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IntroductionAnaerobic–anoxic–oxic (A2/O) and deoxidation ditch (DOD) processes are being increasingly preferred owing to their effectiveness in treating various wastes in wastewater treatment plants (WWTPs). Considering seasonal variations is crucial in optimizing treatment processes, ensuring compliance with regulations, and maintaining the overall efficiency and effectiveness of WWTPs. This study aimed to determine the influence of seasonality on nitrogen removing microbes and functional genes within A2/O and DOD processes in the humid Wuhan and semi-arid Xi’an cities, China.MethodsThe physicochemical parameters of water quality were determined, and molecular and bioinformatic analyses of the bacterial community and nitrogen metabolism functional genes in the two different treatment processes of two WWTPs were performed over four seasons.Results and discussionOur analyses revealed a significant difference in all physicochemical parameters across all experimental groups (p

This study evaluated the feasibility of domesticating the bioflocs with activated sludge as inoculum at high salinity. By using the gradually increase salinity from 0.2 to 4.0%, the study evaluated the effectiveness of bioflocs in sustaining the water quality of aquaculture, the biofloc morphology characteristics and microbial community structure of bioflocs in order to discover the influence of salinity. From the perspective of sustaining the water quality of bioflocs, the COD removal efficiency dropped sharply from 63.9% to 3.7%, the NO3−-N was maintained below 0.5 mg/L but the NH4+-N exceeded the safety threshold of aquaculture at the salinity of 2.5–4.0%. From the pespective of flocculation of flocs, the biofloc volume index and content were maintained at about 30 ml/g and 7 g/L, while the floc particle size (45–200 um) tended to increase cumulatively, showing good agglomeration, sedimentation and stability. From the pespective of floc microbial community structure, Arenibacter, Thauera, Paracoccus and Denitromonas became the dominant genera with relative abundances of 4.8–7.5%, 4.9–17.1%, 3.0–4.7% and 5.3–14.1% at 3.0–4.0% salinity, respectively, however, the relative abundance of Candidatus Competibacter rapidly decreased from 15.0% to 2.5% with the increasing salinity from 1.0% to 4.0%. Furthermore, Redundancy analysis (RDA) indicated that salinity was a key environmental factor affecting floc community, and Functional Annotation of Prokaryotic Taxa (FAPROTAX) confirmed the promoted flocs denitrification as well as inhibited nitrification and hydrocarbon cycling in higher salinity to some extent. This study demonstrated the feasibility of using freshwater activated sludge as a base nucleus for biofloc formation for salinity up to 2% – 2.5%, which provided a useful reference for improving the taste and nutritional value of fish cultured by Biofloc Technology (BFT).

In a mesocosm experiment, the growth and photosynthetic responses of Vallisneria natans (Lour.) Hara was studied monthly in different water depths under flowing and static water. Water depth showed a significant effect on the shoot length, below-ground: above-ground biomass, and total biomass, while water velocity showed only a significant effect on the total biomass. In addition, total biomass and shoot length at 45, 75 and 105 cm was higher in the flowing treatment than that in the static treatment, which suggested that total biomass and shoot length are promoted by water flow to some extent. All of the investigated photosynthetic showed different changes with different months. Water depth exhibited significant effects on the maximum photosynthetic efficiency Fv/Fm, the maximum electron transport rate rETRmax, Chla, Chla + b and Chla/b, while water velocity showed only significant effects on Chla, Chla + b, ETRmax. The rapid light response curves varied differently with the time periods. In October, the time-course of slow chlorophyll a fluorescence induction curves, Fm peak, in the flowing treatment in 45, 75 and 105 cm is higher than that in the static treatment. All the results demonstrated that the differences between flowing and static water resulted in the different life strategy.

In this study, we evaluated the effects of two dominant microfilamentous algae (i.e. Melosira granulata and Oscillatoria sp.), collected from the West Lake, on growth and metabolism of Daphnia magna. Our experiment utilized 13C and 15N dual labeling to calculate the carbon and nitrogen isotopic turnover rates and half-life times in D. magna. The two labeled types of filaments were offered to D. magna as sole food sources or as paired mixtures with the unlabeled Scenedesmus obliquus. Labeled S. obliquus served as the control. Combined results showed that D. magna had a higher grazing rate on Oscillatoria sp. than on M. granulate and a small percentage of unlabeled S. obliquus addition could improve the grazing rate in both filamentous algae, especially for Oscillatoria sp., which had the highest carbon and nitrogen isotopic turnover rates and the lowest half times, even superior to the sole S. obliquus treatment. Our study revealed that D. magna could utilize the two dominant filamentous algae as a food source for their growth and metabolism, and a small percentage addition of S. obliquus could ameliorate the negative impact of these two filamentous algae on D. magna.

A novel bioelectrochemically assisted constructed wetland system (BECW) was investigated using a laboratory-scale experimental apparatus for treating nitrate-contaminated water without an organic carbon source. The BECW was operated at 29 ±1 and 18 ±1°C, respectively, to explore the effects of temperature on the autotrophic denitrification process. The results showed that higher TN removal efficiency (76.30 ±5.08%) was obtained at higher temperature when compared to a lower temperature (48.18 ±4.40%). The effluent concentrations of NO2 N-- and NH4 +-N at 18 ±1°C were 0.40 ±0.11 and 0.50 ±0.42 mg N L-1, whereas those at 29 ±1°C could be neglected. Besides, significant accumulations of NO2 --N and NH4 +-N were observed in the cathode region at 18 ±1°C through quantifying different forms of nitrogen that varied along the flow path. [ABSTRACT FROM AUTHOR]

This research aimed to investigate the phosphorus (P) removal of a series of laboratory-scale unvegetated vertical-flow constructed wetland systems using anthracite, steel slag and related blends as substrate in treatment of low concentration domestic sewage. The long-term performance of P removal was firstly studied by using single substrate of anthracite or steel slag, and three systems applying various combined substrates were investigated when the average P loading rate varied between 0.9 and 1.5 g TP/m2·d. The results demonstrated that both anthracite and steel slag systems were highly effective in removing total P (TP, 77.17±23.34% and 90.26±4.48%) and soluble reactive P (SRP, 92.14±12.56% and 96.20±2.58%). The system filled with anthracite, vermiculite and steel slag from the top down removed 82.45± 9.52% and 87.83±8.58% of TP and SRP, respectively. However, other combined substrate systems showed comparative low and fluctuant P removal. The effluent pH was maintained at 7-9, which met environmental requirements of China. Therefore, anthracite provides a long-term high efficiency of P removal and may be a promising substrate from the standpoint of the effluent pH, and the arrangement of combined substrate has a prominent effect on P removal. [ABSTRACT FROM AUTHOR]