Biological and Membrane Filtration for Small Systems

摘要

The use of spiral wound membranes for treatment of brackish ground water sources has gained widespread acceptance. This technology, however, is not without operational difficulties, one of which is membrane fouling. Ground water supplies in the province of Saskatchewan, Canada are typically very hard, laden with iron, manganese, and often organic carbon and ammonium. Fouling through scaling can be controlled with antiscalant chemicals and recovery but typically some form of pre-treatment is required to reduce the constituents that cause colloidal and biological fouling. Biological filtration prior to membranes has been implemented in some small First Nations water treatment systems in Saskatchewan. The stepwise filtration process targets iron, arsenic, ammonium and organic carbon to reduce these constituents as they can be used as an energy source for bacteria that may populate and foul the membrane elements. This process also reduces the potential for colloidal fouling by oxidized iron and manganese as chemical oxidants are not used. The water produced by the membranes exhibits a very low chlorine demand due to the removal of readily oxidized species. By limiting reliance and demand on chemicals for treatment of the water to only low dosages of membrane antiscalant and chlorine, the First Nation communities have gained a consistent, sustainable, and environmentally friendly method of treating their drinking water, with reduced costs and complications of utilizing chemicals to oxidize and remove potential foulants. The initial installation of this process at the Yellow Quill First Nation was a green-field construction using a water source previously thought unfeasible to treat economically. Building on the success of the Yellow Quill project, an existing manganese greensand process at the Pasqua First Nation was retrofitted to provide biological iron, arsenic, and ammonium reduction followed by membrane treatment to provide higher quality water to the First Nation residents there. The process capacity was similar to the Yellow Quill process but was provided as a plant retrofit within the existing building footprint at Pasqua, at a fraction of the construction cost of the Yellow Quill process. The paper describes the development of the process, types of water it is suitable for, issues encountered, retrofit considerations and the logistics surrounding the process conversion. Cost implications of these processes are also described.