Vincent A. Mudrak Carlos Echevarria Philip Sibrell Steven T. Summerfelt Claude E. Boyd Barnaby J. Watten 2017 <p>Springs serving the Warm Springs Regional Fisheries Center, Warm Springs, Georgia, have pH, alkalinity, and hardness levels thatlie under the range required for successful fish propagation while free CO₂ is well above allowable targets. We evaluate a pretreatment process that exploits limestone’s (CaCO₃) ability to react away hydrogen ions (H⁺) and carbon dioxide (CO₂) while increasing alkalinity (HCO₃⁻) and calcium (Ca2+) concentrations, i.e.</p><p> CaCO₃ + H⁺ ↔ HCO₃⁻ + Ca²⁺</p><p> CaCO₃ + CO₂ + H₂O ↔ Ca²⁺ + 2HCO₃⁻</p><p>Limestone sand was tested in both pilot and full scale fluidized bed reactors (CycloBio®). We first established the bed expansion characteristics of three commercial limestone products then evaluated the effect of hydraulic flux and bed height on dissolution rate of a single selected product (Type A16 × 120). Pilot scale testing at 18C showed limestone dissolution rates were relatively insensitive to flux over the range 1.51–3.03 m³/min/m² but were sensitive (P &lt; 0.001; R² = 0.881) to changes in bed height (BH, cm) over the range 83–165 cm following the relation: (Alkalinity, mg/L) = 123.51 − (3788.76 (BH)). Differences between filtered and non-filtered alkalinity were small(P &gt; 0.05) demonstrating that limestone was present in the reactor effluent primarily in the form of dissolved Ca(HCO₃)₂. Effluent alkalinity exceeded our target level of 50 mg/L under most operating conditions evaluated with typical pilot scale values falling within the range of 90–100 mg/L despite influent concentrations of about 4 mg/L. Concurrently, CO₂ fell from an average of 50.6 mg/L to 8.3 mg/L (90%), providing for an increase in pH from 5.27 to a mean of 7.71. The ability of the test reactor to provide changes in water chemistry variables that exceeded required changes allowed for a dilution ratio of 0.6. Here, alkalinity still exceeded 50 mg/L, the CO₂ concentration remained well below our limit of 20 mg/L (15.4 mg/L) and the pH was near neutral (7.17). Applying the dilution ratio of 0.6 in a full scale treatment plant at the site reduced by 40% the volume of spring water that is directed through each of three parallel reactors that combined react away 49,000 kg of limestone/yr.</p> application/pdf 10.1016/j.aquaeng.2017.03.003 en Aquacultural Engineering Society Performance and application of a fluidized bed limestone reactor designed for control of alkalinity, hardness and pH at the Warm Springs Regional Fisheries Center article