WITHDRAWN: An in situ mescosm to assess the potential of rice husk ash as a diatom growth catalyst and heavy metals adsorbent

Abstract

Many coastal waters suffer from significant silicon deficiency and severe heavy metals contamination, posing a great threat to the ecosystem. The present study evaluated the release of silicate from rice husk ash (RHA) and its effect on the phytoplankton abundance and community composition using an in situ mescosms, and assessed the capacity of RHA to adsorb mercury (Hg2+) under different modification methods. The results showed that the concentration of dissolved silicate in seawater increased with increasing RHA and reached the maximum of 189.77 ± 45.61 μmol L−1 in high RHA treatment (HR) with 1.0 g L−1 of RHA. In the HR treatment group, a significant increase in chlorophyll-a concentraion for nano-phytoplankton (2–20 μm) was observed, with the maximum increase in abundance of ~8 fold as compared to the control group. Furthermore, the maximum abundance of diatoms was observed up to 4217 cells L−1 in the HR treatment group. Diatom species that benefitted from the addition of RHA were Coscinodiscus sp., Nitzschia sp. and Cyclotella sp. In addition, no concentrations of mercury (Hg), lead (Pb), cadmium (Cd), arsenic (As), copper (Cu), zinc (Zn), and chromium (Cr) were detected in any of the silicate enrichment treatments, confirming the safety of the RHA, and the removal efficiency of Hg2+ was up to 97.41% in the treatment of RHA with NaOH. This study revealed that an agricultural waste, RHA, is a good catalyst for diatom growth and adsorbent of heavy metals.