Control and optimisation of a high strength nitrogen industrial wastewater BNR plant

Meat rendering plants produce very high strength nitrogenous wastewater that requires intensive monitoring and control to ensure adequate nitrogen removal. A North Island based rendering plant that produces meat & bone meal, tallow and blood products, with raw wastewater nitrogen concentrations of 730 mg/L, found that its biological nitrogen removal (BNR) part of the wastewater treatment plant was operating poorly, generating a lot of odour and was not meeting the discharge consent compliance limits.

A rigorous troubleshooting programme was initiated to identify the cause of the treatment deterioration. Processes were recognised early during the troubleshooting phase and substantial process train changes were initially implemented to prevent further overloading, stop odours and to allow the BNR plant to recover quickly without compromising the processing ability of the rendering plant.

Following the initial plant reconfiguration, a period of close monitoring was undertaken to identify any potential areas for further system improvements. It was identified that the variable nature of weekly and seasonal processing was resulting in highly variable operating conditions. Alkalinity and carbon level entering the BNR system were marginal for the nitrogen requirements and that a reduction in either parameter was resulting in a rapid decrease in nitrogen removal. Key improvements made to the system included better management of weekly load variations on the BNR system, the inclusion of supplementary carbon to maintain nitrogen removal during seasonal processing fluctuations and an additional system reconfiguration of the BNR system to provide for effluent polishing.

The overall changes to the treatment system have resulted in more consistent loads on the BNR system, enabling consistent nitrogen removal, from an influent nitrogen concentration of 730 mg.NH4-N/L to below 50 mg.NH4- N/L and 80 mg.NO3-N/L. All system upgrades were implemented without significant capital expenditure.