Research On Water Quality Improvement By Distribution Flushing

Pipe flushing is one of the most powerful tools available to water utilities formaintaining water quality in distribution system. Based on water quality monitoringand analysis, the paper studied unidirectional flushing and water quality decay inhydrant dead end and established pipe flushing plan which can tell water utility howto improve water quality through pipe flushing.Unidirectional flushing consists of isolating a particular pipe section throughclosing appropriate valves and exercising the hydrants. Unidirectional flushing isoften associated with establishing velocities of approximately 1.8m/s within each pipesegment being flushed, helps ensure that pipe sections are completely flushed, andavoid moving debris from one part of the system to another. In case studyunidirectional flushing efficacy, HPC and turbidity decreased obviously. Thisindicated that unidirectional flushing would create shear force capable of dislodgingand transporting specific types of particles, film, or scale. Because appropriateflushing velocity wiped off scale on inner wall, and residual chlorine will react withinner wall, residual chlorine was reduced in a short time (a week). After a week,residual chlorine would increase and almost equal to the one before unidirectionalflushing when inner wall was stabilized. Langelier index was reduced in a short time(a week), which indicates that unidirectional flushing can reduce chemical stability influshing region. After a week, langelier index would increase and get back to the onebefore unidirectional flushing. In long run, unidirectional flushing has a littleinfluence on chemical stability. In test, a detailed flushing plan was established andflushing model was used by flow emitter's model. Water in hydrant dead end may backflow into distribution system. Such as, crackpipe, pressure transient, examination, and repair and so on. Through 6 months waterquality monitoring and analysis, we found that water quality in hydrant dead endwould deteriorate quickly. When water age was 3 months, HPC, turbidity, iron andcolor approached maxim in all tests. If water utility changed hydrant discardingperiod to 3months, water quality in distribution system would assured and the risk ofdrinking water contamination would decreased. A detailed flushing plan included "determining the appropriateness of flushingas part of a utility maintenance plan, planning and managing a flushing plan,implementing a flushing plan and data collection, and evaluating and revising aflushing plan". A detailed flushing plan can tell water utility on how to improve waterquality through pipe flushing.