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Treatment of the liquid fraction

Processing methods particularly suitable for very diluted manures or liquid fractions obtained after separation.

The descriptions of these livestock manure processing technologies were based on 'Flotats, Xavier, Henning Lyngsø Foged, August Bonmati Blasi, Jordi Palatsi, Albert Magri and Karl Martin Schelde. 2011. Manure processing technologies. Technical Report No. II concerning “Manure Processing Activities in Europe” to the European Commission, Directorate-General Environment. 184 pp."

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Short description

Membrane filtration targeting removal of solid particles from liquid fractions.

Best Available Technique: Not indicated
Objective

Micro filtration (MF) is often used on the liquid fraction, to separate or remove suspended solids, bacteria and virus. Often micro filtration is a type of pre-treatment for the reverse osmosis treatment (RO). Microfiltration is a low-pressure cross-flow membrane process for separating colloidal and suspended particles in the range of 0.05-10 microns.

Ultra filtration (UF) concentrates suspended solids and solutes of molecular weight greater than 1,000. The permeate has low-molecular-weight organic solutes and salts. Small dissolved molecules pass the filtration and can be removed by reverse osmosis (RO).

Level of complexity

Usual scale

Innovation stage

General diagram

Applied to







Typical technology combinations Coagulation-flocculation, Separation by drum filtration, air flotation, reverse osmosis
Pictures

Illustration from Koch membrane systems (www.kochmembrane.com).

Theroetical fundamentals and process description

There are several different techniques of membrane filtration, and those are categorized according to pore size in the membrane. The size of the particles retained by the membranes, thus decreasing with decreasing pore size. All the four membrane techniques listed in the following table and Figure (www.kochmembrane.com) have the pressure difference across the membrane as the driving force for the process. The smaller pore sizes, the higher the needed pressure.

Membrane type Size of pores, μm Pressure (bar) Flux (l m-2 h-1 bar-1)
Micro Filtration (MF) 0.03 - 10 0.1 - 2.0 >50
Ultra filtration (UF) 0.002 - 0.1 1 - 5 10 - 50
Nano filtration (NF) 0.001 - 0.01 5 - 20 1.4 - 12
Reverse smosis (RO) 0.0001 - 0.001 10 -100 0.05 - 1.4

Membrane processes such as micro filtration (MF) has long been used to provide clean drinking water in areas with poor water resources, but these are relatively new for slurry separation.

Ultra filtration (UF) is made on the liquid separation fraction. It is a type of pre-treatment for the reverse osmosis treatment (RO), both technologies being part of a high tech manure treatment facility where the liquid part is purified up to (or near to) clean water. The ultra filtration process will remove suspended solids as well as bacteria and virus, while small dissolved molecules passes the filtration and can be removed by reverse osmosis, where the pore size of the membranes is smaller.

Schematics of the reverse osmosis process (left) and illustration of a cleaning unit wit reverse osmosis (www.kruger.dk).

Microfiltration and ultra filtration is fundamentally different from reverse osmosis and nano filtration becausethose systems use pressure as a means of forcing water to go from low pressure to high pressure (to control the reverse diffusion through the membrane). MF and UF can use a pressurized system but it does not need to include pressure. The compounds retained in the MF and UF are mainly molecules and colloids, which form a "cake" at the membrane surface.

NF and RO detain mostly ions and the osmotic pressure is the governing parameter for the diffusion of water across the membrane. During NF and RO, it is important to avoid precipitation of solids in the membrane (scaling), as this will cause a pressure drop across the membrane. Therefore, the substance concentration and solubility are limiting factors for membrane plant utilization.

In many membrane plants a flow longitudinally along the membrane (crossflow) is often maintained, to reduce the concentration of substances by the membrane surface. This leads to a reduction of the concentration of retained material, and thereby risk of scaling / fouling decreases.

If the slurry is pressurized on one side of such a membrane, its water content is pushed through the membrane. It is thus possible by the use of membrane filtration to remove ammonia and potassium from the slurry liquid phase. There are many materials that can be used to manufacture membranes, for example cellulose acetate, polyamide and polysulfone. These materials are distinguished by specific characteristics in relation to porosity, pore size and resistance to various substances and environments.

The geometric shape of the membrane is important for internal hydraulic conditions. Moreover, the geometric shape of the membrane affects the physical plant design, and affects how easy the membrane is to be cleaned or recovered.

Environmental effects

Effects on air (emissions):

  • The filtration process has no negative effects in it, concerning emissions or odours.

Effects on water/soil (and management):

  • As regards leaching of N and P, it can have a positive effect, assumed that the products of the process (fibre fraction, concentrate and permeate) are being used in the most optimal way; field crops can be fertilized with more precision according to their demands. High reduction of recalcitrant organic matter.

Other effects:

  • Sanitation and retention of pathogens.
Biosecurity aspects
  • Sanitation and retention of pathogens.
Technical indicators

Conversion efficiency:


The process can remove 99% of the organic matter and up to 99.5% of the salts. For manure treatment the K ion still remain in the water fraction and might be the limiting factor for the use of this water as irrigation water. The input in the process is a liquid fraction, for instance coming from ultra filtration.
  • Net energy consumption - explanation:

    Energy consumption by membrane filtration depends on the pore size, material concentrations, pretreatment and operating pressure. There is a clear correlation between the operating pressure and energy consumption. Below is the energy consumption per m3 of purified liquid; Data is for purification of drinking water:

    Ultra filtration 0.2 - 1.0 kWh/m3
    Nano filtration 0.7 - 1.5 kWh/m3
    Reverse osmosis 1.5 - 10 kWh/m3

     

  • Reagent 1 - explanation:

    There may be addition of chemicals before the membrane process to increase retention of selected substances or to reduce clogging of the membrane. Belgian trials, for instance, showed that acidification before RO increases retention of nitrogen, since RO membrane can better retain charged ions as ammonium rather than non-charged molecules such as ammonia.

Observations
Economic indicators (Economic figures are rough indications, which cannot be used for individual project planning)
  • Operational costs - explanation:

    International experience estimates that the cost of treatment of slurry in a membrane plant will be in the range 1.4 to 8 U.S. dollars (approximately 1 to 7 Euro) per tons of manure.

Literature references
  • Foged, Henning Lyngsø. 2010, Best Available Technologies for Manure Treatment – for Intensive Rearing of Pigs in Baltic Sea Region EU Member States. Published by Baltic Sea 2020, Stockholm. 102 pp.
  • Hinge, J. (2005): Technology for slurry separation – membrane filtration and reverse osmosis. Danish Agricultural Advisory Service, DK 8200 Aarhus – A resume of: Miljøprojekt nr. 882, 2004, Membranfiltrering, erfaring og muligheder i dansk vandforsyning, Miljøstyrelsen
  • Thörneby, L., Persson, K., Trägårdh, G., 1999, Treatment of liquid effluents from dairy cattle and pigs using reverse osmosis. J. Agric. Engng Res. 73, 159-170.
  • Pieters, J.G., Neukermans, G.G.J, Colanbeen, M.B.A., 1999, Farm-scale membrane filtration of sow slurry. J. Agric. Engng Res. 73, 403-409.
  • Fugère, R., Mameri, N., Gallot, J.E., Comeau, Y., 2005, Treatment of pig farm effluents by ultrafiltration. Journal of Membrane Science.
Real scale installation references

Reverse osmosis :
Kumac BV
Lupinenweg 8a
5753 SC Deurne
Tel.: +31 0493-312721
www.kumac.nl

Ultra filtration:
Coöperatie van Veehouders Biogreen UA
Weseperweg 45a
111 PJ Heeten
The Netherlands
Tel: +31 0572-381599
http://www.greenpowersalland.nl/

Examples of suppliers