Effective removal of organic substances and nutrients using microgranular sludge in a sequential batch reactor

Aerobic microgranular sludge was cultivated in a sequential batch reactor (SBR) under varying aerobic and anaerobic conditions with low dissolved oxygen levels to remove the nutrients and organic substances. The study employed synthetic wastewater from an actual wastewater treatment center (Kuala Lumpur, Malaysia) as the medium and initial substrate for SBR using seed sludge as the inoculum. The aerobic microgranular sludge occurred gradually over 140 days, transitioning from anaerobic to aerobic conditions. By day 105, granules with a diameter >0.3 mm constituted approximately 50 % of the total biomass, reaching the minimum threshold of 80 % biomass upon implementation of the aeration. The cultivated aerobic microgranular sludge exhibited 1.8 g/ L of mixed liquor volatile suspended solids (MLVSS) and 85.11 mL/g of sludge volume index (SVI), effectively achieving low effluent concentrations of nitrogen (ammonium, phosphate, nitrate, nitrite) and chemical oxygen demand (COD). Nitrification and denitrification processes were observed with average removal efficiencies of 30.24 % for COD, 15.86 % for ammonium nitrogen, and 7.38 % for phosphate. Nitrospira genes enhanced nitrification, while Denitratisoma organisms were primarily responsible for the denitrification. A decrease in Candidatus Accumulibacter and Candidatus Competibacter led to poor phosphorus removal. Overall, the study suggests that small-sized granules demonstrate comparable efficacy to aerobic granular sludge in removing carbon, nitrogen, and phosphorus with aerobic microgranular sludge showing the potential for effective nutrient removal in wastewater treatment over extended periods.