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Purification of purines through electroflotation

14.01.2003

ADE Biotec and the INASMET Foundation, both from the Basque Country, after three years of working together, have developed a new purification technique for purines. The technique is based on electroflotation and could be very beneficial for agriculture as it has a high level (80%+) of purification and very low costs (1 euro/m3). Most of the development project has been carried out at a pilot plant on a Toledo pig farm.

Nowadays purines (excrements plus sewage water from farms) constitute one of the most important problems for agriculture, both from an environmental point of view (its massive use produces contamination of water and land), as well as from an economic aspect (its management demands a lot of time and dedication).

The key to this problem is found in the intensification of agriculture: pastoral farms have ever-increasing numbers in their herds. This logically results in an increase of purines on the farms, assuming there is no increase in the extension of the land on which this fertiliser is used.

In recent years new technologies have been proposed to solve the problem of the purification of purines: anaerobic digestion, biological reactors, composting, drying through co-generation, etc. Even so, the sector still does not have any economically and environmentally viable technique to tackle the problem. In this sense, electroflotation could provide an important step to the answer.

Electroflotation

Electroflotation consists in transferring the purine from one metal plate to another while injecting a low-voltage electrical current between the plaques. Using this method and, as a consequence of the electric current, two phenomena are observed:

- On the one hand, the iron (Fe2+) from the plates dissolves, coagulating the organic material of the purine and making it flocculent. Thus, the organic material takes the form of small balls and can be easily separated from the water.
- On the other, hydrogen bubbles are created making the organic materia float on the water and creating an upper layer easily extractable.

In this way, more than 80% of the chemical Demand of oxygen (quantity of oxygen consumed by the compounds which are oxidised in the water), phosphorous, and nitrogen can be removed from the purine and thus complying with the requirements for its dumping into tanks or for its use on irrigated land). After the process the purine has the aspect of water that is somewhat clearer than natural cider. Moreover, if the procedure is prolonged, using the appropriate techniques, a liquid which is suitable for release into rivers can be achieved.

Other advantages of this technique are its low costs (1 euro/m3 of purine), chemical reagents being unnecessary and without limitations of scale (i.e. applicable to both large and small farms) as well as its easy automation.

Currently, ADE Biotec has a pilot plant in Santa Cruz de Rematar (Toledo) where 1,000 litres of purine per hour are treated. It is hoped that a new plant will be shortly built with a greater capacity and, thus, to validate the technology at an industrial level.