequencing batch reactor. Also batch tests were conducted with activated sludge from a full-scale waste water treatment plant (WWTP) in order to investigate occurrence and contribution of DPB in phosphorus removal processes. In the experiments for the pH effect, enriched DPB sludge was maintained under anaerobic conditions with acetic acid (HAc) present at 5 different pH conditions (6.0˜8.0), and released phosphorus and consumed HAc concentrations were measured. When the biomass concentration was around 2.7 g-VSS/l, the observed P/C (released-P / consumed-HAc) ratios were 0.7, 1.1 and 1.2 g-P/g-C at pH = 6, 7 and 8. At 4.2 g-VSS/l, the observed P/C ratios were 0.9, 1.3 and 1.2 g-P/ g-C, respectively. The difference between the two experiments resulted from the endogenous phosphorus release. The same pH effect as observed for conventional anaerobic-aerobic SBR sludge, was obtained for the DPB sludge in the range of pH = 6.0˜7.5. However due to precipitates formation at pH = 8.0, the apparent P/C ratio was approximately 20% less than the ratio calculated from the biological released phosphorus concentration by DPB. From the results of the batch tests with activated sludge and observations on the full-scale WWTP, it was also shown that clearly denitrifying dephosphatation occurs and approximately 50% of the phosphorus removal occurs via denitrifying activities in the WWTP.

Kinetic competition between phosphorus release and denitrification on sludge under anoxic condition

The kinetic behaviors of simultaneous phosphorus release and denitrification on sludge were investigated under anoxic condition. A phosphorus enriched sludge produced from Anaerobic-Anoxic-Oxic (AnAO) process under various SRT (5, 10 and 15 days) operation conditions was carried out in a series of batch tests. Experimental results indicated that the available organic substrate determined the kinetic behaviors of phosphorus release/uptake and denitrification. The simultaneous phosphorus release and denitrification demonstrated a kinetic competition under anoxic conditions in the presence of an available organic substrate. When the substrate was abundant, sludge was under “releasable-phosphorus-limited” condition; phosphorus release rate decreased slightly by nitrate inhibition. However, nitrate significantly inhibited phosphorus release when sludge was under “initial-substrate-limited” condition. Moreover, the sludge's phosphorus contents (as created by different SRT processes) dominated the kinetics of competition between phosphorus release and denitrification. The sludge with a high phosphorus content had a higher phosphorus release rate in accordance with a lower denitrification rate. Additionally, the substrate sequestrated rate markedly increased under the condition of simultaneous phosphorus release and denitrification. Finally, a preliminary metabolism model of denitrifying phosphorus removal bacteria was proposed, and found to be capable of adequately accounting for simultaneous phosphorus release and denitrification under anoxic conditions.

Phosphorus and nitrogen removal with minimal COD requirement by integration of denitrifying dephosphatation and nitrification in a two-sludge system

Denitrifying dephosphatation enables the removal of phosphorus and nitrogen with minimal use of COD, minimal oxygen consumption and minimal surplus sludge production. Moreover it would make aeration only necessary for nitrification. Therefore we have studied an anaerobic-anoxic (A 2) sequencing batch reactor (SBR) coupled to a nitrification SBR. Denitrifying phosphorus removing bacteria (DPB) and nitrifiers were completely separated in two sludges in these two SBRs. The nitrified supernatant was recirculated from the nitrification SBR to the A 2 SBR where nitrate was utilized by DPB as an electron acceptor for phosphorus removal. The technical feasibility for simultaneous phosphorus and nitrogen removal in the proposed two-sludge system was evaluated. The benefits of two-sludge systems over single-sludge systems were also discussed. It could be concluded that the separation of the nitrification step leads to an optimal process design for the application of denitrifying dephosphatation. The two-sludge system showed stable phosphorus and nitrogen removal, and enabled the removal of 15 mg-P/1 and 105 mg N/1 at the expense of only 400 mg-COD/1 acetic acid. Stoichiometric calculations showed that, in the two-sludge system the required COD can be up to 50% less than for conventional aerobic phosphorus and nitrogen removal systems. Moreover oxygen requirements and sludge production can be decreased in significant amounts of about 30 and 50%, respectively.