Phytostabilization of fly ash from a coalmine in Botswana and biovalorisation of the recovered Napier grass (Pennisetum purpureum Schumach.)

Abstract

The disposal of fly ash (FA) from coal power plants polluting the air, soil, and groundwater is a major environmental concern. Phytoremediation to rehabilitate fly ash dumpsites is a promising alternative but has practical concerns about the disposal of harvested biomass. This study investigated the effect of supplementing fly ash with fresh sewage sludge (FSS), aged sewage sludge, food waste, and compost (COM) to enhance the phytoremediation potential of Napier grass and its subsequent utilization for ethanol production. The highest removal of Mn (1196.12 g ha⁻¹) and Ni (128.06 g ha⁻¹) from FA could be obtained when Napier is grown in the presence of FSS and inorganic fertilizer (NPK). In addition, the highest bioethanol yield (19.31 g L⁻¹) was obtained from Napier grown in fly ash with COM + NPK, thus providing additional economic benefits aside from the remediation process. Given the significant levels of heavy metals present in the pulp and bio-slurry after ethanol production, further research is required in this area to determine the best ways to utilize this waste such as converting it into biochar.

NOVELTY STATEMENT

Using energy crops as a phytoremediation agent for fly ash dumpsites has the potential to remediate heavy metal contamination and provide additional economic benefits. Napier grass was able to tolerate high concentrations of heavy metals and yield high biomass in fly ash in the presence of organic amendments. The harvested biomass was successfully converted into substrate for bioethanol production using heavy metal-tolerant yeast. This is the first report on the production of ethanol from the phytoremediation biomass of Napier grass.

Keywords:

• Bioethanol
• fly ash dumpsite
• heavy metal accumulation
• Napier grass
• phytoremediation

Disclosure statement

The authors report there are no competing interests to declare.

Ethical approval

This manuscript did not involve any human participants, human data, human tissues, or cloned animals hence ethical approval is not applicable.

Consent to participate

Not applicable

Consent to publish

All authors have full consent to publish the content of the manuscript.

Data availability statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Additional information

Funding

This paper is supported by the BIUST Graduate Research Grant (REF: DVC/RDI/2/1/7 V (22) to KG) and DRST AJ core SusMine (P0081) to Venecio Ultra.

Department of Research, Science and Technology AJ core SusMine;