Aerobic digestion of sewage sludge for waste treatment

Although Saudi Arabia is producing high gross national income per year in the Jeddah city, the sewage treatment and disposal systems does not meet the needs of people sufficiently. The disposal and industrial solid waste treatment and the collection of municipal sewage have been creating problems for a long time in Jeddah. The predictions showed that only 25% of raw sewage has been treated and cesspool system usage is still very common which increases underground water level. Moreover, the investigations depicted that the current location is unsuitable for the sewage and industrial dumping. In this sense, the processes of aerobic digestion carry out the organics through the presence of oxygen. It is well known that as a biological process, aerobic sludge digestion occurs in the existence of oxygen and in this process the bacteria in activated sludge consumes organic matter with oxygen and converts them into carbon dioxide. The achievement of aerobic digestion depends on using diffuser systems or jet aerator for sludge oxidation. The bubble diffusing is a cost-efficient diffusion method, however plugging occurs problems mainly due to sediment trapped in smaller air holes. The positive displacement blowers provides air with high volumes two digesters to establish aerobic conditions. Under these conditions, the bacteria digest the organic substances in the mixture quickly and convert them into carbon dioxide and others. For the reduction of pathogen content, elimination of offensive odors, and reduction/elimination of the putrefaction, during the processing the sludge is stabilized. The stabilization technologies are the lime stabilization, heat treatment, aerobic digestion, anaerobic digestion and composting. The composting process includes the aerobic degradation of organic matters and aerobic microorganisms which converting the organic matters into carbon dioxide and leaving relatively stable odor free has value for fertilizer products.