Application of treated wastewater and digested sewage sludge to obtain biomass from Cynara cardunculus L

Waste from wastewater treatment plants (WWTP) for Cynara cardunculus L. production may be a viable solution to obtain biomass. The term “biomass” refers to organic matter that has stored energy through the photosynthesis process. The study achieved two objectives: firstly, to assess the agronomical viability of waste from the Alcázar de San Juan WWTP in central Spain (wastewater and sludge) for Cynara cardunculus L. production; secondly, the use of biomass from Cynara cardunculus L. grown in this way to obtain thermal energy. Five study plots, each measuring 10 m × 10 m (100 m2), were set up on agricultural land near the Alcázar de San Juan WWTP. Five fertilizer treatment types were considered: drinking water taken as the control, treated wastewater, 1 t ha−1 of air-dried sewage sludge, 2 t ha−1 of air-dried sewage sludge and 0.7 t ha−1 of commercial inorganic fertilizer. The soil, irrigation water, sewage sludge and heating values (higher heating value and lower heating value) of the biomass were monitored. Waste from the Alcázar de San Juan WWTP proved useful to obtain the same biomass heating values as if traditionally cultivated with a commercial fertilizer. However precaution should be taken when irrigating with wastewater because of high salinity.