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Cleansing reactors

Researchers from USP and the Mauá Institute prepare new equipment for the treatment of effluents

MIGUEL BOYAYAN Anaerobic reactor in Mauá: studying the treatment of residual watersMIGUEL BOYAYAN

Now that the International Year of Freshwater has been declared by the United Nations (UN), 2003 expects good news for the conservation of water resources on the planet. The consumption of water is growing, along with the increase of the population and with the rise in agricultural and industrial activities. A situation that cannot do without the reuse of water, even as a means of preserving natural sources, such as rivers, lakes and reservoirs.

A group of researchers from the São Carlos Engineering School (EESC) of the University of São Paulo and from the Mauá Engineering School, of the Mauá Institute of Technology, in São Caetano do Sul, may be contributing towards some good news. They are developing several pieces of equipment that are going to result in new reactors for treating sewage and making the resulting water available for uses that are less noble and do not require it to be potable, such as in industrial activities, washing the streets, or irrigating crops, where the products are not consumed without being cooked.

The focus of the studies by these researchers are systems for treating sanitary sewage and industrial effluents, which use anaerobic microorganisms (bacteria and their relatives, archaea, which do not need oxygen to survive) to carry out the purification of these residual waters. Although still little used in the country, this biological process has a long and traditional line of studies. At the EESC, since the 1970’s, researchers have been studying and developing new configurations for anaerobic reactors.

After so much research, the time has come for some of the systems studied to be put into practice. According to engineer Eugênio Foresti, a director of the São Carlos Engineering School, contacts are being maintained with the government of the State of São Paulo with a view to setting up a pilot anaerobic treatment station in a small sized town in the São Carlos region. It is the opportunity that was lacking for the researchers to show off in practice the effectiveness of the process.

Low cost
“We have maintained the first contacts and we hope to implant soon an anaerobic system on a demonstration scale for the treatment of effluents,” explains Foresti, who is in the coordination of a third thematic project financed by FAPESP on the subject. “We are developing alternative low cost technologies that are more suited to the country,” says Foresti. Five kinds of reactors are being studied in the thematic project: fixed bed horizontal, expanded-fluidified bed, membrane, sequential batches and hybrid. The four first systems are innovative, and the fifth is a modification and perfecting of a reactor known as UASB (Up-flow Anaerobic Sludge Blanket), developed in Holland in the 1970’s.

The anaerobic biological systems were born as an alternative to the aerobic processes (which require the presence of oxygen to survive), a technology that is far more consolidated and employed. The two systems use microorganisms that feed on the pollutants that are present in household sewage and industrial effluents. In other words, they eliminate the organic matter that is dissolved and breaks into particles in the water. For not needing oxygen, the anaerobic processes show an advantage over the aerobic ones, which is their low consumption of energy, since they do not need any process of aeration.

“The spending on energy in the anaerobic treatments is the equivalent to 30%, on average, of the spending in the aerobic ones,” Foresti explains. Another advantage of the anaerobic processes is their lower production of sludge, which does not reach 10% of what is produced by the aerobic processes. The result of this is a considerable saving with the handling and the final disposal of this kind of residue, an unwanted byproduct of the aerobic treatments.

With such clear advantages, the question remains: why, up to today, are the anaerobic treatment systems so little used in Brazil? The reasons are, in part, historical. At the beginning of the 1980’s, studies were started in Brazil for using the UASB reactor. The inadequate exploitation of this reactor by some professionals with little knowledge about the system generated suspicions as to its reliability.

One of the problems was the strong odor exhaled by the reactors, a result of the production of hydrosulfuric acid, a byproduct of the anaerobic process. “In those days, we did not actually know all the details about the system. We cut corners unduly, and this left marks that remain until today,” Foresti admits. With the improvement of the technology, many of those deficiencies were cleared up. There are today several studies that deal with the removal or stabilization of the substances that cause the odor in the anaerobic systems. So these systems are little by little occupying their space. “They are used more and more in industrial units.”

The defenders of the anaerobic technology make a point of stressing: these systems are not being developed to replace the aerobic ones, but rather to supplement them. According to Foresti, the ideal system ought to combine the use of the two kinds of reactors.

Anaerobic systems require another supplementary one, which may be the aerobic one, or physical-chemical ones (microfiltering, chemical precipitation followed by sedimentation, ozonization, disinfection by chlorine or ultraviolet radiation) for the effluents to reach standards of quality. “Without a doubt, the ideal system would be the combination of an anaerobic process followed by an aerobic one, with the latter responsible for only the after treatment and not for the removal of the organic load present in the residual waters. And that is what we are working on,” Foresti says. The result would be a cheaper system with a lower production of sludge and highly efficient.

The Mauá Engineering School has also produced, in recent years, several studies related to the anaerobic processes for treating residual waters, under a project of FAPESP’s Young Researcher Program, coordinated by Professor José Alberto Domingues Rodrigues. “In four years of work (between 1998 and 2002), we managed to set up the Biochemical Engineering Laboratory, and to consolidate our area of research,” says Rodrigues. He and other researchers from the institution, like Professors Walter Borzani and Suzana Ratusznei, are investigating treatment processes operated in the batch and fed batch modes. These processes are related to the way that the anaerobic reactors carry out the treatment of the residual water. If quickly, it is simply batch; if slowly, it is fed.

Ideal configuration
To carry out their experiments, the researchers from the Mauá Biochemical Engineering Laboratory have five reactors. “As these reactors are still not very well understood, we are studying several aspects related to their operational conditions. Our objective with these studies is to bring flexibility to the non-continuous anaerobic systems, in equipment that receives residual water intermittently, as in dairy industries,” says the researcher from the Mauá School of Engineering. “We have not yet succeeded in arriving at an ideal configuration in one of these reactors for industrial use, but I imagine that by the end of 2005, in a thematic project that started in September 2002, in partnership with the EESC and the Federal University of São Carlos (UFScar), we will have made significant headway.”

The project
1. Structure, Composition, Growth and Dynamics of Biofilms in Mixed Anaerobic/Aerobic Systems for Treating Residual Waters (nº 96/04544-8); Modality Thematic project; Coordinator Eugênio Foresti – São Paulo School of Engineering of USP; Investment R$ 199,348.70 and US$ 48,393.40
2. Development of Anaerobic Batch and Fed Batch Processes for the Treatment of Residual Waters (nº 97/05987-3); Modality Young Researcher Program; Coordinator of the project José Alberto Domingues Rodrigues – Mauá School of Engineering of the Mauá Institute of Technology; Investment R$ 104,471.67 and US$ 95,890.23