Experimental assessment and mathematical modelling of the growth of Chlorella vulgaris under photoautotrophic, heterotrophic and mixotrophic conditions.

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.

Application of online instrumentation in industrial wastewater treatment plants - a survey in Flanders, Belgium.

A survey regarding online instrumentation and control was conducted among 90 companies managing their own biological wastewater treatment plant in Flanders, Belgium. In this study, all types of online instrumentation have been found suitable for automatic process control. However, its integration in general process control as well as in nitrogen removal and chemical dosing control appeared to be rather limited. Only dissolved oxygen and pH sensors were widely applied, being present in 96% and 69% of the plants, respectively. Widespread process integration is mainly obstructed by the fact that companies, especially small and medium-sized, still do not regard wastewater treatment as a full-fledged part of the production process. Operators often lack technical expertise in this domain and tend to be skeptical towards automated control mechanisms. In addition, the price of online instrumentation is still perceived as too high, in particular at smaller companies. Lastly, the design of the existing wastewater treatment plant does not always allow for real-time control. Certain measures such as operator training, monitoring of energy and chemical consumption and reduction of instrumentation costs are essential for widespread application of online process control in future years. Additionally, water reuse can create an important incentive.

Physical-chemical treatment of rainwater runoff in recovery and recycling companies: lab-scale investigation.

Scrap material recovery and recycling companies are producing wastewater in which common pollutants (such as COD, nutrients and suspended solids), toxic metals, polyaromatic hydrocarbons (PAH) and polychlorinated biphenyls (PCB) frequently can exceed the discharge limits. Lab-scale optimisation of different possible physical-chemical treatment techniques was performed on the wastewater originating from three different companies in view of further testing at pilot-scale testing and implementation at full-scale. The lab-scale tests demonstrate that sedimentation or hydrocyclone treatment as stand-alone technique cannot be used for proper treatment of this type of wastewater. Dual bed filtration or coagulation/flocculation proved to be more promising with removal efficiencies of about 71-95% (dual bed filtration) and 61-97% (coagulation/flocculation) for the above-mentioned pollutants (metals, PAH and PCB).

Chemical fractionation and speciation modelling for optimization of ion-exchange processes to recover palladium from industrial wastewater.

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.

Structure changes and water filtration properties of electrospun polyamide nanofibre membranes.

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.

Leaching behaviour of different scrap materials at recovery and recycling companies: full-, pilot- and lab-scale investigation.

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.

Parameter study on the efficiency of ozonation for biologically treated landfill leachate.

Ozonation was investigated as a potential post-treatment step for biologically treated landfill leachate to enhance the biodegradability and observe the influence of the initial organic matter concentration and pH. Changes in COD, UV absorption at 254 nm (UVA254) and BOD content were measured during and after ozonation, and the ozone utilisation efficiency at different conditions was calculated. The initial COD concentration was found to influence the absolute removal of UVA254 significantly, but especially changes in pH influenced the ozone reactions. Increased pH (pH 10) most probably increased the overall hydroxyl radical production leading to a higher COD removal and a much better ozone utilisation compared to lower pH. This in contrast to initial COD variations which had little influence on the determined ozone utilisation. Regardless of initial COD content or pH, on average 10% of the initial COD content was converted to BOD, next to 10% COD that was removed.

Comparison of ozone and HO· induced conversion of effluent organic matter (EfOM) using ozonation and UV/H2O2 treatment.

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.

Treatment of rainwater runoff in recovery and recycling companies: Lab and pilot-scale testing.

Wastewater released from the storage and/or processing of recycling and materials recovery can be characterised as rainwater runoff. Recuperation and recycling companies are confronted with wastewater that has a very fluctuating flow rate and composition. The flow rate mainly depends on the amount of rainfall while the composition additionally depends on what is currently stored on site. An analysis of possible physical-chemical treatment (coagulation/flocculation, sand filtration, activated carbon filtration and sedimentation) methods was performed at two different recycling companies in order to find a robust and economical feasible water treatment system that meets the discharge limits at all times. A violation of some measurement values (Cd, Cr, Ni and acenaphthene) after coagulation/flocculation occurred, which could be further reduced by using sand filtration. Good removal is achieved for common parameters as for mono- and poly-aromatic hydrocarbons (MAH and PAH) and polychlorinated biphenyls (PCB). Applying a coupled sand- and activated carbon filtration on runoff resulted in a removal of over 80% of several measurement values (suspended solids, heavy metals). This clearly indicates the applicability of the physical-chemical treatment techniques.

Towards a benchmarking tool for minimizing wastewater utility greenhouse gas footprints.

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.

Individual treatment of hotel and restaurant waste water in rural areas.

About 25 hotels, restaurants and pubs in the rural community Heuvelland are situated in the area designated for individual water treatment. In order to meet the legislation by the end of 2015, each business needs to install an individual waste water treatment system (IWTS). To study this situation, three catering businesses were selected for further research. The aim of the study was to quantify the effluent quality and to assess IWTS performance for these catering businesses. First of all, the influence of discharging untreated waste water on the receiving surface water was examined. The results showed a decrease in water quality after the discharge point at every business. With the collected data, simulations with the software WEST were performed. With this software two types of IWTSs with different (buffer) volumes were modelled and tested for each catering business. The first type is a completely mixed activated sludge reactor and the second type is a submerged aerobic fixed-bed reactor. The results of these simulations demonstrate that purification with an IWTS is possible if the capacity is large enough and if an adequate buffer volume is installed and if regular maintenance is performed.

N2O and NO emissions during autotrophic nitrogen removal in a granular sludge reactor--a simulation study.

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.

Sustainable wastewater treatment of temporary events: the Dranouter Music Festival case study.

Music festivals and other temporary events, such as bicycle races, lay a heavy burden on the surrounding environment. Treatment of the wastewater originating from such events is necessary if no municipal treatment plant is available. This study demonstrated that activated carbon is a performant technique for the treatment of wastewaters originating from these temporary events. Freundlich isotherms and maximum operational linear velocity (6 m/h) were determined on a lab-scale set-up. A pilot-scale set up was used to treat part (5%) of the total volume of the Dranouter Music Festival shower wastewater. On average 90% removal of COD and suspended solids concentration was obtained. Application of the activated carbon filter resulted in the fact that the local discharge limits were met without operational problems.

Sensor validation and reconciliation for a partial nitrification process.

Wastewater treatment plants (WWTP) are notorious for poor data quality and sensor reliability due to the hostile environment in which the measurement equipment has to function. In this paper, a structured residual approach with maximum sensitivity (SRAMS) based on the redundancy of the measurements is used to detect, identify and reconstruct single and multiple sensor faults in a single reactor for high activity ammonia removal over nitrite (SHARON) process. SRAMS is based on inferences, which are insensitive to the faults in the sensor of interest and sensitive to faults in the other sensors. It is used for four types of sensor failure detection: bias, drift, complete failure and precision degradation. The application of sensor validation shows that single and multiple sensor faults can be detected and that the fault magnitude and fault type can be estimated by the reconstruction scheme. This sensor validation method is not limited by the type or application of the considered sensors. The methodology can thus easily be applied for sensor surveillance of other continuously measuring sensors and analysers.

Titrimetric monitoring of a completely autotrophic nitrogen removal process.

Fully autotrophic nitrogen removal processes, such as the combined SHARON-Anammox process, help to improve the sustainability of wastewater treatment. Successful operation of such a completely autotrophic system is, among others, based on the strict control of the SHARON reactor in order to produce an Anammox-suited influent with a 1:1 ammonium:nitrite ratio. The high quality and high frequency measurements provided by a titrimetric set-up measuring the total ammonium (TAN) and total nitrite (TNO2) concentrations facilitate this control considerably. In this study, the use of a titrimetric set-up for monitoring the combined SHARON-Anammox process is investigated. The technique that interprets on-line collected titration curves was applied to a lab-scale system. Comparison with classic colorimetric results gave statistically indistinguishable results for TAN and TNO2 concentrations in the SHARON reactor. In the Anammox reactor, only TAN could be determined by the investigated method due to the very low TNO2 concentrations. Phosphate, a potential inhibitor of the Anammox process, is available as an additional measurement in the effluent of the SHARON reactor. Three measurements are thus combined in one single instrument. The proposed measuring technique holds different advantages over the other TAN and TNO2 measurement techniques such as on-site availability, easy automation, the absence of the need for high dilutions and cost reduction.

Coupling the SHARON process with anammox: model-based scenario analysis with focus on operating costs.

The combined SHARON-Anammox process for treating wastewater streams with high ammonia concentration is discussed. Partial nitritation in the SHARON reactor should be performed to such an extent that an Anammox-optimal nitrite:ammonium ratio is generated. The SHARON process is typically applied to sludge digestion rejection water in order to relieve the ammonium load recycled to the main plant. A simulation study for realistic influent conditions on a SHARON reactor with a fixed volume and operated with constant air flow rate reveals that the actual nitrite:ammonium ratio might deviate significantly from the ideal ratio and might endanger operation of the subsequent Anammox reactor. It is further examined how the nitrite:ammonium ratio might be optimized. A cascade pH control strategy and a cascade O2 control strategy are tested. Simulation results are presented and the performance of the different strategies is assessed and quantified in an economic way by means of an operating cost index. Best results are obtained by means of cascade feedback control of the SHARON effluent nitrite:ammonium ratio through setting an O2-set-point that is tracked by adjusting the air flow rate.

Practical experiences with start-up and operation of a continuously aerated lab-scale SHARON reactor.

Partial nitrification techniques, such as the continuously aerated SHARON process, have been denoted for quite a while as very promising for improved sustainability of wastewater treatment. Combination of such a SHARON process with the Anammox process, where ammonium is oxidised with nitrite to nitrogen gas under anoxic conditions, leads to cost-efficient and sustainable nitrogen removal from concentrated streams. In this study practical experiences during start-up and operation of a lab-scale SHARON reactor are discussed. Special attention is given to the start-up in view of possible toxic effects of high ammonium and nitrite concentrations (up to 4000 mgN/l) on the nitrifier population and because the reactor was inoculated with sludge from a SBR reactor operated under completely different conditions. Because of these considerations, the reactor was first operated as a SBR to prevent biomass wash out and to allow the selection of a strong nitrifying population. A month after the inoculation the reactor was switched to normal chemostat operation. As a result the nitrite oxidisers were washed out and only the ammonium oxidisers persisted in the reactor. In this contribution also some practical considerations, such as mixing, evaporation and wall growth, concerning the operation of a continuously aerated SHARON reactor are discussed. These considerations are not trivial, since the reactor will be used for kinetic characterisation and modelling studies. Finally the performance of the SHARON reactor under different conditions is discussed in view of its coupling with an Anammox unit. Full nitrification was proven to be feasible for nitrogen loads up to 1.5 g/l d, indicating the possibility of the SHARON process to treat highly loaded nitrogen streams.

Ambulatory blood pressure and blood pressure measured at home: progress report on a population study.

To determine reference values for ambulatory blood pressure, a population sample of 718 subjects (20 through 88 years old) was investigated. Ambulatory blood pressure was recorded over 24 h, taking measurements at 20-min intervals from 8 a.m. to 10 p.m. and at 45-min intervals from 10 p.m. to 8 a.m. Trained nurses also measured the conventional pressure at each participant's home. The ambulatory blood pressure in the 718 subjects averaged 119/71 mm Hg over 24 h, 125/76 mm Hg during the day (10 a.m.-8 p.m.), and 108/62 mm Hg at night (0 a.m.-6 a.m.). Compared with the daytime pressure, blood pressure at home was on average the same in all 718 subjects but was 3/1 mm Hg lower in 530 normotensive subjects. The 95th percentiles of the 24-h pressures were 134/85 mm Hg in 182 men below age 50, 145/87 mm Hg in 164 men aged > or = 50 years, 127/80 mm Hg in 198 women below age 50, and 141/81 mm Hg in 174 women aged > or = 50 years. In the normotensive subjects of these four strata, these percentiles were 132/82 mm Hg (n = 149), 128/80 mm Hg (n = 103), 125/79 mm Hg (n = 180), and 131/79 mm Hg (n = 98). In comparison with earlier results in a smaller sample (n = 318) from which treated patients were excluded, this analysis demonstrated consistent results in the determination of a reference frame for ambulatory monitoring. Nevertheless, the prognostic significance of such reference values needs to be established in longitudinal studies and clinical trials.