How is Wastewater Treated? Understanding the Wastewater Treatment Process

1. The Pre-Treatment Stage

When considering the types of industrial water treatment solutions, it’s important to consider the first steps in doing so. Industrial water management includes analysing the chemical components of the contaminated water and correcting them to improve the hygiene of the water.

This process is often called the “pre-treatment” stage.

The pre-treatment stage is designed to remove organic and inorganic contaminants from effluent that’s been produced by the industrial sites. These often include metals, solids, and other dangerous chemicals that affect the water.

Wastewater from both industrial and commercial sectors must be treated properly for it to either be reused or used elsewhere. If the treatment of the water is designed for it to be returned into the water cycle, then it must be handled correctly and returned in an appropriate condition, so it does not contaminate the environment or lead to further pollution.

2. Primary Wastewater Treatment

Following the pre-treatment stage, it’s time to conduct primary treatment of the wastewater. With large solids, metals and products that aren’t meant to be flushed now removed, the primary treatment stage tackles human waste. This stage is crucial to protect further treatment stages. Wastewater is put into settlement tanks where the solids sink to the bottom, settling into ‘sludge’. The sludge is then pumped away for further treatment, where it can then be used to generate energy.

While the sludge sinks to the bottom of the tank, fats will float to the top and be removed by scraper arms. What remains is light organic solids and dissolved materials along with the water to be further treated.

3. Chemical Wastewater Treatment

There are various industrial water management solutions, but the two main stages are filtration and chemical water treatment.

Because industrial effluents are so varied and diverse, particulates that are produced and remain in the wastewater must undergo chemical treatment to remove unwanted solids and improve the overall hygiene of the water.

There are three types of chemical categories that are necessary for industrial water management:

• pH adjusters
• Coagulants
• Flocculants

Using pH adjusters

A pH adjuster works by manipulating the pH level of the wastewater. The chemical reaction that takes place when added to the water will raise the pH level, causing a rise in negatively charged hydroxide ions.

This chemical reaction forces the metal contaminants to bond and form solid particles that can then be removed.

Using coagulants

Effectively, a coagulant brings all the solids in the wastewater together, often formed because of the pH adjusters, clumping the particulates together to then be removed.

Industrial water treatment solutions often use a blend of either organic or inorganic coagulants:

Organic coagulants produce less sludge but are more expensive
Inorganic coagulants work better to absorb the particulates but create more sludge that then needs to be removed after.

Using flocculants

Once the small clumps of solid particulates are formed, a flocculant is added to treat the water, forcing the solids to either float to the surface or sink to the bottom.

Once a flocculant is added, often in conjunction with a coagulant, it can then be easily removed. This is done through a filtration treatment process.

4. Filtration and Separation

Once the wastewater has been chemically treated, the next step is to then run the water through a filtration system to remove the remaining particulates that are still contaminating the water.

There are several industrial water management processes that filter out the remaining waste:

• Filter press
• Centrifuges
• Belt press

Centrifuges

Centrifuges essentially spin the contaminants out of the wastewater, separating the solids from the liquid in order to treat the water.

While a simple and effective method, centrifuges come with several disadvantages; they can be expensive to install and set up and use up large amounts of energy to run too.

Belt presses

Belt filter presses are used as a way of removing excess water from sludge, making it easier to treat. They work through a combination of a gravity drainage system before pressure is gradually applied mechanically, through a system of belts and rollers that squeeze any remaining water from the sludge.

Belt presses tend to work after the industrial water management process undergoes chemical treatment first. However, while a belt press can run continuously allowing wastewater to flow through, it can be slow to produce results and can be expensive to run.

Filter presses

One of the oldest filtration systems is a filter press. This process uses pumps to create pressure that forces the solids from the wastewater, through a succession of filters until it’s clean.

While this form of industrial water treatment solution is dated, it still remains as one of the most reliable filtration methods for treating industrial wastewater.

5. Disposal or Reuse

The final step in the wastewater treatment process is final disposal or reuse. The useful bacteria that’s filtered forms more sludge which can then be recycled back to the chemical wastewater treatment method. Additionally, remaining sludge that is now separated from the rest of the wastewater is collected, either to be recycled and used as fertiliser or used to generate energy. Sludge is also disposed of, either through landfill or incineration, when reuse is not applicable.

There is a specific way of generating power or creating fertiliser using the reusable sludge:

Anaerobic digestion

The sludge is heated to high temperatures in an atmosphere without oxygen, which gets the bacteria inside to break down the waste. Biogas is created which can be burnt to generate electricity. After digestion, the residual sludge becomes rich in nitrogen, phosphorus and potassium, making it perfect as a natural fertiliser for agriculture.

After the wastewater is free of contaminants, it can be safely returned to river and stream systems. Cleanliness is crucial, as it keeps water flowing and protects ecosystems and the wildlife.