Abstract
Spent coffee ground (SCG) may affect wastewater treatment processes due to high coffee consumption worldwide. The impact of the main chemical compounds present in SCG on respiration activity of sewage sludge was investigated. The results showed approximately two times higher respiration in the samples where various types of SCG were present in comparison with samples without SCG. During intense microbial metabolism, statistically significant (p < 0.05) decreases in caffeine, total polyphenols, and chlorogenic acid contents after processing and in filtrate was observed. The monitored compounds (caffeine, polyphenols, and chlorogenic acid) deteriorated due to their probable inclusion in microbiological metabolism. Increase in respiration activity of microorganisms in the presence of cheap waste material such as coffee grounds can help to improve wastewater treatment. The research was focused on spent coffee grounds’ impact on the respiratory activity of microorganisms in the activated sludge taken from small and large wastewater treatment plants. The impact was measured in more detail due to the inclusion of different coffee species (Robusta and Arabica) in diverse concentrations. The novelty of the study can also be seen through the literature overview, where information cannot be found about SCG influence on the respiration activity of microbial communities, and data on the possible SCG aerobic degradation or utilization by a sewage sludge bacterial consortium has also never been reported. The study has shown the possibility of improving wastewater treatment due to respiration activity of microorganisms in the presence of cheap waste material such as coffee grounds.
Highlights
Spent coffee ground (SCG) is the waste that is accumulated after coffee consumption, or it can be described as a byproduct of brewing process
215%, 206%, and 198%, respectively; after 100 min: 219%, 236%, and 235%; at the end: 202%, 220%, and 219% compared to the control samples
This study showed a rapid decrease of chlorogenic acid content by an aerobic microbial consortium in the activated sludge, though it was found that in the presence of Aspergillus alutaceus fungus, the content of chlorogenic acid increased, while it did not have effect on caffeine content [13,33]
Summary
Spent coffee ground (SCG) is the waste that is accumulated after coffee consumption, or it can be described as a byproduct of brewing process. Special attention is given to the accumulation of this food production byproduct due to high coffee consumption worldwide. This statement is supported by the facts: (i) in 2016, 7,200,000 tons of all coffee forms was exported, and from 2000 to 2012, global green. Sci. 2019, 9, 3155 coffee production increased by 17% [1]; (ii) in total, 0.91 g wasted grounds per gram of coffee is produced. Around 6 million tons of spent coffee grounds are produced each year [2]. All waste disposal issues represent big economic and environmental problems [4]
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