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‘Green tide’ to biochar: preparation and adsorption isotherms for three typical organic pollutants

Posted on 2. April, 2018.

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Enteromorpha prolifera (EP) is a typical marine macroalgae and has the characteristics of easy growth and rapid propagation. The rapid proliferation of EP due to eutrophication and climate change can cause outbreaks of ‘green tide’. ‘Green tide’ has frequently broken out in coastal areas of China’s Yellow Sea and it may damage the marine ecosystem and threaten coastal aquaculture. 

It was reported that the quantity of bloomed EP reached 10 million tons in 2015 and this mass of EP is often disposed of in landfills as an ocean waste. In the light of the development of biomass energy, the question of how to transform this waste biomass into value-added products has become a hot research topic.

Biochar is a carbon-rich, porous solid which is obtained when biomass is heated through the process of pyrolysis in a closed reactor with little or no oxygen present. The large specific surface area of biochar means that it can be used as an effective adsorbent to remove pollutants from aqueous solutions. Compared with activated carbon, which is the most commonly employed adsorbent for water purification, biochar appears to be a low-cost adsorbent due to the lower energy consumption in its production and its potential as an abundant and cheap feedstock. EP is mainly made up of polysaccharides, fats, proteins and minerals. Thus, it can be a suitable carbonaceous precursor for producing biochar. Recent studies showed that EP was a promising precursor for the synthesis of heteroatom-doped biochars and EP biochar can be used for CO2 adsorption and the preparation of electrode materials. Unfortunately, few studies focus on EP biochar when used as an adsorbent for the removal of organic pollutants in water and few works have mentioned the mechanism of formation of EP biochar during the heating process.

In the present study, biochars were produced by the pyrolysis of EP. The specific surface areas and surface functional groups were detected by N2-adsorption and Fourier transform infrared (FTIR) spectroscopy. In order to understand the pyrolysis process, EP was analysed using a thermogravimetric (TG) analyser combined with FTIR (TG–FTIR). Moreover, the adsorption capacities of the biochars were compared using three organic compounds, methylene blue (MB), oxytetracycline (OTC) and humic acid (HA) as adsorbates. MB is the most frequently used cationic dye in the textile industry which produces large volumes of wastewater and it has often been used as a model compound to investigate the adsorption behaviours of adsorbents. OTC is one of the most common antibiotics that has been detected in aquatic environments. HA in surface water is responsible for an undesirable colour and has been implicated in the microbial population. Carcinogenic trihalomethanes can be formed when HA-contaminated water is treated with disinfectants. Lastly, the adsorption equilibrium isotherms of the three typical pollutants by the optimum EP biochar were determined. 

Published in Progress in Reaction Kinetics and Mechanism, Volume 43, Number 1, 2018, pp. 30-40.


Authors: Yuhui Ma*, Jing Wang and Yushan Zhang
The Institute of Seawater Desalination and Multi-Purpose Utilisation, State Oceanic Administration (SOA), Tianjin 300192, P.R. China

Keywords: Enteromorpha prolifera, biochar, adsorption isotherm, methylene blue, oxytetracycline, humic acid

Image: (a) 2-D map of volatiles released from pyrolysis of EP and (b) FTIR spectra for pyrolysis products at 240 and 760 °C.