Anaerobinis dumblo pūdymas - tai procesas, kurio metu dalis biomasėje esančių organinių junginių dėl įvairių rūšių mikroorganizmų veiklos yra suardomi. Vykstant šiam procesui, irstančios organinės dalelės verčiamos į biodujas – atsinaujinantįjį energijos šaltinį. Tačiau anaerobinis dumblo pūdymas gali sutrikti dėl įvairių inhibitorinių medžiagų. Norint reikiamą nuotekų išvalymo laipsnį užtikrinti pagal bendrąjį fosforą, naudojamas cheminis fosforo šalinimo būdas, kurio metu į nuotekas įterpiamos Al arba Fe metalų druskos. Šio darbo tikslas ‒ nustatyti, kaip skirtingos aliuminio ir geležies koncentracijos veikia anaerobinio stabilizavimo procesą ir išgaunamų dujų kiekį. Darbui atlikti buvo naudojamas standartinis anaerobinio pūdymo W8 (Armfield Ltd, UK) modelis. Tyrimu nustatyta, kad pūdant dumblą, į kurį buvo dozuota Fe druska, išsiskyrusių biodujų kiekis ml/d buvo artimas kontrolinio pūdytuvo reikšmėms, o pūdant dumblą, į kurį buvo dozuotos Fe ir Al druskos, biodujų ml/d išsiskyrė iki 30 % daugiau, nei palyginus su dumblu, į kurį druskos nebuvo dozuotos. Dozuojant metalų druskas ir esant padidėjusiai pūdytuvo apkrovai bepelenėmis sausosiomis medžiagomis, taip pat buvo nustatyta, kad sumažėja bepelenių sausųjų medžiagų suskaidymo efektyvumas iki 5—12 %. Nepaisant sumažėjusio bepelinių sausųjų medžiagų suskaidymo, biodujų m3/kgBSM suskaidytų padidėjo net iki 43 % pagal vidutines reikšmes. Išanalizavus tyrimų rezultatus pateiktos išvados ir rekomendacijos. Darbą sudaro šios... [toliau žr. visą tekstą] / Anaerobic sludge digestion is a process in which part of organic compounds existing in biomass are destroyed of various microorganisms. In this process volatile solids (VS) are converted into biogas – renewable energy source. Anaerobic digestion can be impaired in presence of inhibitors. Chemical phosphorus removal when Al and Fe metals salts are added to wastewater is used to reach the degree of waste water treatment by total phosphorus. Objective of this work was to investigate impact of different aluminium and iron doses on anaerobic digestion process and biogas produced. The work was carried out using standard anaerobic digestion model W8 (Armfied Ltd. UK). Research showed that biogas produced from Fe-dosed sludge was close to biogas production from un-dosed sludge and during digestion of Al-Fe-dosed sludge biogas ml/d production was 30% higher that from control. The efficiency of volatile solids destruction decreased 5-12% during dosing of metal salts. Biogas production from VS destructed was approx. 43% higher by average values when metal salts were dosed into sludge. The composition of biogas was not measured during research. Conclusions and recommendations are presented.

Anaerobic digestion is a process that simultaneously treats waste and produces renewable energy in the form of biogas. Applications include swine and cattle waste management, which is still dominated by aerobic digestion, a less environmental alternative. The low adoption rates of anaerobic digestion is partly caused by the lack of modelling basis for the technology. This is due to the complexity of the process, as it involves dozens of interrelated biochemical reactions driven by hundreds of species of micro-organisms, immersed in a three-phase, non-Newtonian fluid. As a consequence, no practical computer models exist, and therefore, unlike most other engineering fields, the design process for anaerobic digesters still relies heavily on traditional methods such as trial and error. The current state-of-the-art model is Anaerobic Digestion Model No. 1 (ADM1), published by the International Water Association in 2001. ADM1 is a bulk model, therefore it does not account for the effects of concentration gradients, stagnation regions, and particle settling. To address this, this thesis works toward the creation of the first three-dimensional spatially resolved anaerobic digestion model, called Anaerobic Digestion Model with Multi-Dimensional Architecture (ADM-MDA), by developing a framework. The framework, called Coupled Reaction-Advection Flow Transient Solver (CRAFTS), is a general reaction solver for single-phase, incompressible fluid flows. It is a novel partial differential and algebraic equation (PDAE) solver that also employs a novel programmable logic controller (PLC) emulator, allowing users to define their own control logic. All aspects of the framework are verified for proper function, but still need validation against experimental results. The biochemistry from ADM1 is input into CRAFTS, resulting in a manifestation of ADM-MDA; however the numerical stiffness of ADM1 is found to conflict with the second order accuracy of CRAFTS, and the resulting model can only operate under restricted conditions. Preliminary results show spatial effects predicted by the CRAFTS model, and non-observable in the bulk model, impact the digester in a non-trivial manner and lead to measurable differences in their respective outputs. A detailed discussion of suggested work to arrive at a practical spatially resolved anaerobic digestion model is also provided.

The effect of engineered nanoparticles (ENPs) mixture consisting of silver oxide, (Agg0[Silver Oxide Nanopartical], 20 nm), titanium dioxide, (TiO2[Titanium dioxide], 30-40 nm) and zinc oxide, (ZnO, 20 nm) compared with their bulk metal salts was evaluated against unspiked activated sludge (control) using 3 parallel pilot-scale treatment plants. The total concentration of the ionic species of Ag+ Ti[Silver + Titanium] and Zn(2+) in the effluent of the ENP spiked activated sludge (AS) was below limits of detection and> 99% of the spiked ENP were found in the waste activated sludge (WAS), whereas 39 – 58 % of Ag0[Silver Oxide Nanopartical], 51 – 63 % and 58 – 74 % of ZnO ion concentrations were recovered in the anaerobic digestate (AD) cake suggesting higher affinity of ENPs to WAS than to anaerobic digestate. ENPs induced a 2-fold increase of the microbial community specific oxygen uptake rate (SOUR) compared with the control and > 98 % of ammonia and 80 % of COD were removed from the AS suggesting that the heterotrophic biomass retained their ability to nitrify and degrade organic matter at the spiked ENP concentration. The floc size and cultivable microbial abundance was reduced in the ENP spiked AS with no apparent disruption of the overall AS process efficiency. However, scanning electron microscopic analysis clearly showed damage to specific microbial cells. The lipid fingerprint and 16S rRNA gene-based pyrosequencing evidenced the dominance of Proteobacteria, Firmicutes, and Bacteriodetes with a clear temporal shift in microbial community structure. The prominent nano-tolerant bacterial species identified were Acidovorax, Rhodoferax, and Comamonas whereas Methanocorpusculum and Methanosarcina were recovered in AS and were the dominant Archaea in the AD with 99 and 98 % similarities to the closest culturable relative. Their presence in the AS suggests tolerance to ENPs and oxygen-dependent respiration. V. fisheri activity was not sensitive to the ionic concentrations of the ENP or metal salt mixture in the digestate samples and illustrates the need to develop bioassay using indigenous wastewater microorganisms to detect the potential effect of ENP. Overall, unlike other xenobiotic compounds, ENPs can hasten the natural selection of microbial species in activated sludge and anaerobic digestion processes.

Many of the current methods of assessing anaerobic biodegradability of solid samples require sample modification prior to testing. Steps like sample drying, grinding, re-drying and re-grinding to 2mm or less make the test results difficult to apply to field conditions and could lead to oxygen exposure, possibly distorting the results. Finally, because of a small sample size of about 10-50g w/w, the test result may not be representative of the bulk material. A new tool dubbed ‘tube’ has been developed, made of 10 cm diameter PVC pipe measuring 43.5 cm long with 3600 ml capacity with caps at both ends. For easy sample introduction, one endcap is fixed while the other is screw capped. A distinctive feature is the wide neck opening of about 10 cm where solid samples can be introduced as is, without further sample modification. Research has proven the tube applicable across various types of solid organic waste and conditions provided that a suitable organic loading rate is determined. The tube is best operated using 5-7 days pre-digested digested sewage sludge as seed, with minimal mixing and without the addition of nutrients or alkali solution. The test result can be obtained within 4-6 days to 20 days, signifying a 50-75% and 95% substrate degradation, respectively. Irreproducibility seen in some experiments may not only be a function of the seed and the substrate. The organic loading rate (OLR) at which the test is conducted is also influential especially if test is conducted closer to its maximum OLR tolerance where anaerobic process is more erratic. The performance of a continuous reactor digesting on a similar substrate can be estimated using this new tool. Food waste is established by the tubes to have an ultimate methane potential (B0) of 0.45L CH4/g VS. The same substrate when digested in a continuous reactor will produce about (B) 0.32 L CH4/g VS. The first order rate constant for both systems; batch and continuous are identical at 0.12 to 0.28 d-1. First order kinetics is efficient at modelling the anaerobic degradation when the process is healthy but may be less reliable under an unstable process. This research recommends the use of kinetics in combination with the experimental data (e.g. HRT, OLR, yield) when planning and designing an industrial plant to avoid overdesign and unnecessary building, maintenance and operating costs.

Anaerobic digestion is a process that simultaneously treats waste and produces renewable energy in the form of biogas. Applications include swine and cattle waste management, which is still dominated by aerobic digestion, a less environmental alternative. The low adoption rates of anaerobic digestion is partly caused by the lack of modelling basis for the technology. This is due to the complexity of the process, as it involves dozens of interrelated biochemical reactions driven by hundreds of species of micro-organisms, immersed in a three-phase, non-Newtonian fluid. As a consequence, no practical computer models exist, and therefore, unlike most other engineering fields, the design process for anaerobic digesters still relies heavily on traditional methods such as trial and error. The current state-of-the-art model is Anaerobic Digestion Model No. 1 (ADM1), published by the International Water Association in 2001. ADM1 is a bulk model, therefore it does not account for the effects of concentration gradients, stagnation regions, and particle settling. To address this, this thesis works toward the creation of the first three-dimensional spatially resolved anaerobic digestion model, called Anaerobic Digestion Model with Multi-Dimensional Architecture (ADM-MDA), by developing a framework. The framework, called Coupled Reaction-Advection Flow Transient Solver (CRAFTS), is a general reaction solver for single-phase, incompressible fluid flows. It is a novel partial differential and algebraic equation (PDAE) solver that also employs a novel programmable logic controller (PLC) emulator, allowing users to define their own control logic. All aspects of the framework are verified for proper function, but still need validation against experimental results. The biochemistry from ADM1 is input into CRAFTS, resulting in a manifestation of ADM-MDA; however the numerical stiffness of ADM1 is found to conflict with the second order accuracy of CRAFTS, and the resulting model can only operate under restricted conditions. Preliminary results show spatial effects predicted by the CRAFTS model, and non-observable in the bulk model, impact the digester in a non-trivial manner and lead to measurable differences in their respective outputs. A detailed discussion of suggested work to arrive at a practical spatially resolved anaerobic digestion model is also provided.

Biogas är en förnyelsebar energikälla som tillverkas genom att organiskt material som matavfall bryts ner av mikroorganismer under anaeroba (syrefria) förhållanden. Regeringen har satt upp mål för en högre matavfallsutsortering vilket leder till ökad mängd tillgängligt substrat till biogasproduktion. Matavfallet som samlas in börjar brytas ner under tiden det transporteras och lagras. Syftet med studien var att undersöka hur länge matavfall lagras, ta fram ett representativt recept på ett genomsnittligt matavfall i Sverige och utvärdera hur mycket metanpotential som försvinner från matavfall med avseende på lagringstid, insamlingssystem (papper- och plastpåse) och lagringstemperatur (22°C och 6°C) genom laboratorieförsök. Den genomsnittliga lagringstiden för matavfall från villor och flerbostadshus i undersökningen var sex dagar. Ett recept för matavfall har tagits fram med hjälp av litteratursökning och modifiering av recept i Avfall Sveriges rapport U2010:10. Laboratorieförsöken visade att skillnaden i metanpotential mellan plast och papper var tydlig vid 22°C, då metanpotentialen sjunker, men obefintlig vid 6°C. För att uppnå maximal metangasproduktion från matavfall under den varma delen av året så är plastpåsar bättre då de har en mer konserverande effekt på matavfallet än papperspåsar. Detta kan relateras till att plast är tätare än papper och därför håller inne flyktiga ämnen. / Biogas is a renewable energy source that is produced when organic materials like food waste is degraded by microorganisms under anaerobic (oxygen-free) conditions. The Swedish Government has set goals for a higher sorting of food waste, leading to increased amounts of available substrate for biogas production. Collected food waste begin to break down during the time it is transported and stored. The purpose of this study was to investigate the length of the storage, produce a representative recipe for an average food waste in Sweden and evaluate how much methane potential is lost from food waste with respect to the storage time, collection method (paper or plastic bag) and storage temperature (22°C and 6°C) through laboratory tests. The average storage time of food waste from houses and apartment buildings in the survey was six days. A recipe for food waste has been developed with the help of literature search and modification of recipes in ‘’Avfall Sverige’’ report U2010:10. Laboratory tests showed that the difference in methane potential between the plastic and paper were clear at 22°C, with decreasing methane potential, but non-existent at 6°C. To achieve maximum methane production from food waste during the warmer part of the year, plastic bags are better because they have a preservative effect on the food waste. This can be related to the fact that plastic are denser than paper and therefore holds volatile compounds better.

The effects of UV pretreatment on alkaline bleaching (EOP) wastewater from a kraft pulp and paper mill were investigated prior to anaerobic digestion (AD) in an upflow anaerobic sludge blanket (UASB) reactor. The aim was to enhance the methane production, increase the reduction of total organic carbon (TOC) and determine the best UV exposure time. The exposure time of 2.6 minutes partially degraded the organic material in the EOP wastewater since it generated higher biogas and methane production than the reference period, while it also increased the reductions of solved chemical oxygen demand (CODsol) and TOCsol. The exposure time of 16 minutes, on the other hand, did not show any significant improvement regarding increased biogas and methane production nor did it increase the reduction of CODsol. However, it did increase the reduction of TOCsol, but not to the same extent as the exposure time of 2.6 minutes. The presence of unwanted microbial growth in the system during the experiment might have affected the effectiveness of the UV pretreatment more during the exposure time of 16 minutes as the amount of growth was more substantial during this period of time. Furthermore, no optimal exposure time could be determined due to lack of time.

ABSTRACT Bioreactor landfill operation has been promoted as a means of accelerating the degradation of waste for over 30 years. Accelerating the degradation of waste enables better predictability in biogas production and reduces aftercare costs. Most bioreactor landfill trials focus on the effect of leachate recirculation on otherwise conventional landfill cells. However, there is a range of design and operational measures that can be implemented with standard landfilling machinery to further enhance degradation. This thesis explores degradation rates that can be achieved in a landfill cell, designed to maximise degradation rate, with the constraint that it be constructed by standard earthmoving equipment, the waste be crudely shredded by sheep foot compactors to expose waste, and leachate recirculation be operable by landfill personnel. The major departures of these test cells from a conventional landfill cell operation were: the cells were only 3m deep; MSW loaded into the cell was crushed and bags ruptured with a sheep foot compactor; MSW was pre-mixed prior placement with digested sludge, as a ratio such that the buffering capacity of the sludge was equivalent to an amount of NaHCO3 known to successfully buffer the digestion of packed beds of MSW (10gL-1 NaHCO3 in packed bed at field capacity moisture content plus excess leachate equal to 10% of the bed volume (Lai et al 2001); and the waste was placed rather than compacted into the cell. The thesis examines the performance of two test cells, the second only containing MSW and inoculated and buffered by sequencing with the first. These performances are compared with an exhaustive set of control digestions in 200L laboratory reactors. The laboratory reactors were packed with 50kg sub-samples of the waste used in the cells, shredded to sub 5cm size. The laboratory reactors primarily focussed on the effect of temperature on degradation rates, to identify the optimum degradation rate for this sludge and MSW mixture. The laboratory scale reactors produced 231 L and 202 L of methane per kgVS at the mesophilic temperatures of 38°C and 45°C respectively. The degradation was faster in the 45°C reactor where methane production was completely exhausted after 35 days. A laboratory reactor operated at 55°C reactor showed little degradation activity. The pH of this reactor was initially over 8.5, and ammonia inhibition was suspected. However, the reactor did not respond to pH adjustments with hydrochloric acid, and subsequent step decreases in temperature did not have an effect until 47°C, where degradation suddenly accelerated. This suggests the methanogenic consortia in the sludge could not adapt to thermophilic temperatures. This was confirmed in the 63°C reactor which acidified and did not produce methane, until leachate from this reactor was transferred to the 45°C reactor where an established methanogenic community converted the soluble COD to methane. In order to compare laboratory reactor performance with the general literature, pure cellulose was added in a fed-batch fashion to the stabilised 38°C and 47°C leach-beds. The beds were fed under starved conditions, to clearly distinguish degradation products from the cellulose from background levels. This also allowed for the estimation of biomass growth by measuring the uptake of NH4-N, as all other bio-available N sources such as protein and amino acids were reduced to NH4-N under these starved conditions. Hydrolysis rates were determined to be 0.12±0.01 d-1 and 0.14±0.026 d-1 at the 38°C and 47°C temperatures. Degradation in the two test cells was completed within a 7 month period. Temperature in the cells was maintained between 25 – 30°C by biological activity, levels that were above ambient temperatures, but below ideal mesophilic conditions. Methane composition rapidly approached 50% in both cells, and biogas flow rates were consistent with a degradation timeframe in the order of less than year. Full flow rate data was not obtained from these trials due to mechanical problems with flow meters, however vigorous gas production was evident throughout the trial by monitoring gas composition, and the ballooning effect of the top cover. To confirm the degradation rates in the test cells, samples were collected from the second test cell and digested in laboratory reactors. Methane yields were only 2.4 and 6.4 L CH4 kgVS-1 confirming virtual exhaustion of biogas potential within 7 months of sequencing this MSW cell with the first MSW:sludge test cell. This is the first systematic experimental program that places the degradation performance of a test cell in the context of the potential degradation rate achievable with fine shredding, temperature control and thorough inoculation and buffering. Economically, in cases where degradation residues are left insitu as in landfills, the degradation enhancement in the test cells would effectively yield as much benefit as enhancing the degradation rate to a two to three week timeframe typical of an anaerobic digester (Clarke 2000).

Municipal wastewater and industrial wastewaters like those effluents from brewery, citric acid production, tannery, pulp and paper industry, and mussel processing contain sulphate ranging from 20 mg.L-1 to 11400 mg.L-1. When these wastewaters are treated in an anaerobic system like prefermentors or anaerobic digesters the sulphate is reduced to sulphide by sulphate reducing bacteria (SRB). The presence of sulphate reduction is not desirable as it may reduce methane yield due to partial substrate utilisation by SRB, causes system toxicity and the production of malodor H2S in the gas phase. In this thesis, the effects of operational conditions on sulphate transformation and assimilation was studied in a laboratory scale anaerobic wastewater treatment system. The laboratory scale system consisted of two reactors the first one a well-mixed fermentor (referred to as an acidogenic reactor) and the second an expanded granular sludge blanket reactor (referred to as a methanogenic reactor) with pH and temperature control. Two sets of studies were performed; in the first set both reactors were connected serially to represent a two-stage high-rate anaerobic treatment system. The system was fed molasses and operated at temperature of 35oC. The acidogenic reactor was controlled at pH of 6 while the methanogenic reactor was controlled at pH of 7.2 by automatic addition of caustic. In the second set of experiments only the first reactor was used to represent a prefermentor and the first stage of the two stage. The reactor was fed with glucose at various concentrations, operated at pH of 6 and temperature of 35oC. Information gained from these studies was encapsulated in a mathematical model to describe sulphate reduction in anaerobic treatment systems. This model was also validated using data generated from the experiments. The experimental study showed that · At low sulphate concentrations of about 250 mg.L-1 and COD concentration of 10,000 mg.L-1 in feed, relatively high percentage (up to 35 %) of produced sulphide was assimilated by biomass, while the rest of the sulphur was distributed as unconverted sulphate, dissolved sulphide, H2S gas and to a lesser extent as metallic sulphide precipitates. · The major electron donor for sulphate reduction in both the acidogenic and the methanogenic reactor was hydrogen gas. Therefore, sulphate reduction not only competed with hydrogen utilising methanogens for the available hydrogen, but also changed the distributions of organic acids, which were directly or indirectly influenced by the H2 partial pressure. · Sulphide concentrations of up to 6.5 mM free hydrogen sulphide) at pH of 7.2 was not inhibitory to methanogens · Sulphate reducing bacteria were able to grow even at a low hydraulic retention time of 1.2 hours in the well-mixed acidogenic reactor. It was estimated that the maximum specific growth rate (m) and half saturation constant (ks) of SRB was 1.31 h-1 and 3.8 mg S.L-1, respectively. These values were higher than those reported in literature. · Sulphate reduction was suppressed at high concentration of carbon in the feed. Accumulation of high concentration of volatile organic acids at high feed-carbon concentrations had little effect on sulphate reduction. However, extent of sulphate reduction had a negative correlation with total concentration of biomass. A non-competitive biomass inhibition function was proposed to model the correlation. From this fit it was estimated that a biomass concentration of about 3300 mg-COD.L-1 will completely inhibit sulphate reduction. · Sulphate reduction was affected by redox potential control and pH in the acidogenic reactor. High pH and low redox potential values were essential for sulphate reduction to proceed. At redox potential control of -300 mV, sulphate reduction was inhibited more at pH of 6 than it was at pH of 7. At redox potential values of -250 mV or higher, about 90 % inhibition of sulphate reduction was observed at both pH of 6 and 7. An existing model describing carbohydrate degradation was extended to include sulphate reduction processes. Despite experimentally observing that sulphate reduction only took place from hydrogen, all possible substrates for sulphate reducion was considered. These included: lactic acid, butyric acid, propionic acid, acetic acid and hydrogen. Kinetic parameters for sulphate reduction processes were obtained from documented literature. Inhibition of sulphate reduction by biomass and sulphur assimilation by biomass were included in the model. A new approach to calculate caustic consumption at given pH values was also included. A modification to hydrogen regulation function was also made to better predict product distributions as a function of gas-phase hydrogen concentration. Model validation was performed using data from dynamic experiments. Comparison to actual data was undertaken on several key variables in the acidogenic and methanogenic reactors such as: organic acid concentrations, gas compositions, gas production rates, sulphate and sulphide concentrations and caustic consumption rates. The model satisfactorily predicted sulphate and sulphide concentrations in both reactors. However, discrepancy between predicted and experimental data on organic carbon concentrations was seen, especially during organic carbon concentration step changes.

Municipal wastewater and industrial wastewaters like those effluents from brewery, citric acid production, tannery, pulp and paper industry, and mussel processing contain sulphate ranging from 20 mg.L-1 to 11400 mg.L-1. When these wastewaters are treated in an anaerobic system like prefermentors or anaerobic digesters the sulphate is reduced to sulphide by sulphate reducing bacteria (SRB). The presence of sulphate reduction is not desirable as it may reduce methane yield due to partial substrate utilisation by SRB, causes system toxicity and the production of malodor H2S in the gas phase. In this thesis, the effects of operational conditions on sulphate transformation and assimilation was studied in a laboratory scale anaerobic wastewater treatment system. The laboratory scale system consisted of two reactors the first one a well-mixed fermentor (referred to as an acidogenic reactor) and the second an expanded granular sludge blanket reactor (referred to as a methanogenic reactor) with pH and temperature control. Two sets of studies were performed; in the first set both reactors were connected serially to represent a two-stage high-rate anaerobic treatment system. The system was fed molasses and operated at temperature of 35oC. The acidogenic reactor was controlled at pH of 6 while the methanogenic reactor was controlled at pH of 7.2 by automatic addition of caustic. In the second set of experiments only the first reactor was used to represent a prefermentor and the first stage of the two stage. The reactor was fed with glucose at various concentrations, operated at pH of 6 and temperature of 35oC. Information gained from these studies was encapsulated in a mathematical model to describe sulphate reduction in anaerobic treatment systems. This model was also validated using data generated from the experiments. The experimental study showed that · At low sulphate concentrations of about 250 mg.L-1 and COD concentration of 10,000 mg.L-1 in feed, relatively high percentage (up to 35 %) of produced sulphide was assimilated by biomass, while the rest of the sulphur was distributed as unconverted sulphate, dissolved sulphide, H2S gas and to a lesser extent as metallic sulphide precipitates. · The major electron donor for sulphate reduction in both the acidogenic and the methanogenic reactor was hydrogen gas. Therefore, sulphate reduction not only competed with hydrogen utilising methanogens for the available hydrogen, but also changed the distributions of organic acids, which were directly or indirectly influenced by the H2 partial pressure. · Sulphide concentrations of up to 6.5 mM free hydrogen sulphide) at pH of 7.2 was not inhibitory to methanogens · Sulphate reducing bacteria were able to grow even at a low hydraulic retention time of 1.2 hours in the well-mixed acidogenic reactor. It was estimated that the maximum specific growth rate (m) and half saturation constant (ks) of SRB was 1.31 h-1 and 3.8 mg S.L-1, respectively. These values were higher than those reported in literature. · Sulphate reduction was suppressed at high concentration of carbon in the feed. Accumulation of high concentration of volatile organic acids at high feed-carbon concentrations had little effect on sulphate reduction. However, extent of sulphate reduction had a negative correlation with total concentration of biomass. A non-competitive biomass inhibition function was proposed to model the correlation. From this fit it was estimated that a biomass concentration of about 3300 mg-COD.L-1 will completely inhibit sulphate reduction. · Sulphate reduction was affected by redox potential control and pH in the acidogenic reactor. High pH and low redox potential values were essential for sulphate reduction to proceed. At redox potential control of -300 mV, sulphate reduction was inhibited more at pH of 6 than it was at pH of 7. At redox potential values of -250 mV or higher, about 90 % inhibition of sulphate reduction was observed at both pH of 6 and 7. An existing model describing carbohydrate degradation was extended to include sulphate reduction processes. Despite experimentally observing that sulphate reduction only took place from hydrogen, all possible substrates for sulphate reducion was considered. These included: lactic acid, butyric acid, propionic acid, acetic acid and hydrogen. Kinetic parameters for sulphate reduction processes were obtained from documented literature. Inhibition of sulphate reduction by biomass and sulphur assimilation by biomass were included in the model. A new approach to calculate caustic consumption at given pH values was also included. A modification to hydrogen regulation function was also made to better predict product distributions as a function of gas-phase hydrogen concentration. Model validation was performed using data from dynamic experiments. Comparison to actual data was undertaken on several key variables in the acidogenic and methanogenic reactors such as: organic acid concentrations, gas compositions, gas production rates, sulphate and sulphide concentrations and caustic consumption rates. The model satisfactorily predicted sulphate and sulphide concentrations in both reactors. However, discrepancy between predicted and experimental data on organic carbon concentrations was seen, especially during organic carbon concentration step changes.