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Performance and Cost Review of Existing Desalination Plants which use Conventional and Membrane Pretreatment Processes Prior to RO

Project: 14-07
Estimated Release: TBD
Product: Decision Making Tool

Program: Principal
Funding Partner: NA
Total Investment: $125,000 (Cash: $125,000)

Background

As the demand for desalinated water continues to grow, utilities are forced to consider alternative, more difficult-to-treat waters as supply sources. These waters will often require additional steps in the pre-treatment process to provide effective protection for the downstream reverse osmosis desalination process. Incorporating a robust pre-treatment process in the treatment train is critical to achieving reliable, long-term membrane performance. The goal of pretreatment is to remove as much of the potential foulants as practicable that may impair the downstream desalination membrane’s capability to operate in a long-term, reliable, cost-effective fashion.

Pre-treatment may include chemical coagulation, clarification, dissolved air flotation and filtration stages, with the latter being either granular media or polymeric membranes. Granular media filtration and membranes each have operational advantages and disadvantages when comparing varying feed and filtered water quality and consistency, residuals management, space, and consumables strategy. Additionally, proper selection of the pre-treatment process is critical to achieving cost-effective and long-term reliability of the downstream desalination membrane. The existing peer-reviewed literature on the subject has yet to be analyzed and assembled for use by water treatment industry professionals in qualitative assessment of different pre-treatment strategies to guide the engineer and planner for pretreatment process selection.

Goals and Objectives

The project will:

  • Provide utilities with information on key criteria that can assist during the planning phase for membrane desalination plants, related to the evaluation of different pre-treatment processes.
  • Provide a process selection decision matrix which optimizes capital and operating costs against performance and regulatory requirements.

Research Approach

Task 1: Review of Existing Published Information. The review will focus on documentation of various types of feedwater (e.g. brackish surface/groundwater, seawater open/infiltration, treated wastewater) and the associated variations in feed water quality, identification of equipment operational conditions and constraints, operation and maintenance costs, capital costs, and operation during periods of elevated biomass events.

Task 2: Facility Audits. The audit will be performed by sending custom-developed electronic data forms for facilities to fill out and telephone contact for follow up. In addition, a review of existing plant design and performance, including the factors that each site used in pre-treatment decision making process form the basis for interpretation and development of assessment matrix will be conducted.

Task 3: Analysis. An analysis of the degree of alignment between peer-reviewed research regarding performance characteristics of different pre-treatment processes versus what is the actual industry experience, including the influence of non-water quality related factors (e.g. contract type, environmental and health regulations) will be conducted.

Task 4: Final Report and Decision Matrix. This task will summarize Tasks 1 through 3 into a final report for WRRF. A decision matrix will be built to assist utilities during the planning phase of pretreatment systems for desalination plants utilizing reverse osmosis using the information collected through this research.

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