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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.

Settled algae may be used as nutrient for macrophyte establishment, but also can induce marked macrophyte decline during deep anaerobic decomposition. Sediment microbial fuel cells (SMFCs) may promote the utilization of algae-derived nutrients and relieve bio-toxicity from settled algae to submerged macrophytes, thus facilitating plant production. To test these hypotheses, a 62-day comparative study was designed and conducted in microcosms with the following six treatments: control (open-circuit SMFC), plant (open-circuit SMFC with plants), algae (open-circuit SMFC with algae), algae-plant (open-circuit SMFC with algae and plants), algae-SMFC (closed-circuit SMFC with algae), and algae-plant-SMFC (closed-circuit SMFC with algae and plants). The results showed that the presence of Hydrilla verticillata improved the power generation of SMFCs when algae were used as substrates during the whole operation. The decomposition of sedimented algae experienced two periods since the injection. During the slight decomposition period (14–38 day), the algal retention in sediments was enhanced by H. verticillata as a nutrient source. Nitrogen (N) assimilation in plant shoots was facilitated under electrogenesis due to a simultaneous increase of algae-derived dissolved inorganic carbon (DIC) and ammonium (NH4+) in the water column. At the end of the 38th day, the biomass of H. verticillata were increased by 21.4% and 52.3%, respectively, in the algae-plant and algae-plant-SMFC, compared with that in plant treatment. Obvious NH4+-stress was exerted on H. verticillata during the following intense algal decomposition period (38–62 day). Compared with shoots, roots of H. verticillata were more sensitive to the biotoxicity of algae-derived NH4+. The electrogenetic process diverted the degradation pathway from acetoclastic methanogenesis to electrogenesis via redox cycle, resulting in delayed algal decomposition in algae-SMFC treatment. In addition, electrogenesis enhanced the removal of algae-derived N. As a result, NH4+ toxicity to plant roots was effectively alleviated, and sedimented algae served as a stable nutrient source for plant development. Stable transfer rate of algae-derived N from sediments to plant roots was observed, while the assimilation rate of algae-derived N from water column to plant shoots showed a constant increase in the algae-plant-SMFC treatment. Electrogenesis enhanced N-fixing capacity belonged to rhizosphere of H. verticillata, evidenced by greater enrichment of some plant growth-promoting rhizobacteria (PGPRs), including Bradyrhizobium, Mycobacterium, Paenibacillus, Mesorhizobium, and Roseomonas in the algae-plant-SMFC treatment. At the end of the experiment, marked increases in the production of H. verticillata in algae-plant-SMFC were observed, with 90.1% and 32.8%, respectively, when compared with algae-plant and plant treatments (p

The performance of bioelectrochemically assisted constructed wetland systems planted with Arundo donax were evaluated at applied voltages of 1, 2, 3 and 5 V. The RGR and Proline (Pro) results implied a positive response at the proper applied voltage. In the 3-V group, the RGR sharply climbed to a maximum over two stages, and the Pro reached a higher level of 256.25 μg/g at the end of the first stage without an additional organic carbon source. This result indicated that A. donax was attempting to adapt the 3-V stress via physiological self-regulation and the growth was nearly unaffected. However, in the 5-V group, the great increase in Pro and withering of the aboveground A. donax showed that the voltage stress had become lethal and the plant was not able to endure it through physiological regulation. In addition, Anodic microbial community compositions accumulating on graphite felts were analyzed via high-throughput sequencing. Results showed that there were two clear clusters at different applied voltages. One cluster was assembled from the anodic region of the 0-V and 1-V groups, and the other was collected from the 2-V and 3-V samples. At the phylum level, Proteobacteria, Firmicutes and Bacteroidetes were the most common phyla among the samples. However, at the genus level, the dominant genera varied with the applied voltage. The relative abundance of Desulfovibrio increased with increased applied voltage. The highest total nitrogen removal rate in the 2-V group was closely related to the high abundance of the Acinetobacter genus. Moreover, Exiguobacterium became dominant only in the 5-V sample, suggesting that this genus strongly depended on the interactive environment of exudes from A. donax and applied voltage.

Sediment internal nitrogen release is a significant pollution source in the overlying water of aquatic ecosystems. This study aims to remove internal nitrogen in sediment-water microcosms by coupling sediment microbial fuel cells (SMFCs) with submerged aquatic plants. Twelve tanks including four treatments in triplicates were designed: open-circuit (SMFC-o), closed-circuit (SMFC-c), aquatic plants with open-circuit (P-SMFC-o) and aquatic plants with closed-circuit (P-SMFC-c). The changes in the bio-electrochemical characteristics of the nitrogen levels in overlying water, pore water, sediments, and aquatic plants were documented to explain the migration and transformation pathways of internal nitrogen. The results showed that both electrogenesis and aquatic plants could facilitate the mineralization of organic nitrogen in sediments. In SMFC, electrogenesis promoted the release of ammonium from the pore water, followed by the accumulation of ammonium and nitrate in the overlying water. The increased redox potential of sediments due to electrogenesis also contributed to higher levels of nitrate in overlying water when nitrification in pore water was facilitated and denitrification at the sediment-water interface was inhibited. When the aquatic plants were introduced into the closed-circuit SMFC, the internal ammonium assimilation by aquatic plants was advanced by electrogenesis; nitrification in pore water and denitrification in sediments were also promoted. These processes might result in the maximum decrease of internal nitrogen with low nitrogen levels in the overlying water despite the lower power production. The P-SMFC-c reduced 8.1%, 16.2%, 24.7%, and 25.3% of internal total nitrogen compared to SMFC-o on the 55th, 82th, 136th, and 190th days, respectively. The smaller number of Nitrospira and the larger number of Bacillus and Pseudomonas on the anodes via high throughput sequencing may account for strong mineralization and denitrification in the sediments under closed-circuit. The coupled P-SMFC system has shown good potential for the efficient removal of internal nitrogen.

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.

Phosphorus is a crucial element in the eutrophication process. According to China’s water pollutant discharge Class 1A standard, treated wastewater must meet 0.5 mg/L of phosphorus prior to discharge to a sensitive water body. In recent years, wastewater treatment technologies such as membrane bioreactors have been demonstrated to achieve high-quality effluent and present the potential for wastewater reuse applications. However, an efficient and cost-effective phosphorus removal process is still not warranted. In this study, a submerged membrane bioreactor (SMBR) with addition of a low concentration of aluminum sulfate ([mol Al : mol P ≤ 1] was used to evaluate its treatment performance. The results showed that significant phosphorus removal could be achieved with addition of a low aluminum sulfate dosage to meet national phosphorus discharge standard; however, no significant effect was observed on the removal of COD and ammonia. The addition of a low concentration of aluminum sulfate could offer as an economical solution to increase the phos phorus removal efficiency of a SMBR, and thereby improve the water quality of the water bodies.