http://blogs.washplus.org/drinkingwaterupdates/2013/08/the-impact-of-loading-frequency-and-copper-as-a-biocide-on-biosand-filter-performance/ from the WASHplus Project Tue, 22 Sep 2015 12:34:42 +0000 hourly 1 http://wordpress.org/?v=3.1.4