Norbert Dichtl

Influence of Surface Charge and Exopolysaccharides on the Conditioning Characteristics of Sewage Sludge

Mechanical cell disintegration is a new procedure in the process of sewage sludge treatment. The objective is to improve and accelerate the digestion of sewage sludge and to decrease the amount of sludge to be disposed. Cell disintegration on the other hand has a strong influence on the conditioning and dewatering characteristics. Especially the polymer emand of sludge increases significantly. A correlation between the polymer demand and the surface charge of the sludge particles as well as a correlation between the surface charge and the amount of exopolysaccharides (EPS) were pointed out. The amount of EPS is basically responsible for the polymer demand. Intracellular polysaccharides are released by means of mechanical disintegration and therefore the surface charge of the sludge increases. During the anaerobic digestion the EPS could hardly be degraded so the increased polymer demand of the disintegrated sludges is caused by non-degraded polysaccharides. Applying dual polymer conditioning the polymer demand of the sludge could be reduced.

Sludge treatment and reuse considering different climates and varying other conditions--export-oriented research for developing and threshold countries.

Sewage sludge accumulating during biological wastewater treatment has to be treated appropriately to avoid impacts on the environment and risks to public health. Especially pathogen reduction is necessary when sludge is disposed or reused in such a way that human contact is possible. In industrialized countries various sludge treatment technologies are available, but these are often only approved under local conditions. When exporting these technologies and experiences to other countries, a number of factors have to be taken into account including climatic, sociocultural, political and financial aspects. This paper gives an overview of current knowledge regarding sewage sludge treatment in developing countries. Various sanitation projects are realized worldwide and experiences from these plants already in operation are summarized. Results of on going laboratory experiments in climatic chambers regarding aerobic and anaerobic stabilization as well as lime treatment are shown to define the best-practicable sludge treatment technology for a certain climate. Options for final reuse or disposal are presented depending on end-product quality.