The Role of Hydrolysis for Advanced Digestion

Many of the the companies which have been involved in sewage sludge digestion and are the most experienced in the field are using thermal hydrolysis within their chosen processes. These companies tend to develop their own slant on optimising the hydrolysis stage and to use their own trade name, neverthelsss there is a common reason for doing this and it is to increase the rate of conversion of organic matter, to reduce retention periods within the digester and improve gas yields.

We have uploaded a new page with the title "Hydrolysis, Sewage Sludge and Anaerobic Digestion", to the Anaerobic Digestion Community web site, based upon Veolia's experience with using hydrolysis a part of the digester systems, which provides more information on this.

Sewage sludge digestion has been carried out by anaerobic digestion at some UK sewage works since in the UK sewage sludge first began to accumulate in the new activated sludge type sewage works built from the 1950's in inland areas. However, most of it was simply discharged to the sea untreated until the 1970s including huge tonnages from our large cities. Fortunately, those days are long past with the practice outlawed by the European Union, and ever since then, the huge volumes produced have been treated and disposed of by a variety of methods. All are expensive, and the lowest cost option of discharge untreated to land, brings with it health and soil-metals build up problems, such that its use has to be limited.

As a result, safe and cost-effective disposal of sewage sludge is, without doubt, one of the biggest challenges now facing the wastewater industry. The high cost of energy means that some disposal routes such as incineration which were once favoured are less viable, and others have ceased to be economic.

However, as one technology fades another shines. That process is thermal hydrolysis, and when combined with anaerobic digestion they are a great combination.

Companies such as CAMBI, Monsal, and Veolia Water Solutions & Technologies have recognised this and produced their own proprietary systems. More about advanced AD with hydrolysis.