Granulation of sulfate reducing sludge

Abstract

Numerous sulfate conversion biotechnologies (SCBs) have been developed for treating various sulfate-laden domestic and industrial wastewater generated from natural and anthropogenic activities. Different ambient conditions and fluctuant characteristics of sulfate-laden wastewater such as temperature, pH and salinity constrain the application of current SCBs. Compact and resilient sulfate-converting granular sludge systems may offer a promising solution to overcome these constraints in implementation of SCBs. No study on granulation of SCB sludge in saline wastewater treatment was reported; rather many researches were focused on activity suppression of sulfate reducing bacteria (SRB) in anaerobic treatment processes. The present research, therefore, aimed at developing SRB granular sludge in a lab-scale sulfate reducing up-flow bed reactor (SRUSB), with synthetic saline sewage as the feed and anaerobic digestion sludge as the inoculum. The SRUSB is applied in sulfate reduction, autotrophic denitrification and nitrification integrated process (SANI) as the major reactor to realize organic removal and nitrogen removal in the subsequent anoxic reactor. Granulation successfully appeared at around 30 days and became well established within 60 days after the SRUSB start-up. The physiochemical and biological characteristics of the granules were extensively investigated at this formation stage to the steady state operation stage throughout this 655-day research. The well-developed SRB granules or named mature SRB granules in this study possessed an average diameter of 400-500 μm and stably stayed in the compact (gravity= 1.068-1.074) and porous (pore volume= 0.022 mL/g) structures. The SRB population in the granular sludge reached 44% of the total population, predominately present over the inner granules with other bacteria constituted a thin outer shell on the surface of the granule. The bacteria on the surface are believed to be the acidogens based on molecular microbiological analyses of pyrosequencing and fluorescence in situ hybridization (FISH). Such granule characteristics enabled the SRUSB to sustain 22 g/L biomass concentration effectively and thus achieve 90% of COD removal even under a very short hydraulic retention time (HRT), i.e. 1 h, indicating a very compact and stable SRUSB. Three-dimensional investigation was conducted to optimize operation and design of the SRUSB for performance improvement and scale up. The organics and sulfur conversion profiles along the height of the SRUSB were examined; moreover, the SRUSB internal hydrodynamics and microbial community were analyzed correspondingly. Based on these investigations, a further modification of SRUSB was conducted achieving better organics degradation profile along the reactor. Evaluation of the inhibitions against the activity of SRB granules by temperature, pH, oxygen, nitrite and free nitrous acid (FNA) as well as the reactor resilience was finally carried out. SRB granules had good resilience against dissolved oxygen, high nitrite, low temperature, pH (>5) and FNA (2.3 mgN/L) showed minimal impact on the granular sludge. In conclusion, SRB granulation is proved to be a promising technology for exploring SCB application with respect to enhancement in sludge retention, active bio-volume and substrate loading rate, and reactor resilience.

Date of Award	2014
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology