The wastewater treatment plant (WWTP) of the Empresa Municipal de Agua Potable y Alcantarillado (EMAPET) is located in Barrio Vista Hermosa, San Benito, Petén, Guatemala. The WWTP from EMAPET oversees the wastewater treatment in the Central Area located in San Benito, Petén. The tributary of the WWTP has mainly domestic origin, however, it has some tributaries of commercial activities that are important due to their special nature.
The EMAPET WWTP has a total of 12 ponds (Fig. 1) and a constructed wetland planted with Eichhornia crassipes which is operating since 2019. The first process corresponds to the primary treatment and is made up of four anaerobic ponds (Fig. 2), the secondary treatment is composed by four facultative lagoons and the tertiary treatment is composed by four maturation ponds. In anaerobic lagoons microorganisms are used to decompose organic matter in an anoxic medium in order to remove between 50 to 60% of the BOD. Anaerobic lagoons have a retention time of approximately 5 days and depths of between 3 to 5 m.
Figure 1. Distribution of the EMAPET WWTP. Source: Google maps
Figure 2. Anaerobic lagoon.
Figure 3. Facultative lagoon.
Figure 4. Maturation pond.
The importance of a biological treatment with Eichhornia crassipes is due to the fact that nutrients such as nitrogen and phosphorus are not removed in the treatment lagoons of the EMAPET WWTP, which contributes to the increase in eutrophication levels in Lake Petén Itzá. High levels of nitrogen and phosphorus concentration cause the proliferation of certain algae that use these nutrients for their reproduction. The planted wetland has 2.5 m wide by 6 m long and 1 m deep. About 40 cm of gravel were placed as a substrate and black canvas as waterproofing to prevent the infiltration of sewage. The average flow is 1.5 m3/d with a retention time of 5 d. The experimental wetland was covered with approximately 150 to 200 plants and in addition to this, a grid was placed in the water outlet tube to prevent the plant material from going towards the effluent that empties into the Xucupó stream and in this way avoid the propagation of the Water Hyacinth in the stream.
The artificial wetland built to carry out the experiment corresponds to a surface flow type. The use of macrophytes has been used as an alternative secondary or tertiary treatment for wastewater treatment, proving to be an economical and efficient method in the removal of nutrients such as phosphorus and nitrogen.
Figure 5. Constructed wetland planted with Eichhornia crassipes.
