n Civil Engineering = Siviele Ingenieurswese - Achieving cost-effective and sustainable wastewater treatment using Nereda^® : water engineering

Abstract

Aerobic granular sludge has been developed as an alternative to the activated sludge systems that are commonly applied for municipal and industrial wastewater treatment worldwide (including in South Africa). Activated sludge systems use flocculent biomass which has relatively low settleability, necessitating large secondary settling tanks and low reactor biomass concentrations (3-5 gMLSS/ℓ). In turn, activated sludge systems have a significant footprint (space requirement) and require a relatively large energy input (aeration and recycle pumping). In contrast aerobic granular sludge comprises more compact and dense bio-granules that result in improved sludge settling characteristics (up to > 10 m/h). Aerobic granular sludge is formed by applying specific process conditions that favour slow-growing organisms such as PAOs (polyphosphate accumulating organisms) and GAOs (glycogen-accumulating organisms), and suppression of the growth of flocculent biomass, together with selective wasting whereby slow-settling floc-like sludge is discharged and faster-settling biomass is retained.