Nico Lambert

Evaluation of process parameters of ultrasonic treatment of bacterial suspensions in a pilot scale water disinfection system

In this study, several process parameters that may contribute to the efficiency of ultrasound disinfection are examined on a pilot scale water disinfection system that mimics realistic circumstances as encountered in an industrial environment. The main parameters of sonication are: (i) power; (ii) duration of treatment; (iii) volume of the treated sample. The specific energy (E(s)) is an indicator of the intensity of the ultrasound treatment because it incorporates the transferred power, the duration of sonication and the treated volume. In this study, the importance of this parameter for the disinfection efficiency was assessed through changes in volume of treated water, water flow rate and electrical power of the ultrasonic reactor. In addition, the influences of the initial bacterial concentration on the disinfection efficiency were examined. The disinfection efficiency of the ultrasonic technique was scored on a homogenous and on a mixed bacterial culture suspended in water with two different types of ultrasonic reactors (Telsonic and Bandelin). This study demonstrates that specific energy, treatment time of water with ultrasound and number of passages through the ultrasonic reactor are crucial influential parameters of ultrasonic disinfection of contaminated water in a pilot scale water disinfection system. The promising results obtained in this study on a pilot scale water disinfection system indicate the possible application of ultrasound technology to reduce bacterial contamination in recirculating process water to an acceptable low level. However, the energy demand of the ultrasound equipment is rather high and therefore it may be advantageous to apply ultrasound in combination with another treatment.

Comparison of Different Oxidation Methods for Recalcitrance Removal of Landfill Leachate

In this work several oxidation methods, such as conventional ozonation, O3/UV, O3/UV/ferrous iron and Fenton oxidation, for the removal of recalcitrant organic matter present in landfill leachates are evaluated. The samples of the leachate are taken after a biological treatment and membrane ultra-filtration (UF). The contribution of the UV radiation and the effect of ferrous iron ions on the ozone process efficiency is discussed. At lower ozone dosages, the partial oxidation efficiency is reduced as compared to conventional ozonation and therefore, a higher degree of mineralization of the organic matter is achieved. Finally, the best results are obtained by the Fenton oxidation, however, based on economic considerations this method is not recommended.

Evaluation of power ultrasound for disinfection of both Legionella pneumophila and its environmental host Acanthamoeba castellanii

The objectives of this study were to (1) examine the effect of power ultrasound on the viability of both Legionella pneumophila and Acanthamoeba castellanii trophozoites and cysts, (2) investigate if intracellular Legionella replication in trophozoites positively affects bacterial resistance to ultrasound and (3) study if Legionella renders viable but non-culturable (VBNC) due to ultrasound treatments. Using laboratory scale experiments, microorganisms were exposed for various time periods to power ultrasound at a frequency of 36 kHz and an ultrasound power setting of 50 and 100%. Due to a fast destruction, trophozoite hosts were not able to protect intracellular Legionella from eradication by ultrasound, in contrast to cysts. No significant effects of ultrasound on cyst viability could be detected and power settings of 100% for 30 min only made intracellular Legionella concentrations decrease with 1.3 log units. Due to intracellular replication of Legionella in trophozoites, ultrasound no longer affected bacterial viability. Concerning the VBNC state, ultrasound treatments using a power setting of 50% partly induced Legionella (+/-7%) to transform into VBNC bacteria, in contrast to power settings of 100%. Promising results obtained in this study indicate the possible application of power ultrasound in the control of both Legionella and Acanthamoeba concentrations in anthropogenic water systems.

Modelling of the ultrasonic disintegration of activated sludge

Abstract Ultrasonic treatment of waste activated sludge is one of the possibilities to reduce excess sludge production through the mechanism of sludge disintegration and cell lysis. In the past, several attempts have been made to model the process of solubilisation of the particulate volatile suspended solid part of the activated sludge (VSS) into soluble COD (sCOD). However, the focus of these models was predominantly on predicting an efficiency factor for the release of sCOD (Disintegration Degree, DD COD ) and provided no information on the release of nutrients and the instantaneous reduction of VSS. Moreover, often insufficient influential variables were included in the model equations, making the models only applicable on the training dataset of their own experimental research. This paper, therefore, seeks to build a simple model, which contains all influential input variables, that can predict not only the sCOD release but also the nutrients release (ortho-PO 4 -P and soluble Kjeldahl nitrogen) and VSS reduction simultaneously. Therefore, in first instance, a Principal Component Analysis (PCA) is carried out on the input and output data matrix of obtained experimental observations that will be used as training data. In this way, certain correlated input variables and independent output variables can be removed from the model, in order to increase its simplicity and predictive nature. Then, the model is built on the basis of Partial Least Squares Regression (PLS-R) and a part of the observations is used to validate the predictive strength of the model.

Respirometric Evaluation of Toxicity of 2,4-Dichlorophenol Towards Activated Sludge and the Ability of Biomass Acclimation

In the present research, both direct and co-metabolic biodegradation of 2,4-dichlorophenol by mixed activated sludge cultures are investigated by performing respirometric experiments. Firstly, the biomass inhibition due to the toxic pollutant is studied by performing a respirometric toxicity detection experiment. A lag phase for the activity of the biomass showed up because of 2,4-dichlorophenol. The length of the lag phase increased by increasing the concentration of 2,4-dichlorophenol. At higher concentrations, the micro-organisms required more adaption time to the presence of the toxic pollutant. Remarkably, the biomass restored its activity partially. Furthermore, respirometric experiments are performed for several days to investigate biomass acclimation towards the repeated addition of 2,4-dichlorophenol. A significant decrease of the reaction time needed was obtained by biomass acclimation. Immediately after the second addition, an increase of the biomass activity combined with both COD and 2,4-dichlorophenol degradation were observed. The biomass was able to adapt and even to degrade the toxic pollutant. At the second addition, this acclimation period was not necessary.

Effect of Sludge Retention Time on the Efficiency of Excess Sludge Reduction by Ultrasonic Disintegration

Excess sludge reduction in activated sludge plants can, inter alia, be achieved by the integration of sludge disintegration technology in the recycle stream of activated sludge treatment plants. In previous research by Lambert et al. (2016), a long-term experimental study of 120 days at a biodiesel production plant demonstrated that ultrasonic sludge disintegration can result in a substantial reduction of waste sludge of about 45%, and this at a relatively low specific energy. Moreover, it was revealed from this pilot experiment that the efficiency of the excess sludge reduction, indicated as SRE (Sludge Reduction Efficiency), increases when the activated sludge plant is operated at a higher sludge retention time (SRT). This is an important finding, because this would mean that the ultrasonic technology can be operated more cost efficiently at a higher sludge retention time. To confirm this finding and to give a deeper insight into the underlying mechanisms and long-term effects that promote the excess sludge reduction, lab-scale aerobic digestion experiments were performed. Both the endogenous respiration rate and the VSS concentration were monitored during the 30 days’ experimental period, and could give more information about the fate and the biodegradation of the particulate COD in activated sludge. Modeling the batch tests indicated a higher endogenous residue decay rate (bXE) and a clear instantaneous change in the active biomass concentration, of nearly 50%, which can be directly assigned to the ultrasonic pre-treatment. This has ultimately led to a more thorough VSS reduction at the end of the digestion period.

Integrating ultrasonic disintegration in activated sludge wastewater treatment plant modeling

AbstractThis paper presents an integrated mathematical model that is capable of predicting and assessing the impact of ultrasonic (US) treatment on the excess activated sludge production in an activated sludge wastewater treatment system. Biological processes in the reactor are simulated in Matlab®/Simulink by the ASM1 model into which two algebraic equations, which capture the US treatment, are integrated. Calibration and validation data series come from a pilot plant installed at two locations, i.e. at a communal wastewater treatment plant (Mechelen-Noord) and at an industrial food flavor production site Haasrode, both located in the Flanders region of Belgium. The results show that the built-up model is capable of correctly predicting excess sludge reduction in the treatment system (which is a sequencing batch reactor in both cases). A reduction of approximately 42% for the communal case study can be reported, while the result obtained for the industrial case study, characterized by a very high organic...

Towards a low complexity carbon removal model for the optimal design of compact decentralised wastewater treatment systems

On-site decentralised wastewater treatment systems can provide a financially attractive alternative to a sewer connection in locations far from existing sewer networks. Operational problems and shortcomings in the design of these systems still occur frequently. The aim of this paper is to provide a low complexity (i.e. easy to calibrate) but still accurate mathematical model that can be used to optimise the operational design of compact individual wastewater treatment systems. An integrated hydraulic and biological carbon removal model of a biofilm-based compact decentralised treatment system is developed. The procedure for drafting the model is generic and can be used for similar types of wastewater treatment systems since (i) the hydraulic model is based on an N-tanks-in-series model inferred from tracer test experiments and (ii) (biofilm) respirometry experiments are exploited to determine the biodegradation kinetics of the biomass. Based on the preliminary validation results of the integrated model, the carbon removal in the system can be predicted quite accurately. While some adjustments could further improve the modelling strategy, the here presented results can already assist the manufacturers of compact treatment systems in efficiently (re)designing their systems.