Rotary Kiln Expanded Slate Sand for Industrial Sludge Drying Beds

by Debbie Stringer, Carolina Stalite Company

In 2013, Norfolk Southern Corp. and AECOM evaluated rotary kiln expanded slate washed MS16 medium coarse sand as an alternative to ASTM C33 sand for the caking material in their industrial wastewater sludge beds. The preliminary test results for permeability and total suspended solids (TSS) reduction were positive and the material was installed at the Norfolk Southern Corp DeButts yard in Chattanooga, TN.

The Norfolk Southern DeButts facility is responsible for capturing and treating all of the industrial wastewater runoff at this site where rail cars that typically carry coal, petroleum and chemicals are brought to be cleaned and maintained.

The collected wastewater undergoes a 2-phase treatment process before it is sent to the on-site detention pond. The 2-phase process begins with clarifying to remove debris and large particles of grit. Flocculants are added to solidify chemical contaminants. In phase 2, the wastewater is applied to the surface of the drying beds to allow water to drain from the sludge through the sand filter while retaining solids on the surface. Once the sludge has sufficiently dried, it is mechanically removed and more wastewater is applied.

Since the transition from ASTM C33 to ASTM C330 sand, the clarity of the exfiltrate has improved and the life cycle of the sand filter has been extended, likely due to the more coarse and angular physical property of the sand. The frequent occurrences of fouling and blinding with ASTM C33 sand is no longer an issue. Since the use of washed expanded sand at the DeButts yard has been successful, Norfolk Southern has converted to ASTM C330 sand at two more rail facilities located in Alabama for this application.

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