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As an important primary producer, submerged macrophytes regulate the material circulation and energy flow of the ecosystem, but the recovery process of submerged macrophytes is often plagued by sediments with high organic matter load. The effect of plant growth-promoting rhizobacteria (PGPR) on Vallisneria natans (V. natans) growth and its relationship with sediment nitrogen and phosphorus was studied by inoculating strains PC2 (Bacillus stratosphericus), H19 (Bacillus subtilis) and L3 (Bacillus cereus) under high sediment organic matter load. The results showed that PGPR inoculation significantly promoted the growth of V. natans and the comprehensive effects was PC2>H19>L3. The growth of V. natans grown in the non-inoculated treatment was inhibited. The height, root length, fresh weight of aboveground and underground tissues of V. natans in PC2 treatment group increased by 165.0%, 17.4%, 378.8% and 165.1%, respectively. Through RDA analysis and Pearson correlation analysis, the increment of plant growth index were significantly negatively correlated with the increment of Inorg-N, NO2-N, NO3-N, Inorg-P and Fe/Al-P in the sediment, indicating their potential control sediment Inorg-N and Inorg-P. Therefore, PGPR inoculation is a certain prospective way to solve the problems of submerged macrophytes recovery and internal pollution. [ABSTRACT FROM AUTHOR]

Three novel constructed wetland-microbial fuel cells (CW-MFCs), based on electrode location, were developed for wastewater treatment and sustainable electricity production by embedding a MFC into a CW system. In the three CW-MFCs, electrodes were placed in different locations, including bottom anode-rhizosphere cathode CW-MFC (BA-RC-CW-MFC), rhizosphere anode-air cathode CW-MFC (RA-AC-CW-MFC), and bottom anode-air cathode CW-MFC (BA-AC-CW-MFC), to investigate the combined effects of organic loading rates (OLRs) and reactor configurations on the electrogenesis capacity of the hybrid system. All the systems operated continuously to treat five types of synthetic wastewater with increasing OLRs: 9.2, 18.4, 27.6, 55.2, and 92.0 g chemical oxygen demand (COD) m−2 d−1. The BA-RC-CW-MFC failed to produce electricity at any OLR, whereas the maximum power densities of 0.79 ± 0.01 and 10.77 ± 0.52 mW m−2 were achieved in the RA-AC-CW-MFC with 18.4 g COD m−2 d−1 influent OLR and in the BA-AC-CW-MFC with 27.6 g COD m−2 d−1 influent OLR, respectively. The coulombic efficiencies of the RA-AC-CW-MFC and BA-AC-CW-MFC decreased gradually with the increase in influent OLRs. © 2016 American Institute of Chemical Engineers Environ Prog, 36: 435-441, 2017 [ABSTRACT FROM AUTHOR]

Abstract: Shallow, eutrophic lakes are usually characterized by a turbid state devoid of submerged vegetation subject to human-induced eutrophication. In most cases, it is rather hard to restore a vegetated clear state due to reduced resilience caused by a blend of complicated factors. In this study, we successfully reestablished a plant community in a small hypereutrophic lake over a certain period. In winter and spring with transparency of >55cm and temperature of <20°C, a submerged stands bed formed gradually under strong human interventions. The reestablished plant bed displayed obvious seasonal succession and prolonged the clear-water stage until July 2005, when it collapsed. The regime shift to a turbid state was mainly attributed to the decreasing biomass of stands bed and mechanical damage brought about by the elimination of Spirodela polyrhiza, increasing water temperature, P concentration as well as periphyton biomass, etc. The reestablishment also changed the aquatic ecosystem greatly. A ‘clear-water’ stage was characterized by higher NO3 −–N, NH4 +–N, electrical conductivity, transparency and TN/TP level and more cladocerans (mainly Daphnia pulex), while the turbid state was characterized by higher temperature, chlorophyll a and TP level and more abundant rotifers. It is thus viable to restore submerged macrophytes in such lakes in winter and spring, when transparency is relatively high while temperature and water level are low. Nevertheless, to obtain a long-term, vegetated clear state, control of internal nutrient loading by means of obstruction, purification, dredging or solidification, is extremely necessary since nutrients play an important role in regime shifts as evidenced by the present case, too. [ABSTRACT FROM AUTHOR]

Oxygen is an important limit factor of nitrogen removal in constructed wetlands, so it is the key point for improving nitrogen removal efficiency of constructed wetlands that the optimization of oxygen distribution within wetlands. Therefore, oxygen status, nitrogen removal and purification mechanism of integrated vertical-flow constructed wetland (IVCW) under aeration condition in summer and winter have been studied. The results showed that both oxygen levels and aerobic zones were increased in the wetland substrates. The area of oxic zone I (expressing with depth) extended from 22 cm, 17 cm to 53 cm, 44 cm, in summer and winter, respectively. The electric potential (Eh) profiling demonstrated that artificial aeration maintained the pattern of sequential oxic-anoxic-oxic (O-A-O) redox zones within the aerated IVCW in winter, while only two oxic-anoxic (O-A) zones were present inside the non-aerated IVCW in the cold season. The decomposition of organic matter and nitrification were obviously enhanced by artificial aeration since the removal efficiency of COD, TN and NH4(+) -N were increased by 12.2%, 6.9% and 15.1% in winter, respectively. There was no significant accumulation of NO3(-) -N in the effluent with an aeration cycle of 8 h on and 16 h off in this experiment. Moreover, we found that oxic zone I was the main region of pollutants removal in IVCW system, and artificial aeration mainly acted to enhance the purification capacity of this oxic zone in the aerated IVCW. These results suggest that aeration is important for optimization and application of IVCW system.

Six enzymes and five bacteria physiological groups from the substrate (soil) of integrated vertical flowing constructed wetland are chosen to study temporal and spatial characteristics. The research results show that significant differences existed in each enzyme during different months (p < 0.05). The enzyme activities of cellulase, protease and phosphatase were significantly higher in June, September and December than those in March; The enzyme activity of beta-glucosidase in June was significantly higher than those in other months; While urease activities in both September and December were extremely significantly higher than those in March and in June (p < 0.01); But the dehydrogenase was different from the above-mentioned enzymes, which had higher enzyme activities in June and in December than in March and in September. Compared with the temporal characteristics, the spatial characteristics of all six enzymes show consistency: the enzyme activities in the down-flow chamber were significantly higher than those in the up-flow chamber (p < 0.05), and all of the enzyme activities in both chambers were relatively lower with the increasing depths of substrate layers. The numbers of bacteria physiological groups were at peak in June and September and their spatial characteristics were the same with enzyme activities.