When we think of the world’s water supply, we’re rarely left with images of bereft detachment, or the idea of wells and streams and rivers running dry. We’re led to imagine the vast bodies of water that swathe the Earth, envelope and segregate its land and veil the hidden aquatic worlds that lie miles below the surface. Of course though, this isn’t a real reflection of the water we need to ensure we can function and that our industries can survive. In fact, the world’s water is very much a finite resource, something we must look after carefully to ensure our environment remains and becomes more sustainable for the future. Wastewater needs to be treated and recycled for this to happen, but what actually happens during the treatment process?
Almost all aspects of life seem to create wastewater, from industrial processes to domestic organic pollution. Most of our waste goes through our sewage systems, which diverts the wastewater to a treatment facility. The treatment procedure can then be broken down into four individual stages; preliminary, primary, secondary and tertiary treatment.
Screening the wastewater is part of the initial process, and at this stage it’s also possible to eliminate larger factors such as grit, oil and grease. Screening is a straightforward procedure involving the filtering of the water through ‘screens’, large plates or metal bars that stop larger materials such as wood or paper getting into the treatment system.
The huge tanks that are often the visual calling card of wastewater treatment plants are part of the primary treatment process. As the screened waste comes through into these tanks, they are designed to remove all the remaining solids from the water, by allowing them to sink to the bottom of the tank, and then be scraped out. The remaining water is sent to secondary treatment, whereas the collected solids are concentrated into a slurry that can then be dealt with in an environmental manner as a whole.
Secondary treatment is the most varied component of the process as there are a number of methods often employed by a single plant. Many use the concept of natural processes, but in a controlled environment and sped up by a range of machines or specific procedures. The main two treatment systems are:
- Biological Filtration
- Activated Sludge
Both methods utilize bacteria and micro-organisms to further separate the water from the sludge, usually creating a result suitable enough to send back to the environment. There are three other systems sometimes used alongside or instead of the main two, and these are:
- Hybrid systems
- Membrane Separation
- Nutrient Removal
Lastly, the tertiary treatment is a ‘polishing’ process of sorts that often uses sand or gravel as filters. Fine membrane separation and disinfection via ultra violet light are both tactics employed when the discharges are destined for bathing waters or shellfish growing areas.
These processes allow for the safe and efficient recycling of our water, something that must be done as we work toward a sustainable future. Approximately 150 litres of wastewater are produced per person, per day, and with water a resource that can run out, we must make sure we’re doing everything we can to make recycling it as economical and efficient as possible.