North Head STP:-The Innovative Application of Venturi Technology. Providing Enhanced Operational Security, Process Performance, and Minimising Chemical Consumption

North Head STP is located in Sydney, Australia, and provides high rate primary treatment to a population equivalent of 1.2millon people. Historically odour control for both the liquid and biosolids streams at the plant was provided by conventional packed tower scrubbing systems. These systems were overloaded, and suffered from associated operational problems placing the plant operating licence at risk.To resolve these issues Sydney Water commissioned the Central Odour Control Facility (COCF) Project. The COCF consists of the three stage wet chemical scrubbing system treating 43,000m3/hr (25,310 ft3/min) of foul air. The first stage is a venturi scrubber, designed to operate under modified process conditions to minimise chemical consumption. The second stage packed tower is a caustic/hypochlorite system coupled to an Odorgard™ reactor. The final stage has the ability to operate as either a caustic scrubber for final polishing, or as a conventional caustic/hypochlorite scrubber.The automated control system allows the three stages to re-configure the scrubbing system, between series or parallel operation, to increase treatment capacity from a peak hydrogen sulphide concentration of 292ppmv to over 600 ppmv.The venturi chemical re-use system, combined with a control system to modify process chemistry in the venturi, reduces hypochlorite consumption in the first stage by up to 75% compared to a conventional packed tower under the same duty. Overall the COCF saves between 30 to 40% of feedstock chemical(as compared to a conventional system), resulting in annual operational saving to Sydney Water of 220,000 (USD) due to the reduction in chemical consumption alone.The COCF successfully completed a 3 month performance test in the summer of 2008–2009. This paper describes the design features of the COCF and the reviews the plant's operation during the performance test period.