Journal of Chemical Technology and Biotechnology J Chem Technol Biotechnol 79:851–862 (online: 2004) DOI: 10.1002/jctb.1059 Treatment of settled piggery waste by a down-flow anaerobic fixed bed reactor Enrique S ´ anchez, 1 Rafael Borja, 1∗ Lissette Travieso, 1 Manuel F Colmenarejo, 2 Arturo Chica 3 and Antonio Mart´ ın 3 1 Instituto de la Grasa (CSIC), Avda. Padre Garc´ ıa Tejero, 4, E-41012 Sevilla, Spain 2 Centro de Ciencias Medioambientals (CSIC), c/Serano 115-duplicado, 28006 Madrid, Spain 3 Departamento de Ingenier´ ıa Qu´ ımica, Facultad de Ciencias, Campus Universitario de Rabanales, Edificio C-3, Ctra Madrid-Cadiz, Km 396, 14071 C ´ ordoba, Spain Abstract: A study of the effect of organic volumetric loading rate (B V ) on the performance of a down-flow anaerobic fixed bed reactor (DFAFBR) treating settled piggery waste was carried out at a range of between 1.1 and 6.8 g COD dm -3 d -1 . The reactor operated at good removal efficiencies and stability under the operational conditions studied. Logarithmic empirical equations described adequately the removal efficiency for different parameters studied (COD, SCOD, BOD, TS, VS, TSS, VSS and phosphorous). Although process stability was affected by the increase of B V , process failure was not observed. A logarithmic relationship was found to describe the influence of B V on the TVFA/alkalinity ratio (p). A linear correlation was found between the effluent substrate concentration and the values of p and between p and the CO 2 /CH 4 ratio in the biogas. The effect of the hydraulic volumetric loading rate (H V ) on the flow pattern of the reactor was evaluated. Dispersion number (D n ) was in the range of 0.17–0.37 for the maximum and minimum values of H V studied, respectively. The ratio between the real and theoretical HRT increased as the H V decreased. These results demonstrate that axial dispersion increased as the H V and the Reynolds number decreased. Due to the hydraulic behaviour of the reactor, the kinetic model developed by Lawrence and McCarty was used for describing the experimental results obtained. Maximum specific substrate removal rate (K ), specific organic loading rate constant (K L ), microbial decay coefficient (K d ), microbial yield coefficient (Y ), maximum microbial growth rate (U M ) and saturation constant (K S ) were found to be: 3.1 (g COD g VSS -1 d -1 ), 3.0 (g COD g VSS -1 d -1 ), 0.062 (d -1 ), 0.15 (g VSS g COD removed -1 ), 0.39 (d -1 ) and 2.6 (g SCOD dm -3 ), respectively.  2004 Society of Chemical Industry Keywords: piggery waste; anaerobic digestion; down-flow fixed bed reactor; operational parameters NOTATION AN Ammonia nitrogen concentration (g dm −3 ) B V Organic volumetric loading rate (g COD dm −3 d −1 ) B X Specific loading rate (g COD g VSS −1 d −1 ) BOD Biochemical oxygen demand at non- filtered samples or total BOD (g O 2 dm −3 ) C Tracer concentration (given in conductiv- ity) at the effluent of the process C 0 Initial tracer concentration (given in con- ductivity) COD Chemical oxygen demand at non-filtered samples or total COD (g O 2 dm −3 ) D n Dispersion number DFAFBR Down-flow anaerobic fixed bed reactor E F Fractional removal efficiency E i Quotient between C and C 0 (C/C 0 ) H V Hydraulic volumetric loading rate (dm 3 wastewater dm −3 reactor d −1 ) HRT Hydraulic retention time (d) HRT R Average real hydraulic retention time (d) HRT T Theoretical hydraulic retention time (d) K Maximum specific substrate removal rate (g COD g VSS −1 d −1 ) K d Microbial decay coefficient (d −1 ) K L Specific organic volumetric loading rate at R S equal to K /2 (g COD g VSS −1 d −1 ) K 1 , K 2 Dimensionless empirical constants related to the fractional removal efficiency ON Organic nitrogen concentration (g dm −3 ) p TVFA/alkalinity ratio (equiv acetic acid equiv −1 CaCO 3 ) Phos Phosphorous concentration (g dm −3 ) q Influent flow-rate (dm 3 d −1 ) ∗ Correspondence to: Rafael Borja, Instituto de la Grasa (CSIC), Avda Padre Garc´ ıa Tejero, 4, E-41012 Sevilla, Spain E-mail: rborja@cica.es Contract/grant sponsor: Ministerio de Ciencia y Tecnolog´ ıa; contract/grant number: REN 2001-0472/TECNO Contract/grant sponsor: Junta de Andalucia Contract/grant sponsor: Ministerio de Educaci ´ on, Cultura y Deportes (Received 12 June 2003; revised version received 3 December 2003; accepted 17 December 2003) Published online 19 May 2004  2004 Society of Chemical Industry. J Chem Technol Biotechnol 0268–2575/2004/$30.00 851