15th February, 2016.- The Water Waste Treatment Plant (WWTP) of Archena (Murcia) will host the necessary technology to enable Acciona Agua to carry out the UE project Life Celsius. This project, supported by ESAMUR (Regional body of Murcia for drainage and waste-water treatment), will implement a a wastewater treatment system for warm climate areas, with lower energy cost and greater efficiency.
The plant receives an average flow of 300 cubic meters per hour of raw wastewater from various sources: population of Archena, local food and agriculture industries, canning factories, detergents and bleaches manufacturers, but it also receives rainwater and all the material dragged by it.
We visited the facility with María del Mar Micó, Acciona Agua’s chemical engineer and project director, who helped us understand the purification processes associated with urban wastewater.
Grinding of solids
The process begins when raw water enters into a casket, leading to a series of grids where the removal of coarse or rough parts of solids is carried out (grinding of solids), retaining plastics, rags and woods that may have been driven by a runoff, etc.
María del Mar also explains that: “When this area is clogged by excess solids, a giant mechanical clamp drops, fishes and takes it to a container, which is then removed and the waste is treated”.
De-sanding and De-greasing
Next, the water waste which no longer contains rough solids, passes to a de-sanding area where the smaller particles are eliminated (usually inorganic particles) either because they have not been degraded in the water treatment plant or, “on the contrary, because they hinder the work of the pumps” and finally, all particles are dumped into a container for its residual treatment.
María del Mar explains that this de-sanded water is used to run a small pilot plant, basis of the Life Celsius project. It consists of an anaerobic digester with an outer membrane, installed in the sewage treatment plant, in the framework of the OptiAnMBR project, which has demonstrated today that it is possible to save energy and, at the same time produce biogas.
We continue the visit and the Project Director shows us the degreasing zone and explains that the fats extracted from the waste water have a different origin and at present there is no technology capable of reusing, so they must be treated as waste. María del Mar explains that “we are interested in removing them because they are very harmful to the environment.”
Aerating and decanting
The first phase of the secondary treatment is the biological reactor, where the sewage resulting from de-sanding and de-greasing processes is aired for 18 to 40 hours in a carousel-type rafts, driven by a system of blowers and a ferris wheel, to encourage the growth of bacteria that will degrade the organic matter.
María del Mar assures that: “There are four blowers that work with a motor and a magnetic levitation, whose performance, since no friction occurs, given that the parts are suspended in a magnetic field, result in less energy loss than in a more conventional blower”.
María del Mar continues explaining that in the next phase, there is a secondary sedimentation tank, which is a walkway with a scraper in its lower part that transmits a slow movement “allowing water to calm down and the particles fall to the bottom, where they are pushed to the sewer”, where they will be collected by trucks that carry will transport them and use them as fertilizer.
Fine-tuning the process
The Project Manager points out: “However, we even have a tertiary treatment, in which the above process is refined even more” because “although it cannot be appreciated by the human eye, it must be done to achieve even better qualities”, always bearing in mind the standards stated by the Local Authorities.
This tertiary treatment is the one with the wider range, “there is much physical, but also physical-chemical treatment”.
Specifically, in the WWTP of Archena, this treatment consists of four phases: a few sand filters that retain the smallest particles – called lamellar settling dragged through sand-, a tank of polychloride that helps the dewatering of sludge, ultraviolet treatment and a labyrinth of chlorination.
The aim of the sludge dewatering area is to remove the maximum amount of water possible to reduce weight, resulting in a saving of costs of transportation and management of waste. For this, at the exit of the secondary decanters, these muds are transferred to a tank where its thickening takes place by gravity and then they go through a system of centrifuges that removes excess water before being transferred to a hopper for its removal in trucks.
Disinfection and purification
The Project Director explains that: the water is disinfected by UV light, “which attacks the bacteria cell walls and deactivates them, i.e., hits the proteins that form the cell membrane and breaks it”. Then a chlorination tank makes water circulate in a labyrinth shape, to ensure that the mix with chlorine, which is dosed by bombs, is the correct one.
We end our visit to the Segura River, observing a large-diameter pipe pouring water resulting from this process, odourless and colourless, clean and purified, without affecting the environment.
Traducción: Carmen Gilson