Carollo Engineers maintains rapid small-scale column testing (RSSCT) equipment for evaluating the removal of contaminants by a range of adsorptive media. This equipment can be used to determine performance and cost data for adsorptive media such as granular activated carbon (GAC), ion exchange resins, activated alumina, and granular ferric hydroxide. Applications include the removal of natural organic matter to minimize by-product formation during downstream chlorination, and arsenic removal optimization studies.

Scaling equations, which are used to design the RSSCT tests are based on a dimensional analysis which maintains similitude with the full-scale process. In the case of GAC testing, carbon for the small-scale columns is obtained by grinding GAC from the full-scale application to a smaller size. Specific techniques are used for grinding, sieving, and washing the media to provide a uniformly ground GAC with a low fines content. In the proportional diffusivity design approach, the ratio between the full-scale and the small-scale contact times equals the scaling factor. The ground GAC is typically 1/10 to 1/20 the size of the full-scale carbon. Therefore, the length of time required to develop a breakthrough curve at the small scale is 10 to 20 times shorter than at the pilot- or demonstration scales.

The RSSCT columns are made of glass with inner diameters in the range of 4 to 15 millimeters. The media is carefully installed in the columns to avoid packing the media too densely, and to prevent the formation of air spaces within the bed. The media is supported with either glass beads or glass wool. The test water is pumped through the column in a down-flow mode at the specified flow-rate for the given conditions of contact time and temperature. The effluent water from the RSSCT column is sampled for various parameters. Typically, the target contaminant is measured at a frequency ranging from once per day to once per week. The effluent contaminant concentration data are plotted to monitor breakthrough as the study progresses. Samples may be collected to determine the potential downstream formation of by-products.

For a given application, Carollo prepares an experimental testing matrix and sampling and analysis plan at the start of the study. We then design the small-scale columns to simulate a range of possible full-scale designs. Typically, a 50- to 200-gallon batch of test water is collected as the feed water for the RSSCT system. Water quality parameters in the batch may be adjusted to reflect historical values. Testing can normally be completed in two to six weeks.