Browsing by Author "Lens, Piet N. L."

Now showing 1 - 5 of 5

Biological treatment of selenium-laden wastewater containing nitrate and sulfate in an upflow anaerobic sludge bed reactor at pH 5.0
(2018-11) Tan, Lea Chua; Nancharaiah, Yarlagadda V.; Lu, Shipeng; van Hullebusch, Eric D.; Gerlach, Robin; Lens, Piet N. L.
This study investigated the removal of selenate (SeO42−), sulfate (SO42−) and nitrate (NO3−) at different influent pH values ranging from 7.0 to 5.0 and 20 °C in an upflow anaerobic sludge blanket (UASB) reactor using lactate as an electron donor. At pH 5.0, the UASB reactor showed a 20–30% decrease in reactor performance compared to operation at pH 5.5 to 7.0, reaching removal efficiencies of 79%, 15%, 43% and 61% for NO3−, SO42−, Setotal and Sediss, respectively. However, the reactor stability was an issue upon lowering the pH to 5.0 and further experiments are recommended. The sludge formed during low pH operation had a fluffy, floc-like appearance with filamentous structure, possibly due to the low polysaccharide (PS) to protein (PN) ratio (0.01 PS/PN) in the soluble extracellular polymeric substances (EPS) matrix of the biomass. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) analysis of the sludge confirmed Se oxyanion reduction and deposition of Se0 particles inside the biomass. Microbial community analysis using Illumina MiSeq sequencing revealed that the families of Campylobacteraceae and Desulfomicrobiaceae were the dominant phylotypes throughout the reactor operation at approximately 23% and 10% relative abundance, respectively. Furthermore, approximately 10% relative abundance of both Geobacteraceae and Spirochaetaceae was observed in the granular sludge during the pH 5.0 operation. Overall, this study demonstrated the feasibility of UASB operation at pH values ranging from 7.0 to 5.0 for removing Se and other oxyanions from wastewaters.
Effect of selenite on the morphology and respiratory activity of Phanerochaete chrysosporium biofilms
(2016-06) Espinosa-Ortiz, Erika J.; Pechaud, Yoan; Lauchnor, Ellen G.; Eldon, Rene R.; Gerlach, Robin; Peyton, Brent M.; van Hullebusch, Eric D.; Lens, Piet N. L.
The temporal and spatial effects of selenite (SeO32-) on the physical properties and respiratory activity of Phanerochaete chrysosporium biofilms, grown in flow-cell reactors, were investigated using oxygen microsensors and confocal laser scanning microscopy (CLSM) imaging. Exposure of the biofilm to a SeO32- load of 1.67 mg Se L-1 h-1 (10 mg Se L-1 influent concentration), for 24 h, resulted in a 20% reduction of the O2 flux, followed by a ~10% decrease in the glucose consumption rate. Long-term exposure (4 days) to SeO32- influenced the architecture of the biofilm by creating a more compact and dense hyphal arrangement resulting in a decrease of biofilm thickness compared to fungal biofilms grown without SeO32-. To the best of our knowledge, this is the first time that the effect of SeO32- on the aerobic respiratory activity on fungal biofilms is described.
Selenate removal in biofilm systems: effect of nitrate and sulfate on selenium removal efficiency, biofilm structure and microbial community
(2018-08) Tan, Lea Chua; Espinosa-Ortiz, Erika J.; Nancharaiah, Yarlagadda V.; van Hullebusch, Eric D.; Gerlach, Robin; Lens, Piet N. L.
BACKGROUND Selenium (Se) discharged into natural waterbodies can accumulate over time and have negative impacts on the environment. Se‐laden wastewater streams can be treated using biological processes. However, the presence of other electron acceptors in wastewater, such as nitrate (NO3‐) and sulfate (SO42‐), can influence selenate (SeO42‐) reduction and impact the efficiency of biological treatment systems. RESULTS SeO42‐ removal by biofilms formed from an anaerobic sludge inoculum was investigated in the presence of NO3‐ and SO42‐ using drip flow reactors operated continuously for 10 days at pH 7.0 and 30 °C. The highest total Se (∼60%) and SeO42‐ (∼80%) removal efficiencies were observed when the artificial wastewater contained SO42‐. A maximum amount of 68 μmol Se cm‐2 was recovered from the biofilm matrix in SO42‐ + SeO42‐ exposed biofilms and biofilm mass was 2.7‐fold increased for biofilms grown in the presence of SO42‐. When SeO42‐ was the only electron acceptor, biofilms were thin and compact. In the simultaneous presence of NO3‐ or SO42‐, biofilms were thicker (> 0.6 mm), less compact and exhibited gas pockets. CONCLUSION The presence of SO42‐ had a beneficial effect on biofilm growth and the SeO42‐ removal efficiency, while the presence of NO3‐ did not have a significant effect on SeO42‐ removal by the biofilms.
Simulation of batch-operated experimental wetland mesocosms in AQUASIM biofilm reactor compartment
(Journal of Environmental Management, 2014-02) Mburu, N.; Rousseau, D. P.; Stein, Otto R.; Lens, Piet N. L.
In this study, a mathematical biofilm reactor model based on the structure of the Constructed Wetland Model No.1 (CWM1) coupled to AQUASIMâ€™s biofilm reactor compartment has been used to reproduce the sequence of transformation and degradation of organic matter, nitrogen and sulphur observed in a set of constructed wetland mesocosms and to elucidate the development over time of microbial species as well as the biofilm thickness of a multispecies bacterial biofilm in a subsurface constructed wetland. Experimental data from 16 wetland mesocosms operated under greenhouse conditions, planted with three different plant species (Typha latifolia, Carex rostrata, Schoenoplectus acutus) and an unplanted control were used in the calibration of this mechanistic model. Within the mesocosms, a thin (predominantly anaerobic) biofilm was simulated with an initial thickness of 49 mm (average) and in which no concentration gradients developed. The biofilm density and area, and the distribution of the microbial species within the biofilm were evaluated to be the most sensitive biofilm properties; while the substrate diffusion limitations were not significantly sensitive to influence the bulk volume concentrations. The simulated biofilm density ranging between 105,000 and 153,000 gCOD/m3 in the mesocosms was observed to vary with temperature, the presence as well as the species of macrophyte. The biofilm modeling was found to be a better tool than the suspended bacterial modeling approach to show the influence of the rhizosphere configuration on the performance of the constructed wetlands.
Simulation of carbon, nitrogen and sulphur conversion in batch-operated experimental wetland mesocosms
(2012-05) Mburu, N.; Sanchez-Ramos, D.; Rousseau, D. P.; van Bruggena, J. J. A.; Thumble, G.; Stein, Otto R.; Hook, Paul B.; Lens, Piet N. L.
A simulation model based on Constructed Wetland Model No. 1 (CWM1) using the AQUASIM mixed reactor compartment as a platform was built to study the dynamics of key processes governing COD and nutrient removal in wetland systems. Data from 16 subsurface-flow wetland mesocosms operated under controlled greenhouse conditions with three different plant species (Typha latifolia, Carex rostrata, Schoenoplectus acutus) and an unplanted control were used for calibration and validation in this mechanistic model. Mathematical equations for plant related processes (growth, physical degradation, decay, and oxygen leaching), physical re-aeration, as well as adsorption and desorption processes for COD and ammonium were included and implemented alongside CWM1 in the AQUASIM software, while some CWM1 parameters were adjusted to better fit the model predictions to experimental data during calibration. The simulation results showed that the model was able to describe the general trend of COD (R2 = 0.97–0.99), ammonium (R2 = 0.85–0.97) and sulphate (R2 = 0.71–0.93) removal in the wetland mesocosms and also in their controls (unplanted) through the experimental temperature range of 12–24 °C. Oxygen transfer by physical re-aeration was found to be 0.05 and 0.09 g m−2 d−1 at 12 °C and 24 °C, respectively. The amount of root oxygen transfer was the highest for the planted mesocosms at 12 °C at rates of 1.91, 0.94, and 0.45 g m−2 d−1 in the Carex, Schoenoplectus and Typha mesocosms, respectively, indicating that COD of the bulk wastewater was removed mainly by anaerobic processes under the specific experimental situations. Measured COD removal was better in the planted mesocosms than in the control; differences were effectively modelled by varying the bacteria concentration. The sorption process was found to be important in simulating COD and ammonia removal under these experimental conditions.