Drying and incineration unit at Sloka WWTP in Jurmala
Sloka WWTP in Jurmala is designed for a working capacity of 35 400 PE and treats municipal wastewater via biological phosphorus and nitrogen removal in a circular basin without primary settling tank, no industrial wastewater is accepted. Sludge treatment consists of a two-chamber sludge storage tank, a drum thickener and two decanter centrifuges. Currently approximately 10 tons of dewatered sludge is landfilled daily.
Within the framework of IWAMA project, Sloka WWTP was piloting a drying and incineration unit (hereafter, unit). Unit is designed to reduce the amount of surplus sludge from the wastewater treatment process, using vapor of thermal decomposition of volatile products and non-condensable gases as fuel. It is integrated into the existing technological chain of WWTP.
Components installed in the solution
Unit setup consists of the following sections:
- heating section with automatic control of burning process;
- dryer section where wet sludge is treated with heat while moving through three stage drying feeders;
- gasification section where dried sludge is gasified in microwave assisted gasification process.
Heating unit can work on any small particle biomass – pellets, wood chips, etc., grinded refuse-derived fuel (RDF) can be used too. Wood pellets are initially used in Sloka WWTP. Heating unit is equipped with three stage burning air supply/control to achieve a precise and full burning in vortex burning chamber. This is followed by blowers to produce high speed heat flow through dryer in opposite direction of sludge movement. This way an effective drying is achieved.
Different temperatures, flow speed and sludge moving patterns were tested for process optimization. First tests showed that sludge moisture per cent value from initial 82% to 30% could be achieved, however, process will be further optimized to achieve value < 30% (20-25%).
Dried sludge is moved to gasification section where the end product is ash, which is approximately 11% from dry sludge weight. Thus, waste activates sludge accumulation in the environment will be substantially decreased.
Gas from gasification process is fed to torch and burned today, but it is planned to integrate it into heating or into a small scale electricity generator. Furthermore, it has been also discussed to study the potential use of sludge ash in the production of building materials, excluding landfilling in general.
Energy consumption of the unit is 23.2 kW, from where energy consumption for dryer, heating and gasification are 8.2kW, 10kW and 5kW, respectively.
Overall, as a result of this particular pilot project, an innovative approach has been implemented towards solving the problem of small WWTP surplus sludge utilization.