Dewatering sludge for the food and beverage industry

Wastewater treatment plants that utilise primary and secondary treatment processes will generate two distinctly different types of sludge. In the food industry, the primary sludge typically generated by a Dissolved Air Flotation (DAF) system will often contain a high proportion of grease, whilst the secondary process will generate waste activated sludge which is essentially composed of bacteria and protozoa.

It is often thought that these two different types of sludge should be dewatered independently. There is certainly merit for operating separate dewatering plants on large scale installations where there are quite likely to be significant disposal cost benefits due to the characteristics and disposal routes of the two types of sludge. However, in smaller applications, the cost of installing two dewatering systems usually does not attract a viable payback.

This was the case recently at a Brisbane based food factory whereby due to council’s requirements, Hydroflux installed a process involving HyDAF for primary treatment followed by a Flootech Moving Bed Biological Reactor (MBBR) for secondary biological treatment.

In this particular case, as the volume of dewatered Waste Activated Sludge (WAS) was so low, there was no cost benefit in segregating the two streams, hence the sludge generated from these two processes was blended in a mixed storage vessel prior to dewatering in a Huber screw press.

One of the advantages of the screw press is that it can produce a very dry dewatered cake from slurries with very low concentrations of solids. In fact, many Huber screw presses are operating, and dewatering WAS directly from bioreactors where the concentration is basically the Mixed Liquor Suspended Solids (MLSS) which can be as low as 3000 mg/L. In this case, however, the combined slurry feed solids at approximately 5% was dewatered to spadable cake at more than 28% DS.

There are well over 2000 Huber screw presses operating worldwide in municipal STPs, mine sites and resorts and a variety of industrial applications including the food and beverage sector, construction and tunnelling.

For more information on the Huber screw press and treatment of primary or biological sludge in the food and beverage primary, please click here.