Effects of solid-phase mass transfer on the performance of a stirred anaerobic sequencing batch reactor containing immobilized biomass

Optimizing anammox capacity for weak wastewater in an AnSBBR using aerobic activated sludge as inoculation

Process optimization is essential for improving the efficiency of anaerobic ammonium oxidation (anammox) process in a practical application. In this study, an anaerobic sequence biofilm batch reactor (AnSBBR) inoculated with aerobic activated sludge was chosen as an efficient mainstream anammox reactor for treating low-nitrogen wastewater. To optimize the AnSBBR-anammox process, eight different operation stages lasting for a total of 215 days were conducted by regulating key process parameters. Principal components analysis revealed significant effects of the substrate ratio (SR) and volumetric exchange ratio (VER) on anammox performance, while other parameters (cycle time, hydraulic retention time and nitrogen loading rate) played minor roles. The highest removal efficiencies for ammonia and total nitrogen, respectively, reached 99.8% and 95.3% under optimal conditions. High-throughput sequencing found the anammox species Candidatus Brocadia and Candidatus Kuenenia made up as much as 8.5% and 3.5%, respectively, of the microbial community. Redundancy analysis indicated that these taxa were also greatly influenced by operating parameters, particularly SR and VER. This research helps to decode the correlations among nitrogen removal capacity, process parameters and the microbial community to enhance anammox in an AnSBBR system.

Sulfate and metals removal from acid mine drainage in a horizontal anaerobic immobilized biomass (HAIB) reactor

The acid mine drainage (AMD) can causes negative impacts to the environment. Physico-chemical methods to treat AMD can have high operational costs. Through passive biological methods, such as anaerobic reactors, sulfate reduction, and recovery of metals are promoted. This study evaluated the performance of a horizontal anaerobic immobilized biomass (HAIB) reactor for the treatment of synthetic AMD using polyurethane foam as support material, and anaerobic sludge as inoculum. Ethanol was used as an electron donor for sulfate reduction, resulting in an influent chemical oxygen demand (COD) in the range of 500-1,500 mg/L and COD/sulfate ratio at 1. A gradual increase of sulfate and COD concentration was applied that resulted in COD removal efficiencies higher than 78%, and sulfate removal efficiencies of 80%. Higher sulfate and COD concentrations associated with higher hydraulic retention times (36 h) proved to be a better strategy for sulfate removal. The HAIB reactor was able to accommodate an increase in the SLR up to 2.25 g SO₄^2-/L d^-1 which achieved the greatest performance on the entire process. Moreover, the reactor proved a suitable alternative for reaching high levels of metal removal (86.95 for Zn, 98.79% for Fe, and 99.59% for Cu).

Biomass growth and its mobility in an AnSBBR treating landfill leachate

This work used a pilot scale (with a total volume of 1300 L) Anaerobic Sequencing Batch Biofilm Reactor (AnSBBR) to treat landfill leachate from São Carlos-SP (Brazil) as well as to evaluate the biomass growth and its behavior. Biomass from the bottom of a landfill leachate stabilization pond was immobilized in polyurethane foam cubes as inoculum. The leachate characteristics varied during the experiment. Ethanol or volatile fatty acids were added as additional substrate when the leachate was temporarily recalcitrant. After acclimation, the AnSBBR presented efficiency over 70% (COD removal). A mass balance model, biomass sampling and temporal concentration profiles were performed to obtain a biomass yield coefficient of Y_X/S = 0.0251 ± 0.0006 g_TVS g_{COD removed} (r² = 0.999). Additionally, it was observed that a variable fraction of the attached biomass may detach itself or present mobility during the batch time, however returning to fixed bed depending on the substrate type and concentration. This behavior has never been reported by the literature for attached biomass.

Effect of impeller type and stirring frequency on the behavior of an AnSBBR in the treatment of low-strength wastewater

The influence of impeller type and stirring frequency on the performance of a mechanically stirred anaerobic sequencing batch reactor containing immobilized biomass on an inert support (AnSBBR--Anaerobic Sequencing Batch Biofilm Reactor) was evaluated. The biomass was immobilized on polyurethane foam cubes placed in a stainless-steel basket inside a glass cylinder. Each 8-h batch run consisted of three stages: feed (10 min), reaction (460 min) and discharge (10 min) at 30 °C. Experiments were performed with four impeller types, i.e., helical, flat-blade, inclined-blade and curved-blade turbines, at stirring frequencies ranging from 100 to 1100 rpm. Synthetic wastewater was used in all experiments with an organic-matter concentration of 530±37 mg/L measured as chemical oxygen demand (COD). The reactor achieved an organic-matter removal efficiency of around 87% under all investigated conditions. Analysis of the four impeller types and the investigated stirring frequencies showed that mass transfer in the liquid phase was affected not only by the applied stirring frequency but also by the agitation mode imposed by each impeller type. The best reactor performance at all stirring frequencies was obtained when agitation was provided by the flat-blade turbine impeller.

Biodegradation of propionitrile by Klebsiella oxytoca immobilized in alginate and cellulose triacetate gel

A microbial process for the degradation of propionitrile by Klebsiella oxytoca was studied. The microorganism, K. oxytoca, was isolated from the discharged wastewater of metal plating factory in southern Taiwan and adapted for propionitrile biodegradation. The free and immobilized cells of K. oxytoca were then examined for their capabilities on degrading propionitrile under various conditions. Alginate (AL) and cellulose triacetate (CT) techniques were applied for the preparation of immobilized cells. The efficiency and produced metabolic intermediates and end-products of propionitrile degradation were monitored in bath and continuous bioreactor experiments. Results reveal that up to 100 and 150 mM of propionitrile could be removed completely by the free and immobilized cell systems, respectively. Furthermore, both immobilized cell systems show higher removal efficiencies in wider ranges of temperature (20-40 degrees C) and pH (6-8) compared with the free cell system. Results also indicate that immobilized cell system could support a higher cell density to enhance the removal efficiency of propionitrile. Immobilized cells were reused in five consecutive degradation experiments, and up to 99% of propionitrile degradation was observed in each batch test. This suggests that the activity of immobilized cells can be maintained and reused throughout different propionitrile degradation processes. A two-step pathway was observed for the biodegradation of propionitrile. Propionamide was first produced followed by propionic acid and ammonia. Results suggest that nitrile hydratase and amidase were involved in the degradation pathways of K. oxytoca. In the continuous bioreactor, both immobilized cells were capable of removing 150 mM of propionitriles completely within 16h, and the maximum propionitriles removal rates using AL and CT immobilized beads were 5.04 and 4.98 mM h(-1), respectively. Comparing the removal rates obtained from batch experiments with immobilized cells (AL and CT were 1.57 and 2.18 mM h(-1) at 150 mM of propionitrile, respectively), the continuous-flow bioreactor show higher potential for practical application.