Co-Composting of Khat-Derived Biochar with Municipal Solid Waste: A Sustainable Practice of Waste Management

Zewdu Abebe Tessfaw,Krzysztof Pikoń,Abebe Beyene,Amsalu Nebiyu,Marcin Landrat

doi:10.3390/su122410668

Zewdu Abebe Tessfaw, Krzysztof Pikoń + Show 3 more

Open Access

https://doi.org/10.3390/su122410668

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Abstract

Biochar is a way to improve the performance of the composting process and the quality of compost. This study was aimed to investigate the optimum ratio of khat straw (Catha edulis) biochar and organic municipal solid waste mixtures to improve the quality of the resulting co-composts. Khat-derived biochar during pyrolysis at 350 °C was added to organic municipal solid waste mix and four co-composting treatments were prepared with the compositions (% w/w): control compost (no biochar) and 5%, 15%, and 25% co-composted biochar in three replicates. The total organic carbon, organic matter, total nitrogen, available phosphorus, and potassium values ranged as 16.76–21.45%, 30.77–40.26%, 0.97–1.68%, 0.58–0.76%, and 12.72–15.29%, respectively. The results confirmed that 5% and 15% co-composted khat biochars had significantly reduced (p < 0.05) organic matter loss and increased the contents of cation exchange capacity, pH, phosphorous, potassium, calcium, magnesium, and zinc compared to the control compost, while some heavy metals (Fe, Cu, and Mn) and EC values in co-composted biochars are lower than the control compost. Khat-derived biochar could be added to municipal organic waste mix at 5–15% (w/w) in order to get better quality of compost, which can be used as biofertilizer.

Highlights

The sustainable management of solid waste has become a major problem of the municipalities in the world in general and developing countries in particular [1,2]
Khat biochar has weak alkaline pH (8.9) value, which is important to neutralize the acidic organic waste mix during composting or to amend acidic soil. This pH value was less than the findings by [14] for biochar prepared from holm oak, which was pyrolyzed at 650 ◦C, but greater than the finding by [13] for biochar prepared from Eucalyptus grandis pyrolyzed at 300–450 ◦C
The results showed that khat straw biochar has high organic matter (88.4%) as well as major nutrients such as total nitrogen (1.50%), phosphorous (0.40%), potassium (0.26%), calcium (6.4 g/kg), and magnesium (2.3 g/kg) contents with low levels of trace metals

Summary

Introduction

The sustainable management of solid waste has become a major problem of the municipalities in the world in general and developing countries in particular [1,2]. South-west Ethiopia as city of a developing country, solid waste collection rate is the lowest among the growing cities of Ethiopia, where only 30% of the total waste is collected and disposed on landfills [3]. The remaining part of the waste is usually burned or disposed in open space. According to Getahun et al [3], the total waste generated daily in Jimma city was ca. According to [3], biodegradable organic waste constitutes 88.6% by weight. The proper management of organic solid waste is crucial for the successful disposal of municipal solid waste

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