Investigation of the polyphosphate-accumulating organism population in the full-scale simultaneous chemical phosphorus removal system.

The simultaneous chemical phosphorus removal (SCPR) process has been widely applied in wastewater treatment plants (WWTPs) due to the high phosphorus removal efficiency through the synergy of biological and chemical phosphorus removal (BPR and CPR). However, phosphorus removal reagents could affect the bacterial community structure in the SCPR system and further affect the BPR process. The BPR phenotypes and community structures in the SCPR system, especially the population of polyphosphate-accumulating organisms (PAOs), are not completely clear. In order to clarify these problems, the phosphorus removal performance and the PAO population in a full-scale SCPR system were investigated. Results showed that diverse PAOs still existed in the SCPR system though the BPR phenotypes were not observed. However, the relative abundances of Accumulibacter and Tetrasphaera, the two most important genera of PAOs, were only 0.59% and 0.20%, respectively, while the relative abundances of Competibacter and Defluviicoccus, two genera of glycogen-accumulating organisms (GAOs), were as high as 5.77% and 1.28%, respectively. Batch tests showed that PAOs in the SCPR system still had a certain polyphosphate accumulating metabolic activity, which could gradually recover after stopping the addition of chemical reagents. This study provided a microbiological basis for the SCPR system to recover the enhanced biological phosphorus removal (EBPR) performance under suitable conditions, which could reduce the dosage of chemical reagents and the operational cost.

[Realization of Limited Filamentous Bulking with Type 0092 Filamentous Bacteria as the Dominant Filamentous Bacteria in Shortcut Nitrification].

Type 0092 filamentous bacteria generally do not result in excessive sludge bulking. To take advantage of this, domestic sewage was used to inoculate shortcut nitrification sludge in a sequencing batch reactor (SBR). Sludge settleability, the nitrite accumulation ratio (NAR), pollutant removal characteristics, and the dynamic variation of microbial communities during the system startup and maintenance were investigated. The results indicated that limited filamentous bulking (LFB)with Type 0092 filamentous bacteria combined with shortcut nitrification could be achieved under alternating anoxic and aerobic (four times/cycle;the ratio of anoxic/aerobic was 20 min/60 min) with low dissolved oxygen (DO) content (0.3-0.8 mg·L-1) and a low food/microorganism (F/M) ratio[0.24 kg·(kg·d)-1, COD/MLSS]. The removal rate of COD and total nitrogen (TN) were increased by 13% and 5% when the sludge volume index (SVI) and NAR were maintained at approximately 180 mL·g-1 and 99%, respectively, and aeration consumption was reduced by 62.5% compared to general whole-run nitrification. When the ratio of anoxic/aerobic changed to be 10 min/30 min as alternating times increased to 6 times per cycle, the activity of the nitrite oxidizing bacteria (NOB) recovered, causing shortcut nitrification to be destroyed. In addition, low DO, alternate anoxic/aerobic modes, and low loading rates were the key factors in achieving LFB with Type 0092 filamentous bacteria as the dominant filamentous bacteria. Limited filamentous bulking could not be maintained under low DO and alternating anoxic/aerobic conditions with loading rates above 0.25 kg·(kg·d)-1, COD/MLSS.

[Stability of Nitritation Combined with Limited Filamentous Bulking Under Intermittent Aeration].

Limited filamentous bulking (LFB) combined with nitritation under low dissolved oxygen (DO) is a new technology for enhancing nitrogen removal and reducing aeration requirements. In order to investigate the feasibility and sustainability of this technology, two sequence batch reactors (SBRs) were operated under different regimes to stimulate different aeration modes under low DO (0.3-0.8 mg·L-1). Sludge settleability, nitrite accumulation ratio (NAR), total nitrogen (TN) removal rate, dynamic variation of dominant filaments, and nitrifying bacterial communities were investigated. The results indicated that short-cut nitrification combined with LFB could be achieved under intermittent aeration, and the ratio of anoxic/aerobic was 15 min/30 min, the value of sludge volume index (SVI) was maintained from 170 mL·g-1 to 200 mL·g-1. An NAR above 95% was achieved under real-time continuous aeration. Meanwhile, LFB was induced when nitrite started to accumulate, and the dominant filament was Type 0092. However, the limited bulking was not maintained for the long term. After a transfer from continuous aeration to intermittent aeration, LFB reappeared in 60 days and the value of SVI remained between 170 mL·g-1 and 200 mL·g-1. The process of nitritation combined with LFB was maintained stably for the next two months, and the TN removal rate was above 66%. FISH analysis indicated that the identical dominant filaments were M. parvicella and Type 0092 for maintaining limited bulking in the two reactors. qPCR results showed that proportion of AOB in the total bacteria increased from the previous 0.53% to 2.19% in the end, whereas that of NOB decreased from 17.5% to 3.2% in SBR A. Moreover, the proportion of AOB increased from 0.51% to 1.53%, whereas that of NOB decreased from 18.05% to 11.01% in SBR B.

Energy saving control strategies for Haliscomenobacter hydrossis filamentous sludge bulking in the A/O process treating real low carbon/nitrogen domestic wastewater.

The control strategies of energy saving for filamentous sludge bulking were investigated in the A/O process under low dissolved oxygen (DO) with low carbon/nitrogen (C/N) ratio, and the dominant filamentous bacteria were identified by using fluorescent in situ hybridization. Initially, the sludge volume index reached nearly 500 mL/g and serious bulking occurred when the DO value was 0.5 mg/L, with Haliscomenobacter hydrossis as the major filamentous bacteria in the bulking sludge. Later on, the compartment number increased in the aerobic zone, increasing by this way DO, to control serious bulking. Increasing DO to 1 mg/L based on the increase of compartment number in the aerobic zone was the favorable controlling method, which solved the sludge loss, improved the effluent quality to the national discharge standard and allowed for energy costs saving. As a result, the effective control method for H. hydrossis filamentous sludge bulking provided the economical, convenient and longstanding method for most municipal wastewater treatment plants treating real low C/N domestic wastewater.