Imprimir

Engineering

Purification of the waters

Charging for the use of river water should stimulate the adoption of new technologies for treating and reusing sanitary and industrial effluents

Water is now going to have its price. From June onwards, the inhabitants of 180 municipalities in São Paulo, Rio de Janeiro and Minas Gerais, served by the river basin of the Paraíba do Sul river will have to pay for the use of the water. Today, the fee paid in the so-called “water bill” refers to the treatment, purification and transport carried out by the basic sanitation companies.

There is no charge, therefore, for the water taken from the rivers. For the specialists, the new kind of charge will bring about some developments. The first of them is that the sanitation companies will be investing in treating the sewage and effluents and in adopting new technologies to expand the reuse of water. Today, only 10% of the domestic effluents generated in the country are submitted to any kind of treatment. The rest, the impressive volume of 10 billion liters a day, is thrown into the rivers.

The new bill wasapproved in March by the National Council of Water Resources (CNRH in the Portuguese acronym), an inter-ministerial body of the federal government, and it will affect the lives of 5.2 million persons and hit 8,000 industrial concerns in the region. “The companies are going to perfect their methods and processes for treatment, for the effluents to be sent back with a better quality than that of the untreated water taken from the sources”, is the belief of Ednaldo Mesquita Carvalho, a consultant for the Secretariat of Water Resources of the Ministry of the Environment. “Furthermore, the companies will be adopting increasingly the reuse of water in order to reduce the volumes taken out”, he says.

To start with, only the industries that take the water straight out of the Paraíba do Sul river and the sanitation companies will be paying the bill. In three years, charging will be extended to all the consumers. According to Jerson Kelman, the presiding director of the National Water Agency (ANA), this is the first step towards making charges for the use of water all over the country. At the beginning, the annual income from the new fee is estimated at R$ 14 million, an amount that will be used in recovering the environment in the basin and expanding the treatment of sewage.

The charges obey the following criteria: those who pour water back into the river in a worse condition than when taken out will pay R$ 0.02 for each cubic meter (thousand liters), whereas those who send the water back after treatment will have a cost that is almost three times less: R$ 0.008 per cubic meter. ANA’s calculations indicate that there will be an increase of R$ 1.00 in the bills, if the companies pass on in full the cost to the users. To escape from this additional cost in the financial balance sheet, companies will have to try to find alternatives in order to eliminate all kinds of residues, organic or otherwise, from the water and their effluents. At the moment, filtering systems, biological control in ponds, digesters and chemical treatments are used. They are reliable systems, but in this sector there is still room for more advanced and efficient technologies.

Oxidizing the pollutants
One of these new technologies is the photoassisted electrochemical system, also known as photoelectrochemical, which for the last ten years has been the subject of study by Professor Rodnei Bertazzoli, the coordinator of the Electrochemical Engineering Laboratory of the State University of Campinas (Unicamp). Photoelectrochemical treatment is carried out by a modular reactor made up of two electrodes – metal plates of titanium coated with conducting oxides of noble metals -, one of which remains subject to ultraviolet (UV) radiation. “The principle of the system is very simple”, explains Bertazzoli, the coordinator of the project Treatment of Effluents Derived from the Pulp and Paper Industry by means of Photocatalysis Assisted by Electrolysis.

“It removes organic and inorganic compounds by means of processes where the only reagent is the electron”. Circulating in the reactor, any organic pollutant passes over the surface of the electrode and undergoes oxidation, being transformed at the end of the process into carbon dioxide and water. The pathogenic organisms then present in the effluents are made inactive, and the inorganic compounds, basically heavy metals, remain deposited on the electrode.

According to Bertazzoli, after undergoing this treatment, the residual waters will be ready to be reused inside the company itself, or thrown back into the river, obeying thestandards laid down by Resolution 20/86 of theNational Council for the Environment (Conama in the Portuguese acronym). This resolution, used by the Environmental Sanitation Technology Company (Cetesb) to control the pollution in the sources of São Paulo’s water, sets physical-chemical and microbiological parameters (oxygen dissolved, biochemical demand for oxygen, pH, fecal coliform bacteria, nitrogen, etc.) for household and industrial effluents. The limit for the concentration of each one of them varies in accordance with the classification of the watercourse – the cleaner the river, the greater the requirement as to the degree of purity of the effluents to be issued.

“The great advantage of the photoelectrochemical system is that it does not generate any byproducts – conventional biological treatments produce a large quantity of sludge, which is a serious environmental problem”, says the researcher. Moreover, the system is capable of removing the color and the odor from the pollutant, characteristics that are most often not treated in the traditional processes. Until now, the system has already proved feasible for treating effluents from textile industries, pulp and paper works, and the leachates (a black liquid with a strong smell containing high concentrations of organic and inorganic compounds) from landfill sites. Tests have also started with hospital waste. All these applications have already resulted in 14 patent requests.

Bertazzoli explains that the cost of implementing the process is a little higher with the biological systems, but the operating expenses are low and involve only the payment of electricity, because the process is automated. The average price of an electrochemical reactor is US$600 per square meter of electrode. A medium sized company, with an outflow of 70 cubic meters an hour, would have to make an investment of US$120,000 in a photoelectrochemical station with 200 square meters of electrodes”, Bertazzoli calculates. Tested by means of a prototype, the technology is not yet available commercially, which should only occur two years from now. The researcher is a consultant to Tech Filter, a company that has a project in FAPESP’s Small Business Innovation Research program (PIPE). The objective is to assemble a large scale prototype reactor in the next few months.

Disinfecting by UV
Another line of research related to the treatment of effluents is disinfecting secondary sewage (which has already gone through a previous treatment) with ultraviolet radiation. Studies that were started in 1977 by Professor José Roberto Campos and are currently coordinated by Professor Luiz Antônio Daniel, both from the São Carlos School of Engineering (EESC) of the University of São Paulo (USP), showed that this process is highly effective in making inactive pathogenic microorganisms (viruses and bacteria), and showed advantages over other techniques that use chemical disinfectants like chlorine.

“As it acts in the physical medium, UV radiation does not add any products to the sewage, whereas chlorine generates undesirable organochlorate by products (trihalomethanes, haloaldehydes, haloketons, etc.), which, according to medical literature, can cause diseases like cancer”, explains the researcher from USP, who is receiving funds from FAPESP to carry out the project Inactivation of Pathogenic Microorganisms by Photolysis: Application of Ultraviolet Radiation in Secondary Effluents of Sewage. According to this scholar, the contamination occurs in a chain. When sewage infected with chlorine is thrown back into the river, the organochlorate byproducts can contaminate the water supply, and the residual chlorine can be harmful to irrigated crops. Taking the water for drinking may also be risky.

A sewage treatment station of the Company of Basic Sanitation of the State of São Paulo (Sabesp) in the city of Lins, equipped with an imported photoreactor of the Aquionics brand, ceded by the Brazilian company Germetec, already uses this new technique in an experimental manner and with good results. “The effluents treated at the station are used to irrigate a plantation of corn in the neighboring land that belongs to Sabesp”, says Luiz Daniel. This research is being carried out with the participation of the Luiz de Queiroz College of Agriculture (Esalq), the School of Public Health and the EESC, all from USP, besides Sabesp, and it constitutes one of the themes of the national research network, in the ambit of the Program for Research into Basic Sanitation (Prosab).

This program has the objective of developing and perfecting technologies in the areas of residual waters, water supplies and solid waste that are easy to apply, and have a low cost to implement, operate and maintain. The history of results obtained in the more than 30 years of research into disinfection with ultraviolet radiation carried out at São Carlos has contributed towards the acceptance and trust in the process used in Lins, which is being compared with the laboratory unit set up in São Carlos with funds from FAPESP.

Daniel explains that the inactivation of the pathogenic organisms takes place at the level of the chromosomes. “Radiation modifies the bacterium’s DNA, creating a photoproduct that prevents its duplication”, he explains. Broadly speaking, the reactor is like a tube with mercury vapor lamps that emit UV radiation. During the treatment, the residual waters go into this tube and are irradiated for 5 to 30 seconds.

The limitation of this technology is that the water solution cannot contain much dissolved matter or matter in suspension. This factor prevents the ultraviolet rays from reaching the microorganisms. For this reason, the effluents need to go through a preliminary treatment. “I believe that this technology has the potential to be used on a large scale”, says the researcher from USP. “Its has already proved its technical feasibility and shown that it has a competitive cost. There is a domestic and foreign market, and it would be interesting for Brazilian companies to participate in the development of equipment for use with sewage, because the only ones that exist are imported”.

Betting on anaerobes
The São Carlos School of Engineering also houses a group of researchers that is studying the anaerobic processes – using microorganisms (bacteria andarcheobacteria) that do not need oxygen to survive – for the treatment of sewage. The team has been able to count on funds from Prosab, managed by the Financier of Studies and Projects (Finep), to carry out its studies. This process uses anaerobic microorganisms that transform complex organic compounds into simpler products, such as methane, carbon dioxide and hydrogen sulfide.

For chemical engineer Marcelo Zaiat, the coordinator of the project Study of the Dynamics of the Adhesion of Anaerobic Biomass on Supports and Application in Reactors for the Treatment of Residual Waters, financed by FAPESP, anaerobic treatment shows a series of advantages over the aerobic system, which is the one most used at the moment. “It does not need to be aerated or shaken, and so it requires less electricity and uses less equipment”, Zaiat explains. But its great advantage is something else: as anaerobic microorganisms grow much less than the aerobic ones – when a bacterium needs oxygen -, the amount of sludge generated at the end of the treatment is equivalent to only 10% to 20% of the quantity produced in the aerobic processes.

In spite of these, shall we call them, virtues, the anaerobic processes are still not sufficiently reliable and efficient, which obliges them to undergo an after-treatment. “Our research seeks precisely to perfect the anaerobic systems and increase their efficiency”, explains Zaiat. The kind of material used is vital for the efficiency of the reactor, as the greater the adherence is and the time the microorganisms inside the equipment, the better the result of the treatment will be.

The municipality of Piracicaba, in the interior of the State, was one of the pioneers in the country in the use of an anaerobic reactor for the treatment of sewage. In the 90’s, the local government built a station for treatment with an aerobic reactor with a mantle of sludge[RJS6], based on a Dutch project. Planned to serve roughly 90,000 persons, it works in conjunctionwith an aerobic system and has shown good results. According to Zaiat, the tendency for the future is the combined use of the anaerobic and aerobic systems. USP’s São Carlos itself will shortly be purchasing a treatment station made up of combined systems. It will make it possible to maximize the advantages of the two processes and to rid the effluent of its pollutants, leaving it with the characteristics needed for being sent back or even reused.

Reuse of water
The reuse of water for purposes other than drinking is now a reality in three of Sabesp’s sewage treatment stations in Greater São Paulo, at a lower cost than the normal fee. Together, the stations of the ABC, Barueri and Parque Novo Mundo produce 180 cubic meters an hour of water that has not been filtered or chlorinated. It is a kind of water that can be used in the electricity generation, public cleaning, the refrigeration of equipment, car washing, firefighting and various industrial processes. Since May last year, Sabesp has been supplying the municipal government of São Caetano do Sul recycled water for irrigating parks, washing streets, unclogging the sewage system and rainwater drains of the city. In January this year, another two municipalities, Barueri and Carapicuíba, started to receive reused water from the company.

According to specialists in water resources, all these initiatives are in line with the proposal of the United Nations Environment Program and of the World Health Organization (WHO) to encourage the planned reuse of water, for drinking and non-drinking purposes. The strategic objective is to protect public health, and to guarantee the continued integrity of the ecosystems and the sustained use of water. Accordingly, the new technologies for treating effluents – photoelectrochemistry, disinfection by ultraviolet radiation and anaerobic systems – meet these requirements perfectly.

The phantom of scarcity haunts the world

A report published by the United Nations (UN) at the end of 2001 warns that humanity will shortly face serious problems relating to the scarcity and quality of water. According to the document, by 2025 3 billion inhabitants will be living in countries affected by water stress, with the per capita supply of water lower than 1,000 cubic meters a year, the minimum quantity to meet the needs of one person. “And, in 2050, 4.2 billion human beings, over 45% of the world total, will be living in countries that cannot ensure the daily quota necessary to satisfy basic needs”, the study indicates.

Not even Brazil is free from the threat of a shortage of water, in spite of having one of the largest water reserves in the world. The country stores 12% of all the fresh water on the planet and shares with Uruguay, Paraguay and Argentina the largest natural reserves of underground water on Earth, the Guarani aquifer, with its 1.2 million square kilometers. “Showing off abundance is not important, the important thing is to use it intelligently”, explains Aldo Rebouças, a researcher from USP’s Institute of Advanced Studies and the author of the book Fresh Water in Brazil, a complete study of the country problems with water.

According to the researcher, although the supply of water in the country is abundant, it is poorly distributed, with 70% of the reserves located in the Amazon region, which has only 7% of Brazil’s population. “There will no shortage of water in Brazil, but there will be in the taps at home”, says he. To turn this situation around, the scientist says that waste needs to be reduced, something that, according to his calculations, comes to 40% of all the water consumed in the country. “The techniques that make it possible to reuse water should also be expanded”, says Rebouças. “Studies indicate that about 80% of the water could be reused for purposes other than for drinking”, he concludes.

Research programes with financial support
Financing scientific projects and new technologies intended for perfecting the various uses of water, including the treatment of residual water. This is the objective of the Sectorial Fund for Water Resources (CT-Hidro), created two years ago, by the Ministry of Science and Technology (MCT), and regulated in July 2001.

Last December, 123 projects were chosen that will receive support from the sectorial fund this year. Of this total, 27 are related to the treatment of sewage and industrial effluents. Finep’s website (www.finep.gov.br) brings the complete list of the proposals selected. Those interested should draw up projects on one of the eight technological platforms approved by the fund’s steering committee: rationalization of the use of urban water, reuse, rationalization of irrigation, control of pollution by the food industry, development of products and equipment, quality, desalinization, and underground water.

According to Irene Altafim, from Finep, an organ that is part of the fund’s steering committee, the funds from CT-Hidro originate in a percentage (4%) of the financial compensation currently paid in to the electricity generating companies and is equivalent to 6% of the amount for the production of electricity generated in the country. For the two year period of 2002/2003, the estimate is that the budget will rise to R$ 107 million. CT-Hidro’s intention is to set aside 30% of this amount for projects that benefit the northern, northeastern and center-western regions of the country. 

The project
1. Treatment of  Effluents Derived from the Pulp and Paper Industry by means of Photocatalysis Assisted by Electrolysis (nº 99/06400-1); Modality Regular research benefit project; Coordinator Rodnei Bertazzoli – School of Mechanical Engineering at Unicamp; Investment
R$ 71,819.14 and US$ 56,200.96
2. Inactivation of Pathogenic Microorganisms by Photolysis: Application of Ultraviolet Radiation in Secondary Effluents of Sewage (nº 00/01718-2); Modality Regular research benefit project; Coordinator Luiz Antônio Daniel – USP’s São Carlos School of Engineering; Investment R$ 54,500.00
3. Study of the Dynamics of the Adhesion of Anaerobic Biomass on Supports and Application in Reactors for the Treatment of Residual Waters (nº 99/09592-9); Modality Regular research benefit line; Coordinator
Marcelo Zaiat – USP’s São Carlos School of Engineering; Investment R$ 41,362.01 and US$ 3,880.56

Republish