4.1 Olga Popovic – University of Copenhagen

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WP 4.1: Development of enhanced mechanical separation efficiency by combined separation techniques, pre and post-treatmentOlga Popovic, UTO

Separation efficiency of mechanical slurry separators (producing dry matter and P rich solid fraction) vary widely, due to differences in separator design (e.g. filter or screw press, centrifugation) and variable physical and chemical  composition of animal slurry. Previous studies have shown that inclusion of chemical pre-treatments (e.g. adding salts and polymers) before mechanical separation has the potential to lower the P content in the liquid fraction, reduce the volume of the solid fraction (by reducing water  content) and enhance the capacity of separation equipment.

Further research is needed to optimize currently available (on the market) mechanical separation technologies and to develop enhanced processes further in order to produce “clean” liquid fraction (low dry matter and nutrients concentration), and solid fraction rich in dry matter and nutrients (primarily P and organic N). The objective of the post doc project was to determine the effect of additives addition to the raw pig slurry and co-digestate on separation efficiency (removal of dry matter, N, P and K to solid fraction) of mechanical separation technologies. The first activity set out to optimize the dose of biochar and flocculants as pretreatments so the highest effectiveness of raw and co-digested pig slurry is achieved. Biochar, chitosan, and polyacrilamide-PAM, alone and in combination (biochar+flocculant) were introduced to raw slurry and co-digestate prior to separation. The main findings of this study were that the addition of biochar and flocculants increased mass separation efficiency of mechanical separators. The addition of PAM to biochared slurry showed the highest separation efficiency. There was no effect of PAM addition to co-digestate and the effect of biochar addition to raw slurry on separation efficiency is time dependent.

A second experiment was undertaken to evaluate if the separation efficiency (with respect to DM, N, P, K, Cu, and Zn) of mechanical separators (screw press and centrifuge) was affected when biochar was added to the raw slurry. The effect that adding biochar had on the separation system efficiency, which already included chemical-pre-treatment (flocculant addition), was tested. Main results showed that screw press was more efficient in removing dry matter to solids when compared to centrifugation. In general, all of the pre-treatments performed more efficiently prior to screw press than to centrifuge for all analysed chemical characteristics. The main conclusions from this experiment are i) that pre-treatments had a stronger effect on screw press than on centrifuge, with respect to all analysed parameters; ii) the addition of biochar, chitosan, and their combination did not improve separation efficiency of screw press and centrifugation, and did not increase the elemental content of produced solid fractions; iii) PAM followed by screw press was effective at removing P, Cu, and Zn to solids, and in producing liquid fraction with the lowest dry matter and elemental contents; and iv) in combination with biochar, liquid fractions produced increased total N, and low P, Cu, and Zn content.

In a third experiment, we investigated the effect of anaerobic digestion on efficiency of chemical-mechanical separation system (flocculant+mechanical separation). Five separation treatments were applied to collected co-digestate, at laboratory scale including two polymers namely 1) PAM; and 2) Chitosan, applied prior to screw press and centrifugation. The following central conclusions were reached: i) PAM addition prior to both mechanical separators had very little effect on their performances with respect to total dry matter, N, P, K, Cu and Zn removal to solids fraction; ii) Addition of chitosan to co-digestate followed by screw press and centrifugation resulted in liquid fraction with very low metal (Cu and Zn) content.

  • Popovic Olga, Gioelli Fabrizio, Dinuccio Elio, Balsari Paolo (2014) Improved pig slurry mechanical separation using chitosan and biochar, Biosys. Eng. 127, 115-124. 
  • Popovic, O., Gioelli, F., Dinuccio, E., Balsari, P., 2015. Chitosan effects on centrifugation efficiency in separating co-digestate. Submitted manuscript.
  • Gioelli, F., Popovic, O., Dinuccio, E., Balsari, P., 2014. Effect of different chemical-mechanical separation systems on biogas potential of raw pig slurry and co-digestate solid fractions. Submitted manuscript. 

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