The results show that the shocked sludge system under long time low load running,sludge aging and the lack of oxygen in part of secondary settling tank result in sludge bulking.

The causations of pit mud aging include low water content,high acidity of fermented grains,inappropriate pit mud proportioning,production process out of control,and unbalance pit mud fermentation etc.

Aimed at the problems such as chemical foam,septic floating sludge,denitrifying floating sludge and aged floating sludge occurred in a municipal wastewater treatment plant using the modified oxidation ditch for more than one year,the causes for mentioned problems were analyzed,and the solutions were given respectively.

General research about how to chose the coagulations and decolorants of printing and dyeing wastewater and the sludge drying;

The research progress of sludge drying equipment,common drying process types and their working principle at home and abroad were introduced.

The sludge drying device with rotor drum which uses coal powders as fuel is the main technique in the new design, and the dried sludge can be used as substituted fuel in cement plant.