Phased upgrading for nitrogen removal--a low cost approach.

A phased approach has been adopted for upgrading the Luggage Point WWTP for nitrogen removal. Luggage Point WWTP (900,000 EP) is the largest plant operated by Brisbane Water. Management actions recommended by the South East Queensland Wastewater Management Strategy require the effluent total nitrogen levels to be reduced to less than 5 mg/L (50th percentile) by 2005. Luggage Point WWTP originally featured primary settling and a completely nitrifying activated sludge process. Effluent total nitrogen levels from the plant averaged 27 mg/L. Characteristics of the wastewater are highly variable, with primary settled wastewater having a COD/BOD5 ratio averaging 2.5, a TKN/COD ratio averaging 0.12 and effluent non-ammonia TKN averaging 1.8 mg/L (but up to 5 mg/L). The upgrade presented a substantial challenge, due to the limited available substrate for denitrification, a significant level of unbiodegradeable nitrogen and the low existing bioreactor HRT. The phased upgrading strategy was adopted to overcome these challenges most effectively and at low cost. The first stage of the upgrade included modifications to the existing plant infrastructure, without constructing new tankage. The existing bioreactors have been retrofitted using a five stage Bardenpho nutrient removal process, incorporating significant flexibility. The first phase upgrade has been commissioned and preliminary results indicate that the effluent total nitrogen has been reduced below the required first phase target of 8 mg/L. This represents a reduction of 3 tonnes of nitrogen per day entering Moreton Bay. The process is also operating with good stability and with excellent sludge settleability. The first phase of the upgrade will be completed for 25M AUS dollars, which represents a low cost of 28 dollars per equivalent person. Further upgrade works are likely to include separate treatment of the digested sludge dewatering centrate and advanced control of the biological process. The upgrade of Luggage Pt WWTP has shown that low effluent nitrogen can be achieved at low cost, through optimum utilisation of existing assets and a phased approach to modifications.