Providing potable water from algal filtration: The frontiers of sustainability in your backyard

Background/Question/Methods

Provision of clean drinking water is one of the major global challenges of the 21^st Century. One of the most widespread global issues of the 21st Century is scarcity of clean drinking water in many regions of the world. Lakes and rivers worldwide are becoming contaminated by chemical and biological pollutants, such as Escherichia coli, thus decreasing potability of the water. Overuse of fertilizers and subsequent runoff have led to increased E. coli concentrations and nutrient levels in many lakes and rivers worldwide. Implementing sustainable and affordable methods of remediation is critical to providing clean drinking water to communities worldwide.

The freshwater alga Spirogyra grevilleana can be used in an algal filtration system to reduce levels of Escherichia coli, nitrates and phosphates. Multiple samples of  m³ of water was collected from a 2.32 ha lake in Atlanta, Georgia, USA and maintained under constant laboratory conditions with sixteen hours of continuous lighting on a daily basis. This water was run at a rate of  m³ hr^-1 continuously through the filtration devices under laboratory conditions with two concentrations of S. grevilleana. Samples from both trials were tested over time for E. coli, nitrate, phosphate, dissolved oxygen, and pH levels. 

Results/Conclusions

Use of S. grevilleana as an algal filter is an effective method of E. coli and nutrient reduction in freshwater. The lab-tested filtration device resulted in 100% reduction of E. coli, as well as 23% reduction in nitrate levels and 30% reduction in phosphate levels. This algal filtration device is sustainable, economical, and portable, making it effective to mitigate pollution and to improve access to clean drinking water.

The resultant water is potable and meets EPA potable water standards. Tests show that pH levels were slightly elevated compared to the EPA secondary standard, but these levels are not affecting overall potability. pH levels could be adjusted if needed by using a buffer, such as Na₃PO₄. Utilization of this algal filtration device to remediate water collected from polluted freshwater lakes could potentially provide potable water sources to communities currently lacking access.

Potential usage for the algal filtration device includes tying together several devices to filter larger freshwater lake volumes. The number of devices installed would be dependent on lake volume. An effluent tube could remove a portion of water to be filtered through additional algal filtration devices before being deposited into a potable water reservoir for community pipes or wells.