Treatment and reuse

Wastewater treatment is essential to prevent environmental pollution. Where there is a sewage system, each building wastewater is transported to a wastewater treatment plant ( WWTP ) . In buildings not connected a water treatment is required to later pour them with adequate quality.

Depending on the space required for treatment systems we can group them into:

• Compact systems. Require less space but in return, require power comsumption. They are best used in large populations, and generally where little space is available . Constant monitoring and specialized staff are necessary.

In this category , but on a much smaller scale, treatment systems for homes and buildings would be located . They are easy to install, underground systems that have replaced septic tanks and offer appropriate treatment. There are mainly two types:

a) Biological treatment plants. Not require power comsumption. They consist of a first compartment (commonly referred decanter-digester) where sedimentation of solids and organic matter degradation occurs . In a second compartment of water are poured over a biological filter , where the bacteria carry out an aerobic degradation (with high oxygen concentrations in water) of the organic material .


Biological treatment
Biological treatment

b) Total oxidation treatment plants. There is a first reservoir where a set of nozzles inject air and keep the water in constant oxygenation, stimulating the removal of organic matter by the action of aerobic bacteria. Then the water passes to another compartment where sedimentation of the sludge generated occurs by gravity. This procedure has better performance in the purification of water , but carries a higher energy cost due to the continuous injection of oxygen.

Total oxidation treatment plant
Total oxidation treatment plant

• Semi-intensive systems. They are midway between compact systems or technology intensive and extensive systems . They require less energy but occupy more land.

• Extensive systems. They require little power to operate and low maintenance. Their efficiency is lower and therefore require larger extensions. They have an aesthetic component that other systems do not have it, simulate natural processes and integrate well into the landscape. Among these systems we highlight the lagooning and artificial wetlands in its various forms . They are widely used systems for up to 2,000 population equivalent.

Reuse of treated wastewater

If you intend to reuse the treated water we have two choices , try only gray water or treat all sewage.

• Grey water. From showers and sinks mainly, but also kitchen and washing machines are sometimes included . They have a very low pollutant loading and are practically free from human faecal remains . The treatment is very simple and is usually used for feeding flushing toilets .

The volume of gray water is at least 40% of total domestic use (washbasin + shower) and toilet consumption is estimated at 30% so this expense is covered. With an average per capita consumption in Spain of 144 liters a day we would be saving 43 liters per capita and per day .

• All sewage. Need more infrastructure and increased investment for its treatment, but in return we get a larger volume of water available. We would have an average of 144 liters per capita per day for use again assuming a significant saving.

Uses for treated water

• Recharge of toilet tanks. Only if the water comes from gray water treatment.

• Irrigation. All treated water can be used for irrigation. Care must be taken not to come into direct contact with humans or animals and should not be used in sprinkler systems .


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