Pretreatment of spent coffee grounds with alkaline soju bottle-washing wastewater for enhanced biomethanation
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ORIGINAL ARTICLE
Pretreatment of spent coffee grounds with alkaline soju bottle-washing wastewater for enhanced biomethanation Danbee Kim 1 & Hyungmin Choi 1 & Changsoo Lee 1 Received: 15 September 2020 / Revised: 13 November 2020 / Accepted: 19 November 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The production of spent coffee grounds (SCG) is steadily increasing, and its proper treatment has become an increasingly challenging task. This study explored the potential use of alkaline bottle-washing wastewater (BWW) from a soju (a Korean hard liquor) manufacturer as an alternative pretreatment agent to enhance the biodegradability and thus the biomethanation of SCG through anaerobic digestion. Thermo-alkaline pretreatment with BWW was effective in increasing the soluble organic fraction of SCG (i.e., improved bioavailability) at all temperatures tested (23–70 °C). The disintegration degree of the particulate organic matter in SCG ranged from 8.6 to 13.1% and increased with increasing pretreatment temperature. The 30-day methane yield (per g chemical oxygen demand (COD) of SCG fed) was significantly higher for the BWW-pretreated SCG (342.4– 361.2 mL/g COD) than for the raw SCG (284.7 mL/g COD) and even for the NaOH-pretreated SCG (at the same pH as BWW, pH 12.3) tested for comparison (299.7–320.9 mL/g COD). This significant increase in methane production can be attributed to the presence of readily biodegradable ethanol derived from waste soju in BWW and the alkaline solubilization of SCG. Our results suggest a straightforward way to manage SCG and BWW together in a sustainable and economical manner. Keywords Anaerobic digestion . Bottle-washing wastewater . Ethanol . Methane . Spent coffee grounds . Thermo-alkaline pretreatment
1 Introduction Spent coffee grounds (SCG), the residue remaining after brewing coffee, are very rich in organic matter (86–99% of dry weight) [1, 2] and have a significant potential as a renewable feedstock for biofuels. Nevertheless, in many countries, SCG is typically disposed of as waste in landfills or incinerated because of limited recycling options [3]. World coffee consumption is approximately nine million tons per year, and over eight million tons of SCG are produced annually [4]. With the continuous growth of coffee consumption, the proper management of SCG has become an increasingly challenging task. If not properly treated, the decomposition of the readily degradable fraction of SCG can cause pollution problems along with the release of potentially cytotoxic substances
* Changsoo Lee [email protected] 1
School of Urban and Environmental Engineering, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Eonyang-eup, Ulju-gun, Ulsan 44919, Republic of Korea
such as caffeine, tannin, and polyphenols [2, 5]. Therefore, a sustainable method for effective SCG management is urgently needed. Bioconversion to methane by anaerobic digestion (AD) is an attractive technology that can produce renewable energy while treating organic waste.
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