Sylvana Melo dos Santos

Water quality and microbial diversity in cisterns from semiarid areas in Brazil.

Harvesting rainwater is a common practice worldwide, particularly in areas with no access to a public water supply or insufficient groundwater reserves. More than two million people living in semiarid regions of Brazil consume rainwater stored in cisterns, and little information is available regarding the water quality. Despite the initial good quality of the rainwater, its harvest and storage can introduce contaminants that must be eliminated before consumption. To evaluate the influence of handling, cistern age and precipitation on the quality of harvested rainwater, we monitored seven cisterns in the semiarid Brazilian Northeast over 4 years. Microbial and physicochemical parameters were monitored once a month, and denaturant gradient gel electrophoresis (DGGE) was performed at the end of the monitoring period. Coliform bacteria were detected in 100% of samples, while Escherichia coli were observed in 73.8%. The alkalinity and conductivity were the highest for the recently built cisterns due to the dissolution of construction materials. The DGGE of the 16S r DNA did not reveal the presence of E. coli. Instead, DGGE bands sequencing indicated that species primarily affiliated with Alphaproteobacteria were present in all cisterns, indicating the presence of microbial ecosystems capable of purifying and stabilizing the stored rainwater.

Monitoring of soil subsidence in urban and coastal areas due to groundwater overexploitation using GPS

The global positioning system (GPS) is widely used for determining the three-dimensional position of points on earth surface. In the last few years, its use has also been increasingly employed for obtaining vertical geometric coordinates, which associated with the orthometrical altitude of the point can be employed in various civil engineering applications, as has been seen in diverse localities throughout the world. The satisfactory performance of this technology for obtaining excellent precision in vertical coordinates demands some conditions, related to the satellites, such as transmission of signals and, principally, in the case of urbanized areas, the presence of obstructions in the proximity of the equipment, which interferes with the quality and quantity of the information collected. GPS is an efficient technique for the detection of small movements, including the monitoring of soil subsidence. The present article describes adequate forms of the use of GPS in such a way as to guarantee good precision of the resulting vertical coordinates, even under unfavorable situations, such as in coastal areas, where the reference networks for monitoring are implanted in only one of the sides of the point–object region, which makes the situation more difficult and requires careful planning so that the use of GPS reaches the desired precision.

Telhado verde: desempenho do sistema construtivo na redução do escoamento superficial

Na atualidade, metade da populacao mundial reside em centros urbanos, e os impactos negativos decorrentes de eventos hidrologicos tem sido recorrentes, visto que, com o aumento da impermeabilizacao, ha reducao nas taxas de infiltracao, levando a diminuicao da recarga dos aquiferos e a diminuicao do escoamento de base. Consequentemente, o escoamento superficial e intensificado, aumentando a frequencia e a magnitude dos picos de cheia, o que pode resultar na ocorrencia de inundacoes, especialmente nos centros urbanos. Por outro lado, verifica-se ja ha algum tempo o emprego de telhados verdes em varias partes do mundo para contribuicao arquitetonica estetica e melhoria do conforto ambiental. Alem desses enfoques, esta solucao vem sendo tratada, tambem, como uma estrutura de controle do escoamento pluvial. Considerando caracteristicas reais e os dados obtidos em campo, foi realizada a simulacao da dinâmica da agua em dois telhados verdes, com o emprego do codigo computacional Hydrus-1D, para diferentes intensidades de precipitacao, visando verificar o desempenho desse sistema construtivo na reducao do escoamento superficial. Os hidrogramas de saida mostraram-se qualitativamente adequados e quantitativamente coerentes e pode-se concluir que os telhados verdes constituem importantes dispositivos no amortecimento do escoamento superficial oriundo dos telhados, para as condicoes climaticas da area investigada.

A PVC-pipe device as a sanitary barrier for improving rainwater quality for drinking purposes in the Brazilian semiarid region

We evaluate the behavior of a device designed to automatically divert and store the first flush of harvested rainwater in cisterns. The first phase (PI) was conducted with artificial precipitation in an experimental installation seeking to identify how many millimeters of rainwater should be diverted to preserve the rainwater quality. In the second phase (PII), we designed a PVC-pipe device to store the first millimeter of rainwater, and tested it in field (a rural area in Brazil) during two real rainfall events. In the third phase (PIII), the device and a hand pump were assayed for two years using eight cisterns in a rural area where people drink the rainwater. PI results indicated that the most significant pollution of the rainwater is flushed with the first millimeter of rain, and diversion promoted the removal of 98% and 100% of the total coliforms and Escherichia coli, respectively. The bacteriological behavior was maintained in the subsequent phases. The device was able to preserve the quality of the rainwater most of the time, satisfying drinking requirements for the parameters of turbidity and color. The satisfactory performance of the device was confirmed in the field, behaving as a sanitary barrier for rainwater quality protection.