Controlling effluent suspended solids in the aerobic granular sludge process.

Area of Science:

• Environmental Engineering
• Wastewater Treatment
• Biotechnology

Background:

• Elevated effluent suspended solids (ESS) challenge the efficiency of full-scale aerobic granular sludge (AGS) processes.
• Key contributors to ESS include sludge rising due to nitrogen gas release and washout of non-settleable particles like fats and foams.

Purpose of the Study:

• To identify and quantify the primary processes causing elevated ESS in full-scale AGS reactors.
• To develop and validate strategies for mitigating ESS in AGS systems.

Main Methods:

• Development of a mathematical model to simulate nitrogen gas degasification during the feeding phase in an AGS reactor.
• Implementation of nitrogen stripping and scum baffles in a full-scale Nereda® reactor for a 9-month operational period.
• Monitoring of biomass concentration, granulation grade, influent suspended solids, and effluent suspended solids.

Main Results:

• Nitrogen gas degasification during the feeding phase was identified as a major cause of sludge rising.
• A significant reduction in ESS was achieved by implementing nitrogen stripping and scum baffles.
• The modified Nereda® reactor achieved an average ESS concentration of 7.8±3.8 mg/L with an average biomass concentration of 10 g/L and granulation grade of 84%.

Conclusions:

• Sludge rising due to nitrogen gas release can be mitigated by pre-emptive nitrogen stripping before the settling phase.
• Washout of scum particles can be effectively reduced using vertical scum baffles.
• The combined implementation of nitrogen stripping and scum baffles offers a viable solution for reducing ESS in full-scale AGS wastewater treatment.