Assessment of the Utilization Rate of Organic Substrates by the Microorganisms in Fixed and Suspended Biomass Reactors Treating Sanitary Landfill Leachates

Abstract

In this study, we evaluated the utilization rate of organic substrates contained in sanitary landfill leachates (SLLs) by fixed and suspended biomass reactors. Five bioreactors were designed, constructed, and tested for chemical oxygen demand (COD) removal. We applied three levels of organic loading in the influent for each bioreactor, including (1) a rotating biological contactor (RBC) (12, 20, and 25 g COD/m2/day); (2) a trickling filter (TF) (2.67, 5.33, and 8 kg COD/m3/day); (3) an upflow anaerobic sludge blanket (UASB) (13.31, 15.98, and 18.65 kg COD/m3/day); (4) an upflow anaerobic filter in two separated stages (UAF-2SS) (3.71, 2.76, and 1.8 kg COD/m3/day); and (5) an upflow anaerobic filter in three separated stages (UAF-3SS) (2.25, 3.45, and 4.44 kg COD/m3/day). Two equations for predicting the substrate utilization rate (SUR) of organic compounds by microorganisms were calibrated and validated, modeled under a nonsteady state condition. We modified Monod’s equation to obtain the significant organic SUR and COD removal efficiency by the biomasses. These kinetic parameters were performed by the microorganisms fixing controlled experimental conditions for pH (8–9) and temperature for the UAFs (20°C, 27°C, and 34°C) and the remaining reactors (18°C– 20°C). The SUR and COD removal efficiency results were as follows: for UASB, −400 to −800 mg/L/h, 70% to 85%; for UAF-3SS, −100 to −300 mg/L/h, 85% to 95%; for UAF-2SS, −100 to −200 mg/L/h, 70% to 85%; and for RBC and TF, −50 to −250 mg/L/h, 70% to 80%. The results were mainly influenced by the structural arrangement of the organic compounds being biodegraded and the geometric configurations of the bioreactors in multiple separated stages, allowing the influence of the solubility of the recalcitrant substances, which varied from 7 to 14:1 COD dilition, to obtain subinhibitory levels for the microbial metabolism and achieve a high COD removal efficiency. Two of the five bioreactors evaluated in this study, the upflow anaerobic filter in two separated stages and the upflow anaerobic filter in three separated stages, are proposed and designed as innovative reactors for treating groundwater from tropical aquifers contaminated with hydrocarbons. Additionally, UAFs were configured in a coupled bioreactor arrangement (i.e., a sequencing batch reactor followed by UAFs) to restore water quality by removing organic compounds in tropical rivers. By comparing the five bioreactors, the capacity for the chemical oxygen demand removal was significant related to the organic substrate utilization rate (SUR) for treating sanitary landfill leachates with low recalcitrance levels (i.e., rapidly biodegradable). Rapidly biodegradable SLLs can be associated with La Cortada-SLL percolated from the cells/trenches excavated for the disposal of municipal solid waste (MSW) (i.e., Pamplona Municipality, Colombia) due to the contents of a high fraction of putrescible wastes (67%) and a high biochemical oxygen demand/chemical oxygen demand ratio (62%). This level ratio produced a suitable SUR obtained from the microbial metabolism starting with the upflow anaerobic sludge blanket reactor (−400 to −1,200 mg/L/h) followed by the remaining bioreactors (−150 to −350 mg/L/h). Upflow anaerobic filters in multiple separated stages reactors constitute a feasible technical option for overcoming medium to high recalcitrance levels in SLLs obtained from cells/trenches excavated storing around 25% components fraction (e.g., metals, plastics, rubber, leather, textiles).