Rosazlin Abdullah

Copper (Cu) contamination in water and soil seriously threatens environmental and human health. This study evaluates the synergistic effect of palm kernel shell biochar (PKB) and nano-hydroxyapatite (nHAp) as green adsorbents for Cu remediation. Materials were characterized using SEM, XRD, FTIR, and BET analysis. An adsorption study was evaluated using the batch method, and soil incubation experiments were conducted to determine the soil's physicochemical properties, Cu bioavailability, Cu fractionation in soil, and corn seed germination. PKB exhibited a higher surface area (158.44 m²/g) compared to nHAp (52.65 m²/g), while nHAp showed larger pore volume (0.26 cm³/g) and pore size (19.63 nm). Batch adsorption experiments demonstrated that the Langmuir isotherm model best fit the data (R² > 0.95), indicating monolayer adsorption. The combined adsorbent (CBnHAp at 2.2 g) achieved the highest maximum adsorption capacity (q_max = 3.49 mg/g). In a 6-week soil incubation experiment, CBnHAp (T5) significantly increased soil pH from 5.30 to 6.30 and enhanced soil organic matter (SOM) content to 7.75%. This treatment reduced the available Cu concentration from 166.38 mg/kg to as low as 29.93 mg/kg, achieving up to 74.0% reduction in Cu bioavailability. Sequential extraction revealed that CBnHAp shifted Cu from the more bioavailable fractions (F1 and F2) to less mobile fractions (F3 and F4). Furthermore, a corn seed germination bioassay demonstrated that CBnHAp (T5) improved germination rates by up to 73.00%, with significant increases in root and shoot growth compared to the control. This study demonstrates that CBnHAp is a highly effective, sustainable, and eco-friendly approach for remediating Cu-contaminated environments, offering a promising solution for water and soil decontamination.

This study investigates the physicochemical properties and heavy metal concentrations (As, Cu, Cd, Cr, Ni, Zn, Pb) in the sediments of the Klang Mangrove Area, with a focus on assessing pollution risks associated with Pulau Indah’s industrial activities in Malaysia. The sediments were characterized by moisture content ranging from 31 to 37%, pH levels ranging from acidic to neutral, slightly saline conditions, sandy textures, and organic matter averaging 9.74% (7.04% organic carbon). Heavy metals were analyzed using ethylenediaminetetraacetic acid (EDTA) and Aqua Regia extraction methods to distinguish between bioavailable and total metal concentrations. The study found elevated Cd concentrations across all sites, exceeding both the threshold effect level (TEL) and probable effect level (PEL), reflecting EDTA’s efficiency in mobilizing bioavailable Cd. Pb, Ni, and Cu also exceeded TEL but remained below PEL. Notably, Aqua Regia extraction identified Cu concentrations at Site 3 (175.9 mg kg⁻¹) exceeding TEL (31.6 mg kg⁻¹) and PEL (149 mg kg⁻¹), likely due to Aqua Regia’s capacity to dissolve stable and bioavailable metal forms. Other metals, such as As, Zn, and Cr, remained below harmful thresholds. Based on Hakanson’s classification, the contamination degree (CD) value at site three was 23.75, categorizing it as highly contaminated. The results underscore significant ecological risks at site three, particularly from Cu, along with moderate contamination driven by Cd and Pb. This study highlights the urgent need for remediation strategies and sustainable environmental management to mitigate contamination risks, safeguard aquatic ecosystems, and protect public health in Pulau Indah. The findings contribute novel insights into the region’s sediment contamination, providing essential data for policymakers and stakeholders to implement effective pollution control measures. Graphical abstract

Microalgae have gained significant attention as sustainable alternatives to traditional agriculture and energy resources. The cultivation efficiency of microalgae within hydrogel systems presents a promising avenue for spatially efficient bio-production. However, the optimum cultivation conditions of hydrogel cultivation systems have not been elucidated. This study focused on evaluating the hydrogel-based cultivation of Chlorella vulgaris in symbiosis with Bacillus Strain Salmah Ismail (SI) 139SI. It investigated the impact of hydrogel concentration, pH, light exposure, and system thickness on the growth and chlorophyll production of the algae. Our findings highlighted that, in coculture, a 7% (w/v) hydrogel concentration, pH of 7.4, a 12-h light/dark cycle at a hydrogel concentration of 7% but continuous light exposure under 5% hydrogel concentration, and a system thickness of 10 mm have provided the most favorable environmental conditions for the proliferation and chlorophyll production of C. vulgaris. These conditions significantly enhanced the biomass yields, suggesting that tailored hydrogel environments can substantially improve microalgae productivity.