Problems with bulking sludge in municipality wastewater treatment plants

摘要

Activated sludge process is the most widely used technique for wastewater treatment. It is based on the ability of microorganisms to form flocs when wastewater is aerated. Optimal formation of flocs is essential for sludge quality and clean water exiting the final clarifier. When sludge settles poorly it is generally described as a bulking sludge. This is a condition in which the sludge becomes very light, increases in volume, and will not settle well. The specific cause of sludge bulking is usually the overabundance of filamentous microorganisms in the activated sludge that extend from the floc and interfere with the compaction and settling of the sludge. Bulking is clearly a serious problem in many municipality wastewater treatment plants. It is the main cause of poor effluent quality, environmental damages, and in several cases sludge loss to the effluent. There are several ways of controlling bulking sludge. The growth of filamentous bacteria may be controlled by specific or non-specific methods. Non-specific methods involve the inhibition of the growth of filamentous organisms by the addition of chemicals, usually strong oxidants. In this thesis we investigated the effect of chlorine on activated sludge. In order to evaluate whether sodium hypochlorite can be used as an effective oxidant to reduce the amount of filament in activated sludge, a short term laboratory test was executed. Different dosing rates of chemical solution were added to the samples of aearation from our local wastewater treatment plant in Piran. Each sample was analysed and photographed with a phase-microscope. The main purpose of our experiment was to identify the level of chlorine concentration at which the activated sludge has a better composition.