Showing papers by "Marcelo Zaiat published in 2004"

Comparison of Methanol, Ethanol, and Methane as Electron Donors for Denitrification

Abstract: The results of denitrification assays using three electron donor sources—methanol, ethanol, and methane— are presented and discussed based on the apparent kinetic parameters estimated from the experimental data. The research was carried out in batch reactors fed with synthetic wastewater simulating nitrified effluents from domestic sewage treatment plants. The most effective electron donor was ethanol, which completely removed nitrite and nitrate in 50 min. The same efficiency was achieved by feeding the reactors with methanol and methane for 120 and 315 min, respectively. The kinetic model of two reactions in series, having nitrite as the intermediate compound, adequately represented the denitrification process in the reactors fed with methanol and ethanol. To apply this model, the conversions of nitrate-to-nitrite and of nitrite-to-molecular nitrogen were represented, respectively, by first- and zero-order equations. In both the methanol and ethanol experiments, nitrite conversion was the limiting step ...

Enhancement of the performance of an anaerobic sequencing batch reactor treating low-strength wastewater through implementation of a variable stirring rate program

Abstract: This work focuses on enhancement of the performance of an anaerobic sequencing batch reactor with a six-vertical-blade-disk-turbine impeller, containing granulated biomass treating low-strength synthetic wastewater, through a study of the feasibility of implementing a variable stirring rate program. The reactor was operated at 30oC and a six-hour cycle was used to treat approximately 2.0 L of the synthetic substrate with a chemical oxygen demand (COD) of nearly 500 mg/L. Two different stirring rate program were implemented: a constant rate of 50 rpm and a variable rate consisting of 75 rpm for one hour, 50 rpm for four hours and 25 rpm for 0.5 hour. The last 0.5 hour of the cycle was used for the settling step. In both cases, a very short start-up period and unfiltered and filtered substrate removal efficiencies of 81% and 88%, respectively, were attained. However, use of the variable stirring rate enhanced efficiency of the reactor dynamics without impairing biomass morphology, thus resulting in a reduction in the total cycle time and a possible decrease in energy consumption. Additionally, a simplified model of the anaerobic metabolic activity, using apparent kinetic parameters, was proposed as a consecutive first-order kinetic model with substrate and total volatile acid residual concentrations in order to analyze how the variable stirring rate affects reactor performance.

Evaluation of a mechanistic mathematical model of a packed-bed anaerobic reactor treating wastewater

Abstract: A mechanistic mathematical model is proposed and evaluated for simulating the performance of a bench-scale packed-bed anaerobic reactor that uses polyurethane foam as biomass support. The model developed under rational criteria was based on the study of mass transfer and biochemical kinetics, also considering the hydrodynamic characteristics of the reactor. The data generated by the model adhered well to the experimental data obtained from the operation of the reactor applied to the treatment of a glucose- based substrate. The liquid-phase mass transfer coefficient was found to be the main parameter in the model, and its precise estimation is essential for the model to be successfully applied. Additionally, a case study was used in order to verify the applicability of the model for designing full-scale reactors. The simulations performed permitted to demonstrate the importance of the choice of convenient liquid superficial velocity and polyurethane foam matrix size which have direct influence on the solid- and liquid-phase mass transfers resistance and, consequently on the volume of the designed reactor.

Avaliação de desempenho de sistema anaeróbio em duas fases tratando esgoto sanitário sintético em diferentes temperaturas

Abstract: Marcio Gomes Barboza Professor Adjunto do Centro de Tecnologia da Universidade Federal de Alagoas. Mestre e Doutor em Engenharia Civil, area Hidraulica e Saneamento pela Escola de Engenharia de Sao Carlos – USP. Marcelo Zaiat Professor Doutor do Departamento de Hidraulica e Saneamento da Escola de Engenharia de Sao Carlos – USP. Eugenio Foresti Professor Titular do Departamento de Hidraulica e Saneamento da Escola de Engenharia de Sao Carlos – USP.

Removal of perchloroethylene in two types of lab scale

Abstract: The objective of this work was to evaluate and compare the performance of two labscale,' mesophilic methanogenic complete mix reactors (CM1 and CM2) and a methanogenic fluidized bed reactor (RANLEF) for the removal of PCE when fed a moderate concentration of organic co-substrate' 1000 mg COD-methanollL in the influent. The reactors were started-up with non-anaerobic inocula. The CMs and the RANLEF were operated at loading rates of 0.07 and 1 g COD/(L.d), hydraulic retention times of 15 and 1 day, respectively. The biomass in the RANLEF was attached to granular activated carbon as medium carrier. The experimental design consisted of three periods of operation: 1: methanogenic regime with 1000 mgl~ methanol (MeOH) as carbon source and no PCE, 2: methanogenic regime with MeOH and acclimation to PCE in steps 2.1 with 20 mg/L PCE, and 2.2 with 40 mg/L; and 3: methanogenic regime with MeOH and 40 mg/L PCE in RANLEF and CM1 and 20 mg/L PCE in CM2. In the period 2 step 1 (2.1), both the PCE and COD removals of the RANLEF were higher than those of the CMs (60.5 and 52.4%; 96.2 and 73.4%, respectively, the percentages of the CMs reported as one average). The methane content in the biogas was low and similar for the three reactors, although there was a slight advantage for the RANLEF over the CMs (36.0 vs. 31.5% v/v). The increase of chloride in the reactor liquors (an indication of the dehalogenation of the PCE) was also similar for the three reactors reaching a value of 9 mg CI-/L (compare with a maximum release of chloride of 17 mg/L assuming a 100% dechlorination of 20 mg/L PCE). The RANLEF, during the Period 2.2, increased the removal of PCE up to 81%, suggesting a good acclimation of this reactor to the higher PCE concentration in the influent. The COD reduction was also high, of the same order than that of Period 2.1. 'The methane content in the RANLEF1s biogas reached an average value of 64% v/v, indicating a satisfactory methanogenic regime. The chloride concentration increase was only 12 hg/L (compared to a maximum value of 34 mg CI-/L). On the other hand, the CM reactors experienced a drastic impairment of their performances, presumably due to the increase of the PCE in the feedstock from 20 to 40 mg/L. A decision was made to keep the CM2 reactor fed with an influent with 40 mg PCEIL, and to operate the CM1 reactor with an influent back to 20 mg PCEIL. The performance of CM2 was very poor and the average values of the response variables suggested a drastic deterioration of the methanogenesis and the