26727, Primary Treatment|
Posted by Ananse, Wed Mar-20-02 11:26 AM
The treatment and disposal of wastewater (municipal and industrial) is of the utmost importance within any community. Nonetheless, it often gets ignored or receives little attention from the average person. Wastewater is generated from many sources domestic: commodes, kitchen sinks, bathroom drains, etc.; industrial: manufacturing operations, finishing plants, etc. Those varied sources point to the fact that wastewater constituents also widely vary. Fortunately a few techniques have proven (through a history of use) successful in treating many wastewaters.
Primary treatment encompasses the physical means of removing material before passing it to the secondary stage of treatment. If any of you have ever seen raw wastewater as it enters a plant, you may already know that it can contain any number of items: carcasses of deceased animals, rags, plastic containers, large packages, tree limbs, toys, etc. These items are not easily dealt with in alter process and must be removed immediately. Primary treatment normally consists of comminuters (grinders), bar screens, and grit chambers. The comminuters grind all of the small material while the bar screen catches some of the larger items. Bar screens act as giant sieves only allowing the wastewater to pass. The grit chamber makes use of gravity to allow quiescent settling of sand and other large particles that are not dissolved. For larger WWTPs, the water can then go to an equalization basin. EQ basins serve to equilibrate the flow of the water, so that there is not hydraulic short-circuiting of the system. With biological systems it is necessary to have a minimum flow through the plant at all times. One aspect of our lives that affects WWT and may not have been considered is the diurnal pattern that humans exhibit. WWTPs typically get their peak flows in the mornings (when people are showering and getting ready for work) and in the evening (when people are cooking and showering for bed).