Effect of salinity on removal performance and activated sludge characteristics in sequencing batch reactors

Area of Science:

• Environmental Science
• Microbiology
• Chemical Engineering

Background:

• Wastewater treatment plants face increasing salinity challenges.
• Understanding salinity's impact on activated sludge processes is crucial for effective management.

Purpose of the Study:

• To investigate the effects of varying salinity levels (0-20 g/L) on sequencing batch reactor (SBR) performance.
• To analyze changes in activated sludge characteristics and microbial community structure under saline conditions.

Main Methods:

• Operation of SBRs at different salinity concentrations.
• Monitoring removal efficiencies of ammonium (NH4+-N), total phosphorus (TP), and chemical oxygen demand (COD).
• Analysis of activated sludge properties, including extracellular polymeric substances (EPS), protein (PN), loosely bound EPS (LB-EPS), and dehydrogenase activity (DHA).
• Microbial community analysis using sequence analysis.

Main Results:

• Salinity significantly reduced the removal rates of NH4+-N, TP, and COD.
• Removals of NH4+-N and TP were particularly affected during the aerobic phase.
• Increased EPS content and improved sludge settleability were observed at higher salinities.
• Dehydrogenase activity (DHA) was inhibited by salinity, and microbial communities shifted, with Zoogloea and Thioclava dominating at low and high salinities, respectively.

Conclusions:

• Salinity detrimentally affects SBR removal performance and microbial activity.
• Changes in sludge characteristics, such as increased EPS and better settleability, occur under saline conditions.
• Microbial community shifts, driven by richness variations, are a key response to high salinity in SBRs.