Activity 4: Process steps

Main processes in a sewage treatment plant:

PART ONE: SCREENING

Screening removes large objects like, diapers, nappies, sanitary items, cotton buds and even broken bottles, bottle tops, plastics and rags that may block or damage equipment. 

Special equipment is also used to remove grit that gets washed into the sewer.

PART TWO: PRIMARY TREATMENT

This involves the separation of organic solid matter from the wastewater. 

This is done by putting the wastewater into large settlement tanks for the solids to sink to the bottom of the tank. At the bottom of these circular tanks, large scrappers continuously scrape the floor of the tank and push the sludge towards the center where it is pumped away for further treatment. 

PART THREE: SECONDARY TREATMENT

The water, at this stage, is put into large rectangular tanks. These are called aeration lanes. Air is pumped into the water to encourage bacteria to break down the tiny bits of sludge that escaped the sludge scrapping process.

PART FOUR: FINAL TREATMENT

Next, the ‘almost’ treated wastewater is passed through a settlement tank. Here, more sludge is formed at the bottom of the tank from the settling of the bacterial action. 

Again, the sludge is scraped and collected for treatment. The water at this stage is almost free from harmful substances and chemicals. The water is allowed to flow over a wall where it is filtered through a bed of sand to remove any additional particles. 

Finally, the filtered water is then released into the river. 

Sewage treatment plants close to Barcelona

Besòs 

Baix Llobregat 

Differences between sewage treatment and drinking water treatment

Wastewater treatment refers to the purification of water that has already been used by humans. Such contamination typically comes from municipal sources or industries sources. If the origin includes only municipal sources, the term sewage treatment is used. Wastewater are typically quite badly contaminated with many of the contaminants being dissolved. As such, wastewater treatment involves extensive processes such as biological treatment systems (aerobic, anaerobic, anoxic) and might also involve membrane systems. The treated water is returned to the efluent and, if scarcity of water exists, can be further treated for reuse purposes. 

Water treatment refers to the treatment of water for make it more acceptable for a specific end-use. The end use can be drinking, industrial water supply, irrigation, etc. The processes involved are similar as those involved in a sewage treatment plant, but a final disinfection is required, specially for drinkable water.

Some treatments that could be reproduced in our laboratory are...

1. Settler tank:

A settler tank, also called sedimentation tank, is a component used in the wastewater treatment plant. In a settler tank, the suspended particles settle out of wastewater as it flows slowly through it, providing some degree of purification. 

A layer of accumulated solids, called sludge, forms at the bottom of the tank and is periodically removed. In drinking-water treatment, coagulants are added to the water prior to sedimentation in order to facilitate the settling process, which is followed by filtration and other treatment steps. 

In our lab, we could build up a simplified version of a settler tank and study its performance.

2. Disinfection:

If bleach is added to the river water, and let it pass for a while, the water becomes drinkable. Thus, we could try to reproduce this phenomenon in our lab.  Moreover, since bleach is able to make smell disappear, the odor could be used as an indicator of the treatment performance.

So, we could add different amounts of bleach to beakers with the same amount of wastewater and study the effects, both in the smell and cleaning.

3. Flocculation:

Flocculation a process of contact and adhesion whereby the particles of a dispersion form larger-size clusters.

To see this process we propose to add starch into a solution made by water and clay and mix it and later see if the clay is sedimented at the bottom off the recipient.

4. Phytoremediation:

Phytoremediation refers to the technologies that use living plants to clean up soil, air and water contaminated with hazardous contaminants.

In the school, we can  the next experiment:

We have to take some plandots and put it into a big box. Then, we have to put some water contaminated inside this box and this plants will clean that water.

5.Separation:

In our process we had to separate the lipids with the water in this case the lipids were the oil, we had to put them awesome cause we want to se witch one stand on the top, we observed that because of the water is more dense than the oil, the oil precipitate and the water stand in the top.