Heat treatment of sludges to facilitate dewatering is discussed in Section 7.51 and shown in Figure 7.51.1. After the sludge has been conditioned with heat and pressure, it has a lower COD and can be readily dewatered without chemicals in a decanting and vacuum filter unit.
This process grinds the sludge and pumps through a heat exchanger into a reactor where it is held for 30 to 60 min while steam heats it to 380°F and maintains a high pressure of 160 to 250 psig. The system is a continuous process, and the high-temperature sludge leaving the reactor is used to heat the incoming sludge. The process was developed in Europe by Porteous in the 1930s and is now being applied in the United States. No chemical additives are required to make the treated sludge compatible with vacuum filtering.
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