Team:Hong Kong HKU/project/phosphateremoval


Phosphate Removal

Phosphate concentrations in natural, non-eutrophic freshwaters are usually below 25 μg/L. Concentrations about 50 μg phosphate/L will generally leads to eutrophication. To prevent release of phosphate high waste waters into natural environment, it is important to secure high phosphate removal efficiencies from sewage. In sewage treatment plants, two main process are employed, either separately or in combination: chemical precipitation and “Enhanced Biological Phosphate Removal”.

Chemical Precipitation

Chemical precipitation is the traditional, and still the most common method of P removal from wastewater streams. Common chemicals includes ferric, ferrous, aluminium, or calcium salts. Yet the technique is reliable and capable of meeting the phosphate discharge limits, it is expensive due to the cost of precipitants treatment, potential needs for an additional tertiary filtration step of because of heavy metal contamination and disposal of large excess volumes of sludge produced.

Enhanced Biological Phosphorous Removal (EBPR) Process

EBPR process involves the exploitation of phosphate-accumulating microorganisms (PAOs) in activated sludge. Going through specific stage of EBPR, PAOs take up the available phosphate from the surrounding environments (sewage) and convert into cytosolic polyphosphate (PolyP). PolyP consists of a linear chain of phosphate residues linked together by high energy phosphoanhydride bonds and ranges in length from 3 to greater than 1000 orthophosphate residues.

Inspired by these Enhanced Biological Phosphorous Removal process and phosphate-accumulating microorganisms, we wonder if we can engineer natural existing PAOs or new microbes to further enhance their phosphate uptake efficiencies. Since isolation and manipulation techniques of PAOs are far from mature, we use the well-established model E.coli to test our idea.