Pyrolysis polygeneration of the marine and terrestrial biomass and the chemical activation of bio-char as adsorbent to remove tetracycline hydrochloride from wastewater

Abstract

Pyrolysis polygeneration is one of the promising approaches to convert biomass into bio-gas, bio-char, and bio-oil. In this work, the comparison of the properties of pyrolytic products from terrestrial biomass (poplar wood, PW) and marine biomass (microalgae, Chlorella vulgaris, CV) was carried out. Then, three types of activation agents (e.g., KOH, H3PO4, and ZnCl2) were used to improve the SSA and pore structure of bio-char for the removal of tetracycline hydrochloride (HTC) from wastewater. The yield of bio-char decreased with pyrolytic temperature increasing, while the yield of bio-gas increased. The yield of bio-oil reached the maximum value of 500 ºC. The yields of bio-gas and bio-char of CV were higher than that of PW at different temperatures, while the yield of bio-oil presented an opposite trend. Several nitrogenous chemicals were observed in pyrolytic bio-oil of CV due to thermal degradation of proteins. Among the three type of activation agents (H3PO4, KOH, and ZnCl2), KOH was the best activation agent to obtain activation carbon with highest SSA and pore volume. The CV-derived activated carbon by using KOH as activation agent presented highest specific surface area (1638.85 m2/g) and highest adsorption capacity of HTC (42.7 mg/g). Meanwhile, the CV-500-KOH still retained such high adsorption capacity of HTC (35.8 mg/g) after five cycles, suggesting that the N-doped bio-char possessed the excellent recyclability. In conclusion, compared to the PW-derived bio-char, CV-derived bio-char was a better precursor for production of activation carbon due to the higher N content in CV.