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

-This paper reports the results of applying anaerobic sequencing batch biofilm reactors (AnSBBR) for treating sulfate-rich wastewater. The reactor was filled with polyurethane foam matrices or with eucalyptus charcoal, used as the support for biomass attachment. Synthetic wastewater was prepared with two ratios between chemical oxygen demand (COD) and sulfate concentration (COD/SO 4 2-) of 0.4 and 3.2. For a COD/SO 4 2-ratio of 3.2, the AnSBBR performance was influenced by the support material used; the average levels of organic matter removal were 67% and 81% in the reactors filled with polyurethane foam and charcoal, respectively, and both support materials were associated with similar levels of sulfate reduction (above 90%). In both reactors, sulfate-reducing bacteria (SRB) represented more than 65% of the bacterial community. The kinetic model indicated equilibrium between complete-and incomplete-oxidizing SRB in the reactor filled with polyurethane foam and predominantly incomplete-oxidizing SRB in the reactor filled with charcoal. Methanogenic activity seems to have been the determining factor to explain the better performance of the reactor filled with charcoal to remove organic matter at a COD/SO 4 2-ratio of 3.2. For a COD/SO 4 2-ratio of 0.4, low values of sulfate reduction (around 32%) and low reaction rates were observed as a result of the small SRB population (about 20% of the bacterial community). Although the support material did not affect overall performance for this condition, different degradation pathways were observed; incomplete oxidation of organic matter by SRB was the main kinetic pathway and methanogenesis was negligible in both reactors.

Section: Characteristics and Operation Of The Anaerobic Sequencing Bamentioning

confidence: 99%

Kinetic modeling and microbial assessment by fluorescent in situ hybridization in anaerobic sequencing batch biofilm reactors treating sulfate-rich wastewater

Silva

Domingues

Hirasawa

et al. 2011

“…Agitation may be achivied by recirculating the liquid or gas phases (Brito et al, 1997) or by mechanical stirring (Ratusznei et al, 2000). This fact is directly due to the lack of homogeneity in the reaction medium brought about by low biogas production, which is a result of the low substrate concentration since the start-up of operation.…”

Section: Introductionmentioning

confidence: 99%

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

Rodrigues

Pinto

Ratusznei

et al. 2004

-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 30 o C 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.

“…However, for low strength wastewater the biogas production is insufficient and an alternative mixing may be necessary (Brito et al, 1997). Circulation of the bulk liquid through a pump (Hirl & Irvine, 1996;Brito et al, 1997) or mechanical agitation (Ratusznei et al, 2000) can also be used. The biomass settling, necessary to assure sedimentation of the biomass providing the solids removal efficiency, may be the determining step of the cycle time since it is directly related to the formation of self-immobilized biomass as granules with good settleability.…”

Section: Introductionmentioning

confidence: 99%

“…Hence, immobilization of biomass in inert supports is useful to provide biomass retention even under adverse operating conditions. Ratusznei et al (2000) used anaerobic biomass immobilized in polyurethane foam to treat domestic synthetic wastewater in a stirred ASBR, achieving high organic matter removal efficiency and high solids retention, eliminating the settling step.…”

Section: Introductionmentioning

confidence: 99%

Treatment of low-strength wastewater using immobilized biomass in a sequencing batch external loop reactor: influence of the medium superficial velocity on the stability and performance

Camargo

Ratusznei

Rodrigues

et al. 2002

-An anaerobic sequencing batch bioreactor with external circulation of the liquid phase wherein the biomass was immobilized on a polyurethane foam matrix was analyzed, focussing on the influence of the liquid superficial velocity on the reactor's stability and efficiency. Eight-hour cycles were carried out at 30 o C treating glucose-based synthetic wastewater around 500 mgDQO/L. The performance of the reactor was assessed without circulation and with circulating liquid superficial velocity between 0.034 and 0.188 cm/s. The reactor attained operating stability and a high organic matter removal was achieved when liquid was circulated. A first order model was used to evaluate the influence of the liquid superficial velocity (v S ), resulting in an increase in the apparent first order parameter when v S increased from 0.034 to 0.094 cm/s. The parameter value remained unchangeable when 0.188 cm/s was applied, indicating that beyond this value no improvement on liquid mass transfer was observed. Moreover, the necessary time to reach the final removal efficiency decreased when liquid circulation was applied, indicating that a 3-hour cycle could be enough.