More and more focus is going into establishing more sustainable approaches for wastewater
treatment (WWT) in South Africa as well as around the world. Governments are beginning to
enforce more economical solutions for WWT which will have less impact on costs as well as on
land area requirements. Effective solid-liquid separation in biological wastewater treatment is
an important step in the process as it has a major impact on effluent quality. Traditionally
this has been achieved using Secondary settling tanks (SSTs) for liquid solid separation in
combination with a biological reactor (for biological degradation of organic matter). SSTs
however require a large space which can become onerous on land requirements. Immersed
membrane bioreactors (iMBRs) functions by solid-liquid separation taking place by the passing
wastewater through membranes. These membranes are immersed in the aeration zone of the
bioreactor. This thus eliminates the requirement of SSTs and are becoming more widely used to
treat various types of wastewater due to the decreasing cost of membranes and the resultant
reduced plant footprint. This therefore makes MBR a more sustainable option. Membrane
technology has a high initial capital requirement although this can be offset against the
savings resulting from the omission of SSTs and a decrease in land area requirement. (Ramphao
et al. 2004)
