In many areas of Ohio, natural soil is not deep enough to completely treat wastewater. Rural homes and businesses may need to install an onsite wastewater treatment system if a septic tank-leach line system cannot be used. Sand bioreactors are one option. To learn more, consult Bulletin 876, Sand and Media Bioreactors for Wastewater Treatment for Ohio Communities, available at setll.osu.edu or extensionpubs.osu.edu.
|Figure 1. Sand examples with different uniformity coefficient.|
Size distribution is one of the most important characteristics of treatment media. Sand bioreactor clogging is usually the result of using sand that is too fine, has too many fines or has a weak or platy structure. The most important feature of the sand is not the grains, but rather the pores the sand creates. The treatment of wastewater occurs on sand surfaces, where suspended solids are trapped, microorganisms grow, and air and water flow through. Determination of size distribution of sand particles is a direct measurement of sand media structure. It is usually measured as the effective size and the uniformity coefficient.
The effective size of a given sample of sand is the particle size where 10% of the particles in that sample (by weight) are smaller, while 90% are larger. Usually this is denoted as the D10. The size distribution is represented by the Uniformity Coefficient, which enables you to see how well graded your sand sample is. This is done by taking the D60 and dividing by the D10. Figure 1, for example, represents two typical conditions. The upper picture with all of the grains of sand the same size, has a uniformity coefficient equal to 1. The lower one with sand of different sizes has a uniformity coefficient is greater than 1.
Ohio EPA requires that owners and operators of sand bioreactors use certified sand, which is tested through a sieve analysis and meet the criteria of one of the following standards:
- ASTM C136, “Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates”; or
- ASTM D451, “Standard Method for Sieve Analysis of Granular Mineral Surfacing for Asphalt Roofing Products”
How Is a Sieve Analysis Conducted?
|Table 1. Sieve number (ASTM – E11) and mesh size|
|No.||Mesh Size (mm)||No.||Mesh Size (mm)||No.||Mesh Size (mm)||No.||Mesh Size (mm)|
- Scale (or balance)—0.1 g accuracy
- No. 200 sieve
- A set of sieves, lid, and receiver
- Select suitable sieve sizes (table 1) to obtain the required information as specified, for example Nos. 3/8", 4, 10, 20, 40, and 60
- Drying oven 110 +/–5°C (230 +/–9°F)
- Metal pans—one for each sieve size, plus one for sample
- Mechanical sieve shaker (optional)
- Label metal sample pans (WP) with sieve number or size and weigh, and set aside.
- Begin with about a 100-gram sample of sand. Put sand in a metal pan and dry it in 105–115°C oven for two hours. Weigh dry sand sample with pan (W0). Then subtract the weight of the pan: WDS0 = W0 – WP0.
- Fill the pan and sand sample with tap water, shake and decant wash water through No. 200 sieve. Wash material retained on sieve back into the pan. Repeat several times until wash water is clear. Dry the sample again in 105–115°C oven for two hours. Weigh dry washed sand with pan (W1). Then subtract the weight of pan: WDS = W1 – WP0. Subtract from WDS0 to determine weight of fines: WF = WDS0 – WDS.
- Arrange a set of sieves from largest mesh size to smallest with the pan below the bottom sieve (figure 2). Place the sample on the top sieve. Place lid over top sieve.
- Shake stacked sieves, vibrating, jogging, and jolting them by hand or by mechanical apparatus. Keep the sand in continuous motion for a sufficient period until no more than 1% by weight of the residue on any individual sieve will pass that sieve during 1 minute of additional hand sieving. Five to ten minutes of original sieving will usually accomplish this criterion.
- Pour the sand off each sieve into labeled, weighed pans. Weigh and determine the sample weight (WS) by subtracting the weight of the pan: WS = W – WP.
Record and Calculation
Record all the weights in the “Report” section of this fact sheet and determine the percent passing to 0.1% for each sieve by:
Percent of material retained on the sieve = (WS /WDS) x 100%
Percent passing = percent passing the next largest sieve – percent retained on sieve
Graph the percent passing result for each sieve (blue shaded sections in the table) on semi-log paper as shown in figure 3. From the graph, find the Effective Size as D10, where only 10% of the sample has a smaller size. Also from the graph, find D60, where 60% of the sample has a smaller size. The Uniformity Coefficient is D60/D10.
Figure 2. Sieves with various-sized openings are used for sand analysis. The sieves are arranged largest to smallest from top to bottom.
Table 2. Sand Particle Size Analysis—Calculating Percent Passing Selected Sieves.
Figure 3. Graph of sand sieve analysis to determine effective size and uniformity coefficient
A Chinese version of this fact sheet is available at setll.osu.edu/sites/setll/files/imce/Chinese%20version%20sand%20analysis.pdf.