Formation of aerobic granules in sequencing batch reactor treating diary industry wastewater

Abstract

Aerobic granular technology, compared to conventional activated sludge wastewater treatment plants, is a novel alternative offering numerous advantages such as high biomass retention, good settling ability and simultaneous removal of organic load and nutrients. The main focus of research was to evaluate granules formation and evolution of treatment performances during startup and steady state conditions. The experiments were performed in lab scale sequencing batch reactors with automated control of the operational cycle: anaerobic feeding (45min.), aerobic reaction (11 h), settling (5min.) and effluent withdrawal (10 min.). One of the bioreactors (D) was inoculated with conventional activated sludge while the other one (GM) was inoculated with crushed aerobic granular sludge. Both bioreactors were fed with dairy industry wastewater with high organic and nutrients load (CODCr=1723 – 3550 mg O2/L, BOD5 = 492 – 1806 mgO2/L; NH4 + = 64,6 - 114 mg/L, P tot = 5,04 – 21,5 mg/L). Aerobic granular structures were observed even after 5 days (10 treatment cycles) with 67 to 556 µm in diameter in D bioreactor and with 392 to 1200 µm in GM bioreactor. The granules diameter in D bioreactor increased significantly after 25 days to diameters between 513 µm and 1276 µm and up to 2 mm by the end of the experiment. The granules in GM bioreactor increased to 764- 1482 µm and up to 4 mm in diameter by the end of the experiment. Treatment performances increased rapidly along with the growth of granules size.