Does Methane Contribute to Growth of Invertebrate Communities in Drinking Water?

Abstract

Methane is a potential source of carbon in drinking water. Typically, it is removed at waterworks during an initial treatment step such as aeration or stripping. Remaining methane may be converted by methane-oxidizing bacteria to organic carbon, which is then available for heterotrophic growth and may ultimately contribute to invertebrate growth. We investigated the presence of invertebrates at a waterworks with incomplete methane removal and at a waterworks without methane. Microscopy and analyses of 16S and 18S ribosomal genes were conducted on filter sand from full-scale biological rapid sand filters. Primary filters with methane were dominated by methane- and ammonia-oxidizing bacteria. Upper layers of secondary filters were dominated by heterotrophic bacteria, while the deepest layer contained 92% eukaryote DNA. Rotifers, nematodes, platyhelminths and annelids constituted 22% of the DNA in the secondary filters. Filters with methane contained higher shares of invertebrates (13%) than the filter without methane (7%). Furthermore, pilot studies were conducted to estimate suitable levels of methane when implementing methane removal technologies. Methane concentrations of 0.24 mg/L caused rapid visible growth. Vacuum stripping and nitrogen addition removed methane to 0.018–0.03 mg/L and prevented growth of methane-oxidizing bacteria.