Selection Of Adsorbent Fillers And Their Application In Aerated Buffer Cell In Constructed Wetlands For Wastewater Treatment

Various types of minerals have been selected as potential adsorbents for the removal of metal pollutants from aqueous solutions. Some of them have been utilized as fillers or liner materials in constructed wetlands and landfills for waste disposal. The concentration of metal pollutants in wastewaters varies to a large extent not only with wastewater type but also with time. This has a negative impact on the normal growth of plants as well as on the activity of micro-organisms in the open wetland system. The introduction of an adsorption buffer unit using materials with a high adsorption capacity into a wetland system can thus improve both the treatment capacity and sustainability. There have been so far very few reports concerning comparison of the adsorption capacity among different mineral absorbents and establishment of a buffer unit using mineral adsorbent in constructed wetland system for treatment of wastewaters.The present study was conducted using synthetic zeolite, natural zeolite, swelling vermiculite and the diatomaceous earth (or red soil) as absorbents to compare their ability to adsorb Zn2+ and Cd2+, NH4+ in single and mixed metal ion systems preapared in aqueous solutions and wastewaters within the range of initial ion concentration 50-500 mg/L at a given adsorbent concentration level (100 mg/L). A pilot buffer unit using relevant adsorbents was further established in the constructed wetland system built for wastewater treatment. The objective of this study was to provide basic data and information for selection of proper adsorbent fillers that can be used for establishment of buffer unit in constructed wetland systems. The main results obtained from this study are summarized as follows:1. The equilibrium ion adsorption can be well described by the Langmuir isotherm, the Freundlich equation and the four adsorption component model under the tested conditions.2. Among the minerals tested, the natural zeolite and the swelling vermiculite were found to be the best wetland fillers in terms of cost effective for removal of Cd2+ and Zn2+ ions. Their costs were estimated, respectively, as 6.125 and 8.98 Yuan/m3.3. Adsorption competition among coexisting ionic species was observed in the mixed metal ion systems. The ion adsorption quantity in mixed ionic species system was found to be higher in sewage than in aqueous solutions.4. Establishment of the pilot buffer unit using the selected adsorbent enhanced the treatment efficiency by providing an adequate condition for normal growth of plants in the constructed wetland system. The buffering effect lasted for more than 60 days within which the water quality reached the national wastewater discharge standard in the outlet. Aeration in the buffer unit was found to be effective in improving the treatment efficiency and stability.