Preliminary study on the dynamics of heavy metals in saline wastewater treated in constructed wetland mesocosms or microcosms filled with porous slag

Abstract

This study aims to evaluate the practical potential of using constructed wetlands (CWs) for treating saline wastewater containing various heavy metals. The results demonstrated that CWs growing Canna indica with porous slag as substrate could efficiently remove heavy metals (Cu, Zn, Cd, and Pb) from saline wastewater at an electrical conductivity (EC) of 7 mS/cm, especially under low influent load. Salts with salinity level (characterized as EC) of 30 mS/cm suppressed the removal of some heavy metals, dependent on heavy metal species and their influent concentrations. The presence of salts in CWs can improve the accumulation of Cu, Zn, and Pb in plant tissues as compared to control treatment, irrespective of metal concentrations in solution. The influence of salts on Cd accumulation depended on both salinity levels and Cd concentrations in solution. Although more heavy metals were accumulated in roots than in shoots, the harvesting of aboveground plant materials is still efficient addition for heavy metal removal due to the greater biomass and growth rate of aboveground plant material. Furthermore, replacing all plants instead of preserving roots from harvested plants in CWs over a period of time is essential for heavy metal removal, because the continued accumulation by roots can be inhibited by the increasing accumulated heavy metals from saline wastewater.

Salinity and temperature influence removal levels of heavy metals and chloride from water by wetland plants

“…2 ). These results match those observed in earlier studies, especially in hydroponic conditions (Cheng et al 2012 ; Liang et al 2019 ). Such decreased uptake at high salinity has been explained by lower availability (Costa et al 2020 ), competition between uptake sites (Bond et al 1988 ), and increased exclusion capacity (Mahon and Carman 2008 ).…”

“…Decreased heavy metal removal under saline conditions has earlier been found in biofilters, constructed wetlands, and floating wetlands (Huang et al 2017;Liang et al 2019;Szota et al 2015). This indicates a wider problem with heavy metal removal in plant-based systems under saline conditions, which may limit their usefulness under such circumstances.…”

Removal Efficiency of Heavy Metals Such as Lead and Cadmium by Different Substrates in Constructed Wetlands

“…Liu et al [13] used the vertical subsurface flow CWs to purify the wastewater containing Cd, and found that the removal rate of NO 3 -N and Cd 2+ in the wetland reached more than 80%. Liang et al [14] used the porous slag CWs to treat the saline wastewater containing various heavy metals. The results showed that the CWs were effective for treatment of Cu, Zn, Cd, and Pb in the wastewater, and could enhance the enrichment effect of plants on heavy metals.…”

In situ purification experiment of a mangrove–aquaculture coupling system: A case study of a crab pond in Wanning, Hainan Province

“…Wastewater contains pollutants, such as nitrogen and phosphorus may cause algal blooms if discharged into natural water without treatment (Resende, Nolasco, & Pacca, 2019; Rittmann, Mayer, Westerhoff, & Edwards, 2011). Mariculture tailwater also has high salinity and organic matter content, making its biological treatment more challenging (Fu, Han, Yu, Huangshen, & Zhao, 2019; Liang et al, 2018; Vymazal, 2014).…”