Treatment System Uses Heat and Pressure to Destroy Sludge

Treatment System Uses Heat and Pressure to Destroy Sludge

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The AquaCritox sustainable sludge destruction and wastewater treatment system from SCFI uses super-critical water oxidation (SCWO) to destroy organic waste. The odorless system recovers byproducts such as phosphorus and carbon dioxide without producing hazardous emissions while generating renewable energy. The unit is available in four sizes (A10, A30, A100 and A200) for hydraulic loads from 1.1 to 22 tons per hour.

A sustainable alternative to management methods such as land application, landfilling and incineration, the Irish-based system grows out of 15 years of development. Acquired from Chematur Engineering AB in 2007, the technology was evaluated at demonstration plants in Sweden and Japan from 1998 to 2007. Results showed the technology destroyed organic sludge material, leaving nonleachable inorganic matter. In 2008, SCFI built its first demonstration plant in Ireland. The company has since received an order for a 60-ton-per-day plant in Youghal, Cork, Ireland, that will be operational by the end of the year.

The system works by pressurizing sewage to 3,205 psi and pumping it into an economizer, where it is heated to a super-critical temperature of 705 degrees F. Entering the reactor, heated sludge is mixed with oxygen, raising the temperature to approximately 1,022 to 1,112 degrees F. Excess heat is recaptured for the preheating process. In larger plants, steam can be used to drive turbines for power generation.

Residual effluent, cooled to ambient temperature and returned to atmospheric pressure, passes to the gas/liquid separator where carbon dioxide, nitrogen and oxygen are extracted. Inert and sterile inorganic materials can be treated in a separate step to recover phosphorus, or in the case of drinking water sludge, coagulants.

The remaining water has a COD of less than 5 ppm (better than tap water) and is suitable for discharge or reuse. Plant sizes range from 3,200 square feet (Model A10) to 18,800 square feet (Model A200). Modular systems arrive mounted on skids, fully pressurized and wet-tested. Installation and commissioning takes three months, with an order lead time of 12 to 18 months.

Maintenance is largely confined to the LOX supply area, ensuring there is constant feed to the high-pressure pumps. The system’s control unit limits manual intervention and continually monitors off-gas and effluent quality. It also allows for automatic switchover to a clean-in-place system that uses standby heat exchangers on a predicted cycle to prevent scaling and downtime.


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