Margarida Marchetto

Estimate of denitrifying microbiota in tertiary sewage treatment and kinetics of the denitrification process using different sources of carbon

A study of the kinetics of denitrification was carried out in the laboratory based on the quantification of N2O, the final product of the activity of denitrifying microorganisms, when the enzymatic reduction of N2O to N2 was blocked by acetylene. Concentrated mixed liquor (sludge from a reactor with intermittent aeration used for sewage treatment) was used as the inoculum, while methanol, acetic acid, glucose, effluent sewage from an anaerobic fluidized bed reactor and synthetic substrate simulating domestic sewage were used as carbon sources. The mean concentration of nitrate was 20 mg/L. Maxima of N2O production and NO3- consumption occurred between 0.5h and 2.0h of incubation using all the carbon sources, which characterized the denitrification process. Acetic acid and methanol were responsible for the highest rates of N2O production. The estimated number of denitrifying microorganisms in the reactor with intermittent aeration, using the MPN technique, varied from 109 to 1010 MPN/g VSS, indicating a high potential for the occurrence of denitrification.

Potencial da economia de água potável pelo uso de água pluvial: análise de 40 cidades da Amazônia

Water scarcity is an increasingly severe problem worldwide due to some factors, such as the excessive consumption of raw water, climate changes, water pollution, and unsustainable water resource consumption. Under these conditions, traditional or alternative forms of water resource, such as rainwater, are being considered as attractive options to reduce potable water consumption. In this context, this paper describes the water availability scenario in the Amazon region, Brazilian Northeast, and it evaluates the potential for potable water savings estimated for the residential sector of 40 cities in the region. Results indicate that the potential for potable water savings range from 21 to 100% depending on the potable water demand verified in the 40 cities, with an average potential for potable water savings of 76%. The main conclusion is that if there was a government program to promote potable water savings by rainwater usage, there would be significant potable water savings and a consequent preservation of water resources in the Amazon region.

Otimização multi-objetivo de estações de tratamento de águas de abastecimento: remoção de turbidez, carbono orgânico total e gosto e odor

Traditionally, the design of conventional water treatment plants (WTPs) has considered turbidity and color removal as well as the production of microbiologically safe water as primary goals regarding treatment optimization. In face of new technical challenges, the water quality objectives that must be achieved are far reaching. The purpose of this paper was to study the optimization of Rio Grande WTP in order to define the optimum operating conditions with respect to coagulation which maximize turbidity, natural organic matter (NOM) and taste and odor removal. The experimental results indicated that the coagulation pH in the range 5.8 to 6.5 led to both turbidity removal and NOM removal optimization. In addition to that and regardless of the pH range, taste and odor removal by adsorption was satisfactory. Therefore, the optimization of Rio Grande WTP is technically feasible.

Interferência do processo de coagulação na remoção de compostos orgânicos causadores de gosto e odor em águas de abastecimento mediante a aplicação de carvão ativado em pó

Powered Activated Carbon (PAC) has been widely used in Water Treatment Plants with the purpose of minimizing taste and odor problems in drinking water. Its application can be done immediately before or after coagulant application or in parallel with it. To look into possible interferences of the coagulation process in the adsorption process, an experimental investigation was carried out by means of jar tests, with the purpose of simulating different case scenarios of PAC and coagulant application. For the same PAC type and coagulant dosage, regardless of the application point, it was not observed any significant differences in the removal of taste and odor compounds, thus indicating that under the tested conditions the PAC application point has a much lower importance than the initially expected in adsorption processes.