Combined experiences of thermal hydrolysis and anaerobic digestion
The basic principles of batch thermal hydrolysis process (THP) are well known and have been put into full practice in 20 plants around the world. This paper reviews the historical development of the process and the latest thinking on the application of THP from a number of sources in Europe. An independent investigation of the vendors claims support the data for the benefits claimed to date. The need for energy efficiency suggests that only secondary sludge thermal hydrolysis is a good way of getting maximum benefits for minimum cost and energy demand. Furthermore the benefits can be obtained using a continuous THP that is more cost effective to operate. It is expected that there will be a number of plants in the future using continuous THP of secondary sludge mixed with unhydrolysed sludge. The research into this type of digestion and dewatering reviewed in the paper shows that benefits are expected to be at least 25% increase in digestion rate for short HRT digestion and an improvement of 8 points in dewatering. One full scale plant has been built in Germany where results are expected and others are being proposed.