Using sewage sludge to obtain bioenergy

The Agroenergy Group from the Universidad Politécnica de Madrid (UPM) and researchers of the Universidad Miguel Hernández (UMH) of Elche have carried out a joint research work to determine the fertilization effects with sewage sludge compost into cynara productivity during three years. The results showed that the usage of this fertilizer has clear positive effects since the biomass production and the oilseeds increased up to 40% and 68% respectively, being this a substantial increase of energy crop production.

The usage of sewage sludge to fertilize energy crops could be an opportunity to release residues since these plantations are not intended for food industry.

Energy crops, such as the cynara ones (Cynara cardunculus L.), are crops specifically intended to the production of a renewable energy which is biomass energy or bioenergy. It is an herbaceous perennial crop adapted to Mediterranean climate with annual growth cycles. This will allow the same crop can be harvested every year.

We can obtain two types of biomass from cynara crops every year: the lignocellulosic biomass which is useful both for solid biofuel for thermal energy and for production of advanced biofuels, and the other type of biomass are oilseeds that by extracting the oil can be used for biodiesel production?

Sewage sludge is a residual and organic product rich in nutrients which is increasingly generated as a consequence of the treatment of growing amounts of urban wastewater. Because of its origin and composition, the usage of sewage sludge in agriculture is regulated in order to avoid risks of contamination of food products and the environment.

The fertilization of energy crops is essential in the management of the crop in order to not deplete soils and make them more productive. Using sewage sludge and its derivatives to fertilize crops, instead of mineral fertilizers, do not involve any risk, since these energy crops are not intended for food industry. Therefore, it is needed to study and quantify the effects on the performance of energy crops when using this fertilizer.

This joint research of UPM, with Dr. Lag-Brotons, and researchers from UMH, shows the effects of using sewage sludge compost as fertilizer of energy crop of cynara for three consecutive years. Researchers used four levels of fertilization with composted sludge and they determined during the following crops the performance in lignocellulosic biomass, oilseeds, oil and total energy.

The results showed that deep fertilization with sewage sludge compost has clear positive effects on crop productivity. Using sewage sludge compost has also achieved synergies from diverse areas of interest such as soil protection, the maintenance of its fertilization, the usage of residual products from the management of urban wastewater, and biomass production for energy purposes.