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SCELSE researchers demonstrate phosphorus removal from waste water in tropical climate
12 October 2016

A key goal in waste water treatment is the removal of nutrients such as organic carbon (C), nitrogen (N) and phosphorus (P) – minimising their discharge to the environment where they may cause negative effects such as algal blooms and death of aquatic animals. 

In particular, phosphorus removal is performed by polyphosphate accumulating organisms (PAOs), which are microbes that accumulate P as they grow, a process known as enhanced biological phosphorus removal (EBPR). There is another group in the community called glycogen accumulating organisms (GAOs) which have a metabolism similar to that of PAOs, but cannot accumulate P in excess. Thus, if GAOs become highly abundant, the EBPR process may weaken or fail. 

EBPR was assumed to be unachievable in a tropical climate because previous studies done on lab-scale reactors showed that GAOs can outcompete PAOs at higher temperatures.

SCELSE researchers designed a prospective field survey to characterise the microbial community composition at the full-scale Ulu Pandan Water Reclamation Plant in Singapore, which experiences year-round tropical temperatures. They sampled the activated sludge 10 times over a two-month period and performed 16S rRNA gene amplicon sequencing, whole community shotgun metagenomics and metatranscriptomics, fluorescence in situ hybridisation (FISH), nutrient analyses and in situ tank measurements, and also transported the samples to a lab to test EPBR activity under anaerobic/aerobic batch experiments. 

Interestingly, they detected EPBR activity in the tropical sludge at a level comparable to two other EBPR plants in a cooler climate, and aerobic P uptake rate is actually higher than one of them. This activity is due to the presence of the key PAO Accumulibacter, which is in higher abundance than the GAO Competibacter

When they performed a full-scale perturbation experiment by reducing the oxygenation level in the aerobic tank to favour the growth of Accumulibacter, P-removal efficiency increased by 1.7 times.

SCELSE researchers showed for the first time that it is possible for EBPR to function in tropical climate in a full-scale treatment plant, unlike what previous results from lab-scale reactors suggested. This study provides clear scientific support that EBPR can be routinely applied in tropical regions to remove excessive P and for P-recovery in future sustainable developments.

Please click HERE for publication details.