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4.3 Maria Salud Camilleri Rumbau – University of Copenhagen

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Development of membrane technology for production of concentrated fertilizer and clean water, Maria Salud Camilleri Rumbau, University of Southern Denmark

The global increasing livestock production is reflected in a high rate of animal waste production, commonly known as manure or animal slurry. These effluents are rich in nutrients such as nitrogen, phosphorus and potassium. Solid-liquid separation of farm effluents is a common practice for obtaining a phosphorus-rich fraction and a liquid fraction rich in nitrogen and potassium.  However, the nutrient concentration in the obtained liquid fractions remains unbalanced due to the high water content.

Membrane technologies have previously proved to be a suitable technology for separation and concentration of liquid fractions from farm effluents. Based on literature data, by coupling membrane technologies with a solid-liquid mechanical separation technique with low energy consumption, such as screw presses, membrane systems proved to present the best economic potential compared to technologies with high chemical consumption such as ammonia stripping or struvite precipitation. In this PhD thesis, microfiltration, ultrafiltration, reverse osmosis and forward osmosis have been applied during concentration and separation of raw slurry and digestate liquid fractions. MF membranes showed to be able to retain about 80% of the phosphorus present in digestate liquid fractions when using polysulfone membranes. UF polysulfone membranes further proved to be able to remove Fe, Ca, Al, Cu and Zn with more than 99% retention for liquid fractions which pretreatment had been centrifugation alone or centrifugation assisted with flocculation-coagulation. Moreover, Fe was found to be the dominant element in the inorganic fouling structure in UF membranes. RO processing of swine wastewater using spiral wound membranes could retain more than 98% of TAN in the concentrate.

After chemical cleaning of the RO membranes, it was observed that 99% of the fouling resistance could be removed by flushing the membrane with water, suggesting that most fouling might be due to a transient gel layer. Furthermore, water flux could be recovered in more than 98% by using alkaline cleaning alone (NaOH), alkaline cleaning with anionic surfactants (SDS) or alkaline cleaning with chelating agents (EDTA). This suggests that NaOH could be a good and cheap strategy for cleaning RO membranes. Membrane soaking further helped in increasing the membrane water flux recovery. Forward osmosis (FO) was done using aquaporin based membranes.

During FO processing of digestate liquid fractions, membranes were able to retain ammonia nitrogen -TAN while using a highly saline wastewater from a tannery beam house. A salt rejection higher than 90% was achieved along the experiments. However, when acidification of the feed digestate liquid fraction was used, this could lower the final permeate flux in some cases in about 50%. In conclusion, membrane technologies proved to be a suitable technique during concentration of farm effluents and digestates. Further studies on agricultural application of the obtained concentrated fractions are however necessary to prove the suitability of these fractions as a concentrated organic fertilizer in crop production.

  • Camilleri-Rumbau, M.S., Norddahl, B., Wei, J., Christensen, K.V., Søtoft, L.F. (2015). Microfiltration and ultrafiltration as a post-treatment of biogas plant digestates for producing concentrated fertilizers. Desalination and Water Treatment, 55:6, 1639-1653 
  • M.S. Camilleri-Rumbau, O. Popovic, K. Briceno, K.V. Christensen, B. Norddahl (2015) Ultrafiltration of separated digestate with polysulfone tubular membranes: influence of pretreatment and operation conditions on hydraulic performance and heavy metals removal (Submitted)
  • M.S. Camilleri-Rumbau, L. Masse, M. Mondor, J. Dubreuil, M. Mondor, K.V. Christensen, B. Norddahl (2015) Fouling of a Spiral Wound Reverse Osmosis Membrane processing Swine Wastewater: Effect of Cleaning Procedure on Fouling Resistance. Accepted in Environmental Technology.

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