Equalization basin

If the wastewater is readily degradable, as in a brewery, aeration is provided in the equalization basin to avoid septicity and the generation of odors. 

In order to handle accidental spills or overflows, a spill basin maybe provided, into which the flow is diverted if the concentration of a particular constituent exceeds a predetermined value. If equalization precedes biological treatment, in addition to the organic loading, high fluctuations in temperature, salinity, and toxic organics must also be considered. After the spill is contained, the wastewater flow is diverted back to the equalization basin. The contents of the spill basin are then pumped at a constant controlled rate to the equalization basin. 

Neutralization usually follows equalization so that acidic and alkaline streams can be partially neutralized in the equalization basin. If the wastewater is always acidic, neutralization may occur at a stage prior to the stream reaching the equalization basin, so as to minimize corrosion in the equalization basin. 

Equalizing basin A holding basin in which variations in flow and composition of liquid are averaged. Such basins are used to provide a flow of reasonably uniform volume and composition to a treatment unit. Also called a balancing reservoir. Estuaries Bodies of water which are located at the lower end of a river and are subject to tidal fluctuations. 

Raw wastewaters are commonly collected in equalization basins to even out the flow and the pollutant contaminant load. This permits uniform and controlled operation of subsequent treatment facilities. Wastes in this industry generally require pH adjustment, which can be performed in mixed equalization basins or in separate neutralization reactor basins following equalization.10... 

Equalization basins may be designed to equalize flow, concentrations, or both [27]. For flow equalization, the cumulative flow is plotted vs. time over the equalization period, which is usually 24 hours. The maximum volume above the constant-discharge line is the equalization volume required. The basin may also be sized to restrict the discharge to a maximum concentration of a critical pollutant. For example, if the maximum effluent from an activated sludge unit is 20 mg/L BOD5, the maximum allowable effluent from the equalization basin may be computed and thereby provide a basis for sizing the unit. Novotny and England [44]... 

Figure 8 Water treatment plant with pre-ozonation and intermediate ozonation steps. 1 Pre-ozonation chamber. 2 Equalization basin. 3 Coagulation chamber (C = coagulant). 4 Flocculation. 5 Sedimentation. 6 Ozonators. 7 Ozonation chamber. 8. Active carbon filtration unit. 9 Final disinfection (D = disinfectant).

Neutralization Acidic or basic wastewaters must be neutralized prior to discharge. If an industry produces both acidic and basic wastes, these wastes may be mixed together at the proper rates to obtain neutral pH levels. Equalization basins can be used as neutralization basins. When separate chemical neutralization is required, sodium hydroxide is the easiest base material to handle in a liquid form and can be used at various concentrations for in-line neutralization with a minimum of equipment. Yet, lime remains the most widely used base for acid neutralization. Limestone is used when reaction... 

Determine the effect of the equalization basin on the BOD mass-loading rate. Although there are alternative computation methods, perhaps the simplest way is to perform the necessary computations starting with the time period when the equalization basin is empty. Because the equalization basin is empty at about 8 30 A.M. the necessary computations will be performed starting with the 8-9 time period. 

The first step is to compute the liquid volume in the equalization basin at the end of each time period. The volume required is obtained by subtracting the equalized hourly flowrate expressed as a volume from the inflow flowrate also expressed as a volume. The volume corresponding to the equalized flowrate for a period of 1 h is 0.307 m3/s x 3600 s/h = 1106 m3. Using this value, the volume in storage is computed using the following expression ... 

Thus, using the values in the original data table, the volume in the equalization basin for the time period 8-9 is as follows ... 

Related Calculations. Where in-line equalization basins are used, additional damping of the BOD mass-loading rate can be obtained by increasing the volume of the basins. Although the flow to a treatment plant was equalized in this example, flow equalization would be used, more realistically, in locations with high infiltration or inflow or peak stormwater flows. 

Now, to derive the equalization required, refer to Figure 3.10. The curve represents inflow to an equalization basin. The unit on the ordinate is mVh and that on the abscissa is hours. Thus, any area of the curve is volume. The line identified as average represents the mean rate of pumping of the inflow out of the equalization basin. The area between the inflow curve and this average (or mean) labeled B is the area representing the volume not withdrawn by pumping out at the mean rate ... 

The excess inflow volume over pumpage volume, area B, and the excess pumpage volume over inflow volume, areas A plus D, must somehow be balanced. The principle involved in the sizing of equalization basins is that the total amount withdrawn (or pumped out) over a day or a cycle must be equal to the total inflow during the day or the cycle. The total amount withdrawn can be equal to withdrawal pumping at the mean flow, and this is represented by areas A, C, and D. Let these volumes be V. Vc, and V, respectively. The inflow is represented by the areas B and C. Designate the corresponding volumes as Lb and Vc- Thus, inflow equals outflow. 

From this result, the excess inflow volume over pumpage, Vb, is equal to the excess pumpage over inflow volume, Va + V. In order to avoid spillage, the excess inflow volume over pumpage must be provided storage. This is the volume of the equalization basin—volume Vb. From Equation (3.23), this volume is also equal to the excess pumpage over inflow volume, Va -i- Vb,. 

Q Value of inflow of quality into equalization basin at time t,... 

Value of quality inside equalization basin between time intervals t, i and ti... 

Qi Inflow rate of flow into an equalization basin at time f. 

Inflow rate of flow into an equalization basin at time Mean rate of withdrawal from an equalization basin Time at index i of calculation Time at index f -1- 1 of calculation Top width of channel Top width at critical section Average velocity at cross section of conduit Average velocity at cross section at point 1 Average velocity at cross section at point 2, ) Accumulated volume inside equalization basin between time intervals t 1 and ti... 

Volume of equalization basin Average velocity at critical section of open channel Throat width of Parshall flume... 

The equalized volume is not the volume of the equalization basin. Is this statement true ... 

One other method of design is to use equalization basins ahead of the sedimentation basins. In this case, the inflow would be the equalized flow. There should be no need for recirculation, because only one flow rate is introduced into the sedimentation basin. Design of equalization basins was discussed in Chapter 3. 

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