Barriers to closing the loop on nutrient recycling - a case study on phycoremediation of domestic wastewater in South Africa

Abstract

Sustainable development and the global move towards a more circular use of resources, where waste is reduced and resources are recycled, have caused a paradigm shift within the scientific community with regards to wastewater solutions. Nutrient recovery from organic waste streams is high on the development agenda and extends beyond direct economic benefits, to health and environmental benefits. Phycoremediation provides an alternative low-cost green solution to nutrient recovery from wastewater streams in developing countries. The current study utilizes a specific consortium of microalgal species (Chlorella vulgaris and Chlorella protothecoides) isolated and cultured specifically for their combined nutrient (total nitrogen and total phosphorous) removal efficiencies from domestic wastewater. The treatment was implemented at Brandwacht WWTW, a micro size waste stabilisation pond system managed by Mossel Bay local municipality in the Western Cape Province of South Africa. Total nitrogen removal efficacy after treatment was 73.1%, while total phosphorous removal was 50%. Even though the microbiological indicator, E. coli, were reduced by over 5 logs and the indicator numbers were far below that of the South African effluent discharge standards, the COD and other physicochemical parameters exceeded the discharge standards. The microalgae biomass was harvested by means of flocculation using Zetag 7557 from a small pilot scale plant, but very low concentrations were harvested.