This is a literature review for the year 2009 and contains information specifically related to suspended growth processes including activated sludge and sequencing batch reactors. This review is a subsection of the Treatment Systems section of the annual literature review. The review encompasses modeling, nutrient removal, system design and operation, oxygen transfer and solids separation. Two topics that have seen an increase in activity compared to historical reviews are membrane bioreactors and fate and occurrence of hormones and pharmaceuticals, which are referred to as microconstituents following current WEF terminology. Microconstituents as they relate to suspended growth reactors are covered in this review, while membrane bioreactors are reviewed in another section in this journal. Other subsections from the Treatment Systems section that might also be related to this section include: Wastewater Collection Systems; Biological Fixed Film Systems; and Modeling, Instrumentation, Automation, and Optimization of Wastewater Treatment Facilities. Many of the subsections in the Industrial Wastes, Hazardous Wastes, and Fate and Effects of Pollutants sections could also have some overlap with this section.