• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 174
  • 25
  • 10
  • 8
  • 3
  • 2
  • 2
  • 2
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 251
  • 251
  • 243
  • 92
  • 83
  • 50
  • 40
  • 39
  • 37
  • 26
  • 25
  • 23
  • 23
  • 23
  • 22
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
181

Selective disassembly for re-use of industrial products

Pornprasitpol, Pornwan, Mechanical & Manufacturing Engineering, Faculty of Engineering, UNSW January 2006 (has links)
As a result of rapid product development, the product life cycle has become shorter, and thus the amount of waste from discarded industrial products has risen dramatically. An awareness of the world???s environmental problems has stimulated researchers to explore the opportunities to reuse, recycle and remanufacture end-of-life products. Disassembly is a systematic approach to separating products into components or subassemblies in order to facilitate recovery of components or materials. However, the full disassembly of a product tends to be unproductive due to technical and cost constraints and product conditions after usage. Therefore, selective disassembly has been introduced as a more practical approach, where only a limited number of disassembly paths that lead to selected parts with recovering potential are considered. This research focuses on the development of a selective disassembly methodology by reversing an assembly sequencing approach. The methodology uses a step-by-step approach to generate a disassembly sequence diagram. This involves listing all the parts within the product, generating a liaison diagram to illustrate part relationships and then establishing precedence rules describing prerequisite actions for each liaison. This is followed by segregating disassembly paths that lead to the removal of selected parts or subassemblies. Then a winnowing process is applied to these paths to eliminate invalid disassembly states and transitions. The last step is to select the optimal disassembly path by using the time requirement as the main selection criterion. In order to shorten the time for carrying out the sequencing process, a javabased program that is capable of performing the first three steps has been created. The program requires three basic inputs in forms of precedence rules, and user-required part (s) and disassembly rules, prescribing which liaison (s) should be done subsequent to a particular liaison. The viability of the methodology and the program is proved through seven case studies conducted on a fishing reel, a single-hole punch, a kettle, an entire washing machine and three washing machine subassemblies. The application of the program allows the users to determine an optimal disassembly sequence in a very short time and with only basic product information as the input.
182

Sustainable waste management : a decision support framework

De Beer, Thys 03 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The aim of this thesis is to address the need for sustainable development within waste management. It explores how sustainability can be assessed and used as the basis for high level decision making within waste management. Stellenbosch University (SU) was used as a case study to demonstrate how information can be gathered and used for decision support. The literature reviewed, showed a wide area of focus within which sustainability is defined and how businesses and organisations shift towards a model of corporate responsibility. The concept of sustainability was then presented within waste management. Life Cycle Assessment (LCA) and Multi-Criteria Decision Analysis (MCDA), were presented as management tools that could facilitate the assessment and decision making process within a sustainable waste management framework. The two management tools, Sustainable Life Cycle Analysis (SLCA) and Analytical Hierarchal Process (AHP) (branches of LCA and MCDA respectively), were used to develop a framework to be applied to SU Waste Management System. By integrating the two tools, a framework was established that could measure the sustainability of current waste management practices and provide a decision support tool. The framework was validated by applying it to the Stellenbosch University waste system. The framework that was developed delivered a set of sustainable results from which decision makers could base policy decisions. The framework then facilitated the decision making process and a sustainable waste management policy was selected. The application modelled the decision makers preferences and resulted in a policy being selected which favoured high levels of recycling and waste prevention. The results represented an approach which, when compared to the current practice, was more expensive but more environmentally friendly and socially acceptable. The findings provide an exciting basis for future research, where decisions are based on sustainable principles. The framework has potential to be expanded into other areas of management and is not limited to a university environment. / AFRIKAANSE OPSOMMING: Die doel van hierdie tesis is om die behoefte aan volhoubare ontwikkeling binne afvalbestuur aan te spreek. Die tesis ondersoek hoe die volhoubaarheid in afvalbestuur bepaal kan word, en hoe dit dan gebruik kan word as basis vir beleid besluitneming binne afvalbestuur. Die Universiteit Stellenbosch (US) is as ’n gevallestudie gebruik om te demonstreer hoe inligting versamel kan word en as ondersteuning vir beleidbesluitneming gebruik kan word. Die literatuurstudie dek ’n wye veld waarbinne daar op volhoubaarheid gefokus word. Dit wys ook hoe maatskappye en organisasies na ’n model van korporatiewe verantwoordelikheid beweeg. Die konsep van volhoubaarheid word dan binne die mileu van afvalbestuur aangebied. Die Lewenssiklus Assesering (LSA) en Multi-Kriteria Besluitnemings Analise (MKBA) wat gebruik is, kan dien as bestuur hulpmiddel om die assessering van, en besluitneming binne ’n volhoubare afvalbestuur te vergemaklik. Vanuit die twee hulpmiddels, is Volhoubare Lewens Siklus Analise (VLSA) en Analitiese Hierargiese Proses (AHP), gebruik om ’n raamwerk te ontwikkel wat toegepas is op die US. Deur die twee hulpmiddels te integreer kan ’n raamwerk geskep word wat die volhoubaarheid van die huidige afvalbestuur praktyke en wat kan dien as ‘n ondersteunende hulpmiddel met die besluitnemingsprosesse. Die waardasie van die raamwerk wat ontwikkel was, het ‘n stel volhoubare resultate opgelewer, wat besluitnemers gebruik het om hul beleidsbesluite op te baseer. Die besluitnemers se voorkeure is gebaseer op die bevindinge van die VLSA en het bepaal watter beleid gekies is. Die bevindinge het ’n duurder, maar meer omgewingsvriendelike en sosiaal aanvaarbare beleid verteenwoordig. Hierdie bevindinge bied ’n opwindende basis vir toekomstige navorsingwerk, waar besluitneming op volhoubare beginsels gebaseer is. Die raamwerk het potensiaal vir uitbreiding na ander gebiede van bestuur en is nie beperk tot ’n universiteitsomgewing nie.
183

Use of food waste feeds for culturing low trophic level fish (grass carp, bighead carp and mud carp): persistent toxic substances

Cheng, Zhang 06 March 2014 (has links)
This study aimed at using different types of food wastes as major sources of protein to replace the fish meal used in fish feeds to produce quality fish. The major objectives were to (1) investigate the variations of metalloid/metals, polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) in the fish ponds (pond mud and water), and food wastes used as fish feeds; (2) analyze bioaccumulation and biomagnification of pollutants in the food chains; and (3) evaluate the potential health risks of exposure (to these pollutants) via dietary intake of fish fed with food waste feeds. The traditional fish farming model was used to culture low trophic level fish: a filter feeder (bighead, Aristichthys nobilis), a herbivore (grass carp, Ctenopharyngodon idellus) and a bottom feeder (mud carp, Cirrhina molitorella), which are more environmental friendly as they can utilize more solar energy. Furthermore, low-trophic level fish are less susceptible to the accumulation of toxic chemicals. Two types of food wastes (mainly containing cereal (Food Waste A) and meat waste meal (Food Waste B)) were used as the major source of protein to replace the fish meal in fish feed to culture fish. The concentrations of metalloid (arsenic (As)), metals (mercury (Hg), cadmium (Cd), chromium (Cr), lead (Pb), zinc (Zn), copper (Cu) and nickel (Ni)) in water, suspended particulate matter and sediment of the 3 experimental fish ponds located in Sha Tau Kok Organic Farm were monitored (bi-monthly during the first half year and tri-monthly during the second half year) and the results were similar to or lower than those in the commercial fish ponds around the Pearl River Delta (PRD) region. Results of the health risk assessments indicated that human consumption of grass carp (a herbivore) which fed food waste feed pellets would be safer than other fish species (mud carp, bighead carp and largemouth bass). There were no or lower magnifications, and low concentrations of metalloid/metals contained in the ponds indicated that the practice of traditional pond management by draining pond water regularly can provide a better fish pond habitat for birds and other wildlife. Furthermore, the use of food waste instead of fish meal (mainly consisted of contaminated trash fish) further reduced Hg accumulation in the cultured fish. During October 2011 - December 2012, the concentrations of PAHs and OCPs in three experimental fish ponds were monitored (bi-monthly during the first half year and tri-monthly during the second half year). The results were similar to or lower than those obtained in commercial fish ponds around the PRD region. The mean concentrations of .PAHs and .OCPs in sediment and fish collected from the experimental fish ponds during the 2nd half year (May 2012 to December 2012) were significantly higher (p<0.05) than those in the 1st half year (October 2011 to April, 2012). .PAHs and .DDTs in the two species of fish (grass carp and bighead carp) were significantly increased (p<0.05) with time, and PAHs and DDTs in grass carp and bighead carp fed with commercial fish feed pellets (control group) were significantly higher (p<0.05) than the fish fed with food waste pellets (Food Waste A and Food Waste B). Fruit, vegetables, bone meal and meat products were the major sources of PAHs and OCPs contamination for producing Food Waste A and Food Waste B. No significant increases in PAHs and DDTs concentrations with trophic levels were observed in the experimental ponds, showing that PAHs were not biomagnifed in the omnivorous food chains (plankton, grass carp, bighead carp and mud carp). DDTs were lower magnifications than those predatory food chains (plankton, trash fish, and largemouth bass) in farmed ponds. There was a very low cancer risk for PAHs and DDTs exerted on humans via consumption of bighead carp, grass carp and mud carp (fed with food waste and commercial pellets). Furthermore, the use of food waste instead of fish meal (mainly consisted of contaminated trash fish) further reduced accumulation of PAHs and DDTs in the cultured fish.PAHs and DDTs exerted on humans via consumption of bighead carp, grass carp and mud carp (fed with food waste and commercial pellets). Furthermore, the use of food waste instead of fish meal (mainly consisted of contaminated trash fish) further reduced accumulation of PAHs and DDTs in the cultured fish. The present results revealed that recycling of food waste for cultivating low trophic level fish (mainly bighead carp and grass carp) is feasible, which will also ease the disposal pressure of the large volume of food waste, a common problem encountered in densely populated cites such as Hong Kong.
184

Relationships between social marketing strategies and school participation in environmental competitions: a case study of Collect-a-Can's annual schools competition

Mathabathe, Andrew Tumishe January 2006 (has links)
The South African formal education system has undergone many changes since the formulation of the White Paper on Education and Training in 1995. These developments challenge organisations that want to run successful programmes or projects in schools to adapt their social marketing strategies. Against this background, the aim of the study was to investigate the relationships between social marketing strategies and participation of schools in environmental competitions. The goals of the research were to identify issues that have influenced schools participation in the Collect-a-Can Annual Schools Competition, identify and review social marketing strategies used by Collect-a-Can to influence participation of schools in the competition, and identify relationships between issues that influenced school participation in the competition and the Collect-a-Can’s social marketing strategies. A qualitative design that applied an interpretative case study, which focused on the Collect-a-Can’s Annual Schools Competition was used to explore these relationships. Data was generated through interviews, document analysis and a workshop. Nine respondents from nine schools and three Collect-a-Can management staff members participated in the interview process. Twenty participants from twenty schools participated in the workshop. The findings of the research revealed that there were relationships between the social marketing strategies used by Collect-a-Can and participation of schools in the competition. These relationships were found to be linked mainly to policy changes within formal education which Collect-a-Can could not respond to as a result of various reasons which included among others, the core focus of thecompany, lack of funds and a need to operate in a cost-effective way. The recommendations indicate possible areas for improvement and guidelines which could be used by Collect-a-Can for the competition without digressing from its core focus or incurring additional costs. These include a more responsive and adaptive management approach and a stronger educational orientation.
185

Recycling as a strategy for environmental management in Cofimvaba

Mniki, Yolisa Helen January 2015 (has links)
The success or failure of a local municipality is measured by the efficient provision of basic services to communities within the area of jurisdiction. Waste management is one of the basic services that pose serious environmental challenges. Various strategies have been developed as a means of waste management and recycling is a popular strategy as it has the potential to foster relations between the municipality and the community. Studies by the Department of environmental Affairs have confirmed that the delivery of waste management services by municipalities has capacity constraints including, but not limited to, landfill site operations, waste collection, processing and disposal, and waste management hierarchy (Department of Environmental Affairs, 2008). This research is undertaken to establish how recycling can be effective in environmental management. The findings emphasise strongly, the high level of awareness that communities have on recycling; however there is a need for intensive resource support for the community initiatives to have the desired impact.
186

Educação ambiental e profissionalização dos catadores na política nacional de resíduos sólidos : uma sociologia das ausências?

Vicente, Bianka Biazuz January 2015 (has links)
Este trabalho é resultado da pesquisa desenvolvida para o mestrado acadêmico em Educação, na linha pesquisa de Políticas e Gestão de Processos Educacionais da Universidade Federal do Rio Grande do Sul. O objetivo principal é uma reflexão sobre a experiência de trabalho e Educação que é desenvolvida na Cooperativa de Recicladores de Dois Irmãos, localizada na cidade de Dois Irmãos. A análise ocorre na interlocução com a Política Nacional de Resíduos Sólidos (PNRS) Lei nº 12.305/2010 e demais programas e projetos sob a sua égide, na perspectiva de constituir um traçado investigativo do qual possam emergir elementos capazes de fomentar a seguinte discussão: como vem sendo construída a dimensão Educativa da PNRS. Trata-se de uma pesquisa do tipo qualitativa, combinando estudos de caso e entrevistas com os trabalhadores. Para a produção de dados foram constituídos os seguintes instrumentos: diário de campo, observação direta e questionários semiestruturados para gestores e associados da cooperativa Cumpre esclarecer que a concepção da metodologia de pesquisa e análise dos dados no sentido da orientação teórica, é emanada a partir dos conceitos desenvolvidos por Boaventura de Sousa Santos, que são: a Sociologia das Ausências, no âmbito investigativo; a Sociologia das Emergências, que se refere às questões advindas da investigação; o Trabalho de Tradução, o qual transcende a simples descrição de fatos propondo-se à reflexão. A pesquisa possibilitou analisar como está sendo entendida e construída essa política na comunidade de trabalhadores no ambiente de trabalho; e como ocorre a formação dos trabalhadores. Buscaram-se as bases teóricas em contribuições dos autores Nilton Bueno Fischer, Paul Singer, Zygmunt Bauman, Edgar Morin e Nancy Fraser. Os resultados da pesquisa apontam para a resignificação do trabalho dos Catadores e Recicladores e para a dilatação dos seus espaços de formação e atuação política, além de uma demanda pela ampliação do conhecimento sobre a PNRS para a Educação Ambiental e para a população brasileira. / This work is the result of a research conducted for an academic master's degree in Education, in the research line Policies and Educational Process Management at the Federal University of Rio Grande do Sul. The main objective is to reflect on the work and educational experience developed at the recycling cooperative in the town of Dois Irmãos .The analysis takes place in the dialogue with the National Solid Waste Policy (PNRS) Act 12.305/2010 and other programs and projects under its auspices with a view to establish an investigative outline from which elements can emerge to foster the following discussion: how the Educational dimension of the PNRS is being built. It is a qualitative type research, combining case studies and interviews with the workers. For the production of data the following instruments were used: field diary, direct observation and semi-structured questionnaires applied to managers and cooperative members. The research made it possible to analyse how this policy is being understood and built in the community of workers in their workplace; and how the workers´ education and training takes place. The theoretical basis came from contributions of authors Nilton Bueno Fischer, Paul Singer, Zygmunt Bauman, Edgar Morin and Nancy Fraser Survey results point to the resignification of the work of Waste Pickers and Recyclers and to the expansion of their education and training spaces as well as of their political action. There is also a demand for increasing the knowledge about the PNRS for Environmental Education and for the Brazilian population. It should be clarified that the design of the research methodology and the analysis of data in the sense of theoretical orientation, emanates from concepts developed by Boaventura de Sousa Santos which are: the Sociology of Absences, in the investigative scope; the Sociology of Emergencies, which refers to the questions that emerge from the research and the Work of Translation, which transcends the simple description of facts and proposes to reflection.
187

Educação ambiental e profissionalização dos catadores na política nacional de resíduos sólidos : uma sociologia das ausências?

Vicente, Bianka Biazuz January 2015 (has links)
Este trabalho é resultado da pesquisa desenvolvida para o mestrado acadêmico em Educação, na linha pesquisa de Políticas e Gestão de Processos Educacionais da Universidade Federal do Rio Grande do Sul. O objetivo principal é uma reflexão sobre a experiência de trabalho e Educação que é desenvolvida na Cooperativa de Recicladores de Dois Irmãos, localizada na cidade de Dois Irmãos. A análise ocorre na interlocução com a Política Nacional de Resíduos Sólidos (PNRS) Lei nº 12.305/2010 e demais programas e projetos sob a sua égide, na perspectiva de constituir um traçado investigativo do qual possam emergir elementos capazes de fomentar a seguinte discussão: como vem sendo construída a dimensão Educativa da PNRS. Trata-se de uma pesquisa do tipo qualitativa, combinando estudos de caso e entrevistas com os trabalhadores. Para a produção de dados foram constituídos os seguintes instrumentos: diário de campo, observação direta e questionários semiestruturados para gestores e associados da cooperativa Cumpre esclarecer que a concepção da metodologia de pesquisa e análise dos dados no sentido da orientação teórica, é emanada a partir dos conceitos desenvolvidos por Boaventura de Sousa Santos, que são: a Sociologia das Ausências, no âmbito investigativo; a Sociologia das Emergências, que se refere às questões advindas da investigação; o Trabalho de Tradução, o qual transcende a simples descrição de fatos propondo-se à reflexão. A pesquisa possibilitou analisar como está sendo entendida e construída essa política na comunidade de trabalhadores no ambiente de trabalho; e como ocorre a formação dos trabalhadores. Buscaram-se as bases teóricas em contribuições dos autores Nilton Bueno Fischer, Paul Singer, Zygmunt Bauman, Edgar Morin e Nancy Fraser. Os resultados da pesquisa apontam para a resignificação do trabalho dos Catadores e Recicladores e para a dilatação dos seus espaços de formação e atuação política, além de uma demanda pela ampliação do conhecimento sobre a PNRS para a Educação Ambiental e para a população brasileira. / This work is the result of a research conducted for an academic master's degree in Education, in the research line Policies and Educational Process Management at the Federal University of Rio Grande do Sul. The main objective is to reflect on the work and educational experience developed at the recycling cooperative in the town of Dois Irmãos .The analysis takes place in the dialogue with the National Solid Waste Policy (PNRS) Act 12.305/2010 and other programs and projects under its auspices with a view to establish an investigative outline from which elements can emerge to foster the following discussion: how the Educational dimension of the PNRS is being built. It is a qualitative type research, combining case studies and interviews with the workers. For the production of data the following instruments were used: field diary, direct observation and semi-structured questionnaires applied to managers and cooperative members. The research made it possible to analyse how this policy is being understood and built in the community of workers in their workplace; and how the workers´ education and training takes place. The theoretical basis came from contributions of authors Nilton Bueno Fischer, Paul Singer, Zygmunt Bauman, Edgar Morin and Nancy Fraser Survey results point to the resignification of the work of Waste Pickers and Recyclers and to the expansion of their education and training spaces as well as of their political action. There is also a demand for increasing the knowledge about the PNRS for Environmental Education and for the Brazilian population. It should be clarified that the design of the research methodology and the analysis of data in the sense of theoretical orientation, emanates from concepts developed by Boaventura de Sousa Santos which are: the Sociology of Absences, in the investigative scope; the Sociology of Emergencies, which refers to the questions that emerge from the research and the Work of Translation, which transcends the simple description of facts and proposes to reflection.
188

Reaproveitamento do resíduo Grits proveniente da indústria de celulose Kraft de eucalipto aplicado como carga de reforço na obtenção de compósito com borracha natural /

Bacarin, Giovani Boaventura. January 2018 (has links)
Orientador: Aldo Eloizo Job / Coorientador: Flávio Camargo Cabrera / Banca: Vanusa Dalosto Jahno / Banca: Ana Maria Pires / Resumo: Diariamente toneladas de resíduos industriais são gerados, os quais necessitam de estratégias de gerenciamento a fim de serem descartados ou reciclados corretamente. Por esse motivo, o reuso de resíduos orgânicos e industriais como cargas em compósitos poliméricos tem surgido como um novo campo de estudo. Nessa dissertação, demonstrou-se pela primeira vez o uso do resíduo Grits como carga natural em compósitos de borracha natural a fim de reutilizar os resíduos provenientes da indústria de celulose Kraft de eucalipto, assim como diminuir os custos de produção dos compósitos através da substituição, ainda que parcial, do carbonato de cálcio e do óxido de cálcio, cargas comerciais comumente utilizadas. Os tratamentos com Silano, Lauril sulfato de sódio, Dodigen 1611, além da correção de pH, variação da granulometria e quantidade de enxofre na formulação foram testados com a finalidade de melhorar a adesão interfacial do resíduo com a matriz polimérica, otimizar a formulação e consequentemente melhorar as propriedades mecânicas. Compósitos com 20 phr de Grits mostraram um aumento na tensão de ruptura de aproximadamente 20% comparado à borracha natural. Compósitos com 10 phr do resíduo apresentaram a maior resistência a abrasão, com 72,26 mm3 de perda por abrasão. Os compósitos foram aplicados na produção de chinelos atingindo as especificações recomendadas pelo Instituto de Ensaios e Pesquisa para a Fabricação de Calçados (PFI - Prüf- und Forschungsinstitut), Pirmasens, Alemanha... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Daily tons of industrial residues are generated which require management strategies in order to correctly disposes or recycling. Therefore, the reuse of organic and industrial waste as fillers in polymeric composites has emerged as a distinct new field. Here, it was demonstrated for the first time the use of Grits as filler in natural rubber composites in order to reuse residues from eucalyptus cellulose Kraft industrie as well as decreasing the final cost from rubber products through calcium carbonate or calcium oxide replacement even partially. Treatments with Silane, Sodium Lauril sulfate, Dodigen 1611, besides pH correction, granulometry variation and sulfur content in the formulation were tested in order to improve the adhesion of the waste in the polymeric matrix, optimizing the formulation and consequently improving mechanical properties. The better treatment was prepared with pH correction and treatment with Dodigen 1611. Composites with 20 phr of Grits showed an increase on stress values around 20% compared to the natural rubber and, with 10 phr, presented the highest abrasion resistance of 72.26 mm3. The composites were applied on sandals production reaching the specifications recommended from Testing and Research Institute for the Manufacture of Footwear (PFI - Prüf- und Forschungsinstitut), Pirmasens, Germany. It was added eucalyptus cellulose fiber in order to verify the influence on soil degradation time. Standard cellulose, natural rubber, composites NR/20 phr ... (Complete abstract click electronic access below) / Mestre
189

Cirkulární ekonomika v českém prostředí - zkušenosti firem a pohled odborníků / Circular economy in the Czech surroundings - experience of companies and the view of experts

Leová, Leona January 2021 (has links)
The diploma thesis deals with the concept of circular economy (hereinafter CE) and its application in several Czech and one multinational company. On these specific examples of companies, the work shows how circularity is achieved, with all the essentials of this fact, what support for the concept is offered in the Czech Republic and, last but not least, what obstacles and problems the companies face. Along with this practical experience, opinions by theoretical experts who deal with the issue in their profession are further examined. The aim of the work was to map the matter of use of secondary raw materials and other principles of CE in both practical and theoretical spheres of knowledge, and where possible, to compare these two views. Furthermore, the work focuses on the benefits of real use of the principles of CE in the Czech conditions from an environmental point of view. In its theoretical part, it first addresses the issue of waste in general, especially from the perspective of a global problem. It presents the development, current situation and forecast of the size of waste generation, including its impacts. Furthermore, it has introduced the concept of CE, its various concepts and definitions, together with the main principles. Subsequently, it presents the real adoption of the concept by...
190

Lab-scale assessment and adaptation of wastewater for cultivation of microalgal biomass for biodiesel production

Ramanna, Luveshan January 2015 (has links)
Submitted in fulfillment of the requirements of the degree of Master of Applied Science in Biotechnology, Durban University of Technology, 2015. / In light of the world’s declining fossil fuel reserves, the use of microalgal biodiesel has come to the forefront as a potentially viable alternative liquid fuel. The depleting freshwater reserves make the feasibility of this concept questionable. The use of wastewater reduces the requirement for depleting freshwater supplies. This project aimed to determine the viability of municipal domestic wastewater effluent as a substrate for microalgal growth, in order to generate an economical and environmentally friendly source of biofuel. Wastewater effluents from three domestic wastewater treatment plants were characterized in terms of known microalgal nutrients viz., ammonia, phosphate and nitrates. Phosphate concentrations varied throughout the year and were found to be low (< 3 mgL-1) whilst ammonia and nitrate concentrations ranged from 0 to 10 mgL-1 throughout the experimental period. These wastewaters were found to be suitable for cultivating microalgae. The study explored the cultivation of Chlorella sorokiniana on pre- and post-chlorinated domestic wastewater effluent to assess their potential as a medium for high microalgal culture density and lipid production. Post-chlorinated wastewater effluent was found to be superior to pre-chlorinated wastewater effluent, as evident by the higher biomass concentration. This wastewater stream did not contain high concentrations of bacteria when compared to pre-chlorinated wastewater effluent. Nitrogen is an essential nutrient required for regulating the growth and lipid accumulation in microalgae. Cultures growing in post-chlorinated effluent had a lifespan of 18 d. Residual nitrogen in wastewater effluent supported microalgal growth for limited periods. Supplementation using cheap, readily available nitrogen sources was required for optimal biomass and lipid production. Urea, potassium nitrate, sodium nitrate and ammonium nitrate were evaluated in terms of biomass and lipid production of C. sorokiniana. Urea showed the highest biomass yield of 0.216 gL-1 and was selected for further experimentation. Urea concentrations (0–10 gL-1) were assessed for their effect on growth and microalgal physiology using pulse amplitude modulated fluorometry. A concentration of 1.5 gL-1 urea produced 0.218 gL-1 biomass and 61.52 % lipid by relative fluorescence. Physiological stress was evident by the decrease in relative Electron Transport Rate from 10.45 to 6.77 and quantum efficiency of photosystem II charge separation from 0.665 to 0.131. Gas chromatography analysis revealed that C16:0, C18:0, C18:1, C18:2 and C18:3 were the major fatty acids produced by C. sorokiniana. Wastewater effluent has been considered an important resource for economical and sustainable microalgal biomass/lipid production. The study showed that C. sorokiniana was sufficiently robust to be cultivated on wastewater effluent supplemented with urea. The results indicate that supplemented wastewater effluent was an acceptable alternative to conventional media. Using a relatively cheap nitrogen source like urea can certainly improve the techno-economics of large scale biodiesel production.

Page generated in 0.0763 seconds