Meso and micro-scale effects of loading and air scouring on nitrifying bio-cord biofilm

Abstract

The municipal wastewater treatment industry is currently facing the challenges of increased loading, restricted land availability and stringent discharge regulations. This results in the need for new, compact and cost-effective biological wastewater treatment technologies. The study focuses on the performance of the stand-alone bio-cord biofilm reactors for post carbon removal nitrification at both the meso and micro-scale. In particular, it investigates the effects of ammonia loading, various bio-cord substratum and air scouring on nitrifying kinetics, biofilm mass detachment, biofilm porosity and morphology along with embedded biomass viability. At low to moderate loadings of 0.8 g NH₄⁺-N m⁻² d⁻¹ and 1.6 g NH₄⁺-N m⁻² d⁻¹, the various substratum show stable and high ammonia removal efficiencies of approximately 97%, while unstable performance was observed at a high ammonia loading of 2.4 g NH₄⁺-N m⁻² d⁻¹ for all substratum. Air scouring of the substratum as a means of counteracting instability did not stabilize the performance of the system. Biofilm detachment rates were observed to increase with increasing loading rate. Improved detachment stability was observed with applied air scouring of the substratum. Biofilm porosity was shown to decrease with increasing ammonia loading rates for all substratum, with air scouring of the substratum showing an increase in the biofilm porosity. Embedded biomass viability testing shows that the activity of the bacterial cells and not cell coverage is related to kinetic performance.