Designing and Follow up the Construction of Desalination Plant

According to the previous experience of EMCC in similar assignments and in order to achieve the study objectives the consultant provided technical support to design and follow up the construction of the desalination plant. The methodology structured process consisting of a sequence of distinct and well-defined phases.

Project Mobilization

In this phase of the project, specific notes made by the client on the proposed methodology or by consultant on the TOR solicited. In addition, the PARC team was also be identified and links with them established. During this phase, the consultant in cooperation with the projects team from PARC has performed the following activities:

• Discuss the methodology.
• Issue the time frame of the assignment and due dates.
• Arrange the necessary activities (data collection, meetings, allocation of key staff, interviews with other staff, etc.).
• Provide project documents, forms, progress reports, etc.

Assess the proposed construction locations

EMCC developed selection criteria in a participatory manner to be used by the consultant in assessing the proposed locations for the construction of the desalination plant. The location areas submitted by MoA and PARC, it was 22 Locations, taking into account:

• The well water salinity level, in terms of total dissolved solids (TDS), is between 1000 ppm to 2000 ppm
• The availability of the electrical power in the proposed location
• The location is not planned to be irrigated by either imported water (MEKOROT) or treated wastewater within the next 10 years.
• The well capacity is suitable for installing the proposed desalination plant.
• The farmers in the target area plant drought-resilient crops.

Desalination plan: Conceptual design

Based on several economic and technical aspects (proposed design criteria, construction and operation cost, and agricultural issues), the consultant then produced a conceptual design for the proposed desalination plant which included but not limited to;

• Development and production of schematic diagrams and layouts for different project components with a comprehensive level of integrity for intake (the optimized water well) and brine disposal systems including its associated pipelines, RO desalination site with all components (including pre-treatment and post-treatment stages), water reservoirs, and distribution networks;
• Development of performance criteria of the proposed desalination plant including hourly and daily production of desalinated water for different cases of operations, quality of the produced desalinated water (TDS), power consumption, plant recovery rate, estimated cost of 1m3 to cover the O&M costs, etc.;
• Draft the General specifications and requirements of the desalination plant. Sizing of the main components and roughly estimate the construction cost.

Preliminary Design: General consideration and criteria

The consultant carried out the final design. The consultant optimized the best pretreatment process taking in to account the chemical and physical water properties of the optimized water well. However, groundwater particularly when taken from deep or confined aquifers is more consistent in quality and contains lower levels of contamination than surface water due to the filtering effects of soil barriers, therefore after low-pressure pumps (2-3 bar), at least a cartridge filter used to retain particles of 1 to 20 microns and protect RO membranes. Antiscalant dosing designed at a very low dose, to prevent calcium carbonate to scale on the surface of the RO membrane. High-pressure pump (expected between 8 – 15 bars) designed to fit the targeted permeate concentration (TDS). 8-inch pressure vessels diameter comprising 6 RO filter-elements per each one considered by the consultant through 2 to 3 stages targeting the recovery rate optimized based on the feasibility study (it would be around 70 to 80 %).

Figure 1: shows three stages brackish water RO system

As the produced permeate was aggressive (low pH) and would deteriorate the pipelines, the consultant designed a calcite filter/contactor (as a final stage) to comply with the standards. The consultant evaluated the need for a chlorination dose during the pretreatment process based on the properties of the feed water to prevent biofouling if it could accrue.

The consultant assumes a suitable flux (the production per square meter of membrane surface) to be around 25 liters per square meter per hour as well as a salt rejection by RO units to be around 0.95. The specific energy will be around 1 [kWh/m3], whereas a recovered part of the high-pressure energy will be recommended by the consultant. The consultant will also deign the disposed of the brine/concentrate, drainage pipes, storage tanks and the electrical/control system. The consultant prepared designed criteria and consideration following the international standard codes of practice, norms and guidelines consistent with those practiced and used by the local authorities (PWA).

The consultant used the design software ROSA (Reverse Osmosis System Analysis) for the RO system design.

Preparation of final detailed designs

The consultant started this task after getting approval upon the Preliminary Designed, and produced a detailed design documents including but not limited to:

• Design drawings and maps
• Typical cross-sections for pipes and related installations.
• Profile of pipe routes to a suitable scale.
• Architectural, structural, mechanical and electrical detail drawings for water reservoir, pumps and service building.
• Typical details drawings for pumps including mechanical parts, chambers, manholes, details of connections for water networks and piping.
• General notes, legend and abbreviations
• Drawings Index
• Any other drawings/details that may be deemed necessary for the proper execution of the works or may be requested by the client
• Specifications: General and particular specifications covering material and workmanship for all components that were being incorporated in the works.
• Bill of Quantities: covering the whole scope of the work under each package.

Design the desalination plant along with full tender document:

After selecting the construction location, EMCC designed the desalination plant and prepared all the design documents, including but not limited to:

• Water and soil test reports
• Inspection report including the proposed methodology
• Estimated cost and cash flow
• Bill of quantities
• Time schedule
• Method statement
• Detailed tender drawings, including the civil, mechanical and electrical works
• Technical specifications (general and special)

Based on designated location, EMCC was been responsible for fully developing the tender documents that develop the specifications and descriptions for each item that has been requested from the contractors/suppliers in addition to being part of the technical committee which evaluated the tenderer.

Follow up the construction work:

The consultant was been  responsible for following up all the construction work of the desalination plant, including, but not limited to, the following:

• Direct technical supervision all the process of implementing the desalination unit
• Reporting to the project team about the progress of the implementation
• Documenting the implementation process by reports, photos and video films