Two systems with the same objective
When a home or community does not have a connection to the public sewer system, there are two main alternatives for managing wastewater: septic tanks and mini treatment plants.
Although both systems fulfil the function of treating and discharging water, their technical characteristics, regulations and maintenance requirements are different. Making the right choice not only ensures legal compliance, but also efficient and sustainable operation in the long term.
👉 When emptying septic tanks, we work daily with communities and individuals, and we know that making a good initial decision prevents many future problems.
What is a septic tank?
A septic tank is a primary treatment system that works in a simple way:
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Separate solids from liquids by decanting.
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Allows partial anaerobic digestion of organic matter.
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You need an infiltration field or filter well to drain the treated water.
This is the most common option in rural areas and single-family homes without access to the public network.
Advantages of septic tanks
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More economical installation.
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Simple operation and no electricity consumption.
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Less need for technical supervision.
Disadvantages
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Requires periodic emptying to prevent saturation.
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It does not remove all contaminants.
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It depends on the quality and permeability of the soil.
What is a mini treatment plant?
The mini treatment plant, also known as a compact treatment plant, is a more advanced system that provides secondary treatment:
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It uses aerobic biological processes with oxygenation.
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It allows for much more thorough water treatment.
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Enables the reuse of treated water for irrigation (if permitted by regulations).
Advantages of the mini treatment plant
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Higher quality treated water.
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Complies with the most stringent environmental regulations.
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Possibility of reusing water for non-potable domestic uses.
Disadvantages
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Installation with a higher initial cost.
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Need for constant electricity supply.
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Greater technical complexity and mandatory periodic reviews.
Key differences between septic tanks and mini treatment plants
Although both serve the purpose of treating wastewater in homes without a connection to the sewer system, their differences are notable:
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Treatment: the septic tank performs a primary process based on decantation and partial digestion; the mini treatment plant applies a secondary treatment with aerobic biological processes.
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Treated water quality: septic tanks only allow for basic purification and require land with infiltration capacity; mini treatment plants produce much cleaner water, which is even suitable for reuse in irrigation in accordance with regulations.
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Maintenance: the septic tank needs to be emptied periodically, while the mini treatment plant requires more frequent technical inspections and a constant power supply.
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Applicable regulations: septic tanks are still permitted on rural land, but in environmentally protected areas, regulations usually require the installation of a mini treatment plant.
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Initial cost: the septic tank is cheaper to install; the mini treatment plant requires a greater investment, although it offers long-term advantages.
When to choose a septic tank?
A septic tank is recommended in these cases:
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Rural dwellings with low occupancy rates.
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Land with good infiltration capacity.
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Tight budgets.
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Areas where regulations still permit it.
When to choose a mini treatment plant?
The mini treatment plant is the best option when:
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These are permanent dwellings with high occupancy rates.
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Environmental regulations require secondary treatment.
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The aim is to reuse treated water.
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The soil does not allow for good infiltration.
The role of maintenance in both systems
Both septic tanks and mini treatment plants require proper maintenance to ensure their effectiveness.
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In septic tanks: emptying and cleaning every 1–3 years.
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In mini treatment plants: technical inspections, aerator checks and sludge removal.
👉 With a maintenance contract, you can ensure that both systems operate without incident and comply with current regulations.
In addition, services such as pipe inspection with a TV unit allow for the detection of obstructions, leaks, or root intrusion that compromise the performance of the installation.
Regulations in Spain
In Spain, legislation establishes clear differences between the two systems:
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Septic tanks must comply with Royal Decree 1290/2012, which regulates their design, installation, and maintenance.
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Mini treatment plants, which provide secondary treatment, comply with Directive 91/271/EEC and stricter regional regulations.
Further information in European regulations on wastewater treatment.
Frequently asked questions
Is it legal to install a septic tank on any piece of land?
No. It depends on local regulations and the infiltration capacity of the soil. In many municipalities, the installation of a mini treatment plant is already required.
How often should a septic tank be emptied?
On average every 1–3 years, depending on usage and the number of occupants in the dwelling.
Do mini treatment plants consume a lot of energy?
No. Their consumption is low, although they require a constant power supply.
Can a septic tank be replaced with a mini treatment plant?
Yes, although it involves civil engineering work and technical adaptation. It is a viable option in areas where regulations have changed.
Choosing between a septic tank and a mini treatment plant depends on factors such as the type of dwelling, the land, the applicable regulations and the available budget. While septic tanks remain a valid solution in rural areas, mini treatment plants offer more comprehensive, sustainable treatment that is adapted to new legal requirements.
At Limpiezas Domingo, we help each customer evaluate their options and offer installation, emptying, and maintenance services to ensure the proper functioning of their system.
👉 Consult with professionals and ensure you choose the most suitable solution for your home or community.
