Influence of saline stress in alternating pulses on aerobic granulation and resource production using different inoculum sources.

Aerobic granular sludge (AGS) is a promising technology for wastewater treatment, particularly for its ability to recover valuable resources such as polyhydroxyalkanoates, alginate-like exopolysaccharide, and phosphorus. However, achieving stable granule formation remains a significant challenge. Research has shown that the addition of salt can accelerate the granulation process and enhance bioresource production. The source of the seed biomass is also critical for the system's success, with most AGS studies using activated sludge as the inoculum. This study aims to compare granulation, reactor performance, and bioresource recovery outcomes using inocula from different sources while also evaluating the impact of saline stress. Four sequential batch reactors were monitored, differing in the type of inoculum sludge (biomass from an aerated biofilter or activated sludge systems) and the presence of NaCl in the feed. The saline feed alternated between cycles containing 5 gNaCl/L and conventional feed without NaCl. Osmotic pressure was found to favor granulation and solids accumulation in both types of biomasses. Reactors inoculated with activated sludge and subjected to salt addition achieved complete granulation more rapidly. In contrast, reactors inoculated with submerged aerated biofilter sludge exhibited higher solids concentrations. All systems demonstrated excellent chemical oxygen demand removal, with activated sludge reactors showing superior performance in ammonia and total nitrogen removal and bioresources recovery. Salt addition stimulated the production of extracellular polymeric substances and amino acids such as tyrosine and tryptophan while reducing the intensity of fulvic acid-like substances, irrespective of the inoculum type.