An unusual occurrence of the coexistence of algae, oxygen and hydrogen sulphide from sulphate-reducing bacteria (SRB) in an overseas groundwater production system is described that had an interesting origin and some important implications both for groundwater professionals and for the water industry in general.

A deep, confined anaerobic groundwater source containing SRBs was being pumped to a new municipal water treatment works by underground pipeline from a wellfield some 3 km distant. Pumping continued at a steady rate of around 70 000 m3/d for a period of three months from start-up without significant problems. However, in the fourth month of operation, progressively serious fouling problems appeared in the sand filters that nearly caused a plant shutdown, with the consequent near loss of supply of a major drinking water source for a nearby city.

This paper describes the cause of those problems and highlights both the complex chain of events and the biochemical interactions involved, with particular emphasis on the unusual coexistence of SRBs and algae in a groundwater system. This apparent paradox is explained in terms of an unfolding sequence of seemingly unconnected events with a rather surprising origin.

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