Rogers Ribeiro

Effect of feeding strategy on a stirred anaerobic sequencing fed-batch reactor containing immobilized biomass

The present work reports on the influence of feeding strategy on the stability and performance of a stirred anaerobic sequencing fed-batch reactor containing biomass immobilized on polyurethane foam. The reactor treated low-strength wastewater and was operated at 30 degrees C with an agitation rate of 200 rpm. A 180-min cycle was used to treat approximately 0.5 l of synthetic substrate with a chemical oxygen demand concentration of nearly 500 mg/l. The reactor was operated in batch mode with a 3-min feeding step and in constant rate fed-batch mode with feeding steps of 30, 60 and 180 min. During batch operation, the system attained stability and had a removal efficiency of 86% based on non-filtered substrate concentration. However, during fed-batch operation stability and efficiency were impaired and formation of suspended material was identified. Stability was achieved only for the 30-min feeding step. The poor performance and instability observed in the fed-batch experiments were credited to the formation of considerable quantities of extracellular polymers, which impeded contact between substrate and biomass with consequent negative effect on the mass transfer fluxes. The biopolymer formation was very likely a result of the fed-batch operational mode, in which part of the bioparticles were deprived of contact with the liquid medium for a relatively long period of time.

Morphological study of biomass during the start-up period of a fixed-bed anaerobic reactor treating domestic sewage

This work focused on a morphological study of the microorganisms attached to polyurethane foam matrices in a horizontal-flow anaerobic immobilized biomass (HAIB) reactor treating domestic sewage. The experiments consisted of monitoring the biomass colonization process of foam matrices in terms of the amount of retained biomass and the morphological characteristics of the cells attached to the support during the start-up period. Non-fluorescent rods and cocci were found to predominate in the process of attachment to the polyurethane foam surface. From the 10th week of operation onwards, an increase was observed in the morphological diversity, mainly due to rods, cocci, and Methanosaeta-like archaeal cells. Hydrodynamic problems, such as bed clogging and channeling occurred in the fixed-bed reactor, mainly due to the production of extracellular polymeric substances and their accumulation in the interstices of the bed causing a gradual deterioration of its performance, which eventually led to the systems collapse. These results demonstrated the importance and usefulness of monitoring the dynamics of the formation of biofilm during the start-up period of HAIB reactors, since it allowed the identification of operational problems.

Effect of impeller type and agitation on the performance of pilot scale ASBR and AnSBBR applied to sanitary wastewater treatment

The objective of this work was to assess the effect of agitation rate and impeller type in two mechanically stirred sequencing batch reactors: one containing granulated biomass (denominated ASBR) and the other immobilized biomass on polyurethane foam (denominated AnSBBR). Each configuration, with total volume of 1 m(3), treated 0.65 m(3) sanitary wastewater at ambient temperature in 8-h cycles. Three impeller types were assessed for each reactor configuration: flat-blade turbine impeller, 45 degrees -inclined-blade turbine impeller and helix impeller, as well as two agitation rates: 40 and 80 rpm, resulting in a combination of six experimental conditions. In addition, the ASBR was also operated at 20 rpm with a flat-blade turbine impeller and the AnSBBR was operated with a draft tube and helix impeller at 80 and 120 rpm. To quantify how impeller type and agitation rate relate to substrate consumption rate, results obtained during monitoring at the end of the cycle, as well as the time profiles during a cycle were analyzed. Increasing agitation rate from 40 rpm to 80 rpm in the AnSBBR improved substrate consumption rate whereas in the ASBR this increase destabilized the system, likely due to granule rupture caused by the higher agitation. The AnSBBR showed highest solids and substrate removal, highest kinetic constant and highest alkalinity production when using a helix impeller, 80 rpm, and no draft tube. The best condition for the ASBR was achieved with a flat-blade turbine impeller at 20 rpm. The presence of the draft tube in the AnSBBR did not show significant improvement in reactor efficiency. Furthermore, power consumption studies in these pilot scale reactors showed that power transfer required to improve mass transfer might be technically and economically feasible.

Effect of agitation on the performance of an anaerobic sequencing batch biofilm reactor in the treatment of dairy effluents

Agitation rate is an important parameter in the operation of Anaerobic Sequencing Biofilm Batch Reactors (ASBBRs), and a proper agitation rate guarantees good mixing, improves mass transfer, and enhances the solubility of the particulate organic matter. Dairy effluents have a high amount of particulate organic matter, and their anaerobic digestion presents inhibitory intermediates (e.g., long-chain fatty acids). The importance of studying agitation in such batch systems is clear. The present study aimed to evaluate how agitation frequency influences the anaerobic treatment of dairy effluents. The ASBBR was fed with wastewater from milk pasteurisation process and cheese manufacture with no whey segregation. The organic matter concentration, measured as chemical oxygen demand (COD), was maintained at approximately 8,000 mg/L. The reactor was operated with four agitation frequencies: 500 rpm, 350 rpm, 200 rpm, and no agitation. In terms of COD removal efficiency, similar results were observed for 500 rpm and 350 rpm (around 90%) and for 200 rpm and no agitation (around 80%). Increasing the systems agitation thus not only improved the global efficiency of organic matter removal but also influenced volatile acid production and consumption and clearly modified this balance in each experimental condition.

A simplified analysis of granule behavior in ASBR and UASB reactors treating low-strength synthetic wastewater

This work presents an analysis of the changes observed in granule characteristics of sludge in the treatment of synthetic wastewater at a concentration of about 500 mgCOD/L in batch, fed-batch (ASBR) and continuous (UASB) bench-scale reactors under similar experimental conditions. Physical and microbiological properties of the granules were characterized as average particle size and sedimentation time and by optical and epifluorescence microscopy. Several samples were analyzed in order to identify the morphologies. Granules from sequencing batch and fed-batch reactors, either with or without mechanical mixing, did not undergo any physical or microbiological changes. However, during the experiment granules from the UASB reactor agglomerated due to the formation and accumulation of a viscous material, probably of microbial origin, when operated at low superficial velocities (0.072, 0.10 and 0.19 m/h). When the superficial velocity was increased to 8.0-10.0 m/h by means of liquid-phase recirculation, the granules from the UASB reactor underwent flocculation and the microbiological characteristics changed in such a way that the equilibrium of microbial diversity in the inoculum was not maintained. As a result, the only reactor that maintained efficiency and good solids retention during the assays was the ASBR, showing that there is a correlation between maintenance of microbial diversity and operating mode in the case of anaerobic treatment of low-strength wastewaters.

Pectin Extraction from Mango Peels in Batch Reactor: Dynamic One-Dimensional Modeling and Lattice Boltzmann Simulation

Abstract A dynamic one-dimensional model accounting for pectin generation from protopectin in the solid matrix of mango peels and its degradation in both interstitial and extra-particle (i.e. reactor-filling) acid solution is proposed. The model assumes that pectin diffusive transport occurs in the interstitial fluid while eventual diffusive, thermal and pH influences in the solid phase were lumped into the kinetic coefficient of protopectin-pectin conversion. First-order kinetic was assumed to pectin degradation. Differential equations were numerically solved by adapting an in-house simulator of bioprocesses via the lattice Boltzmann method (LBM). As part of the LBM method, particle distribution functions were assigned to the pectin concentration in interstitial and reactor-filling fluid as well as assigned to the protopectin concentration in the solid phase. Equilibrium distribution functions were adopted by considering stationary solid phase, diffusive transport in interstitial fluid, and no spatial dependence in the reactor-filling fluid. Model parameters were assessed by comparing numerically simulated extraction yield curves with existing experimental data of pectin extraction using a batch reactor under either conventional or microwave heating. While the expected behavior of extraction yield curves was fairly reproduced in LBM simulations, discrepancies with respect to the experimental data can be assigned to assumptions in this preliminary model (e.g. first-order degradation kinetic and/or lumping effects into the protopectin-to-pectin kinetic). Prospective influence of slab thickness on extraction yields was also examined in LBM simulations.

Influence of Extracellular Polymeric Substances on Anaerobic Biofilms Supported by Polyurethane Foam Matrices

This work focused on the process of biofilm formation onto polyurethane foam matrices in differential horizontal anaerobic immobilized sludge reactors fed with a glucose-based substrate. The experi...

Clean Strategies for the Management of Residues in Dairy Industries

The transformation of raw milk into dairy products is one of the most important activities of the dairy industry worldwide. Along with the production of pasteurized and sterilized milks for direct consumption, a variety of processes are used for the production of cheeses, butter, cream, ice-creams, yogurts and other fermented milks. As a consequence, the processing of milk usually generates huge amounts of waste products, such as whey and buttermilk. These products have high nutrient and economic values; therefore they can be used as ingredients for others milk products such as flavored milk beverages, chocolates, candies, cookies, processed cheeses, ice cream, and powdered milk. Because of their intrinsic composition, dairy wastewaters cannot be discharged into septic systems, state waters or direct dumping; appropriate treatment is required before release into the environment. There are many alternatives for the treatment of this type of effluent, all based in a sequence of processes and operations presented as functions of physical-chemical characteristics of dairy waste effluent. The selection of some processes requires careful and must be based on, consideration of technical, economical, and social aspects.

Development of in-house lattice-Boltzmann simulator of bioreactors for wastewater treatment: basic concepts and initial results

While computational modelling has increasingly supported wastewater bioreactor engineering, novel numerical techniques have been developed such as the lattice-Boltzmann method (LBM). With vinasse treatment as case study, this work is a first step towards a comprehensive LBM simulator of a continuous-flow anaerobic packed-bed reactor. Extensions from typical models comprise one-dimensional (besides time) dependence, species transport via convection and diffusion, and imposition of either Dirichlet or Danckwerts condition at inlet. The LBM simulator proved to be operational when simulating the bioreactor at different hydraulic retention times (HRTs). Simulated profiles show that stepwise feeding concentrations are smoothed as they are transported towards the bioreactor exit while concentrations increase or decrease in response to generation or degradation kinetics. Good fitting was observed for concentrations of acetic acid (2.1 kg-COD/m3 for HRT = 24 h) and butyric acid (1.3 kg-COD/m3 for HRT = 16 h) at the exit whereas other concentrations were numerically simulated at proper order of magnitude.

CFD Simulations of Fluid Dynamics Inside a Fixed-Bed Bioreactor for Sugarcane Vinasse Treatment

Vinasse is a by-product from ethanol industry which can be exploited in ferti-irrigation after its treatment via APBR (anaerobic packed bed reactor). Comprehensive understanding of fluid dynamics within APBR is fundamental for its design and the goal of this work was to perform CFD (computational fluid dynamics) simulations of a laboratory-scale APBR by the use of commercial software. Tracer concentration patterns deviated from plain plug flow behaviour.