Crushed glass as a constructed wetland substrate: Invertebrate community responses to simulated wastewater inputs.

Abstract

Constructed wetlands (CWs) are an increasingly common polishing step prior to the release of municipal wastewater treatment facility effluents, especially in smaller and more isolated communities. It is hypothesized that recycled crushed glass could be a suitable alternative matrix for CW construction. In comparison to commonly used substrates, recycled crushed glass has several advantages: it is less expensive, more environmentally friendly, and it can be transformed into various sizes to meet specific design requirements. The material is inert, transparent, has large pore spaces, and significant surface area. Components that impair receiving water quality (e.g., nutrients, pharmaceuticals, and pathogenic bacteria) could be reduced by enhancing light penetration, macrophytes for uptake and assimilation, surface area for microbes, and overall retention time. To explore the ability of crushed glass to support relevant biological communities, twelve outdoor mesocosms were established with and without emergent plants, and crushed glass was contrasted with a typical gravel base in triplicate. Specifically, we examined the response of the zooplankton community. After these systems were acclimated, they were treated with a single pulse of synthetic wastewater (e.g., nutrients, pharmaceuticals, and salts). Mesocosms exposed to the synthetic effluent developed a significantly (p<0.05) different invertebrate community response in total abundance when compared to the unexposed control treatment. There were no significant (p>0.05) differences among the mesocosms with crushed glass as a substrate (including controls) for all diversity indices, indicating that the addition of synthetic effluent and macrophytes had no significant impacts on the invertebrate community structure. Overall, recycled crushed glass was determined to be suitable matrix for zooplankton communities, with water quality and effective treatments being maintained relative to gravel systems. Though the treatments with a gravel substrate had greater total invertebrate abundance, it was found that the gravel treatments were significantly (p<0.05) less diverse (Shannon’s index) and had less evenness than all other treatments with glass substrates. We recommend that future studies should explore the effectiveness of recycled crushed glass in CWs on a larger scale, as these results suggest that recycled crushed glass could be a viable surrogate for gravel in subsurface filtration processes.