SU0002246 SSNL - Laserfiche WebLink

Home Browse Search

Technical Description After a preset period, the mixed liquor is transferred to the clarifier tank for separation of sus- pended solids from the treated wastewater. The biological solids are then returned to the aeration tank to maintain a concentrated population of microorganisms to treat new, incoming waste. DETAILED PROCESS DESCRIPTION Incoming sewage is accepted into the aeration chamber via a mesh-receiving basket in which it is subjected to hydraulic comminution by means of the composite flow of mixed liquor and air di- rected through the basket. This allows only small particles to enter the main area of the chamber, while also assuring odorfree operation by underwater breakdown of solids. The reserve solids in the basket also assist in stabilizing the biologic process during periods of low flow. The amount of air required for complete digestion of sewage is lower in the Nitro-Raptor plant than theoretically required. This is because the operating temperature of the mixed liquor is as much as 5°C higher than the temperature of incoming wastewater, due to the hear exchange from the submerged transfer and aeration pumps-and the closed tank design. This higher temperature, plus the floc-colony breakup and reactivation caused by increased agitation, renders the organic material more readily digestible. This enhanced digestibility, in conjunction with the high level MLSS (3,000 to 6,000 mg/L), increases groups of facultative organisms which are able to initi- ate further waste digestion by utilizing some of the chemically bound oxygen present in the mixed liquor. The elevated operating temperature increases the enzyme and biologic activity, thus considerably less retention,or residence, time in the aeration phase is required. Aeration chamber residence time for the digestible material is 16 hours and is dependent on the final system batch timing, which is based on effluent testing. As the height of the mixed liquor increases in the aeration chamber, a float switch initiates the system microprocessor that, in turn, starts the mixed liquor transfer pump (MLT) and transfers a fixed volume (batch) of mixed liquor to the clarifier. The MLT pump is controlled by time, and the actual programming allows for two or three minutes' of pump overrun to overflow the MLT into the weirs, which skims off the scum and other floatables, which settled to the bottom of the clarifier after the previous batch. These floatables are returned to the aeration chamber for re- processing. Batch time in the clarifier is determined by the amount of time necessary for the remaining bacte- ria and dead cells (which flock together once deprived of food and oxygen) to settle, thereby separating the supernatant from the sludge. This period is sufficient to allow flocculation and set- , ding, but is not long enough to encourage an extended anaerobic condition. Average time is 60 minutes.No coagulants are needed, nor are they recommended. Two very common problems in most extended-aeration, small-flow treatment plants are the deni- trification of the sludge that occurs in the settling tanks, which causes sludge flotation and subse- quent loss over the weir, and surface skimming devices that prevent a quiescent environment which, in turn, prevents efficient settling, thus causing a high amount of suspended solids to be discharged. A third problem, that of sludge bulking, does not occur in Nitro-Raptor systems, as settling takes place under quiescent conditions and therefore there is no motion within the clari- fier to prevent any filamentous organisms from settling. Nitro-Raptor plants do not suffer from either of these problems, as there is no uncontrolled dis- charge over the weir and there are no moving skimming devices. -6- 7-H Technical Services Group,Inc.