Colloide secures Whitchurch Waste Water Treatment Works contract in South East Wales, United Kingdom Colloide’s contract involves the design and build of a tertiary sand filtration plant for treating effluent from a humus tank prior to discharge. Colloide are acting as the specialist design & build contractor supplying 4no. 3m diameter Dynamic Sand Filters including all associated pipe work, valves, platforms, and compressors.