CWA Services has received a contract to design and construct an AMTREAT® sludge liquor treatment plant for the Southern Water Sludge Treatment Centre in Ashford Kent. The contract was placed by Black & Veatch Ltd, the main contractor responsible for upgrading the site.
"AMTREAT® is a purpose-designed, high rate activated sludge process specifically developed for treating high strength ammonia wastewaters" explains David Spurr, ACWA's Business Development Manager. "As legislation on allowable levels of ammonia and total nitrogen in treated wastewater discharged to water course gets ever tighter, returning sludge liquors with high concentrations of ammonia has the potential to overload the main treatment works. In this situation, it is often necessary to increase treatment capacity on the main treatment works or provide a dedicated side-stream facility specifically for the sludge liquor. AMTREAT® is a side-stream technology that delivers a cost-effective solution for reducing ammonia and total nitrogen to acceptable levels in sludge liquors, allowing them to be returned to the main treatment works. This innovative approach reduces load on the main treatment processes and safeguards the final discharge consent."
"The advantages of a high rate ammonia treatment process such as AMTREAT®", says David, "are that the technology and equipment is familiar and easy to operate and control. Due to the significantly higher ammonia loading rates achieved within an AMTREAT® process, it is possible to install the plant on a relatively small footprint when compared with conventional activated sludge treatment processes. Full nitrification of effluent streams with ammonia concentrations of 3000 mg/l and typical ammonical nitrogen removal rates in excess of 97% are achievable."
The Ashford Sludge Liquor Treatment Plant has been designed as a twin stream AMTREAT® process, usually operating at 50% flow per stream, yet with each stream having the capability to handle a throughput of 100% flow.
The liquor treatment plant comprises a balance tank with mixing facility, anoxic tanks, AMTREAT® reactors with fine bubble diffused air systems, stilling tubes and a system to prevent high levels of solids being returned to the main treatment works. A dedicated sodium hydroxide storage and dosing system will provide the required supplemental alkalinity necessary for the nitrification process. The provision of cross connecting pipework through the main process stream will allow flexibility for operation and maintenance.
When fully operational, the process conditions for nitrification will be maintained when the temperature of the influent liquors is above 20 degrees C with an optimum temperature of 25 degrees C. Operation at this temperature overcomes issues associated with seasonal variation that can adversely affect more conventional activated sludge designs. The Ashford plant will be capable of meeting a discharge consent of 200mg/l BOD, 200mg/l SS and and 50mg/l ammoniacal nitrogen by achieving removal rates in excess of 97% and full nitrification of the influent liquor stream ammonia concentrations of 3000mg/l and BOD levels ranging from an average of 650mg/l to 550mg/l maximum.
The twin-stream AMTREAT® process, designed for installation at the Ashford WwTW, will provide a dedicated and cost-effective means of treating sludge liquors from the sludge thickening, dewatering and drying processes. The system will be capable of handling average throughputs of 1200m3/day to maximum levels of 2100m3/day, with typical removal rates in excess of 75% for COD and BOD.
Central to the AMTREAT® process is a purpose-designed, fully mixed, reactor vessel which contains suspended aerobic cultures of predominantly nitrifying bacteria. By careful control of the key design parameters of temperature and the ratio of carbonaceous material to ammonia and alkalinity, the conditions within the Reactor encourage the proliferation of nitrifying bacteria. These become and remain the dominant species. It is this population of nitrifying bacteria that converts ammonia, by complete oxidation, to nitrate.
To ensure complete nitrification in biological treatment systems, it is often necessary to provide a supplemental source of alkalinity. It may also be necessary to provide a heat exchange system to raise or lower the temperature of feed liquors to the required operating temperature. Denitrification can be achieved by the addition of pre-and/or post-anoxic tanks. Depending on the liquor source, it may be necessary to provide a supplemental carbon source to ensure full dentrification.
Whilst the installation of AMTREAT® for Southern Water at Ashford is used for the treatment of sludge liquors, the process is also suitable for treating other high strength ammonia streams such as those found in industrial wastewater.
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© Press Release 2009
