Posted on 11 February 2015
HoSt has started the construction of a Thermal Pressure Hydrolysis (TPH) demo plant for sewage sludge at the wastewater treatment plant Echten, the Netherlands.
This TPH-technology is used to pretreat sewage sludge at high pressure and temperature with the aim of improving the biogas production and the dewaterability. The pre-treament allows additional energy-recovery and is cost effective.
The project is in collaboration with the operator of the wastewater treatment plant, water board Reest en Wieden. The demo plant is expected to be operational in March 2015.
Small scale experiences
HoSt has used a similar technology in biogas plants in the Netherlands and Romania in order to comply with EU hygiene regulations. In these installations, it was found that the biogas production increased.
In laboratory tests, which are conducted by HoSt, this also proved to be the case for the application of sewage sludge. With the demo plant at the WWTP in Echten HoSt wants to demonstrate that this technique is also suitable for treatment of sewage sludge on a larger scale.
Destruction cell structure of organic matter
In the demo plant, sewage sludge is brought under pressure and to a temperature of 160 degrees with the use of steam. With the TPH technology, persistent structures like cells in sludge are degraded.
After the pre-treatment the sludge goes to the digesters.
Here, the bacteria can break down more organic matter, which leads to a higher biogas production. Also, the dewaterability of the sludge is improved which leads to fewer disposal costs.
After the initial trial period, the plant will be operated for a long time during a joint measurement program to measure the effects on the existing digestion plant. The plant will treat a part (50%) of the total sewage sludge.
Water Board Reest en Wieden intends to take over the demo plant and to build a permanent plant if the results are positive.
Current digestion plant
In 2012, HoSt built a thermophilic digestion plant (on top photo) at WWTP Echten. Here water board Reest en Wieden treats annually 193.000 m3 sewage sludge from seven different wastewater treatment plants.
It was the first system in the Netherlands to treat sewage sludge in a thermophilic digester, followed by a mesophilic digester.
In an additional struvite reactor the phosphate is captured for the production of 200 ton struvite as fertilizer.
HoSt is one of the largest suppliers of bio-energy systems in the Netherlands and delivers complete systems, from anaerobic digesters for agriculture and industry, wood-fired boilers and combined heat and power plants to fluidised-bed gasifiers.
HoSt came into existence in 1999 as the result of a joint-venture between Holec Projects and Stork, two well-established suppliers of energy systems. Its activities are fully focused on the development of technology for the processing of biomass flows and the supply of systems for the sustainable generation of energy from biomass.
The current sludge treatment installation of water board Reest en Wieden at WWTP Echten includes digestion for production of biogas and recovery of phosphate as struvite.