1,721,034 research outputs found
Effect of pH on Cu, Ni and Zn removal by biogenic sulfide precipitation in an inversed fluidized bed bioreactor
No full textMining and metallurgical operations have resulted in the disposal of large quantities of non-treated metal rich effluents into the environment. From a techno-economic and environmental view-point, metal recovery from suchwaste streams can solve this persisting problem. This study compares the performance of two sulfate reducing inversed fluidized bed bioreactors (IFBs) to recover heavy metals (HMs) as metal sulfide fromwastewater at neutral and acidic pH. The IFBs were operated at pH 7.0 and 5.0 to study the effect of the pH on the metal (Cu, Ni and Zn) removal efficiency froma synthetic acid mine drainage containing the metals. The electron donor used in the study was ethanol, supplied at an organic loading rate of 1 g COD/L day and a COD/sulfate ratio of 1.0. The average sulfide production was 220.9 mg/L and 152.6 mg/L, respectively, at pH 7.0 and pH 5.0 at a hydraulic retention time of 24 h. The Cu and Zn removal efficiencies were N90% at an initial concentration of 25 mg/L at both operational pH values; however, high concentrations of Ni (25 mg/L) inhibited the sulfate reducing activities. When the influent concentration of each metal was decreased to 10 mg/L, the sulfate reducing efficiency in the IFB was restored. Cu and Zn removal in the IFBs were satisfactorily predicted by the MINTEQ model, while large errors in the Ni removal efficiency were noticed, irrespective of the operational conditions, probably because the MINTEQ model does not take into account NiS polymorphism and binding with the organic compounds present in the biogenic effluent
Copper, lead and zinc removal from metal-contaminated wastewater by adsorption onto agricultural wastes
No full textThe use of agricultural wastes (groundnut shell, orange and banana peel, rice husk, coconut husk and Wawa tree saw dust) as potential cost-effective adsorbent for heavy metal removal from wastewater was evaluated. The effect of pH (2.0-6.0), adsorbent dosage (0.6-2.2 g), contact time (10-130 min) and initial concentration (Pb: 5-105 mg/L, Cu and Zn: 2.5-52.7 mg/L) on the metal removal efficiency and uptake capacity were investigated using response surface methodology to optimize the process conditions. Groundnut shell showed a high potential to remove Cu, Pb and Zn from synthetic wastewater. The highest removal efficiencies with groundnut as the adsorbent were 85% at pH 5.0 for Cu and 98% at pH 3.0 for Pb and Zn. The optimum conditions obtained were 2.5 g adsorbent with 40.7 mg/L Cu at pH 4.4 and 64 min contact time, 2.5 g adsorbent with 196.1 mg/L Pb at pH 5.6 and 60 min contact time and 3.1 g adsorbent with 70.2 mg/L Zn at pH 4.3 and 50 min contact time, for Cu, Pb and Zn, respectively. The regeneration of the groundnut shell was possible for a maximum of three cycles using 0.2 M HCl as the desorbing solution without any significant change in the adsorbing efficiency
Effect of pH on the Performance of Sulfate and Thiosulfate-Fed Sulfate Reducing Inverse Fluidized Bed Reactors
No full textSulfate-reducing bacteria (SRB)-based technologies have gained a lot of attention in the field of wastewater treatment, especially to treat metal-contaminated wastewaters. An inverse fluidized bed (IFB) bioreactor is a versatile bioreactor configuration that uses SRB technology for metal removal and recovery from wastewater. Apart from sulfate, which is commonly used as an electron acceptor, thiosulfate is another potential candidate for this process. In this study, the performance of two IFB bioreactors that were operated at pH 7.0 (R1) and 5.0 (R2) using sulfate and thiosulfate as the electron acceptors were evaluated. The electron donor used in this study was ethanol and the chemical oxygen demand (COD) to electron acceptor ratio (SO42- or S2O32-) was kept constant at 1.0. By using sulfate as the electron acceptor, the average COD removal efficiency was 75.0 and 58.0% at pH 7.0 and 5.0, respectively, while the sulfate removal efficiency was 74.4 and 50.4%, respectively. The average sulfide production was 246.3 and 150.7 mg/L at pH 7.0 and pH 5.0, respectively. Using thiosulfate as the electron acceptor, slightly higher sulfate reduction activities were achieved when compared to sulfate at pH 5.0. The maximum COD removal efficiency was 54.8% and 162.7 mg/L sulfide was produced. The COD and sulfate removal efficiencies as well as the total sulfide production profiles in the IFB reactor fed with sulfate were modeled using a three-layered artificial neural network (ANN). The results showed that the developed ANN model with a topology of 3-7-3 was able to give good predictions of the performance variables. Moreover, the sensitivity analysis from ANN showed that this process is mainly pH dependent
Effect of operational parameters on the leaching efficiency and recovery of heavy metals from computer printed circuit boards
No full textBACKGROUNDElectronic waste (e-waste) is a recent environmental problem worldwide, because it is bulky in size causing solid waste disposal problems, especially due to the release of heavy metals into the environment. On the other hand, metal scarcity is another global issue with e-waste, making it a prominent candidate for metal recovery.
RESULTSDesktop computer printed circuit boards (PCBs) were evaluated as a potential source of Cu, Ni and Zn recovery using a bio-hydrometallurgical method. The process parameters for metal leaching i.e. different particle sizes, leaching agents, contact time, liquid to solid (L/S) ratio, and agitation speed were evaluated in batch systems. At the following optimal conditions of 1molL(-1) HNO3, L/S ratio of 20 with 200rpm agitation speed using 0.5-1.0mm particle size, the concentrations of Cu, Ni and Zn leached out from the PCBs were 450, 8 and 4mgg(-1) PCBs, respectively. Continuous leaching in an up-flow leaching column using the optimized parameters, coupled to sulfide precipitation yielded>90% Cu recovery (0.48gg(-1) PCBs).
CONCLUSIONPCBs are a good candidate for metal recovery, especially Cu. This can be achieved by combining chemical leaching and biogenic sulfide precipitation techniques
Forecasting the effect of feast and famine conditions on biological sulphate reduction in an anaerobic inverse fluidized bed reactor using artificial neural networks
No full textThe longevity and robustness of bioreactors used for wastewater treatment is determined by the activity of the microorganisms under steady and transient loading conditions. Two identical continuously operated inverse fluidized bed bioreactors (IFB), IFB R1 and IFB R2, were tested for sulphate removal under the same operating conditions for 140 d (Periods I–IV). Later, IFB R1 was used as the control reactor (Period V), while IFB R2 was operated under feast (Period V-A) and famine (Period V-B) feeding conditions for 66 d. The sulphate removal efficiency was comparable in both IFB, <20% in Period I and ∼70% during Periods II, III and IV. The robustness of the IFB was evident when the sulphate removal efficiency remained comparable during the feast Period (67 ± 15%) applied to IFB R2 compared to continuous feeding Periods (Period IV (71 ± 4%) for IFB R2 and Period V (61 ± 15%) for IFB R1). The IFB performance was modelled using a three-layered artificial neural networks (ANN) model (5-11-3) and a sensitivity analysis, the sulphate removal was found to be dependent on the COD:sulphate ratio. Besides, the robustness, resilience and adaptation time of the IFB were affected by the degree of mixing and the hydraulic retention time
Hydrodynamics and mathematical modelling in a low HRT inverse fluidized-bed reactor for biological sulphate reduction
No full textBiological reduction of sulphate at low hydraulic retention time (HRT) is presented in this paper. A sulphidogenic inverse fluidized-bed bioreactor (IFBB) was operated successfully at a progressively decreasing HRT from 1 to 0.125 days for a total of 155 days. Synthetic wastewater containing sulphate at a concentration of 745 (± 17) mg/L was used. COD was supplied as lactate in variable concentrations at COD/SO4 2− ratios of 1.2–2.4. The pH of the feed ranged between 5.2 and 6.2. The highest measured removal rates were 2646 and 4866 mg SO4 2−/L day at an HRT of 0.25 and 0.125 days, respectively, using a COD/SO4 2− ratio of 2.3. The biological sulphate reduction was limited by the influent COD concentrations at a COD/SO4 2− ratio < 2.3. The IFBB ensured biomass retention at a maximum liquid residence time of θ = 3.84 (± 0.013), according to the residence time distribution analysis. Hydrodynamic studies were carried out at recirculation rates of 0, 200, 300, 350, 400, and 500 L/h to measure the relative bed expansion, the mixing pattern, and the fluidization characteristics of the reactor. A dynamic model is also developed based on COD and sulphate as the two limiting substrates in a Monod-type kinetic equation describing the kinetics of lactate oxidation by SRB. A set of the following parameters YVSS/COD′ = 0.23 mg COD of VSS/mg lactate, μmax = 1.758 day− 1, KCOD = 956 mg COD of lactate/L, KSO4 = 316 mg SO4 2−/L, kd = 0.024 day− 1, tres = 5.7 days, and kexchange = 0.4 day− 1 simulated adequately the residual effluent COD and sulphate concentrations, the produced sulphide concentration as well as the pH of the IFBB effluent. Low HRT values, shown efficient in this study, are prerequisite for industrial applicability and economic feasibility of the sulphur reduction process. In addition, the developed model can be used for optimum experimental design and further process upscale and development
Lignocellulosic biowastes as carrier material and slow release electron donor for sulphidogenesis of wastewater in an inverse fluidized bed bioreactor
No full textIndustrial wastewaters containing high concentrations of sulphate, such as those generated by mining, metallurgical and mineral processing industries, require electron donor for biological sulfidogenesis. In this study, five types of lignocellulosic biowastes were characterized as potential low-cost slow release electron donors for application in a continuously operated sulphidogenic inverse fluidized bed bioreactor (IFBB). Among them, natural scourer and cork were selected due to their high composition of volatile solids (VS), viz. 89.1 and 96.3%, respectively. Experiments were performed in batch (47 days) and in an IFBB (49 days) using synthetic sulphate-rich wastewater. In batch, the scourer gave higher sulphate reduction rates (67.7 mg SO42- L-1 day-1) in comparison to cork (12.1 mg SO42- L-1 day-1), achieving >82% sulphate reduction efficiencies. In the IFBB packed with the natural scourer, the average sulphate reduction efficiency was 24 (±17)%, while the volumetric sulphate reduction rate was 167 (±117) mg SO42-L-1 day-1. The long incubation time in the batch experiments (47 days) allowed higher sulphate reduction efficiencies in comparison to the short hydraulic retention time (24 h) in the IFBB. This suggests the hydrolysis-fermentation was the rate-limiting step and the electron donor supply (through hydrolysis of the lignocellulosic biowaste) was limiting the sulphate reduction. Lignocellulose as carrier material and slow release electron donor for sulphidogenesis
Anaerobic oxidation of methane coupled to thiosulfate reduction in a biotrickling filter
No full textMicroorganisms from an anaerobic methane oxidizing sediment were enriched with methane gas as the substrate in a biotrickling filter (BTF) using thiosulfate as electron acceptor for 213days. Thiosulfate disproportionation to sulfate and sulfide were the dominating sulfur conversion process in the BTF and the sulfide production rate was 0.5mmoll(-1)day(-1). A specific group of sulfate reducing bacteria (SRB), belonging to the Desulforsarcina/Desulfococcus group, was enriched in the BTF. The BTF biomass showed maximum sulfate reduction rate (0.38mmoll(-1)day(-1)) with methane as sole electron donor, measured in the absence of thiosulfate in the BTF. Therefore, a BTF fed with thiosulfate as electron acceptor can be used to enrich SRB of the DSS group and activate the inoculum for anaerobic oxidation of methane coupled to sulfate reduction
Effect of ammonium, electron donor and sulphate transient feeding conditions on sulphidogenesis in sequencing batch bioreactors
No full textThis work aimed to study the effect of transient feeding conditions on sulphidogenesis in 8 sequencing batch bioreactors (SBR). SBR L1 and H1, operated under steady-state conditions were used as the control reactors, while four SBR were tested under transient feeding conditions, using moderate (L2 and L3, feast and famine: 2.5 and 0 g SO42-.L-1) and high (H2 and H3, feast and famine: 15 and 0 g SO42-.L-1) loads. The sulphate removal efficiency (RE) was ≥ 90% in SBR L2, L3 and H1. The NH4+ famine conditions resulted in a higher sulphate RE (≥ 40% H3) compared to feast conditions (≤ 20% H2). Besides, the sulphidogenic first-order kinetic constant was 4 % larger and the use of electron donor was 16.6% more efficient under NH4+ famine conditions. Sulphidogenesis is robust to transient feeding conditions, but not when applying high loading rates (SBR H2 and H3)
Enrichment of sulfate reducing anaerobic methane oxidizing community dominated by ANME-1 from Ginsburg Mud Volcano (Gulf of Cadiz) sediment in a biotrickling filter
No full textThis study was performed to enrich anaerobic methane-oxidizing archaea (ANME) present in sediment from the Ginsburg Mud Volcano (Gulf of Cadiz) in a polyurethane foam packed biotrickling filter (BTF). The BTF was operated at 20 (±2) °C, ambient pressure with continuous supply of methane for 248 days. Sulfate reduction with simultaneous sulfide production (accumulating ∼7 mM) after 200 days of BTF operation evidenced anaerobic oxidation of methane (AOM) coupled to sulfate reduction. High-throughput sequence analysis of 16S rRNA genes showed that after 248 days of BTF operation, the ANME clades enriched to more than 50% of the archaeal sequences, including ANME-1b (40.3%) and ANME-2 (10.0%). Enrichment of the AOM community was beneficial to Desulfobacteraceae, which increased from 0.2% to 1.8%. Both the inoculum and the BTF enrichment contained large populations of anaerobic sulfur oxidizing bacteria, suggesting extensive sulfur cycling in the BTF
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