Ten Years' Experience in Biological Filtration for Pre-treatment in Reverse Osmosis　Membrane Applications

摘要

Membrane filters have gained widespread acceptance as a treatment technology for brackish groundwater. Often some form of pre-treatment is required, to reduce constituents in the water that contribute to membrane fouling related operational cost increases over time. Operating and maintenance costs of the pre-treatment technologies commonly used may be significant, particularly if the pre-treatment system uses purchased chemicals that also generate residuals needing disposal. Many small water treatment plants in the Province of Saskatchewan, Canada use groundwater as a source. This water typically has high concentration of hardness, TDS, iron, manganese, arsenic and often undesirable levels of other constituents including nitrogen based compounds. Over the past ten years, a number of small water treatment systems located on First Nations Communities throughout Saskatchewan, Canada have employed innovative biological filtration as a pre-treatment process for reverse osmosis (R.O.), and/or nanofiltration membranes. This system promotes effective and chemical-free pre-treatment using biological removal of iron, arsenic, phosphorous, ammonium, and other organic carbon from the raw water, prior to the water coming in contact with reverse osmosis or nanofiltration membranes. As these constituents can create particulate and organic fouling on membranes, their successful removal promotes longer membrane life, reduced anti-scalent and cleaning chemical usage, and lower feed pressure requirements. This in turn leads to lower operational costs. This paper will review seven water treatment plants installed throughout Saskatchewan such as the First Nation communities of Yellow Quill, Pasqua, Kahkewistahaw, White Cap Dakota (community plant and commercial plant), Kawacatoose, Muskeg Lake and Mosquito. This paper also provides background information on process piloting and development, project design and construction, and project capital costs. In addition this paper also summarizes plant performance metrics including water quality, bio-filter and membrane cleaning requirements and condition. The intent of the paper is to provide an overall "track record" demonstrating the success of this biological process, over the past ten years, as a proven application for pre-treating poor quality groundwater in small system membrane water treatment plants.