Start-up of a trickling photobioreactor for the treatment of domestic wastewater.

A stand-alone trickling photobioreactor (TPBR) was seeded with activated sludge and microalgae to treat domestic wastewater. The TPBR was started-up at 12-h hydraulic retention time at room temperature with 12:12 h light:dark cycle. The light was provided by blue LED strips. The reactor has a total volume of 30 L and is divided into six segments. Each segment is 30 cm long and has a diameter of 15 cm. Each segment was packed with polyurethane foam sponge cubes (2.5 × 2.5 × 2.5 cm ) with 40% occupancy. The chemical oxygen demand (COD), total organic carbon (TOC), total nitrogen (TN), and phosphorus (P) of domestic wastewater varied in the range of 164-256 mg/L, 84.4-133.8 mg/L, 34.2-55.6 mg/L, and 24.7-39.3 mg/L, respectively, during this period. The COD, TOC, TN, and P concentrations in the effluent after 45 days of operation were 30.24 ± 3.36 mg/L, 7.69 ± 0.09 mg/L, 16.67 ± 0.39 mg/L, and 17.48 ± 0.5 mg/L, respectively. The chlorophyll-to-biofilm biomass ratio increased during the experimental period. The above results indicate that the algal-bacterial symbiotic relationship is beneficial for carbon and nutrient removal from domestic wastewater. PRACTITIONER POINTS: Trickling photobioreactor works on natural ventilation and has low power requirements and a small footprint. The porous sponge media helped in immobilizing and subsequent harvesting of biomass. The reactor conditions favored the growth of diatoms (brown algae) over green algae.