Next steps in clean water oxygen transfer testing - A critical review of current standards

Current application of clean water aeration test standards for wastewater treatment systems is reviewed with a focus on problematic interpretations and practices of the most commonly and internationally used standards, edited by the ASCE (USA), CEN (EU/EFTA), and DWA (Germany). Remedy is proposed for these practices, with a view to inspire revision of existing standards toward better understanding and achievement of test accuracy with regard to oxygen transfer rate. Themes are (i) the importance of mixing for testing and (ii) the importance of mixing for the relevance of standard oxygen transfer rate for the treatment process, (iii) loop reactor testing and the impact of aeration layout, the circulation time scale and dispersion, (iv) tapered aeration testing, (v) impact of probe response time, (vi) sulfite interference at low temperatures, (vii) the effective depth concept for the dissolved oxygen saturation concentration, and standard corrections to the in situ saturation concentration, (viii) uncertainty estimates on oxygen transfer capacity and efficiency, and (ix) the prospect for simplification and harmonization among existing standards. It is suggested that tests based on an improved understanding of the effects of mixing, probe lag, sulfite oxidation kinetics, and fluctuations, will eventually result in the reduction of costly oversizing of aeration systems and improve the understanding of aeration system design and oxygen transfer rate vis-a-vis energy consumption and substrate conversion in biological wastewater treatment.