Monitoring, isolation and characterization of Microthrix parvicella strains from a Chinese wastewater treatment plant

Microthrix parvicella is a filamentous bacterium that frequently causes severe bulking events in wastewater treatment plants (WWTPs) worldwide. In this study, sludge properties and dynamics of filamentous bacteria in a Beijing WWTP seasonally suffering from M. parvicella bulking were continuously monitored over a duration of 15 months, and the correlations between M. parvicella and operating parameters were evaluated. The predominance of M. parvicella was observed at low temperatures (14–18.8 °C) with the relative abundance of around 30% (estimated by both qPCR and FISH analysis). Using micromanipulation technology, 545 filaments of M. parvicella were micromanipulated from bulking sludge (SVI > 180 mL g−1) on six different media. After 3-month purification and enrichment, six strains, phylogenetically closely related to Candidatus Microthrix parvicella, were successfully acquired on R2A medium (20 °C) in pure cultures. Considering the limitation and extremely slow growth rate of M. parvicella filaments, newly isolated strains represent valuable sources for further investigations on the physiology and behavior of this filamentous bacterium, with the focus on the establishment of bulking control strategy.

Control of Microthrix parvicella and sludge bulking by ozone in a full-scale WWTP

Bulking and rising sludge are common problems in wastewater treatment plants (WWTPs) and are primarily caused by increased growth of filamentous bacteria such as Microthrix parvicella. It has a negative impact on sludge settling properties in activated sludge (AS) process, in addition to being responsible for foam formation. Different methods can be used to control sludge bulking. The aim of this study was to evaluate the dosage of on-site generated ozone in the recycled AS flow in a full-scale WWTP having problems caused by M. parvicella. The evaluation of the experiment was assessed by process data, microscopic analysis and microbial screening on the experimental and control line before, during and after the period of ozone dosage. The ozone treatment resulted in decreased abundance of M. parvicella and improved the settling properties, without impairing the overall process performance. Both chemical oxygen demand (COD)- and N-removal were unaffected and the dominant populations involved in nitrification, as analysed by fluorescent in situ hybridization, remained during the experimental period. When the ozone treatment was terminated, the problems with sludge bulking reappeared, indicating the importance of continuous evaluation of the process.