Effect of hydraulic retention time on the performance of trickling photo-bioreactor treating domestic wastewater: Removal of carbon, nutrients, and micropollutants

Abstract

In this study, the efficiency of a trickling photo-bioreactor (TPBR), seeded with activated sludge and microalgae, was evaluated for domestic wastewater treatment. TPBR was operated completely on natural aeration at 2-, 4-, and 6-h hydraulic retention time (HRT) with a 12:12 h light: dark cycle. The total organic carbon (TOC) and total nutrient (TN) removal were negatively affected by decreasing the HRT from 6 to 2 h. The TPBR was able to reduce TOC from 93 to 9 mg/L, TN from 34 to 18 mg/L, and phosphorus from 23.5 to 4 mg/L at 6-h HRT. The chlorophyll concentration (5 – 7 mg per liter of sponge volume) was observed to be highest in the middle of the reactor. Altogether, 106 organic micropollutants of different classes like pharmaceutical, personal care products, pesticides, herbicides, and fungicides were detected in the influent wastewater sample. However, in the treated effluent, only 17 micropollutants were detected at 6-h HRT. This shows that the algal-bacterial consortia are capable of removing micropollutants from wastewater. The energy input was 0.06 kWh/kg COD removed which is much less than the conventional activated sludge processes. The results indicate that this novel system is capable of providing a sustainable wastewater treatment solution.