Sludge particle size distribution

Research in this area shows great potential. Over the past 30 years, dual systems have been applied mainly in the paper industry. The applicatimi of PECs, described as particle-forming flocculants, provides new possibilities in solid-liquid separation processes. For an effective system, the application parameters have to be optimized (e.g. polymer type, cmicentratiOTi, charge, molecular weight). Therefore, direct and efficient methods for the characterization of the flocculation behavior (sedimentation velocity, packing density of the sludge, particle size distribution) are necessary and will be described. 

Table I compares the predicted shape of the particle size distribution with observations from oceanic waters and sewage sludge digesters. The comparison is limited to the dependence of the particle size distribution on the particle diameter because fluid and particle parameters appearing in the predicted equations were not available. In plots of the logarithm of the size distribution vs. the logarithm of the particle diameter, Equations 10, 11, 12, and 13 become straight lines with slopes —2.5, —4, —4.5, and —4.75, respectively. Oceanic and digested sewage sludge size distributions are also observed to have one or more linear regions in such a plot, as summarized in Table I.

This chapter has presented a theoretical derivation of continuous particle size distributions for a coagulating and settling hydrosol. The assumptions required in the analysis are not overly severe and appear to hold true in oceanic waters with low biological productivity and in digested sewage sludge. Further support of this approach is the prediction of increased particle concentration at oceanic thermoclines, as has been observed. This analysis has possible applications to particle dynamics in more complex systems namely, estuaries and water and waste-water treatment processes. Experimental verification of the predicted size distribution is required, and the dimensionless coeflBcients must be evaluated before the theory can be applied quantitatively. 

Particle Size and Particle Density. An introduction to the importance of particle size distribution for sludge has already been presented. 

Sizing Results. Figures 2 and 3 show particle size distributions, plotted as log (A number/A diameter) vs. log (diameter). Figures 4 and 5 show volume distributions for the same sludges, plotted as differential volume A (volume)/A (log diameter), vs. log (diameter). Six variations of aperture and instrumental settings were used to assemble a particle size distribution over a range from about 1 to 60 /xm. The number distributions taken with different apertures match fairly well. However, the reader should note that the plots are log-log. The volume distributions appear neither as smooth nor as well fitted as the number distributions because of the semilog plots and the reasonably level distributions. 

Table III. Particle Size Distribution by Coulter Counter—Hyperion Mesophilic Sludge...

Figure 2. Particle size distribution—Hyperion mesophilic sludge (apertures (nj 30 [xm 70 fim, (A) 70 (im ( ) 140 fim (JX)...

In all cases, sand was used as the bed material. Spouting air preheated to a controlled temperature up to 500°C was introduced through a single orifice of 19-mm diameter. After steady spouting had been attained at a bed temperature of 350°C and a superficial gas velocity of 1.4 m/s, sludge was fed approximately 3 mm into the spout. Particle size distribution of material was... 

During the combustion of coal, the mineral matter is transformed into ash, part of which is fly ash discharged to the atmosphere as particles suspended in the flue gases and part of which is bottom ash removed from the base of the furnace. Furthermore, scrubber sludge is formed where sulfur dioxide scrubber facilities are employed. The quantity, particle size distribution and properties of fly ash are directly related to the combustion technique applied and the constitution of the coal. 

A sludge is to be clarified in a thickener that is 50 ft in diameter. The sludge contains 35% solids by volume (SG = 1.8) in water, with an average particle size of 25 pm. The sludge is pumped into the center of the tank, where the solids are allowed to settle and the clarified liquid overflows the top. Estimate the maximum flow rate of the sludge (in gpm) that this thickener can handle. Assume that the solids are uniformly distributed across the tank and that all particle motion is vertical. 

The transportation of sludges and slurries in pipelines is advantageous, but poses more problems arising from high viscosity, nonhomogenity of the fluid system and the tendency of suspended materials to segregate and settle. The tendency to settle varies with the particular flow condition. Particle density, shape and size as well as size distribution, concentration and composition influence the settling characteristics. 

Mechanical spreading equipment is generally designed to distribute dry powders with a maximum particle size of less than 5 mm. Some waste products containing calcium carbonate are very fine, but contain moisture (e.g. the sludge from the processing of sugar beet), which necessitates the use of special equipment to obtain an accurate and even spread. 

In this chapter, mechanisms of particle removal are limited to coagulation and sedimentation. Predictions of size distributions are obtained that are in reasonable agreement with measured size distributions from oceanic waters and digested sewage sludge. Sensitivity of the predictions to fluid turbulence and fluid density presents a plausible explanation for zones of higher particle concentration observed in the oceanic water column. The analysis does not include zooplankton fecal pellet production, particle breakup, or dissolution, nor does it directly incorporate biological productivity. 

Measurements indicate that for particles above about 1 /xm in size (that is, those detectable by present electronic or optical measurements) values of p typically range from 2 to 5. For example, Lerman et al. (2) report measurements of size distributions at four locations in the Noith Atlantic. Fifty-three size distributions derived from samples taken at depths ranging from 30 to 5100 m yielded a mean value of p = 4.01 0.28. Hunt (JO) analyzed data obtained by Faisst (7) for two digested sewage sludges and determined values of p from 2.2 to 4.7. 

Kozinski J, Rink K, Eighty JS. Combustion of sludge waste in FBC, distribution of metals and particle sizes. Proc 13 FBC Conf, Orlando, FL, USA, 1995, pp 139-147. 

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