Biofiltration, an alternative for recovering domestic wastewater

Warm greetings, dear friends of Hive.

Wastewater is a topic of interest to everyone, basically produced in huge quantities daily and most of it is discharged directly into rivers and lakes without prior treatment.

This not only represents a great environmental impact on the receiving body, but also intensifies the problems of water shortage in many regions. It is easy to look around and find in many countries populations that still do not have a piped drinking water supply. So, this forces us to work on the use of accessible and economic methods that allow us to recover the wastewater generated in a domestic way, since it is very simple to condition it to be reused in cleaning or irrigation activities, and so it does not reach our ecosystem with a strong pollutant load.

Biofilters are devices used to remove contaminants from water, and their use contributes to avoid the contamination of surface or subway water bodies, caused by pouring the wastewater directly.

Scheme of a biofilter. Source: @yusvelasquez.

Description

At a domestic level, biofilters are used for the treatment of waste water, particularly gray water (that which comes from the kitchen, laundry, washroom and showers), these devices are also known as "biogardens".

In these systems, water treatment is carried out by means of a filtering medium on which a biofilm is developed, in which various microorganisms are responsible for the biological degradation of the contaminants and pathogenic agents found in the wastewater[1].

At present it is a widely used technique, since it represents a very attractive alternative, and studies continue to be carried out to use new materials that allow the replacement of the granular media traditionally used by fibrous media, thus competing with other types of treatments that imply greater complexity of operation, high investment and maintenance costs.

How do they work?

Grey water, which comes from the sinks, showers, the kitchen sink, laundry and other domestic uses, is the one that is produced in the greatest quantity (about 80% of all domestic water in a house)[2]. They are composed of nitrates, phosphates, salts, soap, organic matter, suspended solids, bacteria, food particles. If this water is not treated before it is discharged, the organic matter present undergoes a decomposition process and the bacteria multiply, so it acquires characteristics similar to black water, causing harmful effects to health and the environment.

Biofilters allow the processing of grey water for treatment and reuse, however, water treated with these systems cannot be used for human consumption. They can be built in homes, although they are also systems that can be adapted in larger projects, such as hotels or residential complexes.

Biofilters imitate natural wetlands, where wastewater is treated by natural processes. There are two types of wetlands, which differ according to the water circulation system to be treated:

• Free flow surface: they consist of tanks or channels whose depth varies from 10 to 45 meters, where the water is exposed to the atmosphere, with plants partially submerged in the water and the soil waterproofed. Bacteria attached to the plants treat the wastewater as it flows through the vegetation and through physical and chemical processes.

Surface Flow Wetland. Source: @yusvelasquez.

• Sub-surface flow: consists of a bed or channel, where the water circulates subway through an appropriate granular medium (gravel, sand and stone) that supports plant growth and serves to grow the bacterial film, which is primarily responsible for the treatment that occurs[4].

Subsurface flow wetland. Source: @yusvelasquez.

Can a biofilter be built in the home?

Yes, we can build the biogardens. In this type of biofilter, the gray water passes first through a grease trap, as a pre-treatment to separate solids such as food scraps, greasy particles contained in the water, protecting the filter, avoiding problems of obstruction to the support medium and that this may affect the operation of the system, from there they pass to the biogarden that consists of a ditch or excavation filled with stones and where plants are planted. These systems can reuse up to 70% of the water that enters the filter. Of the remaining 30%, the plants use part for growth and another part evaporates[2].

They have the advantage of being a simple system of operation where the water flows by gravity and no pumping equipment is used. They are easy to build and, in addition to providing natural beauty, they improve water quality.

Diagram of a biofiltration system. Source: @yusvelasquez, contains public domain images: 1, 2, 3.

It is also possible to build residential bio-filters only in concrete, these consist of a single structure where several compartments are located connected to each other. The gray water flows horizontally through the grease trap and then to each of the compartments containing the filter material, no plants are planted in it. They have the advantage of being more resistant to sun and rain, more durable, and easy to maintain.

Horizontal home biofilter. Source: @yusvelasquez.

Another alternative, is the construction of a biofilter where the gray water flows vertically, this type of biofilter is ideal when there is not enough space for installation. It is easier to build and more economical; however, it is less durable and its maintenance is higher. A recycled plastic container with its lid can be used for its construction. It should be placed in shady places such as under the laundry room.

Vertical flow domiciliary biofilter. Source: @yusvelasquez.

In conclusion

Wastewater treatment, especially in isolated regions, faces serious technical and economic difficulties associated with the geographical dispersion and topographical conditions of small municipalities and rural settlements. Conventional technologies are difficult to implement and also require considerable investment and trained technical personnel for operation and maintenance. Unfortunately, the financial availability of these regions is very limited, and technical personnel are often not available to supervise treatment systems. Therefore, offering domestic systems that are easy to operate represents a viable alternative for reducing the environmental impact associated with domestic wastewater.

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Well my friends, as we can see there are several options that we have and that we can implement in our homes. Among the applications that can be given to the treated wastewater, are the reuse in the agricultural area, street washing, cars, bathrooms among others.

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References

[1] Arango, A. (2004). La biofiltración, una alternativa para la potabilización del agua. Revista Lasallista de investigación. (1) 61-66
[2]Biogardeners Manual (2008). Nicaragua
[3] Muñoz, N. (2015). Diseño de un sistema de tratamiento de aguas grises por medio de biojardinera aplicado a viviendas rurales de del departamento de Quiché. Universidad de San Carlos de Guatemala.
[3] Escalona, Z. y Velásquez, Y. (2008). Evaluación de la eficiencia de remoción de contaminantes en aguas residuales domesticas por los humedales construidos. IUTAG