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Heavy metal removal from manure

Final Activity Report Summary - LIGHT MANURE (Heavy metal removal from manure)

In many European countries usage of fertilisers is the main source of heavy metals (HM) input into the agro-ecosystems. In the Netherlands, the main way of the soil pollution by Cu and Zn is liquid manure fertilisation (especially pig manure). The objective of this project was to decrease the environmental risk of using organic fertilisers by removing the heavy metals from it by electro-remediation using DC voltage.

Research revealed that HM mobility is a strong function of manure pH. Remediation results at normal pH levels of 7-8 yielded only a decrease of 25.5 % for Cu and 24.7% for Zn. By changing the experimental setup, it was possible to break the buffering capacity of manure. By placing the anode into the manure, it was possible to obtain manure with a pH below 2 using a current density of 2.8-25 Ampere/m2. Remediation results in this case showed a maximal decrease of 85.4 % for Cu and 87.3 % for Zn. This is an increase in remediation efficiency of more than 300%. The heavy metals end up in the cathode compartment, where they precipitate as hydroxyl salts and partially attached to cathode. The remaining cathode fluid has a high pH (13- 13.5) and a high K+ and NH4+ content.

An additional achievement during the low pH remediation of manure is the enhanced separation of the liquid manure into two self-separating fractions. The liquid top-fraction (55-70 volume %) has a very low dry matter content and contains hardly positive ions such as K+ and NH4+. The sediment bottom-fraction has a very high dry matter and high phosphate content.

Drawbacks of the remediation procedure and technical solutions to resolve these:
- Foam production during the remediation was overcome by the application of liquid paraffin or vegetable oils
- The time necessary for the remediation was influenced by dry matter content (more solids, higher buffering capacity, longer remediation) and the applied current density (higher value, quicker process).

Advantages of the remediation procedure:
- Production of manure products containing low heavy metal concentrations.
- Separation of the manure into valuable products.
- Pasteurisation of manure after electroremediation process.