Hybrid and Coupled Model Predictions on the Performance of Separate Two- and Three-Stage Upflow Anaerobic Filters

Abstract This paper deals with hybrid model (HM) and coupled model (CM) predictions on performance of upflow anaerobic filters (UAF) separated in two and three stages (UAF-2SS and UAF-3SS) for removing organic matter from leachates generated in two sanitary landfills in Colombia. Experimental factors to treat leachates in UAF-2SS involved volumetric organic load (VOL) {[1.8 to 4.64 kg chemical oxygen demand (COD)]/m 3 /d} and temperatures (20°C to 34°C). Leachates were treated in UAF-3SS configuring VOL (1.7 to 17.48 kg COD / m 3 / d ) and temperature (20°C to 36°C). Six HMs and five CMs were analyzed through their kinetic parameters. Among the HMs, HM2 was made up of the main experimental factors controlled in the design and operation of the UAF-2SS and UAF-3SS, such as the depth ratio of the UAFs, temperature, and VOL. For HM5, maximum substrate utilization rate was improved as the depth ( d ) ratio was tested from d 1 / d 2 : 20%/80%, 50%/50%, and 80%/20% in UAF-2SS; and d 1 / d 2 / d 3 : 4%/16%/80%, 10%/10%/80%, and 16%/4%/80% in UAF-3SS. Maximum microbial cell growth rate was significantly increased when temperature was changed from 20°C to 34°C, and methane yield rate tended to slightly vary 10 0 − 10 1 mg CH 4 / d . CM1 to CM5 exhibited adequate trends for the UAF-2SS and UAF-3SS reactors when the substrate utilization rate ( k ) was evaluated using the medium and lower limit of the calibration interval for these models and for feeding VOL to UAF (2 to 5 kg COD / m 3 / d ). In general, experimental data points validated the predictions of HMs and CMs, finding a satisfactory approximation for the curves obtained from the intermediate values with low VOL and those obtained from the lower limit of the calibrated intervals of the parameters with the predicted curves for high VOL, represented for the maximum S e / S i ratios. This study offers comprehensive information for the transport and transformation processes in removing COD contained in leachates from UAF-2SS and UAF-3SS.