Industrial wastewater treatment

Industrial wastewater treatment is a critical component of modern manufacturing, aimed at removing pollutants or reducing them to acceptable levels prior to discharge to protect public health and the environment. Unlike municipal wastewater, which is relatively consistent, industrial wastewater characteristics vary significantly between different industries and even between different processes within the same plant. Industrial facilities in the United States alone discharge over 285 billion gallons of wastewater daily, with approximately two-thirds originating from cooling operations and the remainder from process-related activities such as product washing and transport.

• The Oily Water Sewer: Collects non-corrosive process waste from tanks and exchangers. 
• The Acid (Chemical) Sewer: Handles heavily contaminated, corrosive waste using acid-proof concrete or brick-lined boxes. 
• The Storm Water Sewer: Manages runoff and often includes oil skimmers and trash screens. 
• The Sanitary Sewer: Collects domestic waste from the facility, often discharging into a septic tank.

The most crucial step in managing industrial waste is wastewater characterization through detailed surveys. These surveys establish flow rates, pollutant loadings, and chemical profiles—information essential for determining treatment levels and selecting appropriate technologies. Environmental engineers often develop a mass balance augmented by an understanding of the manufacturing process to account for all water resources and losses. An effective strategy typically involves evaluating compliance with regulations regarding these types of treatment systems, which set effluent limitations based on either control technologies or specific water quality standards.

Before implementing end-of-pipe treatments, industries focus on wastewater minimization to reduce both the volume and the strength of the waste. Volume reduction is achieved through the classification and segregation of waste streams based on quality, water conservation within processes (such as moving from open to closed systems), and the reuse of treatment plant effluents. Strength reduction involves “clean technology” and pollution prevention approaches that minimize waste generation at the source. For example, the sequential reuse of water in canning plants can achieve savings of up to 25%.

Industrial Sewer Design

Large industrial complexes, such as petroleum refineries, utilize specialized sewer systems that are generally incompatible with municipal sanitary sewers. A typical industrial plant may utilize four separate systems:

Primary and Physical Treatment

Initial treatment stages focus on removing larger solids and floating materials. Preliminary processes include screening to protect mechanical equipment and grit chambers to remove heavy mineral materials like sand and metal fragments. For industries like oil refining, gravity oil-water separators (such as API separators) are essential to allow free oil to rise to the surface for removal by skimmers. Flow equalization is also employed as a pretreatment to dampen peaks in flow and organic loads, which prevents the hydraulic overloading of downstream units