[Effect of Ozone Dosage on Sludge Settleability and Biological Nutrient Removal in SBR System].

The effect of ozone dosage on sludge settleability and biological nutrient removal performance in a sequencing batch reactor was investigated by inoculating the bulking sludge with the SVI of 280 mL·g-1 from a wastewater treatment plant in winter. The filamentous mycelium was interrupted, and the SVI was decreased to 125 mL·g-1 after ozone dosage with a low concentration of 0.085 g·g-1(O3/MLSS) for 20 days, which indicated the disappearance of the sludge bulking. The performance of nitrification and phosphorus removal efficiency was not affected obviously. However, the sludge settleability deteriorated with a high dosage of ozone, and the phosphorus removal efficiency was decreased to around 60%. Further study showed that PS/PN had a positive correlation with SVI with the correlation coefficient of 0.9381, which can be used to characterize sludge settleability. A low ozone dosage not only interrupted the filamentous mycelium, but it also affected the content and composition of the EPS, which led to improved settleability.

[In-situ Phosphorus Removal Activity and Impact of the Organic Matter Concentration on Denitrifying Phosphorus Removal in Sludge Aggregates].

In this work, the redox potential, dissolved oxygen, and phosphate microelectrodes were used to quantitatively study the in-situ activity of dephosphorization bacteria and the impact of the organic matter concentration on denitrifying phosphorus removal in sludge aggregates in a sequencing batch reactor. The results showed that the maximum net volume release rate of phosphorus was 3.29 mg·(cm3·h)-1 in the initial anaerobic sludge aggregates, which was approximately 3 times the maximum net volume uptake rate of phosphorus at the initial anoxic stage. The release rate of phosphorus clearly decreased at the final anaerobic stage, and the maximum net volume release rate of phosphorus was only half of that at the initial anaerobic stage. At the final anoxic stage, the maximum net volume uptake rate of phosphorus decreased to 0.14 mg·(cm3·h)-1, and the phenomenon of secondary phosphorus release occurred in the deep area below 1800 µm. When the concentration of COD decreased from 350 mg·L-1 to 250 mg·L-1 and 150 mg·L-1, the maximum net volume release rate of phosphorus of dephosphorization bacteria decreased from 3.27 mg·(cm3·h)-1 to 2.44 mg·(cm3·h)-1 and 2.01 mg·(cm3·h)-1, respectively, and the rapid uptake area of phosphorus narrowed to the surface of the sludge aggregates.

[Effects of Microplastics on Membrane Fouling During a Shortened Ultrafiltration Membrane Process].

Microplastics have garnered much attention worldwide as a new emerging pollutant. As they are gradually detected in freshwaters, understanding how microplastics will behave during current drinking water treatment processes is urgently needed. In recent years, the shortened process with an ultrafiltration (UF) membrane has shown excellent performance because of its low land use and high water purification efficiency. In this work, the membrane performance induced by microplastics was investigated with a shortened UF membrane process. The results showed that membrane fouling was always induced by the cake layer before and after coagulating with microplastics. Owing to the small UF membrane pore size (d<0.1 µm), slight membrane fouling was caused by microplastics (d<5 mm) alone. However, although the loose cake layer was formed because of the existence of flocs, the cyberspace formed by flocs was easily entered by small microplastics with increasing coagulant dosage. As a result, server membrane fouling was induced because of the formation of a dense cake layer. It was shown that the specific membrane flux induced by flocs alone was 0.82 and 0.76 in the presence of 0.1 mmol·L-1 and 0.9 mmol·L-1 FeCl3·6H2O, respectively. However, after coagulation the specific membrane fouling induced by the 0.1 g small microplastics (d<0.5 mm) was 0.76 and 0.62 with 0.1 mmol·L-1 and 0.9 mmol·L-1 FeCl3·6H2O, respectively. In addition, microplastics were always negatively charged in water. In comparison with alkaline conditions, Fe-based flocs were positively charged under acidic conditions, which were also much smaller. Therefore, microplastics were more easily adsorbed by Fe-based flocs under acidic conditions, leading to severe membrane fouling because of the dense cake layer formed. After coagulating with 0.3 mmol·L-1 FeCl3·6H2O, the specific membrane flux induced by 0.1 g small microplastics (d<0.5 mm) was 0.55 and 0.79 at pH 6.0 and 8.0, respectively.

[Enhanced Short-cut Denitrification by Fe(0)-activated Carbon and Its Influencing Factors].

In order to reduce the carbon source for biological short-cut denitrification, Fe(0)-activated carbon was used to enhance nitrogen removal in the absence of organic carbon, and the influences of the Fe/C mass ratio and initial pH value on the nitrogen removal efficiency were explored. The results showed that the nitrite removal efficiency increased from 7.4% to 31.1% when the Fe(0)-activated carbon was used to enhance short-cut denitrification. When the Fe/C mass ratio was reduced from 2:1 to 1:1 and 1:2, both the denitrification rate and nitrite removal efficiency first increased and then decreased. At a Fe/C mass ratio of 1:1, a maximum denitrification rate of 5.58 mg·(g·h)-1 and a maximum nitrite removal efficiency of 41.1% were achieved, respectively, and 0.1 mg of nitrous oxide was emitted. When the pH value was increased from 6.0 to 9.0, the denitrification rate decreased from 7.39 to 5.96 mg·(g·h)-1, and the nitrous oxide emission decreased from 0.19 to 0.12 mg. Therefore, a higher nitrogen removal efficiency could be achieved by Fe(0)-activated at a Fe/C mass ratio of 1:1 and pH value of 6.0. However, more nitrous oxide would be emitted at a low pH value.

Cloning and Overexpression of the Mitomycin C Resistance Gene (mcr) from Streptoverticillium caespitosum.

Streptoverticillium caespitosum ATCC27422 is a major producer of an anti-cancer drug, mitomycin C. A 6.6 kb DNA fragment containing the mitomycin C resistance gene (mcr) was isolated from ATCC27422 by shotgun method in order to learn the molecular mechanism of mitomycin C resistance. By constructing a series of subclones from this 6.6 kb DNA fragment, the mitomycin C resistance gene was localized on a 3.1 kb DNA fragment. Sequence analysis revealed that the open reading frame of mcr gene was 1 347 bp in size, encoding 448 amino acids with ATG as initiation codon and TGA as termination codon. The mcr gene was specifically expressed under the control of T7 promoter in E.coli, and the resistance to mitomycin C in the transformant was over 100-fold higher than that in wild-type strain. The overexpression of mcr gene in E.coli is very helpful for the further research about the molecular mechanism of drug resistance.