Efficient removal of chromium by a novel biochar-microalga complex: Mechanism and performance

The biochar has been considered as a high-efficiency bio-adsorbent for treating heavy metal wastewater. Microalgae are abundant in various aquatic systems, and carry specific functional groups on their surfaces that could also aid chromium removal (i.e., -COOH, -OH, -CHO, -O-). The previous studies have focused on metal uptake from wastewater by biochar, few have conducted in-depth research on its removal mechanism and performance to heavy metals when combined with microalgae. Here, the comprehensive study revealed chromium functional diversity and adsorption mechanisms on Coconut shell activated carbon (Csac) loaded with microalgae Chlorella (Csac@Chlorella) in greater detail than ever before. The chromium treatability of 0.5 Csac@1.0 Chlorella immobilized complex to electroplating chromium wastewater were 28.95% and 30.16% great higher than that of 0.5 Csac and 1.0 Chlorella in 120 min, respectively. And the adsorption equilibrium time was also significantly shortened to 20–40 min. This study further investigated the effect of Csac@Chlorella immobilized complex on chromium removal for electroplating chromium wastewater (the Cr removal ability of 0.5 Csac@1.0 Chlorella was 70.94%) and several potential influencing factors (i.e., t, pH, dosage). We identified carboxyl, carbonyl, cyanide ions and hydroxyl functional sites and found the chromium proportion in these functional groups were varied. Carboxyl and hydroxyl were the main groups that reacted with chromium, followed by carbonyl and cyanide ions. This study clearly indicated that a novel biochar-microalga immobilized complex could enhance the adsorption capacity of chromium, which have significant implications for the application of Csac@Chlorella biological resources in aquatic environment.