Wastewater treatment viabiliry is a pressing problem, espeeially for small eommunities in regions eharaeterised as "sensible". I t is, rherefore, neeessary to develop new low eost installation and operation teehnologies. These must effieient!y remove organie and nutrient loads, allowing water reuse and biomass utilisation in order to reduee operating eosts. Stabilisation ponds are among these effieient low eost teehnologies, neverrheless, their dependency on climate condirions ealls for funher srudies on rheir applieabiliry in extreme climatie gradienrs. Treatment systems based on mieroalgal eultures are partieularly suitable beeause of rheir phorosynrhetie eapaeiry, whieh allows in situ oxygen generation for biodegradation of organie matter and its transformation ro utilisabJe biomass (SHELEF 1980, RJCHMOND 1986). Besides mixotrophie and autotrophie assimilation of nutrients, photosynrhetie aetiviry-related physieo-ehemieal proeesses (mainly phosphate preeipitation and ammonia removal) eontribute to a reduetion of pathogens in the reeeiving waters (BOROWITZA 1988).