domestic_sewage treament

In rural areas where there is no mains sewage system it used to be common practise for domestic properties to have an underground tank (or just a big deep hole!) that the sewage would go into (pozo negro) and the liquid from this would simply soak away . This system was cheap to install and would only need emptying every couple of years or so by a Desotoro (sewage removal) company who would come along and suck it all up and take it away for around 150 euros.

Since 1986 following "Regalamento del Dominio public hydraulico Real Descreto 849/1986" it has been illegal in Spain to have a "pozo negro" system for the disposal of human effluent.

With the massive expansion of domestic dwellings being built in the countryside, concern arose on the impact of literally thousands of this type of system on the environment, in particular on pollution of the the water table especially around the many man made reservoirs such as Lake Vinuela where the water collected there is eventually used as drinking water.
Bacterial levels in lake Vinuela have risen alarmingly and this is being attributed to the use of these systems.

Although the decree prohibiting this system has been in force for more than twenty years it seems that a blind eye approach was adopted by building inspectors and town halls.

Now local authorities are actively examining the systems in use in domestic properties in rural locations with resulting fines for offenders.

The correct domestic effluent treatment system seems to have many names here in Spain: Fosa Oxidacion Total, Tratamento de aqua residual, Fosa Biologica are three that I have heard of. The thing definitely not to buy is the Fosa Septico: the old type septic tank.

The correct system basically works as follows:

The effluent enters a chamber where the solids and liquids begin to separate and a second chamber is filled by the liquid. Aerobic bacteria which use the organic matter in the effluent as food are encouraged to grow , but need oxygen to do so.
This is provided by the use of an external air pump which continuously circulates fresh air through the system.
The system produces an acceptable liquid waste product that can be legally allowed to soak away or can be used for irrigation.
Once installed the system takes around six weeks for bacterial levels to reach an effective level to break down the pollutants.
The system does need to be emptied every 6 months or every year, but must not be completely emptied to maintain a residual level of the aerobic bacteria.

Be careful when employing builders for this job as I have seen quotes for 6,800 euros just for the treatment plant!
Also confirm with your townhall what the requirements actually are for your area.

Antonio from Piscinas Axarquia in Nerja was extremely helpful and supplied a legal 10 person Fosa Oxidation Total System for 2,521 euros and it came with a certification of compliance with Spanish Directive RD 606/2003

The installation was carried out by CNN Property Services of Nerja.

Here are the photographs of the installation, slightly different in this case as there was no way to allow the output of the treatment plant to soak away because the ground is rock which is not porous, nor could it directly irrigate the gardens because of the location, so a 4000 litre underground tank (deposito) was installed at the same time to collect the waste water from the treatment plant.
A submersible pump was fitted, controlled by a timer to pump the water around and behind the villa to irrigate the gardens during the night.

All waste water from the property is now recycled and used to irrigate the gardens, now that is green.