The industry of water and wastewater treatment plant construction can be a bit challenging to navigate. Courtesy of DESCCO Water, your most trusted water and wastewater treatment plant contractors, here are a few clear and concise answers to some of the most frequently asked questions in the world of wastewater treatment, water treatment plant design, and wastewater treatment plant construction.
Typically, there are two main types of wastewater sources: domestic sewage, and non-sewage. Domestic sewage includes all wastewater generated from residential communities, public restrooms, hotels, golf courses, restaurants, schools, hospitals, and other health centers. Non-sewage includes all industrial wastewater, storm water, runoff, and water from swimming pools, car garages, and cleaning centers.
There are many stages to the effective treatment of biological wastewater. At DESCCO Water Treatment Construction, we carefully consider the effectiveness and efficiency of each stage during the design of any water treatment plant project. The stages of biological wastewater treatment is as follows:
Preliminary Treatment – The removal of wastewater constituents such as rags, sticks, floatables, grit, and grease that may cause maintenance or operational problems with the treatment operations, processes, and ancillary systems of a wastewater treatment plant construction.
Primary Treatment – The removal of a portion of the suspended solids (solids physically suspended in sewage that can be removed by proper laboratory filtering) and organic matter (the waste from homes or industry of plant or animal origin that can be broken down by bacteria)
from the wastewater.
Advanced Primary Treatment – An enhanced removal of suspended solids and organic matter from the wastewater, typically achieved by chemical addition and/or filtration.
Secondary Treatment – The removal of biodegradable organic matter (in solution or suspension) and suspended solids. Disinfection is also typically included in the definition of conventional secondary treatment.
Secondary With Nutrient Treatment – The removal of biodegradable organics, suspended solids, and nutrients (nitrogen, phosphorous, or both nitrogen and phosphorous).
Tertiary Treatment – The removal of suspended solids (after secondary treatment) usually by granular media filtration or microscreens. Disinfection is also typically a part of tertiary treatment. Nutrient removal is often included in this definition.
Advanced Treatment – The removal of dissolved and suspended materials remaining after normal biological treatment when required for various re-use applications.
BOD stands for biological oxygen demand. It is the amount of oxygen required for aerobic biological microorganisms (bacteria that require free oxygen for growth) to decompose organic material in a given water source at a certain temperature over a given time period. In waste treatment language, BOD is most frequently stated as the percentage of waste removed or remaining after treatment.
COD stands for chemical oxygen demand. It is a measurement of the oxygen required to oxidize soluble and particulate organic matter in water using a strong oxidizing agent. The COD level can be determined more readily than BOD, but this measurement does not indicate how much waste can be decomposed by biological oxidation.
The typical processes that occur at biological wastewater treatment plants are as follows:
- Suspended-Growth – In these wastewater treatment plant processes, microorganisms are maintained in suspension within the liquid being treated.
- Attached-Growth – In these wastewater treatment plant processes, microorganisms are attached to some inert medium, such as rocks, slag, or specific ceramic or plastic materials.
- Combined Processes – These wastewater treatment plant processes combine elements of both suspended-growth and attached growth processes
- Lagoon Processes – In these wastewater treatment plant processes, wastewater is treated through a combination of physical, biological, and chemical systems. Much of the treatment occurs naturally, but some systems use aeration devices to add oxygen to the wastewater. Aeration makes treatment more efficient, so that less land area is necessary.
SRT stands for solid retention time. It refers to the average time that activated sludge solids (sludge consisting of microorganisms, non-living organic matter, and inorganic materials) are in a wastewater treatment system. SRT is an important operating parameter for wastewater treatment plant contractors and the design of water treatment plant projects, as it is crucial in the activated sludge process.