Practice question

Rhizofiltration specifically uses plant root systems grown hydroponically in greenhouse to develop extensive fibrous mass before transfer to contaminated water to filter, adsorb and absorb contaminants from groundwater, effluents and radioactive ponds. Dense mats of sunflower Helianthus annuus accumulating uranium and cesium, Indian mustard Brassica juncea removing lead and chromium, and bulrush Scirpus for selenium provide 10 to 20 square meters surface per plant coated with mucilage and biofilm containing phytochelatins that precipitate and chelate metals via ion exchange. Mechanism involves physical filtration of suspended particles, apoplastic uptake and symplastic transport via IRT1 transporter, vacuolar sequestration and microbial degradation in rhizosphere for organics. Water flows with retention hours to days achieving efficiencies above 90 percent for radionuclides Cs-137, Sr-90, lead at 0.1 to 10 mg per L. After saturation indicated by breakthrough curves, plants harvested, dried and ashed for disposal, making technique suited to low to moderate strength wastewaters rather than highly contaminated soils where metals less mobile and root contact limited.