HSGAC - A Site Specific Granular Activated Carbon Model Design Tool
- Allison Reinert, EIT, Erik Rosenfeldt, PE, PhD, Mark Bishop, PE, Ben Stanford, PhD - Hazen and Sawyer
- Viking Edeback, Detlef Knappe, PhD - North Carolina State University
With more stringent disinfectant/disinfection byproduct (D/DBP) rules, utilities are evaluating advanced treatment techniques to control DBPs and their precursors, such as organic matter. Granular activated carbon (GAC) adsorption is an advanced treatment option that has been proven effective for removal of organic matter. Conducting pilot tests and rapid small scale column tests (RSSCTs) are useful tools for determining GAC life and effectiveness, but little work has been done on the prediction of future DBP levels once GAC contactors are installed. The principal objective of this work was to develop a computer, spreadsheet-based model that could be used to predict DBPs after GAC treatment is in use from historical demand and total organic carbon (TOC) data, anticipated future demand data, and pilot, RSSCT, and simulated distribution system (SDS) testing results for a given utility.
The creation of the Hazen and Sawyer GAC (HSGAC) model allows for the evaluation of different GAC treatment schemes to meet utility specified DBP goals. By using utility and site specified historical flows and TOC data, among other collected and imported data, the results of GAC treatment can be estimated. The model allows for 0-100% plant flow treatment as well as user specified DBP goals. Simulations can be run for treatment that minimizes overall capital costs of GAC installation in addition to scenarios that minimize operations and maintenance costs for carbon change out, replacement, and regeneration. Through the use of the HSGAC model, different layers of conservatism, the sensitivity of different design parameters, different DBP goals, and different levels of treatment can all be evaluated and used to make informed design decisions.
The creation of this unique tool to capture the potential benefits of GAC treatment, specific to an individual utility or treatment plant, for the control of DBPs and their precursors, allows utilities to anticipate what large investments in activated carbon adsorption can achieve. In previous applications, HSGAC has allowed utilities and their directing boards to make informed decisions about how much GAC treatment to add (in terms of number of contactors and seasonal versus year round treatment) in addition to finding the most effective operation and carbon change out schedule to meet their water quality goals.
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