Volcanic ash, pumice and Moringa oleifera (M. oleifera) were investigated as indigenous materials for removal of natural organic matter (NOM) at Kampala and Masaka water treatment plants in Uganda. Coagulation and filtration experiments were done using raw water at Kampala (Ggaba) and Masaka (Boma) National Water &amp; Sewerage Corporation water treatment plants. Assessment of the two plants was done and they were found to be faced with differing challenges given the nature of their raw water sources. Therefore, the study was conducted to seek appropriate treatment processes that suite the conditions at the respective plant and avoid or minimize formation of unwanted chlorination by-products. The results from the study indicated that there were both operational and design handicaps at the Ggaba treatment plant with a need to modify the filtration and clarification units. At Masaka, pre-chlorination led to increases in total trihalomethanes as high as 4000%. The characterization studies indicated the major fraction of NOM to be hydrophilic and there was no variation in the character of NOM along the unit treatment processes investigated. On the other hand experiments conducted at both the pilot and laboratory scale gave promising results. Simple horizontal flow roughing filter at Masaka gave rise to dissolved organic carbon (DOC) and ferrous iron removals of 27% and 89% respectively. With a combined use of pumice and hydrogen peroxide in the filter, DOC removals of up to 68% were achieved. The results from jar test experiments also indicated that use of alum with M. oleifera coagulant extracted with sodium chloride solution as coagulant aid is promising as a first stage in the treatment train for waters with a humic materials and high content of iron, typical of swamp water sources. Therefore the findings show that it is possible to avoid the formation of unwanted by-products by application of roughing filtration with hydrogen peroxide in place of the pre-chlorination process. Assessment of the characteristics of the volcanic ash showed that it meets the requirements for a filtration material; and results obtained from the pilot study showed that it was a suitable alternative material for use in a dual media filtration system. There was an increase in the filter run length of about two and half fold in the dual media filtration column compared to the mono medium column. / Vulkanaska, pimpsten och Moringa oleifera (M. oleifera) undersöktes som inhemska material for borttagande av naturligt organiskt material (NOM) i Kampala och Masaka reningsverk i Uganda. Koagulation och filtreringsexperiment gjordes med hjalp av råvatten i Kampala (Ggaba) och Masaka (Boma)reningsverk, som ingår i Nationella Vatten- och avloppsreningsverk, ett företag i Uganda. En bedömning av de två anläggningarna gjordes och det visade sig stå inför olika utmaningar på grund av de olika råvattnens karaktär. Den här studien genomfördes för att söka lämpliga processer för behandling av anpassade till förhållandena vid respektive anläggning samt för att undvika eller minimera uppkomsten av olika klorerade biprodukter. Resultatet från studien visade att det fanns problem både när det gäller design och arbetsrutiner på reningsverket Ggaba med ett behov att ändra filtrerings- och klarningsenheternaI Masaka ökade förkloreringsprocessen den totala mängden trihalometaner med 4000 %. Karakteriseringen av naturligt organiskt material (NOM) visade på en stor andel hydrofilt material och att ingen förändring av det organiska materialets karaktär skedde längs den undersökta processenheten. Å andra sidan visade både laboratorieförsök och experiment i pilotanläggningen att lovande resultat. Ett enkelt horisontellt flöde genom ett grovt filter i pilotanläggningen i Masaka resulterade i 89% mindre järn och 27% mindre NOM. Med en kombination av pimpsten och väteperoxid i filtret var avlägsnandet av löst organiskt material(DOC) från vattnet 68%. Resultaten från batchexperiment (jar test) i laboratoriet visade också lovande resultat för aluminium tillsammans med en koagulant extraherad med natriumklorid från Moringa oleifera (MOC-SC), som ett första steg för vatten från sumpmark med höga halter av järn och organiskt material. Således visar resultaten att det går att undvika bildandet av höga halter av trihalometan (THM) genom genom tillämpning av grovfitrering med väteperoxid i stället för förkloreringsprocessen. Utvärderingen av vulkanaskans egenskaper visade att vulkanaskan uppfyller kraven på ett filtermaterial och resultaten från pilotanläggningen visade att det är ett lämpligt material i ett filtreringssystem med två media. Den utnyttjade delen av filtret var 2,5 gånger längre i körningen med dubbla medier jämfört med ett medium. / <p>QC 20120910</p> / MAKERERE – Sida/SAREC RESEARCH COLLABORATION

Slow sand filtration is a proven and sustainable technology for drinking water treatment in small communities. The process, however, is sensitive to lower water temperatures that can lead to decreased biological treatment, and high raw water turbidity levels that can lead to premature clogging of the filter and frequent cleaning requirements, resulting in increased risk of pathogen breakthrough. Multistage filtration, consisting of roughing filtration followed by slow sand filtration, can overcome these treatment limitations and provide a robust treatment alternative for surface water sources of variable water quality in northern climates, which typically experience water temperatures ranging down to 2&deg;C. Prior to this study, however, multistage filtration had yet to be systematically challenged in colder climates, including testing of its performance under increased hydraulic loadings and elevated influent turbidity together with cold water conditions. The primary goal of this research was to demonstrate the reliability of multistage filtration for small communities in northern climates with reference to the Ontario Safe Drinking Water Act. In this research, testing was conducted on two different pilot multistage filtration systems and fed with water from the Grand River, a municipally and agriculturally impacted river in Southern Ontario. One system featured pre-ozonation and post-granular activated carbon (GAC) stages, and shallower bed depths in the roughing filter and slow sand filter. The other system featured deeper bed depths in the roughing filter and slow sand filter, two parallel roughing filters of different design for comparison, and a second stage of slow sand filtration for increased robustness. Removal of turbidity, total coliforms, and fecal coliforms under a range of influent turbidities (1 to >100 NTU), water temperatures (~2 to 20&deg;C), and hydraulic loading rates (0. 2 to 0. 8 m/h) were investigated. In addition, the slow sand filters in each pilot system were challenged with high concentrations (~10⁶ oocyst/L) of inactivated <i>Cryptosporidium parvum</i> oocysts. The performance of both pilot multistage filtration systems was highly dependent on the biological maturity of the system and its hydraulic loading rate. In a less mature system operating in cold water conditions (<5&deg;C), effluent turbidity was mostly below 0. 5 NTU during periods of stable influent turbidity (no runoff events) and a hydraulic loading of 0. 4 m/h, however, runoff events of high influent turbidity (>50 NTU), increased hydraulic loadings (0. 6 m/h), and filter cleaning occasionally resulted in effluent turbidity above 1 NTU. Furthermore, in a less mature system operating during runoff events of high turbidity, reducing the hydraulic loading rate to 0. 2 m/h was important for achieving effluent turbidity below 1 NTU. However, in a more mature system operating in warm water conditions (19-22&deg;C), effluent turbidity was consistently below 0. 3 NTU at a hydraulic loading rate of 0. 4 m/h, and below 0. 5 NTU at 0. 8 m/h, despite numerous events of high influent turbidity (>25 NTU). It remains to be seen whether this performance could be sustained in colder water temperatures with a fully mature filter. Removal of coliform bacteria was occasionally incomplete in a less mature multistage system, whereas, in a more mature system operating in warm water conditions (>9&deg;C), removal was complete in all measurements. Furthermore, the average removal of <i>Cryptosporidium</i> was greater than 2. 5 logs in both systems (with hydraulic loading rates ranging from 0. 4 to 0. 8 m/h) and improved with increased filter maturity. Each individual stage of the multistage system was an important treatment barrier in the overall process of turbidity and pathogen removal. The roughing filter was not only important for protecting the slow sand filter from solids loading and increasing its run length, but was also a significant contributor to coliform removal when the system was less mature. Removal of turbidity was significantly improved when the roughing filter was more mature, suggesting that biological treatment was an important treatment mechanism in the roughing filter. Although pre-ozonation was used mainly for the removal of organic carbon and colour, it achieved complete removal of coliform bacteria and was also suspected to be important for enhanced removal of turbidity. The second slow sand filter in series provided additional robustness to the process by reducing effluent turbidity to below 1 NTU during cold water runoff events of high turbidity and increased hydraulic loadings (0. 6 m/h), while achieving effluent below 0. 3 NTU during normal periods of operation. It also provided additional removals of coliforms under challenging operating conditions, and contributed an additional average removal of <i>Cryptosporidium</i> of 0. 8 logs, which resulted in cumulative removal of 3. 7 logs, approximately 1 log greater than all the other challenge tests. Collectively, the entire multistage system performed well with water temperatures ranging down to 2&deg;C, limited filter maturity, elevated raw water turbidities, and increased hydraulic loading rates. Its ability to meet the current Ontario turbidity regulations and greater than 2 log removal of <i>Cryptosporidium</i> over a range of operating conditions, with little or no process adjustment, is a testament to the robustness and minimal maintenance requirements of the process, which are desirable attributes for small water systems that are often located in rural areas. While this research demonstrated the performance of multistage filtration using pilot scale testing, it is important to note that full-scale plants tend to produce significantly better results than pilot facilities, due to long term biological maturation of the system. Overall, multistage filtration is a sustainable and cost-effective technology that, through this research, appears to be a safe, reliable, and robust treatment alternative for small and non-municipal water systems in North America and the developing world. Further, based on its performance with challenging influent water quality and cold water conditions, multistage filtration holds particular promise for small communities in northern climates that are required to meet safe drinking water regulations, but are dependent on surface water sources of variable water quality and temperatures.

Slow sand filtration is a proven and sustainable technology for drinking water treatment in small communities. The process, however, is sensitive to lower water temperatures that can lead to decreased biological treatment, and high raw water turbidity levels that can lead to premature clogging of the filter and frequent cleaning requirements, resulting in increased risk of pathogen breakthrough. Multistage filtration, consisting of roughing filtration followed by slow sand filtration, can overcome these treatment limitations and provide a robust treatment alternative for surface water sources of variable water quality in northern climates, which typically experience water temperatures ranging down to 2&deg;C. Prior to this study, however, multistage filtration had yet to be systematically challenged in colder climates, including testing of its performance under increased hydraulic loadings and elevated influent turbidity together with cold water conditions. The primary goal of this research was to demonstrate the reliability of multistage filtration for small communities in northern climates with reference to the Ontario Safe Drinking Water Act. In this research, testing was conducted on two different pilot multistage filtration systems and fed with water from the Grand River, a municipally and agriculturally impacted river in Southern Ontario. One system featured pre-ozonation and post-granular activated carbon (GAC) stages, and shallower bed depths in the roughing filter and slow sand filter. The other system featured deeper bed depths in the roughing filter and slow sand filter, two parallel roughing filters of different design for comparison, and a second stage of slow sand filtration for increased robustness. Removal of turbidity, total coliforms, and fecal coliforms under a range of influent turbidities (1 to >100 NTU), water temperatures (~2 to 20&deg;C), and hydraulic loading rates (0. 2 to 0. 8 m/h) were investigated. In addition, the slow sand filters in each pilot system were challenged with high concentrations (~10⁶ oocyst/L) of inactivated <i>Cryptosporidium parvum</i> oocysts. The performance of both pilot multistage filtration systems was highly dependent on the biological maturity of the system and its hydraulic loading rate. In a less mature system operating in cold water conditions (<5&deg;C), effluent turbidity was mostly below 0. 5 NTU during periods of stable influent turbidity (no runoff events) and a hydraulic loading of 0. 4 m/h, however, runoff events of high influent turbidity (>50 NTU), increased hydraulic loadings (0. 6 m/h), and filter cleaning occasionally resulted in effluent turbidity above 1 NTU. Furthermore, in a less mature system operating during runoff events of high turbidity, reducing the hydraulic loading rate to 0. 2 m/h was important for achieving effluent turbidity below 1 NTU. However, in a more mature system operating in warm water conditions (19-22&deg;C), effluent turbidity was consistently below 0. 3 NTU at a hydraulic loading rate of 0. 4 m/h, and below 0. 5 NTU at 0. 8 m/h, despite numerous events of high influent turbidity (>25 NTU). It remains to be seen whether this performance could be sustained in colder water temperatures with a fully mature filter. Removal of coliform bacteria was occasionally incomplete in a less mature multistage system, whereas, in a more mature system operating in warm water conditions (>9&deg;C), removal was complete in all measurements. Furthermore, the average removal of <i>Cryptosporidium</i> was greater than 2. 5 logs in both systems (with hydraulic loading rates ranging from 0. 4 to 0. 8 m/h) and improved with increased filter maturity. Each individual stage of the multistage system was an important treatment barrier in the overall process of turbidity and pathogen removal. The roughing filter was not only important for protecting the slow sand filter from solids loading and increasing its run length, but was also a significant contributor to coliform removal when the system was less mature. Removal of turbidity was significantly improved when the roughing filter was more mature, suggesting that biological treatment was an important treatment mechanism in the roughing filter. Although pre-ozonation was used mainly for the removal of organic carbon and colour, it achieved complete removal of coliform bacteria and was also suspected to be important for enhanced removal of turbidity. The second slow sand filter in series provided additional robustness to the process by reducing effluent turbidity to below 1 NTU during cold water runoff events of high turbidity and increased hydraulic loadings (0. 6 m/h), while achieving effluent below 0. 3 NTU during normal periods of operation. It also provided additional removals of coliforms under challenging operating conditions, and contributed an additional average removal of <i>Cryptosporidium</i> of 0. 8 logs, which resulted in cumulative removal of 3. 7 logs, approximately 1 log greater than all the other challenge tests. Collectively, the entire multistage system performed well with water temperatures ranging down to 2&deg;C, limited filter maturity, elevated raw water turbidities, and increased hydraulic loading rates. Its ability to meet the current Ontario turbidity regulations and greater than 2 log removal of <i>Cryptosporidium</i> over a range of operating conditions, with little or no process adjustment, is a testament to the robustness and minimal maintenance requirements of the process, which are desirable attributes for small water systems that are often located in rural areas. While this research demonstrated the performance of multistage filtration using pilot scale testing, it is important to note that full-scale plants tend to produce significantly better results than pilot facilities, due to long term biological maturation of the system. Overall, multistage filtration is a sustainable and cost-effective technology that, through this research, appears to be a safe, reliable, and robust treatment alternative for small and non-municipal water systems in North America and the developing world. Further, based on its performance with challenging influent water quality and cold water conditions, multistage filtration holds particular promise for small communities in northern climates that are required to meet safe drinking water regulations, but are dependent on surface water sources of variable water quality and temperatures.

Submitted in fulfillment for the requirements of the degree of Master of Engineering, Department of Chemical Engineering, Durban University of Technology, KwaZulu-Natal, South Africa, 2016. / A large fraction of the world's population, around 1.1 billion people, do not have access to acceptable sources of water. In South Africa there is a growing pressure on the available freshwater resources. New sources of freshwater supply are becoming increasingly scarce, expensive or politically controversial. This has led to large scale interest in the application of water reclamation and reuse of domestic, mining and industrial wastewater as an alternative water supply sources. This is becoming critical to sustain development and economic growth in the Southern African region. This research aims at providing both social and scientific information on the importance of greywater reuse and recycling as an alternate source to aid water demand management under South African conditions. The approach to this research work was divided into two main thrusts: the first was to gain an understanding of the public attitudes towards the idea of reusing greywater that is usually perceived as wastewater which pose health concerns. The second was to provide an understanding of typical greywater quality in a peri-urban community in Durban, South Africa as well as investigate the suitability of a horizontal roughing filtration system in reducing pollutant strength of contaminants found in greywater for non-potable reuse applications. In order to achieve the central aim of this research study, the following objectives were considered: • Investigation of public perception and attitudes towards the reuse of greywater. • Determination of greywater quality in a peri-urban community in Durban South Africa. • Investigation of the performance of a horizontal roughing filtration system for the treatment of greywater collected from a peri-urban community in Durban, South Africa. It was important to have an understanding of public perception and attitudes towards the reuse of greywater because of the fact that the success of any reuse application depends on the acceptance of the public. The methodological approach for this aspect of the research work involved administering of structured questionnaires to residents within the community through field visits. The questionnaire addressed issues related to attitudes towards the reuse of greywater, perceived advantages related to the reuse of greywater and concerns related to public health issues regarding the reuse of greywater. The successful implementation of any greywater treatment process depends largely on its characteristics in terms of the pollutant strength. The methodological approach for this aspect of the research work involved physico- chemical characterization of the greywater collected from different sources within the households in the peri-urban community. Greywater samples were collected from the kitchen, shower and laundry within each of the households. This aspect of the research work was undertaken to gain an understanding of greywater quality from different sources within and between households. In order to achieve the third objective of this research work, a pilot plant horizontal roughing filtration system was designed and fabricated for the treatment of greywater. The system consisted of three compartments containing different sizes of gravel that served as the filter media. This was done in order to investigate the effect of varying filter media size on the performance of the horizontal roughing filtration system in treating greywater. The system had an adjustable manual valve used in varying the filtration rate. The impact of varying filtration rate on the performance of the horizontal roughing filtration system in treating greywater was also investigated. The main findings of this research were: • From the survey conducted, the percentage of the public willing to accept the reuse of greywater within the community was far higher than the percentage opposing its reuse. Concerns have often been expressed by the public that the reuse of greywater could pose possible adverse effects to public health. However, in this pilot study it was found that a higher percentage of respondents (>60%) disagree that the reuse of greywater could negatively impact on public health compared to less than 20% of the respondents that agree. An interesting finding of this study was that a greater percentage of the respondents were willing to have a dual water distribution system installed in their current place of residence. • The physico-chemical characterization of greywater from different sources within the households investigated indicated that, the quality of greywater varies considerably between all sources and from household to household. None of the households investigated produced the same quality of greywater. It was also found that greywater generated from the kitchen contains the most significant pollutants in terms of the physico-chemical parameters considered in this study compared to the other sources within the household. • The pilot plant horizontal roughing filtration system demonstrated its suitability for the treatment of greywater for non-potable reuse applications. It was observed that 90% turbidity and 63% Chemical Oxygen Demand reduction was achieved over the entire duration of operation of the horizontal roughing filter. It was also observed that the removal efficiency was significantly higher in the compartment with the smallest filter media size and the removal efficiency was significantly higher at lower filtration rates. It is therefore concluded from the investigation conducted in this research that the role of the public is a vital component in the development and implementation of any reuse system / application. It was found that there was a relatively high level of acceptance for the reuse of greywater among the respondents within the community where the study was conducted. The greywater characteristics results obtained from this investigation indicated the necessity of treatment prior to disposal in the environment. Also, a low BOD5/COD ratio of 0.24, which is significantly lower than 0.5, is an indication that the greywater generated from the community cannot be easily treated using biological treatment processes and/or technologies. The pilot horizontal roughing filtration system used for the treatment of greywater in this study demonstrated its suitability for the treatment of greywater for non-potable reuse applications such as irrigation, toilet flushing and washing activities. / M

The fate of antimicrobials entering the aquatic environment is an increasing concern for researchers and regulators, and recent research has focused on antimicrobial contamination from point sources, such as wastewater treatment facility outfalls. The terraccumulation of antimicrobials and mobility in diffuse pollution pathways should not be overlooked as a contributor to the spread of bacterial resistance and the resulting threat to human drug therapy. This review critically examines recent global trends of bacterial resistance, antimicrobial contaminant pathways from agriculture and water treatment processes, and the need to incorporate diffuse pathways into risk assessment and treatment system design. Slow sand filters are used in rural regions where source water may be subjected to antimicrobial contaminant loads from waste discharges and diffuse pollution. A simple model was derived to describe removal efficiencies of antimicrobials in slow sand filtration and calculate antimicrobial concentrations sorbed to the schmutzdecke at the end of a filtration cycle. Input parameters include water quality variables easily quantified by water system personnel and published adsorption, partitioning, and photolysis coefficients. Simulation results for three classes of antimicrobials suggested greater than 4-log removal from 1 ��g/L influent concentrations in the top 30 cm of the sand column, with schmutzdecke concentrations comparable to land-applied biosolids. Sorbed concentrations of the antimicrobial tylosin fed to a pilot filter were within one order of magnitude of the predicted concentration. To investigate the behavior of antimicrobial contaminants during multi-stage filtration, five compounds from four classes of antimicrobials were applied to a mature slow sand filter and roughing filter fed raw water from the Santiam River in Oregon during a 14-day challenge study. Antimicrobial removal efficiency of the filters was calculated from 0.2 mg/L influent concentrations using HPLC MS/MS. and sorption coefficients (K[subscript d], K[subscript oc], K[subscript om]) were calculated for schmutzdecke collected from a mature filter column. Sulfonamides had low sorption coefficients and were largely unaffected by multi-stage filtration. Lincomycin, trimethoprim, and tylosin exhibited higher sorption coefficients and limited mobility within the slow sand filter column. The lack of a significant increase in overall antimicrobial removal efficiency indicated biodegradation is less significant than sorption in multi-stage filtration. / Graduation date: 2004

Em instalação piloto, de 06/1998 a 10/1999, utilizando-se água natural de superfície com baixas turbidez e cor, foram avaliados dois sistemas de dupla filtração, com pré-tratamento em filtração direta ascendente em areia com taxas de 200 a 360 m3/m2.dia (sistema S01) e em filtração direta ascendente em pedregulho com taxas de 80 a 190 m3/m2.dia (sistema S02) e com tratamento final em filtração rápida descendente com taxas de 115 a 480 m3/m2.dia. As dosagens do coagulante (produto comercial de sulfato de alumínio) foram definidas utilizando-se filtro de laboratório de areia, havendo indicações de coagulação no mecanismo de adsorção, com neutralização parcial de carga. Foram executadas descargas de fundo intermediárias nas unidades de filtração direta ascendente, com significativa redução na perda de carga no meio granular de pedregulho. A turbidez, cor aparente, Fe e Mn totais dos efluentes finais dos sistemas atenderam às Normas Brasileiras para produção de água potável. No sistema S02 o crescimento da perda de carga no meio granular foi menos intenso na unidade de filtração direta ascendente do que no filtro rápido descendente, ocorrendo o inverso no sistema S01, no qual, em alguns ensaios, o filtro rápido descendente mostrou-se desnecessário. As carreiras de filtração foram de 27 a 88 h no sistema S01 e de 14 a 35 h no sistema S02. Em determinados casos, a floculação predominou na unidade de filtração direta ascendente em pedregulho, prejudicando a qualidade do seu efluente. O sistema S02 mostrou-se mais vantajoso que o sistema S01, exceto quando, neste, a filtração rápida descendente foi desnecessária. / Based on me investigation carried out in pilot plant, from June 1998 to October 1999, using natural surface raw water with low turbidity and color, two systems of two-stage filtration have been evaluated. As a pretreatment, the first system (S01) used direct up-flow sand filtration (with filtration rates from 200 to 360 m3/m2.day), and the second system (S02) used direct up-flow roughing filtration (with filtration rates from 80 to 190 m3/m2.day), both with final treatment based on rapid filtration (with filtration rates from 115 to 480 m3/m2.day) The coagulant doses (commercial product of aluminum sulfate) have been established through the use of laboratory scale sand filter, presenting signs of coagulation in the adsorption mechanism, with partial charge neutralization. Intermediate bottom discharges in the direct up-flow filtration units have resulted in significant reduction in thee headloss in gravel granular medium. The turbidity, apparent-color, total iron and manganese concentrations of the final effluents of the systems have attended the Brazilian Standards for drinking water production. The increase of headloss in gravel granular medium in system S02 was smaller in me direct up-fiow filtration unit than in the rapid filter, the opposite occurring in system S01, where some tests have proved lhe rapid filter redundant. The filter runs time were 27 to 88 hours in system S01 and 14 to 35 hours in system S02. In certain cases, flocculation was predominant in the direct up-flow roughing filtration unit, jeopardizing the effiuent quality. System S02 has proved advantageous in relation to system S01, except when in system S01 the rapid filter was redundant.

Em instalação piloto, de 06/1998 a 10/1999, utilizando-se água natural de superfície com baixas turbidez e cor, foram avaliados dois sistemas de dupla filtração, com pré-tratamento em filtração direta ascendente em areia com taxas de 200 a 360 m3/m2.dia (sistema S01) e em filtração direta ascendente em pedregulho com taxas de 80 a 190 m3/m2.dia (sistema S02) e com tratamento final em filtração rápida descendente com taxas de 115 a 480 m3/m2.dia. As dosagens do coagulante (produto comercial de sulfato de alumínio) foram definidas utilizando-se filtro de laboratório de areia, havendo indicações de coagulação no mecanismo de adsorção, com neutralização parcial de carga. Foram executadas descargas de fundo intermediárias nas unidades de filtração direta ascendente, com significativa redução na perda de carga no meio granular de pedregulho. A turbidez, cor aparente, Fe e Mn totais dos efluentes finais dos sistemas atenderam às Normas Brasileiras para produção de água potável. No sistema S02 o crescimento da perda de carga no meio granular foi menos intenso na unidade de filtração direta ascendente do que no filtro rápido descendente, ocorrendo o inverso no sistema S01, no qual, em alguns ensaios, o filtro rápido descendente mostrou-se desnecessário. As carreiras de filtração foram de 27 a 88 h no sistema S01 e de 14 a 35 h no sistema S02. Em determinados casos, a floculação predominou na unidade de filtração direta ascendente em pedregulho, prejudicando a qualidade do seu efluente. O sistema S02 mostrou-se mais vantajoso que o sistema S01, exceto quando, neste, a filtração rápida descendente foi desnecessária. / Based on me investigation carried out in pilot plant, from June 1998 to October 1999, using natural surface raw water with low turbidity and color, two systems of two-stage filtration have been evaluated. As a pretreatment, the first system (S01) used direct up-flow sand filtration (with filtration rates from 200 to 360 m3/m2.day), and the second system (S02) used direct up-flow roughing filtration (with filtration rates from 80 to 190 m3/m2.day), both with final treatment based on rapid filtration (with filtration rates from 115 to 480 m3/m2.day) The coagulant doses (commercial product of aluminum sulfate) have been established through the use of laboratory scale sand filter, presenting signs of coagulation in the adsorption mechanism, with partial charge neutralization. Intermediate bottom discharges in the direct up-flow filtration units have resulted in significant reduction in thee headloss in gravel granular medium. The turbidity, apparent-color, total iron and manganese concentrations of the final effluents of the systems have attended the Brazilian Standards for drinking water production. The increase of headloss in gravel granular medium in system S02 was smaller in me direct up-fiow filtration unit than in the rapid filter, the opposite occurring in system S01, where some tests have proved lhe rapid filter redundant. The filter runs time were 27 to 88 hours in system S01 and 14 to 35 hours in system S02. In certain cases, flocculation was predominant in the direct up-flow roughing filtration unit, jeopardizing the effiuent quality. System S02 has proved advantageous in relation to system S01, except when in system S01 the rapid filter was redundant.