Braedon Humeniuk, Luis Gerardo Chaves Barquero, Charles Wong, Mark Hanson

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

Introduction

Crushed glass as a constructed wetland substrate: invertebrate community responses to simulated wastewater inputs.. Explore crushed glass as a constructed wetland substrate, analyzing invertebrate community responses to simulated wastewater. It's a viable, eco-friendly alternative to gravel for water quality.

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.

Review

This paper investigates the promising potential of recycled crushed glass as an alternative substrate in constructed wetlands (CWs), a critical component for polishing wastewater effluents. The authors posit that crushed glass offers economic, environmental, and functional advantages over traditional gravel, citing its inertness, transparency, large pore spaces, and surface area as beneficial for enhancing light penetration, supporting macrophytes and microbes, and improving retention time for pollutant reduction. To explore its capacity to support biological communities, the study utilized an outdoor mesocosm setup, directly comparing crushed glass with gravel, both with and without emergent plants, and assessed the responses of the zooplankton community to simulated wastewater inputs. The experimental findings provide compelling support for crushed glass as a viable substrate. While exposure to synthetic wastewater naturally led to a significant differentiation in total invertebrate abundance from unexposed controls, the study remarkably found no significant differences in diversity indices among the crushed glass treatments, regardless of wastewater exposure or the presence of macrophytes. This suggests a robust and stable community structure within the crushed glass medium. Critically, although gravel treatments exhibited higher total invertebrate abundance, they were significantly less diverse and less even in their community composition compared to all crushed glass treatments. The authors conclude that crushed glass effectively maintained water quality and treatment efficacy relative to gravel, affirming its suitability for supporting zooplankton communities. While the study provides a strong preliminary case for crushed glass, several avenues for future research emerge. The mesocosm scale, though appropriate for this foundational work, necessitates larger-scale field trials to validate these promising results under real-world operational conditions and continuous effluent flows. Furthermore, while the abstract mentions pollutant reduction potential, direct comparative data on specific removal efficiencies for nutrients, pharmaceuticals, and pathogenic bacteria between crushed glass and gravel systems would significantly strengthen the argument for its practical implementation. Despite these recommendations, this paper represents a significant contribution, offering robust evidence that recycled crushed glass is a highly promising, sustainable, and effective alternative to gravel in CWs, deserving of further exploration and broader application.

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