Abstract
This study aims to evaluate the sorption characteristics of NH 4 + -N and PO 4 3 − -P onto the surface of natural zeolites coming from Chile and their potential application in the subsurface-flow treatment wetlands for wastewater treatment in rural areas. For this purpose, adsorption experiments onto the zeolite were developed in batch assays. The effects of the adsorbent quantity (20 g and 50 g) and particle size (0.2–1.0 mm; 1.5–3.0 mm, and 5.0–8.0 mm) were evaluated in terms of adsorption capacity at different NH4+-N and PO4−3-P concentrations. Then, the obtained laboratory results were adjusted to theoretical models: Saturation-growth-rate and Langmuir. The saturation adsorption of NH4+-N on the zeolite increases at the same time that the initial concentration increases for the same zeolite quantity; however, the saturation values were similar between the different zeolite sizes tested. For PO4−3-P, the adsorption did not have a direct relationship with the initial concentration nor zeolite quantity and better results were only achieved for zeolite sizes of 1.5–3.0 mm. Regarding the Langmuir model, sizes of 1.5–3.0 mm had the best adsorption characteristics, with the maximum adsorption capacity of up to 1.58 mg/g for NH4+-N and up to 0.08 mg/g for PO4−3-P. Therefore, a new material—a natural zeolite from the Maule Region of Chile—is described as a potential support medium for treatment wetlands.
Highlights
Subsurface-flow treatment wetlands (SSF-TWs) are an alternative to traditional activated sludge systems for the treatment of wastewater in rural areas [1,2]
This characteristic is important for the use of Chilean natural zeolite as a support medium in treatment wetlands and the possibility of using its various sizes was tested in this work (0.2–1.0 mm, 1.5–3.0 mm, and 5.0–8.0 mm)
The results of this study confirm that Chilean natural zeolites can be used for both N and P removal from wastewater and that their potential application as a support medium for treatment wetlands is similar to that of other natural zeolites previously used for this purpose [30,40,54]
Summary
Subsurface-flow treatment wetlands (SSF-TWs) are an alternative to traditional activated sludge systems for the treatment of wastewater in rural areas [1,2]. In SSF-TWs, the removal process can be intensified by different operational strategies and innovative designs, improving removal efficiencies to reach levels of. 50–90% [6,7,8] One of these operational strategies is the use of media to enhance the adsorption process, and natural zeolites are one of the potential removal media studied for use in TWs [9,10]. Natural zeolites are promising as a support medium in SSF-TWs because they are abundant, relatively inexpensive (0.6–1.6 USD/kg), have appropriate hydraulic characteristics, and have regenerative capacities [9,10,11]. The ion exchange that results from the negative charge on the zeolites surface and the sorption capacities are important for NH4+ -N removal [15], while precipitation with divalent and trivalent metal cations and the sorption onto natural zeolite are important for PO3−
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