Evaluation of metal hydroxide sludge for reactive dye adsorption in a fixed-bed column system

The capacity and performance of small-scale column, containing coarse particles of metal hydroxide sludge, were evaluated using 30 mg l−1 dye solutions of C.I. Reactive Red 141. The studied bed depths were 2.5–20 cm and the studied flow rates were 1.1, 2.2 and 3.3 ml min−1 cm−2. At the breakthrough point of 0.1 Ct/C0, the breakthrough volume was increased with increasing bed depth or decreasing flow rate, due to an increase in empty bed contact time (EBCT). The data followed the bed depth service time model, and the adsorption capacity was 24–26 mg cm−3 or 27–29 mg dyes g−1 adsorbent. The minimum bed depths should be higher 1.02, 2.04 and 2.59 cm with flow rates of 1.1, 2.2 and 3.3 ml min−1 cm−2, respectively, while the ratio of bed depth to diameter should not be higher than 6. With EBCT above 5 min, the usage rate of metal hydroxide sludge was 1.3 g l−1. Using the bed depth of 5 cm and the flow rate of 0.55 ml min−1 cm−2, 87% of dominant colour, 78% of COD, and 99% of SS could be removed from the textile wastewater, and the leachate of toxic heavy metals was under the standard limitations.