Abstract
Natural coagulants from plants resources have gained a lot of attention as it is renewable, biodegradable, non-hazardous, lower cost, and less sludge generated compared to chemical coagulants. However there are still some drawbacks, namely long settling time and possible increase of dissolved organic carbon in the treated water. In this paper we tried to address these drawbacks by utilizing citrate modified Fe3O4 to adsorb protein from Leucaena leucocephala as the active coagulating agent. The effect of trisodium citrate concentration and protein adsorption pH to the adsorbed protein was investigated. It was found that the trisodium citrate concentration of 0.5 M and pH 4.0 gave the highest protein adsorption. The obtained magnetic coagulant was furthermore characterized using Scanning Electron Microscopy, X-ray Diffraction, Fourier Transform Infrared Spectroscopy, and Transmission Electron Microscopy to observe the characteristics before and after protein adsorption. Furthermore, the effect of pH (2 to 10) and coagulant dosage (60 to 600 mg L− 1) to the removal of synthetic Congo red wastewater and sludge volume formation was investigated. It was found that pH 3 was the best pH for coagulation due to charge neutralization mechanism of leucaena protein. Furthermore the highest removal was obtained at dosage 420 mg L− 1 with 80% removal. This result was comparable with crude extract of leucaena with half settling time (20 min) and lower increase of permanganate value, indicating lower increase of dissolved organics in the treated water.
Highlights
In recent years, utilization of various natural resources as natural coagulant has gained a lot of interest due to its various advantages, such as: lower cost compared to chemical coagulants, it comes from renewable sources, less sludge volume generated, and biodegradable- nonhazardous sludge [1, 2]
Effect of pH and trisodium citrate concentration on the protein adsorption As mentioned before, the citrate ion was used as a bridge between Fe3O4 and leucaena protein, making the adsorption process effectively
The highest protein adsorption capacity was obtained at pH 4.0, which was near pI of leucaena protein
Summary
Utilization of various natural resources as natural coagulant has gained a lot of interest due to its various advantages, such as: lower cost compared to chemical coagulants, it comes from renewable sources, less sludge volume generated, and biodegradable- nonhazardous sludge [1, 2]. There are some drawbacks in natural coagulant application, which we addressed in this research. There were some researchers that combined iron oxide nanoparticles and natural coagulant to improve the coagulation performance, especially in terms of settling time [4,5,6,7,8,9,10]. Kristianto et al Sustainable Environment Research (2020) 30:32 been used, firstly the protein as active coagulating agent was used to functionalize the surface of iron oxide nanoparticles, secondly, the iron oxide nanoparticles were dispersed in crude extract of natural coagulant. Okoli et al [4] synthesized magnetic coagulant using composite of Fe3O4 and γ-Fe2O3 water-oil emulsion and functionalized with purified protein from Moringa oleifera. It was reported that 90% turbidity removal was obtained at 12 min settling under external magnet force, compared to gravitation only (240 min)
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