Impacts of seasonality and operating conditions on water quality of algal versus conventional wastewater treatment: Part 1

Abstract

Municipal wastewater is a reliable source from which water, renewable energy, and nutrients could be recovered for beneficial use. Our previous efforts have documented that an innovative algal-based wastewater treatment (WWT) system could recover energy and nutrients from wastewater while having a lower energy footprint than conventional WWT processes. As a biological treatment process, the algal WWT can be affected by algal species, operating conditions, and meteorological factors. This study aimed to identify suitable algal cultures to treat municipal wastewater during warm and cold weather. The algal system achieved the secondary effluent discharge standards for biochemical oxygen demand and nutrients within 2-3 days during warm weather (May to October, 25-55 °C) using an extremophilic algal strain Galdieria sulphuraria; and within 1-2 days in winter (November to April, 4-17 °C) using polyculture strains of algae with bacteria. The impact of seasonal variation and operating conditions on the water quality of pilot-scale algal bioreactors was compared with a full-scale conventional WWT system. The treatment performance of the algal system (NH₄-N: 1.3 ± 1.25 mg/L in winter and not detected in summer and conventional system; PO₄-P: 0.89 ± 0.6 mg/L in winter, 0.02 ± 0.03 mg/L in summer and, 5.93 ± 1.32 mg/L in conventional system) was comparable or better than that of the conventional WWT in nutrients removal and other contaminants were below the discharge standards. This study indicates that the algal system can be engineered for reliable wastewater treatment independent of seasonal variations.

Keywords: Algal wastewater treatment; Nutrients removal; Resource recovery; Water quality; Water reuse.