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Project Grade 12 Engineering & Design

Choosing Fenmarsh's Treatment Upgrade: Conventional Versus Membrane

A grade 12 engineering capstone where teams weigh a conventional filtration expansion against a membrane plant for a fictional growing town, then recommend one.

Objectives

  1. Students will specify measurable criteria and constraints for a drinking-water treatment upgrade.
  2. Students will estimate and compare the energy use of a conventional and a membrane option.
  3. Students will recommend one option using a weighted trade-off analysis and defend it to a fictional board.

Vocabulary

Key words: conventional filtration, membrane treatment, brackish, trade-off, decision matrix

Teacher overview

The fictional town of Fenmarsh is growing, and its river source is turning saltier as drought lets salt water from the coast push farther upstream. The town must add treatment capacity, and it faces a real engineering choice: expand its conventional filtration plant, which is cheaper to run but cannot remove salt, or build a reverse osmosis membrane plant, which removes salt but uses far more energy. Over four sessions, teams define the criteria, estimate the energy for each option, weigh the trade-offs, and recommend one option to the fictional Fenmarsh Water Board.

Choosing Fenmarsh's Treatment Upgrade: Conventional Versus Membrane — Grade 12 Engineering & Design
Name: ____________________________ Date: ______________

Project Brief

Driving question: Should Fenmarsh expand its conventional filtration plant, or build a membrane plant, to add treated-water capacity as its source turns saltier?

Scenario: The fictional Fenmarsh Water Board must add capacity within a few years. The board has asked your engineering team to study two options and recommend one, with reasons.

Given data for this fictional project:

  • The town must add 2.0 MGD of new treated-water capacity.
  • Option A expands the conventional filtration plant. It uses about 1 to 2 kWh of energy per 1,000 gallons. It cannot remove dissolved salt. Its estimated capital cost is 3,500,000 dollars.
  • Option B builds a reverse osmosis membrane plant. It uses about 3 to 4 kWh per 1,000 gallons. It removes dissolved salt. Its estimated capital cost is 5,500,000 dollars.
  • Both options must deliver finished water at or below 0.3 NTU turbidity.
  • The capital budget is 6,000,000 dollars.
  • The source is brackish and getting saltier, so salt removal may soon be required.

Constraints:

  • The recommendation must meet the 2.0 MGD capacity target and the 0.3 NTU turbidity limit.
  • The recommendation must fit the 6,000,000 dollar budget.
  • The recommendation must account for the rising salinity of the source.

Final deliverable: A three-to-five-page engineering recommendation memo to the fictional Fenmarsh Water Board. It must include the criteria list, an energy comparison, a decision matrix, and a clear recommendation with reasons.

Milestones

  1. Session 1 (60 min) - Define criteria and constraints: Teams list the measurable criteria for the upgrade. These include the 2.0 MGD capacity, the 0.3 NTU turbidity limit, the 6,000,000 dollar budget, and the salt problem. Output: a one-page criteria and constraints sheet.

  2. Session 2 (60 min) - Estimate the energy: Teams estimate the daily energy for each option to make 2.0 MGD. That flow is 2,000 thousand-gallon units. At 2 kWh per 1,000 gallons, Option A uses 4,000 kWh per day. At 4 kWh per 1,000 gallons, Option B uses 8,000 kWh per day. Output: an energy comparison table.

  3. Session 3 (60 min) - Weigh the trade-offs: Teams build a decision matrix. They score each option on capacity fit, energy use, cost, and salt removal. Teams pick weights for each criterion and total the scores. Output: a completed, weighted decision matrix.

  4. Session 4 (60 min) - Write and present the memo: Teams write the recommendation memo and present it to the class, who role-play the water board. Output: the finished memo and a short presentation.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Rubric
Criterion Emerging Developing Proficient Advanced
Criteria and constraints Criteria are missing or vague Some criteria are listed but not all are measurable All four criteria (capacity, turbidity, budget, salinity) are stated and measurable All criteria are measurable and the team explains why each matters to the choice
Energy and cost analysis Energy is not estimated for either option Energy is estimated for one option or contains a unit error Energy is estimated correctly for both options with units shown Energy and budget fit are both analyzed, and the team notes how running cost differs from capital cost
Trade-off recommendation No clear recommendation is made A recommendation is stated but not tied to the matrix The recommendation follows from the weighted matrix and cites the salinity issue The recommendation follows from the matrix, weighs the salinity risk over time, and anticipates a board question

Differentiation

Support

Provide the energy estimate for Session 2 already worked, so teams can focus on the criteria and the decision matrix. Give a decision-matrix template with the criteria rows already labeled.

Extension

Ask teams to add a third option, such as a conventional plant now with membrane treatment added later, and to argue whether phasing the investment is wiser than committing to one path today.

ELL supports

Provide a labeled diagram comparing a conventional plant and a membrane plant, with each stage named. Give a memo template with headed sections and sentence frames for the recommendation.

Extensions

Invite a local utility engineer to review the class recommendations and describe how a real utility weighs energy cost, capital cost, and source-water reliability when it plans a treatment upgrade.