Alkalinity role in recovery of disintegrated halophilic aerobic granular sludge treating high salt-alkali wastewater: Insights into community ecology of fungi and bacteria

The overgrowth of filamentous fungi is a major factor causing the disintegration of halophilic aerobic granular sludge. However, controlling filamentous fungal overgrowth and sustaining the niche balance between fungi and bacteria remain largely unknown. In this study, the influence of alkalinity on the fungal and bacterial community ecology were revealed when treating high salt-alkali wastewater, proposing a strategy to restore disintegrated HAGS. Changes in alkalinity resulted in remodeling the community ecology of fungi and bacteria. With an increase in alkalinity, the population diversity of fungi and bacteria declined; fungi in the Nectriaceae family were enriched, and the relative abundance of bacterial genus TM7x gradually increased. The growth of filamentous fungi was significantly inhibited under high alkalinity, and bacteria obtaining a greater substrate competitive advantage. When the alkalinity was restored to 600 mg CaCO3/L, the decrease in the fungal population size and the increase in the secretion of extracellular polymeric substances promoted the reconstructed of dense granules. This study found that alkalinity could make influences on the substrate competitive advantage of fungi and bacteria, and thus filamentous fungal overgrowth can be controlled. This finding provided a solid theoretical basis for controlling fungal overgrowth and restoring the structural stability of disintegrated HAGS.