Proceedings

Already across AMP7 and expected for AMP8, there are hundreds of new or tightening phosphorus removal schemes across the industry. The default solution for many of the water companies is to install chemical dosing and tertiary treatment as this appears to be the simplest solution with the lowest capital cost. However, the main chemicals used for P precipitation (iron and aluminium salts) are not a sustainable resource and the demand is expected to exceed the supply in the not-toodistant future. Population growth and supply chain issues also exacerbate this issue. Therefore, an alternative solution that does not rely on unsustainable chemicals needs to be established.

Enhanced biological phosphorus removal (EBPR) is one such alternative that is well understood and has been implemented on activated sludge plants for several decades. However, one of the main limiting factors of successful EBPR is the amount of volatile fatty acids (VFAs) that are present within the incoming wastewater which can vary massively from site to site. These VFAs act as a food source for phosphate accumulating organisms (PAOs) that perform the EBPR; hence low VFAs means low phosphorus removal.

Primary sludge fermentation is a known method of naturally producing VFAs from primary sludge. The VFA rich water can then be dosed back into the main treatment line to boost the performance of EBPR in an activated sludge plant. This consequently reduces or completely eliminates the need for chemical precipitation, making it a more natural solution.

This paper gives an overview of the fermentation process and highlights a unique primary sludge fermentation process which aims to maximise VFA production using advanced process control.

Keywords
Enhanced biological phosphorus removal, Primary sludge fermentation, Reduction in chemical usage