The Ipojuca river, a river in Northeast Brazil extending from west to east, is situated in the semiarid interior and rainy coastal zone of Pernambuco state. The river basin covers an area of 3,514 km 2 , with a total river length of 215 km. The water flow regime is characterized by the annual change from dry to rainy season as well as periodically occurring dry cycles. Mean flow rates vary between 2 and 35 m 3 s −1 . The dominant impacts on water quality of the river are domestic sewage input in the upper catchment and sugar cane cultivation and processing in the lower catchment. Long-term monitoring data used to demonstrate the impact of sewage discharge on the river's self-purification capacity indicated a severe change to the worse in the lower course. One reason is the use of stillage (wastewater from cane processing) for fertilization and irrigation (fertigation). Pathways of contamination have been identified by evaluating cultivation and processing techniques of a bio-alcohol factory with annexed sugar cane cultivation. The river's main ecological problems are water heating, acidification, increased turbidity, oxygen imbalance, and increased coliform bacteria levels. Precipitation-related wash-off and wash-out causes significant contamination within one to two days after rainfall. The increase in coliform bacteria is a consequence of secondary contamination.To determine the impact of the sugar cane industry on the river, the Brazilian bio-alcohol program must be subject to a critical evaluation. Environmentally friendly sugar cane cultivation methods need to be developed, and sugar cane factories must use wastereducing technologies and water cycling processes in order to protect the region's water resources.

The growing global water supply crisis highlights the need to implement tools that guide policy makers in controlling effluent discharges into surface water bodies, considering that the consequent poor water quality makes it unavailable for certain uses. This study proposes a methodology to aid water managers regarding licensing effluent discharge into water bodies, using a mathematical water quality model and proposing criteria to be adopted in analyzing the licensing process. The study area used to apply the water quality model and the simulation scenarios was a stretch of about 22km along the Capibaribe river between the cities of São Lourenço da Mata and Recife, Pernambuco-Brazil. The mathematical model was the QUAL-UFMG. The analyzed parameters were BOD and DO. The results showed that less than 10% of the stretch under study presents these parameters within the limits established by law for its water quality class considering preferred uses. Furthermore, it was possible to identify the critical points where it may be necessary for installed industrial plants to adapt, and points where the river still retains some depuration ability . The simulated scenarios showed that the implementation of progressive goal-setting may classify the effluent according to standards established for the river water quality class.

RESUmO: As atividades humanas e os usos múltiplos das bacias hidrográficas produzem impactos nos ecossistemas, provocando a deterioração da qualidade das águas e prejuízos aos seus usos preponderantes, bem como podem causar prejuízos à saúde da população, por meio do consumo direto ou do contato primário da exposição a águas contaminadas. Desta forma, o objetivo desse trabalho é propor um índice de qualidade de água, buscando sua interação com parâmetros que possam aumentar a segurança na confiabilidade dos resultados, de forma a preservar a saúde da população, como também contribuir para fomentação de medidas de monitoramento e gestão da qualidade das águas superficiais das bacias hidrográficas e reservatórios pelas agências de controle. Nesse estudo foram utilizados dados secundários disponíveis no Relatório de Monitoramento da Qualidade da Água de Reservatórios do Estado de Pernambuco do ano de 2008 realizado pela Agência Estadual de Meio Ambiente e Recursos Hídricos-CPRH, através do convênio com a Secretaria de Recursos Hídricos-SRH. Dentro desse contexto, foi proposto o Índice de Qualidade de Água Bruta para Abastecimento Público (IQABP), o qual foi criado a partir da inclusão na fórmula do IQA-CETESB do parâmetro Densidade de Cianobactérias, utilizando as faixas de números de células de cianobactérias e a sua respectiva taxação, usadas no cálculo do Índice de Substâncias Tóxicas e Organolépticas (ISTO)-CETESB. Os resultados do monitoramento dos 111 reservatórios recalculados com a nova fórmula indicaram valores mais representativos da preservação ambiental do manancial, refletindo a real condição de qualidade da água do reservatório estudado, demonstrando que quando o IQABP indicar água para abastecimento público de boa qualidade, a população terá a garantia que a toxicidade provocada pelas florações tóxicas de cianobactérias, estará dentro dos limites estabelecidos pela legislação vigente.

The Pirapama system in Pernambuco, Northeast Brazil, is one of the last major sources of adequate water supply in the state. A reservoir was constructed to store water for domestic, agricultural and industrial use. However, the formation of the reservoir pool flooded the marginal vegetation, starting an organic matter mineralization process, which resulted in eutrophication of the waters and depletion of dissolved oxygen concentrations, reaching anoxic conditions near the reservoir bed. This water body is also impacted by upstream inputs of domestic sewage, agricultural run-off and effluents from sugar-cane mills and distilleries. This work applied a one-dimensional vertical approach (CE-QUAL-R1) in order to simulate the formation of the reservoir pool, analysing the different operational alternatives. Eutrophication, anoxia and stratification potentials were studied. Water quality data obtained during 17 months are used to adjust the model rates and parameters. After model calibration-validation, hypothetical operational scenarios were simulated, taking into account different ways for water pumping (outtake elevations) and for discharging outflow excess (spillways or bottom outlet). Strong anoxic conditions (DO concentrations of less than 1.0 mg.L -1 ), associated to high eutrophication levels (high PO 4 and Chlorophyll-a concentrations), were found in all simulated scenarios. Regarding water quality conditions in the reservoir, the use of bottom outlet for reservoir water releases presented better results than the other operational alternatives, since it makes possible releasing anoxic waters from the deepest layers of the reservoir pool. However, in these conditions, the water quality downstream from the reservoir was severely compromised.

Abstract