Optimization of the design and operation of sewage treatment systems by means of activated sludge with extended aeration

Abstract

The activated sludge process with extended aeration has widespread use for the treatment of sewage from communities of various sizes, both under continuous and intermittent flow. It features high efficiency in removing biodegradable organic matter and may also ensure the biological removal of nitrogen. It can be adapted for phosphorus removal and the high level of clarification of the final effluent makes the disinfection process able to be efficient. It has high efficiency in removing biodegradable organic matter and may also ensure the biological removal of nitrogen. It can be adapted for the removal of phosphorus and the high degree of clarification of the effluent allows disinfection to occur efficiently. The main downside is its high operating cost, especially due to the high energy consumption and the high sludge production, relative to other processes. Recently, the process known as SND - Simultaneous Nitrification and Denitrification has been developed. In this process an activated sludge system with extended aeration has its aeration system tightly controlled so as to always remain low values of dissolved oxygen in the aeration tanks, around 0.5 mg / L. Nitrification is still possible, keeping the solids retention time high enough and, according to the theory, under these conditions the interior of biological floc remains anoxic and denitrification can take place. Thus, besides the incorporation of the important benefits of nitrogen removal, energy consumption is low, both for maintaining low levels of DO in the aeration tanks and the consumption of organic loading under anoxic conditions. The wastewater treatment plants that employ extended aeration activated sludge process can be upgraded for simultaneous nitrification and denitrification. The purpose of this research is to propose actions to improve the operational conditions of a WWTP by extended aeration activated sludge in full scale, treating 500 L / s of wastewater in order to obtain the removal of nitrogen from sewage and reduction in the cost of energy for aeration. Three sensors and controllers of dissolved oxygen will be installed along the length of each aeration tank of the Limoeiro WWTP, located in Presidente Prudente / SP, which will command the air flow to be sent by the blowers. It will be made physical, chemical and biological analysis of samples of the raw and treated sewage and sludge of the aeration tanks, mainly to evaluate the removal of organic matter and nitrogen. Respirometry tests must be made in order to determine the velocities of nitrification and denitrification. (AU)