Bacteria and micro-organisms involved in water treatment

What are they used for?

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

Wastewater treatment is as essential to human health as it is to environmental protection. Indeed, the use of these bacteria accelerates the treatment of pollution on a small surface: the purification plant. And the river has its own purification process, exactly the same as occurs in the environment. However, atmospheric pollution levels are currently too high and can disrupt the natural cycle. 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. Microorganisms are used to break down organic waste. These micro-organisms use the wastes as a source of food and energy to develop and reproduce.

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

Where are bacteria present?

Everywhere, from the water arriving at the treatment plant to its outlet. The operating parameters set in the treatment ponds influence the development of various microbial structures and the species that compose them. 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 agglutinate into a flake-like mass in free cultures, 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 mud. In addition, in fixed cultures, similar biofilms develop on contact surfaces. For example, biofilters and biological disks are fixed cultures.

Some factories use UV reactors to eliminate any remaining bacteria in the water. Some factories use UV reactors to eliminate any remaining bacteria in the water. This is the case in Australia and New Zealand.

Who are these micro-organisms?

First of all, before knowing who they are, we must understand the parameters that influence their growth. First, the geographical location. Secondly, the type of pond in which bacteria will be grown. Thirdly, the characteristics of the wastewater entering the plant. Finally, system operating parameters including aeration, agitation and chemical injection. All these factors generate quantitative changes between autotrophic and heterotrophic bacteria. In municipal wastewater treatment plants, the proportion of gram-negative bacteria, particularly proteobacteria, is 21-65%. Betaproteobacteria, the most abundant group, have a major contribution to the elimination of organic elements and nutrients. The other phyla are Bacteroidetes, Acidobacteria and Chloroflexi (Nielsen and al., 2010; Nguyen and al. 2011; Wan and al., 2011; Hu and al., 2012; Wang and 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, three different types of bacteria are used to treat the waste coming into 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 great ecological and economic interest. It effectively exploits natural degradation processes to treat pollution. This method is significantly less expensive than conventional physical-chemical or mechanical techniques.

The use of bacteria is different from usual treatment methods in that it uses simple, natural processes. Their performance results in pollution treatment without the creation of new contaminations. Most of the time, their installation requires the use of a dedicated bioreactor, as well as the nutrients necessary for their multiplication in large numbers. Dosing is easy and requires 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 is based on the recirculation of a clever mixture of adapted substrate and bacteria selected so that they settle in very quickly. Under these favorable conditions, bacteria rapidly form flocs or biofilms. After a few days, the environment becomes suitable for wastewater discharge.
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 design is available on the microbiological optimization page.

Solving the presence of undesirable bacteria

In activated mud 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 design 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 design is available on the microbiological optimization page.

By increasing the presence of good bacteria

As expected, the technique of injecting a mixture of suitable substrate and selected bacteria is still the most effective. Therefore, the rapid adsorption of these products in the environment allows to improve the efficiency of the following systems:

Activated mud (fine bubble aeration)
Natural and artificial lagoons and ponds
Biofiltres
Thrickling filter
Rotating biological contactors

The design 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 et 12°C),
eaux chaudes (entre 30°C et 50°C ou plus)

The design is available on the microbiological optimization page.

Design tools

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