Tertiary wastewater filtration: an analysis of crushed recycled glass as an alternative to sand filter media
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Date
2019-03-27
Authors
Salzmann, Rena
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Abstract
This study evaluated the performance of sand (ES: 0.17 mm, UC: 3.13) and crushed recycled glass (ES: 3.59 mm, UC: 4.18) in pilot-scale subsurface filters treating municipal wastewater. The system provided on-site treatment for secondary lagoon effluents from the Village of Dunnottar, on the southwest shore of Lake Winnipeg, MB. Filters operated at a 24-hour HRT, with active treatment seasons from May to September. System performance was assessed over a two-year period (2017 - 2018), with regards to total suspended solids (TSS), chemical oxygen demand (COD), nitrogen (N) and phosphorus (P). TSS were removed equally well in sand and glass filters, with removal efficiencies above 90%. Sand and glass filter effluents contained mostly dissolved COD, except within the first month of operation, during which both media failed to achieve local BOD guidelines. Dissolved COD removal was 29% less in glass, due to smaller media surface area. NH4+–N reductions exceeded 90% in both filters. Effluent N guidelines were always met by sand filters, whereas glass exceeded the limit 33% of the time in 2018. Both sand and glass failed to reduce P below 1 mg/L. Sand filters seemed to predominantly remove P through mineral precipitation with Ca and Mg compounds. This contributed to concretion (hardening) of top sand filter layers. P removal was significantly less in glass, due to decreased Ca availability within the media. Obtained results indicate that crushed recycled glass can be used as filter media in tertiary wastewater treatment systems, especially to remove TSS, COD and NH4+–N.
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Keywords
Tertiary wastewater treatment, Wastewater filtration, Filter media, Sand, Crushed recycled glass, Contaminant removal