Microalgae are not an umbrella solution for power industry waste abatement but could play a role in their valorization

Microalgae have long been regarded as a promising solution for biological carbon abatement from the power industry, offering renewable biomass without competing for land or water resources used for food crops. In this study, we extensively examined the application of photosynthetic microorganisms for closing carbon, nitrogen, and micronutrient loops in the power industry. Subsequently, we explored the bottom-up integration of algal biorefineries into power industry waste streams for increased economic benefits and reduced environmental impacts. Analysis of the available data indicated that microalgae integration with the power industry is primarily performed using flue-gas-assisted cultivation. This approach allows for carbon sequestration typically below one gram per liter per day, too low to significantly impact carbon abatement at achievable scales of microalgae cultivation. Alternative approaches are also being explored. For example, soluble bicarbonate platforms allow for higher biomass productivity and temporary carbon storage. Meanwhile, the use of ashes and waste heat and thermophilic strains can result in lower cultivation costs and better control of cultivation conditions. These approaches offer further incremental improvement to microalgae-based carbon abatement systems in the power industry but are unlikely to be an umbrella solution for carbon reduction. Consequently, in the near term, microalgae-based carbon valorization systems are likely to be limited to niche applications involving the synthesis of high-value products. For microalgae to truly transform carbon abatement processes radical improvements in both biology and engineering approaches are urgently needed.

Effects of Low Temperature, Nitrogen Starvation and Their Combination on the Photosynthesis and Metabolites of Thermosynechococcus E542: A Comparison Study

Both low temperature and nitrogen starvation caused chlorosis of cyanobacteria. Here, in this study, for the first time, we compared the effects of low temperature, nitrogen starvation, and their combination on the photosynthesis and metabolites of a thermophilic cyanobacterium strain, Thermosynechococcus E542. Under various culture conditions, the growth rates, pigment contents, and chlorophyll fluorescence were monitored, and the composition of alkanes, lipidomes, and carbohydrates were determined. It was found that low temperature (35 °C) significantly suppressed the growth of Thermosynechococcus E542. Nitrogen starvation at 45 °C and 55 °C did not affect the growth; however, combined treatment of low temperature and nitrogen starvation led to the lowest growth rate and biomass productivity. Both low temperature and nitrogen starvation caused significantly declined contents of pigments, but they resulted in a different effect on the OJIP curves, and their combination led to the lowest pigment contents. The composition of fatty acids and alkanes was altered upon low-temperature cultivation, while nitrogen starvation caused reduced contents of all lipids. The low temperature did not affect carbohydrate contents, while nitrogen starvation greatly enhanced carbohydrate content, and their combination did not enhance carbohydrate content, but led to reduced productivity. These results revealed the influence of low temperature, nitrogen starvation, and their combined treatment for the accumulation of phycobiliproteins, lipids, and carbohydrates of a thermophilic cyanobacterium strain, Thermosynechococcus E542.

Comparison of Photocatalytic and Photosensitized Oxidation of Paraben Aqueous Solutions Under Sunlight

It is well-established that aquatic wildlife is exposed to natural and synthetic endocrine disrupting compounds which are able to interfere with the hormonal system. Although advanced oxidation processes (AOPs) have shown to be effective, their application is limited by a relatively high operational cost. In order to reduce the cost of energy consumed in the AOPs, widely available solar energy instead of UV light may be applied either as photocatalytic oxidation or as photosensitized oxidation. The main goal of the present study was to investigate the sunlight photodegradation of paraben mixture. Two processes, namely the photocatalytic oxidation with modified TiO2 nanoparticles and photosensitized oxidation with photosensitive chitosan beads, were applied. The oxidants were identified as singlet oxygen and hydroxyl radicals for photosensitized and photocatalytic oxidation, respectively. The toxicity, as well as ability to water disinfection of both processes under natural sunlight, has been investigated. Application of sunlight for the processes led to degradation of parabens. The efficiency of both processes was comparable. Despite the fact that singlet oxygen is weaker oxidant than hydroxyl radicals, the photosensitized oxidation seems to be more promising for wastewater purification, due to the possibility of chitosan bead reuse and more effective water disinfection. Graphical Abstractᅟ.

The effect of initial organic load of the kitchen waste on the production of VFA and H2 in dark fermentation

Dark fermentation of kitchen wastes was studied in batch bioreactors, with no pH adjustment, to evaluate the effect of the initial organic load on the process performance in terms of volatile fatty acids and H₂ production. Initial organic load of the kitchen wastes ranged from 4.1 to 48.2gVS/L. Acetic and butyric acids were produced in the largest amount. At the initial organic load of 48.2KWgVS/L the highest concentration of volatile fatty acids was 9.81g/L. The maximum production yield of H₂ (76.1mL/gVS) was found for the initial organic load of kitchen wastes at 14.3gVS/L. The carbon balance calculation showed that the maximum CO₂ yield of 0.34 gC/gC was attained in the bioreactor with the initial organic load of 14.3gVS/L. The microbiological analysis revealed that the predominant microorganisms in the dark fermentation process were Bacteroidetes, Firmicutes, Spirochaetes and WWE1 at phyla level.

Decomposition of xenobiotics during visible light irradiation in the presence of immobilised photosensitisers: kinetics study

The objective of this work was to study the photosensitised oxidation of the xenobiotics benzylparaben (BeP) and 2,4dichlorophenol (2,4DCP) in aqueous solutions using photosensitisers immobilised into chitosan carrier particles and visible light radiation. Zn(II) phthalocyanine tetrasulfonate tetrasodium salt and Al(III) phthalocyanine chloride tetrasulfonic acid were used as photosensitisers. The major role of the singlet oxygen during photodegradation was proven by using scavengers of reactive oxygen species. The influence of initial xenobiotic concentration and temperature on degradation rate was examined. The investigations were focused on kinetics (Langmuir-Hinshelwood model) as well as activation energy determination. Moreover, the adsorption isotherms of BeP and 2,4DCP into chitosan carrier were determined using the Brunauer-Emmett-Teller model.

Modern morphological engineering techniques for improving productivity of filamentous fungi in submerged cultures

Morphological engineering techniques have recently gained popularity as they are used for increasing the productivity of a variety of metabolites and enzymes in fungi growing in submerged cultures. Their action is mainly associated with the changes they evoke in fungal morphology. Traditional morphological engineering approaches include manipulation of spore concentration, pH-shifting and mechanical stress exerted by stirring and aeration. As the traditional methods proved to be insufficient, modern techniques such as changes of medium osmolality or addition of mineral microparticles to the media (microparticle-enhanced cultivation, MPEC) were proposed. Despite the fact that this area of knowledge is still being developed, there are a fair amount of scientific articles concerning the cultivations of filamentous fungi with the use of these techniques. It was described that in Ascomycetes fungi both MPEC or change of osmolality successfully led to the change of mycelial morphology, which appeared to be favorable for increased productivity of secondary metabolites and enzymes. There are also limited but very promising reports involving the successful application of MPEC with Basidiomycetes species. Despite the fact that the mineral microparticles behave differently for various microorganisms, being strain and particle specific, the low cost of its application is a great benefit. This paper reviews the application of the modern morphology engineering techniques. The authors critically assess the advantages, shortcomings, and future prospects of their application in the cultivation of fungi.

Application of Fenton oxidation to reduce the toxicity of mixed parabens

The aims of the present work were to assess the application of a chemical process to degrade a mixture of parabens and determine the influence of a natural river water matrix on toxicity. Model effluents containing either a single compound, namely methylparaben, ethylparaben, propylparaben, butylparaben, benzylparaben or p-hydroxybenzoic acid, or to mimic realistic conditions a mixture of the six compounds was used. Fenton process was applied to reduce the organic charge and toxic properties of the model effluents. The efficiency of the decontamination has been investigated using a chemical as well as a toxicological approach. The potential reduction of the effluents' toxicity after Fenton treatment was evaluated by assessing (i) Vibrio fischeri luminescence inhibition, (ii) lethal effects amongst freshwater Asian clams (Corbicula fluminea), and (iii) the impact on mammalian neuronal activity using brain slices. From the environmental point of view such a broad toxicity analysis has been performed for the first time. The results indicate that Fenton reaction is an effective method for the reduction of chemical oxygen demand of a mixture of parabens and their toxicity to V. fischeri and C. fluminea. However, no important differences were found between raw and treated samples in regard to mammalian neuronal activity.

Bioprocess Engineering Aspects of the Cultivation of a Lovastatin Producer Aspergillus terreus

The aim of this work is to review bioprocess engineering aspects of lovastatin (antihypercholesterolemia drug) production by Aspergillus terreus in the submerged culture in the bioreactors of various scale presented in the scientific literature since the nineties of the twentieth century. The key factor influencing the cultivation of any filamentous species is fungal morphology and that is why this aspect was treated as the starting point for further considerations. Fungal morphology is known to have an impact on the following issues connected with the cultivation of A. terreus reviewed in this article. These are broth viscosity in conjunction with non-Newtonian behaviour of the cultivation broths, and multistage oxygen transfer processes: from gas phase (air) to liquid phase (broth) and diffusion in the fungal agglomerates. The latest achievements concerning the controlling A. terreus morphology during lovastatin biosynthesis with the use of morphological engineering techniques were also reviewed. Last but not least, some attention was paid to the type of a bioreactor, its operational mode and kinetic modelling of lovastatin production by A. terreus.

Degradation of municipal solid waste in simulated landfill bioreactors under aerobic conditions

In this study the municipal solid waste degradation processes in simulated landfill bioreactors under aerobic and anaerobic conditions is investigated. The effect of waste aeration on the dynamics of the aerobic degradation processes in lysimeters as well as during anaerobic processes after completion of aeration is presented. The results are compared with the anaerobic degradation process to determine the stabilization stage of waste in both experimental modes. The experiments in aerobic lysimeters were carried out at small aeration rate (4.41⋅10(-3)lmin(-1)kg(-1)) and for two recirculation rates (24.9 and 1.58lm(-3)d(-1)). The change of leachate and formed gases composition showed that the application of even a small aeration rate favored the degradation of organic matter. The amount of CO2 and CH4 released from anaerobic lysimeter was about 5 times lower than that from the aerobic lysimeters. Better stabilization of the waste was obtained in the aerobic lysimeter with small recirculation, from which the amount of CO2 produced was larger by about 19% in comparison with that from the aerobic lysimeter with large leachate recirculation.

Calibration of a complex activated sludge model for the full-scale wastewater treatment plant

In this study, the results of the calibration of the complex activated sludge model implemented in BioWin software for the full-scale wastewater treatment plant are presented. Within the calibration of the model, sensitivity analysis of its parameters and the fractions of carbonaceous substrate were performed. In the steady-state and dynamic calibrations, a successful agreement between the measured and simulated values of the output variables was achieved. Sensitivity analysis revealed that upon the calculations of normalized sensitivity coefficient (S_i,j) 17 (steady-state) or 19 (dynamic conditions) kinetic and stoichiometric parameters are sensitive. Most of them are associated with growth and decay of ordinary heterotrophic organisms and phosphorus accumulating organisms. The rankings of ten most sensitive parameters established on the basis of the calculations of the mean square sensitivity measure (δ_j^msqr) indicate that irrespective of the fact, whether the steady-state or dynamic calibration was performed, there is an agreement in the sensitivity of parameters.

Trends in NO(x) abatement: a review

Implementation of stringent regulations of NO(x) emission requires the development of new technologies for NO(x) removal from exhaust gases. This article summarizes current state of NO(x) abatement strategy. Firstly, the influence of NO(x) on environment and human health is described. The main focus is put on NO(x) control methods applied in combustion of fossil fuels in power stations and mobile vehicles, as well as methods used in chemical industry. Furthermore the implementation of ozone and other oxidizing agents in NO(x) oxidation is emphasized.

Kinetic investigations of methane co-fermentation of sewage sludge and organic fraction of municipal solid wastes

In the presented study the co-fermentation, fermentation of sewage sludge (SS) and fermentation of organic fraction of municipal solid waste (OFMSW) were compared. The goal of experiments was determination of the processes carbon balance and proposal of the simple kinetic model of anaerobic digestion. Three batch experiments with above mentioned feedstocks were conducted in large scale laboratory reactor of working volume of 40 dm(3). The cumulative biogas production for sewage sludge (180.59 dm(3)) was lower than that for co-fermentation (232 dm(3)) or OFMSW (228.34 dm(3)). During fermentation of the OFMSW an accumulation of volatile fatty acids (VFA) caused pH decrease and strongly inhibited gas production. The addition of co-substrate improved buffering capacity of fermentation broth. The suggested mathematical descriptions of carbon division in anaerobic digestion processes gave the satisfying conformity with the experimental values.

Simultaneous biosynthesis of (+)-geodin by a lovastatin-producing fungus Aspergillus terreus

The simultaneous biosynthesis of lovastatin (mevinolinic acid) and (+)-geodin by Aspergillus terreus ATCC 20542 with regard to the medium composition, i.e. the concentrations of carbon and nitrogen source, was described in this paper. A. terreus is a lovastatin producer but the formation of lovastatin was accompanied by the significant amounts of (+)-geodin, when the elevated concentration of carbon source (lactose) was still present in the medium in the idiophase and nitrogen source (yeast extract) was deficient. It was observed for runs, in which the higher (above 20 g l(-1)) initial lactose concentration was applied or when the nitrogen deficiency led to the decrease of biomass content in the system. In contrast to lovastatin, there was not optimum initial concentration of yeast extract, as its lowest tested initial concentration (2 g l(-1)) led to the highest (+)-geodin volumetric formation rates and final yield. What is more, even higher final (+)-geodin concentrations were achieved at elevated initial lactose concentration (40 g l(-1)) and in the lactose-fed fed-batch run. In the fed-batch run lovastatin concentration increased significantly too, as this metabolite formation is also carbon source dependent. Finally, (+)-geodin occurred to be a metabolite, whose formation, in contrast to lovastatin, is non-growth associated.

Singlet molecular oxygen application for 2-chlorophenol removal

A special kind of photocatalysis-a photosensitized oxidation involving singlet molecular oxygen ((1)O(2)) was applied to decomposition of 2-chlorophenol (2-CP) in water solution. The photoprocess was carried out in a homo- and heterogeneous system using rose bengal (RB) as a sensitizer. In the homogeneous solution the influence of initial 2-CP concentration and pH on reaction rate was observed. Based on the kinetic model, the rate constants of (1)O(2) quenching and reaction with 2-CP and the rate constant of excited sensitizer quenching by 2-CP were determined. In the heterogeneous system, silane gel was a carrier for the immobilized sensitizer. In order to estimate kinetic parameters, an attempt was made to describe the process using Langmuir-Hinshelwood (L-H) type mechanism. The Langmuir equilibrium constants for oxygen and 2-CP adsorbed on the gel surface were also estimated.

A macrokinetic modelling of the biosynthesis of lovastatin by Aspergillus terreus

In this work a simple kinetic model to describe the biosynthesis of lovastatin by Aspergillus terreus ATCC 20542 was proposed. Several series of experiments were conducted at different media compositions. The concentrations of C- and N-sources were changed over a wide range and so were the initial biomass concentrations. From these runs the relationships ruling the substrates uptake, biomass and product formation were learnt. Lovastatin biosynthesis appeared to be partly growth associated. The inhibitive effect of organic nitrogen on lovastatin biosynthesis was found and lactose appeared to be an important limiting substrate in the formation of lovastatin. The parameters of the model were evaluated on the basis of the kinetic data obtained in the separate experiments made in triplicate at two chosen media compositions. Other results obtained at different media compositions were independent of the ones mentioned above and used for the verification of the model. The validity of the model was also examined for the lactose-fed fed-batch run. Finally, a sensitivity analysis of the model parameters was performed. The formulated model, although relatively simplified, described the experimental data quite well and could be regarded as the background for further attempts to mathematically describe the process of lovastatin biosynthesis.

Supplementation of the cultivation media with B-group vitamins enhances lovastatin biosynthesis by Aspergillus terreus

The impact of the supplementation of cultivation media with B-group vitamins on the biosynthesis of lovastatin (mevinolinic acid) by Aspergillus terreus ATCC20542 was investigated. A hypothesis was formulated that as the biosynthesis of lovastatin requires a high throughput of coenzymes in the cells, the application of its precursors in the form of B-group vitamins might positively influence the process. In a nitrogen-deficient medium the B-group vitamins, both single, especially nicotinamide, pyridoxine and calcium D-pantothenate, and a mixture of thiamine, riboflavin, pyridoxine, calcium d-pantothenate and nicotinamide increased the efficiency of lovastatin biosynthesis. The vitamin supplementation also increased both volumetric and specific production rates of mevinolinic acid, especially before 80 h of the process, when no lactose limitation had been observed yet.

Equilibrium and dynamic investigations of organic acids adsorption onto ion-exchange resins

The aim of the study was to determine properties of selected ion-exchange resins for citric and lactic acids recovery, to define sorption isotherms for these acids at different temperatures (in the range of 20-60 degrees C) and to determine diffusion coefficients inside sorbent particles. A mathematical model of the ion-exchange process in the chromatographic column and its experimental verification is also presented. During investigations 18 types of ion-exchange resins were tested. It was found that weakly basic resins were more suitable for the recovery process than strongly basic ones. The best resin for the separation of citric acid was Amberlite IRA-67 and for lactic acid Amberlite IRA-92. As a result of transient-state sorption experiments diffusion coefficients of the citric acid inside the sorbent particle at different temperatures were obtained. It was found that D(p) increased with the temperature by two times in the range of 20-60 degrees C, and its value at 60 degrees C was 7.2 x 10(-10) m(2)/s. The proposed mathematical model was applied to identify bed operation parameters in the column for the needs of the simulated moving bed chromatography method.

Microbial removal of ionic mercury in a three-phase fluidized bed reactor

The reductive biotransformation of mercuric ions to elemental mercury was studied by applying a model system with a genetically engineered Pseudomonas putida strain in a lab scale three-phase fluidized bed (TPFB). The aim was to demonstrate the suitability of the TPFB to demercurize effluent streams containing up to 10 mg Hg2+ dm(-3). The TPFB is used, first, to carry out the biotransformation on the alginate immobilized biocatalyst and, second, to remove the produced Hg0 by volatilization into the gas phase followed by its recovery through fast oxidative absorption. Targeted experiments with the immobilized biocatalyst were designed and carried out to determine mercury adsorption data on the biomass and all relevant mass transport rates at conditions prevailing in the TPFB. The evaluation of the performance data in the TPFB revealed almost complete reaction control and hence negligibility of mass transfer resistances. This simplifies the scale-up of larger TPFB reactors for mercury removal as it can be based on the known kinetics alone. The measured biotransformation capacities in the TPFB are similar to those reported for the fixed bed technology which has already proven its applicability at an industrial scale in long time runs. However, the TPFB offers some advantages over the fixed bed and could therefore possibly be a favorable, reliable, and less costly alternative to the existing technology.

Stoichiometry of the aerobic biodegradation of the organic fraction of municipal solid waste (MSW)

An elemental analysis was applied to describe the composition of the organic fraction of municipal solid waste (MSW). The initial elemental composition was constant at C5H8.5O4N0.2. The changes of the composition during the biodegradation process and the final waste composition were strictly dependent on the process conditions. The decrease in carbon content due to biodegradation increased with temperature at which the experiments were conducted, from 20% at 20 degrees C to about 40% at 37-42 degrees C after 96 hours. It was correlated with the amount of oxygen that was utilised in the investigated processes of aerobic biodegradation of the waste suspension. The amount of oxygen required for biodegradation of organic fraction of MSW was estimated on the basis of stoichiometric equations and increased from 0.92 moles per 1 mole of waste at 20 degrees C to 1.6 moles at 42 degrees C within 96 hours of the experiments.

Laboratory simulation of anaerobic digestion of municipal solid waste

Landfill processes were simulated in lab-scale bioreactors--lysimeters. The changes in leachate characteristics as well as the influence of the leachate recirculation on the processes taking place in the landfill were investigated. Lysimeters were filled with material simulating municipal waste in the city of Lodz, Poland. Compost in the amount of 30% w/w and the methanogens inoculum were added in order to enhance a development of methanogenic phase. Leachate produced in lysimeters was recirculated once, twice a week, or everyday. The leachate composition and biogas changes showed trends confirming that the bench-scale lysimeters appeared suitable to simulate processes taking place in the landfill. It was also proved that leachate recirculation accelerate these processes.

Estimation of viable biomass in aerobic biodegradation processes of organic fraction of municipal solid waste (MSW)

2-(p-Iodophenyl)-3-(p-nitrophenyl)-5-phenyltetrazolium chloride (INT) dehydrogenase test and RNA assay were introduced to evaluate biomass in the processes of aerobic biodegradation of the organic fraction of municipal solid waste (MSW) in bioreactors. It was found that RNA quantification by KOH/UV method delivered reliable and repeatable results. Relative standard deviation (RSD) for INT test was significantly higher than for RNA assay and achieved values of 3-15%. Moreover, it occurred that the optimum temperature for the growth of autochthonic biomass, which takes part in the biodegradation process, was in the range from 25 to 37 degrees C.

Kinetics of the aerobic biological degradation of shredded municipal solid waste in liquid phase

The organic fraction of municipal solid waste (OFMSW) should be utilised by means of biological methods. The biodegradation of solid wastes can be intensified owing to application of the bioreactors. Estimation of the optimum values of the organic load is one of the most important tasks for the aerobic biodegradation processes. The kinetic model of biological oxidation of the organic wastes has been presented in this paper. The experiments were carried out in batch 6-l working volume stirred tank bioreactors at constant temperature of 25 degrees C. Initial total solids have been at the levels of 15, 19, 34, 55 and 66 g l(-1). The kinetics of microbial decomposition of organic substances was described by means of an unstructured model. The satisfactory time courses for substrate chemical oxygen demand in the solid (CODs) and liquid phase (CODL) and biomass concentration (RNA) have been achieved. Also, the influence of the initial TS on the kinetics of the biodegradation process was investigated and the optimum value of initial TS for this type of processes was estimated at 34-55 g l(-1).

Degradation of household biowaste in reactors

Household derived biowaste was degraded by biological methods. The system involves the combined method of low-solids (up to 10% w/v of total solids (TS)) anaerobic digestion and aerobic degradation for the recovery of energy (biogas) and the production of fine humus-like material which can be used as a soil amender or a substrate for further thermal treatment (pyrolysis, gasification). The performance of batch and continuous processes carried out in bioreactors (stirred tank reactor, air-lift) of working volume 6 and 18 dm(3), at different temperatures (25-42 degrees C) was monitored by reduction of TS, volatile solids, chemical oxygen demand, total organic carbon, C/N in time. The application of continuous process with recirculation (33%) caused that for residence time of 8-16 h the obtained degree of organic load reduction was similar to that obtained after 72-96 h of the batch process. The experimental data of batch aerobic degradation was also subjected to kinetic analysis. The sequence of the two processes: aerobic and anaerobic or anaerobic and aerobic showed that the degree of organic load reduction was similar in both cases, while the amount of produced biogas was four times higher when the first stage was anaerobic. The final product after dewatering was subjected to pyrolysis and gasification. The gases obtained were characterised by a high heat of combustion of about 11-15 MJ Nm(-3).

Biodegradation, decolourisation and detoxification of textile wastewater enhanced by advanced oxidation processes

Recently, an increasing application of so called advanced oxidation processes (AOPs) to industrial wastewater has been observed. In particular, an integrated approach of biological and chemical treatment of wastewater is advantageous conceptually. The subject of our study was synthetic wastewater, simulating effluents from knitting industry. The wastewater contained components that are very often used in Polish textile industry: an anionic detergent Awiwaz KG conc., a softening agent Tetrapol CLB and an anthraquinone dyestuff-Acid Blue 40, CI 2125. The toxicity of the detergents and the dye was determined in terms of effective concentration EC50 using mixed cultures of activated sludge as well as pure culture of luminescent bacteria Vibrio fischerii NRRLB-11177. The dye did not undergo biodegradation without AOPs pretreatment, therefore a degree of its removal (decolourisation) by the AOPs has been determined and its bio-sorption properties on the flocks of activated sludge have been studied. The dye adsorption onto flocks of activated sludge was described by Henry's isotherm. Our investigations focussed on the influence of various oxidants like O3, H2O2 and UV light on biodegradation of single components aqueous solution as well as of the whole textile wastewater. The results of kinetic measurements of the biodegradation (by means of acclimated activated sludge) was described by Monod type of kinetic equation. The experimental evidence of the positive effect of chemical oxidation pretreatment on the biodegradation of recalcitrant compounds was quantified by estimation of the kinetic parameters of the Monod equation. Due to the AOPs pretreatment a decrease of the Monod constant and an increase of maximal specific growth rate was observed. The activity of degradative enzymes of activated sludge was assayed by the methods of 2-[4-iodophenyl]-3-[4-nitrophenyl]-5-phenyltetrazolium chloride test.

Ozonation of Reactive Blue 81 in the bubble column

The decolourisation process of the Reactive Blue 81 was carried out in a laboratory bubble column reactor with inner diameter 110 mm and working height 550 mm, equipped with a porous glass ozone diffuser (diameter 50 mm). A model of ozone absorption with the chemical reaction in the liquid phase was employed. It was found that the decolourisation proceeds in the fast pseudo first-order regime. The average value of the enhancement factor was calculated from the experimental results and compared with those calculated according to the theory of mass transfer with a second-order chemical reaction. In order to determine the intrinsic kinetics of ozonation, a stopped-flow technique was employed. The rate constant of the dyestuff reaction with ozone was determined as equal to 4.5 x 10(7) mol/(dm3.s).

Thermal processing of sewage sludge by drying, pyrolysis, gasification and combustion

Thermal processing of sewage sludge including drying, pyrolysis and gasification or combustion may be an alternative to other ways of utilising it. In this paper thermogravimetric analysis (TGA) was employed in the investigation of thermal decomposition of sewage sludge. The kinetic parameters of drying, pyrolysis and gasification or combustion of sewage sludge have been determined in an inert-gas (argon) and additionally some series of the sludge decomposition experiments have been carried out in air, in order to compare pyrolysis and combustion. The pyrolysis char has been gasified with carbon dioxide. A typical approach to the kinetics of thermal decomposition of a solid waste is to divide the volatile evolution into a few fractions (lumps), each of which is represented by a single first-order reaction. If these lumps are assumed to be non-interacting and evolved by independent parallel reactions the first-order kinetic parameters such as activation energy Ei and pre-exponential factor Ai can be determined from mathematical evaluation of TG or DTG curves. The object of our investigations was a municipal sludge from the two wastewater treatment plants (WTP) in Poland. The experiments have been carried out in the thermobalance Mettler-Toledo type TGA/SDTA851 LF, in the temperature range 30-1,000 degrees C. Five different values of heating rate have been applied beta = 2, 5, 10, 15 and 20 K/min. The values of Ei and Ai have been determined for all recognised lumps of gaseous products. The method employed has also revealed its usefulness for the determination of kinetic parameters for municipal sludge, that possess an undefined content. An alternative route to combustion of sewage sludge is its gasification, which significantly increases the gaseous product (pyrolytic gas + syngas). Besides pyrolysis kinetics, gasification or combustion process kinetics have also been determined.