Towards more efficient sludge drying

Within the framework of the quest for the circular economy and the energy efficient water treatment systems being developed worldwide, the emergence of a process destined to enhance and simplify the complex process of WWTP sludge drying is of particular interest. BioCon™ is a process developed by Veolia Water Technologies.

Considered one of the safest systems in its field, BioCon™ is a dual conveyor, low temperature process for drying mechanically dewatered sludge at municipal and industrial facilities. One of the main distinguishing features of this technology is the system by which the sludge is deposited in the form of fine strings on the first drying belt. This affords greater exposure to the drying air and also enables control over the final degree of sludge dryness, which can be as high as over 90%.

BioCon™ is currently implemented in over 22 facilities worldwide. Seven of these are located in the United States and the remainder in Europe, particularly in France, home to the largest facility, the Marquette-lez-Lille WWTP in the north of the country, which treats over 16,800 tonnes of dewatered sludge per annum.

In Spain, the Lagares WWTP in Vigo, currently under construction, is a pioneering facility in terms of the implementation of this Veolia Water Technologies solution. Thus, this €230 million, 800,000 population-equivalent plant is set to become one of the most advanced water infrastructures to be developed by the Ministry of Agriculture, Food and Environmental Affairs.

Another great benefit of BioCon™ is the large number of options it provides in terms of sludge recovery or final disposal. The dry sludge can be reused in agriculture, composting, incineration and co-incineration.

Energy efficiency

Apart from ease of operation and maintenance, flexibility is another great advantage of the BioCon™ drying process. It can be installed with a number of different configurations to meet the specific needs of the facility, thereby resulting in greater energy efficiency. With the BioCon™ Energy Recovery System (BERS), sludge is reduced to ashes with a volume of approximately 10% of the sludge generated at source at the WWTP. All this is carried out with thermal energy generated in the process itself, using sludge with a dry matter content of 20-23% as raw material.

The BioCon™ Energy Exchange System (BEES) enables recovery of the residual energy from the drying process. This energy, in combination with anaerobic sludge digestion, can be used to heat the digesters, thus maximising the use of biogas in the thermal drying process and significantly reducing the need for an external supply of energy.

This thermal drying process is also very flexible with respect to alternative energy sources to create the heating medium needed for the heat exchanger in the dryer. Hot air, hot water, steam or thermal oil can be used and the system can be combined with CHP gas engines, boilers, steam generators, air heaters, or with the BERS or BEES systems.

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Article published in: FuturENVIRO #33 September 2016