A novel strategy for rapid development of a self-sustaining symbiotic algal-bacterial granular sludge: Applying algal-mycelial pellets as nuclei

Algal-bacterial granular sludge (ABGS) is a promising technology for wastewater treatment, benefiting from the synergetic interactions between algae and bacteria. However, the rapid start-up of the ABGS system is not trivial. Herein, a novel strategy was proposed by applying the algal-mycelial pellets (AMPs) as the primary nuclei for accelerating the development of a self-sustaining symbiotic ABGS system. The results indicated that by using this strategy complete granulation was shortened to 12 days, much shorter than the control system without AMPs dosage (28 days). The ABGS had a large particle diameter (3.3 mm), compact granular structure (1.0253 g/mL), and excellent settleability (SVI30 of 53.2 mL/g). Moreover, 98.6% of COD, 80.8% of TN and 80.0% of PO43--P were removed by the ABGS. The nuclei of targeted algae (Chlorella) and filamentous fungi (Aspergillus niger), the enhanced production of extracellular polymeric substances (especially proteins) and the enrichment of functional bacteria (such as Neomegalonema and Flavobacterium) facilitated the granules development. The low surface free energy (-69.56 mJ/m2) and energy barrier (89.93 KT) were the inherent mechanisms for the strong surface hydrophobicity, the easy bacterial adhesion, and the short granulation period. This study provides an economically feasible approach to accelerate ABGS granulation and sustain system stability.