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The thesis, through experimental and numerical investigations reports on the work related to packed bed reactors in co-current configuration for biomass gasification. This study has extensively focused on the gasification operating regimes and addressing the issues of presence of tar, an undesirable component for engine application. Systematically, the influence of fuel properties on the gasification process has been studied using single particle analysis and also in packed bed reactors. Studies related to the effect of fuel properties - size, surface area volume ratio and density on the reactor performance are addressed. The influence of these parameters on the propagation rate which indirectly influences the residence time, tar generation, gas compositions is explicitly elucidated. Most of the reported work in literature primarily focuses on counter-current configurations and analysis on propagation flame front/ignition mass flux and temperature profiles mostly under the combustion regime. In this work, flame propagation front movement, bed movement and effective movement for a co-current packed bed reactor of different reactor capacities and a generalized approach towards establishing ‘effective propagation rate’ has been proposed. The work also reports on the importance of particle size and sharing of air from the top and through nozzles on tar generation in the open top down draft reactor configuration. Firstly, pyrolysis, an important component of the thermochemical conversion process has been studied using the flaming time for different biomass samples having varying size, shape and density. The elaborate experiments on the single particle study provides an insight into the reasons for high tar generation for wood flakes/coconut shells and also identifies the importance of the fuel particle geometry related to surface area and volume ratio. Effect of density by comparing the flaming rate of wood flakes and coconut shells with the wood sphere for an equivalent diameter is highlighted. It is observed that the tar level in the raw gas is about 80% higher in the case of wood flakes and similar values for coconut shells compared with wood pieces. The analysis suggests that the time for pyrolysis is lower with a higher surface area particle and is subjected to nearly fast pyrolysis process resulting in higher tar fraction with low char yield. Similarly, time for pyrolysis increases with density as observed from the experimental measurements by using coconut shells and wood flakes and concludes the influence on the performance of packed bed reactors. Studies on co-current reactor under various operating conditions from closed top reactor to open top reburn configuration suggests improved residence time reduces tar generation. This study establishes, increased residence time with staged air flow has a better control on residence time and yields lower tar in the raw gas. Studies on the influence of air mass flux on the propagation rate, peak temperature, and gas quality, establishes the need to consider bed movement in the case of co-current packed bed reactor. It is also observed that flame front propagation rate initially increases as the air mass flux is increased, reaches a peak and subsequently decreases. With increase in air mass flux, fuel consumption increases and thereby the bed movement. The importance of bed movement and its effect on the propagation front movement has been established. To account for variation in the fuel density, normalized propagation rate or the ignition mass flux is a better way to present the result. The peak flame front propagation rates are 0.089 mm/s for 10 % moist wood at an air mas flux of 0.130 kg/m2-s and while 0.095 mm/s for bone-dry wood at an air mass flux of 0.134 kg/m2-s. These peak propagation rates occur with the air mass flux in the range of 0.130 to 0.134 kg/m2-s. The present results compare well with those available in the literature on the effective propagation rate with the variation of air mass flux, and deviations are linked to fuel properties. The propagation rate correlates with mass flux as ̇ . during the increasing regime of the front movement. The extinction of flame propagation or the front receding has been established both experimentally supported from the model analysis and is found to be at an air mass flux of 0.235 kg/m2-s. The volume fraction of various gaseous species at the reactor exits obtained from the experiment is 14.89±0.28 % CO2, 15.75±0.43 % CO and 11.09±1.99 % H2 respectively with the balance being CH4 and N2. The model analysis using an in-house program developed for packed bed reactor provide a comprehensive understanding with respect to the performance of packed bed reactor under gasification conditions. The model addresses the dependence on air mass flux on gas composition and propagation rate and is used to validate the experimental results. Based on the energy balance in the reaction front, the analysis clearly identifies the reasons for stable propagation front and receding front in a co-current reactor. From the experiments and modelling studies, it is evident that turn-down ratio of a downdraft gasification system is scientifically established. Both the experimental and the numerical studies presented in the current work establishes that the physical properties of the fuel have an impact on the performance of the co-current reactor and for the first time, the importance of bed movement on the propagation rate is identified.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Solar energy is by far the greatest energy resource available to generate power. One of the difficulties of using solar energy is that it is not available 24 hours per day - some form of storage is required if electricity generation at night or during cloudy periods is necessary. If a combined cycle power plant is used to obtain higher efficiencies, and reduce the cost of electricity, storage will allow the secondary cycle to operate independently of the primary cycle. This study focuses on the use of packed beds of rock or slag, with air as a heat transfer medium, to store thermal energy in a solar thermal power plant at temperatures sufficiently high for a Rankine steam cycle. Experimental tests were done in a packed bed test section to determine the validity of existing equations and models for predicting the pressure drop and fluid temperatures during charging and discharging. Three different sets of rocks were tested, and the average size, specific heat capacity and density of each set were measured. Rock and slag samples were also thermally cycled between average temperatures of 30 ºC and 510 ºC in an oven. The classical pressure drop equation significantly under-predicts the pressure drop at particle Reynolds numbers lower than 3500. It appears that the pressure drop through a packed bed is proportional to the 1.8th power of the air flow speed at particle Reynolds numbers above about 500. The Effectiveness-NTU model combined with a variety of heat transfer correlations is able to predict the air temperature trend over the bed within 15 % of the measured temperature drop over the packed bed. Dolerite and granite rocks were also thermally cycled 125 times in an oven without breaking apart, and may be suitable for use as thermal storage media at temperatures of approximately 500 ºC. The required volume of a packed bed of 0.1 m particles to store the thermal energy from the exhaust of a 100 MWe gas turbine operating for 8 hours is predicted to be 24 × 103 m3, which should be sufficient to run a 25-30 MWe steam cycle for over 10 hours. This storage volume is of a similar magnitude to existing molten salt thermal storage. / AFRIKAANSE OPSOMMING: Sonenergie is die grootste energiebron wat gebruik kan word vir krag opwekking. ‘n Probleem met die gebruik van sonenergie is dat die son nie 24 uur per dag skyn nie. Dit is dus nodig om die energie te stoor indien dit nodig sal wees om elektrisiteit te genereer wanneer die son nie skyn nie. ‘n Gekombineerde kringloop kan gebruik word om ‘n hoër benuttingsgraad te bereik en elektrisiteit goedkoper te maak. Dit sal dan moontlik wees om die termiese energie uit die primêre kringloop te stoor, wat die sekondêre kringloop onafhanklik van die primêre kringloop sal maak. Dié gevalle studie ondersoek die gebruik van ‘n slakof- klipbed met lug as hitteoordragmedium, om te bepaal of dit moontlik is om hitte te stoor teen ‘n temperatuur wat hoog genoeg is om ‘n Rankine stoom kringloop te bedryf. Eksperimentele toetse is in ‘n toets-bed gedoen en die drukverandering oor die bed en die lug temperatuur is gemeet en vergelyk met voorspelde waardes van vergelykings en modelle in die literatuur. Drie soorte klippe was getoets. Die gemiddelde grootte, spesifieke hitte-kapasiteit en digtheid van elke soort klip is gemeet. Klip en slak monsters is ook siklies tussen temperature van 30 ºC en 510 ºC verkoel en verhit. Die klassieke drukverlies vergelyking gee laer waardes as wat gemeet is vir Reynolds nommers minder as 3500. Dit blyk dat die drukverlies deur ‘n klipbed afhanklik is van die lug vloeispoed tot die mag 1.8 as die Reynolds nommer groter as omtrent 500 is. Die ‘Effectiveness-NTU’ model gekombineerd met ‘n verskeidenheid van hitteoordragskoeffisiënte voorspel temperature binne 15 % van die gemete temperatuur verskil oor die bed. Doloriet en graniet klippe het 125 sikliese toetse ondergaan sonder om te breek, en is miskien gepas vir gebruik in ‘n klipbed by temperature van sowat 500 ºC Die voorspelde volume van ‘n klipbed wat uit 0.1 m klippe bestaan wat die termiese energie vir 8 ure uit die uitlaat van ‘n 100 MWe gasturbiene kan stoor, is 24 × 103 m3. Dit behoort genoeg te wees om ‘n 25 – 30 MWe stoom kringloop vir ten minste 10 ure te bedryf. Die volume is min of meer gelyk aan dié van gesmelte sout store wat alreeds gebou is.

Modelos matemáticos oferecem grandes benefícios para a compreensão dos mecanismos envolvidos nos processos de tratamento de águas residuárias uma vez que fornecem interpretações e possibilitam previsões de desempenho, comparações de alternativas de tratamento, otimização de futuras plantas ou o aprimoramento das existentes, podendo subsidiar a elaboração de projetos em escala real. Em virtude disto, nesta pesquisa visou-se o desenvolvimento de um modelo bioquímico-matemático para descrever o processo de degradação da glicose em um reator anaeróbio de leito fixo com fluxo ascendente, com a resultante produção biológica de hidrogênio por meio do processo de fermentação. O desenvolvimento do modelo foi baseado em estudos sobre a cinética bioquímica e as características hidrodinâmicas do sistema. Os parâmetros de ajuste do modelo aos dados experimentais foram as constantes de velocidade das reações bioquímicas envolvidas na produção de hidrogênio. A calibração foi realizada manualmente buscando minimizar o desvio global. Para a determinação dos parâmetros foi utilizada a técnica de geração de números aleatórios com distribuição de freqüência uniforme e em seguida, o método de inversão de matrizes. O modelo matemático se revelou bastante adequado para a previsão do perfil de concentrações ao longo do reator, e possibilitou a representação das rotas de utilização da matéria orgânica. A reação de oxidação do ácido propiônico pelas bactérias acidogênicas produtoras de hidrogênio constitui a principal via de produção de \'H IND.2\' no sistema. / Mathematical models bring benefits to the understanding of mechanisms involved on wastewater treatment processes because they provide interpretations and make possible performance predictions, evaluation of design alternatives, optimization of future plants or the improvement to existing systems. Therefore, in this work a mathematical model to describe the glucose degradation process, with hydrogen production through the fermentation, in an upflow anaerobic packed-bed reactor is developed. The model equations were based on studies of biochemical kinetics and hydrodynamics features of the system. The parameters considered were the rates of the biochemical reactions involved in the hydrogen production. The calibration was made through the minimization of the global deviation. The parameters determination was obtained with the use of a technique of generation of aleatory numbers, and after that, the method of matrices inversion for the solution of the system of linear equations. The mathematical model developed showed to be adequate for the concentrations prediction along the reactor, and it made possible the representation of the routes of organic material utilization. The oxidation reaction of propionic acid is the main hydrogen production route in the reactor.

"Multitubular packed bed reactors with low tube-to-particle diameter ratios (N) are especially selected for strongly endothermic reactions such as steam reforming and propane dehydrogenation. For low N tubes, the presence of the wall causes changes in bed structure, flow patterns, transport rates and the amount of catalyst per unit volume. In particular, the particles close to the wall will behave differently to those inside the bed. The problem is that, due to the simplifying assumptions, such as uniform catalyst pellet surroundings, that are usual for the current pseudo-continuum reactor models, the effects of catalyst pellet design changes in the near-wall environment are lost. The challenge is to develop a better understanding of the interactions between flow patterns, species pellet diffusion, and the changes in catalyst activity due to the temperature fields in the near wall region for the modeling and design of these systems. To contribute to this improved understanding, Computational Fluid Dynamics (CFD) was used to obtain detailed flow, temperature, and species fields for near-wall catalyst particles under steam reformer and propane dehydrogenation reactor inlet conditions. As a first step, a reduced size model was generated by only considering a 120 degree segment of an N = 4 tube, and validated with a larger size complete bed model. In terms of the flow and temperature contours and profiles, the complete tubes can be represented well by the reduced size models, especially focusing on the center particles positioned in the middle of the near wall region. The methane steam reforming heat effects were implemented by a user-defined code with the temperature-dependent sinks in the catalyst particles, near to the pellet surfaces for different activity levels. For the sinks terms, bulk phase species concentrations were used in the reaction rates, and with the reaction heat effects inclusion, significant pellet sensitivity was observed with different activity levels. Furthermore, non-symmetric temperature fields in and around the near wall particles were noticed as contrary to the conventional approach. In order to focus on the 3D intra-pellet distributions of temperature and species, diffusion and reaction were coupled to the external flow and temperature fields by user-defined code. Strong deviations from uniformity and symmetry on the temperature and species distributions existed as a result of the strong wall heat-flux into the particles Additionally, the pseudo-continuum type of packed bed model was created, which considers the simplified environment for the reacting particles. The results obtained by the diffusion reaction application in the 3D discrete packing model could not be re-produced by the conventional simplified pseudo-continuum approach, no matter which parameter values were chosen for the latter. The significance of these observations is that, under the conventional assumption of symmetric particle surroundings, the tube wall temperature and reaction rates for catalyst particles can be incorrectly evaluated and important design considerations may not be well predicted, thus, negative consequences on the plant safety and efficiency may be observed. "

O hidrogênio é estudado como alternativa ao uso de combustíveis fósseis para geração de energia, uma vez que é um combustível renovável, apresenta alta concentração de energia por unidade de massa e não gera gases causadores do efeito estufa. Entre os processos de produção de hidrogênio destaca-se o processo fermentativo, pois é um processo de baixo custo quando comparado com outros processos e possibilita unir tratamento de efluente e geração de energia. Neste sentido, este trabalho teve como proposta estudar parâmetros envolvidos no processo de produção fermentativo do \'H IND.2\'. O trabalho envolveu três etapas. Na primeira etapa, foi estudada a produção de hidrogênio a partir de sacarose empregando reatores anaeróbios de leito fixo de fluxo ascendente. Na primeira fase, comparou-se o desempenho de diferentes matérias suportes (argila, carvão vegetal e polietileno) e tempos de detenção hidráulica (TDH) (0,5 e 2h). Na segunda fase, testaram-se diferentes porosidades (50, 75 e 91%) do leito de polietileno TDH de 0,5 h. Os resultados mostraram que TDHs menores e maiores porosidades promovem maiores e contínuas produções de \'H IND.2\'. Na segunda fase, avaliou-se a produção de \'H IND.2\' a partir de quatro inóculos: metanogênico tratamento termicamente e três provenientes de biomassa aderidas aos materiais suportes empregados na primeira etapa. Todos inóculos produziram \'H IND.2\'. Na terceira etapa, avaliou-se a viabilidade de produzir \'H IND.2\' a partir de diferentes águas residuárias (sacarose, esgoto sanitário, vinhaça e glicerina). Houve conversão de hidrogênio a partir de todas as águas residuárias e a vinhaça mostrou ser o efluente mais promissor para esta finalidade. As análises biológicas mostraram baixa diversidade de fungos e bactérias, porém todos associados com o processo de formação de \'H IND.2\'. A varredura dos parâmetros estudados neste trabalho proporcionou o entendimento do processo, assim como, o mapeamento das variáveis adequadas para o projeto e viabilidade da aplicação de reatores desenvolvidos para geração de hidrogênio. / The hydrogen obtained by fermentative production is studied as an alternative process to provide energy instead of fossil fuel application. Moreover, hydrogen is a renewable fuel, has high energy content per unit weight (122 kJ/g), generates clean energy without pollution and produces no greenhouse gases. The fermentative process has low cost when it is compared with traditional process and photosynthetic process, because hydrogen can be produced from wastewater by anaerobic treatment process. For that reason, the aim of this research was to study some parameters involved in the hydrogen production by fermentative process. Three steps were developed. In the first step, it was studied the hydrogen production from sucrose using up-flow anaerobic packed-bed reactor, this step was divide in two phases. In the first phase three support materials (clay beads, vegetal coal and polyethylene) and two hydraulic retention times (0.5 and 2 h) were tested. In the second phase three porosities (50, 75 and 91%) of polyethylene bed were tested. The results demonstrated that the low HRT and high porosities provided high hydrogen production, although, the support materials did not show significant difference in the hydrogen production and in the biomass developed. In the second phase, four inocula were used in order to produce hydrogen: thermal pre-treated methanogenic sludge; and the others three came from the reactors used in the first phase. All inocula were able to produce hydrogen. In the third step hydrogen production was obtained from three wastewaters (domestic wastewater, vinasse and glycerol) and a control (sucrose) in batch reactors. The wastewaters and control produced hydrogen and the vinasse showed the highest production. This research makes available the comprehension on the influence of the different parameters in processes projected for hydrogen production and it makes viable to apply in full-scale.

Cette thèse présente une étude numérique d’un séchoir solaire indirect à convection naturelle destiné à sécher les produits agricoles (les figues). La première partie analyse un séchoir solaire contenant une chambre de séchage couplée à un absorbeur inversé et une cheminée solaire. Les simulations ont été faites afin de déterminer les champs dynamique et thermique sous l’influence de la variation de la configuration de la cheminée solaire et la taille de l’ouverture d’admission. Les équations de conservations basées sur le modèle de turbulence k-ε standard sont résolues par la méthode des volumes finis à l’aide du code commercial ANSYS-Fluent. La deuxième partie analyse l’effet d’ajouter un stockage thermique sous forme d’un lit en gravier dans la chambre de séchage. Le lit est modélisé comme un milieu poreux. En plus, cette étude propose l’utilisation d’une deuxième entrée d'air dans la chambre de séchage afin d’assurer une distribution thermique plus homogène au niveau des claies et de garantir un séchage plus uniforme. / This thesis presents a numerical study of an indirect natural convection solar dryer for drying agricultural products (Figs). The first part analyzes a solar dryer containing a drying chamber coupled to a reversed absorber and a solar chimney. Simulations were made to determine the dynamic and thermal fields under the influence of the variation of the solar chimney configuration and the size of the inlet opening. The governing equations based on the standard k-ε turbulence model are solved by the finite volume method using the ANSYS-Fluent commercial code. The second part analyzes the effect of adding a thermal storage in the form of a gravel bed in the drying chamber. The bed is modeled as a porous medium. Furthermore, this study proposes the use of a second air inlet in the drying chamber in order to ensure a more homogeneous thermal distribution at the level of the racks and to guarantee a more uniform drying.

The firing of fuel wood has been identified as one of themain causes of pollutant emissions from small-scale (<100kW) combustion of wood fuels. The emissions are a result ofinsufficient combustion efficiency. This thesis presents a newmeasurement method to analyse the thermochemical conversion ofbiofuels in general, as well as to explain the main reason ofthe inefficient combustion of fuel wood in particular. In general, small-scale combustion of biofuels are carriedout by means of packed-bed combustion (PBC)technology. Acomprehensive literature review revealed that textbooks,theories, and methods in the field of thermochemical conversionof solid fuels in the context of PBC are scarce. This authorneeded a theoretical platform for systematic research on PBC ofbiofuels. Consequently, a new system theory - the three-stepmodel - was developed, describing the objectives of, theefficiencies of, and the process flows between, the leastcommon functions (subsystems) of a PBC system. The three stepsare referred to as the conversion system, the combustionsystem, and the heat exchanger system (boiler system). A numberof quantities and concepts, such as solid-fuel convertibles,conversion gas, conversion efficiency, and combustionefficiency, are deduced in the context of the three-step model.Based on the three-step model a measurement method washypothetically modelled aiming at the central physicalquantities of the conversion system, that is, the mass flow andstoichiometry of conversion gas, as well as the air factor ofthe conversion system. An uncertainty propagation analysis ofthe constitutive mathematical models of the method was carriedout. It indicated that it should be possible to determine themass flow and stoichiometry of conversion gas within the rangesof relative uncertainties of ±5% and ±7%,respectively. An experimental PBC system was constructed,according to the criteria defined by the hypothetical method.Finally, the method was verified with respect to total massflow of conversion gas in good agreement with the verificationmethod. The relative error of mass flow of conversion gas wasin the range of ±5% of the actual value predicted by theverification method. One experimental series was conducted applying the newmeasurement method. The studied conversion concept correspondedto overfired, updraft, horizontal fixed grate, and verticalcylindrical batch reactor. The measurements revealed newinformation on the similarities and the differences in theconversion behaviour of wood chips, wood pellets, and fuelwood. The course of a batch conversion has proven to be highlydynamic and stochastic. The dynamic range of the air factor ofthe conversion system during a run was 10:1. The empiricalstoichiometry of conversion gas during a run was CH3.1O:CH0O0. Finally ,this experimental series revealed one ofthe main reasons why fuel wood is more difficult to burn thanfor example wood pellets. The relatively dry fuel wood (12-31g/m2,s) displayed a significantly lower time-integratedmean of mass flux of conversion gas than both the wood pellets(37-62 g/m2,s) and the wood chips (50-90 g/m2,s). The higher the mass flux of conversion gasproduced in the conversion system, the higher the combustiontemperature for a given combustion system, which in turn ispositively coupled to the combustion efficiency. In future work the method will be improved so thatmeasurements of combustion efficiency can be carried out. Othertypes of conversion concepts will be studied by the method. Keywords: Packed-bed combustion, thermochemical conversionof biomass, solid-fuel combustion, fuel-bed combustion, gratecombustion, biomass combustion, gasification, pyrolysis,drying.

Naphthenic acids (NAs) comprise a complex mixture of alkyl-substituted acyclic and cycloaliphatic carboxylic acids. NAs are present in wastewaters at petroleum refineries and in the process waters of oil sands extraction plants where they are primarily retained in large tailing ponds in the Athabasca region of Northern Alberta. The toxicity of these waters, primarily caused by NAs, dictates the need for their treatment.Bioremediation is considered as one of the most cost-effective approaches for the treatment of these wastewaters. Ex-situ bioremediation conducted in a bioreactor optimizes the microbial growth and activity by controlling environmental conditions resulting in efficient conversion of the contaminants to less harmful compounds. In this work, a circulating packed bed bioreactor (CPBB), with improved mixing, mass transfer and biomass hold-up has been used to study biodegradation of several model NA compounds: namely trans-4-methyl-1-cyclohexane carboxylic acid (trans-4MCHCA), a mixture of cis- and trans- 4-methyl-cyclohexane acetic acid (4MCHAA), and octanoic acid as well co-biodegradation of these naphthenic acids with octanoic acid, using a mixed culture developed in our laboratory. The biodegradation rates achieved for trans-4MCHCA in the CPBB are far greater than those reported previously in the literatures. The maximum biodegradation rate of trans-4MCHCA observed during batch operation was 43.5 mg/L-h, while a rate of 209 mg/L-h was achieved during continuous operation. Although cis-4MCHAA is more resistant to biodegradation when compared with trans-4MCHCA, the experimental results obtained from this study indicated both isomers were effectively biodegraded in the CPBB, with the maximum biodegradation rates being as high as 2.25 mg/L-h (cis-4MCHAA) and 4.17 mg/L-h (trans-4MCHAA) during batch operations and 4.17 mg/L-h(cis-4MCHAA) and 7.80 mg/L-h (trans-4MCHAA) during the continuous operation. Optimum temperature for biodegradation of 4MCHAA was determined as 25 aC. Furthermore, the biodegradation rate of single ring NAs (trans-4MCHCA and 4MCHAA) were found to be significantly improved through utilization of octanoic acid as a co-substrate. For example, the maximum biodegradation rate of trans-4MCHCA obtained during batch operation with the presence of octanoic acid was 112 mg/L-h, which was 2.6 times faster than the maximum value of 43.5 mg/L-h when trans-4MCHCA was used as a sole substrate. Similarly, the highest biodegradation rates of cis-4MCHAA and trans-4MCHAA were 16.7 and 28.4 mg/L-h in the presence of octanoic acid, which were 7.4 and 6.8 times higher than the maximum rates of 2.25 and 4.17 mg/L-h in the absence of octanoic acid.

Naphthenic acids (NAs) comprise a complex mixture of alkyl-substituted acyclic and cycloaliphatic carboxylic acids. NAs are present in wastewaters at petroleum refineries and in the process waters of oil sands extraction plants where they are primarily retained in large tailing ponds in the Athabasca region of Northern Alberta. The toxicity of these waters, primarily caused by NAs, dictates the need for their treatment.Bioremediation is considered as one of the most cost-effective approaches for the treatment of these wastewaters. Ex-situ bioremediation conducted in a bioreactor optimizes the microbial growth and activity by controlling environmental conditions resulting in efficient conversion of the contaminants to less harmful compounds. In this work, a circulating packed bed bioreactor (CPBB), with improved mixing, mass transfer and biomass hold-up has been used to study biodegradation of several model NA compounds: namely trans-4-methyl-1-cyclohexane carboxylic acid (trans-4MCHCA), a mixture of cis- and trans- 4-methyl-cyclohexane acetic acid (4MCHAA), and octanoic acid as well co-biodegradation of these naphthenic acids with octanoic acid, using a mixed culture developed in our laboratory. The biodegradation rates achieved for trans-4MCHCA in the CPBB are far greater than those reported previously in the literatures. The maximum biodegradation rate of trans-4MCHCA observed during batch operation was 43.5 mg/L-h, while a rate of 209 mg/L-h was achieved during continuous operation. Although cis-4MCHAA is more resistant to biodegradation when compared with trans-4MCHCA, the experimental results obtained from this study indicated both isomers were effectively biodegraded in the CPBB, with the maximum biodegradation rates being as high as 2.25 mg/L-h (cis-4MCHAA) and 4.17 mg/L-h (trans-4MCHAA) during batch operations and 4.17 mg/L-h(cis-4MCHAA) and 7.80 mg/L-h (trans-4MCHAA) during the continuous operation. Optimum temperature for biodegradation of 4MCHAA was determined as 25 aC. Furthermore, the biodegradation rate of single ring NAs (trans-4MCHCA and 4MCHAA) were found to be significantly improved through utilization of octanoic acid as a co-substrate. For example, the maximum biodegradation rate of trans-4MCHCA obtained during batch operation with the presence of octanoic acid was 112 mg/L-h, which was 2.6 times faster than the maximum value of 43.5 mg/L-h when trans-4MCHCA was used as a sole substrate. Similarly, the highest biodegradation rates of cis-4MCHAA and trans-4MCHAA were 16.7 and 28.4 mg/L-h in the presence of octanoic acid, which were 7.4 and 6.8 times higher than the maximum rates of 2.25 and 4.17 mg/L-h in the absence of octanoic acid.