Thesis (M.S.)--Virginia Polytechnic Institute. / Also available via the Internet.

Submitted in fulfillment of the requirements of the degree of Master of Engineering: Chemical Engineering, Durban University of Technology, Durban, South Africa, 2015. / The implementation of new water regulations from the local government has been a motivation for most industries to treat the effluent before disposal or reuse within the plant, in order to save costs and avoid sanctions. Tongaat-Huletts sugar refinery has therefore invested in this collaborative research with the Durban University of Technology in order to investigate new technologies for wastewater treatment and water recovery using an organic coagulant called chitosan. Chitosan is a natural non-toxic polymer extracted from the exoskeleton of crustaceans. Chitosan has gained extensive attention as a coagulant in the treatment of wastewaters from various industries. However, no attention has been given to the coagulation of effluents from the sugar industry using this polymer. In this work, chitosan coagulant (CCo) was prepared by dissolution of known amounts of chitosan powder in aqueous acid at 50℃. The solution was diluted to desired concentrations using distilled water at room temperature. The removal of impurities using chitosan was investigated for two effluent streams from the sugar refinery, namely the final effluent (FE) and the resin effluent (RE) by applying the one-factor-at-a-time (OFAT) method. The optimum chitosan loading was found to be 138 mg/l for the RE and 7.41 mg/l for the FE, beyond which the efficiency of the coagulant decreased. The coagulation of FE removed 97% of the total suspended solids (TSS), 61% colour and 35% chemical oxygen demand (COD). The treatment of RE resulted in the removal of 68% TSS, 30% colour and 15% COD due to its high content of impurities. Therefore, RE was not considered for statistical studies. The Box-Behnken (BBD) design, which is a statistical response surface methodology (RSM) model was used to study the simultaneous effect of pH, coagulant loading and settling time on the removal of the COD, TSS and colour, with the help of an overlay plot for the FE. The optimum values from the overlay plot were 92% for TSS, 83% for colour and 29% for COD. The model equations generated by the BBD for individual responses involved all the manipulated variables contrary to the OFAT which only considered one manipulated parameter per response. Moreover, the BBD allowed the simultaneous analysis of all the parameters and the identification of interactions which occur when the effect of one factor is dependent on the level of another. The most important interaction for the removal of TSS was the combination of the variation in pH and coagulant dosage. The COD removal was mostly affected by the interaction between the coagulant loading and the settling time. The colour removal increased with the simultaneous increase of the pH and the settling time. A comparative study between the wastewaters from the sugar industry, the brewery industry and milk processing industry revealed that the performance of the chitosan was also affected by the amount of total dissolved solids (TDS) in the wastewater. A model was developed relating the TSS, COD and TDS from all these wastewaters, and was used to predict the TSS removal for the effluent from the olive oil mills and the wastewater from the winery. Chitosan can be considered as a good alternative to inorganic and synthetic coagulants for the pre-treatment of the FE due to its ability to efficiently remove the levels of TSS and colour. Furthermore, the production of chitosan from crustacean shells is a good method of reducing pollution from the fishery industry. Chitosan can be produced locally at low cost due to both the abundance of crustacean shells in the coastal regions of South Africa and the simplicity of its preparation process. It is recommended that a mathematical model be developed to accurately predict the influence of chitosan on all types of effluent. Such a model will provide an indication of the performance of the chitosan and guide experimenters. It is further recommended that the effect of the use of organic coagulants on the destabilization of dissolved solids in wastewater be given greater attention.

Orientador: Adriano Luiz Tonetti / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo / Made available in DSpace on 2018-08-25T22:32:30Z (GMT). No. of bitstreams: 1 Manfio_DeniseVazquez_M.pdf: 2805484 bytes, checksum: 374139de08b3238bfbe4a44bf8b51f46 (MD5) Previous issue date: 2014 / Resumo: O gerenciamento do lodo de tanque séptico é uma atividade complexa, de alto custo e pode promover impactos ambientais negativos caso seja mal executada, sendo que a etapa mais crítica é a de desaguamento. O leito de secagem é uma das principais técnicas, mas demanda grandes áreas e muito tempo para remoção da torta seca. A modificação destes leitos, utilizando pavimentos permeáveis e polímeros podem diminuir o tempo e área deste leito. O objetivo do trabalho foi comparar a eficiência de desaguamento da porção de água livre contida no lodo de tanque séptico com o emprego de leito de secagem convencional e leito de secagem composto por pavimento permeável e avaliar a eficiência da utilização de polímeros naturais oriundos da mandioca (Manihot esculenta Crantz), moringa (Moringa oleifera) e quiabo (Abelmoschus esculentus) como auxiliares do processo. A avaliação foi realizada em escala de bancada. Somente o polímero sintético mostrou-se eficiente no condicionamento do lodo. O lodo não condicionado desaguou nos sistemas: pavimento permeável e pavimento permeável e areia, convencional: 611, 620 e 547 mL em média e no lodo condicionado: 1464, 1434 e 1214 mL, respectivamente. Os teores de sólidos da torta seca do lodo sem polímero foram de 24,08, 26,67 e 29,92% para os sistemas: pavimento permeável e pavimento permeável e areia e convencional respectivamente e, no lodo com polímero foram de 23,95, 25,19 e 28,59%. O tempo médio de desaguamento do lodo sem condicionamento foi de 35 dias, enquanto que no lodo condicionado foi de 6 dias. Estes resultados apontam que as tortas secas obtiveram resultados próximos entre si, porém o lodo com adição de polímero teve maior volume desaguado e menor duração. Os leitos alternativos produziram lodos com umidade semelhante ao leito convencional em menor tempo, podendo otimizar o desaguamento do lodo em Estações de Tratamento de Esgoto / Abstract: The slugde management is a complex and high cost activity. It can promove negatives impacts if it is poorly executed, and the most critical step is the dewatering. The drying bed is one of the principal techniques, but it demands big areas and a long periods for the sludge cake removal. The drying beds change can decrease the time and the area of them, if using permeable paving and polymers,. The objective of this work was to compare the efficiency of two techniques to dewatering the bulk water portion inside the septic tank sludge. It was compared the conventional drying bed and the drying bed made of permeable paving. It was also evaluate the efficiency of naturals polymers from cassava (Manihot esculenta Crantz), moringa (Moringa oleifera) and okra (Abelmoschus esculentus) as auxiliaries in the process. The evaluation was performanced in bench scale. The main results showed that only the synthetic polymer was efficient in sludge conditioning. The unconditioned sludge dewatered from the systems: permeable paving, permeable paving plus sand and conventional: 611, 620 and 547 mL on average and for conditioned sludge: 1464, 1434 and 1214 mL, respectively. The dry solids cake in unconditioned sludge was 24,08, 26,67 and 29,92% and in conditioned sludge was 23,95, 25,19 and 28,59% for systems: permeable paving, permeable paving plus sand and conventional, respectively. The average time for dewatering sludge without conditioning was 35 days, whereas in sludge conditioning was 6 days. These results show that the dry solids cake obtained similar results, however the conditioned sludge had higher volume dewatered and shorter time duration. The alternative drying beds produced sludges with suchlike dry solids results dry solids as compared to conventional drying bed in a shorter time, it may optimize sludge dewatering in Waste Water Treatment Plants / Mestrado / Saneamento e Ambiente / Mestra em Engenharia Civil

This thesis shows how the first plan of the Air War Plans Division (AWPD-l) became the most important document in the development of American strategic bombing doctrine in World War II. This plan was not only the first in the Air War Plans Division. but it was the first of its kind in the world. Beyond the history and importance of the plan itself, this study testifies to the success of a handful of dedicated airmen who believed in the power of a strong air force. General Henry H. Arnold deserves tribute for having had the wisdom and foresight to pick a former Air Corps Tactical School (ACTS) instructor to head the AWPD. Finally, the unofficial acceptance of AWPD-l was a triumph for the ACTS itself. Significantly, all four officers ultimately responsible for completing A WPD-l had been instructors at the ACTS. / Master of Science

Thesis (Ph.D.)--University of Wollongong, 2005. / Typescript. This thesis is subject to a two year embargo until 17/11/2007 and may only be viewed and copied with the permission of the author. For further information please Contact the Archivist. Includes bibliographical references: leaf 226-249.

Yes / The Sustainable Development Goal (SDG) 6.1, established by the United Nations General Assembly in 2015, targets universal and equitable access to safe and affordable drinking water for all by 2030. An essential factor in achieving this goal is the harnessing of “green” coagulants – naturally occurring, environmentally friendly materials which are effective coagulants for use in water treatment, with good availability in developing countries, inherent renewable properties and ease of biodegradation. In order to gain from these benefits, it is essential to fully understand how such coagulants may best be utilised, particularly concerning their practical application in developing countries. In this study, three different plant-based coagulation products (PCPs), namely Hexane (HxKP), saline (StKP) and crude (CrKP) extracts of Kenaf plant seed (Hibiscus cannabinus, a species of the Hibiscus plant), were applied to high (HTW), medium (MTW) and low (LTW) turbidity water in order to determine their performance and coagulation ability. The ability of the three Kenaf coagulant products (KCPs) to remove hydrophobic fractions of natural organic matter (NOM) was measured. The impact of KCPs on the treated water organic matter content (a known disinfection by-product (DBP) precursor) was examined using known surrogates of natural organic matter (NOM) i.e. the dissolved organic carbon (DOC), ultraviolet absorbance at 254 (UV254) and specific ultraviolet absorbance (SUVA254). Results obtained quantify the implications of using these coagulants during the water disinfection process. A parametric study, measuring the effect of different operating parameters, such as untreated water turbidity, pH, dosages, retention time, and KCP storage time, was completed. Turbidity removal performance for HxKP and StKP was very good with > 90% removal recorded for HTW and MTW, respectively, at pH seven within 2 hours retention time. Images obtained from scanning electron microscopy (SEM) analysis revealed a high likelihood of the coagulation mechanism of KCPs to be adsorption-interparticle bridging brought about by their flake-like structures and surfaces charges. Varying pH had no measurable influence on the coagulation performance of the KCPs. Comparing their efficiency with Moringa Oleifera (MO, a previously researched PCP) and alum showed that HxKP had a negligibly different particle removal as MO. StKP turbidity removal performance was below HxKP by 1% for HTW and LTW and 2% for MTW but performed higher than the CrKP by 5% and 7% in HTW and MTW, respectively. The optimum dosage of HxKP and StKP reduced DBP surrogate values, indicating that its precursor is also minimized, although a slight shift from this optimum dosage showed a significant rise in their concentration thus signifying a potential increase in DBPs during disinfection.

<p>Cilj ove doktorske disertacije je bio da se ispita mogućnost dobijanja prirodnih<br />koagulanata iz zrna pasulja koji bi se koristili u obradi različitih voda i otpadnih voda. U okviru izvedenih eksperimenata su utvrđeni najbolji uslovi za ekstrakciju prirodnih koagulanata iz pasulja, određen je hemijski sastav sirovih ekstrakata dobijenih na različite načine, proverena je trajnost i određen način čuvanja sirovih ekstrakata i ispitan uticaj različitih parametara na koagulacionu aktivnost sirovih ekstrakata.<br />S obzirom na to da su prirodni koagulanti organskog porekla, oni povećavaju sadržaj organskih materija u tretiranoj vodi, pa su u okviru rada ispitane i upoređene različite metode preči&scaron;ćavanja sirovog ekstrakta pasulja, a zatim određen uticaj sirovog ekstrakta i preči&scaron;ćenih koagulanata na sadržaj organskih materija u obrađenoj vodi.<br />Kako bi se ispitala efikasnost prirodnih koagulanata iz zrna pasulja u realnim vodama,<br />oni su bili primenjeni u otpadnim vodama od proizvodnje bioetanola. Pored toga, ispitana je mogućnost njihove primene u kombinaciji sa konvencionalnim koagulantima, i na samom kraju je ispitan sastav pasulja koji preostane nakon ekstrakcije prirodnih koagulanata kako bi se utvrdilo da li je pogodan za kori&scaron;ćenje kao<br />dodatak stočnoj hrani.<br />Dobijeni rezultati su pokazali da se iz zrna pasulja može dobiti ekstrakt visoke koagulacione aktivnosti, koji se dalje može efikasno prečistiti tako da ne povećava sadržaj organskih materija u obrađenoj vodi, već ga naprotiv smanjuje. Takođe, prirodni koagulanti iz pasulja se mogu uspe&scaron;no primeniti za tretman otpadnih voda od proizvodnje bioetanola, mogu biti pomoćni koagulanti aluminijum-sulfatu, a pasulj nakon ekstrakcije prirodnih koagulanata sa destilovanom vodom se može iskoristiti kao<br />dodatak stočnoj hrani.</p> / <p>The aim of this PhD thesis was to investigate the possibility to obtain natural coagulants from common bean which could be used for different waters and wastewaters treatment. The optimal conditions for extraction of natural coagulants from common bean, the chemical composition of crude extracts obtained in different ways and the influence of various parameters on coagulation activity of crude extracts were determined within the performed experiments. The durability of crude extracts was checked and the way of their storage defined.<br />Considering the fact that natural coagulants are of organic origin, they increase the content of organic matter in treated water. Hence, the different methods of purification of common bean crude extract were investigated and compared, and thereafter the influence of crude extract and purified coagulants on organic matter content in treated water was determined.<br />Natural coagulants obtained from common bean were applied in bioethanol stillages in order to explore their efficiency in real waters. Besides, the possibility of their usage combined with conventional coagulants was investigated. At the end, the composition of common bean that remains after extraction of natural coagulants was determined in order to to prove if it was appropriate as addition to feed.<br />Obtained results showed that extract of high coagulation activity can be obtained from common bean. It can be efficiently purified so as not to increase the organic matter content of the water, but on the contrary, to decrease it. Natural coagulants from common bean can be successfully applied for treatment of wastewaters remained after bioethanol production, they can be used as coagulant aid with alum, and the common bean remained after extraction of natural coagulants with distilled water can be utilized as addition to feed.</p>

Made available in DSpace on 2015-05-14T12:09:15Z (GMT). No. of bitstreams: 1 ArquivoTotal.pdf: 1961421 bytes, checksum: 973f1642f643f82ef2c4091be77d57aa (MD5) Previous issue date: 2013-03-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In the steps of the process of plastics recycling, the washing process produces an effluent with high organic load that requires treatment for disposal. In order to evaluating the organic load physicochemical parameters were analyzed in order to establish the best form of treatment for the effluent reuse in a plastic recycler at the washing process. Sample collection was made in the washing tank at the end of the washing process at determined cycles around 12:00h. According to the obtained results the need arises for the treatment of effluent, both to frame it in the discard parameters established by the legislation of the national council of the environment (CONAMA), and to reuse it inside the recycler. As proposal was used for washing effluent treatment the coagulation/flocculation process, where was applied three types of coagulants (ferric chloride, aluminum sulfate and polychloride aluminum) at doses ranging from 5mg.L-1 of 65mg.L-1 and the Fenton oxidative process. For the effluent under study, it was concluded that the ferric chloride has a higher efficiency in the reduction of parameters analyzed, turbidity, pH, COD, BOD, TSS and TOC in relation to sulfate aluminum e polychloride aluminum, when comparing the physical and chemical characteristics of raw and treated effluent. Through the analysis it was found that the Fenton process has an efficiency on average of 92% of turbidity and 94% of COD and 90,5% of BOD, in reaction time of 60 minutes with agitation magnetic. The treated effluent presents values compatible for reuse. / Nas etapas do processo de reciclagem, a lavagem dos plásticos produz um efluente de elevada carga orgânica que requer tratamento para o descarte. Com intuito de avaliar a carga orgânica, os parâmetros físico-químicos foram analisados possibilitando estabelecer a melhor forma de tratamento para reciclagem do efluente tratado, gerado na lavagem dos plásticos de uma recicladora para fins de reuso. A coleta foi feita no tanque de lavagem no final de cada ciclo de lavagem em torno das 12h00. A partir dos resultados obtidos surge à necessidade do tratamento do efluente, tanto para enquadrá-lo nos parâmetros de descarte estabelecidos pela legislação do Conselho Nacional do Meio Ambiente (CONAMA), quanto para reusá-lo dentro da própria recicladora. Como proposta foi utilizado para o tratamento do efluente de lavagem o processo de coagulação/ floculação, sendo aplicados três tipos de coagulantes (cloreto férrico, sulfato de alumínio e policloreto de alumínio) em dosagens na faixa de 5mg.L-1 a 65mg.L-1 e o processo oxidativo avançado Fenton. Para o efluente em estudo, concluiu-se que o cloreto férrico tem uma maior eficiência na redução dos parâmetros analisados pH, turbidez, Demanda Química de Oxigênio (DQO), Demanda Bioquímica de Oxigênio (DBO), Sólidos Suspensos Totais (SST), Carbono Orgânico Total (COT) em relação ao sulfato de alumínio e o policloreto de alumínio, quando comparados as características físico-químicas do efluente bruto. Através das análises foi possível constatar que o processo Fenton apresentou uma eficiência em média 92% de turbidez e 94% de DQO, DBO 90,5% em tempo de reação de 60 minutos com agitação em que o efluente tratado apresenta valores compatíveis para o reuso.

Orientador: José Euclides Stipp Paterniani / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agrícola / Made available in DSpace on 2018-08-16T22:17:56Z (GMT). No. of bitstreams: 1 Franco_Monalisa_M.pdf: 2504289 bytes, checksum: c3dab56362e90efdcc7aec3f404bc2bb (MD5) Previous issue date: 2010 / Resumo: A água é recurso indispensável para a sobrevivência do ser humano. Em comunidades onde os sistemas convencionais de tratamento de água enfrentam difícil implantação é necessária a busca por tecnologias adequadas. Os filtros lentos apesar da simples manutenção e baixo custo se tornaram limitados devido à degradação da qualidade dos mananciais, sendo necessário o uso de pré-tratamentos para melhoria da qualidade de água para o seu emprego. Coagulantes naturais, dentre eles aquele produzido a partir de sementes de Moringa oleifera são alternativas para o tratamento de água para regiões desprovidas de tecnologias convencionais. Portanto, o objetivo deste trabalho é avaliar a influência de diferentes dosagens do coagulante natural de Moringa oleifera na eficiência das etapas do sistema de filtração em múltiplas etapas no tratamento de água. O sistema foi constituído por pré-filtro dinâmico, pré-filtros de fluxo ascendente e filtros lentos, e em alguns ensaios por floculador granular. Em seguida, foram definidas as dosagens de 131mg.L-1 de solução coagulante de Moringa oleifera a ser aplicada na etapa da pré-filtração e 106 mg.L-1 e 53mg.L-1 a serem aplicadas nas etapas de filtração lenta, que poderiam passar pelo floculador ou não. No filtro lento em que houve a introdução da solução coagulante foram testados primeiramente três camadas de mantas não tecidas de gramatura de 400g.m-2 e em seguida uma camada de 150 g.m-2 no topo da camada de areia. A aplicação da solução coagulante proporcionou na etapa da pré-filtração, média de turbidez de 11NTU e cor aparente de 73mg.L-1 PtCo. Na etapa da filtração lenta esses valores foram 1,15NTU e 11mg.L-1PtCo, para dosagem de 106mg.L-1 de Moringa oleifera e de 5NTU e 42mg.L-1PtCo para a dosagem de 53mg.L-1 da solução coagulante. A aplicação de apenas uma camada de manta não tecida no topo do meio filtrante do filtro lento demonstrou ser benéfica para o sistema, pois manteve o alto índice de eficiência de remoção de turbidez e cor aparente. Deste modo conclui-se que o uso do coagulante extraído das sementes de Moringa oleifera melhorou a eficiência do tratamento de água pelo sistema de filtração em múltiplas etapas, principalmente quando o coagulante foi aplicado na etapa de pré-filtração. Entretanto, a aplicação direta da solução coagulante no filtro lento causou rápida colmatação da manta e menor tempo de duração da carreira, além disso a passagem da solução coagulante pelo floculador granular não apresentou resultados satisfatórios / Abstract: Water is the most important resource for human survival. In communities where the conventional water treatment faces difficult deployment is necessary to search for simple technologies. Simple maintenance and low cost are presented for slow sand filter, however the water degradation has limited this operation system and now pre treatments are necessary for using this technology. Natural coagulants and among them those produced from Moringa oleifera seeds are alternatives for water treatment in regions where there is not conventional technologys. Therefore, this study aims is evaluate the influence of different dosages of natural coagulant extracted from Moringa oleifera seeds on multistage filtration system. The system was composed with dynamic roughing filter, uplflow roughing filters, slow sand filters and some tests by granular flocculator. The dosage of 131mg.L-1 of Moringa oleifera solution was defined to be applied on upflow roughing filter and the dosages of 106mg.L-1 and 53mg.L-1 on slow sand filter, which could pass through flocculator or not. The slow sand filter that received the coagulant solution was tested with three layers of nonwoven blankets with 400g/m² and afterward with one layer of nonwoven blanket with 150g/m² at the top of the sand. After the application of natural coagulant solution in upflow roughing filter, the mediums values of turbidity and apparent color were 11NTU and 73mg.L-1 PtCo, respectively. In slow sand filtration stage these values were 1,15NTU and 11mg.L-1PtCo for the dosage of 106mg.L-1 of Moringa oleifera, and 5NTU and 42mg.L-1PtCo for the dosage of 53mg.L-1 of the coagulant solution. The application of a single layer of nonwoven blanket on top of slow sand filter proved to be beneficial to the system because it maintained a high rate of removal efficiency of turbidity and apparent color. Thus it is concluded that the use of coagulant extracted from Moringa oleifera seeds improved the efficiency of water treatment by multistage filtration system. However, the direct application of the coagulant solution into the slow sand filter caused rapid clogging of the blanket and shorter career length. Furthermore, unsatisfying results was showed from the passage of the coagulant solution by granular flocculator / Mestrado / Agua e Solo / Mestre em Engenharia Agrícola

Orientadores : Salvador Massaguer Roig , Carlos Raimundo Ferreira Grosso / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-07-22T17:21:26Z (GMT). No. of bitstreams: 1 Dornellas_JoseRaimundoFerreira_M.pdf: 9840953 bytes, checksum: dc81a98e72ffc4f8215d12d6c0b32120 (MD5) Previous issue date: 1997 / Resumo: Avaliou-se neste estudo o emprego de três agentes coagulantes ( bovino, microbiano e obtido por fermentação de E. colí K12, modificada geneticamente) na fabricação do queijo Minas Frescal. Objetivou-se avaliar o "shelf life" do queijo Minas Frescal com o uso dos agentes coagulantes conjuntamente com o uso de fermento lático e ácido lático 85%. Cinco tratamentos repetidos em três dias diferentes, utilizando-se 50 litros de leite para cada tratamento, foram denominados da seguinte forma: BOF (coalho bovino e fermento lático); MICA (coagulante microbiano e ácido lático); MICROF (coagulante microbiano e fermento lático); CHA (coalho obtido por fermentação e ácido lático); CHF (coalho obtido por fermentação e fermento lático). Avaliação do rendimento, proteólise, textura instrumental, cor, microbiologia e sensorial foi efetuada semanalmente, durante o período de um mês, para cada repetição. Não foram detectadas diferenças significativas para as porcentagens de transição de proteína, gordura e extrato seco total. Não foram observadas diferenças significativas no rendimento dos tratamentos, muito embora o rendimento em quilos de leite por quilos de queijo tenha sido maior para o coalho obtido por fermentação, o que sugere uma maior retenção de água no produto final. Os teores de Nitrogênio Solúvel a pH 4,6 e de nitrogênio Solúvel em TCA 12% (NNP), aumentaram significativamente durante o período de "shelf life"do produto ( p=0,0001). Os dados sugerem que a variação do teor de sal no queijo Minas Frescal influenciam os indices de maturação , o que pode ser justificado pela diferença de umidade encontrada entre as repetições. A análise eletroforética dos queijos mostrou maior degradação dos produtos fabricados com coagulante microbiano e fermento lático (MICROF), seguido por coagulante microbiano com ácido lático (MICA), coalho bovino com fermento lático (BOF), coalho obtido por fermentação com fermento lático (CHF) e finalmente por coalho obtido por fermentação com ácido lático (CHA). A degradação da a. 81 ­caseína ocorreu em todos os tratamentos, porém com menos intensidade em CHA. A as1-caseína também apresentou proteólise , com decréscimo perceptível durante o experimento, menos para CHA, onde a ß-caseina praticamente manteve-se intacta. Parece haver um efeito sinergístico acentuado entre o coagulante microbiano e o fermento lático, com o primeiro fornecendo substratos de fácil acesso às enzimas do fermento lático. O queijo processado com o coagulante mais utilizado no país (BOF), mostrou um padrão eletroforético onde a as1-caseína foi nitidamente proteolisada com o tempo. A ß-caseina também foi proteolisada , com decréscimo perceptível durante o experimento. O coalho obtido por fermentação com fermento (CHF), apresentou desdobramento quase que total da a as1-caseína. Estes resultados estão em concordância com os valores de NS a pH 4,6 e TCA 12%. MICROF, BOF, CHF, perderam sua forma física nos primeiros 15 dias de estocagem. A avaliação de textura instrumental para este queijo fica invalidada, devido a heterogeneidade do produto, provocando alta variabilidade entre repetições de um mesmo tratamento. Com relação ao sabor, os tratamentos utilizando coagulante microbiano, foram os únicos que não apresentaram diferença significativa durante o experimento. O ácido lático mostrou ser uma boa alternativa para aumentar o "shelf life" do produto, quanto aparência e forma física, porém o queijo ficou mais exposto ao ataque de microorganismos contaminantes / Abstract: Three coagulating agents (bovine, microbial and one obtained by fermentation using a genetically modified E. col; K12) were evalueted for their use in the processing of Minas cheese. The objetive was to evaluate the shelf life of the cheeses using these coagulating agents together with mesophilic starter and 85%lactic acid. Cheeses were processed on three separate days using approximately 50kg milk for each batch and were denominated as follows: BOF (bovine coagulant plus mesophilic starter); MICA (microbial coagulant plus lactic acid); MICROF (microbial coagulant plus mesophilic starter); CHA (coagulant from fermentation plus lactic acid); CHF (coagulante from fermentation fermentation plus lactic acid). No signifcant differences were found in the percentagen recoveries of the protein, fat and total dry matter. No significant differences were observed in the yields from the treatments although the yield of cheese per kilo of milk was greater using the coagulant obtained by fermentation, suggesting a greater water retention in the final product. The levels of nitrogen soluble at pH 4.6 and in 12% TCA (NNP), increased significanly during the shelf life of the products (p=0,0001). The data suggest that the differences in salt content of the cheeses influenced the indices of proteolysis, which could be justified by the difference in the moisture content found between replicates. WIth respect to the electophoretic behaviour, the greatest protein degradation was shown by the microbial coagulant plus mesophilic starter (MICROF), followed by the microbial coagulant plus lactic acid (MICA), bovine coagulant plus mesophilic starter (BOF), coagulant obtained by fermentation plus mesophilic starter (CHF) and finally the coagulant obtained by fermentation plus lactic acid (CHA). Degradation of as1-casein occurred with all the treatments but was less intense in CHA. The ß casein also showed proteolysis with a perceptible decrease during the experiment, except for CHA, in which the ß-casein remained practically intact. There was apparently an accentuated synergistic effect between the microbial coagulant and the mesophilic starter , with the former providing substrates easily attacked by the enzymes of the latter. The cheese processed by the most commonly used combination in Brazil (BOF), showed an electrophoretic pattern in which the as1- casein was clearly proteoysed with time. The ß - casein was also proteolysed, showing a perceptible decrease during the experiment. The coagulant obtained by fermentation plus mesophilic starter (CHF) resulted in almost complete degradation of the as1-casein. These results are in accordance with the values for nitrogen soluble at pH 4.6 and 12% TCA. MICROF, BOF, and CHF lost their physical form during the first 15 days of storage. The instrumental evaluation of the texture of these eheeses was invalidated on aeeount of the heterogeneity of the products. The sensory evaluation determined the significant differences between the treatments with respect to time. The use of lactie aeid was shown to be a good alternative to inerease the shelf life of the products with respect to appearance and physical form, although it was the most liable to attack by contaminating mieroorganisms / Mestrado / Mestre em Tecnologia de Alimentos