Due to the increasing number of water-efficient technologies and the increasing number of mills that can reuse and treat wastewater, industries have become more effective at managing water usage. This article provides a comprehensive overview of the water industry’s various strategies and practices to reduce its water consumption.
The various treatment steps performed on wastewater can be categorized into three categories: primary, secondary, and tertiary. The primary process involves separating the floating and settleable materials in the wastewater. This process can be carried out through gravity separation, screening, and sedimentation.
After the primary process, the effluent is sent to a dissolved air flotation (DAF) unit. The unit type used should be evaluated based on the influent conditions, required outlet conditions, and the type of operations necessary. A well-designed sedimentation tank can help remove up to 85% of the suspended solids in the wastewater. It can also reduce the overall BOD load by up to 40%.
In the secondary treatment process, biological agents are utilized to remove the organic compounds that were previously deposited in the primary process. The main biological treatments used are the suspended growth processes and the attached growth processes.
The suspended growth process is carried out by microorganisms designed to remain in the liquid for a certain time. These microorganisms then use the liquid’s organic constituents as their food source. They then form an active biomass that can oxidize the incoming feed wastewater’s organic content. The most common type of activated sludge process is the ASP.
The clarifier, an ASP, is a component of the treatment process composed of an aeration tank, an air intake system, and a clarifier. The primary treatment process’s wastewater enters the aeration tank first, where it is mixed and aerated with microbial suspension. Continuous air injection is then used to maintain the solid and aerobic environment. The mixed liquor suspended solids in the tank are referred to as mixed liquor-suspended solids (MLSS). The organic portion of this substance is called mixed liquor volatile suspended solids (MLVSS).
After the effluent from the aeration tank has been sent to the clarifier, the portion of the biomass that’s been recirculated back to the tank is then turned into waste-activated sludge. This process continuously biodegrades the organics in the wastewater.
After the clarifier has completed its work, the effluent is sent to a tertiary treatment facility. This process can help reduce the BOD and COD in the wastewater.
In addition to the biological agents, ASP can be utilized combined with powdered activated carbon (PACT) to increase the overall biological oxidation, aided by carbon adsorption.
Instead of being suspended in the liquid, microorganisms are typically attached to an inert material during an attached growth process. This process is not commonly utilized in the industry due to its size and constraints.
Reducing contaminants in the wastewater to meet the regulations is a part of a tertiary treatment process. This process can be carried out through various treatment technologies.
One of the most common methods of treating wastewater is by using sand filtration. This process can effectively remove the high levels of suspended particles in the wastewater. This process occurs through a filter bed composed of various filter media, such as sand and anthracite.
Chemical oxidation is another process that can reduce the non-biodegradable and residual COD in wastewater. Advanced methods such as wet oxidation, ozone oxidization, and Fentons reagents are commonly used to destroy non-chromophoric and chromophoric pollutants.
A membrane filtration process is another technique that can be used to remove heavy metals, total dissolved solids, and BOD and COD from the wastewater stream.
Treating wastewater can be incredibly beneficial, especially if you’re planning to recycle the water. These are just a few of the main ways that you can treat your wastewater.