Project Grade 11 Engineering & Design

Quillhaven Slow Sand Biofilter: A Build-and-Test Design Project

A grade 11 engineering build project where teams design, construct, and iteratively test a slow sand biofilter for the fictional Quillhaven field station within a budget.

Grade: Grade 11
Subject: Engineering & Design
Material: Project
Time: 4 sessions, ~240 min total
Prep: Moderate prep
Materials: Clear 2-liter plastic bottle with the bottom removed, inverted as a column (1 per team), Fine sand, about 3 cups per team (rinsed), Coarse sand and pea gravel, about 1 cup each per team, Cotton or a coffee filter for the outlet, Aquarium tubing and a clamp to control outlet flow (1 per team), Graduated cylinder or measuring cup, 100 mL, Stopwatch or phone timer, Cloudiness comparison card, a 1-to-5 scale (1 clear, 5 very cloudy), Muddy source water, soil stirred into water, about 2 liters per team, Teacher-provided materials price sheet

Standards

HS-ETS1-2 NGSS

Design a solution to a complex real-world problem by breaking it down into smaller, more manageable problems that can be solved through engineering.

How this material aligns: Teams break the treatment goal into filtration and biological-layer sub-problems and build a column that solves each, the engineering decomposition this standard requires.

All materials for HS-ETS1-2 →

HS-ETS1-3 NGSS

Evaluate a solution to a complex real-world problem based on prioritized criteria and trade-offs that account for a range of constraints, including cost, safety, reliability, and aesthetics as well as possible social, cultural, and environmental impacts.

How this material aligns: In the final milestone teams evaluate their design against prioritized criteria and trade-offs of clarity, flow rate, and budget, exactly the evaluation this standard describes.

All materials for HS-ETS1-3 →

Download Word file

This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-07-17.

Objectives

Students will design and build a layered slow sand filter that meets clarity, flow, and budget constraints.
Students will collect turbidity and flow data across several days and refine one design variable.
Students will evaluate their final design against prioritized criteria and defend it in a written proposal.

Vocabulary

Slow sand filter: A slow sand filter cleans water by letting it trickle very slowly through a deep bed of sand, where a thin layer of living microorganisms on top helps trap and break down impurities. It is one of the oldest and simplest ways to treat water, still used today in some small systems.
Turbidity: Turbidity is a measure of how cloudy or murky water looks because of tiny particles floating in it. Clear water has low turbidity, and muddy water has high turbidity.
Flow rate: Flow rate measures how much water moves past a point in a certain amount of time, like gallons per minute through a garden hose. Bigger pipes and stronger pushes give bigger flow rates.

Also: schmutzdecke, constraint, iteration

Teacher overview

Slow sand filters are one of the oldest water treatment methods still in use, and part of how they work is biological: a living layer of microbes, called the schmutzdecke, begins to form on the sand surface within days, matures over several weeks, and helps trap and break down contaminants. Over four sessions, teams design, build, and improve a bench-scale slow sand filter for a fictional remote site, the Quillhaven field station, working within a materials budget. The final deliverable is a working filter plus a one-page proposal to the site's board. The driving question is how to clarify cloudy water reliably with simple materials, and the project is quantitative because teams track cloudiness ratings and flow rate at each test.

Quillhaven Slow Sand Biofilter: A Build-and-Test Design Project — Grade 11 Engineering & Design

Name: ____________________________ Date: ______________

Project Brief

Driving question: How can a team build a slow sand filter that clears cloudy water to a set clarity target, at a usable flow rate, and within a fixed budget?

Scenario: The fictional Quillhaven field station needs a low-cost filter its staff can build and maintain without electricity. The station board has asked student teams to design, build, and test a bench-scale slow sand filter and to recommend one design.

Constraints:

Budget: each team has $40 of build materials, priced from the teacher's price sheet. The final design must total $40 or less.
Clarity target: the filter must lower a cloudiness rating of 5 down to a rating of 2 or lower on the 1-to-5 card.
Flow window: the outlet must run slowly, between 20 and 60 mL per minute, because a slow sand filter that runs too fast lets particles pass and never forms a biological layer.
Size: the filter column must fit inside a single 2-liter bottle.

Real-world tie-in: A conventional municipal plant must reach 0.3 NTU turbidity in nearly all of its monthly samples, a far stricter target than a classroom card can measure. Teams should treat their 1-to-5 rating as a simple stand-in for turbidity, not an official reading, and note that a real slow sand filter is only one step in a full treatment train.

Safety: Do not drink or taste the source water or the filtered water at any stage. A classroom filter can make water look clearer without making it safe to drink. Wash hands after handling the muddy water and wet sand.

Final deliverable: A working filter, a data table covering every test, and a one-page written proposal to the Quillhaven board that states the final design, reports the clarity and flow results, itemizes the cost, and explains one trade-off the team made.

Milestones

Session 1 (specify and plan): Teams study how a layered sand filter works and write a specification sheet listing the three targets they must meet: the clarity target, the flow window, and the budget. Using the price sheet, they sketch a layered design and estimate its cost. Output: a specification sheet and a costed design sketch totaling $40 or less.
Session 2 (build and baseline test): Teams build version one, rinsing the sand first, layering gravel, coarse sand, and fine sand, and adding the outlet filter and flow clamp. They pour a measured, rated sample through, record the cloudiness before and after, and time the outlet flow in mL per minute. Output: a built filter and a baseline data row.
Session 3 (run, observe, and refine): Teams keep their sand column damp and run a measured volume of the muddy source water through it daily so a biological layer can begin forming on the sand surface, then re-test with a fresh cloudy sample and compare with their baseline. Each team changes exactly one variable, such as sand depth or flow-clamp setting, staying within budget. Output: a multi-day data table and one documented design change with its reason.
Session 4 (final test and proposal): Teams run a final rated sample, record clarity and flow, confirm the cost, and write the one-page proposal to the Quillhaven board. Teams present their filter and results to the class acting as the board. Output: a completed proposal 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
Clarity performance	Filtered water stays above a rating of 2	Reaches a rating of 2 only inconsistently	Reliably reaches a rating of 2 or lower on the final test	Reaches a rating of 1, with data across sessions showing steady improvement
Flow rate constraint	Flow falls outside the 20-to-60 mL per minute window with no adjustment	Flow is near the window but not verified with timed measurement	Flow is inside the 20-to-60 mL per minute window, confirmed by measurement	Flow is inside the window and the team explains how they tuned the clamp to hold it there
Budget constraint	Cost exceeds $40 with no adjustment	Cost is near $40 but not itemized	Cost is at or under $40 with an itemized list	Cost is at or under $40, itemized, with a stated trade-off the team made to stay within budget
Iteration and evidence	No design change or supporting data	A change was made but not tied to data	One change is justified with before-and-after data	The change is justified with data and the team explains why the biological layer affected the result

Differentiation

Support

Provide a pre-built demonstration filter and a labeled cross-section diagram so teams can copy a known-good layer order, and give a simplified price sheet with fewer material choices to keep the budget math manageable.

Extension

Ask teams to calculate how many liters their filter could treat in one hour at its measured flow rate, then estimate how long the field station's daily need would take and whether one column is enough or several would run in parallel.

ELL supports

Provide a picture sequence of the build steps and a labeled diagram naming each layer, and allow the written proposal to combine short sentences with labeled sketches. Pre-teach "layer," "flow rate," "clarity," and "schmutzdecke" with images before Session 1.