Impacts of residual aluminum from aluminate flocculant on the morphological and physiological characteristics of Vallisneria natans and Hydrilla verticillata.

Aluminate is generally used as a flocculant in water and wastewater treatment processes, but the residual aluminum (Al) may have toxic effects on aquatic organisms when the concentration accumulates beyond a threshold level. The in situ and laboratory tests were conducted to evaluate the impact of residual Al on submerged macrophytes in West Lake, Hangzhou, China, which receives Al flocculant-purified water diverted from the Qiantang River. The responses of Vallisneria natans and Hydrilla verticillata were investigated based on their morphological and physiological parameters in pot culture and aquarium simulation experiments. In the pot culture experiments, the biomass, seedling number, plant height, stolon number, stolon length, and root weight were significantly higher at a site located 150m from the inlet compared with those at a site located 15m from the inlet (P < 0.05), thereby indicating that the residual Al significantly inhibited the morphological development of V. natans and H. verticillata. The variations in the chlorophyll-a, protein, and malondialdehyde contents of the two species in both the pot culture and aquarium simulation experiments also demonstrated that the two submerged macrophytes were stressed by residual Al. V. natans and H. verticillata accumulated 0.052-0.227mg of Al per gram of plant biomass (fresh weight, mg/g FW) and 0.045-0.205mg Al/g FW in the in situ experiments, respectively, where the amounts of Al were significantly higher in the plants in the treatment aquaria during the laboratory experiments than those in the controls. These results may have important implications for the restoration of submerged macrophytes and ecological risk assessments in Al-exposed lakes. It is recommended that the Al salt concentration used for the control of lake eutrophication should be reduced to an appropriate level.

[Removal nitrogen of integrated vertical-flow constructed wetland under aeration condition].

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.

[Temporal and spatial characteristics of substrate enzyme activities and bacteria physiological groups in constructed wetland].

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.