Chelant-enhanced phytoextraction method has been put forward as an effective soil remediation method, whereas the heavy metal leaching could not be ignored. In this study, a cropping-leaching experiment, using soil columns, was applied to study the metal leaching variations during assisted phytoextraction of Cd- and Pb-polluted soils, using seedlings of Zea mays, applying three different chelators (EDTA, EDDS, and rhamnolipid), and artificial rainfall (acid rainfall or normal rainfall). It showed that artificial rainfall, especially artificial acid rain, after chelator application led to the increase of heavy metals in the leaching solution. EDTA increased both Cd and Pb concentrations in the leaching solution, obviously, whereas EDDS and rhamnolipid increased Cd concentration but not Pb. The amount of Cd and Pb decreased as the leaching solution increased, the patterns as well matched LRMs (linear regression models), with R-square (R2) higher than 90 and 82% for Cd and Pb, respectively. The maximum cumulative Cd and Pb in the leaching solutions were 18.44 and 16.68%, respectively, which was amended by EDTA and acid rainwater (pH 4.5), and followed by EDDS (pH 4.5), EDDS (pH 6.5), rhamnolipid (0.5 g kg−1 soil, pH 4.5), and rhamnolipid (pH 6.5).
• The combination of NaOH and nitrite was used to control harmful gas in sewers.• Hydrogen sulfide and methane in airspace were reduced by 96.01% and 91.49%.• Changes in sewage quality and greenhouse effect by chemical dosing were negligible.• The strong destructive effects on biofilm slowed down the recovery of harmful gases.• The cost of the method was only 3.92 × 10−3 $/m3. An innovative treatment method by the combination of NaOH and nitrite is proposed for controlling hydrogen sulfide and methane in gravity sewers and overcome the drawbacks of the conventional single chemical treatment. Four reactors simulating gravity sewers were set up to assess the effectiveness of the proposed method. Findings demonstrated hydrogen sulfide and methane reductions of about 96.01% and 91.49%, respectively, by the combined addition of NaOH and nitrite. The consumption of NaNO2 decreased by 42.90%, and the consumption rate of NaOH also showed a downward trend. Compared with a single application of NaNO2, the C/N ratio of wastewater was increased to about 0.61 mg COD/mg N. The greenhouse effect of intermediate N2O and residual methane was about 48.80 gCO2/m3, which is far lower than that of methane without control (260 gCO2/m3). Biofilm was destroyed to prevent it from entering the sewage by the chemical additives, which reduced the biomass and inhibited the recovery of biofilm activity to prolong the control time. The sulfide production rate and sulfate reduction rate were reduced by 92.32% and 85.28%, respectively. Compared with conventional control methods, the cost of this new method was only 3.92 × 10−3 $/m3, which is potentially a cost-effective strategy for sulfide and methane control in gravity sewers. 相似文献
Eutrophication and harmful cyanobacterial blooms threaten water resources all over the world. There is a great controversy about controlling only phosphorus or controlling both nitrogen and phosphorus in the management of lake eutrophication. The primary argument against the dual nutrients control of eutrophication is that nitrogen fixation can compensate the nitrogen deficits. Thus, it is of great necessary to study the factors that can significantly affect the nitrogen fixation. Due to the dif... 相似文献