Ocean Desalination Water Quality Integration Study at West Basin

Authors:

  • Nicole Blute, Xueying Wu, Kenny Chau, Lynn Grijalva - Hazen and Sawyer
  • Justin Pickard - West Basin Municipal Water District

Pipe loops were constructed to evaluate a range of materials typically found in potable water distribution systems, including copper.

West Basin Municipal Water District is planning to construct an ocean water desalination facility near Los Angeles that will supply water to its customer agencies. This presentation will provide the approach and results of a Desalinated Water Quality Integration Study led by West Basin to examine the impact of a new, desalinated water source introduced into distribution systems that have previously carried imported Metropolitan water and groundwater sources.

Integration of New Water Supply
Prior to introduction into a drinking water distribution system, desalinated (reverse osmosis) water requires post-treatment. This treatment involves the addition of some minerals back into the water to provide a water quality that is non-corrosive toward distribution system materials. In particular, desalinated water requires the addition of alkalinity (buffer capacity), calcium, and pH adjustment. Without post-treatment, the water can extract metals or cement from pipes, which can result in regulatory level exceedances, aesthetic concerns, and infrastructure issues. With proper stabilization, desalinated water can be integrated into a distribution system without incident. This project identified and tested potential post-treatment water quality targets and explored the impacts of blending desalinated ocean water with treated surface water and groundwater sources.

Pipe Loop Materials
Blends of desalinated ocean water, treated surface water and local groundwater were circulated through pipe loops to identify potential impacts to potable water distribution systems from the differing water qualities. The pipe loops were constructed to evaluate a range of materials typically found in potable water distribution systems. Materials used in the testing included 6” diameter unlined cast iron pipe removed from a local distribution system with significant buildup of iron and manganese deposits; new 4” diameter cement mortar-lined pipe (with fresh cement linings, representing cement most susceptible to leaching); new ¾” copper pipe with lead solder (also representing non-passivated surfaces providing a worst-case scenario); and brass meters harvested from the distribution system (more likely to leach lead than new lead-free versions). Six loops for each type of material were constructed to allow direct comparison of different water qualities.

Corrosion Analysis
Unlined cast iron pipe was evaluated for release of iron and manganese; cement mortar-lined pipe was evaluated for leaching of aluminum indicative of corrosion; and copper pipe and brass meters were analyzed for metals release including lead, copper, and zinc. Pipe loops were operated with either circulation for one week to represent typical distribution system age (e.g., unlined cast iron and cement mortar-lined pipe) or flow-through conditions to simulate diurnal household use (e.g., copper pipe with lead solder and brass meters).

Permeate Stabilization and Disinfection
Pipe loop testing involved post-treatment stabilization of desalinated ocean water to achieve water quality targets for alkalinity, pH, and calcium. An extensive literature review and utility survey were initially conducted to develop water quality targets for post-treatment stabilization. Calcite contactors with upstream pH reduction by sulfuric acid were used to stabilize the desalinated water. Chloramines were added to the desalinated water and chloramine degradation assessed.
In each pipe loop, desalinated ocean water and treated surface water were used as controls and compared to blends of groundwater (high in bromide, iron, and manganese), desalinated ocean water and/or treated surface water.

Results
Results that will be discussed in this presentation include the sufficiency of the post-treatment desalinated ocean water stabilization process to protect potable water distribution system infrastructure while avoiding regulatory issues and aesthetic concerns, compared with water sources currently provided to West Basin’s customer agencies. Specifically, metals release from the pipe loop materials and post-treatment procedures will be presented, as well as challenges and lessons learned in this pipe loop study.

For more information, contact the author at nblute@hazenandsawyer.com.

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