Abstract
Twelve bioretention filter columns with different media were designed to study the effects of media on dissolved heavy metals in bioretention systems by changing three test conditions (inflow concentration, discharge ratio, and recurrence interval). The results showed that the average load reduction efficiency of the bioretention soil media (BSM)+10%water treatment residue, BSM+10%green zeolite, and BSM+10%medicinal stone for Cu and Zn was larger than 80%. The highest volume reduction efficiency is 39.25% by BSM+coconut bran. Among the three factors selected in tests, inflow concentration had the biggest degree of influence, followed by discharge ratio and recurrence interval. The media of the upper, middle, and lower layers of each filter column were detected before and after the treatment to study the accumulative characteristics of heavy metals in the bioretention system. The accumulation of Cu, Zn, and Cd in the media of BSM+medicinal stone, BSM+fly ash, BSM+vermiculite, and BSM+turfy soil was relatively low. The contents of the three metals were positively correlated with urease and negatively correlated with protease in the media, but no obvious rule was showed in the accumulation of dissolved heavy metals with depth.
Highlights
One of the major sources of heavy metals in surface and subsurface water is stormwater runoff [1].Concentrations of heavy metals such as copper, zinc, cadmium in waterbodies and sediments receiving stormwater runoff from densely populated urban areas are high enough to impair the health of aquatic organisms [2,3]
(1) The treatment effect of dissolved heavy metals in 12 filter columns is analyzed, and the effective modified media for bioretention are determined; (2) the treatment effects under different test conditions are compared to determine the influence of different test factors on the treatment efficiency of dissolved heavy metals in bioretention media; and (3) the contents of heavy metals and enzyme in upper, middle, and lower layers in different media are tested before and after the treatment to investigate the accumulative characteristics of heavy metals and correlation between enzymes and heavy metals in the bioretention system
The modified media were prepared by mixing modifiers including water treatment residue (WTR), green zeolite (Gz), medicinal stone (Ms), vermiculite, turfy soil (Ts), coconut bran, and fly ash and bioretention soil media (BSM) with different proportions [22]
Summary
One of the major sources of heavy metals in surface and subsurface water is stormwater runoff [1]. A considerable number of studies have focused on particulate heavy metals, but the removal of dissolved metals has attracted significant attention in recent years [7] Physical processes, such as settling and filtration, are effective at removal of particles and their associated pollutants [8,9]. The present work seeks to examine large-capacity and high-efficiency bioretention media, the influence of different factors on bioretention, and find out the accumulative characteristics of heavy metals in different media. (2) the treatment effects under different test conditions are compared to determine the influence of different test factors on the treatment efficiency of dissolved heavy metals in bioretention media; and (3) the contents of heavy metals and enzyme in upper, middle, and lower layers in different media are tested before and after the treatment to investigate the accumulative characteristics of heavy metals and correlation between enzymes and heavy metals in the bioretention system
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