Activated sludge reactor

Inputs from WWTP effluents can also affect the hydrologic and nutrient concentration regimes of recipient streams at different temporal scales. Daily variations of these parameters may be exacerbated in streams below the WWTP input by the diel patterns of the effluent discharge associated with plant operation [46]. In contrast, at the annual scale, seasonal variations of physical and chemical parameters upstream of the WWTP may be dampened by the constant input of additional water and nutrients from the WWTP. At its extreme, naturally intermittent or ephemeral streams may turn into permanent streams downstream of WWTPs [28, 30]. In these effluent-dominated streams, the relative contribution of WWTP inputs may vary widely on an annual basis, as shown by the 3-100% range measured in a Mediterranean stream [47]. Finally, WWTP inputs also cause shifts in the relative availability of N and P as well as in the relative importance of reduced and oxidized forms of N in the stream [30, 47]. The magnitude of these shifts depends on the level of wastewater treatment (i.e., primary, secondary, or tertiary treatment), the type of WWTP infrastructure (e.g., activated sludge reactor. 

Acid Orange 10, Acid Red 14 and 18 Anaerobic digester sludge and aeration tank mixed liquor Decolorization ranging from 65-90% was observed in a two-stage anaerobic-aerobic fixed film fluidized bed activated sludge reactor [175]... 

Fig. 2 Startup of the continuous activated sludge reactor with recycle ratio R = 0.3.

Melcer and Bedford (1988) studied the fate of pentachlorophenol in municipal activated sludge reactor systems that were operated at solids retention times of 10 to 20 d and hydraulic retention times of 120 d. Under these conditions, pentachlorophenol concentrations decreased from 0.1 and 12 mg/L to <10 pg/L. At solids retention times of 5 d or less, pentachlorophenol degradation was incomplete. 

Two phases exist in the activated sludge reactor the liquid phase consists of water, soluble ions and soluble substrate while the solid phase (biomass or sludge) has setdeable waste materials, dead and alive MOs in it. Metals associated with these phases were investigated in this study. The material balance for the metals at the steady state is defined as follows ... 

Nyholm, N., Jacobsen, B.N., Pedersen, B.M., Poulsen, O., Damboroj, A., Schultz, B. (1992) Removal of organic micro pollutants at ppb levels in laboratory activated sludge reactors under various operating conditions Biodegradation. Water Res. 26,339-353. 

Determine the amount of benzene that can be stripped in a complete-mix activated-sludge reactor equipped with a diffused-air aeration system. Assume the following conditions apply ... 

Example 9.6 An activated sludge reactor is aerated using a turbine aerator located 5.5 m below the surface of the mixed liquor. What is the pressurizing pressure if the prevailing barometric pressure is 761 mm Hg and the water temperature 20°C ... 

Consider ihe contents inside an activated sludge reactor laden with dissolved oxygen and pollutants subjected to aeration. Also, consider the sedimentation basin that follows the reactor and all the associated pipings. For the purpose of performing the material balance, let the boundaries of these items encompass the control volume. According to the Reynolds transport theorem, the total rate of increase of the concentration of dissolved oxygen is equal to its partial (or local) rate of increase plus its convective rate of increase. 

The sizing of aeration basins (for the activated sludge reactor, for example) are determined using the parameters of hydraulic detention time and mean cell retention time. Hydraulic detention time is the average time that the particles of water in an inflow to a basin are retained in the basin before outflow. Mean cell retention time, on the other hand, is the average time that cells of organisms (not water) are retained in the basin. 

In other situations, contact time is not equal to detention time. For example, in the case of the activated sludge reactor, contact time is the rise time of the bubbles to the surface, whereas detention time is the average time of travel of the water between the inlet to the outlet of the reactor. Contact time refers solely to the bubbles contacting the water during the time they were rising from the diffusers. Hydraulic detention time, in this case, has no relation to the contact time. 

Example 9.11 An aerator in an activated sludge reactor is located 3.5 m below the surface. The temperature inside the reactor is 30°C. What are the rise velocity of the bubbles, contact time for aeration. Re, Gi and G2 The approximate average diameter of the bubbles at mid-depth is 0.25 cm. 

A chemical engineer plans to purchase an aerator for a proposed activated sludge reactor. In order to do so, he performs a series of experiments obtaining the following results a= 0.91, = 0.94, and AOR = 1.30 kg/m day. 

An activated sludge reactor is aerated using a turbine aerator. The pressurizing pressure is calculated to be 101,436 nW at a prevailing barometric pressure of 760 mm Hg. If the water temperature is 20°C, determine the depth of submergence of the aerator. 

Fig. 1 Bioreactors. (A) activated sludge reactor (B) stirred tank reactor and (C) rotating biofilm reactor. (View this art in color at www.dekker.com.)...

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