Application of treated wastewater and digested sewage sludge to obtain biodiesel from Helianthus annuus L. seeds oil

ABSTRACT

Waste from wastewater treatment plants (WWTP) for Helianthus annuus L. production may be a viable solution to obtain biodiesel. This study achieved two objectives: assess the agronomical viability of waste (wastewater and sludge) from the Alcázar de San Juan WWTP in central Spain for H. annuus L. production; use H. annuus L. seeds grown in this way to obtain biodiesel. Five study plots, each measuring 6 m × 6 m (36 m²), were set up on the agricultural land near the Alcázar de San Juan WWTP. Five fertilizer treatment types were considered: drinking water, as the control; treated wastewater; 10 t ha⁻¹ of air-dried sewage sludge; 20 t ha⁻¹ of air-dried sewage sludge; 0.6 t ha⁻¹ of commercial inorganic fertilizer. Soil, irrigation water, sewage sludge, crop development and fatty acid composition in achenes oil were monitored. The 20 t ha^–1 dose of sewage sludge proved effective to grow H. annuus L. with similar results to those grown with a commercial fertilizer. However, precautions should be taken when irrigating with wastewater because of high salinity and nutrient deficiency. Sunflower oil was composed mostly of linoleic and oleic acid. The remaining fatty acids were linolenic, estearic, nervonic, palmitoleic, and palmitic.

KEYWORDS:

• Biodiesel
• energy crops
• environmental sustainability
• Helianthus annuus L.
• sewage sludge
• wastewater

Acknowledgments

We wish to thank María Cruz Cano for her collaboration in the fieldwork. Finally, thanks go to Helen Warburton for reviewing the English text.

Funding

The authors are grateful to the municipally owned company “Aguas de Alcázar” and the Alcázar de San Juan Town Hall for financial support through the project entitled: “Aptitud para usoagrícola del Agua y lodos procedentes de la depuradora de aguas residuales de Alcázar de San Juan”.