Abstract
Chitosan/organic rectorite (CTS/OREC) composites were prepared and characterized by Fourier transform infrared spectrometry and X-ray diffraction. Polyphenol oxidase (PPO) was immobilized on CTS/OREC by physical adsorption (APPO) and covalent binding (CPPO). Taguchi method was applied in the optimization of immobilization conditions resulting in the highest enzyme activity of 16.37 × 103 and 8.92 × 103U/g for APPO and CPPO, respectively. APPO enzyme activity was higher than that of CPPO, while CPPO showed the higher enzyme loading capacity than that of APPO. The removal percentage of phenolic compound, including phenol (PH), 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP), by immobilized PPO was also explored. The results indicated that APPO was more efficient in phenolic compounds removal than CPPO. APPO contributed to a quick removal in the first hour, and the removal percentage of PH, 4-CP and 2,4-DCP could reach 69.3 ± 4.2%, 89.8 ± 2.5% and 93.8 ± 1.7% within 2 h, respectively. The order of removal percentage of phenolic compounds for both immobilized PPO was 2,4-DCP > 4-CP > PH. After 10 consecutive operations, the removal percentage of 2,4-DCP reached 73.2 ± 2.6% and 60.3 ± 1.5% for APPO and CPPO, respectively. The results introduced a novel support for PPO immobilization, and the immobilized PPO had great potential in wastewater treatment.
Highlights
Phenolic compounds have been listed as priority pollutants by the US Environmental Protection Agency due to their acute toxicity and bio-recalcitrant nature
The study is the first report of immobilization Polyphenol oxidase (PPO) on CTS/ organic rectorite (OREC) composites
A different immobilization strategy determined the microenvironments of the enzyme, and the immobilized PPO showed different enzyme activity and properties
Summary
Phenolic compounds have been listed as priority pollutants by the US Environmental Protection Agency due to their acute toxicity and bio-recalcitrant nature. Conventional physical, chemical and physico-chemical technologies for the phenolic compounds removal from industrial effluents, including extraction, adsorption, chemical oxidation and electrochemical methods, have faced some limitations such as low efficiency, high cost, high energy requirements, applicability to limited concentration range and formation of hazardous by-products that are even more toxic than the original phenols. Compared with physico-chemical technologies, biological technologies are considered as ecofriendly, cost-effective and viable alternatives for treatment of phenolic compounds. Biological technologies have their own limitations such as inability to treat high concentration phenolic compounds, lower degradation rate and production of sludge. An enzymatic method, which may be an alternative method, has great potential in the treatment of phenolic compounds because of mild reaction conditions, high specificity and selectivity, biodegradability and is environmentally friendly (Jun et al )
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