Adsorptive removal of atmospheric pollutants over Pyropia tenera chars

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    As a replacement for activated carbon, biochar was synthesized and used for the adsorptive removal of formaldehyde and nitrogen oxide. Biochar was produced from the fast pyrolysis of the red marine macro alga, Pyropia tenera. The P. tenera char was then activated with steam, ammonia and KOH to alter its characteristics. The adsorption of formaldehyde, which is one of the main indoor air pollutants, onto the seaweed char was performed using 1-ppm formaldehyde and the char was activated using a range of methods. The char activated with both the KOH and ammonia treatments showed the highest adsorptive removal efficiency, followed by KOH-treated char, ammonia-treated char, steam-treated char, and non-activated char. The removal of 1000-ppm NO over untreated char, KOH-treated char, and activated carbon was also tested. While the untreated char exhibited little activity, the KOH-treated char removed 80% of the NO at 50℃, which was an even higher NO removal efficiency than that achieved by activated carbon.


    Pyropia tenera char , activation , adsorption , formaldehyde removal , NO removal

  • 1. Introduction

    Rapid urbanization has caused a number of environmental problems, including heavy metal-containing wastewater, air pollutants from vehicles and factories, and global warming due to the increasing fossil fuel consumption; which increasingly threaten the quality of human life [1-8]. In particular, indoor air pollution, which is known to cause “sick building syndrome,” has attracted significant attention because the time urban residents spend indoors has become an increasing portion of their total activities. Construction materials, interior pieces and wallpaper, and furniture used during the construction of houses and buildings, contain a range of volatile organic compounds, including benzene, toluene, and formaldehyde. In addition, other air pollutants, such as nitrogen oxide, carbon monoxide, and asbestos, are also emitted indoors. Exposure to these pollutants in closed spaces can cause headache, dyspnea, atopic dermatitis, urticaria, heart disease, and cancer [9-11].

    Formaldehyde is a representative indoor air pollutant among those responsible for sick building syndrome. Efforts have been made to remove formaldehyde effectively using photocatalytic oxidation [12], catalytic oxidation [13], and biodegradation [14]. Nitrogen oxides are not only indoor air pollutants, but are also the main industrial gaseous wastes emitted from coal combustion processes as well as urban air pollutants emitted from vehicles. The most popular technology for removing nitrogen oxides is selective catalytic reduction [15]. This method, however, cannot be used at room temperature and consumes a large amount of energy. This is why there is still demand for a simpler, more effective, and more economical pollutant removal technology.

    Activated carbon is used widely for the adsorption of noxious gases and heavy metals, as well as for wastewater treatment because of its large adsorption capacity, large surface area, and high porosity [16-25]. On the other hand, the price of commercial activated carbon produced from bituminous coal, coconut shell, wood, or peat is relatively high because of the costly raw materials and expensive activation process [26].

    One of the most important global problems is climate change due to global warming. The application of biomass-derived char as an adsorbent is beneficial not only to the removal of pollutants but also to the reduction of carbon emissions. In particular, use of the byproduct biochar (obtained from fast pyrolysis of biomass aimed at the production of bio-oil) would provide an additional economic advantage [27-39].

    Biochar is obtained from the pyrolysis of a wide range of biomass materials, such as woody materials and agricultural wastes (olive husk, corncob, tea waste, green waste, etc.) [30,40-44]. Having a microporous structure and high C content, biochar can be used in a range of applications [45]. On the other hand, it has an important drawback: its specific surface area, and therefore its adsorption capacity, is smaller than that of activated carbon. Various activation treatment methods have been proposed to enhance the adsorption capacity of biochar [16,46].

    There are approximately 10,000 different species of seaweeds (marine macroalgae), which is more than the number of all land species providing useful biomass. Seaweeds are abundant in coastal regions worldwide. Their life cycle is short; hence the rate of reproduction is high. They are inexpensive and easy to handle. The advantages of seaweeds make them potentially important energy resources [47,48]. Furthermore, they have high selectivity toward the removal of various heavy metal ions, such as gold, cadmium, copper, and zinc (they have exceptional metal binding capacity), making them potential biosorbent materials [49,