ADSORPTIVE PERFORMANCE EVALUATION OF GRANULAR ACTIVATED CARBON IN AQUACULTURE AND AQUARIA: A SUCCINCT METHOD

A principle concern for aquaculture operations and aquaria is the control and removal of dissolved organic matter (DOM), to the ends of maintaining aquatic health, controlling biofiltration efficiencies, and water clarity.  Besides the roles of mechanical and biological filtration, activated carbon is often integrated to remove dissolved matter via physical and chemical mechanisms. Granular activated carbon (GAC) is a well-established medium for the adsorption of aromatic compounds, and many non-polar organic substances. While many industrial applications formulate and utilize quality control standard testing regimes, the selection and scrutiny of GAC in aquaria and in aquaculture is not well-established. Powered filtration units which contain GAC, distributed in the aquarium market are predominantly rated for a range or specific volume of water, and not specified for species, temperature, or chemistry. As GAC can be sourced from a plethora of different organic sources and prepared/activated in a variety of methods, for optimal design and control of filtration in aquaculture and aquaria, new sources and separate lots of GAC should be tested in scheduled quality control for a particular operation. Provided the highly heterogeneous constituency of aquaculture and aquarium waters, principally composed of dissolved organic matter, a single testing indicator compound may not sufficiently describe the adsorptive capacity (i.e. performance) of a specific filter equipped with a GAC stage for a given physical, chemical, and biological context.

This study advances an uncomplicated methodology to characterize and contrast filter and commercially available GAC performance in clearing DOM from the water column with two indicator compounds that represent components targeted for use of GAC, methylene blue and a mixture of tannic and humic substances. For each test, two treatment groups representing the two filters were tested with 20-gallon aquaria (n=5) filled with unchlorinated municipal water, and dosed separately with the indicating compound. The filters were permitted to run for 144 hours, and spectroscopic absorbance was tracked at intervals for each testing substance to characterize adsorption from GAC. Performance was contrasted against mature aquaculture water in a similar fashion to observe 'real-world' applicability of the methods. Standard aquarium filters of two different manufacture, rated for identical volumes of water and both containing a GAC stage, were tested as representative of different GAC types. Significant difference (P<0.05) were found in comparing non-linear kinetics of each filter group for both indicating substances, and similar trends were found by filtering aquaculture water. These methods can be adopted to scale for commercial aquaculture operations to assist selection of a particular type of GAC for specific contexts.