MORPHOCHEMISTRY IN SECONDARY SLUDGE FILTRATION CAKES - A CASE-STUDY

Light Microscopy, Transmission Electron Microscopy (TEM, EDXS), and Fo urier Transform Infra Red MicroSpectroscopy (FTIRMS) were used to desc ribe the organization and chemical distribution of major constituents in a sludge filtration cake. Samples were obtained from a municipal wa stewater treatment plant using conventional ferric chloride and lime s ludge conditioning. Various samples collected at different stages of t he process were embedded in an Epoxy resin after acetone-dehydration, and sectioned using an ultramicrotome. The thickness of the sections w as adapted to the experimental techniques used. TEM showed that in the activated sludge, bacterial colonies, isolated bacteria and debris ar e trapped within a gel matrix of exocellular polymeric substances, whe reas those same components are compacted and distorted in the filtrati on cake. Furthermore, conditioning chemicals appeared in the cake as a morphous aggregated colloids and acicular particles which do not form inside the colonies. A chemical mapping was obtained by determining an d integrating FTIR bands characteristics of specific components of the cake. Preliminary results showed that the amounts of resin can be use d to assess the relative compacity at different levels of the cake. (C ) 1997 IAWQ. Published by Elsevier Science Ltd.