Partitioning and removal of Cd and Mn using a simulated mangrove wastewater treatment system

A greenhouse experiment was conducted to study the partitioning and removal of Cd and Mn from wastewater using constructed mangrove (Kandelia candel) wetland treatment system. Three different strengths of artificial wastewater passed through the system in fixed quantities. Artificial seawater was used as a control. Three different compositions were natural wastewater concentration (C1), medium wastewater concentration (C5) and concentrated wastewater concentrations (C10). C1 had the characteristics and strength similar to natural municipal wastewater while C5 and C10 contained five and ten times of the nutrients and heavy metals in C1, respectively. Results showed that the major portion of the Cd and Mn entering the simulated wastewater treatment system entered the sediment pool where approximately 88% to 95% of the Cd, and between 63% and 89% of Mn, was retained. The amount of added Cd and Mn in the wastewater found in plants were between 0.16% to 1.1%, and 1.7% to 13.9%, respectively. Within the total plant pool, roots accounted for between 30% and 39% of Cd, and from 0.65% to 7.3% of Mn; leaves contained between 19.9% to 30.5% of Cd, and from 7.8% to 41.0% of Mn; litterfall contained 12.3% to 20.6% of Cd, and from 15.2% to 70.3% of Mn, respectively. The averaged accumulative coefficients concentration in plant tissues/concentration in sediment in plant for Cd and Mn were 1.22 to 2.40 and 0.02 to 0.08, respectively. Assimilated Cd and Mn were stored in non-activity plant zones such as cell wall, supplimentary cells of the lenticel, stone cells, cell gaps in root and stem, etc. Kandelia candel seedlings had a relative high toxicity resistance to the two heavy metals.