[Aerobic Granulation Stability and Microbial Diversity of Filamentous Bulking Sludge].

Filamentous bacteria, as one of the common bacteria types in wastewater biological treatment, are considered to be the main factor to induce sludge bulking. However, because of its special filamentous shape, it plays a crucial role in the formation of sludge particles. Taking filamentous bulking sludge as the research object, the effect of filamentous bacteria on the sludge granulation process and maintaining the stability of sludge granules was studied, and the microbial diversity of the sludge system was analyzed. Filamentous bulking sludge (SVI=241.56 mL·g-1) and flocculated sludge (SVI=64.22 mL·g-1) were respectively inoculated to carry out granulation culture. The results showed that the time of particle appearance of bulking sludge and flocculated sludge was 20 days and 40 days, respectively; the mature particle sizes were 650 µm and 700 µm, respectively; and the granulation time of bulking sludge was only half that of flocculated sludge. After adding the anoxic zone, the granules were broken to differing degrees, but the SV30/SV5 value of mature granules recovered to 1 after short-term fluctuation, and the stability of the mature granules was stronger. The analysis of microbial community structure showed that the relative abundance of norank_o__Saccharimonadales, unclassified_o__Saccharimonadales, and unclassified_f__Saccharimonadaceae increased from 0.05%, 0.01%, and 0.01% to 4.09%, 3.15%, and 1.12%. The existence and accumulations of these hydrophobic bacteria were important for rapid granulation. The removal rates of COD, NH4+-N, and TN were 94%, 99%, and 35% and 92%, 97%, and 30%, respectively, in SBR1 of bulking sludge and SBR2 of flocculated sludge, and the removal rates of TP were 60% and 30%, respectively.

[Microbial Diversity of Filamentous Sludge Bulking at Low Temperature].

To investigate the characteristics of microbial diversity during filamentous bulking at low temperature, the induction of sludge bulking was successfully carried out using a low-temperature sequencing batch reactor(SBR). With the help of Illumina MiSeq high-throughput sequencing technology, the overall changes in the microbial community structure of activated sludge, the characteristics of each specific microbial community, and the specific genera were all investigated under different sludge sedimentation performances. The results showed that filamentous bulking can be successfully induced after the system operating temperature drops to (14±1)℃, and the COD and TN removal rates can still be maintained at approximately 90% and 86%, respectively, with the sludge volume index deteriorating to 663.99 mL·g-1. The occurrence of sludge bulking at low temperature will not only reduce the overall diversity and uniformity of microorganisms in the system and increase the abundance of filamentous bacteria from 0.49% to 26.04% but also cause the abundance of denitrifying bacteria to reduce from 21.04% to 13.99% and that of dephosphorization bacteria to reduce from 4.25% to 1.93%. Of the five filamentous genera founded, the abundances of three filamentous bacteria represented by Thiothrix increased, whereas only that of the Haliscomenobacter decreased. Of the 19 denitrifier genera founded, the abundances of five species represented by Nitrosomonas increased, whereas those of seven species represented by Nitrospira decreased. Moreover, the abundances of Pseudomonas and Tetrasphaera increased out of the eight phosphorus-removing bacteria genera, whereas the abundances of the five bacteria genera represented by Candidatus_Competibacter decreased. Although sludge bulking has a significant impact on the structure of the microbial community, the 477 operational taxonomic units and 227 bacterial species that are always present in the different sludge samples indicate that the main microorganisms in the reactor are still relatively stable during the bulking process.

[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.

[Induction of low dissolved oxygen limited filamentous bulking and optimization of nitrogen and phosphorus removal].

Actual domestic sewage was treated by SBR process operating in Anoxic/Oxic pattern. Limited filamentous bulking was induced by low dissolved oxygen at normal temperature, and SVI was maintained 150-220 mL/g. Occurrence of limited filamentous bulking and growth of microorganism were researched, as well as optimization of nitrogen and phosphorus removal. Results showed that filamentous bacteria that led to limited filamentous bulking were H. hydrossis, 0803 type, and M. parcicella, which were the dominant filamentous bacteria by the biggest percentage. It was discovered that during phase of low dissolved oxygen, removal rate of NH4(+) -N decreased significantly, from above 95% to 65%, with obviously less PO4(3-) -P and a little higher COD in effluent. Removal rates of NH4(+) -N and TN were greatly improved to above 95% by new operating pattern of Anaerobic/Oxic/Anoxic: transient inlet --> anaerobic stir (0.75 h) --> aeration (5 h) --> anoxic stir (2.25 h) --> settling, drainage (1 h). So efficient, simultaneous removal of nitrogen and phosphorus was realized in system of low dissolved oxygen limited filamentous bulking.

[Nitrogen removal by enhanced endogenous denitrification with excess activated sludge reduction technology].

In order to increase the efficiency of nitrogen removal by endogenous denitrification, and to realize the excess activated sludge reduction in the traditional wastewater treatment process, this investigation proposes a hydrolysis/anoxic/oxic (H/A/O) process utilizing nitrogen removal with excess activated sludge reduction. The experimental equipment for continuous treatment of domestic wastewater was set up and the pilot experiment was conducted. The results showed that, without adding external carbon sources and alkalinity, the removal efficiency of COD, NH4+-N and TN were higher than 90%, 95% and 75%, respectively, under the condition that the hydraulic retention time was 10 h and the backflow ratio of nitrification liquor was 300%, the COD of influent between 220-410 mg/L, the NH4+-N of influent between 36-58 mg/L. When the carbon source was not the limiting condition of the denitrification, with the increasing of the return nitrification liquor, the nitrogen removal efficiency increased. On the contrary, with the increasing of the return nitrification liquor, the nitrogen removal efficiency decreased. It has been tested that the reduction rate of excess activated sludge in the system reached 56.2%. The nitrogen removal efficiency was improved greatly by the wastewater and excess activated sludge hydrolysis. It's proved that using hydrolysis as pre-treatment of wastewater and excess activated sludge is feasible, thas it not only improved the biodegaradability of wastewater and the nutrient removal efficiency, but also enhanced the stability for the operation of the wastewater treatment system, and then the wastewater and excess activated sludge were treatment simultaneously.

[On-line control of external carbon addition to predenitrification process].

With domestic wastewater of low ratio of carbon and nitrogen (C/N), the control of external carbon dosage was studied for the predenitrification process with continuous flow. The objective is to keep the external carbon usage as low as possible while nitrate plus nitrite concentrations (NOx(-)-N) of outflow under demand. The experimental results show that nitrogen removal efficiency couldn't be improved by increasing total recirculating rate with total recirculating rate more than 2 for lack of carbon source and removal efficiency of TN couldn't be largely improved by double dosage of carbon source with constant recirculating rate when NOx(-)-N concentration reaches about 2 mg/L. Based on the analysis of the relationship between the external carbon addition and total recirculating rate, a control method was proposed. The external carbon dosage is controlled by keeping NOx(-)-N concentration of anoxic zone at the level of 2 mg/L, and the total recirculating rate is determined by stated effluent NOx(-)-N concentration. The control method not only can determine the reference point of carbon dosage, but also can optimize the usage of carbon addition. It is easy to be carried out in wastewater treatment plants.

[Effect of nutrient on sludge settling property and bulking controls].

The effect of nutrient (N and P) deficiency on activated sludge settleability and characteristics of activated sludge flocs in Sequencing Batch Reactor (SBR) fed with brewery wastewater were investigated. The results showed that the activated sludge had good settling properties at influent BOD5/N/P was 100/5/1,100/5/0.8 and 100/4/0.8 respectively. When BOD5/N/P was 100/0.94/0.31,100/2/0.4,100/3/0.6 respectively, the sludge settleability became worse due to excessive growth of filamentous. When BOD5/N/P was 100/0.94/1,100/5/0.31,100/5/0.4,100/5/0.6 respectively, non-filamentous activated sludge bulking occurred. Adding sufficient nutrient to the influent, the sludge bulking was controlled effectively and the low SVI was recovered. When increasing COD loading rate, the duration of recovery could be diminished. When nitrogen and phosphorus were insufficient synchronously, aerobic granular sludge was formed which was averagely 2mm-6mm in diameter.