Primary sedimentation

A tmospheric — Outdoor Primary sedimentation tank Zinc 8-12... 

Water that drops down a foot or two from the outlet weir can cause the emission of odourous gases from the sewage. This is usually a problem only after primary sedimentation. 

A primary sedimentation tank has been designed for the pretreatment of 0.312 MOD of fermentation waste generated from the pharmaceutical industry. The raw waste SS concentration is 1660 mg/L. At a detention time of 2 hours the effluent SS concentration is reduced to 260 mg/L. Determine (i) the SS removal efficiency of the sedimentation tank and (ii) the quantity of sludge generated per day. Assume the specific gravity of sludge (5si) is 1.03, which contains 6% solids. 

A trickling filter is designed to treat 435 m /day of acid waste stream generated from a synthetic organic chemical plant. The BOD5 of the acid waste before and after the primary sedimentation is 3250 mg/L and 2850 mg/L, respectively. The efficiency of the filter at a recirculation ratio of 4.5 is 92%. If the depth of filter is restricted to 1.6 m and the value of the constant in Eckenfelder s equation is n = 0.5, determine the value of constant assuming the hydraulic loading rate = 17.5 m /m day. 

Kempton S, Sterrit RM, Lester JN. 1987. Heavy metal removal in primary sedimentation. I. The influence of metal solubility. Sci Total Environ 63 231-247. 

ESTIMATION OF SLUDGE VOLUME FROM THE CHEMICAL PRECIPITATION OF PHOSPHORUS WITH LIME IN A PRIMARY SEDIMENTATION TANK... 

Estimate the mass and volume of sludge produced in a primary sedimentation tank from the precipitation of phosphorus with lime. Assume that 60 percent of the total suspended solids (TSS) is removed without the addition of lime and that the addition of 400 mg/L of Ca(OH)2 results in an increased removal of TSS to 85 percent. Assume the following data apply ... 

The surface overflow rate (SOR) for primary sedimentation is normally held close to 40.74 mV(m day) [1000 gal/(fU day)] for average flow rates, depending upon the sohds characteristics. Lowering the SOR below 40.74 m7(m day) does not produce improv ed effluent... 

Fig. 39. Relationships between iron compounds in various primary sediments for activity of Uf g-ion/I A = oxide B = silicate C = carbonate D = sulfide (Uj = 10 g ion/1).

Carbonate iron sediments are formed when iron is precipitated in the presence of dissolved carbonic acid or as a result of interaction of the primary sediments with organic matter in the course of diagenesis. The determination of the stability of primary iron carbonates with respect to iron oxides and hydroxides was made on the basis of using the functional dependence of and on pH, calculated by the method of Garrels and Christ (1968) for the system carbonate-water. According to this dependence, in conditions of FeCOj in equilibrium with water the value of partial pressure of carbon dioxide decreases in proportion to increasing pH. 

The relationships between the silicate and sulfide sediments are also determined mainly by the content of sulfur in the water, and pH and Eh. For given sulfur activities the sulfide field is curtailed due to formation of silicates only in highly alkaline environments (pH >11). Deposition of silicates in environments close to neutral occurs in the stabihty field of magnetite. Magnetite is not formed in primary sediments in the presence of active forms of Si02. As the sulfur content in the waters decreases, the boundaries between the iron sulfide and iron sihcate fields shift toward neutral environments. In waters with pH = 8 pyrrhotite begins to be replaced by silicates at < 10and pyrite at Og 10 g-ion/1. 

Plaksenko suggested, in accordance with the theoretical ideas of Strakhov, that the primary sediments consisted of iron hydroxide which then was reduced to a ferrous form, producing the whole gamut of observed mineral associations in diagenesis under the influence of organic matter. 

Figure 5.4 shows a portion of a circular primary sedimentation basin used at the Back River Sewage Treatment Plant in Baltimore City, MD. In this type of clarifier, the raw sewage is introduced at the center of the tank and the solids settled as the wastewater flows from the center to the rim of the clarifier. The schematic elevational section in Figure 5.5 would represent the elevational section of this clarifier at the... 

Design Parameters and Criteria for Primary Sedimentation Basins... 

Example 5.9 To meet effluent limits, it has been determined that the design of a primary sedimentation basin must remove 65% of the influent suspended solids. The average influent flow is 6,000 mVd the peak daily flow is 13,000 mVd and the minimum daily flow is two-thirds of the average flow. It was previously determined that 65% removal corresponds to an overflow rate of 28 m/d. Design a circular basin to meet the effluent requirement at any cost. 

Phosphorites are generally thought to be the result of postdepositional concentration of CFA from a primary sediment deposit, which contained more disseminated CFA, by secondary physical processes such as winnowing and reworking. The classical depositional environments in which... 

The suspended solids in the composite wastewater samples from the detergent and soap factory were a fine divided colloidal type which require a very long detention time to achieve not more than 10% removal ratio. On this basis the primary sedimentation unit of the conventional activated sludge system was eliminated. 

When freshwater lake sediments were treated with hydroxylamine hydrochloride or sodium acetate, which are effective extractants for the removal of Mn (Oscarson et al., 1981b), the oxidation of As(III) to As(V) by the treated sediments was greatly decreased relative to untreated samples of the sediments (Table 8-2). Although the hydroxylamine hydrochloride treatment also removes Fe oxide, the evidence obtained from colorimetry and x-ray photoelectron spectroscopy shows that a redox reaction between Fe oxide and As(ni) does not occur within 72 h, indicating that the kinetics of the redox reaction between As(ni) and Fe(IIl) is relatively slow. This supports evidence that Mn oxide is a primary sediment component responsible for the oxidation of As(ni). 

The purpose of primary sedimentation is to remove settleable solids. About 50-70% of TSS and 30-40% of the BOD5 can be eliminated during this operation, which necessitates a residence time in the clarifier of about 2 h. Figure 11 shows the settling effect on UV spectra, and spectra related to settleable matter and suspended matter (after filtration at 1.2 xm) are presented in Fig. 12. 

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