A biological approach for water reuse in the mining industry

Friday, November 25, 2011

Industrial water use is a growing concern in Chile, particularly for the country's lucrative mining sector. With many areas currently suffering from drought, and the main mining operations located in the country's arid northern regions, developing new techniques to capture and reuse industrial wastewater has become a priority.

One novel approach to water reuse in industrial processes has been the incorporation of biological agents, such as plants and microorganisms. The process is currently only used for small volumes of water, but is an interesting alternative as it requires little construction and offers low energy consumption.

State copper producer Codelco, in association with the Universidad de Santiago (USACH), recently began developing a pilot plant to treat tailings effluents based on an artificial wetland system. The initiative aims to reduce the concentration of sulfate and other elements at the Talabre tailings dam in the company's Chuquicamata division, allowing previously contaminated water to be reused.

BNamericas sat down with USACH professor Claudia Ortiz, the project's director, to discuss the initiative and its wider implications for water use in Chile.

BNamericas: This pilot project is aimed at treating tailings effluent. What is this, and what is its importance in the industrial process?

Ortiz: Tailings effluent is all the water that is part of a tailings dam, and which, after treatment, can be returned to the productive process.

This type of water is saturated with sulfates, in our case, and to a lesser degree, chlorides. It also has copper in it, because it has gone through the productive process several times.

All of these elements, particularly sulfates and chlorides, are above the permitted level of concentration. What we're planning is to treat this water and lower the level of sulfates and copper, so it can become, say, irrigation-quality water.

BNamericas: So the water would not only have the quality to go into an industrial cycle but to the water cycle in general?

Ortiz: There are two possibilities, and that will depend on what the company wants to do with the water. They can inject it back into the industrial process, optimizing its industrial usage. Or they can use the water for other purposes, for example, to recharge aquifers in the area, or for irrigation.

What we're seeking is to establish a biological-based treatment process that is a passive system, which means it won't require giant pumps or industrial treatment plants.

BNamericas: The project you're working on is a built wetland system. What does this involve?

Ortiz: Wetlands are very complex ecosystems from a biological standpoint, because they not only have plants, but also microorganisms such as yeasts, fungi and bacteria. The same wetland model that exists in nature is artificially recreated for this project.

We're using plants that are tolerant to the elements that we're treating, so in our case they have a high tolerance to copper, sulfates and other elements.

The cycle is like this: water exits the dam, then is pre-treated with bacteria to lower its sulfate level. It then enters the wetland, which reduces other elements, such as organic material and copper.

BNamericas: Is this wetland system used in other industrial process in Chile?

Ortiz: Yes, we've seen a wetland-type system with waste coming from the wine industry. For example, the Santa Ema winery has a wetland as a secondary treatment system, ending up with high-quality water to irrigate its vines.

There was a similar experience to ours in Codelco's Andina division, which subcontracted a German company, Leipzig-based BioPlanta, which is now our partner, to install a small wetland-type treatment plant.

BNamericas: Going back to your project, how is it that you ended up at the Talabre tailings dam in Chuquicamata?

Ortiz: Well, we've worked with Codelco for approximately six years. A student from our university conducted some research and installed a pilot treatment plant for solid materials in the tailings dam. This was the first phytostabilization plant, which means the use of plants for remediation of environmental problems, and it worked really well.

From that small pilot plant we got a government grant from [scientific and technological development promotion fund] Fondef. Codelco was our strategic partner, providing funding, infrastructure and logistic support. That project ended in March of this year.

BNamericas: And what was the investment in that project?

Ortiz: This was a large project, around 1bn pesos (US$1.91mn). We worked with other partners, such as the Universidad Católica de Valparaíso, [state minerals company] Enami, Codelco, and others.

It was during that project when we started thinking - if this type of treatment works on solid materials, what about in water? That was when we launched a project funded by state development agency Corfo in 2010, in which Codelco is a partner.

BNamericas: How big is the Corfo project in terms of investment?

Ortiz: This is a smaller project, some 500mn pesos, in which we also have BioPlanta and a company called Wetland as partners. It's scheduled to wrap up in 2013, and the plant should be running next year.

BNamericas: You're currently working on a pilot plant. What's the capacity of that plant?

Ortiz: We're working with a volume of 8l/s, which is the treatment volume that we will be able to handle.

We're working on two parallel lines at Talabre, which handle 4l/s each, which is a good volume for a biological treatment plant. It's important to note that biological treatment has some limitations: they are very effective, but they have technical limitations in terms of volumes.

The plant is on a 0.5ha area, which is not a small terrain, but is clearly not an industrial-sized system. For an industrial system, we're talking about a volume of 60l/s, which is the maximum volume we've seen in wetland-type treatment plants in the world.

BNamericas: Once you're done with the pilot stage, will you continue working with a larger volume?

Ortiz: In the next stage of our experiment, we hope to start making industrial-scale implementations. The idea of the pilot plant is to conduct in situ testing, for example, increase or decrease the volume size, diversify the types of plants, so we can optimize the system.

Once we gain that knowledge, we would be able to offer this technology, so we can work with larger volumes, which would mean working with plants of larger scale, or several plants working simultaneously.

BNamericas: Have other mining companies shown interest in the system?

Ortiz: Yes, we've had conversations with Collahuasi, which was very interested in this treatment. However, they are facing a bigger problem, which is access to water, because they are in the process of expanding operations.

Today, the "classic" water treatment plants are active systems, for example reverse osmosis treatment plants, similar to desalination plants, which require an enormous energy input, as well as having limitations regarding volume.

With the emergence of alternatives, our biological alternative hasn't been validated yet. One of the objectives of this project is to validate this technology at a semi-industrial level, to prove the usefulness of the system, and that you can build bigger plants. I think that will create much more interest.

BNamericas: Finally, how developed is Chile compared with other countries in the region when it comes to R&D for water technology?

Ortiz: I think that in terms of research, Chile is very well positioned within the region. Unfortunately, from a legislative standpoint - which, in the end is what forces companies to implement new technologies - we're somewhat behind.

Peru, for example, has very strict legislation from the point of view of managing waste that comes from mining processes; Brazil is also very advanced. I'd say that Argentina is at the same level as we are.

Chile is well positioned within the region, but we are in need of that legislative push.

About Claudia Ortiz

Claudia Ortiz is a biochemist and professor at the Universidad de Santiago's school of chemistry and biology, with a PhD in biology from the Universidad de Chile.