Heat recovery during treatment of highly concentrated wastewater: economic evaluation and influencing factors.

This paper assesses the economics of heat recovery from biological wastewater treatment plants (WWTPs) treating concentrated wastewater, as higher concentrations result in higher heat generation in the treatment basin. A heat balance model has been applied to calculate the amount of recoverable heat from the system and the effect of the heat extraction capacity on the economics of a heat pump installation, evaluated using the internal rate of return. A sensitivity analysis has been performed to evaluate the effect of several parameters on the economics of heat recovery in this type of WWTP: the electricity price, the price of the fuel substituted by heating savings, the investment costs, the coefficient of performance (COP) and the amount of heat extracted from the system. It was calculated that the heat pump capacity has to be high enough to recover a significant amount of heat, but low enough to improve the economics of the system. The economic performance of the system is very dependent on the energy prices of both electrical power to run the heat pump and the fuel (heat) cost substituted by the heat pump.

Effect of foam on temperature prediction and heat recovery potential from biological wastewater treatment.

Heat is an important resource in wastewater treatment plants (WWTPs) which can be recovered. A prerequisite to determine the theoretical heat recovery potential is an accurate heat balance model for temperature prediction. The insulating effect of foam present on the basin surface and its influence on temperature prediction were assessed in this study. Experiments were carried out to characterize the foam layer and its insulating properties. A refined dynamic temperature prediction model, taking into account the effect of foam, was set up. Simulation studies for a WWTP treating highly concentrated (manure) wastewater revealed that the foam layer had a significant effect on temperature prediction (3.8 ± 0.7 K over the year) and thus on the theoretical heat recovery potential (30% reduction when foam is not considered). Seasonal effects on the individual heat losses and heat gains were assessed. Additionally, the effects of the critical basin temperature above which heat is recovered, foam thickness, surface evaporation rate reduction and the non-absorbed solar radiation on the theoretical heat recovery potential were evaluated.

Development of an imaging system for single droplet characterization using a droplet generator.

The spray droplets generated by agricultural nozzles play an important role in the application accuracy and efficiency of plant protection products. The limitations of the non-imaging techniques and the recent improvements in digital image acquisition and processing increased the interest in using high speed imaging techniques in pesticide spray characterisation. The goal of this study was to develop an imaging technique to evaluate the characteristics of a single spray droplet using a piezoelectric single droplet generator and a high speed imaging technique. Tests were done with different camera settings, lenses, diffusers and light sources. The experiments have shown the necessity for having a good image acquisition and processing system. Image analysis results contributed in selecting the optimal set-up for measuring droplet size and velocity which consisted of a high speed camera with a 6 micros exposure time, a microscope lens at a working distance of 43 cm resulting in a field of view of 1.0 cm x 0.8 cm and a Xenon light source without diffuser used as a backlight. For measuring macro-spray characteristics as the droplet trajectory, the spray angle and the spray shape, a Macro Video Zoom lens at a working distance of 14.3 cm with a bigger field of view of 7.5 cm x 9.5 cm in combination with a halogen spotlight with a diffuser and the high speed camera can be used.

Quantification of microparticle coating quality by confocal laser scanning microscopy (CLSM).

In this work, a novel protocol was developed for determining film coating thickness and coating quality of microparticles, based on the use of confocal laser scanning microscopy (CLSM). CLSM was found to be an adequate non-destructive technique for the quantification of the coating thickness and coating quality of individual thin-coated small particles. Combined with image analysis, it was possible to derive with high accuracy the coating thickness distribution of a representative number of microparticles. The performance of the novel methodology was assessed by the quantification of the coating thickness and coating quality of protein-coated microparticles produced by fluidized bed coating. It was found that the CLSM data on coating layer thickness were generally in good agreement with the results from chemical analysis, down to a thickness of 1-1.5 microm. Using CLSM the importance of setting up the appropriate distance between the coating nozzle and the powder bed with respect to microparticle coating quality in fluidized bed processing was illustrated. Coating quality was found to decrease with increasing distance the coating droplets have to travel before impinging onto the core particles as a result of spray-drying of the coating droplets. Also, coating quality decreased with increasing viscosity of the coating droplets, resulting in reduced spreading on the cores.

Polycyclic aromatic hydrocarbons (PAHs) and estrogenic compounds in experimental flue gas streams.

The importance of combustion processes as a source of substances with estrogenic activity in the environment was investigated. Wood (nontreated and treated with wood preservatives), barbecue charcoal, meat, and kitchen waste were combusted in a laboratory-scale incinerator. Flue gas emissions (particulates and gaseous pollutants) were trapped in polyurethane foam cartridges. The cartridges were subjected to Soxhlet extraction and part of the extracts redissolved in dimethylsulfoxide (DMSO) for analyses of estrogenic activity by means of the yeast-based human estrogen receptor (hER) bioassay. A synthetic estrogen, 17-alpha-ethinylestradiol (EE2), was used as the reference estrogenic compound. Part of the extracts was analyzed for the 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs). Estrogenic compounds in the flue gas (wood) were as high as 234 +/- 25 ng m(-3) EE2 equivalent compared with 27 to 81 ng m(-3) EE2 equivalent in flue gas from combustion of barbecue charcoal. Concentrations of polycyclic aromatic hydrocarbons in both flue gas streams were in the range of 21,000 +/- 2000 and 240 +/- 110 ng m(-3), respectively. In general, the concentrations of EE2 equivalent in the flue gas samples were at least a factor of 1000 lower than total PAH concentration. The EE2 levels were not related to the concentration of PAHs in any flue gas sample.

CFD approach for modelling microbial inactivation during thermal processing of intact eggs.

Combined conductive and convective heat transfer during thermal pasteurisation of intact eggs was studied using a commercial Computational Fluid Dynamics (CFD) package. A kinetic inactivation model for Salmonella enteritidis was combined with the CFD model, enabling evaluation and assessment of egg pasteurisation processes. Simulated temperature profiles were found to be in good agreement with experimentally observed data. The obtained results offer a useful tool for assessment and optimisation of egg pasteurisation processes.

Assessment of the estrogenic activity of flue gases from burning processes by means of the yeast based human estrogen receptor (hER) bioassay.

Combustion processes are known to produce organic micro-pollutants in the flue gas at concentrations ranging over several orders of magnitude. Some organic micro-pollutants are suspected of being pseudo-estrogens and as such they can affect the public health. In this study, the possible application of the yeast based human estrogen receptor (hER) bioassay to screen flue gas streams for the presence of estrogenic active micro-pollutants was explored. Specifically, the protocol was modified to allow the detection and quantification of the potential estrogenic active non-polar organic micro-pollutants contained in the flue gas matrix. The modified assay was calibrated using a model estrogenic compound (17-alpha-ethinylestradiol (EE2)) dissolved in methylene chloride at concentrations ranging from 3 ng l(-1) to 3000 ng l(-1). The effective concentration to elucidate a 50% response (EC50) was 87 ng l(-1) of equivalent dissolved in methylene chloride. Samples of methylene chloride used to trap non-polar micro-pollutants in flue gas from combustion of pine wood were found to clearly register estrogenic activity by the bioassay under certain conditions. The combustion tests were performed with pinewood alone and with pine wood in the presence of both Copper-naphthenate and copper(II)chloride at 600 degrees C and 1000 degrees C. These conditions must be considered as experimental rather than practical. Overall, the results suggest that, by means of this modified assay, it is possible and warranted to screen systematically for estrogens in flue gas combustion processes.