Piloting an MBBR to Treat Pond Effluent for Nitrogen Removal

Andreas Fischer, Louis Ortenzio (Lutra)

Oxidation pond-based wastewater treatment plants (WWTPs) are common across New Zealand. Many pond-based WWTPs in New Zealand inconsistently meet compliance requirements for nutrients based on several factors including retention time, pollutant loading, aeration intensity, temperature etc. As effluent nutrient loading becomes a greater focus across New Zealand environments, the expectations are for resource consent requirements on nutrient discharge to become significantly more stringent. This will make the feasibility of using oxidation pond-based treatment plants to meet resource consent requirements in the future a higher risk proposition. To address this risk, significant investment in these oxidation pond-based WWTPs is necessary.

Moving bed biofilm reactors (MBBR) provide a reliable technical solution to remove nitrogen from wastewater. Use of MBBR technology is established and widespread outside of New Zealand, but there are only a handful of full-scale installations within New Zealand. The MBBR technology is a cost-effective, low footprint treatment process, which can be used in combination with existing pond-based systems as a bolt-on augmentation for effective nitrogen removal at treatment plants.

The paper introduces the MBBR process basics. It discusses the design, configuration and performance of a two-stage pilot plant that treated wastewater from a municipal pond system for total nitrogen removal using acetic acid as the exogenous carbon source. The pilot trial went from 12 April to 5 August 2022, for a total of 114 days.

The plant operated during winter temperatures between 10 and 13°C. It was able to remove total ammoniacal nitrogen (TAN) and nitrate concentrations to below 1 mg/L. The measured empirical surface area removal rates (SARR) were comparable to expected theoretical design values.