Wastewater Reuse: Analysis and Practice

By Nathan Wang

Although saving our water supply is plausible with water conservation and management, there will inevitably be wastewater. In today’s world, we need to find a new way to efficiently reuse this water in order to save the dwindling water supply and provide safe drinking water for everyone.

What is Wastewater?

Wastewater: water that has been adversely affected through human behavior, and contains waste and other contaminants that lower its quality

Wastewater includes but is not limited to sewage, municipal wastewater, industrial waste, agricultural return, storm water. These waters are dangerous to consume and are unsafe for human use. Though some may be reclaimed for other uses (more on that later). Wastewater needs to be collected and treated, because they contain toxins, organic and inorganic waste, minerals, solid waste, and pathogens that are dangerous for humans.

Industrial Wastewater Treatment

In developed countries, most urban wastewater goes down a sanitary sewer or a storm sewer or a combined sanitary and storm sewer to a wastewater treatment plant (WWTP).

Chart of industrial wastewater treatment process

There the water gets processed to remove impurities. The wastewater first gets filtered. Then through sedimentation, more solid wastes are removed. The water is transferred to a sludge pond where organisms consume the organic waste in the water. Finally, the water can be further filtered, disinfected, and other fine impurities can be removed if desired.

Although these WWTP’s are capable of transforming wastewater into any quality of drinking, or potable, water, they do not always aim for the highest quality of water. Often they do not purify the water to its highest quality, partly because of economic and time feasibility and partly because many uses do not require a super high quality of water (ex. Human consumption). Many traditional WWTP’s aim only to limit wastes enough for the water to be dumped back in

to the body of water and for the water to be indirectly used again down river. When a WWTP’s tanks cannot hold all the water, especially in heavy rains, it simply opens a release valve and dumps all the untreated water into a nearby body of water. Even more alarming, in the developing world, 90% of wastewater is simply dumped back into the rivers, untreated. One in five does not have access to safe drinking water.

Reuse

In order to conserve the water supply and provide safe water for everyone, we must find methods of reusing wastewater.

One method is to harvest rainwater, either from a roof runoff drain or other rainwater collection source. The rainwater is collected in a tank and purified for use. (This system is described in more detail in “Roof Catchment Rainwater Harvesting System”)

Another similar method is the use of passive rainwater harvesting systems. These systems are often at grade and are designed to direct the rainwater to irrigate surrounding foliage or to benefit the surrounding landscape. One example is where the City of Portland, Oregon, retrofitted street curbs to direct street runoff from storm sewers that fed into the Willamette River, to water surrounding greenery.

Fog collection is another method of catching natural water that would otherwise be waste. In this low-tech but efficient method, large find nets are stretched between to poles. When the fog moves by the nets, it condenses and falls into a reservoir. In Canada, FogQuest, a nonprofit organization, is looking to implement this technology all over the world.

There are also many technologies that help make homes self-sufficient, in reusing current water supplies.

Potter for Peace, a South American organization, is making a cheap, low-tech water purifier called Filtron. This purifier consists of a pot containing sawdust and colloidal silver. This technology purifies the water by filtering with sawdust and clay, and killing bacteria with the silver. The purifier only costs 9 dollars and is being used by the Red Cross and Doctors With-out Borders in rural communities.

There are also solar based purifiers that clean wastewater into drinking water. Most work through evaporating the water with the sun’s heat. Then condensing the water vapour into clean drinking water.

Another invention that helps us reuse wastewater is an alternative sewage treatment marsh. These mini-treatment plants can provide recycled water for consumption for a small community. The treatment system mimics that of a marsh. Hardy plants like cotton tails consume and filter toxins form the wastewater and bacteria clean out organic waste. In the end, what you get is a supply of clean drinking water.

The recycling shower is another option to help you reuse wastewater. Water from the shower drain of the recycling show is immediately brought into a treatment system where the water is clean, then reheated and comes back out of the showerhead.

Case study: EcoHous

A prime example of reusing waste water to preserve the water supply is the EcoHous located in the Urca neighborhood in Rio de Janeiro, Brazil. In this house, a raincatchment system is deployed. Rainwater is caught from the roof and patio into a drain and through a gravity driven filter. The water is then brought to a water recycling tank. And from there is gravity fed to areas throughout the house for reclaimed non-potable water use. The system comprised of 28% of water use in the house.

There is also a sewage recycling system where gray water, water from sinks, showers, washing machines, are purified and reused in much the same manner as the rain catchment system.

A green roof is also watered by natural rainwater. The garden feeds the residents of the house while using rainwater that would have gone to waste. This house proves that wastewater reuse is a practical idea for today’s homes.

Through the development of new ideas and techniques, it will be possible to reuse most wastewater and consequently save our water supply and provide safe drinking water for many.