Pyrolysis of algal biomass and coal in a rotary kiln reactor: Pyrolysis behaviour, product distribution and kinetic analysis
- Authors: Nyoni, Bothwell
- Date: 2023-12
- Subjects: Algal biofuels , Biomass energy , Coal -- South Africa
- Language: English
- Type: Doctorate theses , text
- Identifier: http://hdl.handle.net/10948/62550 , vital:72823
- Description: There are two primary reasons why the global economy is gradually reducing its dependence on coal as an energy source. Firstly, coal reserves are finite, and while some argue that current reserves will last for generations, the reality is that coal is a non-renewable resource. Secondly, the emissions associated with coal usage have adverse effects on both the environment and human health. While European countries have adopted seemingly aggressive strategies to replace coal and other fossil fuels, South Africa and other developing nations face economic constraints that limit such actions. Fortunately, there are more conservative approaches that can be employed, one of which involves a gradual introduction of renewable energy sources into the energy grid. Wind, solar, and biomass currently stand as the major renewable energy sources under consideration. However, it's worth noting that the intermittent nature of wind and solar energy production poses a significant challenge. Biomass holds the potential to replace coal in retrofitted coal-fired plants. However, the unchecked utilisation of biomass can lead to deforestation and have adverse effects on the human and animal food supply chain, as many essential food items are derived from plants. The debate over using biomass as a fuel source, especially when some types of biomasses can serve as food for humans and animals, has been a subject of ongoing discussion. Furthermore, biomass exhibits a lower energy density when compared to coal. Combustion stands as the primary technology for converting coal into energy and is widely used in most coal-based power plants. Gasification, on the other hand, has been employed for years in South Africa as a coal-to-liquids technology to supplement transportation fuel requirements and reduce reliance on crude oil imports. Pyrolysis, too, has found application as a key method for obtaining high-energy coal char, serving both as an energy source and a reducing agent in blast furnaces for the steelmaking industry. Pyrolysis technologies are gaining popularity in biomass-to-liquids processes due to their simplicity. Currently, there is growing research interest in simultaneous pyrolysis of coal and biomass. The study presented in this thesis focuses on investigating the pyrolysis of Scenedesmus algae biomass and low-grade coal in a small-scale rotary kiln, with particular emphasis on the synthesised liquid products. Algae represent a unique type of biomass that can be cultivated in photo-bioreactors with minimal use of agricultural land. This suggests significant potential for large-scale cultivation of algae, and ongoing efforts are exploring strategies for the mass production of algal biomass.Firstly, pyrolysis studies were carried out via thermogravimetric analysis instruments. It was revealed that because of algae’s considerably higher volatile content and lower carbon content when compared to coal, the pyrolysis process of algal biomass occurred at a faster rate. The highest pyrolytic reactivity of algae was 0.41 mg/min occurring at approximately 290 ᵒC in comparison with coal’s 0.06 mg/min occurring in the approximate temperature range of 550 – 600 ᵒC. The magnitude of the reactivity of the blends depended on the coal/algae ratios used. Furthermore, kinetics analysis revealed that the overall pyrolytic decomposition of coal followed 2nd order kinetics with an activation energy of 81.8 kJ/mol. The decomposition of algae and coal-algae blends occurred in two stages; the first stage decomposition followed 2nd order kinetics with activation energies in the range 130.3 – 145.5 kJ/mol. The second stage decomposition of algae followed 1st order kinetics with an activation energy of 27.3 kJ/mol, whilst coal-algae blends followed 2nd order decomposition with an activation energy range of 69.4 – 74.2 kJ/mol. Secondly, pyrolysis studies were carried out in a rotary kiln reactor wherefrom the char products were collected, and pyrolytic gases condensed to obtain pyroligneous liquid. It was found that the composition of oils synthesised from the pyrolysis of coal was rich in paraffins (52.6 % at 550 ᵒC), however the yield of oil from the pyrolysis of coal was low (6.9 %). Oils from algae and coal-algae blends were dominated by alcohols, fatty acids, fatty acid esters and poly-cyclic aromatic compounds. For example, the most abundant compounds in algae oil produced at 550 ᵒC were fatty acid esters (28.8 %), alcohols (17.6 %), fatty acids (10.8 %) and unsaturated aliphatics (10.7 %); the oil yield obtained from pyrolysis of algae was 40 %. The yields and composition of oils obtained from coal-algae blends were linked to individual contributions from coal and algae, especially at 550 ᵒC; however, the contributions were not proportional due to synergistic effects. This kind of study will contribute to the already existing but limited literature on coal-algae pyrolysis. Furthermore, this study demonstrates the potential of using low-grade coals (an abundant resource in Southern Africa) in conjunction with algal biomass (a renewable resource), in large-scale synthesis of liquid fuels and valuable chemicals via a simple pyrolysis process. , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-12
- Authors: Nyoni, Bothwell
- Date: 2023-12
- Subjects: Algal biofuels , Biomass energy , Coal -- South Africa
- Language: English
- Type: Doctorate theses , text
- Identifier: http://hdl.handle.net/10948/62550 , vital:72823
- Description: There are two primary reasons why the global economy is gradually reducing its dependence on coal as an energy source. Firstly, coal reserves are finite, and while some argue that current reserves will last for generations, the reality is that coal is a non-renewable resource. Secondly, the emissions associated with coal usage have adverse effects on both the environment and human health. While European countries have adopted seemingly aggressive strategies to replace coal and other fossil fuels, South Africa and other developing nations face economic constraints that limit such actions. Fortunately, there are more conservative approaches that can be employed, one of which involves a gradual introduction of renewable energy sources into the energy grid. Wind, solar, and biomass currently stand as the major renewable energy sources under consideration. However, it's worth noting that the intermittent nature of wind and solar energy production poses a significant challenge. Biomass holds the potential to replace coal in retrofitted coal-fired plants. However, the unchecked utilisation of biomass can lead to deforestation and have adverse effects on the human and animal food supply chain, as many essential food items are derived from plants. The debate over using biomass as a fuel source, especially when some types of biomasses can serve as food for humans and animals, has been a subject of ongoing discussion. Furthermore, biomass exhibits a lower energy density when compared to coal. Combustion stands as the primary technology for converting coal into energy and is widely used in most coal-based power plants. Gasification, on the other hand, has been employed for years in South Africa as a coal-to-liquids technology to supplement transportation fuel requirements and reduce reliance on crude oil imports. Pyrolysis, too, has found application as a key method for obtaining high-energy coal char, serving both as an energy source and a reducing agent in blast furnaces for the steelmaking industry. Pyrolysis technologies are gaining popularity in biomass-to-liquids processes due to their simplicity. Currently, there is growing research interest in simultaneous pyrolysis of coal and biomass. The study presented in this thesis focuses on investigating the pyrolysis of Scenedesmus algae biomass and low-grade coal in a small-scale rotary kiln, with particular emphasis on the synthesised liquid products. Algae represent a unique type of biomass that can be cultivated in photo-bioreactors with minimal use of agricultural land. This suggests significant potential for large-scale cultivation of algae, and ongoing efforts are exploring strategies for the mass production of algal biomass.Firstly, pyrolysis studies were carried out via thermogravimetric analysis instruments. It was revealed that because of algae’s considerably higher volatile content and lower carbon content when compared to coal, the pyrolysis process of algal biomass occurred at a faster rate. The highest pyrolytic reactivity of algae was 0.41 mg/min occurring at approximately 290 ᵒC in comparison with coal’s 0.06 mg/min occurring in the approximate temperature range of 550 – 600 ᵒC. The magnitude of the reactivity of the blends depended on the coal/algae ratios used. Furthermore, kinetics analysis revealed that the overall pyrolytic decomposition of coal followed 2nd order kinetics with an activation energy of 81.8 kJ/mol. The decomposition of algae and coal-algae blends occurred in two stages; the first stage decomposition followed 2nd order kinetics with activation energies in the range 130.3 – 145.5 kJ/mol. The second stage decomposition of algae followed 1st order kinetics with an activation energy of 27.3 kJ/mol, whilst coal-algae blends followed 2nd order decomposition with an activation energy range of 69.4 – 74.2 kJ/mol. Secondly, pyrolysis studies were carried out in a rotary kiln reactor wherefrom the char products were collected, and pyrolytic gases condensed to obtain pyroligneous liquid. It was found that the composition of oils synthesised from the pyrolysis of coal was rich in paraffins (52.6 % at 550 ᵒC), however the yield of oil from the pyrolysis of coal was low (6.9 %). Oils from algae and coal-algae blends were dominated by alcohols, fatty acids, fatty acid esters and poly-cyclic aromatic compounds. For example, the most abundant compounds in algae oil produced at 550 ᵒC were fatty acid esters (28.8 %), alcohols (17.6 %), fatty acids (10.8 %) and unsaturated aliphatics (10.7 %); the oil yield obtained from pyrolysis of algae was 40 %. The yields and composition of oils obtained from coal-algae blends were linked to individual contributions from coal and algae, especially at 550 ᵒC; however, the contributions were not proportional due to synergistic effects. This kind of study will contribute to the already existing but limited literature on coal-algae pyrolysis. Furthermore, this study demonstrates the potential of using low-grade coals (an abundant resource in Southern Africa) in conjunction with algal biomass (a renewable resource), in large-scale synthesis of liquid fuels and valuable chemicals via a simple pyrolysis process. , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-12
An investigation into water and sanitation in the Eastern Cape Province and potential for implementation of biotechnology platforms
- Authors: Gumunyu, Wilbert
- Date: 2022-10-14
- Subjects: Sewage South Africa Eastern Cape , Sanitation South Africa Eastern Cape , Algae Biotechnology , Biotechnology , Sewage Purification Biological treatment , Algal biofuels
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/362830 , vital:65366
- Description: In contemporary South Africa, a country in transition, destruction rather than reconstruction seems commonplace. Electricity supply is at an all-time low and ‘load shedding’ is an almost daily occurrence. Similarly, more fragility of water delivery and sanitation service is being reported with the likelihood of ‘water shedding’ a soon-to-be reality. In view of the ever-increasing reported mismanagement of South Africa’s water and sanitation infrastructure, which is likely nearing the point of collapse if not already collapsed, this thesis set out to interrogate at a provincial and municipal level the status of water and sanitation in Chris Hani District Municipality (CHDM), Eastern Cape Province. One major driver behind this study was to evaluate provincial and municipal water/wastewater infrastructure as a platform to support implementation of locally developed bioprocess technologies. First, publicly available historical data was used to derive a baseline or benchmark from which to determine gains/losses in compliance, water quality and efficiency. The period 2009-2013/4 during which Blue and Green Drop reporting was routine, was used as an appropriate start point. Data thus derived indicated that, at provincial and district municipality (DM) level, potable water supply was by bulk water schemes and, sanitation was typically by waste stabilization pond (WSP) treatment of municipal sewage. The derived benchmark for the period 2009-2013/14 indicated that most plants were not compliant (~75% of the Eastern Cape Province water treatment plants (WTP) operating between average performance to critical state), operated either at- or above design capacity (Eastern Cape Province, 16%; CHDM, 19%). A large number of plants for the province (62.4%) and district (81.25%) had hydraulic design capacity or average daily flows that were unknown (information not provided in available literature or plant reports) and final effluent did not always meet the general standard (70.3% of the CHDM wastewater treatment works (WWTW)). To determine the contemporary state (2020 - 2022) of water and sanitation within CHDM, a scoping exercise of WTP and WWTW in selected local municipalities was carried out. This was done along a west-east transect by appraising WTP and WWTW in the towns of Cradock, Tarkastad, Komani, Tsomo, Cacadu, and Ngcobo. Furthermore, targeted assessment of the Queenstown WTP and the Cradock WWTW was used to derive real-time data on the status of water and sanitation infrastructure. Results showed that water and sanitation services within CHDM had, in the years between 2009-2013/14 to date, deteriorated. Freshwater demand significantly exceeded capability of water supply schemes, where demand was as much as three times greater than reported available supply. For most WWTW, operation was in excess of capacity and between 1.52 and 12 times installed hydraulic loading. The targeted scoping exercise revealed that Queenstown WTP is a moderate risk plant (Cumulative risk rating, CRR = 11 and maximum risk rating, MRR = 47.8%), whereas Cradock WWTW was in working condition but with challenges and some infrastructural dysfunction. Assessment of water/effluent quality revealed that turbidity and TOC were above SANS 241 general limit. Non-compliance in terms of nitrate/nitrite-N, ammonium-N, phosphate-P, TSS, total coliforms, E. Coli, and free chlorine was evident at Cradock WWTW. Unstructured interviews with plant operators corroborated these findings. The overwhelming support for bulk schemes for potable water provision and WSP for sanitation indicated a partially water secure municipal district but derelict in terms of its sanitation services. The later, it was concluded, in particular provides an ideal opportunity for implementation of platform technologies to support bioprocesses for entrepreneurship, employment, economic benefit and to secure a closed circular economy for regional water and sanitation through valorisation of co-product streams. Among the co-product streams considered in this thesis are biomass, biogas, biofertilizers, biofuels and several high value chemical products. , Thesis (MSc) -- Faculty of Science, Institute for Environmental Biotechnology, 2022
- Full Text:
- Date Issued: 2022-10-14
- Authors: Gumunyu, Wilbert
- Date: 2022-10-14
- Subjects: Sewage South Africa Eastern Cape , Sanitation South Africa Eastern Cape , Algae Biotechnology , Biotechnology , Sewage Purification Biological treatment , Algal biofuels
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/362830 , vital:65366
- Description: In contemporary South Africa, a country in transition, destruction rather than reconstruction seems commonplace. Electricity supply is at an all-time low and ‘load shedding’ is an almost daily occurrence. Similarly, more fragility of water delivery and sanitation service is being reported with the likelihood of ‘water shedding’ a soon-to-be reality. In view of the ever-increasing reported mismanagement of South Africa’s water and sanitation infrastructure, which is likely nearing the point of collapse if not already collapsed, this thesis set out to interrogate at a provincial and municipal level the status of water and sanitation in Chris Hani District Municipality (CHDM), Eastern Cape Province. One major driver behind this study was to evaluate provincial and municipal water/wastewater infrastructure as a platform to support implementation of locally developed bioprocess technologies. First, publicly available historical data was used to derive a baseline or benchmark from which to determine gains/losses in compliance, water quality and efficiency. The period 2009-2013/4 during which Blue and Green Drop reporting was routine, was used as an appropriate start point. Data thus derived indicated that, at provincial and district municipality (DM) level, potable water supply was by bulk water schemes and, sanitation was typically by waste stabilization pond (WSP) treatment of municipal sewage. The derived benchmark for the period 2009-2013/14 indicated that most plants were not compliant (~75% of the Eastern Cape Province water treatment plants (WTP) operating between average performance to critical state), operated either at- or above design capacity (Eastern Cape Province, 16%; CHDM, 19%). A large number of plants for the province (62.4%) and district (81.25%) had hydraulic design capacity or average daily flows that were unknown (information not provided in available literature or plant reports) and final effluent did not always meet the general standard (70.3% of the CHDM wastewater treatment works (WWTW)). To determine the contemporary state (2020 - 2022) of water and sanitation within CHDM, a scoping exercise of WTP and WWTW in selected local municipalities was carried out. This was done along a west-east transect by appraising WTP and WWTW in the towns of Cradock, Tarkastad, Komani, Tsomo, Cacadu, and Ngcobo. Furthermore, targeted assessment of the Queenstown WTP and the Cradock WWTW was used to derive real-time data on the status of water and sanitation infrastructure. Results showed that water and sanitation services within CHDM had, in the years between 2009-2013/14 to date, deteriorated. Freshwater demand significantly exceeded capability of water supply schemes, where demand was as much as three times greater than reported available supply. For most WWTW, operation was in excess of capacity and between 1.52 and 12 times installed hydraulic loading. The targeted scoping exercise revealed that Queenstown WTP is a moderate risk plant (Cumulative risk rating, CRR = 11 and maximum risk rating, MRR = 47.8%), whereas Cradock WWTW was in working condition but with challenges and some infrastructural dysfunction. Assessment of water/effluent quality revealed that turbidity and TOC were above SANS 241 general limit. Non-compliance in terms of nitrate/nitrite-N, ammonium-N, phosphate-P, TSS, total coliforms, E. Coli, and free chlorine was evident at Cradock WWTW. Unstructured interviews with plant operators corroborated these findings. The overwhelming support for bulk schemes for potable water provision and WSP for sanitation indicated a partially water secure municipal district but derelict in terms of its sanitation services. The later, it was concluded, in particular provides an ideal opportunity for implementation of platform technologies to support bioprocesses for entrepreneurship, employment, economic benefit and to secure a closed circular economy for regional water and sanitation through valorisation of co-product streams. Among the co-product streams considered in this thesis are biomass, biogas, biofertilizers, biofuels and several high value chemical products. , Thesis (MSc) -- Faculty of Science, Institute for Environmental Biotechnology, 2022
- Full Text:
- Date Issued: 2022-10-14
Nutrient removal and biofuel potential of MaB-floc biomass from an integrated algal pond system treating domestic sewage
- Authors: Sibelo, Linda
- Date: 2020
- Subjects: Biomass energy , Waste products as fuel , Algal biofuels , Sewage -- Purification -- Nutrient removal
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/144955 , vital:38395
- Description: Integrated algal pond systems (IAPS) are a passive water treatment technology derived from the Oswald designed advanced integrated wastewater pond systems (AIWPS®) and effect wastewater treatment based on biological activity of microorganisms within the system, solar energy and gravity. The technology consists of an advanced facultative pond (AFP), a series of interconnected high rate algal oxidation ponds (HRAOP) and algal settling ponds. The symbiotic relationship between microalgae and bacteria facilitated by paddlewheel mixing of HRAOP results in the formation of biomass aggregates known as MaB-flocs. MaB-floc formation enhances nutrient abstraction, gravitational sedimentation and separation from water hence forming two product streams; recyclable water and biomass, both with valorisation potential. This work aimed to determine the suitability of MaB-floc biomass generated in the HRAOP of an IAPS treating domestic sewage as feedstock for biofuel production based on the content of carbohydrate and lipid. Nutrient removal efficiency, biomass productivity and bulk lipid and carbohydrate concentration were monitored for two consecutive three-month periods in the winter and summer seasons of 2018/19. Maximum removal efficiencies of nitrogen and phosphorus were determined as 71% and 75% respectively, demonstrating the efficiency of IAPS as a wastewater treatment technology. MaB-floc biomass productivity in winter and summer was 9.4 g/m2/d and 16.5 g/m2/d respectively indicating the heavy influence of seasonal temperature, possibly day length, and solar irradiation on biomass productivity in the HRAOP. Summer productivity was lower than the maximum theoretical productivity of 25 g/m2/d possibly due to photoinhibition of photosynthesis as well as grazing pressures caused by the proliferation of rotifers mainly of the Brachionus genus. MaB-floc biomass consistently contained higher amounts of carbohydrate than lipid despite the changes in species dominance from Scenedesmus sp. and Desmodesmus sp. in winter to Pediastrum sp. in summer. Variations in MaB-floc biomass carbohydrate content were linked to changes in nitrogen concentration, mainly in the form of nitrates. Lower nitrogen concentration significantly increased the carbohydrate content of MaB-floc biomass from 17.5 ± 0.15% to 33.5 ± 0.3 % recorded in summer. In winter, biomass carbohydrate increased from 18.3 ± 1.2% to 35.8 ± 0.3%.To induce accumulation of carbohydrates through nitrogen starvation, isolated microalgal species native to the HRAOPs of the IAPS at Institute for Environmental Biotechnology Rhodes University(EBRU) were used. The outcome from the laboratory studies showed that carbon partitioning within isolated strains could be altered from carbohydrate to lipid which is more energy-rich. Hence, exploring the biodiesel production option using HRAOP MaB-floc biomass, which had a lipid content ranging between 12.1 ± 0.64 % and 13.9 ± 0.5 %, would require a preconditioning step in the form of nitrogen starvation to enhance its lipid content. Overall, the outcome of outdoor monitoring studies on biomass biochemical composition indicated that HRAOPs operating under natural environmental conditions preferentially generated a biomass rich in carbohydrate. Therefore, anaerobic digestion may be a more viable option for HRAOP MaB-floc biomass because of the high carbohydrate levels ranging between 24.9 ± 0.6 % and 25.6 ± 1.3 % of the dry MaB-floc biomass weight. Despite the low biomass C/N ratio (7.1 to 7.8), the MaB-floc biomass can be anaerobically co-digested with a higher C/N ratio (24) substrate such as in-pond digester sludge, to improve methane yields calculated to be between 0.31 m3 CH4/ kg MaB-floc biomass and 0.33 m3 CH4/ kg MaB-floc biomass. Anaerobic digestion of biomass also produces CO2 which can be recovered and added to HRAOPs to enhance MaB-floc biomass productivity while lowering greenhouse gas emissions from a wastewater treatment plant. The digestate from the anaerobic process, which is rich in nitrogen and phosphorus can be used as a biofertiliser. Thus, a potential MaB-floc biomass biorefinery consisting of biogas and bio-fertiliser pathways can be established using IAPS treating sewage as the platform technology. IAPS is a system designed to operate in a way that is passive and without substantial environmental impact but technological innovations and a reduction in the size of the system are required to make the technology more acceptable.
- Full Text:
- Date Issued: 2020
- Authors: Sibelo, Linda
- Date: 2020
- Subjects: Biomass energy , Waste products as fuel , Algal biofuels , Sewage -- Purification -- Nutrient removal
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/144955 , vital:38395
- Description: Integrated algal pond systems (IAPS) are a passive water treatment technology derived from the Oswald designed advanced integrated wastewater pond systems (AIWPS®) and effect wastewater treatment based on biological activity of microorganisms within the system, solar energy and gravity. The technology consists of an advanced facultative pond (AFP), a series of interconnected high rate algal oxidation ponds (HRAOP) and algal settling ponds. The symbiotic relationship between microalgae and bacteria facilitated by paddlewheel mixing of HRAOP results in the formation of biomass aggregates known as MaB-flocs. MaB-floc formation enhances nutrient abstraction, gravitational sedimentation and separation from water hence forming two product streams; recyclable water and biomass, both with valorisation potential. This work aimed to determine the suitability of MaB-floc biomass generated in the HRAOP of an IAPS treating domestic sewage as feedstock for biofuel production based on the content of carbohydrate and lipid. Nutrient removal efficiency, biomass productivity and bulk lipid and carbohydrate concentration were monitored for two consecutive three-month periods in the winter and summer seasons of 2018/19. Maximum removal efficiencies of nitrogen and phosphorus were determined as 71% and 75% respectively, demonstrating the efficiency of IAPS as a wastewater treatment technology. MaB-floc biomass productivity in winter and summer was 9.4 g/m2/d and 16.5 g/m2/d respectively indicating the heavy influence of seasonal temperature, possibly day length, and solar irradiation on biomass productivity in the HRAOP. Summer productivity was lower than the maximum theoretical productivity of 25 g/m2/d possibly due to photoinhibition of photosynthesis as well as grazing pressures caused by the proliferation of rotifers mainly of the Brachionus genus. MaB-floc biomass consistently contained higher amounts of carbohydrate than lipid despite the changes in species dominance from Scenedesmus sp. and Desmodesmus sp. in winter to Pediastrum sp. in summer. Variations in MaB-floc biomass carbohydrate content were linked to changes in nitrogen concentration, mainly in the form of nitrates. Lower nitrogen concentration significantly increased the carbohydrate content of MaB-floc biomass from 17.5 ± 0.15% to 33.5 ± 0.3 % recorded in summer. In winter, biomass carbohydrate increased from 18.3 ± 1.2% to 35.8 ± 0.3%.To induce accumulation of carbohydrates through nitrogen starvation, isolated microalgal species native to the HRAOPs of the IAPS at Institute for Environmental Biotechnology Rhodes University(EBRU) were used. The outcome from the laboratory studies showed that carbon partitioning within isolated strains could be altered from carbohydrate to lipid which is more energy-rich. Hence, exploring the biodiesel production option using HRAOP MaB-floc biomass, which had a lipid content ranging between 12.1 ± 0.64 % and 13.9 ± 0.5 %, would require a preconditioning step in the form of nitrogen starvation to enhance its lipid content. Overall, the outcome of outdoor monitoring studies on biomass biochemical composition indicated that HRAOPs operating under natural environmental conditions preferentially generated a biomass rich in carbohydrate. Therefore, anaerobic digestion may be a more viable option for HRAOP MaB-floc biomass because of the high carbohydrate levels ranging between 24.9 ± 0.6 % and 25.6 ± 1.3 % of the dry MaB-floc biomass weight. Despite the low biomass C/N ratio (7.1 to 7.8), the MaB-floc biomass can be anaerobically co-digested with a higher C/N ratio (24) substrate such as in-pond digester sludge, to improve methane yields calculated to be between 0.31 m3 CH4/ kg MaB-floc biomass and 0.33 m3 CH4/ kg MaB-floc biomass. Anaerobic digestion of biomass also produces CO2 which can be recovered and added to HRAOPs to enhance MaB-floc biomass productivity while lowering greenhouse gas emissions from a wastewater treatment plant. The digestate from the anaerobic process, which is rich in nitrogen and phosphorus can be used as a biofertiliser. Thus, a potential MaB-floc biomass biorefinery consisting of biogas and bio-fertiliser pathways can be established using IAPS treating sewage as the platform technology. IAPS is a system designed to operate in a way that is passive and without substantial environmental impact but technological innovations and a reduction in the size of the system are required to make the technology more acceptable.
- Full Text:
- Date Issued: 2020
Resource recovery options in brewery effluent treatment using activated sludge and high rate algal ponds: assessing environmental impacts
- Authors: Taylor, Richard Peter
- Date: 2020
- Subjects: Sewage -- Purification -- Activated sludge process , Sewage disposal plants , Sewage -- Purification -- Biological treatament , Sewage -- Purification -- Nitrogen removal , Brewery waste , Breweries -- Waste disposal , Microalgae -- Biotechnology , Algal biofuels
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/153746 , vital:39507
- Description: Wastewater treatment plants (WWTPs) are designed to clean effluents, but they also consume resources and produce waste. Various treatment technologies allow for the recovery of energy, nutrients and water from effluents turning this waste into products, which increases their sustainability and decreases the impact of WWTPs on the environment. There is a lack of literature which comprehensively compares the treatment performances, environmental impacts and beneficial downstream uses of the biomass generated by high rate algal pond (HRAP) and activated sludge (AS) treatment systems. This thesis aimed to compare (1) effluent treatment performance, (2) emissions and (3) downstream use of algae cultured in HRAP to sludge produced in AS and to obtain data to conduct a life cycle analysis (LCA) to compare the systems. The focus was on adding value to the effluent treatment process, while identifying the associated environmental impacts and contributing to the first ever zero-waste brewery effluent treatment system. Furthermore, these data were used to provide a basis to critically review and contribute to improving the methods used in the LCA of effluent treatment systems; particularly since this was the first wastewater treatment LCA that compared AS and HRAP using data collected from the same temporal and geographic location and from a single effluent stream. The electrical consumption water emission and land application of waste biomass caused the major environmental impacts of both treatment systems. The HRAP had less than 50 % of the electrical energy consumption (0.11±0.01 kW/m3 of effluent treated) compared to the AS system (0.29±0.11 kW/m3) which resulted in the technology having a lower climate change, photochemical oxidant formation, freshwater and marine ecotoxicity and fossil fuel depletion impact. It is imperative to understand the method of electrical energy (fossil fuel vs renewable) generation when conducting a LCA and deciding which technologies to use, since they have a major influence on the aforementioned impacts. The biogas yield of algal and sludge substrates was similar with an average gas production of 241 ml/g volatile solids fed. Biogas from algae fed digesters had a significantly higher methane content (64.73±0.81 %) and lower carbon dioxide content (22.94±0.24 %) when compared to WAS fed digesters (60.08±0.18 % and 27.37±0.43 %) respectively due to it being a less oxidised substrate. Swiss chard plants (Beta vulgaris) fertilised with anaerobically digested (AD) algae or sludge had a significantly higher mean biweekly yield (5.08±0.73 kg/m2) when compared to the inorganic-fertiliser control (3.45±0.89 kg/m2; p<0.0001). No difference was observed in the soil’s physical fertility when algae or sludge were applied to the soil (p>0.05). The HRAP produced more biomass (317.18±27.76 g/m3) than the AS (83.12±64.91 g/m3), which resulted in a significantly greater downstream production of biogas and fertiliser per volume of effluent treated. According to the LCA, this also resulted in the HRAP system having a higher terrestrial ecotoxicity, due to the greater volume of solids and thus heavy metals applied to the soil. This interpretation can be misleading, because the mass of heavy metals released into the environment is the same for both systems, with a greater portion being applied to the land in the HRAP scenario and discharged into fresh water in the case of AS. Future LCA models should clarify if these biomasses are going to be applied to a single piece of land or multiple sites as this will influence the risk of contamination via pollutant build up in the soil. The application of sludge or algae on soil increased the soil’s sodium concentration and sodium absorption ratio from 774.80±13.66 mg/kg to 952.17±34.89 mg/kg and 2.91±0.04 to 3.53±0.13, respectively. Regulations on the application of algae or sludge on agricultural soils should be altered to consider the limit values for sodium and future LCA’s associated with effluent treatment facilities should incorporate the possibility of soil contamination through sodium build-up. This work also conceptualised the importance of reporting water emissions in wastewater treatment LCA in as much detail as possible, because this had a significant influence on the eutrophication impacts on water systems. Reporting water emissions as total nitrogen underestimated downstream eutrophication impacts compared with those using nitrogen-species concentration (ammonia, nitrite, nitrate etc). A marine eutrophication sensitivity co-efficient should be included in future LCA models which accounts for the probability of nitrogen and phosphorus emissions entering the coastal environment as well as the vulnerability of the marine environment to eutrophication. Activated sludge systems are favourable for situations where space is limited, were there are inadequate options for biomass disposal (biomass not be used in agriculture or AD) and were electricity is generated from a renewable source; whereas, HRAP are more suitable under circumstances where electricity production relies on fossil fuel that carries a high environmental impact and where options are available to use the biomass for economic gain such as biogas and fertiliser production. This thesis contributes towards a zero-waste brewery effluent treated process. The HRAP and AS treated effluent for reuse in the brewery or in agricultural irrigation. The solids were anaerobically digested, and the carbon was recovered as a biogas, while the digestate was applied as an agricultural fertiliser. This allowed for the recovery of water, nutrients and carbon.
- Full Text:
- Date Issued: 2020
- Authors: Taylor, Richard Peter
- Date: 2020
- Subjects: Sewage -- Purification -- Activated sludge process , Sewage disposal plants , Sewage -- Purification -- Biological treatament , Sewage -- Purification -- Nitrogen removal , Brewery waste , Breweries -- Waste disposal , Microalgae -- Biotechnology , Algal biofuels
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/153746 , vital:39507
- Description: Wastewater treatment plants (WWTPs) are designed to clean effluents, but they also consume resources and produce waste. Various treatment technologies allow for the recovery of energy, nutrients and water from effluents turning this waste into products, which increases their sustainability and decreases the impact of WWTPs on the environment. There is a lack of literature which comprehensively compares the treatment performances, environmental impacts and beneficial downstream uses of the biomass generated by high rate algal pond (HRAP) and activated sludge (AS) treatment systems. This thesis aimed to compare (1) effluent treatment performance, (2) emissions and (3) downstream use of algae cultured in HRAP to sludge produced in AS and to obtain data to conduct a life cycle analysis (LCA) to compare the systems. The focus was on adding value to the effluent treatment process, while identifying the associated environmental impacts and contributing to the first ever zero-waste brewery effluent treatment system. Furthermore, these data were used to provide a basis to critically review and contribute to improving the methods used in the LCA of effluent treatment systems; particularly since this was the first wastewater treatment LCA that compared AS and HRAP using data collected from the same temporal and geographic location and from a single effluent stream. The electrical consumption water emission and land application of waste biomass caused the major environmental impacts of both treatment systems. The HRAP had less than 50 % of the electrical energy consumption (0.11±0.01 kW/m3 of effluent treated) compared to the AS system (0.29±0.11 kW/m3) which resulted in the technology having a lower climate change, photochemical oxidant formation, freshwater and marine ecotoxicity and fossil fuel depletion impact. It is imperative to understand the method of electrical energy (fossil fuel vs renewable) generation when conducting a LCA and deciding which technologies to use, since they have a major influence on the aforementioned impacts. The biogas yield of algal and sludge substrates was similar with an average gas production of 241 ml/g volatile solids fed. Biogas from algae fed digesters had a significantly higher methane content (64.73±0.81 %) and lower carbon dioxide content (22.94±0.24 %) when compared to WAS fed digesters (60.08±0.18 % and 27.37±0.43 %) respectively due to it being a less oxidised substrate. Swiss chard plants (Beta vulgaris) fertilised with anaerobically digested (AD) algae or sludge had a significantly higher mean biweekly yield (5.08±0.73 kg/m2) when compared to the inorganic-fertiliser control (3.45±0.89 kg/m2; p<0.0001). No difference was observed in the soil’s physical fertility when algae or sludge were applied to the soil (p>0.05). The HRAP produced more biomass (317.18±27.76 g/m3) than the AS (83.12±64.91 g/m3), which resulted in a significantly greater downstream production of biogas and fertiliser per volume of effluent treated. According to the LCA, this also resulted in the HRAP system having a higher terrestrial ecotoxicity, due to the greater volume of solids and thus heavy metals applied to the soil. This interpretation can be misleading, because the mass of heavy metals released into the environment is the same for both systems, with a greater portion being applied to the land in the HRAP scenario and discharged into fresh water in the case of AS. Future LCA models should clarify if these biomasses are going to be applied to a single piece of land or multiple sites as this will influence the risk of contamination via pollutant build up in the soil. The application of sludge or algae on soil increased the soil’s sodium concentration and sodium absorption ratio from 774.80±13.66 mg/kg to 952.17±34.89 mg/kg and 2.91±0.04 to 3.53±0.13, respectively. Regulations on the application of algae or sludge on agricultural soils should be altered to consider the limit values for sodium and future LCA’s associated with effluent treatment facilities should incorporate the possibility of soil contamination through sodium build-up. This work also conceptualised the importance of reporting water emissions in wastewater treatment LCA in as much detail as possible, because this had a significant influence on the eutrophication impacts on water systems. Reporting water emissions as total nitrogen underestimated downstream eutrophication impacts compared with those using nitrogen-species concentration (ammonia, nitrite, nitrate etc). A marine eutrophication sensitivity co-efficient should be included in future LCA models which accounts for the probability of nitrogen and phosphorus emissions entering the coastal environment as well as the vulnerability of the marine environment to eutrophication. Activated sludge systems are favourable for situations where space is limited, were there are inadequate options for biomass disposal (biomass not be used in agriculture or AD) and were electricity is generated from a renewable source; whereas, HRAP are more suitable under circumstances where electricity production relies on fossil fuel that carries a high environmental impact and where options are available to use the biomass for economic gain such as biogas and fertiliser production. This thesis contributes towards a zero-waste brewery effluent treated process. The HRAP and AS treated effluent for reuse in the brewery or in agricultural irrigation. The solids were anaerobically digested, and the carbon was recovered as a biogas, while the digestate was applied as an agricultural fertiliser. This allowed for the recovery of water, nutrients and carbon.
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- Date Issued: 2020
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