Insights into the water depth for the non-aerated microalgal-bacterial granular sludge process via kinetic analysis

Abstract

Water depth, consisting of supernatant height and granule bed height, is a key parameter for the non-aerated microalgal-bacterial granular sludge (MBGS) since it is closely related to food-to-microorganism (F/M) ratio and light intensity. This study evaluated the effect of water depth on pollutants removal by MBGS using kinetic analysis. The results showed that the reduction of pollutants followed first-order reaction kinetic under F/M ratios of 0.177–0.273 g COD/ (g VSS d), but being poor at a lower F/M ratio of 0.084 g COD/ (g VSS d). Moreover, it was found that the light intensity of the granule bed surface could strongly affect the rate of pollutant degradation, and granule bed surface light intensities from 115 to 250 μ mol/m2/s were within the tolerable range of MBGS. Furthermore, water depth was eclucidated under outdoor light conditions, indicating that the desirable water depth might be 9–50 cm with the granule bed height of no more than 5 cm for MBGS. This study adds insights into the water depth for the non-aerated MBGS process, which is expected to be an important guideline for the further application of MBGS.