A mathematical model and criteria for designing horizontal-¯ow anaerobic immobilized biomass reactors for wastewater treatment

The development and the preliminary evaluation of a mathematical model used to design a horizontal-¯ow anaerobic immobilized biomass (HAIB) reactor applied to domestic sewage treatment is presented. The in¯uences of both the liquid super®cial velocity and the bioparticle size on the overall reaction rate were examined. The size of the particle used as biomass support was found to a€ect strongly the total volume of the designed unit since the e€ectiveness factor decreased as the bioparticle size increased. On the contrary, the overall organic matter conversion rate was not substantially in¯uenced by the liquid velocity. Based on these data obtained from the mathematical model, a pilot-scale HAIB reactor was constructed adopting some design parameters and following the design criteria established. The HAIB reactor comprised a 14.5 cm internal diameter PVC tube with length of 14.4 m divided in to ®ve stages of 2.88 m each. Polyurethane foam cubic matrices with 1 cm side were used as support for biomass immobilization. The reactor was operated at a mean hydraulic retention time of 4.3 h at mean sewage temperature of 25 ‹ 1°C and mean liquid ¯ow rate of 20 L hÿ1. A preliminary evaluation of the mathematical model proposed to design the HAIB reactor was performed based on data of chemical oxygen demand (COD) pro®les along the reactor length. Although deviations were observed between experimental and theoretical data, the proposed model was found to be suitable for predicting the overall behavior of the reactor.