Carbon availability regulates fungal and bacterial populations in halophilic aerobic granular sludge treating saline wastewater.

Abstract

Fungal overgrowth in halophilic aerobic granular sludge (HAGS) is a severe problem, leading to granule disintegration. However, it is still mostly unclear how to control fungal overgrowth. This study explored the effects of carbon availability in saline wastewater with a salinity of 20 g/L on fungal and bacterial population sizes, community compositions, and network interactions in HAGS by manipulating different carbon-to‑nitrogen ratios (C/N). Bacterial population size increased from 6.42 × 10⁶ copies/ng DNA to 8.67 × 10⁶ copies/ng DNA as the C/N ratio increased from 4 to 20. In contrast, fungal population size decreased from 1.24 × 10⁶ copies/ng DNA to 8.05 × 10³ copies/ng DNA. The maximum removal rate of ammonia by fungi decreased from 5.02 ± 0.04 mg·L^-1·h^-1 to 1.72 ± 0.30 mg·L^-1·h^-1. Nitrosomonas, Thauera, and Planktosalinus competed for nutrients with the dominant fungi Cosmospora, being in antagonism. Carbon availability in the saline wastewater could regulate the population of bacteria and fungi, laying a theoretical foundation for controlling HAGS disintegration.