The hydrolysis of complex organic heteropolymers contained in municipal wastewater to simpler monomers by extracellular hydrolytic enzymes is generally considered the rate-limiting step of the biodegradation process. Previous studies of the Recycling Sludge Bed Reactor (RSBR) revealed that the hydrolysis of complex particulate organics, such as those contained in primary sludge (PS), was enhanced under anaerobic biosulphidogenic conditions. Although the mechanism was not fully understood, it appeared to involve the interaction of sulfide and sludge flocs. The current study was conducted using a 3500 ml laboratory-scale RSBR fed sieved PS at a loading rate of 0.5 kg COD/m³.day and an initial chemical oxygen demand (COD) to sulfate ratio (COD:SO₄) of 1:1. There was no significant accumulation of undigested sludge in the reactor over the 60-day experimental period and the quantity of SO₄ reduced indicated that the yield of soluble products from PS was at least as high as those reported previously for this system (> 50%). In the current study, the specific activities of a range of extracellular hydrolytic enzymes (L-alanine aminopeptidase, L-leucine aminopeptidase, arylsulphatase, α-glucosidase, β- glucosidase, protease and lipase) were monitored in a sulfide gradient within a biosulphidogenic RSBR. Data obtained indicated that the specific enzymatic activities increased with the depth of the RSBR and also correlated with a number of the physicochemical parameters including sulfide, alkalinity and sulfate. The activities of α- glucosidase and β-glucosidase were higher than that of the other enzymes studied. Lipase activity was relatively low and studies conducted on the enzyme-enzyme interaction using specific enzyme inhibitors indicated that lipases were probably being digested by the proteases. Further studies to determine the impact of sulfide on the enzymes, showed an increase in the enzyme activity with increasing sulfide concentration. Possible direct affects were investigated by looking for changes in the Michaelis constant (Km) and the maximal velocity (Vmax) of the crude enzymes with varying sulfide concentrations (250, 400 and 500 mg/l) using natural and synthetic substrates. The results showed no significant difference in both the Km and the Vmax for any of the hydrolytic enzymes except for the protease. The latter showed a statistically significant increase in the Km with increasing sulfide concentration. Although this indicated a direct interaction, this difference was not large enough to be of biochemical significance and was consequently not solely responsible for the enhanced hydrolysis observed in the RSBR. Investigation into the floc characteristics indicated that the biosulphidogenic RSBR flocs were generally small in size and became more dendritic with the depth of the RSBR. Based on the above data, the previously proposed descriptive models of enhanced hydrolysis of particulate organic matter in a biosulphidogenic RSBR has been revised. It is thought that the effect of sulfide on the hydrolysis step is primarily indirect and that the reduction in floc size and alteration of the floc shape to a more dendritic form is central to the success of the process.

Anaerobic treatment is widely used around the world as a biological stage in both domestic and industrial wastewater-treatment plants. The two principal advantages of anaerobic over aerobic treatment are the production of biogas, which can be used as fuel, and the lower rate of biomass production, which results in lower maintenance costs for the plant. The upflow anaerobic sludge blanket (UASB) reactor is an attractive alternative for regions in hot climates since it works better under mesophilic conditions and it does not need any supporting structure for the development of microorganisms, which grow in the form of granules. In this thesis, a model describing the UASB reactor behaviour with respect to substrate degradation, microorganism growth and granule formation was developed. The model is transient and is based on mass balances for the substrate and microorganisms in the reactor. For the substrate, the processes included in the model are dispersion, advection and degradation of the organic matter in the substrate. The reaction rate for the microorganisms includes the growth and decay of the microorganisms. The decay takes into account the microorganism dying and the fraction of biomass that may be dragged into the effluent. The microorganism development is described by a Monod type equation including the death constant; the use of the Contois equation for describing the microorganism growth was also addressed.  An equation considering the substrate degradation in the granule was required, since in the UASB reactor the microorganisms form granules. For this, a stationary mass balance within the granule was carried out and an expression for the reaction kinetics was then developed. The model for the granule takes into account the mass transport through the stagnant film around the granule, the intraparticle diffusion, and the specific degradation rate. The model was solved using commercial software (COMSOL Multiphysics). The model was validated using results reported in the literature from experiments carried out at pilot scale. A simplified model was also developed considering the case in which the microorganisms are dispersed in the reactor and granules are not formed. The UASB reactor is then described as formed by many well-stirred reactors in series. The model was tested using experimental results from the literature and the sensitivity of the processes to model parameters was also addressed. The models describe satisfactorily the degradation of substrate along the height in the reactor; the major part of the substrate is degraded at the bottom of the reactor due to the high density of biomass present in that region. This type of model is a useful tool to optimize the operation of the reactor and to predict its performance. / QC 20110203

As the microbrewery industry expands, disposal of brewery wastewater is becoming more of a concern, both for brewery operators and for local municipal wastewater authorities. Brewery wastewater is characterized as containing high strength organics and high variability in both organic and hydraulic loading. This high variability increased the challenge of treating brewery wastewater properly. Therefore, it is significant for optimizing the operation condition for the small-scale wastewater treatment system. This study conducted a batch study and a field study for optimizing a craft brewery on-site wastewater treatment system, which is equipped with two moving bed biofilm reactors (MBBR). In the batch study, a two-factor Box-Wilson central composite design (CCD) was adopted to find optimum biomethane production conditions for the digestion of brewery wastewater with a dairy manure inoculum. The effects of two major influencing factors of temperature (T) (25-49°C) and brewery wastewater concentration (BWC) (2-9 g VS/L) on biochemical methane potential (BMP) (CH₄ yield) and CH₄ maximum production rate (Rmax) were evaluated by applying response surface methodology (RSM). All of the trials presented a high organic removal efficiency with volatile solid (VS) 82-91%, soluble chemical oxygen demand (sCOD) 77-88%, and total chemical oxygen demand (tCOD) between 47% -76%. The experiment result suggested that the first-order kinetic rate constant and biogas content (methane percentage in the biogas) can be affected by the temperature. The mesophilic regime had the highest average rate constant, and the psychrophilic regime rate constant was significantly lower than the mesophilic and thermophile regime. The conditions in the thermophile range present a high variability for the first-order rate constant. The methane ratio in the biogas increased and stabilized by the operation time. Mesophilic and thermophilic regimes obtained a stabile biogas content around 25 days, and the psychrophilic regime spent extra time to stabilized. At the end of the anaerobic digestion, the psychrophilic, mesophilic, and thermophilic regimes had an average methane percentage of 47%,65%, and 67% respectively. Optimum BMP and Rmax were achieved under conditions of 49 °C and BWC of 5g VS/L. Correspondingly, the BMP and Rmax were 141.40 mL CH₄/g VS added and 36.5 mL CH₄/ day, respectively. However, by pursuing stability the preferable operational condition T=35℃ and BWC=5 g/L is recommended, at this condition methane yield is 110.07 CH₄/g VS added and maximum methane daily production is 28.06 CH₄/ day, which is similar to the maximum result. In field study, an on-site brewery wastewater treatment system equipped with two MBBR reactors was evaluated from October 12th, 2018 to February 10th, 2020 in Beau`s All-Natural Brewing Company, Vankleek Hill, Ontario, Canada. The aim of the study was to characterize the wastewater production (flow and organic loading rate), evaluate the operating conditions and performance of the MBBR system, and recommend improvements. Discharge from the brewery is highly variable for both organic and hydraulic loading with flow balancing recommended. The MBBR full-scale reactors operated at relatively stable conditions at a surface area loading rate (SALR) of less than 25 g/m2.d and dissolved oxygen (DO) greater than 2mg/L. Kinetic rate constants for suspended growth and attached growth biomass in the reactors were found to be similar at 0.0764-0.0908 h-1, however, a much larger attached growth mass in the reactors suggests that only a fraction of the attached growth biofilm is active. Effluent recycle was shown to be effective at controlling filamentous bacteria (type-0041) sludge bulking, reducing suspended solid concentration, and sCOD concentration.

No description available.

The anaerobic treatment of waste water has been studied with an emphasis on the Up- flow Anaerobic Sludge Blanket (UASB) reactor. A model to describe the processes occurring in a UASB reactor was developed and an experimental study of the anaerobic wastewater treatment systems in Nicaragua was also performed. Experimental work was carried out in order to link the study to the wastewater treatment situation in Nicaragua, a developing country. In order to assess the performance of the treatment plants, the methanogenic activity of sludge from seven anaerobic wastewater treatment plants was first addressed. Due to a lack of Standards for the measurement of methanogenic activity, a laboratory method was developed based on the methods found in the literature. An additional aim of this study was to find adequate inoculum for the wastewater treatment plant in a brewery using an anaerobic reactor. Physic-chemical characteristics of the sludge were also determined to provide a basis for decisions regarding the agricultural employment of the sludge from the treatment plants. A one-dimensional model describing the physical and biological processes occurring in an Up-flow Anaerobic Sludge Blanket reactor has been developed. These processes are advection, dispersion and reaction in the granule, including mass transport at the interface and diffusion within the particle. The advection-dispersion equation is used to describe these phenomena in the reactor. Dispersion is mainly caused by the gas bubbles rising up through the reactor and the granules in the ascending flow. The extent of the dispersion is expressed by the dimensionless Peclet (Pe) number. It is assumed that the biological degradation takes place at the surface and within the granules. The processes occurring in the granules formed by the microorganisms are described in detail; they include diffusion in the stagnant film around the granule, diffusion within the particle, and a degradation reaction. From these processes, the reaction term is analytically determined. The granules were modelled as spherical porous biocatalysts of different sizes. The biochemical degradation reactions were assumed to follow Monod type kinetics of the first order. For the numerical solution of the model, a standard program was used (Within MATLAB). The model was applied to some experimental data taken from the literature. An important characteristic of the model is that it can simultaneously take into account reactions in granules of different sizes. At present, the parameters of the model are calculated using data from the literature; but experimental measurements of the main parameters are planned. The impact of the different parameters was studied by numerical simulation and its validity was tested using experimental data reported in the literature. The model could be a useful tool in the performance optimization of UASB reactors by predicting the influences of different operational parameters. / QC 20101116

Dissertation submitted in fulfillment of academic requirements for the Degree of Master of Technology: Chemical Engineering, Durban University of Technology, 2008. / Currently KwaZulu-Natal (KZN) province is populated with textile industry, which produces wastewater, some of which is not biodegradable. Due to the stringent environmental regulations the wastewater cannot be discharged into the rivers or public owned treatment systems. The alternative solution is to co-dispose this wastewater with easily biodegradable waste (labile effluent). The aim of this investigation was to develop a process protocol for the codigestion of high strength and toxic organic effluents under mesophilic conditions (35°C ± 2°C), with emphasis on the effect of biomass acclimation. A total of four effluents were chosen for this study, two labile (distillery and size) and two recalcitrant (scour dye and reactive dye). Two anaerobic batch experiments and two pilot scale trials were performed. The first batch anaerobic experiment investigated the influence of biomass source in anaerobic treatability. The second batch test investigated, whether biomass acclimation enhanced the biodegradability of pollutants. The pilot scale trials were the scale up version of the biomass acclimation test. The results showed sludge from Umbilo Wastewater Treatment Works was a superior biomass source, producing more gas and methane compared to Mpumalanga waste. For the high strength organic waste, the acclimated size and distillery samples produced 50% more biogas and methane compared to non-acclimated samples. This confirms that the biomass acclimation enhances the biodegradability. The biomass acclimation did not enhance the biodegradability of the recalcitrant effluent (scour dye). The pilot scale trials did not yield meaningful data; therefore it could not be proven if acclimation works on a larger scale. / Water Research Commission

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: It was found that bacterial sludge from anaerobic water treatment systems is produced internationally at a rate of 60 grams per person per day and the accumulation of the potentially hazardous by-product has become of increasing concern. The produced bacterial sludge is frequently pumped into dams, dried out and used as agricultural fertilizer. This bacterial sludge is expected to have a relatively high heating value and as such, has the potential to produce energy from the biomass. It is, therefore, advisable to utilize this energy potential as an alternative to conventional sludge disposal. This project aimed to improve the yield of syngas by optimizing the reactor design to partially oxidize bacterial sludge using a sonochemical reactor that is operated at bulk atmospheric conditions. The effect of different conditions was investigated and the optimum settings for syngas production were found by investigating temperature, pressure and the effect of the amplitude of operation that regulates the energy input by the ultrasonic equipment. The optimum conditions were used to investigate the kinetics involved in this process as well as to determine the energy consumption by the process. It was also required to study the feasibility of partially oxidizing bacterial sludge using a sonochemical reactor instead of conventional steam gasification and also as an alternative means of sludge disposal. By eliminating this pollutant source, the future environmental threat posed by an increasing population size will be minimized and energy will be utilized from a thus-far wasted energy source. The syngas that is produced is used as a green alternative to fossil fuels in the Gas-to-Liquids (GTL) process to produce liquids fuels. A thus-far wasted energy source will be consumed and fossil fuels can be saved in the process. It was found that the maximum hydrogen mole percentage produced is 0.141 mole % of the vapour phase with the maximum carbon monoxide mole percentage in the vapour phase at 1.896 mole %. This shows an improvement on work conducted by Beyers (2011) of 59 % for hydrogen, 92% for carbon monoxide and a reduction of 49 % for carbon dioxide. A kinetic study of the process indicated that the rate equations that describe the hydrogen and carbon monoxide production are zero order and, therefore, independent of initial concentration of the sludge. The rate constants were 0.0146 (mol % hydrogen/s) and 0.0183 (mol % hydrogen/s) for hydrogen and carbon monoxide, respectively. It was found that the most severe change to the higher heating value of the feed was a mere 0.27 mJ/kg from an original value of 9.81 mJ/kg. This therefore confirms that the reaction has not proceeded to completion. The statistical model predicted a maximum value for hydrogen production at 0.151 mole % in the product gas, 0.01 mole % from the measured maximum. It was also found that hydrogen is produced during the sonolysis of distilled water and that this confirms that the hydrogen production during partial oxidation of the sludge sample comes mainly from the water present in the sludge. The hydrogen produced when only using water, was found to be 0.127 mole % and when using the active sludge, the value was 0.116 mole % hydrogen in the vapour phase. The thermal decomposition of calcium carbonate in the lime that is used to treat the pH of the unit where the sludge originates from, followed by the formation of carbon monoxide during the Boudouard reaction, led to an increased amount of carbon monoxide present in the product gas. Ultrasonic intensity is defined as the amount of energy that is transferred to the sample per cubic meter of the internal surface area of the reactor vessel. It was found that the intensity that was delivered to the reactant was lower than expected as the reactor was operating at an efficiency of only 36%. The design intensity was 1.44 W/m2 and the actual delivered intensity was 0.52 W/m2. Based on a maximum yield of 0.00012 Nm3/kg, the cost of syngas production under the conditions described by this study, would amount to R 19.98/Nm3. This cost only implicates the operational expenses and does not take further downstream processing and initial capital investment repayments into account. Conventional steam gasification at a yield of 0.67 Nm3/kg has an operational syngas production cost of R 1.48/Nm3. This process was therefore found to not be economically feasible as the cost of utilizing ultrasound as opposed to normal steam gasification is more than ten times more expensive. It was concluded that the process was successfully optimized by the redesigning of the reactor and that carbon dioxide production was limited by excluding oxygen from the feed gas. It was also concluded that the sonolysis of water and the thermal decomposition of calcium carbonate, followed by the conversion of carbon dioxide to carbon monoxide, supplements the syngas production under the current operational conditions. Based on the production of no methane during the course of this study, the sonochemical process can be tied into the GTL process after the steam reforming unit. Due to the relatively high carbon dioxide content, the process will need to join the main feed gas stream that is fed into the carbon dioxide removal unit before it enters the GTL process to correct the desired feed gas ratio. Based on the very low syngas yields, the low hydrogen to carbon monoxide ratio in comparison to the required ratio of 2 as well as the high energy intensity required for this process, it can be concluded that the partial oxidation of biomass sludge in a sonochemical reactor is not feasible as an alternative technology to conventional steam gasification. The operating costs of the sonochemical unit would be nearly ten times that of steam gasification and is therefore concluded to not be a competitive technology to conventional steam gasification. It is recommended that the reactor design is reinvestigated to improve the delivered ultrasound intensity as well as the surface area where the ultrasonic waves are intensified. This would eliminate dead-zones. It was also recommended that the argon gas is continuously bubbled through the reactant mixture during experiments to eliminate the degassing effect caused when the ultrasound is initially emitted. The gas outlet of the process can then be connected to an online gas chromatograph (GC) with a thermal conductivity detector (TCD) and flame ionization detector (FID) methanizer in series as the TCD does not destroy the sample and this setup would improve the analytical process. The production of carbon monoxide from lime as well as the production of hydrogen from water during sonolysis needs to be investigated. The effect of radicals can also be studied by the addition of a radical scavenger to the process. It is recommended that the experimental design is reinvestigated and a design that will deliver similar information utilizing fewer data points should be chosen. Based on this model as well as further kinetic testing, it is recommended that a complete ASPEN model is developed to simulate the energy requirements to tie the ultrasonic process into the commercial plant. Based on this model, a complete feasibility study can then be conducted to determine the capital costs involved, the operating costs, the repayment period as well as taking the current costs of sludge disposal into account. / AFRIKAANSE OPSOMMING: Daar is gevind dat bakteriele slik internasionaal geproduseer word deur anaerobiese waterbehandelingseenhede teen ‘n tempo van 60 gram per person per dag en dat die opberging van hierdie gevaarlike byproduk ‘n groeiende probleem word. Die geproduseerde bakteriele slik word in damme gestoor, uitgedroog of gebruik as kunsmis in die landbou bedryf. Daar word vermoed dat hierdie baketriele slik oor ‘n hoe verwarmings waarde beskik en het daarom die potensiaal om energie te produseer uit die biomassa. Daarom is dit voorgestel om alternatiewe prosesse te ondersoek om van hierdie slik ontslae te raak en moontlik die energie wat beskikbaar is te gebruik. Die projek is daarop gefokus om die produksie van syngas te verbeter deur die reaktorontwerp te optimeer deur gebruik te maak van parsiele oksidasie van slik onder atmosferiese kondisies deur klankgolwe te gebruik. Die effek van verskillende operasionele kondisies is ondersoek en die optimale vlakke van syngas produksie is gevind deur temperatuur, druk en amplitude wat die hoeveelheid energie wat oorgedra word aan die reaktor reguleer, te ondersoek. Die optimale kondisies is ook gebruik om die kinetiese aspekte van die proses te ondersoek en ook om te kyk wat die sisteem se energie benodighede behels. Die haalbaarheid om baketriele slik parsieel te oksideer in ‘n sonochemiese reaktor is vergelyk met dit van konvensionele stoom vergassing van die biomassa en is ook ondersoek as ‘n alternatief om van die slik ontslae te raak. Deur die slik te verwyder as ‘n potensiele bron van besoedeling, kan die toekomstige omgewing’s risiko wat deur die toename in die bevolkkingsgroote tot gevolg is, verwyder word deur ‘n energie bron te gebruik wat tot dusver geignoreer is. Die syngas wat geproduseer word kan dan gebruik word in die “Gas-to-Liquids” (GTL) process om vloeistof brandstowwe te produseer. Dus sal ‘n omgewingsrisiko verminder word, ‘n energiebron word benuttig wat nooit van tevore benuttig is nie en fosiel brandstowwe kan gespaar word. Die maksimum waterstof wat geproduseer is, was 0.141 mol % in die gas fase met ‘n maksimum waarde vir koosltof monoksied van 1.896 mol % in die gas fase. Dit toon ‘n verbetering van 59 % vir waterstof, 92 % vir koolstof monoksied en ‘n vermindering van 49% in die koolstof dioksied wat deur Beyers (2011) geproduseer is. Die kinetiese studie het ondervind dat die “rate equation” van waterstof en koolstofmonoksied beskryf word deur nul-orde kinetika. Hierdie konstantes was 0.0146 (mol % waterstof/s) en 0.0183 (mol % waterstof/s) vir waterstof en koolstofmonoksied. Daar is ook gevind dat die grootste moontlik verandering in die hoe verwarmings waarde van die biomassa is ‘n skamele 0.27 mJ/kg van die oorspronklike waarde van 9.81 mJ/kg. Hierdie waarneming staaf dus die uitkoms dat die reaksie dus nie tot die einde verloop het nie. Die statistiese model het ‘n maksimum van 0.151 mol % voorspel wat 0.01 mol % meer was as die waarde wat gemeet is. Dit is ook gevind dat waterstof geproduseer word deur die sonoliese van water en dat hierdie bykomende waterstof deel uitmaak van die produkgas aangesien die slik grootliks uit water bestaan.Die hoveelheid waterstof in die gas fase wat geproduseer is tydens sonoliese van ‘n suiwer water monster, was 0.127 mol %. Die hoeveelheid waterstof in die gas fase wanneer die slik behandel is ten optimal kondisies, was 0.116 mol % gemiddeld. Die hitte degradering van kalsium karbonaat wat teenwoordig is in die kalk wat gebruik word om die pH van die produksie eenheid te reguleer, gevolg deur die Boudouard reaksie, het tot gevolg dat addisionele koolstof monoksied ook gevorm word. Ultrasoniese intensiteit kan gedefineer word as die hoeveelheid energy wat oorgedra word aan ‘n reaktant gebasseer op die oppervlak area aan die binnekant van die reaktor. Die intensiteit waarteen die voermateriaal blootgestel word aan die klankgolwe was laer as verwag met ‘n 36 % effektiwiteit. Die ontwerp spesifiseer ‘n intensiteit van 1.44 W/m2 en die intensiteit wat fisies gelewer is, was 0.521 W/m2. Die maksimum produksie van syngas was 0.00012 Nm3/kg, wat lei tot ‘n operasionele koste van R 19.98/Nm3 onder die kondisies van hierdie studie. Hierdie koste neem nie die oorsponkilke kapitaal vir die konstruksie, of die koste van verdere behandelik van die gas, in ag nie. Konvensionele stoom vergassing teen ‘n opbrengs van 0.67 Nm3/kg het ‘n operasionele koste van R 1.48/Nm3 tot gevolg. Die proses is dus ekonomies nie ‘n aantreklike opsie nie aangesien die kostes van syngas produksie met ultraklank meer as tien keer meer is as konvensionele stoom vergassing. Daar is tot die gevolgtrekking gekom dat die reaktor optimering suksesvol was en deur geen stuurstof te voer nie, die koolstofdioksied persentasie verminder is. Daar is ook tot die gevolgtrekking gekom dat die sonoliese van water, en die hitte degradering van kalsium karbonaat, gevolg deur die Boudouard reaksie, die syngas produksie supplementeer. Aangesien geen metaan gedurende hierdie studie geproduseer is nie, kan die sonochemiese proses inskakel by die GTL aanleg na die stoom hervormingseenhed. As gevolg van die hoe koolstofdioksied konsentrasie, sal die prosesstroom gemeng moet word met die produk stroom uit die stoom hervormings proses, wat gevoer word na die koolstofdioksied verwyderings eenheid. Hierdie eenheid is daarvoor verantwoordelik om die korrekte verhouding van gasse vir die GTL voer stroom te reguleer. Gebasseer op die baie lae syngas opbrengs, die lae waterstof tot koolstofmonoksied verhouding en die hoe energie behoeftes, is daar tot die gevolgtrekking gekom dat die parsiele oksidasdie van die biomassa in ‘n sonochemiese reaktor nie ‘n haalbare alternatief is vir konvensionele stoom vergassing nie. Die operasionele koste van die sonochemiese eenheid is ongeveer tien keer meer as die van stoom vergassing en daarom is die proses nie kompeterend nie. Daar word voorgestel dat die reaktor ontwerp hersien word om die gelewerde intensiteit te verbeter, sowel as om die kontak area waar die klankgolwe gekonsentreer is, te vergroot. Dit sal dooie sones uitskakel. Daar word ook voorgestel dat argon gas gedurende die eksperiment aanhoudende geborrel word deur die reaktant vloeistof in die reaktor om die ontgassingseffek uit te skakel sodra die klankgolwe aangeskakel word. Die gas uitlaat kan dan inlyn gekoppel word aan ‘n gas chromatograaf met ‘n termiese geleidings detektor (TCD) en ‘n vlam ionisasie detektor (FID) met metaan omskakeling, aangesien die TCD nie die monster vernietig nie. Hierdie opstelling behoort analitiese methodes te verbeter. Die produksie van koolstofmonoksied uit kalk sowel as die produksie van waterstof uit water gedurende sonoliese, moet verder ondersoek word. Die effek van radikale kan ook verder bestudeer word deur die gebruik van ‘n radikaal rower gedurende die proses. Daar word ook voorgestel dat die statistiese ontwerp herondersoek word sodat minder eksperimente gebruik kan word om soortgelyke resultate te bekom met minder data punte. Gebasseer op hierdie nuwe model en ‘n kinetiese studie, word dit aangeraai dat ‘n volledige ASPEN model gebou word om te simuleer hoe hierdie sonochemiese eenheid sal inskakel met die kommersiele eenheid. Dit sal dan moontlik wees om die energie benodighede van die proses te verstaan en gebasseer daarop, kan ‘n volledige haalbaarheid studie gedoen word wat kyk na oorspronklike installasie kostes, onderhouskostes, operasionele kostes sowel as die terugbetaling van die konstruksie kostes. Dan kan ‘n vergelyking getref word met die huidige kostes om van hierdie slik ontslae te raak en om die slik as ‘n brandstof te benut.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2005. / The Up-flow Anaerobic Sludge Blanket Reactor (UASB) provides a state-of–the-art solution to effluent treatment by anaerobic digestion: sludge production is dramatically lower than in other digestion processes, and energy is gained from the system if the produced biogas is converted to electricity and/or heat. The UASB is a modified fluidised bed reactor, with the solid state ‘catalyst’ being granulated anaerobic sludge, and the liquid phase the effluent that needs to be treated. A gas cap is installed to serve as a carbon dioxide and methane collector. This biogas (carbon dioxide and methane) is produced by the stepwise decomposition of complex carbohydrates and proteins via a consortium of micro-organisms living in a symbiotic environment known as a granule. A typical UASB reactor has an organic removal rate of 89-93% Chemical Oxygen Demand (COD) and operates optimally at loadings of 9.8-11 kg COD/ m3 reactor volume/day. Unfortunately, one major problem hampers the efficiency of this reactor to such an extent that the unit is only economically viable in exceptional cases; if the reactor is inoculated with un-granulated anaerobic sludge, start-up times of up to 12 months can be expected. The lengthy start-up times motivated the search for an artificial way to cultivate USAB granules. Early research (done on lab-scale, 400ml vessel volumes) proved that, under a specified set of environmental conditions, granule growth can occur in an artificial environment. Yet these laboratory-scale vessels did not facilitate scale-up or the study thereof. This led to the main problem statement of this research project: namely to design, commission, and optimise benchscale bioreactors that will generate granulated anaerobic sludge in an incubation period of 20 days. These units should also facilitate in the determining of parameters that will assist in the design of a scale-up to a UASB granule producing reactor of economically viable size. Two bench-scale reactors were initially designed specifically to “mimic” the motion found in the laboratory-scale vessels. The results from these initial reactors proved that granulation cannot only be enhanced, but granules can actually be cultivated from dispersed anaerobic sludge in a larger artificial environment over an incubation period of only 20 days. The results were still far from satisfactory, as the granules produced were irregular in shape and the yield of usable granules (2.2 kg/m3 reactor volume) insufficient. A third test reactor was designed to “mimic” roller table movement and baffles were included. These results were much better and the yield was 4.4 kg/m3 reactor volume at a baffle tipspeed of 0.0055 m/s. The optimisation was extended further to include the inoculation sludge and the feed medium. A C:N:P ratio of 10:1:4 proved to yield the best results. Monovalent anions, hydrogen concentration and a pH-level outside the 6.5 to 7.2 range evidently had an inhibitory effect on the granulation rate. After the optimisation study the third test unit produced a usable granule yield of 15.2 kg/m3 reactor volume over the 20-day incubation period. The incubation period can be separated into 3 distinct phases, namely the acidification, stabilisation and growth phases. From the mass balance it was found that most of the COD and nutrients were used for ECP production in the acidification phase. During the stabilisation phase, the COD and nutrients were mostly used for nucleus formation, and finally in the growth phase the COD was used for granule growth. To study the effect the internal surface area of the reactor has on the granulation process, 3 scale-down versions of the third test unit were constructed. Within the studied range, a yield of usable granules of 40 kg/m2 reactor internal surface area was obtained.

Thesis (PhD (Food Science))--University of Stellenbosch, 2009. / In the absence of anaerobic granules, anaerobically digested sewage sludge is frequently used to seed industrial upflow anaerobic sludge blanket (UASB) reactors. Because of its flocculent nature, start-up with digested sludge instead of granular sludge proceeds much slower and presents various operational problems. Any manner in which the granulation of digested sludge can be enhanced would benefit UASB reactor start-up and application in developing countries such as South Africa. The main objective of this dissertation was to improve granulation and reduce UASB reactor start-up by using pre-treated digested sludge as seed. The sludge was pre-treated based on the batch granulation-enhancement model of Britz et al. (2002). The main aim of the model was to improve extracellular polymer (ECP) production of lactate-utilising populations by applying short-term controlled organic overloading in a mechanically agitated environment. The batch granulation-enhancement (pre-treatment) process was applied to an ECP-producing digester strain, Propionibacterium jensenii S1. Non-methanogenic aggregates were formed when batch units were incubated on a roller-table instead of a linear-shake platform. Larger, more stable aggregates were obtained in the presence of apricot effluent medium. Preliminary batch granulation-enhancement studies confirmed that using the roller-table as mixing system had a positive influence on batch granulation-enhancement. The roller-table showed the most potential for handling larger volumes in comparison to a linear-shake waterbath and linear-shake platform. The addition of 450 mg.L-1 Fe2+ at the start of the study also influenced aggregate numbers positively. These studies revealed that pre-treatment results varied depending on the seed sludge source. A denaturing gradient gel electrophoresis (DGGE) method was applied for the detection of Archaea in digested sludges and UASB granules. In addition, a methanogenic marker containing methanogens important to the granulation process was constructed to aid identification. The positive influence of DMSO and “touchdown” PCR on the elimination of artifactual double bands in DGGE fingerprints were also demonstrated. Results revealed that only one of the four digested sludges tested contained Methanosaeta concilii (critical to granular nuclei formation) while it was present in all the UASB granules regardless of substrate type. Four digested sludges were obtained from stable secondary digesters. DGGE indicated the presence of M. concilii in all sludges. The Athlone 4Sb-sludge was the only sludge which exhibited measurable methanogenic activity during substrate dependent activity testing. The ST-sludge showed the highest increase in volatile suspended solids (VSS) particles ≥0.25 mm2. Laboratory-scale UASB reactor start-up was done with both sludges and start-up proceeded better in the Athlone 4Sb-reactor. Athlone 4Sb-sludge batches were pre-treated in a rolling-batch reactor in the presence of either lactate or sucrose and used to seed lab-scale UASB reactors B (sucrose seed) and C (lactate seed). Start-up efficiencies were compared to a control (Reactor A). Overall Reactor B was more efficient that the control. At the end of the study the Reactor B sludge had a higher methanogenic activity than the control reactor. It also had the highest increase in VSS ≥1.0 mm2. Pre-treatment of digested sludge in the presence of sucrose, therefore, aided granulation and reduced UASB reactor start-up time.

Dentro do escopo de estudo de aspectos fundamentais e tecnológicos, este trabalho foi direcionado à avaliação do comportamento da estabilidade e da eficiência de um reator anaeróbio contendo biomassa imobilizada em espuma de poliuretano para o tratamento de água residuária sintética com concentração de aproximadamente 500 mgDQO/L. O reator, de 6 litros de volume nominal, mantido à temperatura de 30 +/- 1ºC e sob a agitação mecânica de 500 rpm, foi operado em bateladas seqüenciais com a renovação de apenas parte do volume de água residuária tratada por ciclo, ou seja, a descarga do reator não foi completa, mas apenas parcial. Neste contexto, a principal característica operacional investigada foi a relação entre o volume de água residuária afluente, o qual era alimentado a cada novo ciclo de operação, e o volume de meio contido no reator, o qual não era descarregado no ciclo anterior, mantendo-se a mesma carga orgânica volumétrica. Desta forma, foi possível verificar a flexibilidade operacional do sistema com relação ao volume de água residuária tratada a cada ciclo e o tempo de duração do ciclo para uma mesma carga orgânica. Os resultados indicaram que o reator pôde operar com diferentes relações entre o volume alimentado e o volume de meio reacional sem diminuição significativa do seu desempenho, permitindo-se, assim, maior flexibilidade operacional. Para as condições em que o volume renovado foi maior ou igual a 50% do volume de meio do reator (ciclos de 4 a 8 horas), as eficiências de remoção de matéria orgânica filtrada e não filtrada mantiveram-se no patamar de 84 e 79%, respectivamente, enquanto que nas demais condições de maior diluição inicial do afluente (ciclos de 1 e 2 horas), essas eficiências foram ligeiramente menores, em torno de 80 e 74%, respectivamente. A alta velocidade de formação de material viscoso de aparência polimérica, nas condições de maior diluição inicial do afluente, dificultou a manutenção do volume de meio reacional do reator constante. / An assessment was performed on the stability and efficiency of an anaerobic reactor containing biomass immobilized on polyurethane foam for the treatment of synthetic wastewater with organic loading of approximately 500 mgCOD/L. The reactor had a total volume of 6 L. Batch operation took place at a temperature of 30 +/- 1ºC and an agitation rate of 500 rpm. During operation only part of the treated wastewater was renewed per cycle, i.e., reactor discharge was not complete, but partial. The main operation characteristic investigated was the ratio between influent wastewater volume, which was fed at each cycle, and the volume of medium contained in the reactor, which had not been discharged in the previous cycle, maintaining the same volumetric organic load. This way, it was possible to verify operation flexibility of the system regarding treated wastewater volume in each cycle as well as cycle time duration for the same volumetric organic loading. Results indicated that the reactor was able to operate at different ratios between feed and reaction medium volume without significant loss in performance, allowing, hence, greater operation flexibility. For conditions at which renewed volume was greater than or equal to 50% of the reactor medium (cycles from 4 to 8 hours), filtered and non-filtered organic matter removal efficiencies were about 84 and 79%, respectively, whereas at conditions of higher initial influent dilution (cycles from 1 to 2 hours) these efficiencies were slightly lower, about 80 and 74%, respectively. The high formation rate of viscous polymer-like material probably of microbiological origin, at the conditions of higher initial influent dilution hindered maintenance of constant reactor medium volume.