Abstract
Currently, research trends on aerobic granular sludge (AGS) have integrated the operating conditions of extracellular polymeric substances (EPS) towards the stability of AGS systems in various types of wastewater with different physical and biochemical characteristics. More attention is given to the stability of the AGS system for real site applications. Although recent studies have reported comprehensively the mechanism of AGS formation and stability in relation to other intermolecular interactions such as microbial distribution, shock loading and toxicity, standard operating condition control strategies for different types of wastewater have not yet been discussed. Thus, the dimensional multi-layer structural model of AGS is discussed comprehensively in the first part of this review paper, focusing on diameter size, thickness variability of each layer and diffusion factor. This can assist in facilitating the interrelation between disposition and stability of AGS structure to correspond to the changes in wastewater types, which is the main objective and novelty of this review.
Highlights
Intensive works on applied biological treatments over the last 20 years have found that granular sludge has the potential to be a substitute method for conventional activated sludge systems (Liu & Tay 2004; Adav et al 2008)
sequencing batch reactor (SBR) is commonly used to stimulate the evolution of aerobic granular sludge (AGS) which can be manipulated with short cycles and reduced settling time (Wagner & Costa 2013)
Low-strength wastewater is defined as sewage having chemical oxygen demand (COD) values of less than 2,000 mg/L (Supplementary information Table A.1), while high-strength wastewater is defined as industrial wastewater with COD values greater than 2,000 mg/L (Supplementary information Table A.2)
Summary
Intensive works on applied biological treatments over the last 20 years have found that granular sludge has the potential to be a substitute method for conventional activated sludge systems (Liu & Tay 2004; Adav et al 2008). Critical comparisons have been made between the effects of wastewater types on stability and crucial operating conditions which occur during the formation of AGS while referring to process performance, and physical, chemical and biological properties are rarely discussed. In this review, the relationship between the multi-layer structural model of AGS and crucial operating conditions applied is discussed thoroughly with the aim of improving the understanding of the effect of wastewater types on stability performance. In this discussion, the wastewater is classified into two types: lowstrength wastewater and high-strength wastewater. Low-strength wastewater is defined as sewage having chemical oxygen demand (COD) values of less than 2,000 mg/L (Supplementary information Table A.1), while high-strength wastewater is defined as industrial wastewater with COD values greater than 2,000 mg/L (Supplementary information Table A.2)
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