MINI-REVIEW M. C. M. van Loosdrecht á C. M. Hooijmans D. Brdjanovic á J. J. Heijnen Biological phosphate removal processes Received: 3 April 1997 / Received revision: 9 June 1997 / Accepted: 14 June 1997 Abstract Biological phosphate removal has become a reliable and well-understood process for wastewater treatment. This review describes the historical devel- opment of the process and the most important micro- biological and process-engineering aspects. From a microbiological point of view, the role of poly(hydroxy- alkanoates) as storage material in a dynamic process and the use of polyphosphate as an energy reserve are the most important ®ndings. From a process-engineering point of view, the study of biological phosphate removal has shown that highly complex biological processes can be designed and controlled, provided that the impor- tance of the prevailing microbiological ecological pro- cesses is recognised. Introduction Biological phosphate removal (BPR) has become a well- established process and is applied in many full-scale wastewater treatment processes. The process as such does not only oer a good opportunity to remove phosphate in an ecient way from wastewater, it is also interesting to study for microbial ecological research. The organisms involved in BPR have a complex physi- ology in which the formation and consumption of storage polymers [polyphosphate, glycogen, poly(hy- droxyalkanoates) (PHA)] play a dominant role. Biological phosphate removal was discovered by ac- cident in full-scale wastewater treatment plants around 1959, and the ®rst full-scale processes were designed and introduced at the end of the 1970s. Initially most of the research was practically oriented, aimed at achieving systems for BPR and paying limited attention to the basic mechanisms underlying the phenomenon. In the 1980s the research ®eld became more interdisciplinary, with microbiological and process-engineering research resulting in a better understanding of the basic phe- nomena. Biological phosphate removal has been a ®eld of research where it was virtually impossible to make progress without an interdisciplinary approach. This is largely due to the complexity of the organisms involved, which require a good background in microbiological physiology for continuing research. However, groups applying a strictly microbial approach have often ig- nored important observations, leading to research on organisms that do not play a signi®cant role in the process. In this review we will brie¯y review the historical developments of the process, indicating the interaction between dierent research groups. Thereafter the es- sential microbiological aspects will be discussed brie¯y (for a more detailed discussion the reader is referred to Mino et al. 1997) followed by a longer discussion on the process-engineering aspects. Historical development The ®rst indication of biological phosphate removal occurring in a wastewater treatment process was described by Srinath et al. (1959) from India. They observed that sludge from a certain treatment plant exhibited excessive (more than needed for cell growth) phosphate uptake when aerated. It was shown that the phosphate uptake was a biological process (inhibition by toxic substances, oxygen requirement). Later, this so- called enhanced phosphate removal was noticed in other (plug ¯ow) wastewater treatment plants. Appl Microbiol Biotechnol (1997) 48: 289±296 Ó Springer-Verlag 1997 M. C. M. van Loosdrecht (&) á D. Brdjanovic á J. J. Heijnen Department of Biochemical Engineering, Delft University of Technology, Julianalaan 67, 2628 BC Delft, The Netherlands Tel.: 31 15 2781618 Fax.: 31 15 2782355 email: Mark.vl@STM.TuDelft.NL C. M. Hooijmans á D. Brdjanovic Department of Environmental Engineering, IHE-Delft, PO Box 3015, 2601 DA Delft, The Netherlands