Utilization of rice husk ash as a potential catalyst for diatom growth and adsorbent for heavy metals in aquaculture systems

Many aquaculture environments suffer from significant silicon deficiencies and severe heavy metal contamination, posing substantial risks to both production and safety in aquaculture. This study aimed to assess the release of silicate from rice husk ash (RHA) and its impact on phytoplankton abundance and community composition, which are key factors affecting shellfish growth and survival. Additionally, the capacity of RHA to adsorb mercury (Hg2+) 2+ ) was examined using different modification methods. The results demonstrated that the concentration of dissolved silicate in seawater increased with higher RHA doses, reaching a maximum of 189.77 +/- 45.61 mu mol L- 1 in the high RHA treatment (HR) with 1.0 g L- 1 of RHA. Notably, the HR treatment group exhibited a significant increase in chlorophyll-a concentration for nano-phytoplankton (2-20 mu m), with an up to eightfold rise in abundance compared to the control group. Moreover, the HR treatment resulted in a maximum diatom abundance of 4217 +/- 741.98 cells L- 1 , benefiting diatom species such as Coscinodiscus sp., Nitzschia sp., and Cyclotella sp. These findings underscore the potential of RHA as a catalyst for diatom growth, which in turn supports the growth of shellfish. Furthermore, 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. The treatment of RHA with NaOH achieved an impressive removal efficiency of Hg2+, 2+ , reaching up to 97.41 +/- 0.33 %. This study highlights the promising application of agricultural waste RHA as a catalyst for diatom growth and an adsorbent for heavy metals in water systems relevant to aquaculture practices.