Journal
ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH
Volume 28, Issue 20, Pages 25664-25678Publisher
SPRINGER HEIDELBERG
DOI: 10.1007/s11356-021-12442-7
Keywords
Floating treatment wetland; Constructed wetlands; Plant coverage; Eichhornia crassipes; Heavy metals; Lake water; Water depth; Hydraulic retention time
Categories
Funding
- Shore Processes Lab, Marine Environment Division, National Institute of Oceanography and Fisheries, Alexandria, Egypt
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The use of water hyacinth in floating treatment wetlands is an effective method for removing pollutants, with high efficiency in removing nutrients and heavy metals in the polluted Marriott Lake in Egypt.
Though having an economic and ecological impact on Marriott Lake management in Egypt, water hyacinth (Eichhornia crassipes) is an aquatic floating macrophyte with a known phytoremediation potential. In order to assess its remediation potential, pilot floating treatment wetlands (FTWs) with E. crassipes were built in duplicates to evaluate the removal of nutrients and heavy metals from the polluted lake water. The experimental design included units with different water depths (15, 25, and 35 cm; D-15, D-25,D- and D-35, respectively) and plant coverage (90, 70, 50, and 0%; P-90, P-70, P-50,P- and P-0, respectively). The pilot FTWs were monitored over a 7-day operation cycle to identify the optimum combination of design (plant coverage, water depth) and operation (hydraulic retention time; HRT) parameters needed for maximum BOD5, TN, NH4-N, and TP removal. NH4-N removal reached 97.4% in the D25P50 unit after 3 days, BOD5 75% in the D15P90 after 3 days, TN 82% in the D25P70 after 4 days, and TP 84.2% in the D35P70 after 4 days. The open-water evaporation rate was higher than the evapotranspiration rate in the planted units, probably due to the warm climate of the study area. Metals were also sufficiently removed through bioaccumulation in plant tissues in the order of Fe > Pb > Cu > Ni (62.5%, 88.9%, 81.7%, and 80.4% for D25P50, D25P70, D25P50, and D25P90, respectively), while most of the assimilated metal mass was translocated to the plant roots. The biochemical composition of the plant tissue was significantly different between the shoot and root parts. Overall, the FTW with 70% E. crassipes coverage, 25-cm water depth, and an HRT of 3-5 days was identified as the optimum design for effective remediation of the polluted Marriott Lake in Egypt.
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