Granulation in thermophilic aerobic wastewater treatment
Abstract
Thermophilic aerobic wastewater treatment may be preferred over mesophilic aerobic treatment when the influent wastewater is already in thermophilic temperature ranges. Higher biodegradation rates, low sludge yield, inactivation of pathogenic organisms and elimination of cooling requirements prior to the treatment are advantages of thermophilic aerobic treatment. However, solid-liquid separation is often reported to be a major problem after treatment. Hence, high effluent solids concentrations are likely. The purpose of this research was to develop thermophilic aerobic granules. Granules are biological structures having high density and a high concentration of biomass. Their settling velocity is high and high organic loading rates are achievable. Anaerobic granules are well known and have been used in full scale and bench scale for over 20 years. Mesophilic aerobic granules, on the other hand, have only been cultured in the past 5 years and mostly using sequential batch reactors (SBRs). Granulation under oxygen limited conditions was also observed. However, no published accounts of thermophilic aerobic granules exist to the author's knowledge. Aerobic granules were cultured at 55°C using serum bottles and SBRs employing a feed/react schedule proposed by Ferguson (1999). Granules cultured in serum bottles had diameters between 1 and 7 mm, whereas granules from SBRs were between 1.1 and 1.9 mm. The settling velocities, aspect ratios and integrity coefficients were higher than 20 m/h, 60% and 70%, respectively. SCOD removals in both serum bottles and SBRs were higher than 90%. Microbiological studies showed that filamentous growth is dominant in granular biomass. Isolation studies resulted in the isolation of Bacillus flavothermus and Pseudoxanthomonas taiwanensis from the granules. Fatty acid methyl ester analysis showed that granular biomass and seed culture are significantly different in terms of microbial community. Using these granules, higher degradation rates may be achieved as well as good solid-liquid separation for wastewaters, like pulp and paper effluents, and many food processing effluents, which are often discharged at thermophilic temperatures.
This paper has been withdrawn.