The toxicity of heavy metals can cause water pollution and has harmful effects on human health and the environment. Various methods are used to overcome this pressing issue and each method has its own advantages and disadvantages. Membrane filtration technology such as nanofiltration (NF) produces high quality water and has a very small footprint, which results in lower energy usage. Nanofiltration is a membrane-based separation technique based on the reverse osmosis separation process developed in the 1980s. NF membranes have a pore size of 1 nm and molecular weight cut off (MWCO) of 300 to 500 Da. The properties of NF membranes are unique since the surface charge of the membranes is dependent on the functional groups of the membrane. The rejection mechanism of NF membrane is unique as it is a combination of various rejection mechanisms such as steric hindrance, electric exclusion, dielectric effect, and hydration mechanism. However, these mechanisms have not been studied in-depth due to their complexity. There are also many factors contributing to the rejection of NF membrane. Many junior researchers would face difficulty in studying NF membrane. Therefore, this paper is designed for researchers new to the field, and will briefly review the rejection mechanisms of NF membrane by both sieving and non-sieving separation processes. This mini-review aims to provide new researchers with a general understanding of the concept of the separation process of charged membranes.
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 (qmax = 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.