COFFEE WASTE BIOCHAR: A WIDELY AVAILABLE AND LOW-COST BIOMASS FOR PRODUCING CARBONACEOUS ADSORBENTS TO TREAT GREYWATER

Abstract

Coffee, the second-most consumed commodity, is grown in more than 50 nations, in the world. Accordingly, an enormous amounts of spent coffee grounds (SCGs) are produced from the coffee brewing processes. This waste stream is abundant and can be easily separated, allowing for its cost-effective valorization. This study focuses on its use as a new adsorbent in the greywater treatment field. This study employed dried SCG to make “biochar” by pyrolyzing the biomass at low 300 (BC 300°C), medium 450 (BC 450°C), and high 600 °C (BC 600°C) temperatures. The biomass and biochar were characterized to examine the biomass alterations during pyrolysis and the benefits of biochar adsorption for greywater treatment applications against compounds of daily skin/body products. The electrical conductivity (EC) of the biochar at BC 600 °C was higher than that of SCG biomass. BC 450°C and BC 600°C have the highest negative zeta potential in comparison to the potential of the biomass. The highest CEC was 29 cmolc.kg-1 for BC 450°C. BC 300 °C and BC 600 °C contained 63% to 88% of C content, respectively, whereas the biomass had a 43% C content. Three fixed-bed column configurations were set and packed with: SCG BM, BC 450 °C, and BC 600 °C in the greywater treatment system and each controlled at three different flowrates 0.5, 1.5 and 3 mL.min-1. The SCG biomass had its maximum TOC removal of 67% at a flow rate of 1.5 mL. min-1 after 5 h. In comparison, BC 450 °C and BC 600 °C achieved similar performance to each other with 70-80 % removal at both 0.5 and 1.5 mL.min-1 flow rates, respectively. Corresponding to TOC removal, the two biochar conditions attained similar reduction to each other in UV absorbance at the maximum wavelength (UVAλ310), which exceeded that of SCG BM. The reduction of UVAλ310 was similar amongst the three flow rates, except SCG biomass, which was slightly less at 1.5 mL.min-1. The removal of organics from three column runs was also evaluated by two surrogate parameters; specific UV absorbance (SUVA) and octanol-water partition coefficient (log Kow). These parameters demonstrated BC 450 °C and BC 600 °C were more efficient to adsorb most of the hydrophobic compounds. SCG BM showed a higher adsorption rate for tetratriacontane compound and a lower adsorption rate for benzene (C6H6). BC 600 °C and BC 450 °C had a lower rate for cyclohexanemethanol and 4-methylene- (C8H14O). At a lower flowrate, the two biochar columns showed good removal of nitrogen, phosphorous and metals compared to biomass. Between the two biochar columns, BC 450 °C had the maximum phosphorous removal, which occurred at a flow rate of 0.5 mL.min-1. Overall, this study demonstrated that SCG biomass is an efficient carbonaceous adsorbent to remove organic and inorganic pollutants, but that its conversion to biochar provides additional treatment performance. Despite differences in certain characteristics, BC 450, and BC 600 ℃ had very similar treatment performances. Therefore, users should assess whether the yield loss and processing costs of BC 450 ℃, as well as its improved stability, make an economical and practical choice over direct SCG biomass utilization for greywater fixed bed treatment.

Date of Award	2022
Original language	American English
Awarding Institution	HBKU College of Science and Engineering