The sanitary engineer explains that these systems retain some of the solids and reduce the organic matter in wastewater, but they need additional processes to meet environmental discharge standards
SANTO DOMINGO.- Septic systems with filters installed in numerous homes and real estate developments in the Dominican Republic can put groundwater at risk when effluents are discharged into the subsoil without receiving sufficient treatment, warned sanitary engineer Raymond Martínez, president of Sistemas Hidrosanitarios & Asesoría Ambiental SRL (SIHISA).
“There are environmental implications, because you are directly contaminating the aquifer,” the specialist warned, referring to the consequences of infiltrating wastewater that still contains pollutants.
Martínez explained that septic tanks are primarily designed to separate settleable solids and partially reduce the organic load present in wastewater. However, he clarified that their operation in isolation does not guarantee that the resulting liquid meets the environmental parameters required for final disposal.
“A septic tank is a structure” whose purpose is to retain some of the settleable suspended solids, the engineer explained. This limitation is especially relevant in the country, where these systems are used as an alternative to the sanitary sewer system in various residential communities.
Septic tanks only retain a portion of the contaminants
According to Martinez, a conventional septic system can remove approximately 60% of settleable suspended solids and, as a result of that process, between 30% and 35% of the organic matter associated with the retained solids.
The specialist explained that the procedure takes place inside a chamber where the heavier particles settle to the bottom. Meanwhile, anaerobic microorganisms, which function in the absence of oxygen, break down some of the accumulated organic waste.
As a result of this biological activity, gases such as methane and carbon dioxide are produced, components of the biogas generated during the process.
However, the water leaving the reservoir still contains substances that were not removed in that first phase. Therefore, the engineer emphasized that these structures should not be confused with complete wastewater treatment systems.
“A septic tank per se does not meet the discharge standards of this country or any other,” Martínez argued, explaining the limitations of this sanitation solution.
Hence, sedimentation and anaerobic decomposition constitute only a part of the procedure required to reduce the pollutants present in domestic liquid waste.
They incorporate additional cameras to improve the treatment
Given these limitations, the president of SIHISA pointed out that, for approximately 15 or 20 years, some projects have begun to incorporate a complementary chamber with a bed of stone, called a bacterial bed, to promote the degradation of the organic matter that remains in the liquid.
“We are adding another chamber, which is a stone bed,” Martínez explained, describing the evolution of these installations in certain real estate developments.
This component enhances the initial purification process through the activity of microorganisms that help reduce the organic load. However, the engineer cautioned that this additional phase alone does not guarantee that the effluent will reach the required quality levels before being discharged.
“Obviously, it doesn’t comply either. So we would still need disinfection,” he noted, referring to the need to incorporate additional mechanisms to complete the process.
For this reason, he considered that the installation of complementary elements should be part of a comprehensive design and not simply a matter of adding successive chambers. Each stage, he specified, must fulfill a specific function in improving water quality before its final disposal.
The risk of discharging wastewater into the subsoil
Beyond the technical limitations, Martínez warned that one of the main environmental problems arises when the liquid from these mechanisms infiltrates the ground and can reach underground aquifers.
Although treatment through septic tanks and trickling filters reduces some of the pollution, the resulting water may still contain substances capable of degrading the quality of water supplies. Therefore, the disposal of this effluent requires an assessment that considers both the treatment applied and the surrounding environmental conditions.
The specialist considered it especially important to examine the sanitation solutions used in housing estates and other residential complexes that do not have a connection to a public sewer network, due to the possible repercussions on underground resources.
“That’s why it’s a low-flow, almost rural solution, but we are using it in the Dominican Republic,” he stated, questioning the application of these systems in the Dominican context.
In that regard, he argued that liquid waste management must consider the effective treatment capacity, soil characteristics, and groundwater protection conditions. Otherwise, an alternative designed to address sanitation needs could become a source of environmental pollution.
He also stated that the evaluation of these facilities should cover all the necessary phases for treating effluents, from solids retention and organic matter reduction to disinfection, where appropriate, according to the characteristics of the system and applicable requirements.
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