Effect of pot-ale enrichment on the treatment efficiency of primary settled wastewater by the microalga Chlorella vulgaris

This study evaluated the performance of microalgae under static cultivation for primary settled municipal wastewater (PSW) treatment as a low energy treatment process. The availability of a suitable carbon substrate was determined to be the main limiting factor affecting the algal treatment performance. To overcome the material cost of applying commercial sources of organic carbon, we evaluated pot ale – a carbohydrate-rich by-product from the production of malt whiskey – as a carbon substrate to promote microalgae growth and the removal of nitrogen (NH3–N) and phosphate (PO4–P) in PSW. For this, the mixotrophic microalgal species Chlorella vulgaris was used in batch experiments of PSW enriched with pot ale. Characterisation of the wastewater in the microalgae treatments compared with the control treatments (WWC) and wastewater with pot ale (WWPA) highlighted that C. vulgaris was a key organism in the algal-bacterial consortium responsible in inorganic N and P removal. We also observed a high variability in the characteristics of PSW across independent batches enriched with pot ale, which resulted in variability in the N and P removal efficiency by the alga, from 99% to 58% at reducing NH3–N, and from 94% to 58% at reducing PO4–P. As an extension of these batch-wise operated treatments, we investigated removal of NH3–N and PO4–P under semi-continuous operation with pot ale enrichment and found this to be a viable system for potential further development. This work highlights the use of pot ale enrichment with microalgae as a promising application for enhancing the efficiency of inorganic nutrient removal from PSW.