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WATER QUALITY AND TREATMENT CONSIDERATIONS FOR CEMENT-LINED AND A-C PIPE
Schock*, M R. WATER QUALITY AND TREATMENT CONSIDERATIONS FOR CEMENT-LINED AND A-C PIPE. Presented at New England Water Works Association, Spring Operations Conference, Worcester, MA, 4/3-5/2001.
Both cement mortar lined (CML) and asbestos-cement pipes (A-C) are widely used in many water systems. Cement linings are also commonly applied in-situ after pipe cleaning, usually to prevent the recurrence of red water or tuberculation problems. Unfortunately, little consideration is often given to the stability of these materials in different water quality, and unwanted side-effects are sometimes generated. Occasionally utilities notice considerable pH increases, turbid water, material accumulation in dead ends, ineffectgive lead or copper control with phosphate inhibitors, or decreased chlorine residual effectiveness. Sometimes the adverse effects are not picked up in normal regulatory monitoring programs, and utilities first find out by calls from irate consumers. Aside from water quality degradation, filling new CML pipes or freshly-rehabilitated ones with aggressive water also can cause utilities to lose much of their monetary investment in cleaning, replacement ore relining of the pipes in a short period of time. An overview will be given of principles of cement corrosion and effects of water quality on leaching properties. Research from studies of asbestos-cement pipe corrosion and other corrosion control studies will be used to provide guidelines to the beneficial and detrimental combinations of Lead and Copper Rule and red water control strategies that could affect the stability and longevity of cement and cement-lined pipes. New regulations affecting organic or microbial removal may also provide a motivation for substantial treatment changes, including the use of membrane processes. One internationally-reported case occurred where the combination of membrane treatment and sequestration caused deaths of kidney dialysis patients from elevated aluminum levels coming from the pipes. Critical considerations and decision points for post-treatment requirements for water stabilization will be described, and pros and cons of different corrosion control approaches will be covered for utilities of all sizes. Topics included will be: orthophosphate versus zinc orthophosphate; silicates versus caustic; lime versus caustic or inhibitors; balancing iron and manganese sequestration with corrosion control; silicates versus polyphosphates; aeration versus limestone contactors and chemical additions; integrating cement corrosion control with lead and copper control. Ways ot monitor for water stability and cement pipe deterioration will also be covered.