Nitrogen removal optimisation from complex wastewater

Wallace Corporation Ltd, utilise a common biological effluent treatment plant to treat high strength wastewater from an industrial complex consisting a meat processing plant, tannery and meat rendering plant. The combined wastewaters entering the treatment plant contain high levels of nitrogen and substantial nitrogen removal is required to ensure compliance with the sites discharge limits.

While the site utilises a combination of discharge to surface water during high river flows and discharge to land during drier periods, maintaining compliance with the consented nitrogen loading rates to land has historically been difficult due to the limited performance of the biological nitrogen removal (BNR) system. In an attempt to overcome the challenges of the annual nitrogen loading rate, Wallace Corporation Ltd sought independent advice to assist with optimising the wastewater treatment plant, especially the BNR system.

An assessment of the waste stream entering the BNR reactors identified that the feed wastewater was carbon short, which was limiting denitrification, in turn preventing alkalinity return and further nitrification. Specific internal carbon sources were identified from one of the processing plants and diverted to the BNR reactor. Given that the BNR reactor was subjected to high strength nitrogenous wastewater, the operational control was modified to ensure pH depletion did not occur.

While the initial plant upgrades resulted in a significant improvement in nitrogen removal, additional opportunities were identified for further nitrogen removal that included changing the process trains and conversion of a reactor to a dedicated anoxic reactor.

The system optimisation was able to utilise existing infrastructure with only minor changes to pipework and control systems. Operational costs were reduced significantly as alkalinity augmentation was eliminated in its entirety and aeration needs were reduced by up to 15%.

The overall improvements to the BNR system have resulted in significantly improved nitrogen removal rates, to over 75% removal, and a reduction in annual nitrogen loading rates to available land by more than 35%. The reduction in annual nitrogen loading rates has created greater opportunities for the dairy farms receiving the treated wastewater, with farm managers now having the capacity to optimise nitrogen application, improving pasture growth and increasing farm yield.

While further improvements to nitrogen removal have been identified, Wallace Corporation can now look forward to greater flexibility with processing rates within the industrial plants and improved farm management