Sengupta, M. and Dalwani, R. (Editors). 2008 Proceedings of Taal2007: The 12 th World Lake Conference: 918-922 Use of Polyphosphate Accumulating Organisms (Pao) For Treatment Of Phosphate Sludge Shyam S. Bajekal and Neelam S. Dharmadhikari Department of Microbiology, Yashwantrao Chavan College of Science, Karad, Vidyanagar, KARAD – 415 124. (Maharashtra, India) E-mail: shhamus@yahoo.co.in, neelam_sd@rediffmail.com ABSTRACT Phosphate removal from wastewaters has been quite a problem over the years. The method largely employed these days is chemical precipitation although biological methods are regarded as preferable due to the fact that this phosphate can then be easily recovered in a relatively pure form. The role of Biological Phosphate Removal (BPR) in waste treatment often described as a `novel waste treatment tool’ has been known since some time. Microbial constituents of activated sludge remove phosphate by accumulating it as polyphosphate within their cells and are known as Polyphosphate Accumulating Organisms (PAO). Though this technology is presently available for phosphate removal from liquid wastes, there is no reason why it cannot be adapted and developed for the removal of phosphate from solid sludge generated by metal processing industries. This study reports precisely that kind of work done on phosphate removal from solid sludge generated from the painting department of a local industry. Microorganisms were enriched from garden soil and the solid sludge obtained from the industry using suitably amended nutrient media. Three isolates including two bacteria and a yeast showed tremendous potential in this respect in laboratory scale experiments. The mass of sludge was reduced by more than half (52 to 57%) and phosphate removal was to the extent of almost 78%. The removal of phosphate being due to intracellular accumulation by the organisms was confirmed by microscopic observation. The most efficient organism in this respect was found to be the yeast, confirmed by the microscopic observation and action of chitinase enzymes. Scale up studies for large-scale application that also include removal of Zn and Cu are in progress. INTRODUCTION Waste treatment technologies presently available for phosphorous stripping include physical, chemical, and biological treatments. Among these, the greatest interest and most recent progress made have been in the alternative biotechnological approach of Enhanced Biological Phosphate Removal (EBPR) used in activated sludge digestion processes. The EBPR has the potential to reduce ‘P’ down to very low levels at relatively lower costs (Strom, 2006). Under favourable conditions this removal from influent can be as high as 80 – 90%, achieving residual `P’ levels of less than 1mg/L in the effluent (McGrath and Quinn, 2003) This process involves a group of microorganisms (that include a variety of bacteria and yeasts), called Polyphosphate Accumulating Organisms (PAOs) that actively take up soluble `P’ from the system and accumulate it in the form of polyP granules (commonly known as `volutin’ or `metachromatic’ granules when observed by staining with the basic dye Toluidine Blue). This uptake, known as the `luxury uptake’ is seen to be enhanced when the organisms are alternated between a carbon- rich anaerobic environment and carbon-poor aerobic environment specially managed in an activated sludge digestion plant (Mino et al, 1998). McGrath and Quinn (2001) however, also showed that this uptake in many microorganisms was increased by 50% to 143% when the growth pH was acidic and that too in solely aerobic conditions in the absence of any kind of stress. EBPR technology has been developed mainly for treatment of liquid wastes considering the removal of ‘P’ from domestic sewage being disposed into surface water. Several researchers have also combined the removal of other waste materials with that of `P’ removal, such as metals, nitrates, nitrogen and carbon (Meknassi et al 2005). Chavez et al (2004) observed degradation of polychlorinated biphenyls simultaneously with massive accumulation of polyP in some microorganisms and concurrent accumulation of polyhydroxyalkanoates with polyP was observed in Pseudomonas strains by Tobin et al (2007). Several steel and metal processing industries generate phosphate wastes as solid sludge. Present methods for the disposal of such wastes are dumping or burning followed by dumping. The idea of applying the EBPR concept to such solid wastes was thus an attractive one. This paper reports results of work done by us in this direction on the solid sludge generated by a local metal processing industry.