No description available.

Two different sludge pretreatments were investigated in an attempt to improve the management and performance of processes for the co-digestion of biosolids with fats, oils, and grease (FOG). The mechanisms of long chain fatty acids (LCFA) degradation in thermal hydrolysis pretreatment and the influence of pH on LCFA degradation in two-phase co-digestion systems were studied. LCFA thermal hydrolysis was investigated at different temperatures (90-250 °C) and reaction times (30 minutes and 8 hours). Approximately 1% of saturated fatty acids were degraded to shorter chain fatty acids at 140 and 160 °C (8-hr thermal hydrolysis). Only 1% or less of unsaturated fatty acids were degraded from 90 to 160 °C (8-hr thermal hydrolysis). Little degradation (< 1%) of both saturated and unsaturated LCFAs was observed at a 30-min reaction time. Both groups of LCFAs were stable up to 250 °C (30-min hydrolysis). The use of chemical-thermal treatments was also investigated. Only unsaturated LCFAs, C18:1 and C18:2, were degraded when thermally hydrolyzed with hydrogen peroxide coupled with activated carbon or copper sulfate. Semi-continuous, acid-phase digesters (APDs) under different pH conditions were studied in order to understand the effects of pH on FOG degradation. Increases in soluble chemical oxygen demand (SCOD) were observed in all APDs. However, the APDs with pH adjustment appeared to perform better than the controls in terms of solubilizing organic compounds. Approximately 38% and 29% of total COD (TCOD) was solubilized, and maximum volatile fatty acid (VFA) concentrations of 10,700 and 7,500 mg/L TCOD were achieved at pH 6 and 7, respectively; It is useful to note that the feed sludge had a VFA concentration of 2,700 mg/L COD. Higher pH (6.0-7.0) showed less accumulation of LCFA materials and more soluble LCFAs in the APDs. This indicates that the lower pH in the APDs was most likely the cause of precipitation and accumulation of LCFAs due to saturation of unsaturated LCFAs. / Master of Science

The increased demand for advanced sludge stabilization in wastewater treatment facilities over the past decade has led to the implementation of various pretreatment techniques prior to anaerobic digestion. In an attempt to reduce sludge volumes and improve sludge conditioning properties, the use of thermal hydrolysis process before anaerobic digestion has been adopted with an increase in solids destruction, COD removal, and methane gas. In this study, the evaluation of thermal hydrolysis process as a viable pretreatment strategy to anaerobic digestion has been conducted in order to assess its capacity for solids solubilization. Solubilization experiments were conducted at temperatures ranging from 130 to 170℃ and reaction times between 10 and 60 min. Anaerobic biogas production by thermally pre-treated sludge was carried out through a mesophilic anaerobic digester. The results showed that solids solubilization increased with increases in temperature and time, while temperatures above 160℃ for 30 min strongly affected the sludge characteristics. Ammonia production via deamination by thermal hydrolysis was less significant than protein solubilization at a temperature of 170℃. Both protein and carbohydrate solubilization were more dependent on temperature than reaction time. The enhancement of the biogas production was achieved with increases in temperature as pretreatment of 170℃ yielded 20% more biogas than at 130℃. However, it seems the enhancement was linked to the initial biodegradability of the sludge. / Master of Science

Yes / Positron emission particle tracking (PEPT) was used to visualise the flow patterns established by mixing in two laboratory-scale anaerobic digesters fitted with mechanical mixing or gas mixing apparatus. PEPT allows the visualisation of flow patterns within a digester without necessitating the use of a transparent synthetic sludge. In the case of the mechanically-mixed digester, the mixing characteristics of opaque sewage sludge was compared to a transparent synthetic sludge at different mixing speeds. In the gas-mixed apparatus, two synthetic sludges were compared. In all scenarios, quasi-toroidal flow paths were established. However, mixing was less successful in more viscous liquids unless mixing power was increased to compensate for the increase in viscosity. The robustness of the PEPT derived velocities was found to be significantly affected by the frequency with which the particle enters a given volume of the vessel, with the accuracy of the calculated velocity decreasing in regions with low data capture. Nevertheless, PEPT was found to offer a means of accurate validation of computational fluid dynamics models which in turn can help to optimise flow patterns for biogas production. / The first author was funded via an EPSRC CASE award in conjunction with Severn Trent Water. The second author was funded via a University of Birmingham Postgraduate Teaching Assistantship award.

The main goals of this research are to investigate the anaerobic digestibility of algae and to investigate the effects of growth media on the growth rates, nutrient removal kinetics, and extracellular polymeric substances (EPS) characteristics of wild type green algae. Anaerobic co-digestion of algae with sewage sludge is proposed to improve the digestibility of algae. It is hypothesized that the addition of sewage sludge improves the hydrolysis rate of algae, which is often the rate-limiting step for anaerobic digestion. It is also hypothesized that the composition and concentration of nutrients in growth media will affect the kinetics of nutrient removal and the content of EPS, which will influence algae flocculation and subsequent anaerobic digestion. In this research, algae collected from a local wastewater treatment plant were cultivated in synthetic medium, primary wastewater effluent and pure or diluted anaerobic sludge centrate. Light cycles and the level of CO2 addition were varied at different stages of cultivation for nutrient removal and physiochemical properties of algae. Harvested algae were then anaerobically co-digested with varying proportions of sewage sludge under mesophilic condition. Results showed that when algae were digested alone (i.e. no sludge addition) with a small amount of seed sludge, algae were poorly digested. When algae were co-digested with sewage sludge, the gas yield was improved and the gas phase (CH4 generation) was reached faster. The biogas yield of algae increased to a comparable level to that of digestion of waste sludge when 44% (by VS) of seed sludge was inoculated for digestion. The addition of sewage sludge improved the hydrolysis rate and the overall digestibility of algae. Algae grown in primary effluent, which had a balanced N/P ratio showed a higher nutrient removal efficiency. The P-limitation in sludge centrate led to lower nutrient removal efficiency and higher EPS production compared to algae grown in primary effluent, indicating that sludge centrate was a harsher medium for algae growth. In conclusion, microalgae can grow in primary effluent and anaerobic sludge centrate for nutrient removal. Anaerobic co-digestion of algae withwaste sludge was strongly recommended to enhance the biogas generation.

<p> Biodegradation of benzene, a common groundwater contaminant, occurs readily in the presence of oxygen; however, at contaminated sites, aerobic bacteria often deplete the available oxygen, resulting in anaerobic conditions. Field and laboratory studies have shown that the anaerobic biodegradation of other aromatic hydrocarbons such as toluene occurs readily, while anaerobic benzene biodegradation has only been documented in a handful of studies. Despite these difficulties, benzene biodegradation has been shown to occur under iron-reducing, sulphate-reducing and methanogenic conditions, but not under nitrate-reducing conditions.</p> <p> The goal of this thesis research was to enrich and characterize the benzene-degrading microbial populations in microcosms and transfer cultures derived from soil from four different sites. Cultures were amended with potential exogenous electron acceptors (nitrate, sulphate, ferric iron) and the rates of biodegradation under different terminal electron accepting processes were determined. Sustained, anaerobic benzene biodegradation was obtained in transfer cultures containing less than 1% of the original soil inoculum. The rate of benzene degradation was variable, ranging from 1 μM/d to more than 75 μM/d. Growth of bacteria was linked to benzene degradation under sulphate-reducing and nitrate-reducing conditions. Growth was very slow, with doubling times of 9-30 days estimated by modelling benzene depletion curves to the Monod kinetic equation. The rate of benzene degradation was influenced most by biomass concentration and much less by the terminal electron accepting process.</p> <p> The ratio of moles of electron acceptor depleted to moles of benzene degraded was calculated and compared to the theoretically predicted ratios to confirm putative terminal electron acceptors. Anaerobic benzene degradation linked to iron reduction, sulphate reduction and methanogenesis was observed in enrichment cultures, corroborating results from previous studies. In addition, in some enrichment cultures, benzene degradation was linked to nitrate reduction. This is the first report demonstrating benzene degradation linked to nitrate reduction.</p> / Thesis / Master of Engineering (MEngr)

The influence of Al 3+ on the anaerobic treatment of a poultry slaughterhouse wastewater was studied in this work. The soluble COD (SCOD), volatile acid (VA) concentrations, and methane yield values were measured and compared for zero, 15, and 40 ppm Al 3+ runs. Methane yields of 55.4, 144.2, and 215.4 ml CH4/g. COD for zero, 15, and 40 ppm Al 3+ concentrations, respectively, were observed. Furthermore, SCOD and VAs were not detectable in the reactor that was seeded with 40 ppm Al 3+. It was concluded that inhibitory effects of long chain fatty acids (LCFAs) on aceticlastic methanogens were reduced by aluminum ion. This conclusion was also corroborated by a new mathematical model for estimating the Monod parameters developed in this work. The main characteristic of this new model is that estimated parameters must satisfy some restrictions, which provides consistency for the estimated parameters.

No description available.

No description available.

No description available.