What is anaerobic granular sludge treatment process?

 Anaerobic granular sludge treatment processes have been evolving, although the granulation process of anaerobic sludge is not well understood. In this review, up-flow anaerobic sludge tanks (UASB), expanded granular sludge tanks (EGSB) and static granular bed reactors (SGBR) are presented as representative components of anaerobic granular sludge treatment processes. The characteristics and application trends of each reactor are presented.The UASB reactor was developed in the late 1970s and its use has rapidly spread due to its excellent performance. With activated granules, this reactor can treat a wide range of high strength wastewaters and municipal wastewater. Most soluble industrial wastewaters can be effectively applied using UASB. the EGSB reactor was developed to provide more contact between the wastewater and the particulate matter. In this reactor, a fast rise rate separates the dispersed sludge from the mature particles. the EGSB reactor has shown excellent performance in treating low and/or high strength wastewater, especially at low temperatures. The SGBR, developed at Iowa State University, is one of the anaerobic granular sludge treatment processes. Despite the very simple configuration of the SGBR, the system's performance is similar to that of a UASB or EGSB reactor. In laboratory, pilot-scale tests, the anaerobic sludge granulation process has shown excellent performance for a wide range of wastewaters at a wide range of organic loading rates. This has led to the establishment of thousands of full-size granulation processes already operating widely around the world.

Thick electroactive biofilms are the key to successfully developing microbial electrochemical systems and technologies (MET). Complete anaerobic granular sludge (AGS) is a spherical and dense assemblage of microorganisms that has been successfully demonstrated to be a novel and efficient biocatalyst in METs such as microbial fuel cells. Three different strategies were explored to change the microbial composition of the AGS from methanogenic to exogenous microorganisms, including changing the external resistance and organic loading and manipulating the anode potential. In all strategies, the AGS was successfully converted from methanogenic to exogenous conditions, such as a significantly high current response (10.32 A/m 2 ) and 100% organic carbon removal from the wastewater, only if the anode potential was positive. In addition, current production and organic removal from the AGS bioanode did not decrease significantly at pH 5, indicating that AGS is well tolerated to acidic conditions. Finally, 16S rRNA sequencing revealed enrichment of exoelectrogen and suppression of methanogenic bacteria in the AGS microbial community following anodic potential control. This study provides proof of concept for the extraction of electrical energy from organic waste via exogenous electrical AGS and simultaneous wastewater treatment, while opening up a new paradigm to create an efficient and cost-effective exogenous electrical biocatalyst for industrial applications of MET.

 

Characterisation of anaerobic granular sludge

As AGS is a functional material for accomplishing the biodegradation of pollutants in anaerobic bioreactors, we investigated its detailed physicochemical properties at different sampling time points and sampling heights. At different sampling time points, significant differences in SV were only observed between the fourth and fifth sampling, however, MLSS, MLVSS and particle size did not show statistically significant differences. MLSS, MLVSS, and SV decreased progressively from the first to the last sampling port at different sampling heights. In particular, there is a significant difference between the first and seventh sampling ports for MLSS and SV. In addition, the diameter of AGS averaged approximately 900 μm and did not differ significantly between the seven sampling ports. These results indicate that AGS concentration and biomass decreased vertically along the AnaEG reactor. More importantly, this reactor's smaller particle size and greater homogeneity allow for high substrate-microbial contact. SEM observations of the appearance show that the AGS are smooth black spherical or oval particles. Its boundaries are regular and the surface is free of obvious cavities and cracks. An abundance of filamentous and coccolithophore microorganisms constituted the surface matrix. no significant differences in AGS morphology were observed between the seven sampling ports. In addition, SEM observations of the sections showed that different types of microorganisms were randomly interwoven throughout the cross-section. Cocci and rod-shaped microorganisms could also be observed in the particles. Previous studies have suggested that they belong to Methanosarcina and Methanosaeta (Nizami and Murphy, 2011). Although a variety of microorganisms were observed in different pellets, the overall morphology suggests that AGS consists of filamentous and bacteriophage-like microorganisms.