A ‘managed eutrophication’ approach to wastewater treatment, aimed at preventing eutrophication in aquatic ecosystems, is under investigation by University of Bath and Wessex Water, UK, researchers. The idea is to use algal ponds for wastewater processing and for phosphorus removal.

Excess phosphorus levels in the environment stimulate algal blooms, resulting in oxygen depletion and the potential release of toxins from algae. Eutrophication is of concern as many waterways and lakes in the UK are currently failing to meet the strict standards set for nutrient levels under the nation’s Water Framework Directive.

A pilot High-Rate Algal Pond (HRAP) system has been installed at Wessex Water’s sewage treatment works in One of the HRAPs operating at Wessex Water. Image credit: University of BathOne of the HRAPs operating at Wessex Water. Image credit: University of BathBeckington, Somerset. After treatment, the plants can be removed and recovered as a resource before water enters the river. The polished water should be of a quality that it can be directly discharged to the environment.

About 3,000 liters of wastewater per day are being treated, with 80-96 percent phosphorus removal, during the trial phase. The researchers will analyze performance, costs, reliability and practicality of this sustainable technology in order to determine whether it can be a suitable solution for phosphorus removal in realistic conditions. The approach will also be tested across the different UK seasons that experience varying light and environmental conditions.

In two shallow ponds at Beckington, which have a total functional area of 60m2 and capacity of 18,000 liters, wastewater is continuously circulated by paddlewheels. The HRAPs are seeded with the desired species of algae and fed with final wastewater effluent, which would otherwise be released into the environment. The algae use nutrients in the wastewater, thereby reducing overall nutrient loads.

A proportion of the water and algae mixture is then moved to a settling tank and separated daily, while fresh effluent is added to top off the ponds. This results in polished wastewater with lower levels of harmful nutrients, and algae rich in nutrients that can be used for various purposes such as bioplastics, biofuel and agricultural fertilizer.

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