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WHY A FEASIBILITY STUDY

The steps of a project on wastewater treatment and disposal

STEPS IN A SEWAGE TREATMENT AND DISPOSAL (or REUSE) PROJECT.

A project on sewage treatment and disposal usually requires the following steps:
  1. Pre-Feasibility Study (or preliminary study, 'anteproyecto' in Spanish).
  2. Feasibility study.
  3. General and detailed design.
  4. Preparation of TOR for bid or direct contract.
  5. Bid call and assignment and/or contract.
  6. Construction and inspection.
  7. Start-up.
  8. Normal operation.

The steps may be somewhat different in BOT (build, operate and transfer) projects, but the essential procedure is the same.

THE PRE-FEASIBILITY STUDY.

What is a Pre-feasibility Study ?

The Pre-Feasibility Study includes:

Preliminary recompilation of data, mainly:

General geography of the region (maps 1:50,000).
Climate (temperatures, winds, rain, evaporation).
General socio-economic level of the population.
Preliminary estimate of flow quantity and quality, and projections.
Existing sewage network and treatment facilities.
Availability of land to construct the treatment plant and land cost.
Availability of energy and energy cost.

Propose the potential limits of the project (physical limits and design horizon in time).
Identify potential alternatives for the disposal of the treated effluents.
Propose sewage treatment technologies that may be used.
Perform a preliminary estimate of project cost.
Identify lacking information which will be necessary for the Feasibility Study.
Identify potential financial sources for the project.
Prepare the TOR to contract the Feasibility Study (if the conclusion of the Pre-Feasibility Study is that the project is feasible).

If reuse of the treated effluents for irrigation is a potential disposal alternative, the Pre-Feasibility Study will also address the:

General characteristics of agriculture in the region (soils, crops, land ownership, farmers organizations, irrigation practices, etc.).
Water demand for irrigation (existing demand or potential one).
Potential crops to be irrigated.
Quality required for the treated effluents to be used for irrigation.

Who should perform the Pre-feasibility Study ?

In some cases the organization/institution that requires the study (water company, municipality, etc.) has the technical capacity to perform the Pre - Feasibility Study by itself.

If an external consultant is contracted, it must be an independent consultant, i.e., a consultant who is not a provider of equipment or products for sewage treatment and disposal / reuse.

Providers of equipment and products are more interested in selling their products than in minimizing the investments and O&M (operation and maintenance) costs.

What is the cost of a Pre-feasibility Study ?

The cost of this study depends on the location, size and complexity of the project. A typical Pre - Feasibility Study performed by an international consultant will last about two weeks and will fall in the range of US$ 10,000 - 15,000 including traveling costs (air tickets, etc.).

THE FEASIBILITY STUDY

What is a Feasibility Study for Sewage Treatment and Disposal ?

The Feasibility Study is the key step in the development of a project. The Feasibility Study will determine the data to be used for design, the disposal of the treated effluents, the required quality, the treatment technology, lay-out and size of the treatment units, and cost of the project. The Feasibility Study will prepare the TOR to contract the detailed engineering design.

The Feasibility Study includes:

Build-up the database of the project with all relevant data on:

Topography (maps 1:25,000 up to 1:5,000 if necessary).
Climate (temperatures, winds, rain, evaporation).
Socio-economic level of the population.
Population and future projections.
Water sources and water consumption.
Final determination of sewage flow quantities and qualities, and future projections.
Existing sewage network and treatment facilities.
Alternative sites to construct the treatment plant and land cost.
Availability of energy and energy cost.

Recompilation of lacking information (it may be necessary to perform sampling and analysis of raw sewage, request aerial photography, topography of some areas, etc.).
Disposal of the treated effluents:

Alternatives for the disposal of the treated effluents (reuse in irrigation, lake, sea, river, infiltration in the aquifer, etc.).
Quality of effluents required for each disposal alternative.
Environmental and public health impact of each alternative.

Alternative technologies for sewage treatment and storage:

Intensive technologies (activated sludge, UASB anaerobic reactors, high-rate trickling filters, etc.)
Super-Intensive technologies (e.g., membrane reactors, activated sludge combined with fixed biomass).
Extensive technologies (waste stabilization ponds, wastewater reservoirs, SAT-Soil Aquifer Treatment, constructed wetlands, macrophyte ponds, etc.).
Semi-intensive technologies (low energy aerated lagoons, low-rate trickling filters, high rate stabilization ponds, etc.).

Construction steps (immediate, medium-term, long-term).
Comparison between alternatives:

Engineering advantages and disadvantages.
Environmental and public health impact.
Construction and O&M costs.

Recommended process design of the treatment plant, size of the units, lay-out and preliminary hydraulic profile.
Construction costs of the selected alternative.
Operational and maintenance costs of the selected alternative.
TOR to contract the detailed engineering design of the treatment plant.

If irrigation with treated wastewater is a feasible alternative, the Feasibility Study will also address:

Characteristics of agriculture in the region (soils, crops, land ownership, irrigation practices, farmers organizations).
Water demand for irrigation (existing demand or potential one).
Potential crops to be irrigated and the market.
Expected attitude of local population to wastewater irrigation practice.
Quality required for the treated effluents to be used for irrigation.

What is the difference between a Feasibility Study and a Master Plan ?

A Feasibility Study addresses one particular project, while a Master Plan has a regional scope and states how the sewage treatment and disposal problems of a whole region must be solved.

Some professionals refer to Master Plans as Regional Feasibility Studies.

Who should perform the Feasibility Study ?

An independent consulting firm.
That means a consultant firm that is not a provider of equipment or products for sewage treatment and disposal.

Providers of equipment and products are more interested in selling their products than in minimizing the investments and O&M costs of the client.

Providers can not perform an objective comparison between different treatment and disposal alternatives, because they will benefit by recommending the alternative which makes use of the equipment and products they sell.

Recompilation of local data is an important part of the Feasibility Study. Thus, if an international consultant firm is contracted to perform the Feasibility Study, it has to work together with a local engineering firm.

What is the cost of a Feasibility Study ?

The cost depends on several parameters, mainly on:

Size and complexity of the project.
The amount of lacking information which is needed in order to perform the Feasibility Study: maps, air photographs, topography, proper characterization of the quantity and quality of raw sewage, other.

A generally accepted rule is that a Feasibility Study should cost about 1-2 % of the cost of the designed treatment plant. For example: if the Pre-Feasibility Study estimated the cost of the treatment plant in 10 million dollars, the Feasibility Study should cost about US$ 100,000 - 200,000 .

But this rule has severe limitations:

A good Feasibility Study may develop a conceptual solution and treatment technology which is 2 or 3 million dollars cheaper than the 10 million estimated by the Pre-Feasibility Study. Or it may find unexpected problems which will increase the actual costs of the project by another 2-3 million dollar.
Thus, it is not wise to try to save a few thousand dollars in a study whose results will determine costs of several million dollars and avoid future problems in the operation and performance of the system. A good Feasibility Study may be expensive, but it will save much more money and headaches than its own cost.