I am planning to use a modified biosand filter for my new AP system. I Have constructed a number of biosand filters and I can see some potential of it in AP system. Although I am new to AP and may have overlook some of the important matters to consider. In this link you can learn how a BSF works  http://www.sswm.info/content/biosand-filter and here is a qoute from the site "There is a standing wa…