This is a repository copy of Note to Editor: Microalgae cultivation for wastewater treatment and biofuel production: a bibliographic overview of past and current trends.

The separation of sewage solids from water remains a fundamental issue in sewage treatment. Recent research undertaken by us has shown that hydrocyclone performance can be dramatically improved by reducing fluid shear at the vessel walls and improving the capture of the concentrate immediately adjacent to the wall. It has been shown that our approach allows the rotation (and therefore gravitational force) that can be applied to the fluid to be substantially increased whilst significantly decreasing turbulent mixing that diffuses enhanced particle concentration from the outer wall to the interior of the fluid.We have shown that low density solids (and, by implication, activated sludge) can be concentrated by this approach. The studies have consisted of four key components: conceptual numerical modelling of particle motion within flow through a rotating annular cavity; laboratory tests to demonstrate that low density solids can be separated by this approach; computational fluid dynamics modelling to determine the optimal inlet and outlet arrangements; and, field testing in activated sludge.A family of devices are been developed that are capable of concentrating activated sludge and sample conditioning prior to on-line chemical analysis.