Recommended CitationHashad, M. F., S. Sharma, L. F. Nies, and J. E. Alleman. Study of Salt Wash Water Toxicity on Wastewater Treatment. Publication FHWA/IN/JTRP-2005/21. Joint Transportation Research Program, Indiana Department of Transportation and Purdue University, West Lafayette, Indiana, 2006. doi: 10.5703/1288284313386.
This research effort focused on evaluating the toxicity of the saline waste water generated from washing of Indiana Department of Transportation (INDOT) deicing trucks and to study the feasibility of discharging it into wastewater treatment plants. Performance of activated sludge treating wastewater under varying levels of salt concentration was studied by measuring the Chemical Oxygen Demand (COD), activated sludge oxygen uptake rate (OUR) and Turbidity. For the COD tests, wastewater was tested with salt concentrations ranging from 0 mg/L – 1500 mg/L. Within this range there is no impact of salt on COD stabilization, suggesting that the microorganisms are not adversely impacted by salinity in this range. Turbidity tests were conducted for salt concentrations of 0 - 10,000 mg/L. Below a concentration of 3000 mg/ L salt did not have any significant impact on the turbidity. Concentrations above 3000 mg/L aided in flocculation of particles and resulted in faster settling of colloidal solids and reduction in turbidity. Another component of the study was to examine the fate and chemistry of ferric ferro/ferri cyanide, an anti-caking complex that is added to deicing salt. Although, the complex form of cyanide is harmless, in the presence of sunlight it can dissociate to form free cyanide that is highly toxic. Deicing salts collected from INDOT’s West Lafayette and Lafayette Facilities were tested for total and amenable cyanide levels. Lafayette road salt had high levels of cyanide that could lead to violation of pretreatment standards on cyanide, if this salt wash water is discharged to wastewater treatment plant. Respirometry was used for the impact assessment of variable salt concentrations on the biological performance of a low strength activated sludge samples for a POTW using a static liquid – gas flow (GFS) respirometer with salt concentrations varying from 0 – 10% . Generally, positive effect in oxygen uptake rate (OUR) was noticed on low salt concentrations up to 2% and a sharp decrease thereafter. A salt concentration of 6% resulted in a 50% decrease in respiration rate of the tested activated sludge. Further studies should involve the effect of saline shock loads in the specific ammonia uptake rate (SAUR) and specific nitrate uptake rate (SNUR) in addition to the final effluent quality.
activated sludge, deicing salt, snow control, oxygen uptake rate, saline wastewater, respirometry, SPR-2625
Joint Transportation Research Program
West Lafayette, IN
Date of this Version