Anoxygenic phototrophic bacteria are divided into six families. They can be purple or green, with both existing in sulfur and non-sulfur forms. These bacteria are found in a wide range of aquatic habitats, primarily where there is sulfide presence, pollution from effluents, high concentrations of proteins, and/or molecules containing sulfur atoms.

These bacteria belong to a large group of metabolically diverse microorganisms, grouped based on their use of sulfide and their characteristic pigmentation. They play an important role in the anaerobic metabolism of organic matter, either as primary producers or as consumers of reduced organic compounds.

The anaerobic zone (stagnant water), when exposed to sunlight, promotes sulfide production through the decomposition of organic matter, thus creating ideal conditions for the growth of these bacteria. They can reach extremely high densities and become visible due to the blooming of pink, red, brown, or green colors on the surface of the lagoon.

Seasonal changes, differences in atmospheric pressure, temperature, signs of organic overload, and the presence of sulfate-reducing anaerobic bacteria are factors that can increase algal mortality and lead to the dominance of sulfurous purple phototrophic bacteria. The potential consequences of such surface blooms in wastewater treatment lagoons include:

• Depletion of available dissolved oxygen
• Reduction of photosynthesis and light penetration in the lagoon and/or receiving body
• Decreased BOD removal efficiency
• Lower efficiency in the removal of fecal coliforms

Although they do not produce toxins, the aforementioned factors can lead to fish kills and harm the fauna in the receiving bodies (AGUILA, 2007). The recommended alternative for controlling their proliferation is bioremediation.

Through phase-contrast microscopy, qualitative analysis of anoxygenic phototrophic bacteria can be performed. The classification system adopted aligns with Garrity, Bell & Lilburn (2005).

Taxonomic identification of the algae specimens found in the analyzed sample.

With the microscopy report, actions are suggested and immediately implemented, such as the application of a specific bioremediator to compete for nutrients and sulfur, along with the precipitation by suspended calcium hydroxide. The system is brought under control within a few days.

Start of application / After 90 days of application