Purifying Wastewater Through Aquatic Means In Greenhouses

By Brian Groen

wetland picture obtained form www.rtbb.com/%7E.swg

The above picture of a natural wetlands and its scummy water generally don’t conjure up thoughts of clean, drinkable water. Ironically however this system of nature is perhaps the most efficient way of purifying water of almost any contamination. With advanced technology and understanding, this process is now becoming an economical and smart alternative to the conventional ways in which wastewater was handled.

Many problems arise with the rate of growth in our country. Extending sewer service is a challenging and expensive endeavor in many areas. Dumping of waste in many counties causes concern for pollution. The afore-mentioned reasons are motivation enough for locations that are seeking new wastewater facilities to look for other alternatives.

Large scale production green houses fit this bill perfectly. John Todd, a non-profit inventor has come up with the answer in a technology he has named Solar Aquatics. The technology makes use of the natural ecological and microbiological processes to treat greenhouse wastewater. While the many rows of translucent tanks where this all takes place utilize a sizeable amount of room, they get the job done. Engineered streams and marshes that are home to many types of plants, animals, and organisms accompany the tanks in the process. Water flows throughout the tanks through pipes in a specific sequence. This process removes contaminants while nutrients are metabolized or bound up as the water moves throughout the system. This is wastewater management Solar Aquatic style in a nutshell. To get a full understanding of how it works we need to look more closely at each cycle.

Wastewater begins the treatment when it is first screened and degritted. The water then enters the first tank where fine bubble aeration blends and mixes it. Next the solids in the water are kept suspended to make the readily available for biological breakdown in the solar tanks and ponds. Wastewater then leaves the blending tank to be split in equal portioned streams. The streams flow by gravity’s force through the series of connected clear tanks. It is in these tanks filled with floating and racked plants with their long extending roots where the water is further filtered.

The type of plants used depends on many factors such as availability, appropriateness in the region they are being used, and the contaminants that are being filtered. Plant roots are home to microbes that are necessary in the degradation of contaminants. An added bonus from the dense plant cover is their ability to utilize nutrients such as phosphorous and nitrogen in the wastewater. These plants in conjunction with an aeration system get rid of unpleasant odors from the wastewater. Worms, frogs, fish, and snails can also be used in these systems to clean the sides of tanks and eliminate sludge that gathers on plant roots.

If the desired use of the water after it has been purified is for irrigation, such as a farm, orchard, or gulf course, the process may be over now. These types of applications make it desirable to have nitrogen in the water since it is a plant fertilizer.

However, if the water is destined to be drinking water, it must continue on through a constructed marsh. The marsh has an oxygen free environment that reduces nitrates to harmless nitrogen gas. Marsh plants and the marsh substrate absorb Phosphorous in the water. Also plants such as cattails, iris, bulrushes, etc. destroy pathogenic bacteria.

The last step in the purification process involves the wastewater passing through an ultraviolet unit for final disinfections. To keep bacteria in the system a portion of the sludge that was a byproduct of the treatment process is recycled to the beginning blending tank.

This system is still relatively new and not much past the experimental stages. It has however proven effective and will be seen increasingly more as time goes on. The first pilot facility was able to treat about half of the wastewater for the town of Harwich, Massachusetts to the highest standard. Current systems range in size from ones that can handle 15,000 gallons all the way up to 1,000,000 gallons per day. This all goes to show us that like many things, the answers to our problems for the treatment of wastewater can be found in nature, the first and more successful system.