Anaerobic Baffled Reactor (ABR) for Wastewater Treatment

The anaerobic baffled reactor (ABR) was developed in the early 1980s, and consists of a series of compartments (up to 8) in one reactor which are baffled to force the incoming wastewater up through a series of sludge blankets, thereby reducing the loss of biomass. It can also be operated with granules or internal media which enhance its stability. Hence the sludge retention time (SRT) can be separated from the hydraulic retention time (HRT), leading to good chemical oxygen demand (COD) and solids removal, low sludge production, and a small footprint. Tracer studies have shown that the reactor approximates to a series of completely stirred tank reactors (CSTRs), and this promotes the separation of bacterial trophic groups down the length of the ABR enhancing performance and stability. Due to its design, the reactor can tolerate both severe hydraulic and organic shock loads without failing, and is now starting to be used at full scale in many developing countries as a cheap and efficient method of low cost sanitation, and industrial wastewater treatment, often with the added benefit of energy production. This chapter reviews the current state of knowledge with ABRs focussing on: reactor development, hydrodynamics, performance, biomass characteristics and retention, soluble microbial products (SMPs), modelling, and full-scale operation.