Microalgae show great potential for wastewater treatment and nutrient recovery. However, microalgae cultivation and harvesting are affected by the low biomass concentrations which are inherent to the ...photoautotrophic growth process. Mixotrophic growth can be a solution as it increases microalgae biomass concentration independently from the incident light intensity. In this work, a combined respirometric-titrimetric unit was used to assess the microalgae kinetics during such mixotrophic growth conditions for Chlorella vulgaris. Based on the experimental results, a microalgae model was extended in order to gain more insight in the delicate balance between photoautotrophic and heterotrophic growth. The results suggest that during heterotrophic growth with light in absence of external inorganic carbon sources (i.e. photoheterotrophic growth), all CO2 produced by the heterotrophic pathway is internally recycled for photoautotrophic growth. Moreover, it was shown that photoautotrophic growth is the preferential growth mechanism under mixotrophic cultivation conditions (i.e. light + inorganic carbon + organic carbon), but that high oxygen concentrations activate the heterotrophic growth pathway to avoid photorespiration. The extended microalgae model supports these findings, with good model performance for all conducted experiments.
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•Combined respirometry-titrimetry was used to quantify growth modes of C. vulgaris.•All CO2 produced during photoheterotrophic growth seems to be internally recycled.•Mixotrophic growth did not occur at oxygen concentrations lower than 15–20 mg.L−1.•The mixotrophic growth pathway was activated to avoid photorespiration.•A microalgae model was developed to describe the mixotrophic growth kinetics.
This study experimentally examined the impact of oxidation on the properties of effluent organic matter (EfOM) using two different oxidation techniques: ozonation and UV/H2O2 treatment. Multiple ...surrogates for EfOM related to its spectral properties, molecular size, concentration, polarity and biodegradability were used to study the oxidant induced conversions. Spectral calculations as differential absorbance spectra (DAS) and absorbance slope index (ASI) were applied for the first time to describe EfOM oxidation and proved to be useful to unravel differences in working mechanism between ozone and hydroxyl radical (HO) induced transformation of EfOM. Effluent ozonation inherently led to significant HO production as a result of electron transfers between ozone and electron rich moieties of EfOM. HO production increased as function of ozone dose and was strongly correlated to UV absorption at 254 nm (UV254). During the UV moderated process, pseudo steady-state behaviour of the HO concentration was observed. Ozone decomposition was extremely sensitive to EfOM reactivity. Most likely, the degree of dissociation of EfOM controlled its reactivity towards ozone. The pH effect was quantified by calculating the pseudo-first order decay constant for ozone as function of reaction time and pH. Treatment with both processes led to more oxygen rich, less hydrophobic and more biodegradable EfOM.
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► EfOM conversion and HO production during O3 and UV/H2O2 treatment were compared. ► Both techniques affected differential absorbance and absorbance slope index differently. ► Significant HO production occurred during both processes. ► pH extremely impacted EfOM reactivity. ► HO production was strongly correlated to UV absorption at 254 nm during ozonation.
The aim of this study was to evaluate the use of functionalised electrospun nanofibre microfiltration membranes, spun by an innovative electrospinning technique, for water disinfection. As such, this ...study bridges between development in electrospinning techniques for the production of flat sheet membranes and the application of these membranes in water filtration and disinfection. Different functionalising agents (nanosilver, bronopol, WSCP, …) were initially evaluated in short term experiments. The most performing agent (WSCP) resulted in a 5.2 log₁₀ colony forming units removal per 100ml (CFU/100ml) hospital wastewater when a 5omf% WSCP functionalised membrane was applied. Long term lab scale tests showed a 5.6 log₁₀ CFU/100ml removal for Staphylococcus aureus and a 4.0 log₁₀ CFU/100ml removal for Escherichia coli, indicating a better removal of Grampositive bacteria. Leaching experiments showed a 10% wash-out of the applied functionalising agent. This leaching did not obstruct the pathogen removal capacity of the functionalised nanofibres. Further research should be conducted towards the reproducibility and controllability of electrospinning of functional nanofibres.
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•Leaching behaviour of different scrap materials was investigated.•Different experimental scales give different contaminant concentrations.•Actions to prevent contamination of ...rain-water run-off were recommended.•Sedimentation and filtration are found to be a promising treatment techniques.
Scrap material recovery and recycling companies are confronted with waste water that has a highly fluctuating flow rate and composition. Common pollutants, such as COD, nutrients and suspended solids, potentially toxic metals, polyaromatic hydrocarbons and poly chlorinated biphenyls can exceed the discharge limits. An analysis of the leaching behaviour of different scrap materials and scrap yard sweepings was performed at full-scale, pilot-scale and lab-scale in order to find possible preventive solutions for this waste water problem. The results of these leaching tests (with concentrations that frequently exceeded the Flemish discharge limits) showed the importance of regular sweeping campaigns at the company, leak proof or covered storage of specific scrap materials and oil/water separation on particular leachates. The particulate versus dissolved fraction was also studied for the pollutants. For example, up to 98% of the polyaromatic hydrocarbons, poly chlorinated biphenyls and some metals were in the particulate form. This confirms the (potential) applicability of sedimentation and filtration techniques for the treatment of the majority of the leachates, and as such the rainwater run-off as a whole.
•Nanofibre membranes were tested for effluent treatment.•TiO2 functionalised nanofibres showed photodegradation of humic acids and S. aureus.•Effluent filtration with nanofibre membranes improved ...water quality significantly.•Nanofibres could be used as high-flux filtration method for effluent recuperation.
This study presents contact experiments and filtration tests with nanofibre membranes containing TiO2 nanoparticles in view of effluent treatment. The first part of this study focuses on the removal of dissolved organic matter, more specifically humic acids. Removal of humic acids from secondary wastewater treatment plant effluent as well as from synthetic water solutions was tested. Also the bactericidal effect of the TiO2 functionalised nanofibre membranes was examined. Contact experiments with TiO2 functionalised membranes showed removal of humic acids (83% degradation after 2h) and Staphylococcus aureus (4.5log10/100ml after 6h). Also the possibility of using (TiO2 functionalised) nanofibre membranes for effluent filtration in view of water reuse, was examined. Such secondary effluent filtration tests improved water quality as a reduction in turbidity (69%), humic acids (37%) and bacterial activity (76%) was observed. It can be concluded that nanofibre membranes could be used as a high-flux filtration technique for effluent recuperation.
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•ANR biological system was applied for nitrogen removal from landfill leachate.•Post-treatment techniques (O3/GAC and their combinations) were compared.•Recycling ozonated ANR ...effluent to the ANR reactor resulted in improved performance.
The aim of this study was to determine an appropriate combination for effective and economical COD and nitrogen removal from landfill leachate. Biological (nitrogen) treatment was performed with the autotrophic nitrogen removal (ANR) process. The (post-) treatment performances of (i) ozonation alone, (ii) adsorption to granular activated carbon (GAC) alone, (iii) the combination of O3 and GAC and (iv) an integrated approach with continuous recirculation of ozonated ANR effluent were investigated. It was observed that ANR post-treatment with ozonation was able to remove only 15.2% of residual COD and 14.0% of total nitrogen in the effluent whereas using activated carbon a 73.6% removal efficiency of COD and 17.3% of total nitrogen was achieved. The best performance was obtained for an ANR post-treatment combination of ozonation and GAC, ensuring a high removal for both COD and total nitrogen. When different ratios of ozonated effluent were mixed with the influent of the ANR, it was found to be possible to reach COD removal as high as 40% in the ANR with a slightly decrease in nitrogen removal of around 70–80% compared to respectively 5.31% (COD) and 85.9% (total nitrogen) when no ozonated leachate was recycled to the ANR reactor. Taking the overall performance and operational expenses into account, a combination of ANR biological treatment and its different (post-) treatments (ANR+ozonation+GAC) results in a good performance and a lower cost compared to traditional treatment.
A benchmark simulation model, which includes a wastewater treatment plant (WWTP)-wide model and a rising main sewer model, is proposed for testing mitigation strategies to reduce the system's ...greenhouse gas (GHG) emissions. The sewer model was run to predict methane emissions, and its output was used as the WWTP model input. An activated sludge model for GHG (ASMG) was used to describe nitrous oxide (N(2)O) generation and release in activated sludge process. N(2)O production through both heterotrophic and autotrophic pathways was included. Other GHG emissions were estimated using empirical relationships. Different scenarios were evaluated comparing GHG emissions, effluent quality and energy consumption. Aeration control played a clear role in N(2)O emissions, through concentrations and distributions of dissolved oxygen (DO) along the length of the bioreactor. The average value of N(2)O emission under dynamic influent cannot be simulated by a steady-state model subjected to a similar influent quality, stressing the importance of dynamic simulation and control. As the GHG models have yet to be validated, these results carry a degree of uncertainty; however, they fulfilled the objective of this study, i.e. to demonstrate the potential of a dynamic system-wide modelling and benchmarking approach for balancing water quality, operational costs and GHG emissions.
Palladium is used in several industrial applications and, given its high intrinsic value, intense efforts are made to recover the element. In this hydrometallurgic perspective, ion-exchange (IEX) ...technologies are principal means. Yet, without incorporating the chemical and physical properties of the Pd present in real, plant-specific conditions, the recovery cannot reach its technical nor economic optimum. This study characterized a relevant Pd-containing waste stream of a mirror manufacturer to provide input for a speciation model, predicting the Pd speciation as a function of pH and chloride concentration. Besides the administered neutral PdCl2 form, both positively and negatively charged PdCln(2-n) species occur depending on the chloride concentration in solution. Purolite C100 and Relite 2AS IEX resins were selected and applied in combination with other treatment steps to optimize the Pd recovery. A combination of the cation and anion exchange resins was found successful to quantitatively recover Pd. Given the fact that Pd was also primarily associated with particles, laboratory-scale experiments focused on physical removal of the Pd-containing flow were conducted, which showed that particle-bound Pd can already be removed by physical pre-treatment prior to IEX, while the ionic fraction remains fully susceptible to the IEX mechanism.
This contribution deals with NO and N₂O emissions during autotrophic nitrogen removal in a granular sludge reactor. Two possible model scenarios describing this emission by ammonium- oxidizing ...biomass have been compared in a simulation study of a granular sludge reactor for one-stage partial nitritation–Anammox. No significant difference between these two scenarios was noticed. The influence of the bulk oxygen concentration, granule size, reactor temperature and ammonium load on the NO and N₂O emissions has been assessed. The simulation results indicate that emission maxima of NO and N₂O coincide with the region for optimal Anammox conversion. Also, most of the NO and N₂O are present in the off-gas, owing to the limited solubility of both gases. The size of granules needs to be large enough not to limit optimal Anammox activity, but not too large as this implies an elevated production of N₂O. Temperature has a significant influence on N₂O emission, as a higher temperature results in a better N-removal efficiency and a lowered N₂O production. Statistical analysis of the results showed that there is a strong correlation between nitrite accumulation and N₂O production. Further, three regions of operation can be distinguished: a region with high N₂O, NO and nitrite concentration; a region with high N₂ concentrations and, as such, high removal percentages; and a region with high oxygen and nitrate concentrations. There is some overlap between the first two regions, which is in line with the fact that maximum emission of NO and N₂O coincides with the region for optimal Anammox conversion.
Nanofibre membranes are studied extensively in water treatment. Inappropriate storage, however, could alter their performance, e.g. regarding water filtration. This shows the need for investigating ...this effect in more detail so as to offer a solution for long-term behaviour and stability. In this study, polyamide nanofibre membranes were treated under different conditions, simulating the diverse storage conditions and to simulate their use in water filtration systems. Under all these different settings, nanofibre properties (scanning electron microscope pictures, dimensional changes, tensile strength) and water filtration performance (clean water permeability (CWP), bacterial removal) were investigated. The results demonstrate that, as soon as the dimensional change of a membrane is >2%, the CWP, tensile strength and bacterial removal significantly decrease. These dimensional changes occurred when the membrane became dry after it had been in contact with water. As such, it is important to keep the membrane either in dry or in wet conditions to store its unique properties. When heat-treated, the membrane had a higher tensile strength and kept its morphology and characteristics better during storage.
