Bacteriological Quality of a Forage Grass (<i>Pennisetum purpureum Schumach</i>) Used in Constructed Wetland Removing Domestic Wastewater Pathogenic Microorganism

Abstract

Constructed Wetlands (CWs) are an adequate wastewater treatment system with possibility to generate income, in particular by the use of plants of economic interest. However, very few studies deal with the bacteriological quality of plants after wastewater treatment. Thermotolerant coliforms and Sulfite-reducing bacteria were investigated on the above-ground biomass of a species of forage plant (Pennisetum purpureum) as well as their removal in an experimental pilot consisting of four beds, for three months. Two beds were planted and two unplanted beds were used as control. Germs in the wastewater were significantly reduced in both filtrates, with higher removal efficiency of 97.4% for Thermotolerant coliforms and 87.5% for Sulfite-reducing bacteria, in the planted bed. Wastewater treatment resulted in bacteriological contamination of the above-ground plant biomass with a significant decreases in number of germs from 660 to 28 CFU/g (Thermotolerant coliforms) and from 15 to 0 CFU/g (Sulfite-reducing bacteria), when the harvest height increased from the base to the upper end of the plants. However, averages of 305 CFU/g of Thermotolerant coliforms and 5 CFU/g of Sulfite-reducing bacteria were obtained in the above-ground plant biomass which would not present any potential risks for a possible use of the plant biomass as fodder. Thus, the use of forage plant suggests good prospects for upgrading said plants for animal feed.

Pennisetum purpureum Improved Polycyclic Aromatic Hydrocarbons Removal in Weathered-Petroleum Contaminated Soil

“…Plants are known to release from their roots compounds that are readily utilized by microorganisms as carbon and energy sources. Zahui et al, (2021) reported the bacterial population in the rhizosphere of P. purpureum to reach 7.7×10 6 cfu/g in a constructed wetland and attributed it to exudates secreted by plants in the root zone. There are indication that high number of PAH degraders also correlates well with the amount of PAH biodegradation activity in soil and soils with a high total PAH content contain more PAH utilizers (10 5 -10 10 bacteria per gram of soil) than soils with low PAH content (Cerniglia, 1993).…”

Assessment of secondary metabolites in Pennisetum purpureum planted into constructed wetlands using shale and laterite as substrate for wastewater treatment

“…The results showed that the plants were equally well adapted to the shale-filled and laterite-filled constructed wetlands, as evidenced by the heights achieved (77.6 and 50.9 cm in the shale- and laterite-lined beds respectively) and the above-ground biomass produced (14.7 kg m −2 in the shale lite and 12.5 kg m −2 in the laterite lite). This is linked to the used nature of the water supplied to the different beds during experimentation, as indicated by Zahui et al [ 7 ]. However, P. purpureum grown in the natural environment produced larger stems and above-ground biomass compared with plants in constructed wetlands.…”

“…The beds were planted with P. purpureum seedlings (20 cm tall) from nurseries set up for this purpose on the experimental site. Three (3) plant seedlings of equal vigour were transplanted onto each bed, with a spacing of 30 cm between seedlings, relatively similar to that used by Zahui et al [ 7 ]. The beds were fed for three days during the week ( i.e.…”

“…), due to their low installation and operating costs, ease of use and good integration into the landscape [ 1 ]. Indeed, the constructed wetland process has been used successfully around the world in the removal of organic pollutants [ 2 , 3 ], nutrients [ 4 , 5 ], pathogens [ 6 , 7 ] and emerging pollutants [ [8] , [9] , [10] ] in domestic, industrial and agricultural wastewater.…”

“…In addition, P. purpureum has very high productivity, as a biofuel crop [ 47 , 48 ]. Thus its use in constructed wetlands could generate income likely to ensure the maintenance of the process, especially since the quality of its biomass post wastewater treatment has been proven [ 7 ]. Furthermore, the study of the production of secondary metabolites of P. purpureum would constitute added value to scientific knowledge relating to the adaptation mechanisms of this plant in constructed wetlands treating wastewater.…”