The results of this study showed that the CW system contributed to the removal of heavy metals from agricultural and aquaculture wastewater in subtropical regions. The increase in depth and higher organic matter mineralization during the rainy season may have caused oxygen depletion in the upper layer of the sediment and the release of reduced metals into the water. This fact, coupled with an increase in the HLR, may have affected the efficiency removal rates of heavy metals from water during the rainy season. The metals were especially immobilized through the sedimentation process and
were removed weakly through uptake by macrophytes, except for Mn. The deposition in the sediment was higher in the inlet location of the CW system because of rooted vegetation; i.e., the root structure affects the substrate oxygenation and increases the retention of metals. Although the sediment was the main compartment for heavy metal retention in the CW system, the advantage of macrophytes is the harvested ability, especially free floating species. The present work recommends the use of the floating aquatic macrophyte E. crassipes and the rooted macrophyte T. domingensis in CWs designed for heavy metal removal of agricultural wastewater because of their high and efficient metal removal ability. Many aquaculture farms have ditches that can be planted with aquatic vegetation to provide some degree of effluent treatment.
The results of this study showed that the CW system contributed to the removal of heavy metals from agricultural and aquaculture wastewater in subtropical regions. The increase in depth and higher organic matter mineralization during the rainy season may have caused oxygen depletion in the upper layer of the sediment and the release of reduced metals into the water. This fact, coupled with an increase in the HLR, may have affected the efficiency removal rates of heavy metals from water during the rainy season. The metals were especially immobilized through the sedimentation process andwere removed weakly through uptake by macrophytes, except for Mn. The deposition in the sediment was higher in the inlet location of the CW system because of rooted vegetation; i.e., the root structure affects the substrate oxygenation and increases the retention of metals. Although the sediment was the main compartment for heavy metal retention in the CW system, the advantage of macrophytes is the harvested ability, especially free floating species. The present work recommends the use of the floating aquatic macrophyte E. crassipes and the rooted macrophyte T. domingensis in CWs designed for heavy metal removal of agricultural wastewater because of their high and efficient metal removal ability. Many aquaculture farms have ditches that can be planted with aquatic vegetation to provide some degree of effluent treatment.
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