Master of Science By Research

Permanent URI for this collectionhttp://192.248.9.226/handle/123/743

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item: Thesis-Full-text
Climate change impact on the spatial distribution of droughts in Kirindi oya and Maduru oya dry zone river basins in Sri Lanka
(2023) Wijekoon, WMRTY; Rajapakse RLHL
Drought, a consequence of prolonged precipitation deficiencies, is a significant hazard exacerbated by climate change. Sri Lanka, highly susceptible to extreme climatic events, faces drought as its most prominent hazard, necessitating a comprehensive assessment of its impact. This study focuses on the escalating impact of drought intensified by climate change on the Maduru Oya and Kirindi Oya dry zone basins, crucial due to their vulnerability to altered hydroclimatic dynamics. With the substantial contribution of the dry zone to the paddy cultivation of the country, early detection of agricultural droughts is crucial for effective water allocation planning. Recognizing the importance of meteorological droughts as precursors to physical droughts, proactive monitoring and forecasting are essential for planning against subsequent agricultural droughts, while monitoring hydrological droughts is imperative for ensuring a reliable water supply for irrigation and other purposes. Thus, this research primarily focuses on evaluating meteorological and hydrological droughts. The research employs the Standardized Precipitation Index (SPI) and the Streamflow Drought Index (SDI) for the monitoring of meteorological and hydrological droughts, respectively. It considers six CMIP6 (sixth Phase of the Coupled Model Inter Comparison Project) Global Climate Models (GCMs), and the CNRM-HR-1 model was selected as the preferred model. The two future projection scenarios, SSP1-2.6 and SSP5-8.5, were selected for the analysis. In the meteorological drought assessment, maps illustrating the spatial distribution of meteorological droughts were generated for both current and future climate scenarios. In order to generate maps, a future gridded rainfall dataset was developed by developing statistical relationships with the Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS) set and observed precipitation data. For the hydrological drought assessment, machine learning methods, including Recurrent Neural Network and Random Forest Algorithm, were used to predict future streamflow at specific gauging stations, with the Random Forest model selected for its superior performance. Additionally, the climatic indices formulated by the Expert Team on Climate Change Detection and Indices (ETCCDI) were used in this study to monitor the occurrence of climate extremes of precipitation in the past. The meteorological and hydrological drought assessments reveal significant insights into the anticipated impacts of climate change. In the Maduru Oya basin, meteorological droughts exhibit varying percentage increases under SSP1-2.6 and SSP5-8.5 scenarios. Extreme and severe droughts experience increases of 18%, and 16%, respectively, under SSP1-2.6, and 31%, and 2%, under SSP5-8.5. Conversely, the Kirindi Oya basin displays significant susceptibility to extreme meteorological droughts, with increases of 49% under SSP1-2.6 and 37% under SSP5-8.5, particularly with extreme droughts surging by over 35% under both scenarios. Furthermore, the hydrological drought assessment highlights the heightened vulnerability of the Padiyathalawa sub-basin in the Maduru Oya basin, indicating a significant increase in the occurrence of moderate hydrological droughts at the 12-month timescale under both future scenarios. Conversely, the Wellawaya sub-basin in the Kirindi Oya basin also shows susceptibility to frequent moderate hydrological droughts along with an 80% increase in the occurrence of severe hydrological droughts under the SSP5-8.5 scenario at the 12-month scale. Therefore, both basins are expected to face water scarcity in the future, emphasizing the importance of implementing measures to ensure a reliable water supply for irrigation and domestic purposes, given the substantial impact of climate change on watershed hydrology. Keywords: Climate-driven water stress, CMIP6 GCM projections, Drought resilience in water resources, Drought vulnerabilit
item: Thesis-Full-text
Process simulation-based life cycle assessment for fuel-grade bioethanol production from paddy rice straw
(2023) Jayasundara, UWPM; Rathnayake HHMP; Sethunga, GSMDP
For the life cycle scenario of bioethanol production from unutilized rice straw, the life cycle stage of paddy rice cultivation can be excluded with a zero-inventory allocation rule, i.e., rice straw with no applied valorization in current practice. This study evaluates the life cycle net energy analysis, greenhouse gas (GHG) assessment, and comparative life cycle environmental impact assessment for nine (09) scenarios of scaled-up bioethanol production process routes using unutilized rice straw as the feedstock. Three different feedstock pretreatment technologies and three different bioethanol dehydration technologies are incorporated to develop the process route scenarios for scaled-up processing plant models. The process simulation technique is integrated to model the scaled-up production plants to produce bioethanol at 99.7 vol% purity from unutilized rice straw, and the simulation results are retrieved to calculate inventory data for life cycle assessment (LCA). This research aims to determine the most environmentally benign scenario of the process route to produce fuel-grade bioethanol at an industrial scale from unutilized rice straw. The simulated mass flow and energy flow results are comparable with those of real plants, reported in the published literature, which validates the process simulation results in this study. According to the overall results, fuel-grade bioethanol production using rice straw via adopting dilute acid pretreatment technology for feedstock pretreatment and extractive distillation technology for bioethanol dehydration showcases the most sustainable routine from environmental and energy perspectives. Inclusive of energy generation using the waste flows in the process (i.e., spent wash and solid residues), the life cycle net energy analysis results show a net energy gain of 7,804.0 MJ/m3 of bioethanol with a net renewable energy gain of 38,230.9 MJ/m3 of bioethanol that corresponds to a net energy ratio of 1.20 and renewability factor of 5.49 for the base-case scenario developed for Sri Lankan context with dilute acid pretreatment and extractive distillation. The life cycle GHG assessment exhibits a net global warming potential of 584.8 kg CO2 eq/m3 of bioethanol. The effect of system boundary expansion up to the end-of-life stage as gasohol (E10), the sensitivity of the key process parameters, and the economic benefit via valorization of unutilized rice straw are further analyzed and discussed. Keywords: Bioethanol production, Unutilized rice straw, Simulation integrated LCA, Net energy analysis, GHG assessment
item: Thesis-Abstract
Investigation on stability of dry anaerobic flow reactors treating lignocellulose biomass
(2023) Weerasooriya DP; Rathnasiri PG
Anaerobic co-digestion is a prominent and environmentally friendly technology in agricultural, domestic and industrial bio waste management. It is the most economical and effective method for treating animal waste bedded with lignocellulosic agriculture waste as anaerobic co-digestion of lignocellulosic waste with animal manure proceeds effective C/N ratio and regular nutrient supply mainly from manure in fact it is enriched with different types of nutrients. Lignocellulosic structures are mainly consisted of carbon and hydrogen which resulted in creating lower operating pH values via acidification during its hydrolysis phase. All intermediary steps in digestion process coexist with each other. Thus, an inhibition in a single step can directly affects the entire operation. Main inhibitory substances in AD are undissociated VFA and Free Ammonia Nitrogen (FAN). The main objective in the research is to increase pH by improving buffer capacity via facilitating alkaline and nitrogenous compounds into the system to reduce undissociated VFA concentration. Conversely, use acclimatizing feeding technique to increase the tolerance against FAN inhibition. Experiments were conducted in two reactor configurations namely Plug flow reactor (PFR) and Semi batch reactor (SBR). As continuous mixing in high solid digestion process reported instabilities at high OLRs, performance of the semi batch reactor was investigated at different mixing conditions. Cattle manure was collected from a farm in Carcassonne France. In order to facilitate substantial alkalinity for proper buffering capacity, inoculum was prepared by mixing granular sludge with digestate obtained from a pilot scale anaerobic batch reactor which treated chicken manure bedded with straw. In order to facilitate step wise increase in ammonia concentration, weekly OLR was started from 0.71gVS/L.d and increased gradually by 20% each week. Both systems were continuously monitored by measuring relevant parameters. In SBR, Optimum specific methane yield (SMY) and specific methane production rate (SMPR) were achieved at OLR of 3.07gVS/L.d. and 3.69gVS/L.d. respectively. They were 0.170NLCH4/g.VS and 4.08NLCH4/L.d. In PFR, optimum SMY and SMPR were achieved at OLR of 5.35gVS/L.d. They were 0.197NLCH4/g.VS and 7.37NLCH4/L.d respectively. Better results were obtained in PFR with compared to past investigations mainly due to higher withstand ability for VFA and FAN inhibitions. PFR can be iii recommended to utilize for treating cow manure co-digested with different substrates which include higher biodegradable organic content with lower lignocellulosic content such as fruit and vegetable waste under given acclimatizing feeding technique. SBR should be operated with lower mixing intensities.
item: Thesis-Abstract
Development of a computational fluid dynamics model for pollutant dispersion in complex terrain
(2023) Sivakunalan I; Narayana M
This research investigated the issues of vehicular-emitted pollution in Kandy City, a valley-like environment experiencing severe air pollution problems due to a higher traffic volume, topographical aspect, and prevailing weather conditions. The COPERT emission model was used to calculate the total emission rates of 𝑁𝑂 , 𝐶𝑂, and 𝑃𝑀 in major road segments of the city. An OpenFOAM-based CFD model was developed to predict dispersion characteristics over the complex terrain, considering physical phenomena such as surface roughness, wind shear, Coriolis’s effect, surface heat flux, buoyancy effect, and turbulence. The developed model was validated against experimental results to investigate its sensitivity and efficiency, and it was found to show good agreement. 2 The developed CFD model was then applied to simulate the dispersion of vehiculargenerated air pollutants in Kandy City, considering the region’s two main wind patterns NE and SW, topography, and emission rates of major road segments. The model’s concentration and dispersion pattern of pollutants were found to vary with urban topography and wind pattern, with higher concentrations of pollutants observed in areas with high traffic volume and severe traffic congestion, such as the central business district and areas close to bus stands. The model was also used to investigate pollution dispersion patterns in 27 locations at the pedestrian level, with good agreement found between the model’s predicted concentrations of 𝑁𝑂 and experimental results. Overall, this study highlights the significance of considering topography and me- 2 teorological conditions when evaluating pollution dispersion mechanisms in urban environments. The developed CFD model can be used as a promising tool for predicting pollutant transport and wind flow in the built environment, aiding in proper urban planning to reduce pollution accumulation in significant locations. This research can contribute towards effective policies and interventions to mitigate the impacts of vehicular-generated air pollution in valley cities.
item: Thesis-Full-text
Investigation of the effect of preprocessing parameters on the efficacy of chlorophyll removal from mychonastes homospaera for biofuel production
(2021) Kulasinghe KBYM; Ariyadasa TU
Microalgal lipids have become a potential candidate for biofuel production in recent years. High lipid accumulation and shorter doubling time enabling higher growth rate are foremost factors in microalgae to compete with first and second-generation biodiesel feedstocks. However, high levels of chlorophyll in feedstock limit its large-scale application. Chlorophyll makes oil more susceptible to photo-oxidation, decreases the storage stability, causes low-quality oil with a dull and dark color, and decreases the transesterification efficiency and combustion efficiency of biodiesel. This study aimed to develop a novel preprocessing method to identify the best solvent ratios, temperature, and reaction time for chlorophyll removal from the selected microalgae to synthesize high-quality biodiesel. Mychonastes homosphaera isolated from Beire Lake, Colombo, Sri Lanka with a doubling time, and the lipid accumulation of 2.89 d and 58 % (w/w) was selected for the study. The results indicated that the best solvent ratio (NaOH: ethanol), temperature, and reaction time were 7:3, 60 0C, and 90 min, respectively.
item: Thesis-Full-text
Assessment of the feasibility of co-production of fucoxanthin, omega-3 fatty acids and bioethanol from marine microalgae
(2021) Premarathne R G M M; Ariyadasa TU; Attalage R A
The marine microalga Tisochrysis lutea is renowned for its ability to synthesize fucoxanthin and docosahexaenoic acid (DHA), which are nutritionally valuable high- value compounds. Although numerous studies in literature have assessed fucoxanthin and DHA production by T. lutea, very few have evaluated the feasibility of comprehensively utilizing biomass for co-production of these metabolites within the framework of biorefineries. To this end, the current study focused on the synthesis of fucoxanthin and DHA by cultivation of T. lutea under two different initial nitrate concentrations (1x: 882 μM, 3x: 2,646 μM) and three different illuminance levels (LL: 3,750 lux; ML: 7,500 lux; HL: 11,250 lux). The maximum fucoxanthin yield of 8.80 ± 0.30 mg/L (14.43 ± 0.52 mg/g) and DHA yield of 7.08 ± 0.02 mg/L (11.90 ± 0.14 mg/g) were achieved in the 3x HL culture at the end of 16 days of cultivation. Thereafter, a biphasic solvent extraction procedure using ethanol/n-hexane/water (10:9:1 v/v/v) was utilized for co-extraction of 97.96 ± 0.54% fucoxanthin and 74.11 ± 1.49% DHA from 3x HL biomass, and products were separated into two fractions. Fermentation of the residual biomass obtained from co- extraction resulted in a bioethanol yield of 48.49 ± 0.58 mg/g. Thus, results showcase the efficacy of the developed co-extraction procedure and the biorefinery potential of T. lutea.
item: Thesis-Abstract
Development of a biogas combustion CFD model for the analysis of trace emissions
(2021) Bandara AMJN; Narayana M; Bayer C
Biogas is emitted from landfills, anaerobic digesters, and many other biomass sources. Emitted biogas is usually burnt in order to reduce greenhouse effect and to get energy. Burning of biogas emits several pollutants, mainly CO 2 . Reducing the of emissions is very important in combustion. Emissions of combustion can be analysed experimentally or by computer simulations. Experiments are very accurate and expensive. Computer simulation is an economic way of analysing combustion systems. In this study emissions of biogas combustion are analysed with computer simulations. There are several methods of reducing emissions in combustion such as excess air control, air staging, fuel Staging, flue gas recirculation etc. In this study, the effect of excess air in biogas combustion is analysed. The range of optimum equivalent ratio was found as 0.85-1.1. Emitted gasses get dissipated in the atmosphere with the wind. The environmental effect from emissions of a 20kW industrial biogas burner in Colombo area was analysed using CFD simulations. Results show that the ground level is below environmental standard limits. , NO x and SO 2
item: Thesis-Full-text
Modelling the drying kinetics of microwave drying of coconut chips
(2020) Muhammed Aadhil MFH; Amarasinghe ADUS; Narayana M
Drying of coconut chips has been of interest for research due to the commercial value of coconut oil and desiccated coconut. More recently the industry has called for cost effective solutions for the drying unit operation of coconut chips used in the production of virgin coconut oil and desiccated coconut. This study was carried out to identify the parameters on which microwave assisted coconut drying kinetics were impacted and a mathematical model was developed to predict the microwave assisted drying behaviour of coconut chips. Drying time of coconut was found to depend on the microwave power and the mass loading when external parameters such as air velocity, air humidity, and shape factors of the coconut chips were kept constant. The drying behaviour was accurately predicted by several thin layer drying models and the Page model was selected due to its accuracy and simplicity. A new model was proposed to represent the parameters of the Page model as a function of microwave power. The proposed new model is given by, 𝑀𝑅=𝑒𝑥𝑝(𝑎.𝑒𝑥𝑝(𝑀𝑃).𝑡(𝑐.𝑃+0.6)) where, a = -0.07 min-1, M=37.29 Js-1 and c = 0.0007 sJ-1. Parameter t (time) needs to be substituted in minutes and P (power) in watts (W). Moreover, the impact of mass loading was found to be effective only when the ratio of microwave power to mass loading (MPML) factor exceeded a value of about 3.7 Wg-1. Under this condition, the diffusivity per unit of microwave power was found as 1.31×10-11 m2s-1W-1. A sharp decrease in the drying rate was observed when the moisture content approached approximately 30 % (w/w dry basis), indicative of changing from the removal of free moisture to removal of bound moisture. The quality of the desiccated coconut and virgin coconut oil were analysed based on the standards stipulated by the Sri Lanka Standards Institute and Coconut Development Authority. A process development road map was proposed based on the drying kinetics, rehydration ratio, cooling time and maximum temperature to meet the quality requirements.
item: Thesis-Full-text
Single and binary adsorption of nickel and zinc ions from aqueous solutions using coirpith as the adsorbent
(2020) Ranasinghe EN; Amarasinghe BMWPK
This study analysed the competitive adsorption of multicomponent systems onto coir pith, readily available and environmentally friendly adsorbent chosen for the study. The efficacy of unmodified coir pith as an adsorbent as well as its physical and chemical characteristics were studied to analyse single and binary systems of nickel and zinc adsorption onto coir pith as well as the effects of temperature, concentration, adsorbent dose and pH to determine the optimal conditions for adsorption. The equilibrium data for the single system adsorption of nickel and the single system adsorption of zinc at 30 °C was analysed using the Langmuir and Freundlich isotherm models while the multicomponent adsorption was analysed using the Langmuir, the Freundlich, the competitive Langmuir, the non-competitive Langmuir, the modified competitive Langmuir and the Langmuir Freundlich isotherm models. The single system adsorption data for both nickel and zinc fit the Freundlich model which showed the adsorption surface was heterogeneous. The multicomponent adsorption system data fit the Langmuir isotherm model the best which showed the adsorption surface formed a monolayer. Most adsorption occurs at a higher pH value. To decrease costs and possibility of metal hydroxide precipitation the adsorption should be carried out at a neutral pH. The kinetics of single system and binary system adsorption of nickel and zinc was studied using Lagergren pseudo first order model, pseudo second order model and the intraparticle diffusion model. The experimental data showed all of the systems could be described using pseudo second order model which shows adsorption occurs primarily through chemisorptions. In the single system the coir pith had a higher capacity for zinc than nickel. In the single system adsorption of nickel the adsorption increases with temperature which shows the adsorption of nickel is an endothermic process. In the zinc single systems the adsorption decreased when temperature increased which shows zinc adsorption is an exothermic process. In the adsorption capacity in the binary system is less than either of the single systems which prove in the presence of competitive species metal ion adsorption is hindered. The data was analysed using the Intraparticle diffusion model which showed intraparticle diffusion in the nickel single system and in the zinc single system at 30 °C but little to no intraparticle diffusion at higher temperatures or in the multicomponent system The FTIR analysis of the surface of coir pith before and after adsorption shows that adsorption decreases the presence of hydroxyl (-OH) bonds. This confirms the results of the kinetic analysis that the adsorption is a chemical process which breaks and forms bonds with the functional groups on the coir pith surface. The metal ion forms a complex with the polar surface functional groups during adsorption and the metal ion remains bonded to the surface even when the adsorbent is removed from the water and dried. This confirms coir pith is an effective adsorbent for the removal of heavy metals from aqueous solution. To optimise multicomponent adsorption of nickel and zinc it should be carried out close to 30 °C in a solution of neutral pH and allowed to reach equilibrium.
item: Thesis-Abstract
A Three dimensional computational fluid dynamics model for pyrolysis of thermally thick biomass particles
(2020) Wickramaarachchi WAMKP; Narayana, M
The solid biomass especially the wood has been used as a source of energy for centuries in the world. However, the present world has started giving it a more value not because it is known for a longer time. But as a renewable energy source it lessens the fossil fuel depletion and be a part of climate change mitigation. Conversion of biomass to energy is done through several methods such as bio-chemical conversion and thermo-chemical conversion. In the present work, the drying and pyrolysis process of a thermally thick single wood particle has been investigated. A novel approach has been introduced considering the two-phase gas and solid inside the particle are not in thermal equilibrium. Mathematical relationship was built to determine distinct temperatures at the boundaries of solid and gas. An unsteady threedimensional (3D) model is developed and simulated in Computational Fluid Dynamics (CFD) framework. The Euler-Euler approach for modeling of single biomass particle has been succeeded with the help of C++ CFD toolbox in OpenFOAM. The 3D model can simulate the thermochemical conversion process of different particle types, particularly for different shapes to examine the spatial variations during the process. The model was validated by comparing the simulation results with data obtained by experiments conducted using a single particle reactor. Further, the model was applied in torrefaction of single wood particle then expanded to thermochemical conversion in packed bed.
item: Thesis-Full-text
Evaluation of moisture diffusivity in copra at different drying condition
Mendis, ARL; Amarasinghe, ADUS; Narayana, M
Copra is one of the major traditional products processed from coconuts and is used primarily as a source of coconut oil. It is the kernel of coconut after reducing the moisture content from about 50% (dry basis) to about 6% (dry basis) by drying. Traditional drying processes are vastly used in manufacturing of copra and that has created many quality problems leading to hygienic and health issues which can be minimized by using controlled drying techniques. Controlled drying is also a primary requirement in producing edible copra and premium products like virgin coconut oil. Accurate prediction of moisture diffusivity of porous materials like food under given conditions is important in analysing the drying process. In this study drying behaviour of copra was examined and two methods were suggested to predict the moisture diffusivity of copra. In the first method, the moisture diffusivity of copra was determined for the first and second falling rate periods. A critical moisture content of 30% (dry basis) was identified as the probable limit between the first and second falling rate periods. A computational fluid dynamic model was used to fine-tune the system parameters with experimental data and the effective moisture diffusivity values at 55 ºC for first and second falling rate periods were found to be 1.10 × 10-8 and 1.99 × 10-9 m2s-1 respectively. In the second method, moisture diffusivity of copra was found as a function of drying temperature and dry basis moisture content. Drying experiments were performed for seven different temperatures in the range of 45 – 75 ºC to obtain drying curves of copra. The moisture diffusivity was found to be an exponential function of moisture content where the model parameters were linearly varied with temperature. Further the volume shrinkage of copra was linearly correlated with moisture content. A three-dimensional numerical model was developed to predict the spatial distribution of moisture inside the copra using computational fluid dynamics (CFD) with OpenFOAM software. Results of the spatial moisture distribution were graphically presented. The results of simulation were in agreement with the experimental observations and the optimum temperature for drying of copra was found to be about 60 ºC for 20 hours of drying time.
item: Thesis-Abstract
Development of a pilot-scale biogas plant to utilize biomethane as a transport fuel
Kularatna, MADIC; De Alwis, Ajith
This project was to develop a system to utilize Biomethane as a transport fuel. It was started at the Department of Chemical and Process Engineering, University of Moratuwa funded by the Ministry of Science and technology. In this project, initially a suitable process was developed to produce biogas utilizing food waste obtained from university canteens and upgraded as a vehicle fuel. Then the pilot-scale biogas plant was designed and construction ofthe building and fabrication of equipments were preceded. Initially laboratory scale experiments were conducted to find out the design parameters such as analysis of food waste, composition for optimum gas production rate, etc. According to that, the total solid content (TS) is 37% and total volatile solid content (TVS) is 23%. The best composition for optimum gas production is 10% solid in the slurry. The pilot-scale biogas plant was operated and produces biogas utilizing food waste and upgraded using a water scrubber to remove C02 and H2S. After that, the cleaned gas, which is having a composition of 85% CEU, was used as a vehicle fuel. For the initial trials, biogas was replaced with LPG in a LPG three-wheeler without any modification to the three- wheeler system and it was successfully operated. According to the emission tests carried out for biogas vehicle fuel, it shows that it is operating environment friendly than gasoline.
item: Thesis-Full-text
Study of the effects of binding agents on the properties of compost pellets
Hettiarachchi, LG; Gunawardena, SHP; Fernando, S
Composting of the organic Municipal Waste (MW) is one of the sustainable answers for the management of MW. The bulky nature of the loose compost is one of the main drawbacks in promoting the use of compost in agriculture governed by various practical and economic reasons. Pelletization of compost seems to be the solution to offset the drawbacks caused by loose compost. The pelletizing process with a die and roller pelletizer is comparatively less complex compared to other common pelletizing methods. This research identified the optimum conditions to form a pellet with the desirable properties of high density, compressive strength, ideal pellet length and disintegration ability with three mesh sizes (2.5 mm, 3.5 mm, and 5 mm sieves), five moisture contents (25%, 30%, 35%, 40%, and 45%), three binding agents (Rice Flour (RF), Lime, Eppawala Rock Phosphate (ERP)) and three different binding agents’ percentages (1%, 2%, and 3%) by weight basis. The pelletizing process increases the bulk density of compost by about 30%. Pellets made with ≤ 5mm particles are longer and show higher strength (50% more) than those prepared with the other two particle sizes (≤ 2.5 mm & ≤ 3.5 mm). It was evidenced that 25% moisture content produces the highest strength pellets than higher moisture contents. Pellets with binding agents at ≤ 5mm particle size and 25% moisture content were tested for bulk density, strength, percentage of long pellets and disintegration ability. It was observed that the tested properties have varied compare to pellets without binding agents. Lime and ERP showed promising results that enhancing pellets’ bulk density and compressive strength and percentage of long pellets than RF. However, the disintegration ability nearly 100% in RF added pellets, which was less than 30% and 10% in ERP and Lime respectively and 0% in non-binding agent added pellets over one month of time in immersed water. With the increasing weight percentages of the binding agents, pellets strength increased in Lime and ERP and the same decreased with RF. Disintegration ability improved in RF and increased with the increased weight percentages. Same decreased in Lime and ERP and when increase the binding agents’ weight percentages, longer the time to disintegration the pellets.
item: Thesis-Full-text
Effect of enzymatic hydrolysis pretreatment on batch anaerobic digestion of wastewater generated in desiccated coconut processing plants
(2019) Samarasiri BKT; Rathnasiri PG
Enzymes are widely used to accelerate the biochemical reactions in biological wastewater treatment processes. Commercially developed enzymes such as amylases, proteases and lipases improve microbial biodegradation by accelerating the hydrolysis rate of carbohydrates, proteins and lipids. In this study, wastewater generated in desiccated coconut processing plants were pre-treated with lipase originated from porcine pancreas and then anaerobic digestion was performed to evaluate the effect of enzymatic hydrolysis pre-treatment. Hydrolysis pre-treatment was performed using three different concentrations of lipase i.e. 0% enzyme, 0.01% (w/v) enzyme and 0.1% (w/v) enzyme. Following hydrolysis pre-treatment, anaerobic batch digestion was performed in twenty-four 50 ml reactors under two scenarios i.e. scenario 1: twelve reactors under pH adjusted condition and Scenario 2: 12 were pH not adjusted. Under scenario 1, hydrolyzed pre-treated wastewater samples with three separate enzyme concentrations i.e. 0%, 0.01% and 0.1% were used as substrates and at each enzyme concentration four different inoculum to substrate ratio in volume basis of 1:4, 2:3, 3:2 and 4:1 were used. Similar procedure was followed under Scenario 2 as well. All anaerobic batch experiments were conducted under atmospheric temperature of 31±1°C and pressure of 0.997±0.002atm. Batch experiment was conducted for 60 days and during this period, samples were analyzed. The highest initial biogas production rate of 25.43 ml/day and highest average gas production rate during first 10 days of 7.16 ml/day were achieved for the sample with 0.1% lipase at inoculum to substrate ratio in volume basis of 2:3 under scenario 1. Following 60 days of complete degradation, for the same sample, experimental bio-methane yield of 42.75 mlCH4/gVS substrate added, cumulative biogas production of 95ml, cumulative methane production of 81.55ml, TS reduction of 51.77% and VS reduction of 67.68% were also achieved. The wastewater generated in desiccated coconut processing plants consists of high concentrations of medium chain saturated triglycerides. These triglycerides were hydrolyzed quickly when enzyme was added during enzymatic pre-treatment, resulting higher initial biogas production rate in the beginning as well as higher daily biogas production rate during first 10 days. The initial biogas production rate and daily biogas production rate during first 10 days of the initially pH-adjusted samples into pH 7.0 showed higher biogas production rate than pH not adjusted samples because it was the most favorable pH value for the methanogens for their optimal growth. The bio-methane potential increased when the inoculum to substrate ratio decreased because quantity of hydrolyzed triglycerides available for the anaerobic microorganisms to convert into methane gas was higher. The bio-methane yield of enzyme added samples were much higher than the enzyme iii not added samples because enzymes accelerated the hydrolysis of lipids. According to this research study, it can be concluded that adding enzymes will improve the batch anaerobic digestion process of wastewater generated in desiccated coconut processing plants.
item: Thesis-Full-text
Rice bran based nanofibers for stabilization of phytase enzyme
Rathnayake, UA; Kottegoda, N; Gunawardena, SHP
Phytases is an enzyme belonging to the histidine acid phosphatase family which has the capability to initiate the stepwise dephosphorylation of phytate, the primary storage form of phosphorus in most seeds and cereal grains. Phytase enzyme has become the most widely used enzyme in the world, particularly in poultry and swine industries as a source for the dephosphorylation of phytic acid, the primary storage form of phosphorus in most seeds and cereal grains. The problem involved with the phytase applications in animal feed is its thermal instability. Hence, a substantial thermal stabilization of the enzyme is required to increase its practical applications. In this research, phytase enzyme was stabilized in to agro waste based nanaofibers. Nanofibers with a fiber diameter ranging from 30 - 50 nm were produced successfully using electrospinning techniques. For the best of our knowledge only few researches have reported on the nanofiber synthesis from agro waste and probably this could be the first study that reports the use of rice bran for this purpose. # First, rice bran received from a local mill was characterized and the soluble fiber fraction without any fat was isolated. This fiber solution was used for electrospinning. The apparatus containing the high voltage supply, electrodes, solution input compartment and the collector plates were fabricated in-house and the instrument was automated prior to electrospinning of fibers. The initial polymer solution parameters such as pH, viscosity, and conductivity were adjusted in order to facilitate the spinning process. The solution viscocity was modified using a food grade bio-polymer, polyvinyl alcohol (PVA). Then, the spinning parameters such as accelerating voltage, distance between the two electrodes, PVA content were optimized to result in nanofibers with uniform diameter. After achieving the best conditions for electrospinning, two different techniques were investigated to encapsulate phytase enzyme in to nanofibers synthesized from rice bran. First, attempts were made to in-situ encapsulatie the phytase enzyme into nanofibers. Here, electrospinnig process was carried out in the presence of phytase enzyme in the initial polymer solution followed by cross-linking of the fibers using boric acid. Secondly, phytase enzyme was immobilized into the nanofibers as a post modification after spinning followed by cross linking with sodium tripolyphosphate. The activity of the phytase enzyme in the encapsulated product was established at the gutter pH. 2.5 and at different temperatures up to 170 °C . The presence of nanofibers was essential to offer a large surface area for large amount of enzyme encapsulation. The morphology and the size of the fibers were studied using scanning electron microscopic technique and the elemental composition was determined using energy dispersive X-ray analysis. It was possible to produce nanofibers with uniform diameter between 30 - 50 nm by this technique. However, when the phytase enzyme was encapsulated a beaded-string like morphology was observed. The bonding and extent of encapsulation was studied using Fourier transform infra-red spectroscopy FT-IR).'Any changes in the peak positions or shape allowed predicting about the nature of bonding. Based on the FTIR data it was confirmed that the enzyme was H-bonded to the nanofiber surface. Differential scanning calorimetric studies further confirmed the successful encapsulation of the phytase enzyme. Melting point of the enzyme has increased by 40 °C due to the encapsulation. Thermal stability of the final product was investigated using thermogravimetric analysis (TGA) technique. It was observed that the decomposition temperature of the enzyme has increased from 238 °C to 348 °C due to the encapsulation. Interestingly, as expected it was found that the thermal stability of the enzyme has increased almost by 100% after encapsulated into the nanofibers followed by crosslinking. It was found that the pure enzyme loses its activity at 70 °C while after encapsulafion into nanofibers based on rice bran, it is active up to 170 °C.
item: Thesis-Abstract
Encapsulation of nanoparticles in layered materials to be used in agricultural applications
Madusanka, AN; Kottegoda, N; Ismail, M
Layered materials, which consist of stacks of layers, where the thickness of those layers occur, in the nanometer scale with interlayer charge balancing ions are interesting due to their potential applications in catalysis, biomedical applications, environmental remediation and controlled/ slow release applications in agriculture. Montmorillonite (MMT) is one of the smectite type clay composed of tetrahedral sheets of silica sandwiched between octahedral sheets aluminaand it can be used as a stable host matrix for storage, and delivery of encapsulated plant nutrients, which are released in a given medium for extended periods in a sustainable manner. In an attempt to address the unsolved problems in fertilizer use in agricuhure which is the loss of nitrogen due to leaching and evaporations as gaseous matter, a controlled release fertilizer nanocomposite formulation based on montmorillonite clay was developed. The resulting nanocomposite was prepared by the encapsulation of urea modified hydroxylapatite nanopartiles into montmorollinite clay. The resulting nanocomposites were characterized using a number of solid state characterization techniques such as Powder X-ray Diffraction (PXRD), Fourier Transform Infrared spectroscopy (FTIR) and Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and Thermogravimetric Analysis. The release behavior of the nutrients in ^ the fertilizer compositions were studied in acidic soils (pH- 4.2 and pH -5.2) and in neutral sandy soil for over 60 days. The release bahaviour was compared with a commercial NPK fertilizer composition, which is currently used in tea industry. A sustained release of nitrogen was observed for the two acidic soils with the new fertilizer composition. iii
item: Thesis-Full-text
Optimization of process parameters of fluidized bed biomass combustor using CFD modeling
(2018) Wickramasinghe, DGC; Narayana, M; Amarasinghe, ADUS
The present work is focused on mathematical modelling of fluidized bed combustion of biomass by means of computational fluid dynamics (CFD). Introducing a stable CFD solver for combustion of solid fuel with Large-Eddy Simulation (LES) turbulence modeling and diffusion corrective velocity is the novelty of this study. A great part of the work is devoted to development of a reliable algorithm to solve the fluidized bed combustion model and to improve the accuracy of simulation results. A three-dimensional transient model is developed with a special emphasis on the conservativeness property of energy and mass. The second part of the work is devoted to development of C++ libraries for the open source CFD tool kit OpenFOAM for coupling fluidized bed model with gas phase combustion. The created CFD solver has capability to adept with wide range of application of fluidized bed combustion. The presented results contribute to better understanding of numerical modelling and simulation of fluidized bed combustion, especially optimizing of combustor geometries. The performance of fluidized bed biomass combustor depends on the turbulence of freeboard. The optimum amount of secondary air ratio is 1.6%, which gives higher freeboard temperature while maintaining minimum emission. The optimum excess air ratio is 10% for 0.1125 kg/h. In the case of suspension combustion, maximum combustor temperature has been obtained for optimum airflow, which was 5.5 ms-1 of inlet air velocity for a 0.00171 kg/s of fuel feeding rate (65% amount of excess air).
item: Thesis-Abstract
Simulation and optimization of up flow anaerobic sludge blanket reactors (UASBS) in a dairy waste water treatment plant
Godawita, AS; Rathnasiri, PG
Anaerobic digestion is commonly used in industrial waste water treatment applications and it is a combination of many biochemical and physicochemical processes. Modeling and simulation of an anaerobic digestion is very vital to identify the behavior of industrial waste water treatment plant to optimize its operations. In this research, anaerobic digestion model called ADM1(Anaerobic digestion model no 1) developed by IWA task group is applied to model and simulate UASB reactors. ADM1 model comprises with dynamic state variables which represent all biological and physic chemical reactions. This model was built in simulator called Aquasim 2.1f (Reichert, 1998).To model UASB reactors, simplified model is proposed based on different research compartments.UASB modeled by simulator taking as three CSTR compartments named sludge bed, blanket and settler. Influent for experimented waste water plant is waste water generated from dairy plant. Experiments were conducted at waste water treatment plant (WWTP) under three volumetric flow rates 10m3/d,15m3/d and 25m3/d. plant is actually operates at 25m3/d. Three parameters such as cumulative gas volume, pH and COD were measured. At the same volumetric flow rate WWTP was simulated with the new model and parameters such as VFA, gas composition ,inhibition and biomass growth rates were obtained. By varying recycle ratio from bed to blanket and settler to blanket, appropriate recycle ratio is replaced to get best fitted model. (bed to blanket-0.8 and settler to blanket 0.6). Optimization was performed under two scenarios.ie by varying volumetric flow rates and input COD level. it was found that above 30m3/d UASB become unstable producing 21% of CH4 and 75% of CO2 .Also it can be found that 7500mgCOD/l can be treated at the volumetric rate of 30m3/d without any instability
item: Thesis-Full-text
Computational fluid dynamics modeling of thermo-chemical processes in an updraft biomass gasifier
(2016-09-15) Fernando, N; Narayana, M
Biomass is recently gaining popularity in industry as a promising source of renewable energy. Gasification of biomass is a major thermal conversion method to improve the efficiency of raw biomass fuel. It is a process by which biomass is partially oxidized to produce a combustible gas named Syngas; a mixture of carbon monoxide, hydrogen and methane. Although the gasification technology is used throughout the history and there are a large number of gasification plants worldwide, their smooth operation remains questionable. This is due to a lack of understanding of proper design criteria. In order to gain insights to optimal design parameters, mathematical models and computer simulations based performance analysis can be used. Recently Computational Fluid Dynamics (CFD) analysis has been applied by many researchers as a tool for optimizing packed bed processes including gasification process. In this research study, a two dimensional CFD model has been developed for an updraft biomass gasifier. The model uses air as the gasifying medium and a fixed batch of biomass. The model is capable of tracking the movement of interface between solid packed bed and gas free board due to bed shrinkage. The two phase model is developed using the Euler-Euler approach. The model consists of several sub models, including reaction models, turbulence model for packed bed gas phase and free board, a radiation model for solid phase, a bed shrinkage model, and interphase heat transfer models. The final mathematical model is converted into a numerical model using open source CFD tool OpenFOAM. Required code was developed by using C++ language in OpenFOAM package, including all the relevant differential equations and procedures in the CFD model. To validate the CFD model, simulation results for gas temperature and gas compositions are compared against experimental gas temperatures and compositions measured from an operational laboratory gasifier. The validated model is used to perform air flow rate optimization. A series of CFD simulations were performed for air flow rates ranging from 3 m3/hr to 10 m3/hr for a computational geometry corresponding to the experimental gasifier and cumulative CO was calculated. It is found that cumulative CO production maximized at 7 m3/hr airflow rate. The maximum cumulative CO volume was 6.4 m3.
item: Thesis-Full-text
Environmental assessment of parboiled paddy production by life cycle assessment
(2016-09-15) Nadeeshani, E; Gunasekera, M.Y.
Rice is the most popular food in Sri Lanka where approximately 70% of the paddy production goes through the parboiling process. Parboiling process is a hydrothermal treatment method. This treatment process consumes energy, water and other environmental resources and adds air and solid emissions, effluents and wastages back to environment which cause adverse environmental impacts. Total environmental input and output emissions of the parboiling process depend on the selected treatment method and the type of equipment used. Therefore the total environmental effects of each and every step in the life cycle of the production process needs to be considered in order to identify the most environmental friendly paddy parboiling method. The overall objective of this work is to assess environmental impacts of different parboiled paddy production methods adopted in Sri Lanka by using life cycle assessment (LCA) approach. LCA is a methodological context to estimate the environmental effects caused by the life cycle of a product, service or process. Goal and scope definition, life cycle inventory analysis, life cycle impact assessment and interpretation are the four major steps in LCA methodology. The environmental performance of three parboiling methods named as modern method with hot soaking and mechanical drying, modern method with hot soaking and sun drying and semi modern method with cold soaking and sun drying were assessed and compared quantitatively and qualitatively. Processes from paddy harvesting to rice cooking are included in the system boundary. According to the results, highest impact of parboiled rice production is given by the cooking step. The highest impacts from cold soaking operation method were observed in eutrophication, depletion of abiotic resources and climate change impact categories. The hot soaking method resulted highest impacts on human toxicity, photo oxidant formation and acidification.