This document is an instructional module package prepared in objective form for use by an instructor familiar with operation and maintenance of a trickling filter wastewater treatment plant. Included are objectives, instructor guides, student handouts and transparency masters. This is the second level of a three module series and considers types of filters, filter loadings, recirculation ratios, design evaluation and normal and abnormal conditions. References needed are listed on the summary pages at the first of the module. (Author/RH)