Study On The Influence Factors And Control Strategies For Activated Sludge Bulking By Microthrix Parvicella

Sludge bulking is still a challenge in the operation of activated sludge process. Previous studies summarized effective control methods, such as anaerobic selector, operational optimization, bactericide additives and so on. However, the validation and application of such methods are in short and required in actual wastewater treatment plants(WWTPs). In this study, by targeting the microthrix parvicella(MP) sludge bulking in a typical WWTP in north China, the influence factors, control strategies and emergency measures were studied in this paper, and a practical framework of early warning and control strategies for activated sludge bulking was proposed for operators.At first, after the literature review and field surveys, we correlated the influent loading rates and its gradient along process to the filamentous bacterial growth. By lab experiments, the growth of MP were obviously affected by the influent organic loading rates in the AAO, AO and step recirculating and influent. We examined the minimum concentration range of to control the growth of MP in different conditions.Secondly, we studied and optimized enhancing coagulation by dosage of coagulants before secondary clarifier, in order to deal with the early stage filamentous bulking. By batch experiments, we studied the influent of dosage on the size distribution of flocs, the settling velocity and the operation of clarifier. With the help of state point analysis(SPA) model of secondary clarifier, we established the optimizing strategy for the coagulant dosage. Furthermore, the cost-benefit analysis was conducted in a case study to demonstrate the necessity of process optimization.Thirdly, we studied the optimal dosage of hypochlorite to control the sludge bulking in emergency. The key of the techniques is the trade-off between inhibition of MP and maintain the activity of functional bacteria in activated sludge. By batch experiments of microscopic analysis, settling tests and ammonium uptake rate(AUR) tests, we identified the dosing effects of hypochlorite on the amount and morphology of filamentous bacteria, the particle size and settling velocity of activated sludge, and the ammonia oxidation efficiency. By the quantification model correlating the hypochlorite dosage and the settling velocity, as well as AUR inhibition, we proposed an integrated optimization method to easily find optimal dosage by surface loading of secondary clarifier and influent ammonium loading.At last, we summarized the above control techniques and case studies, and proposed a framework on the early warning and control strategies MP sludge bulkin, with the actual operation data in a case plant. The methods and strategies in this paper is expected helpful for process operators to control the sludge bulking.