Fats, oils and grease management in separators.

Abstract

The fat, oil and grease (FOG) problem may be the 21st Century’s ‘perfect storm’: an outcome of urbanisation, population and economic growth, compounded by changing weather patterns causing inundation and exceedance of sewerage infrastructure capacity. FOG dramatically affects sewer capacity by gradually coating sewer walls with what is frequently termed a FOG compound. Often hard and difficult to remove, large aggregated masses of FOG combined with other ‘non-flushable’ product make headline news when they do break away and the term ‘fatberg’ has been coined to describe the enormity and destructive potential of the phenomenon. For food service establishments (FSEs), FOG presents hygienic issues, cost and operational disruption. Despite the global significance to developing economies, FOG mitigation management is challenged by inadequate knowledge of fundamentally important factors such as wastewater character and flow rates: factors that are essential to any attempt to improve mitigation efficiency. Source control can be taken as a central tenant and clear progress can be made in developing device test protocols that accommodate variable flows and particle size distributions (PSD) that are representative of actual loads. A number of positive outcomes may result: improved product performance standards, greater ‘trust’ in the product marketplace leading to wider market application serving small but ubiquitous FSEs. Innovation and product development will follow; ultimately it is hoped, turning the problem into a resource. This study seeks to characterise real wastewater FOG using a combination of microscopy and image processing to reveal the underlying PSD which directly translates to the extent to which FOG might be treated by separation. Separation and retention of FOG is then influenced by flow rate, which in turn drives the physical device size required. Spatial limitations in many FSEs prevent use of the large separators that are qualified under the only current Euronorm Standard. This work illustrates that FOG flow in real systems might be more appropriately conceived as a pseudo batch separation process, the full ramifications of which will be explored in FOG mitigation product development. Finally the use of a novel recirculating separator test platform is shown to facilitate study of both capture and retention of FOG present in droplets: the median size of which has been considered untreatable by conventional (low cost) separation technology.