The oil demand is projected to register double growth by 2045, says a report from India Brand Equity Foundation (IBEF). Moreover, the production of oil and gas is accompanied by the usage of water and the production of high amounts of wastewater.

A colossal amount of produced water is handled as wastewater in oil and gas industries, and generally, a substantial amount of wastewater is managed by disposing it through underground injection, where it cannot be used or accessed. However, such contaminated water, if treated, can be reused for various purposes. Moreover, oil and gas wastewater treatment is also essential to address the problem of water scarcity in arid regions.

What is produced water in the oil and gas industry?

Produced water naturally comes out of the ground during oil and gas production, and though oil and water cannot mix well, several separation techniques are required to split the two. Moreover, the produced water in the oil and gas industry comprises the most significant by-product stream. 

The amount of produced water varies from region to region, and generally, the ratio of produced water to oil is either more than 3 or 20 in some of the world’s areas. 

What is the composition of produced water?

The composition of produced water in the oil and gas industry varies in different areas. However, it generally contains soluble and non-soluble organic molecules, oil molecules, salts, aromatic hydrocarbons, suspended solids, dissolved solids, dissolved gases, and several chemicals used in production. 

Types of wastewater treatment methods used in oil and gas industries

Primary treatment

The primary stage in the oil and gas wastewater treatment focuses on removing hydrocarbons from the produced water and uses one or many of the following treatment methods depending on wastewater quality. 

• • A gravity separator is a rectangular tank that allows the settling of heavy particles, which are then skimmed off by skimmers. 
  • Corrugated plate separators (CPS) or corrugated plate interceptors (CPIs) consist of angled corrugated plates. It reduces the settling distance for suspended solids and increases the space for free oil and gas particles. The impurities are then skimmed off.
  • In hydrocyclone separators, wastewater enters the cyclone chamber and is rotated under intensive centrifugal force, which causes the separation of oil and water. 

Secondary treatment

In secondary wastewater treatment, industries use one of the following treatment methods: 

• • In induced gas floatation, gas is incorporated into the wastewater stream through top mixers to create a su[persaturaed solution. The solution is then injected into a floatator, where bubbles are formed that carries solid particles to the surface, which are then removed. 
  • In dissolved air flotation, the air is introduced through a pump into the wastewater. Air molecules bind with oil particles and other solid materials, causing them to float on the surface. As a result, impurities are taken off from the surface.

Tertiary treatment

Generally, tertiary treatment involves the use of filtration in oil and gas wastewater treatment. Types of filtration systems can be:

• • Nutshell or walnut shell filters are typically designed to remove oil from water and operate with 90 – 95 % removal efficiency. Here, a bed of nutshell has an affinity to oil particles and retains them from passing through the filter. The filters are then backwashed regularly to remove solids and oil particles.
  • Multimedia filters contain several media, which retain numerous contaminants from passing through them. As a result, it is efficient and used widely for water polishing during wastewater treatment.
  • The ultrafiltration technique is commonly used as an advanced tertiary wastewater treatment method for the removal of leftover suspended solids.

Why is oil and gas wastewater treatment necessary?

• • To avoid penalties imposed by the central government for trespassing the wastewater discharge rules.
  • The treated wastewater can be used to flush oil into the production well.
  • The treated water can be used to maintain the pressure of the reservoir and draw out more oil, saving money.
  • To avoid degradation of soil and groundwater.

When oil and gas industries do not treat wastewater and release untreated water in rivers, lakes, or deep into the grounds, it harms humans, flora & fauna, and aquatic life. Moreover, as the government has made wastewater discharge laws more stringent, industries fall prey to high penalties. Thus, wastewater treatment is essential to avoid capital loss and save the environment.