Investigating the Factors Affecting the Bulking Phenomenon in the Activated Sludge Aerobic Treatment System in the Petrochemical Plant Effluent

Abstract

Undoubtedly, the activated sludge process is one of the most common methods of biological wastewater treatment. Among the most common problems of activated sludge process systems is bulking of sludge (bulking). More than 50% of activated sludge wastewater treatment plants worldwide constantly or occasionally face this problem. In this case, the relative density of the flocs is low. It causes inappropriate sedimentation in secondary ponds and causes problems such as reducing treatment efficiency and imposing additional costs in the treatment and disposal of excess activated sludge. The current study, which was carried out on a laboratory scale (pilot) in the refinery unit of Shahid Tondgoyan Petrochemical Company, to investigate the factors affecting the creation of bulking. Factors include process parameters such as adjusting the ratio of input feed to microorganism (F/M), microorganism concentration, supply of nitrogen and phosphorus nutrients, dissolved oxygen, temperature, pH, and the use of cationic polyelectrolyte coagulant to improve the sedimentation rate of activated sludge. The optimal parameters in the amount of sedimentation are F/M equal to 0.35, MLSS in the range of ppm 2500 to 3000 ppm, nitrogen, and phosphorus nutrients relative to the amount of pollution (COD/N/P) in the range of 100/4/1 until 100/5/1, dissolved oxygen 2 to 3 mg/L, temperature 25-35 °C, pH range 8.5 and in the dose of 4.8 mg/gr TSS/L of cationic polyelectrolyte coagulant in 180 min. In general, by adjusting the process parameters in the indicated range, the amount of SVI can be controlled in the desired range of close to 150 mg/L.

Keywords

• activated sludge
• bulking
• svi
• microorganism concentration