Email
Five students in matching 'got water?' shirts hold an oversized cheque made out to Ramblin' Mech for one thousand dollars, marked Best Mechanical Engineering and dated 12-1-25. They stand in front of a Georgia Tech Capstone Design Expo backdrop with a faculty member and the Georgia Tech mascot.
01Team Ramblin' Mech, Capstone Design ExpoBest Mechanical Engineering Project at the Fall 2025 Capstone Design Expo.

Biochar Arsenic Water Filter for Households in Guatemala

Georgia Tech Capstone Design · with Ecofiltro and Design for Planet Impact

Role
Mechanical Engineer, Team Ramblin' Mech
Group
George W. Woodruff School of Mechanical Engineering — Capstone Design
Location
Atlanta, GA and Guatemala
Dates
August – December 2025

Designed a modular, low-cost, off-grid water filter targeting arsenic-contaminated water in rural communities in Guatemala. Gravity-fed, easily replaceable, and built to be manufactured within the communities that use it.

Synthesized biochar from agricultural waste, sized the filter bed for the required contact time and service life, built the housing and screen stack, and tested flow through the cartridge.

Won Best Mechanical Engineering Project at the Fall 2025 Capstone Design Expo, where 620 students showed 118 senior design projects.

Background

Volcanic geology puts arsenic into groundwater across much of Guatemala. It is present in 33.6% of the country's urban and developed areas, and worldwide about 140 million people in at least 70 countries drink water contaminated with it. Short-term exposure causes vomiting, abdominal pain, diarrhea, numbness, and muscle cramping. Long-term exposure causes skin lesions, skin and lung cancer, intellectual impairment, and stunted growth. However, it does not change the taste, the color, or the smell of the water making it difficult to detect and even more dangerous.

We worked with Ecofiltro, an already well established water filter company in Guatemala. It's a gravity-fed household unit built around a fired clay element impregnated with colloidal silver and activated carbon, made locally from local materials, and it is in enough Guatemalan homes to count as the default. It removes microbial and bacterial contamination, but it does not target arsenic.

This informed out goal, a compatable design for the filter that people already own, at a price they already pay, made from materials the same factory can already get.

Six Ecofiltro household water filters on a wooden rack in a covered outdoor walkway. Three white plastic units with lidded tops and plastic spigots stand on the upper shelf beside a stack of drinking cups; three smaller blue enamelled units stand below. Each carries the Ecofiltro logo.
02Ecofiltro units in serviceThese are Ecofiltro's that were being used at a local school. The filter was commonplace in homes and schools, and the team had to design a part that would fit into it without changing the user's experience.

Field visit

We spent time in Guatemala early in the semester, including a visit to the Ecofiltro factory. The plant fires its clay filters in gas kilns in batches of a few hundred, then flow-tests every element in open tanks before it ships.

Interior of a filter factory under a steel truss roof. Hundreds of unglazed clay filter elements stand in rows on steel racks over long open water tanks, with more stacked on shelves along the far wall. A digital display on the near wall reads 22.
03Flow testing on the factory floorFired elements over the test tanks. Every element is flow-tested here before it ships.
A row of gas-fired kilns in a factory. The near kiln stands open with its refractory lining exposed; a worker in a hard hat and high-visibility jacket stacks unfired clay filter elements on the kiln floor. Yellow gas lines and burner assemblies run along the kilns on the left.
04Kilns, Ecofiltro factoryFilter elements loaded for firing. The plant's process semi-automated between forming the clay, firing in the kiln, and testing.
Two students in hard hats stand against a white wall at the factory, either side of a large Ecofiltro logo made from green glass bottles set into wooden boards. Small potted cacti sit on wall-mounted shelves to each side; stacked yellow water jugs stand at the right.
05At the factory

Requirements and interface

The insert had to fit the existing spigot thread, with no tools and no change to the filter body. We set a 5,000 liter service life, a flow rate above 2 L/hr so the insert would not become the bottleneck, and a target of under 10 µg/L arsenic in the treated water, which is the World Health Organization's guideline value.

The assembly is a threaded cartridge body holding the adsorbent, two screen plates that retain the packed bed while passing water, and a cap that carries the original spigot.

CAD render of the cartridge exploded along its axis: a cylindrical body with a moulded end pattern, a threaded neck, a red screen plate, a blue mesh disc, a cap with a hexagonal boss and internal thread, and a black plastic spigot at the right.
06Cartridge, explodedThe screen stack holds the packed bed in place while passing water, and the cap carries the original spigot.
CAD render of the assembled cartridge shown with translucent walls, so the internal screen plates are visible through the body. The black spigot is threaded into the hexagonal boss on the cap.
07Cartridge, assembled

Adsorbent selection and synthesis

Biochar can be made from agricultural waste that Guatemala already produces in quantity, for example banana peel and watermelon rind. Published capacities put its arsenic uptake at roughly 3 to 11 mg/g, with removal reported between 92 and 100% and best performance near pH 7 to 8.

We synthesized our own biochar in a controlled lab. Feedstock is rinsed in distilled water, cut down, air-dried, then oven-dried at 158 °F for 24 hours. The dried material goes into a ceramic crucible, wrapped in foil to starve it of oxygen, and pyrolyzed at 400 °C for two hours. The char is then weighed and crushed to particle size.

Sizing the packed bed

The bed is sized from four relations. Internal cross-sectional area follows from the cartridge bore, A = π(D/2)². Packed volume is that area times packed height, V = AH. Flow is expressed both as a volumetric rate Q and as a velocity through the bed, v = Q/A. Empty-bed contact time is the residence time that follows, EBCT = V/Q = AH/Q.

Service life depends on the biochar's arsenic capacity. Biochar mass, capacity, and influent concentration determine how much water the cartridge can treat, which is the basis for the 5,000-liter target.

Flow at the spigot

We timed 2 liter draws through a loaded cartridge at three reservoir head heights. The requirement was above 2 L/hr, so the insert does not restrict the filter in any way a user would notice.

Design Expo

The project was shown at the Fall 2025 Capstone Design Expo and was judged Best Mechanical Engineering Project.

It was one of four teams in Design for Planet Impact, a Woodruff School initiative that ran its first cohort that semester and pointed capstone teams towards overlooked problems in Guatemala.

The team's Capstone Design Expo poster, titled Project H2O. Three columns: problem statement, Ecofiltro background, and concept ideation on the left; the objective, an exploded prototype render, the specifications, and the four-step biochar synthesis down the centre; the engineering analysis equations, the flow rate and fill time charts, and future steps on the right.
08Project H₂O, Capstone Design Expo poster

Skills applied

Mechanical design
  • CAD
  • Health standards and regulatory compliance
  • Design for manufacturing
  • 3D resin printing
Water treatment
  • Adsorption calculations
  • Biochar synthesis by pyrolysis
  • Service lifecycle estimation

Sources