Bactéries et micro-organismes

Advantages and applications for water treatment

Bacteria and microorganisms involved in water treatment

What are they used for?

Biological wastewater treatment is the most common sanitation method in the world. This technology uses different types of bacteria and other microorganisms for the treatment and purification of polluted water.

Wastewater treatment is as essential to human health as it is to the protection of the environment. The use of these bacteria accelerates the process of treating pollution on a small surface: the wastewater treatment plant. It’s better than letting the river handle it, because even though it’s the same purification process that occurs in nature, the quantities of pollution discharged today are too high to keep the natural cycle intact. Thus, sewage treatment plants can prevent eutrophication of rivers, for example, but also prevent the diffusion of diseases.

Municipal and industrial effluent is the main source of wastewater. And thanks to the use of micro-organisms, we are able to degrade the content of these organic wastes as they are used as a source of food and energy to grow and multiply.

You got it, bacteria are the heart of the process. And finally, a wastewater treatment plant is like a farm where micro-organisms are grown on a large scale.

Where are bacteria present?

Everywhere, from the water arriving at the treatment plant to its outlet. The operating parameters defined in the treatment tanks influence the development of various microbial structures and species. This complex combination of micro-organisms, rich in species, achieves a high level of biodegradation over a wide range of substrates, unlike the use of single species. This is the main factor influencing the quality of treated wastewater.

Usually, these organisms swarm and aggregate into a flake-like structure within the free culture called the Floc. These flocs, visible to the naked eye, contain living and dead cells of bacteria, fungi, protozoa and metabolic products. They agglomerate around the suspended organic matter on which they feed. This is the case, for example, with activated sludge. In addition, in fixed cultures, similar biofilms develop on contact surfaces. For example, biofilters and biological disks are fixed cultures.

Some plants are equipped with UV reactors or chlorine injection to eliminate the remaining bacteria in the outlet water before discharge into the river. One example is Australia and New Zealand.

Who are these microorganisms?

First, before we know who they are, we need to understand the parameters that influence their growth. Firstly, geographical location. Secondly, the type of pond in which bacteria will be grown. Thirdly, the characteristics of the wastewater entering the plant. Finally, the operating parameters of the system, such as aeration, agitation, chemical injection. All of these factors create quantitative changes between autotrophic and heterotrophic bacteria. In municipal wastewater treatment plants, for example, gram-negative bacteria of the proteobacteria type are predominant (21-65%) of which Betaproteobacteria is the most abundant class, largely responsible for the elimination of organic elements and nutrients. The other branches are Bacteroidetes, Acidobacteria and Chloroflexi (Nielsen et al., 2010; Nguyen et al., 2011; Wan et al., 2011; Hu et al., 2012; Wang et al., 2012). The most numerous types of bacteria are Tetrasphaera, Trichococcus, Candidatus Microthrix, Rhodoferax, Rhodobacter, Hyphomicrobium (McIllory et al., 2015).

Among fungi, Ascomycetes are the most common, accounting for 6.3 to 7.4% of micro-organisms. Then come the archaeobacteria, with Euryarcheota (1.5% of micro-organisms, Wang et al., 2014b). In addition, in presence of ammonia and oxygen, Nitrosomonas is very present. Finally, a high sludge age allows protozoa and rotifers to colonize the environment.

Temperature affects the presence of certain species. Thus, the effect of geographic location affects species composition. On the other hand, in industry, for example, the presence of predominantly well-defined micro-organisms can be explained by their ability to biodegrade specific components of industrial wastewater.

Bacteria are further categorized by how they get oxygen. In wastewater treatment, there are three types of bacteria used to treat wastewater entering the treatment plant: aerobic, anaerobic and facultative.

Their impacts and the treatment solutions

The presence of bad bacteria (or the absence of good ones) can cause in particular:

  • Low biogas efficiency of the anaerobic digester
  • Poor flocculation and sedimentation
  • An excess of filamentous bacteria
  • Excess of phosphorus
  • Low nitrogen removal efficiency (NH4, NO3)
  • The production of unpleasant odours
  • Excess consumption of chemical products
  • In an anaerobic digester, foam production

There are generally three ways to restore an effective treatment. First, by changing the operating settings, and waiting for the right species to colonize the environment again. Second, by completely removing the microorganisms in place when the first solution did not work. Be careful, this method is not recommended because the biomass will take several days to develop, so the water will not be properly treated during this period. The third solution consists in injecting specially selected, cultured and multiplied bacteria in order to recover the advantage over the undesirable bacteria present in the environment.

Frequent applications

Microbial biotechnology offers innovative scientific applications of high ecological and economic interest. It maximizes the natural degradation processes and thus eliminates pollution at significantly lower costs than conventional physicochemical or mechanical treatment processes.

The use of bacteria differs from common process techniques in that it involves simple and natural methods, the end-result of which makes it possible to eliminate pollution without generating new pollution. Most of the time, their implementation requires the use of a dedicated bioreactor, as well as the nutrients needed to multiply them in large numbers. The dosing is easy and requires very little operating time.

 

Accelerate plant startup / Get a quick start on bacterial seeding for a mobile plant

The colonization of an environment by the needed bacteria and microorganisms necessary for the purification generally lasts between 4 and 8 weeks. Once again, it is the temperature that has the most influence on this growth time.

There are solutions to reduce this time to about a week, through seeding with selected and multiplied bacteria. There are two main advantages here:

  • Reduce the start-up time of a wastewater treatment plant
  • Accelerate the start-up of a mobile processing unit (e. g. in case of accident at the main plant)

The technique consists in recirculating a well-adapted combination of substrate and selected bacteria so that they settle very quickly. Under these favorable conditions, bacteria develop flocs or biofilms very quickly. Under these favorable conditions, bacteria develop flocs or biofilms very quickly. Finally, after a few days, the habitat is ready and wastewater can be discharged.

We have selected a range of bacteria to start your installation in one week under normal conditions, with water temperatures between 12 and 30°C.

The sizing is available on the microbiological optimization page.

 

Solving the presence of undesirable bacteria

On activated sludge plants, the presence of filamentous bacteria is a real problem. First, the solution consists of extracting as much sludge as possible and increasing aeration. The good bacteria can take several days to recover the environment. If this does not work, then it is possible to destroy these bacteria with chlorine. The problem is that it kills all bacteria. Then it will take a few weeks for normal conditions to be reached again.

While the majority of operators continue to inject chlorine, we recommend the injection of dedicated bacteria. As for the accelerated start-up of a plant, the massive addition of these good populations makes it possible to quickly restore the balance in the tanks.

For example, here is an illustration of the removal of floats in a clarifier.

The sizing is available on the microbiological optimization page.

How to improve treatment efficiency:

By eliminating the fats and oils responsible for the habitat degradation

Lipophilic bacteria are specialized in the decomposition of animal and vegetable fats and oils in urban WWTPs and industrial treatment plants. These bacteria are easily adaptable to all current treatment systems.

On the market, there are products such as completely natural bacteria and enzymes, designed and selected for their ability to dissolve and digest fats and sludge. Some bacteria are so specialized in the degradation of fats that they are capable of degrading high loads, up to 300,000 mg/L COD.

The sizing is available on the microbiological optimization page.

 

By increasing the presence of good bacteria

Comme on peut s’y attendre, la technique consistant à injecter un mélange de substrat adapté et de bactéries sélectionnées est encore la plus efficace. Ainsi, l’istallation très rapide de celles-ci dans le milieu permet d’améliorer les rendements d’épuration sur les systèmes suivants :

  • Activated sludge (fine bubble ventilation)
  • Natural and artificial lagoons and ponds
  • Biofilters
  • Thrickling filter
  • Rotating biological contactors

The sizing is available on the microbiological optimization page.

 

By adding bacteria for the treatment of cold or hot water

The majority of micro-organisms generally develop more rapidly at high temperatures, up to 38°c max. However, their development becomes very slow below 12°c, or almost nil below 5°C. These low temperatures are often reached when sewage treatment plants are located in geographic areas such as Canada or northern Europe. During the snow melting, these bacteria must treat the pollution while living in cold water. The main parade consists in significantly increase the size of the plant to compensate the lack of microbial activity. However, this solution, although still widely practiced, is very expensive.

By contrast, some industrial processes generate water above 38°C. The most common bacteria cannot survive under these conditions.

This is why there are effective bacterial mixtures for the treatment of different types of water. Thus, before a cold event, for example, it is possible to pre-seed the biological reactor with specially selected bacteria for these conditions. They will then take over the existing populations, and ensure effective treatment under these difficult conditions.

We have a selection of bacteria for these difficult conditions:

  • cold water (between 1°C and 12°C),
  • hot water (between 30°C and 50°C or more)

The sizing is available on the microbiological optimization page.

Sizing tools

In the Tools section, you will find all the mathematical and cost information that will allow you to estimate a project.