Comparison of heavy metal and nutrients removal in Canna indica and Oryza sativa L. based constructed wetlands for piggery effluent treatment in north-central Nigeria

Abstract

Batch-fed horizontal sub-surface flow constructed wetlands (HssFCW) were developed to compare the potential of Canna indica and Oryza sativa L. in removing heavy metals and nutrients from piggery effluent. Piggery effluent samples were characterized for nutrients (N and P) and metals (Mg, Al, Ca and Fe) before and after introducing them to the HssFCW with hydraulic retention time (HRT) of 3 days and operational flowrate of 0.014 m³/day. Three sets of constructed wetlands (CWs) were monitored during the dry season for 3 months. The bioconcentration factor (BCF) and translocation factor (TF) for the plants were evaluated. The results were all significantly different at p ≤ 0.05. O. sativa L removes more nutrients and metals than C. indica. The BCF for O. sativa L. was higher than for C. indica, while the TF for C. indica was higher for O. sativa L., indicating a higher metal translocation potential. Use of C. indica, a non-food crop, poses no health risks in HssFCWs whereas the grains of O. sativa L. are consumed directly by humans, presenting potential risks when used in HssFCWs. Compared to an annual O. sativa L., the perennial C. indica can be grown continuously in CWs for the phytoremediation of piggery effluent.

Novelty statement

• No known work about the phytoremediation potential of the two studied macrophytes in the agro-ecological zone is known. The study also provides insight into the bioconcentration of metals in the edible part of Oryza sativa L. FARO 44 (SIPI 692033).

• The characterization of piggery effluent revealed that its compositions were above the allowable limit for reuse and recycling despite the adoption of low-water use intensive method.

• The study showed that Oryza sativa L accumulates more metals in the above-ground tissues than in its root and provide insight into its use as a phytoremediation plant in the study area.

• The footprint of pollutants and metals in Oryza sativa L makes a perennial C. indica more suitable than O. sativa L. in piggery effluent phytoremediation.

Keywords:

• Canna indica
• Oryza sativa L.
• piggery effluent
• bioconcentration
• metals

Acknowledgments

The authors would like to express their gratitude to the staff of the environmental engineering laboratory and the students at Landmark University for their assistance during the fieldwork. We gratefully acknowledge the critical comments and corrections of respected reviewers whose comments and corrections improved this work considerably.

Disclosure statement

No potential conflict of interest was reported by the author(s).