Christensen, Morten Lykkegaard

Keiding, Kristian

Animal production is becoming increasingly concentrated on large farms. Large amounts of manure are produced of which the N:P ratio often differs from the crop requirements. A possible solution is to separate manure into a P-rich solid fraction and a liquid fraction, which would improve the distribution of N and P on the fields. Filtration is a useful method for such a separation. Furthermore, chemicals can be added to flocculate the solids and thereby increase the filterability i.e. the specific filter-cake resistance can be reduced from 1015 m/kg to 1011 m/kg. Both the amount of added chemicals, and the mixing procedure affect the result, and lab-scale experiments are often used to study how these pre-treatments influence the filtration process. However, the existing mathematical filtration models are based on filtration of inorganic particles and cannot simulate the filtration data obtained when manure is filtered. Hence, it is not possible to scale up the experiments, and it is therefore difficult to optimize the flocculation and estimate the needed filter media area. Similar problems have been observed when sewage sludge and synthetic core-shell colloids are filtered, and it has been suggested that the discrepancy between the filtration theory and the observed filtration behaviour is due to a time-dependent collapse of the formed cake (creep). This can also explain the observed behaviour when flocculated manure is filtered. The filtration data can be simulated if cake creep is adopted in the filtration model. The calculation shows that the specific filter-cake resistance increases by a factor of 3 during the filtration. Thus, the impact of cake creep is significant when organic materials such as manure are filtered

    Aalborg UniversitetCake creep during filtration of flocculated manureChristensen, Morten Lykkegaard; Keiding, Jens KristianPublication date:2007Document VersionEarly version, also known as pre-printLink to publication from Aalborg UniversityCitation for published version (APA):Christensen, M. L., & Keiding, K. (2007). Cake creep during filtration of flocculated manure. Poster sessionpresented at European Congress of Chemical Engineering, København, Denmark.General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.            ? Users may download and print one copy of any publication from the public portal for the purpose of private study or research.            ? You may not further distribute the material or use it for any profit-making activity or commercial gain            ? You may freely distribute the URL identifying the publication in the public portal ?Take down policyIf you believe that this document breaches copyright please contact us at vbn@aub.aau.dk providing details, and we will remove access tothe work immediately and investigate your claim.Downloaded from vbn.aau.dk on: April 30, 2017Cake creep during filtration of flocculated manureIntroduction Compression of cakesMorten Lykkegaard Christensen and Kristian KeidingDepartment of Biotechnology, Chemistry and Environmental Engineering, Aalborg University, DenmarkSwine production is more and more concentrated on large farms. Largeamount of manure are produced and several problems have been reportedsuch as losses of nutrients to the environment, ammonia emissions, andodor. Manure separation may solve some of the problems.Manure can be separated into a high dry-matter and nutrient-rich fiberfraction and a liquid fraction. It is thereby possible toThe specific filter-cake resistance depends on cake porosity. At lowpressure a loosely packed cake is form with low resistance. At higherpressures the cake is compressed and the resistance increases. Hence,compressible cake are more compact near the filter media than at the top.Different mechanism can be suggested for cake compression, such as:Rearrangement:1. Reduce cost for transportation of nutrients to fields with nutrientdefiant2. Adjusting the distribution of nitrogen and phosphorus on the fieldswith crop demands3. Minimize odor problems4. Remove heavy metalsSieves, screw presses, belt presses, and decanter centrifuges have beend F th h i l F Cl Al (SO ) C (OH) l hDeformation:Compression:use . ur er, c em ca s e.g. e 3, 2 4 3, a 2 or po ymers avebe added to flocculate manure and improve removal of dry matter andphosphorus from the liquid fraction.Lab scale experiments can be used to study the dewatering process SuchIt is in the conventional filtration theory assumed that cake porosity is aunique function of pressure. As a consequence the specific filter-cakeresistance is constant during filtration. The filtration theory has been testedon inorganic particles such as anatase, bentonite, and china clay.Compression of these cakes is mainly due to rearrangement. Nevertheless,both deformation and compression of individual particles are important forwater-containing particles. Deformation and compression of individualparticles are time-dependent processes (creep phenomena). Hence, thecake porosity is a function of both pressure and time.Figure 1. Flocculated manure. Irregular water-containing flocs (0.1 - 5 mm) formed during flocculation- .knowledge can be of great value in order to optimize the chemical pre-treatment and dimensioning the equipment. However, the problem is thatthe existing models cannot describe dewatering processes for flocculatedmanure satisfying. The idea of this work is to used pressure filtration tostudy dewatering of flocculated manure in order to better understand theprocessFilt ti thSimple model for cake resistanceThe specific filter-cake resistance has been calculated by introducing aninitial resistance (α0), a resistance increase (Δα) and a time constant (τ):( )τααα /0 1 te−−Δ+=ra on eoryDuring filtrations, a suspension is pressed towards a filter mediumpermeable to the liquid but impermeable to the particles. Particlestherefore deposits on the media forming a three-dimensional networkstructure (cake). The filtrate rate is mainly controlled by the hydraulicresistance of the cake.The equation has been used to simulate a filtration experiment of swinemanure flocculated with FeCl3 and cross-linked cationic polymer.Flocculated Figure 2. Filtration principleFigure 3. Filtration of manureFiltration of 56 g/L manure at 2 bar.              Dotted line (conventional model): α = 2.4·104 m/kgSolid line (creep model) : α0 = 2.4·104 m/kg, Δα = 7 2 104 /k d  75Filtrate (mL)406080100Piston touches cakeIn conventional models, the filtrate rate (q) is a function of appliedpressure (P), filtrate viscosity (µ), specific filter-cake resistance (α), andmass of cake per media area. It is assumed that the mass of cake increaseIt is thereby possible to simulate the data until the piston touches the cake.Final remarksCakemanureFilter mediaFlocs are deposed on the filter media during the filtration and forms a continuous network structure (cake). The liquid have to pass the cake during the dewatering process and the filtrate rate is mainly determined by the properties of the cake.. ·  m g, an  τ =  s.Time (min)0 1 2 3 4 5020proportional with filtrate volume.However, the model do not fit filtration data for flocculated manureDeformation and compression of individual water-containing particles leadsto cake creep and cannot be simulated by existing filtration models. Hence,new models for cake compression are needed. These models have to betested by using simple well-characterized model materials.αωµPq =

Cake creep during filtration of flocculated manure

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Cake creep during filtration of flocculated manure

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