Anthraquinone-2-sulfonate enhances endogenous denitrification and phosphorus removal: Electron shuttle-mediated syntrophic partnerships.

The phosphorus uptake rate characteristics have been investigated in different electron acceptor conditions (NO3-, O2, O2 and NO3- coexisting). The sludge was transferred from CAS, AO MBR, AOA MBR, A2O MBR or the A, B tank of MUCT-MBR systems. The results show that the phosphorus uptake rate (SPUR) have the same rule for the sludge in different electron acceptors, that is NSPUR (NO3- as the electron acceptor) <ASPUR (O2 as the electron acceptor) <TSPUR (both O2 and NO3- as the electron acceptors). There exists the aerobic denitrifying phosphorus removal process in mixed electron acceptor system. And this process shows a positive correlation with the ability of denitrifying phosphorus removal improved. The higher ability of denitrifying phosphorus uptake the sludge have, the faster nitrate consumption rate could be shown through the phosphorus uptake process under the condition of in O2 and NO3- coexisting. That is TSDNR（AO）<TSDNR（AOA）<TSDNR（A2O）. The relationship between the nitrate consumption rates is ASDNR (only O2 exist) <TSDNR (TP and O2 coexist) <NSDNR (only TP exist). The phosphorus removal mechanism might include three parts: the aerobic phosphorus uptake, the anoxic denitrifying phosphorus uptake and the aerobic denitrifying phosphorus uptake.

Operation performances of phosphorus removal sludge with different electron acceptors in three parallel SBRs were firstly compared in the present study, and the effect of post-aeration on denitrifying phosphorus removal was also studied. Moreover, community dynamics of different phosphorus removal sludge was systematically investigated with high-throughput sequencing for the first time. TP removal rates for nitrate-, nitrite-, and oxygen-based phosphorus removal sludge were 84.8, 78.5, and 87.4%, with an average effluent TP concentration of 0.758, 0.931, and 0.632mg/l. The average specific phosphorus release and uptake rates were 20.3, 10.8, and 21.5, and 9.43, 8.68, and 10.8mgP/(gVSSh), respectively. Moreover, electron utilization efficiency of denitrifying phosphorus removal sludge with nitrate as electron acceptor was higher than nitrite, with P/e(-) were 2.21 and 1.51mol-P/mol-e(-), respectively. With the assistance of post-aeration for nitrate-based denitrifying phosphorus removal sludge, settling ability could be improved, with SVI decreased from 120 to 80 and 72ml/g when post-aeration time was 0, 10, and 30min, respectively. Moreover, further phosphorus removal could be achieved during post-aeration with increased aeration time. However, the anoxic phosphorus uptake was deteriorated, which was likely a result of shifted microbial community structure. Post-aeration of approximately 10min was proposed for denitrifying phosphorus removal. Nitrate- and nitrite-based denitrifying phosphorus removal sludge exhibited similar community structure. More phosphorus accumulating organisms were enriched under anaerobic-aerobic conditions, while anaerobic-anoxic conditions were favorable for suppressing glycogen-accumulating organisms. Significant differences in pathogenic bacterial community profiles revealed in the current study indicated the potential public health hazards of non-aeration activated sludge system.

Denitrifying phosphorus accumulating organ- isms (DPAOs) using nitrite as an electron acceptor can reduce more energy. However, nitrite has been reported to have an inhibition on denitrifying phosphorus removal. In this study, the step-feed strategy was proposed to achieve low nitrite concentration, which can avoid or relieve nitrite inhibition. The results showed that denitrification rate, phosphorus uptake rate and the ratio of the phosphorus uptaken to nitrite denitrified (anoxic P/N ratio) increased when the nitrite concentration was 15 mg$L -1 after step- feeding nitrite. The maximum denitrification rate and phosphorus uptake rate was 12.73 mg NO - 2 -N$g MLSS -1 ⋅h -1 and 18.75 mg PO 3- 4 -P$g MLSS -1 ⋅h -1 , respec- tively. These rates were higher than that using nitrate (15 mg$L -1 ) as an electron acceptor. The maximum anoxic P/N ratio was 1.55 mg PO 3- 4 -P⋅mg NO - 2 -N -1 . When the nitrite concentration increased from 15 to 20 mg NO - 2 -N ⋅L -1 after addition of nitrite, the anoxic phosphorus uptake was inhibited by 64.85%, and the denitrification by DPAOs was inhibited by 61.25%. Denitrification rate by DPAOs decreased gradually when nitrite (about 20 mg $L -1 ) was added in the step-feed SBR. These results indicated that the step-feed strategy can be used to achieve denitrifying phosphorus removal using nitrite as an electron acceptor, and nitrite concentration should be maintained at low level (<15 mg$L -1 in this study).

To supply the valuable operating parameters for the popular usage of the new denitrifying phosphors removal process, it is essential to study the dominant biochemical reactions and the characteristics of denitrifying phosphorus removing bacteria (DPB). Thus, parallel batch experiments using DPB sludge were carried out to assess the effect of substrates (sewage, HAc, and endogenous carbon source) on denitrifying dephosphorus removal efficiency in this study. The results showed that the initial specific phosphorus release rate increased with the high concentration of the short-chain volatile fatty acids ratio in the influent, and sufficient phosphorus was released by DPB. This improved the subsequent denitrification and phosphorus uptake efficiency. The specific endogenous denitrification mainly relies on the internal carbon source (PHB) stored by poly-P bacteria. Denitrifying phosphorus removing bacteria were very hungry when the internal PHB was consumed. Consequently, the specific endogenous denitrification rate was low and the phosphorus uptake did not happen. On the other hand, in the experiment, the denitrifying phosphorus removal performance under two temperature conditions (8–10°C and 25–26°C) was also investigated and analyzed. It was found that the lower temperature decreased the specific phosphorus release and uptake rate, but did not inhibit the denitrifying phosphorus removal completely. Therefore, the negative influence of the low temperature on the overall phosphorus removal was not significant.

Advanced nitrogen and phosphorus removal by combining endogenous denitrification and denitrifying dephosphatation in constructed wetlands

Abstract:Intermediate products of biological nitrogen removal process, nitrate and nitrite, could be used as electron acceptors for phosphorus removal. This study investigated the effects of nitrite on phosphorus uptake in anaerobic/oxic (A/O) biological phosphorus removal process. The results indicated that in addition to oxygen and nitrate (DPB(Na), Denitrifying Phosphorus removal Bacteria with nitrate as electron acceptor), to some extent, nitrite can also serve as electron acceptor to achieve the nitrite denitrifying phosphorus removal (DPB(Ni)). The quantity and rate of phosphorus uptake of DPBNi, however, were evidently lower than that of DPBN,. The nitrite existed in anoxic reactor made no difference to the quantity and rate of denitrifying phosphorus removal. But it would reduce the consumption of nitrate. Moreover, the data showed that the aerobic phosphate uptake of DPBNi was lower than that of anaerobic phosphorus-released sludge in traditional A/O process. However, there was no much difference between these two kinds of sludge in terms of the total phosphorus uptake quantity and the effluent quality.

Simultaneous nitrification and denitrification (SND) were coupled with a denitrifying phosphorus removal (DPR) to achieve simultaneous nutrient and carbon removal. With influent chemical oxygen demand (COD), ammonia-N (NH4 +-N), and total phosphorus (TP) concentrations of 250, 50, and 8 mg/L, the SND-DPR coupled system achieved stable nutrient removal efficiency of COD, NH4 +-N, TN and TP were 91.8 ± 1.7%, 88.4 ± 1.8%, 64 ± 3.3% and 99.2 ± 0.6%, respectively. Enhancing the C/N ratio strengthened the storage of intracellular polymers and provided sufficient intracellular carbon sources for phosphorus uptake. The nutrient removal efficiency reached the highest level at a C/N ratio of 5, and no advantage was observed after increasing the C/N ratio to 7. Nutrients were mainly removed during the aerobic stage at a low DO concentration as well during the anoxic stage, which helped achieve concurrent nitrification and denitrification by ordinary heterotrophic organisms (OHOs), promote denitrifying and aerobic phosphorus removal, and conserve organic carbon demand and energy consumption for aeration. The system was limited for DO in the aerobic stage at a low DO concentration, resulting in a deficiency in electron acceptors (O2 and NO3 –N) and limiting the subsequent promotion of phosphorus uptake and TN removal. The limited DO content in the low DO stage was the key factor involved in enhancing the nutrient removal efficiency along with the increasing influent C/N ratio.

Efficient amino acid capture from sludge fermentation by Tetrasphaera enhances simultaneous nitrification, endogenous denitrification and phosphorus removal.

Advanced nitrogen and phosphorus removal by the symbiosis of PAOs, DPAOs and DGAOs in a pilot-scale A2O/A+MBR process with a low C/N ratio of influent

The anaerobic-anoxic oxidation ditch (A2/O OD) process is popularly used to eliminate nutrients from domestic wastewater. In order to identify the existence of denitrifying phosphorus removing bacteria (DPB), evaluate the contribution of DPB to biological nutrient removal, and enhance the denitrifying phosphorus removal in the A2/O OD process, a pilot-scale A2/O OD plant (375 L) was conducted. At the same time batch tests using sequence batch reactors (12 L and 4 L) were operated to reveal the significance of anoxic phosphorus removal. The results indicated that: The average removal efficiency of COD, NH4+, PO43−, and TN were 88.2%, 92.6%, 87.8%, and 73.1%, respectively, when the steady state of the pilotscale A2/O OD plant was reached during 31–73 d, demonstrating a good denitrifying phosphorus removal performance. Phosphorus uptake took place in the anoxic zone by poly-phosphorus accumulating organisms NO2− could be used as electron receptors in denitrifying phosphorus removal, and the phosphorus uptake rate with NO2− as the electron receptor was higher than that with NO3− when the initial concentration of either NO2− or NO3− was 40 mg/L.

A synthetic wastewater was employed to investigate the realization of short-cut nitrification and its phosphorus removal performance in a CAST reactor operated at 22℃, 25℃, and 28℃. The results showed that TN removal of the system was stable and higher than 80% at different temperatures, and NH4+-N removal performed well. When the temperature was at 22℃ and 25℃, nitrite accumulation was not observed in the system and the phosphorus removal rate were 94.3% and 86.9%, respectively. When the temperature was increased to 28℃, nitrite accumulation efficiency in the reactor reached 87.2%, implying the system achieved a stable short-cut nitrification. In addition, in the short-cut nitrification stage at high temperature (28℃), the phosphorus release and uptake capacity of the system decreased. The anaerobic phosphorus release/COD consumption (P/C) ratio was much lower compared those at 22℃ and 25℃. However, the phosphorus removal performance of the reactor did not deteriorate at this stage. The phosphorus removal rate was 68.9%, indicating that a sufficient carbon source in the influent could not only guarantee the removal of TN, but also detoxify NO2- to reduce its inhibitory effect on the phosphate accumulating organisms (PAOs). The batch tests of phosphorus uptake by the sludge under different temperature conditions revealed that O2, NO3-, and NO2- could all be used as electron acceptors for phosphorus uptake. The aerobic phosphorus uptake rate was higher than that with NO3- and NO2- as electron acceptors. The phosphorus uptake rates of O2 and NO3- as electron acceptors were also found to be negatively correlated with temperature.

Advanced nutrient removal and functional microorganism enrichment in AOA system reinforced by side-stream sludge fermentation

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

Successful start-up of a novel integrated denitrifying phosphorus removal and partial denitrification coupled with anammox process for simultaneous nitrogen and phosphorus removal with fully ordinary suspended sludge

In this paper, a review on the mechanism of denitrifying phosphorus removal and the enrichment of denitrifying phosphorus-accumulating organisms in the process of nitrogen and phosphorus removal, such as A 2 /O and SBR, were presented, as well as the influence factors of enrichment were also carried out. And finally, the outlook of denitrifying phosphorus removal process for future research was suggested. Conventional biological treatment process can effectively reduce BOD5 and SS of inflow, but the removal efficiencies of nitrogen and phosphorus in wastewater are not effective, which cause that a large amount of sewage containing nitrogen and phosphorus directly discharge into water body. Therefore, the nitrogen and phosphorus pollution is the primary cause for water entrophication. Although the government put forward more and more strictly requirements for sewage discharge, it is difficult to remove nitrogen and phosphorus efficiently for the conventional nitrogen and phosphorus removal process, because of various reasons, such as carbon-nitrogen ratio in the city sewage. So it is necessary to develop more stable, economical and efficient process for nitrogen and phosphorus removal. Denitrifying phosphorus removal process is to complete domestication and enrichment of denitrifying phosphate-accumulating organisms (DNPAOs) by using anaerobic/anoxic alternate environment instead of the traditional anaerobic/aerobic environment. DNPAOs can use NO3 - as electron acceptor in denitrifying phosphorus removal system, meanwhile through their metabolism complete excess phosphorus uptake and denitrification process at the same time to achieve the dual purpose of nitrogen and phosphorus removal. Application of denitrifying phosphorus removal process for treatment of municipal wastewater can not only save aeration quantity, but also reduce the amount of residual sludge. And it also can cut down investment and operation costs. In recent years, many scholars did a number of researches on denitrifying phosphorus removal technology. Due to the varying techniques, enrichment mode and denitrifying phosphorus removal degree, the conclusion was not entirely consistent.