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Project Name: Preliminary Engineering Report for Wastestream Containing Nitroso DAHP Cyanide
Country: USA
Description: The client operates a chemical processing plant in Virginia which produces feedstocks for pharmaceutical products. Wastewater from this facility is discharged under a pretreatment program to the local city's publicly owned treatment works (POTW). There were no wastewater treatment processes being applied to the discharge. The discharge flowrate and totalized flow was measured and recorded. Samples were taken for lab analyses to determine compliance with pretreatment permit limits. The Wastestream discharged from the Nitroso DAHP process contained cyanide concentrations ranging from 40 to 90 mg/l. The discharge limit for cyanide from the client's chemicals facility to the POTW was 2 mg/l. While significant dilution of the Mother Liquor discharge occurred when combined with other discharges from the facility, it was desirable to minimize the cyanide concentration to avoid peaks caused by batch operations. Although chlorine is often used for cyanide oxidation, the potential for noxious gas formations exist. For this reason, the client proposed to use hydrogen peroxide as an oxidant for cyanide destruction. The Wastewater is discharged in 9000 liter batches. Laboratory studies have shown than only around 90% of the cyanide present is amenable to chlorine or hydrogen peroxide oxidation. Thus, to avoid excessive peak discharges of cyanide, treatment for cyanide, flow equalization, and flow metering was desirable. Assisted the client in evaluating alternatives to address the problem with cyanide discharge described above. The objective of the evaluation was to arrive at a treatment and discharge scheme that would not result in more than 2 mg/l of cyanide in the facility’s total wastewater stream at any time. Developed a Preliminary Engineering Report consisting of the following: 1. Description of process and wastewater characterization based on available information provided by the client, 2. Evaluation of certain tanks and equipment, selected by the client, as potential treatment system components, 3. Description of pumping and piping requirements, 4. Description of flow metering and control requirements, 5. Description of pH control requirements. The conclusion of the evaluation was that the existing equipment could be utilized for the proposed pretreatment process with relatively little capital requirement. The client was pleased to have a cost effective solution which could be implemented in a timely manner.
 

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