The aerated pond wastewater treatment system at DBC during the ammonia oxidation phase

Nitrogen Removal
R Kurup
Publication Date (Web): 8 January 2018

The anammox project was implemented at Dardanup Butchering Company (DBC) in Picton, Western Australia. The original refurbished wastewater treatment system of 0.5 MLD was implemented in 2011, and included construction of a high rate anaerobic reactor, and a BNR (biological nitrogen removal) system for nitrogen removal using the industry standard nitrification-denitrification pathway. The plant was designed to treat wastewater with a biological oxygen demand (BOD) of 9,000 mg/L and total nitrogen (TN) of 350 to 450 mg/L at a flow rate of 0.5 ML per day. 

The BNR system was in operation for over 3 years, but slaughtering process changes in the abattoir resulted in a low BOD, high nitrogen wastewater. This lack of available carbon (low BOD: TN ratio) significantly affected the nitrogen removal. The bio-available carbon (BOD) in the influent has, over the years, reduced to about 900-1,200 mg/L. This restricted the viability of the conventional nitrification-denitrification system to treat the TN to the required effluent value of 45 mg/L without external carbon addition. The plant was adding methanol for this purpose, costing $109,000 per annum. 

EEI was commissioned to examine the opportunity to implement a cost-effective alternative to the nitrification-denitrification BNR system implanted in an aerated lagoon that followed the conventional activated sludge process. The anaerobic ammonium oxidation (anammox) process has recently been receiving interest from the Australian water industry due to its many benefits. When compared with the conventional nitrification-denitrification pathway for nitrogen removal, anammox consumes only 38% of the oxygen required by the conventional method and does not require any carbon source. As aeration is one of the highest energy uses for a wastewater treatment plant, the application of anammox to the treatment process would significantly reduce the operating cost.

However, implementation of the anammox process has been proven to be difficult. Anammox bacteria have a very slow growth rate, with a doubling time ranging from nine days to two weeks. The anammox bacteria are also sensitive to sudden changes in environmental or process conditions. The operational control required for the anammox is still unclear to the water industry. However, the industry has determined that the potential advantages of the process outweigh any disadvantages. 

Several studies on the application of the anammox process have been conducted by research organisations with varying success. However, a full-scale trial and application of the anammox process in a WWTP has not been reported in Australia. EEI carried out laboratory research in 2013-14, and implemented the system by modifying the operation of the existing plant at DBC. In early 2016, an upgrade of the sensors and control system were completed for the treatment plant to validate and optimise the anammox process. Based on the continuous online monitoring, it has been confirmed that the nitrogen removal from the wastewater reaches over 90%, with a fraction of the energy required in comparison to the previous operations. In addition, excellent nitrogen removal was also observed during winter periods without any heating to maintain the anammox process below 20°C.

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