Nitrification preservation in activated sludge during curative bulking chlorination

Area of Science:

• Environmental Engineering
• Microbiology
• Water Treatment

Background:

• Activated sludge bulking is a common issue in biological wastewater treatment plants.
• Sodium hypochlorite is frequently used to control bulking by injection into the return activated sludge (RAS) stream.
• The impact of chlorination on the nitrifying flora, crucial for ammonia removal, needs careful consideration.

Purpose of the Study:

• To analyze the impact of sludge pass frequency at the chlorine dosing point on nitrifying flora.
• To evaluate the effectiveness of different pass frequencies in controlling activated sludge bulking.
• To assess the preservative effect of low chlorine concentrations on nitrifying activity.

Main Methods:

• Two pilot plants fed with synthetic wastewater were used.
• Sludge pass frequency at the chlorine dosing point was varied (one for pilot plant 1, two for pilot plant 2).
• A consistent chlorine dose (4.85 +/- 0.05 g/kg/MLVSS per day) was applied.
• Oxygen uptake rate was measured to monitor chlorination effects on nitrification.

Main Results:

• The study evidenced a preservative effect on nitrifying activity at the lowest chlorine concentration at the dosing point.
• This preservative effect correlated with the highest pass frequency (two passes per day).
• Monitoring oxygen uptake rate allowed early detection of chlorination's impact on nitrification before ammonia concentration increased.

Conclusions:

• Optimizing the pass frequency of sludge at the chlorine dosing point can mitigate negative impacts on nitrifying flora.
• Higher pass frequencies, associated with lower chlorine concentrations at the dosing point, are more protective of nitrification.
• Oxygen uptake rate is a valuable tool for real-time monitoring of chlorination effects in wastewater treatment.