If Nature Can Keep Clean Without Chemicals, Why Can’t We?


Adapting techniques pioneered by environmental engineer Dr. John Todd, I set out to create a model that replicates and accelerates natural water purification processes.

Zainub Dhanani, Article Image

Historically, wetlands have served as our natural water filtration systems. By passing water through vegetation, microbes, sediments, and small aquatic organisms, ecosystems have been purifying wastewater without human input for millennia. Sustainable wastewater treatment lies in our ability to mimic this natural system. Using techniques pioneered by environmental engineer Dr. John Todd at the University of Michigan, I set out to create a model that replicates and accelerates natural water purification processes. My rendition of the Living Machine, the system that Dr. Todd pioneered for renewing human waste, not only mimics the biological systems that allow for natural purification, but also acts as a prototype for environmentally and economically sustainable waste management.

In the process of renewing the fish wastewater, waste and byproducts produced by organisms within each tank of the system provide nutrition for organisms in the subsequent tank. By connecting the tanks using siphons, the model reduces its need for outside energy sources by utilizing the gravimetric pull created by a height difference between the various tanks. The four-tank system is created such that each tank has a specific purpose: (1) Sedimentation and Decomposition, (2) Rock Filtration and Hydroponics, (3) Algae Production, and (4) Fish Ecosystems.

The primary tank receives the initial wastewater via a low-energy pump, simulating what would otherwise be the entrance of human waste into the system. In the first phase, solid waste particles fall through the sediment layers, in which aquatic animals such as ramshorn snails and insect nymphs begin their decomposition processes. Suspended nutrients are absorbed by the roots of hanging plants. Partially filtered water moves into the second tank, where bacteria aid help decompose toxic ammonia, and algae and zooplankton absorb excess nutrients. In this phase, I also incorporated a hydroponics system, which shows how the Living System can be used to produce food, rather than just neutralize waste. Lettuce and basil were used for the hydroponics in this tank, and roots from the raft plants use excess nutrients to help clean the water. Submerged plants help settle any remaining solids that are suspended in the water.

The following tank receives nearly purified water, with only aqueous nutrients remaining, which are used in the production of algae. The algae are then transferred to the fourth tank as a food source for the fish. In the final tank, I used algae-eating catfish and particular breeds of tilapia, which also act as a source of new waste. This waste is transferred into the first tank to continue the cycle, thus creating a self-sustaining environment.

The system that I created serves as a prototype for how we can clean pollutants without using toxic chemicals.This type of research helps bridge environmental studies with engineering and design, a field that has traditionally taken its inspiration from natural structures and ecosystems. Versions of the Living Machine have been installed on numerous college campuses for purifying water for toilets and showers. By creating an ecosystem for aquatic life while purifying wastewater, eliminating the use of unnecessary toxic chemicals, and producing marketable crops all within a self-sustaining system, the Living Machine fulfills an ever-growing need for solutions that are both practical and friendly to our environment.

Zainub Dhanani is a Brevia staff writer. She can be reached at zainubdhanani@college.harvard.edu.