Researchers from the Universidad Politécnica de Madrid and the Universidad Miguel Hernández of Elche have found the way to increase biomass production by using sewage sludge as energy crop fertilizers. The idea’s press release is getting international attention.

Its not a new idea exactly. The City of Milwaukee Wisconsin has been the source of “Milorganite“, one of the oldest branded fertilizers on the market today, since 1926. Milorganite is the trademark of a biosolids fertilizer produced by the Milwaukee Metropolitan Sewerage District. Get it at a Home Depot near you. It is composed of heat-dried microbes that have digested the organic matter in wastewater. The Milorganite program is one of the world’s oldest and largest recycling efforts.

The Spaniard’s idea is a little different, though. They have carried out joint research work to determine the fertilization effects with sewage sludge compost. That’s quite a different thing. The effects were tested on cynara productivity over 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 – a substantial increase of energy crop production.  The team’s paper has been published in The Journal of Cleaner Production.

Sewage Sludge in a Dewatered Form.  Click image for the largest view.

Sewage Sludge in a Dewatered Form. Click image for the largest view.

The usage of sewage sludge to fertilize energy crops could be an opportunity to reuse the fertility elements since these farm products are not intended for the human food industry.

Recovery and reuse of metropolitan sewage is rife with frightening problems. Sewage can contain horrific microbes like polio, cholera and a broad array of other scary things like heavy metals. Its not exactly cheap to clean it up enough for your garden. The clever folks in Milwaukee have done just that by going one more step and harvesting the microbes without the chemicals and diseases going along too.

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

There producers can obtain two types of biomass from cynara crops every year. One is the lignocellulosic biomass which is useful for a solid biofuel in producing thermal energy. The other type of biomass is an oilseed that by extracting the oil can be used for advanced biofuels such as biodiesel production.

Sewage sludge is a residual and organic product rich in nutrients that 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 to make them more productive. Using sewage sludge and its derivatives to fertilize crops, instead of mineral fertilizers, does not involve any direct risk because these energy crops are not intended for food industry. The Spaniards believe study is needed to quantify the effects when using this fertilizer on the performance of energy crops.

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 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.

All well and good, if a little vague. So folks, “What does it cost to do it this way?”

There is a huge value of natural fertilizer being generated every day across the developed world that can be found at the water treatment facilities of every town and city. People are at the top of the food chain, or more adroitly, the carbon cycle. It seems quite weird that the planet’s top critter’s waste is the last one to be regularly returned to the natural order of things. Lazy people.

Think about it the next time you consider pouring chemicals down the drain.


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