Investigations of Mixed Media for Use in Constructed Wetlands in the Eastern Yucatan

Constructed wetlands are currently used in the Village of Akumal, Quintana Roo, Mexico to treat sewage effluent. These systems perform variably and although they have been shown to significantly reduce the main components of wastewaster, their efficacy in treating heavy metals and refractory organic pollutants are undetermined.

One factor limiting wider implementation of these systems is aggregate cost. Calcareous beach sands are a public resource in Mexico and may be a viable alternative to existing aggregate. However, these sands have a comparably high permeability and have a very soluble mineralogy consisting of Mg-calcite, aragonite, and calcite.

One method to potentially improve beach sands for use in constructed wetlands and to remove heavy metals and refractory organic pollutants from waste water is to add clay minerals into the system. Palygorskite and montmorillonite are clay minerals well recognized for absorbing pollutants, including heavy metals and organic contaminants. A local deposit of palygorskite- rich clay exists containing 85% palygorskite and 15%montmorillonite. The clay can be made into granules by gentle crushing. Transmission electron microscopy (TEM) investigation indicates palygorskite and montmorillonite have typical chemical compositions and morphologies. No environmentally suspect minerals have been observed.

Mixtures of beach sand and the palygorskite clay varying from 4.76% to 23.07% clay granules by volume were prepared. The permeability systematically decreased from 0.0077 cm/s to 0.0003 cm/s with a line of fit being y=24.024e(-217.44x) and r2 = 0.9534. This suggests that the media is highly tunable to meet engineering requirements.

This investigation suggests that palygorskite-montmorillonite-calcareous beach sand mixtures may be an effective media to replace existing aggregate choices in constructed wetlands in the Akumal area. The production and broader use of specialized constructed wetland media may also add depth to a tourist dominated economy. Industrial mineralogy may be a key to environmental preservation for the Yucatan.