A Comparison of a Conventional Chemical Coagulant and a Natural Coagulant Derived from Cassia fistula Seeds for the Removal of Heavy Metal Ions

Synthesis of metal-organic framework immobilized bromelain complex and its application in corn starch wastewater treatment

Pineapple leaves and stems are often treated as agricultural waste during pineapple harvesting. Disposing of or incinerating pineapple leaves and stems contributes to environmental pollution and results in the waste of recyclable resources. Currently, a viable approach is to extract bromelain from pineapple leaves and stems. Bromelain exhibits broad applicability, capable of catalyzing the hydrolysis of numerous plant proteins, hence it can be effectively utilized in the treatment of wastewater with high protein content. In this study, bromelain isolated from pineapple leaves and stems was immobilized within a zeolitic imidazolate framework (ZIF-8) via a one-step co-precipitation method, synthesizing the bromelain@ZIF-8 complex. The results show that (1) the immobilization of bromelain did not alter the morphology or crystalline structure of ZIF-8, while the thermal stability of the enzyme was significantly enhanced; (2) when take bovine serum albumin and corn starch wastewater as substrates, the bromelain@ZIF-8 complex exhibited better performance in protein hydrolysis applications under the synergistic effect of bromelain and ZIF-8, demonstrating great potential in removing proteins from industrial wastewater; (3) when treating corn starch wastewater by coagulation, the optimal treatment effect of the wastewater was achieved by sequentially adding 300 ppm flocculant polyaluminum chloride (PAC), 5 ppm bromelain@ZIF-8 complex, and 667 ppm coagulant aid polyacrylamide (PAM), resulting in a COD reduction of 25.22%, and reductions in color and suspended solids by 97.80% and 90.84%, respectively. This work not only reduces the environmental pollution, but also provides a new possibility for the treatment of high plant protein wastewater.

Annona glabra L. Seeds: An Agricultural Waste Biosorbent for the Eco-Friendly Removal of Methylene Blue

The seeds of Annona glabra L., an invasive plant in Vietnam, were first employed as a new biosorbent for the adsorption of methylene blue (MB) from aqueous media. The characterizations of the material using FT-IR, SEM, nitrogen adsorption-desorption analysis, and point of zero charge reveals that it possesses a rough and irregular surface, various polar functional groups, and pHpzc of 5.5. Certain adsorption conditions including adsorbent dose, solution pH, contact time, and initial concentration of MB were found to affect adsorption efficiency. The kinetic data are well fitted with pseudo-second-order model with the adsorption rate of 0.002 g mg-1 min-1 and initial rate of 4.46 mg g-1 min-1. For the adsorption isotherm, three nonlinear models were used to analyze the experiment data, including Langmuir, Freundlich, and Temkin. The results indicate that the Langmuir model best describes the adsorption of Annona glabra L. seeds powder (AGSP) with a maximum adsorption capacity of 98.0 mg g-1. The investigation underpins the adsorption mechanism, whereby the electrostatic attraction between positively charged MB and negatively charged surface of AGSP is expected to be the predominant mechanism, together with hydrogen bonding and pi-pi interaction. These results make AGSP an interesting biosorbent concerning its environmental friendliness, cost-effectiveness, and relatively high dye adsorption capacity.