System with the objective of separating manure into two flows: a concentrate (solid fibre fraction) and a diluted fraction (liquid fraction). 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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Physical- Chemical system where separation is enhanced by the help of a chemical agent (coagulant or flocculant) which improves the aggregation of colloids. Usual inorganic flocculants are multivalent cations such as aluminium, iron, calcium or magnesium, added as salt or hydroxide, and the organics ones are polyelectrolyte polymers such as polyacrylamide.
The main objective of chemical pre-treatment such as coagulation and flocculation is to improve the mechanical separation of livestock slurries by particle properties modification (aggregation/sedimentation/flotation)
Mixing chamber of pig manure with a polymer followed by a rotating screen at Pigneto di Prignano, MO, Italy, (left) courtesy of SELCO MC.
Coagulation and flocculation are chemical pre-treatments that improve the mechanical solid-liquid separation of many suspensions. In most suspensions, colloidal particles will not aggregate because the particles are negatively charged and repel each other. However, aggregation will be facilitated by adding (1) multivalent cations (Al2(SO4)3, FeCl3, etc.) that cause coagulation and/or (2) polymers (polyacrylamide -PAM-, chitosan, etc.), whereby flocculation occurs. The addition of multivalent cations will also enhance the precipitation of phosphorus. Multivalent ions and polymers need to be added carefully to the slurry to achieve satisfactory particle aggregation. If both additives are used, the multivalent ion is added first to the slurry, which is then stirred to ensure homogeneous distribution of ions and dry matter. Then, several minutes of slow stirring are necessary for the charge neutralization and coagulation to occur. Next, the polymer is slowly added in small doses during vigorous stirring, followed by slow stirring, which is necessary for polymer bridging and patch flocculation to occur. The stirring applied (for example, by the impeller, i.e. time and speed), has a large impact on the formation of the aggregates; too low stirring causes the aggregates to be non-uniform and unstable with low particle catchment, while too high stirring causes the aggregates to be destroyed. After the coagulation-flocculation process, the slurry may be transferred to ordinary solid-liquid separators.
Effects on air (emissions):
Performance of some systems implies a high exposition of manure/slurry to atmosphere (high stirred systems) and therefore a risk of gaseous emissions (COV) and odour problems arises. Also during flotation (aeration) a high proportion of ammonia can be discharged into the air. It is therefore necessary to treat or collect the exhaust air from flotation equipment
Effects on water/soil (and management):
As many of solid/liquid separation techniques, nutrients (N, P, K) can be concentrated in the solid fraction enhancing the capability of manure/slurry management. Solid fractions can be more easily exported to areas with low livestock density, reducing problems derived from nutrient surplus, whereas liquid fractions can be used or further processed in site
Separated products are often destined to be deposited in landfills or applied to cultivated fields. Thus, the environmental and health consequences of the polymer used must be considered. The monomers of PAM (acrylamide), used in most slurry separation studies, can be toxic, and specifically carcinogenic. However, a study on separated slurry products showed the risk to be minimal if a biological post-treatment is applied, since PAM is degraded in biological processes without acrylamide accumulation (Campos et al., 2008). In any case, a minimal concentration of the monomer can be found in raw PAM and it must be managed with care. There is a need for further studies to determinate the potentially toxic effect of other alternative polymer types or components produced during its degradation. The possible problems related to PAM use limit the acceptability of this technology as BAT.
Coagulation-flocculation can increase the amount of nutrients in the solid fraction, compared with other S/L separation techniques. Average separation indexes following coagulation and flocculation using different separation techniques were identified by Hjort et al. (2010) as: 22% volume; 70% dry matter; 43% Total-N; 20% NH4-N; 79% Total-P. Summary on separation efficiencies reported using different reagents or polymers can be found in the same reference.
Net energy consumption - explanation:
Energy consumed during stirring (low)
Reagent 1 - explanation:
Chemical reagents used as flocculants or coagulants such as multivalent cations, or polymeric substances
Improvement of separation efficiencies compared to other techniques (by reagent addition).
Coagulation – Flocculation equipment estimated total cost 50.000 € (Foged, 2010). Investment cost per ton is calculated at 5 % interest rate, 10 year depreciation period, 10.000 tons treated each year (167 days x 6 tons/hour x 10 hours/day).
Investment cost - basic price, €:
Investment cost - variable price, € per ton:
Operational costs - explanation:
~ 0.80 €/tonne input slurry (Foged, 2010)
Operational costs - € per ton:
Non economically quantifiable benefits:
Improved separation efficiency