O aprimoramento de sistemas de tratamento de água e de esgoto tem sido limitado pelo pouco conhecimento dos fenômenos ocorridos no interior das unidades e pela utilização de "parâmetros" não específicos (DBO, DQO etc.) no monitoramento e controle de processos e operações. Por outro lado, fenômenos como transferência de massa, adsorção, difusão e reações bioquímicas são todos influenciados pela distribuição de tamanho de partículas, de modo que o emprego da análise de tamanho de partículas pode auxiliar na escolha e no aprimoramento de tecnologias de tratamento e na adoção de procedimentos operacionais apropriados. Neste artigo, são apresentadas as principais técnicas de determinação de tamanho de partículas e os potenciais benefícios de sua utilização em pesquisas e no aperfeiçoamento de projetos e rotinas de operação de sistemas de tratamento de água e esgoto sanitário.

The good composition and activity of biofilms are very important for successful operation and control of fixed-film biological reactors employed in liquid effluents treatment. During the last decade, microsensors have been applied to study microbial ecology. These sensors could provide information regarding the microbial activity concerning nitrification and denitrification that occur inside biofilms. Other techniques of molecular biology, such as fluorescence in situ hybridization (FISH), have also contributed to this matter because their application aids in the identification of the bacterial populations that compose the biofilms. The focus of this paper was to study the loading rate and surface velocity to promote the development of nitrifying biofilms in three distinct flow cells that were employed in the post treatment of a synthetic wastewater simulating the effluent from a UASB (Upflow Anaerobic Sludge Blanket) reactor. Using the FISH technique, it was found that the population of ammonia-oxidizing-bacteria was greater than that of nitrite-oxidizing-bacteria; this was also supported by the lower production of nitrate determined by physicochemical and microsensor analyses. It was verified that the loading rate and surface velocity that promoted the greatest nitrogen removal were 0.25 g N-amon m(-2)biofilm day(-1) and 1 m h(-1), respectively.

This article relates two experiments with wastewater treatment in the food processing industry. One of them refers to the use of an anaerobic filter (meat processing industry) and the other to the use of an upflow anaerobic sludge blanket reactor-UASB (vegetable and fruit processing industry). In the first case, the study describes the performance of an anaerobic filter which has been working for 6 years and provides COD removal efficiency (including primary treatment) equal or better than 80% with an organic loading of 1.4 kg of COD/m3 day. The reactor has a bed of broken stones with size of 0.75 m having a medium hydraulic detention time of 13 h. Discharges of accumulated sludge in a false bottom below the filter are made at intervals of 2 or 3 months.In the second case, the study describes the performance of an upflow anaerobic sludge blanket reactor (88 m3) during 255 days of operation including the adaptation phase or startup. This reactor receives wastewater from vegetable and fruit processing including tomato , corn, guava and peach. At the end of each operational phase studied, the COD removal efficiency was about 80%. In the last phase (7.5 h hydraulic detention time), the organic loading was 1.4 kg of COD/m3 day and the hydraulic loading was 3.2 m3/m3 day.

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 10 9 to 10 10 MPN/g VSS, indicating a high potential for the occurrence of denitrification.

This article demonstrates the potential use of residual sand removed from grit chambers, which are used in the primary treatment of Wastewater Treatment Plants (WWTPs), as an alternative material to commercial sand in the production of non-structural concrete in civil construction. The results indicated that the residual sand has a high percentage of total fixed solids (96.9%), high moisture content (14.8%) and significant total coliform [average of 3.84 × 107(100 mL)−1] and fecal coliform densities [average of 5.22 × 105 (100 mL)−1]. The sand cleaning and drying procedure used in the research was effective, since it achieved the following removal efficiencies: about 98.8% of moisture, 67.1% of total volatile solids and 4-log E. coli. After cleaning and drying the residual sand, different amounts of this material were used to prepare the test specimens, which underwent tensile tests. The results of this study confirmed the viable use of residual sand as fine aggregate in concrete for non-structural purposes, and the best performances were verified in tensile and compressive tests (fck) and tensile strength tests (fctk) using 30% (in mass) of the residual sand as fine aggregate (values of 16.6 and 1.60 MPa, respectively).