miguel boyayanSewage and industrial wastewater: biomass with added valuemiguel boyayan
The fact that hydrogen produces no residue or polluting substance of any sort is the main attribute in favor of hydrogen as a fuel to generate power. Hydrogen powers the fuel cells, the equipment that extracts hydrogen electrons to produce environmentally-friendly power. The problem is that hydrogen (H2) does not exist in free form in nature; it is always linked to other substances, such as water (H2O). One of the alternatives, in the wake of environmental concerns, is to reuse water to produce renewable energy, by resorting to sewage and industrial waste, as shown by a group of researchers from the University of São Paulo /USP’s School of Engineering in São Carlos/EESC. The group was awarded the 5th Mercosur Science and Technology Award, 2008, under the Integration category. The award was granted for the research paper “Produção de bio-hidrogênio a partir de águas residuárias para ser utilizado como fonte alternativa de energia,” (“Production of bio-hydrogen from residual waters, to be used as an alternative water source”), co-authored by researchers from Uruguay’s Universidade de La Republica. This year’s theme was Biofuels and the event was sponsored by the United Nations Educational, Scientific and Cultural Organization/UNESCO, among other entities.
Professor Marcelo Zaiat, from EESC’s Hydraulics and Sanitation Department, is one of the research project’s coordinators. He says that the project focuses on sewage and industrial wastewater, which are considered a type of biomass because they transform refuse into a means of generating energy. Although this is a laborious process, it is cheap, environmentally-friendly, and sustainable in comparison to electrolysis. Electrolysis is a more common process to extract hydrogen from water; it is not used to a great extent because it wastes electricity to generate more electricity without providing any significant gains. Hydroelectric power plants alone are equipped with the ideal conditions to produce low-cost energy through this process, but this can only be done at night, when demand slows down or during very rainy seasons. The technological progress of fuel cells in the 1990’s, currently being experimentally produced and sold by only a few companies and used in electric power generators and automobile prototypes, triggered the race to find the means to produce this fuel.
Zaiat’s group developed a hydrogen production method in a continuous flow reactor, which is constantly fed by refuse that would normally be disposed of, with no treatment, into rivers and lakes. In this system, anaerobic bacteria of the Clostridium kind, which do not need oxygen to survive, adhere to polyethylene particles inside the reactor. The fermentation of the organic material in the water and the resulting release of hydrogen (H2), carbon dioxide ( CO2,) and hydrogen sulphyde acid (H2S) in the form of hydrogen bubbles, occurs according to parameters related to acidity, to the time the raw material remains in the system, and to other parameters. One can install a gas catchment system on the sealed head of the reactor, for subsequent separation.
The next goal is to produce hydrogen in the reactor on a pilot scale, because so far only lab-scale reactors were operating. This might be feasible in 2010, at a pilot station scheduled to be installed at the university’s second campus in São Carlos; the station, to be fed with sanitation sewage, will be in a room next to the sewage system of the building that houses the environmental engineering department. The resulting gas may be used, for example, by the group headed by Ernesto Gonzalez, from USP’s Chemistry Institute in São Carlos/IQSC), which is doing research on fuel cell systems.
No waste
The EESC group’s first research study was conducted with lab-produced synthetic water to which sucrose was added to characterize the system. Zaiat has also tested the system with wastewater from a soft drinks factory and with domestic sewage. “The wastewater from the soft drinks factory is full of sugar, which facilitates the production of hydrogen. The potential is not too high in the case of sewage, but the use of sewage is justified in terms of sustainability, because this is reusable energy that will no longer be wasted,” he says. He is also beginning to do research on the extraction of hydrogen from vinasse, a residue that is produced by the sugarcane ethanol industry. “This has good potential.”
The quantity of extracted hydrogen was quantified better in the experiment with sucrose from the soft drinks plant. Each gram of sugar resulted in 47 milligrams (or 0,047 grams) of gas. Zaiat says that this quantity is favorable for the process because cars, for example, would use very little hydrogen to move. Data extracted from scientific literature states that these numbers range from 1 to 10 grams of hydrogen per kilometer in the case of cars running on fuel cells.
In addition to the purified hydrogen recovered from the anaerobic reactor, other studies conducted by the same group used other gases, such as CO2 and H2S. In the case of the H2S, which is a problem for fuel cells, this element can be removed from the gas by means of reactors containing bacteria that consume this material. This study is being conducted by a group from the Chemical Engineering Department of the Federal University of São Carlos/UFSCar, under the coordination of professor Edson Luiz Silva. Methane and CO2 can be used in physical-chemical processes to generate more hydrogen and synthesis gas, a product that can be transformed into gasoline and methanol, for example. “Specific catalysts (substances that promote a chemical reaction) have to be added to gases in liquid fuels,” says professor Elisabete Moreira Assaf, from the IQSC, who is coordinating research studies on the leftover gases from the production of hydrogen from effluents. She is also a member of the Hydrogen Production Network of the National Cell Fuel Program run by the Ministry of Science and Technology/MCT.
Zaiat has already counted 220 scientific articles written on the subject since 1996, when the first paper was published. This paper describes how the team coordinated by professor Yoshiyuki Ueno, from Japan’s Kajima Institute of Technical Research, showed in the laboratory that it was possible to extract hydrogen from industrial wastewater by using anaerobic bacteria. “Experiments of this kind have been conducted ever since then,” says Zaiat. Five experiments were conducted in 2000, ten in 2001, and 220 experiments have already been carried out this year “Most of the research work is still on a lab scale, but future perspectives are very bright because the processes use a very small amount of low-power energy. There are some systems in which the water flows into the reactor by means of gravity, requiring no electricity,” says Zaiat. He conducted the first part of the research with a Regular Research Awards grant from FAPESP. He is currently involved in a theme project coordinated by Eugênio Foresti, which includes the research work of professor Elisabete. Researchers from UFSCar and from the Mauá School of Engineering/EEM in the city of São Caetano do Sul are also involved in the project.
The Projects
1. Production of hydrogen in an anaerobic packed-bed reactor (nº 05/00789-7); Modality Regular Research Awards; Coordinator Marcelo Zaiat – USP; Investment R$ 60,829.64 and US$ 27,770.92 (FAPESP)
2. Development of combined water treatment systems for treatment of wastewater, with the aim of removing pollutants and recovering energy and products from the carbon, nitrogen and sulphur cycles (nº 05/51702-9); Modality Theme Project; Coordinator Eugênio Foresti – USP; Investment R$ 896,854.66 and US$ 239,417.81 (FAPESP)
