Marcelo Zaiat

Sulphate removal from industrial wastewater using a packed-bed anaerobic reactor

Abstract The feasibility of sulphate removal from sulphate-rich wastewater using an anaerobic fixed-bed reactor was investigated. The bioreactor was installed at a chemical industry producing organic peroxides, which generate wastewater with sulphate concentrations ranging from 12,000 to 35,000 mg SO 4 2− l −1 . A pilot-scale anaerobic fixed-bed reactor with a 94.2-l volume was tested to treat part of the wastewater. The reactor was filled with 1-cm 3 polyurethane foam cubes and operated, initially, in discontinuous regime. Five batch tests were performed with diluted industrial wastewater. The sulphate reduction efficiency and the chemical oxygen demand (COD) removal efficiency were evaluated as a function of the COD to [SO 4 2− ] ratio in each batch test. The effect of the addition of supplementary ethanol on the sulphate-reducing bacteria growth was also evaluated. The reactor was then fed in a semi-continuous regime with raw industrial wastewater with high sulphate concentration. The addition of ethanol stimulated the sulphate-reducing bacteria, which predominated over the methane-producing organisms even at a high COD to [SO 4 2− ] ratio. A maximum sulphate removal efficiency of 97% was reached during discontinuous and semi-continuous operations.

Anaerobic sequencing batch reactors for wastewater treatment: a developing technology

Abstract This paper describes and discusses the main problems related to anaerobic batch and fed-batch processes for wastewater treatment. A critical analysis of the literature evaluated the industrial application viability and proposed alternatives to improve operation and control of this system. Two approaches were presented in order to make this anaerobic discontinuous process feasible for industrial application: (1) optimization of the operating procedures in reactors containing self-immobilized sludge as granules, and (2) design of bioreactors with inert support media for biomass immobilization.

Feasibility of a stirred anaerobic sequencing batch reactor containing immobilized biomass for wastewater treatment

This paper proposes a new configuration of a stirred anaerobic bioreactor to improve the biomass retention in sequencing batch processes for treating low strength wastewater. In the proposed configuration, the biomass was immobilized on a polyurethane foam matrix, thus resulting in the elimination of or reduction in settling time. The reactor was operated at a temperature of 30°C and an agitation rate of 500 rpm supplied by means of a stirring bar at the bottom of the reactor. An 8-h cycle was used to treat 0.5 l of a synthetic substrate containing a chemical oxygen demand (COD) of 485 mg/l. The overall COD removal efficiency attained 86% in the first 3 h of the cycle, as shown by the concentration profile.

Microbial colonization of polyurethane foam matrices in horizontal-flow anaerobic immobilized-sludge reactor

Abstract This paper presents the anaerobic biomass characterization and the bacterial framework inside polyurethane foam matrices taken from a horizontal-flow anaerobic immobilized-sludge (HAIS) reactor treating a glucose-based substrate. Ultrastructure polyurethane foam analyses carried out using scanning electron microscopy (SEM) in samples treated with hexamethyldisylazane showed three different patterns of biomass retention inside the polyurethane foam matrices: micro-granules ranging from 270 μm to 470 μm were entrapped in the porous medium thin multi-cellular films were attached to the inner surface, and individual cells adhered to the support. The use of SEM and epifluorescence microscopy permitted inferences to be made on the bacteriological composition of the immobilized sludge formed by different morphotypes (rods, cocci and filaments) and on the ecological significance of their framework inside the matrices. Polyurethane matrices were found to offer excellent conditions for anaerobic growth and retention, favoring the flux of substrate and products. Such outstanding characteristics were confirmed by the short start-up period observed during the operation of the HAIS reactor.

Influence of carbon sources and C/N ratio on EPS production in anaerobic sequencing batch biofilm reactors for wastewater treatment.

The objective of this work was to evaluate the influence of different carbon sources and the carbon/nitrogen ratio (C/N) on the production and main composition of insoluble extracellular polymers (EPS) produced in an anaerobic sequencing batch biofilm reactor (ASBBR) with immobilized biomass in polyurethane foam. The yield of EPS was 23.6 mg/g carbon, 13.3 mg/g carbon, 9.0 mg/g carbon and 1.4 mg/g carbon when the reactor was fed with glucose, soybean oil, fat acids, and meat extract, respectively. The yield of EPS decreased from 23.6 to 2.6 mg/g carbon as the C/N ratio was decreased from 13.6 to 3.4 gC/gN, using glucose as carbon source. EPS production was not observed under strict anaerobic conditions. The results suggest that the carbon source, microaerophilic conditions and high C/N ratio favor EPS production in the ASBBR used for wastewater treatment. Cellulose was the main exopolysaccharide observed in all experimental conditions.

Influence of agitation rate on the performance of an anaerobic sequencing batch reactor containing granulated biomass treating low-strength wastewater

Abstract The present work reports on the influence of the mechanical agitation rates on the performance of a stirred anaerobic sequencing batch reactor with a six-vertical-blade disk turbine on the basis of chemical oxygen demand (COD). The reactor containing granulated biomass treating synthetic domestic wastewater was operated at 30 °C and an 8-h cycle was applied to treat approximately 2.0 l of the synthetic substrate with COD of nearly 500 mg/l. The studied agitation rates ranged from no agitation to 75 rev./min. The system attained non-filtered and filtered substrate removal efficiency of 80 and 88%, respectively, at the agitation rate of 50 rev./min, presenting a relatively good solid retention and no granule break-up. Moreover, the use of agitation mainly increased the efficiency throughout the cycle of the reactor and, consequently, enabled reduction of the total cycle time. An empirical equation and a first order kinetic model with a residual organic matter concentration were proposed to analyze the influence of agitation rates on the reactors performance.

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

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 ...

Anaerobic treatment of sulfate-rich wastewater in an anaerobic sequential batch reactor (AnSBR) using butanol as the carbon source

Biological sulfate reduction was studied in a laboratory-scale anaerobic sequential batch reactor (14 L) containing mineral coal for biomass attachment. The reactor was fed industrial wastewater with increasingly high sulfate concentrations to establish its application limits. Special attention was paid to the use of butanol in the sulfate reduction that originated from melamine resin production. This product was used as the main organic amendment to support the biological process. The reactor was operated for 65 cycles (48 h each) at sulfate loading rates ranging from 2.2 to 23.8 g SO(4)(2-)/cycle, which corresponds to sulfate concentrations of 0.25, 0.5, 1.0, 2.0 and 3.0 g SO(4)(2-) L(-1). The sulfate removal efficiency reached 99% at concentrations of 0.25, 0.5 and 1.0 g SO(4)(2-) L(-1). At higher sulfate concentrations (2.0 and 3.0 g SO(4)(2-) L(-1)), the sulfate conversion remained in the range of 71-95%. The results demonstrate the potential applicability of butanol as the carbon source for the biological treatment of sulfate in an anaerobic batch reactor.

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

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.

The use of the carbon/nitrogen ratio and specific organic loading rate as tools for improving biohydrogen production in fixed-bed reactors

Highlights • The effects of the carbon/nitrogen ratios of 40, 90, 140, and 190 on hydrogen production are evaluated by varying the nitrogen source in an upflow fixed-bed anaerobic reactor.• An optimal C/N ratio of 137 to produce 3.5 mol H2 mol−1 sucrose is estimated by a mathematical approximation.• Continuous decreases in the specific organic loading rate as a function of time seemed to be responsible for the instability of the system.• A microbial biology analysis identified hydrogen-producing and -consuming microorganisms from natural inoculum.