Polyacrylamide For Turbidity Control in Runoff: Effects of Polyacrylamide, Soil, and Solution Properties
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Date
2003-08-04
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Abstract
Eroded soil discharged from construction sites is a major water quality issue. North Carolina regulations require that the turbidity of discharged waters from construction sites to non-trout streams or reservoirs not exceed 50 nephelometer turbidity units (NTU) and 10 NTU in trout waters. Polyacrylamide (PAM) has been demonstrated to reduce erosion and turbidity in runoff, but there is little information on the interactions between PAM properties and that of the water or suspended solids. Our study tested eight PAM products (Cytec Superfloc A100, A110, A150, N300, 1606; Ciba Soilfix Polybead; Applied Polymer Systems 705; Chemtall 923VHM) at concentrations from 0 to 10 mg L-1 for turbidity reduction in suspensions of 13 soils from active construction sites around North Carolina. For five soil suspensions, with turbidities of up to 3000 NTU, PAM reduced turbidity to below 50 NTU in 30 s. In addition turbidity reductions to the 10 NTU level were observed for two soils. Overall, turbidity reductions of greater than 86% were achieved for all soils. Optimal PAM concentrations of soils tested were 1-2 mg L-1, with higher concentrations causing turbidity increases in some soils. Sediment properties drastically affected the response to PAM, which indicates the need to have site-specific recommendations for PAM use. Sediments with turbidity reductions below the 50 NTU standard had kaolinite as the dominant clay mineral (70-90%), a pH between 5-6, and very low organic matter. Soils from the Coastal Plain had poor turbidity reduction with most PAMs. APS705, which contains a mixture of polymers with different molecular weights and charge density, was the only polymer that effectively reduced turbidity in all Coastal Plain soils. An evaluation using combinations of low and high molecular weight PAM products to try and mimic APS705 effects gave limited turbidity reduction of Coastal Plain soil suspensions. Combined treatment of gypsum and PAM appears to have either positive or negative effects depending on PAM concentration and soil properties. When gypsum was added to a Piedmont soil sample, it decreased the efficacy of PAM at polymer concentrations below 1 mg L-1. For PAM concentrations at or above 1 mg L-1, gypsum had a positive combined effect, although no significant effect occurred above 50 mg L-1 gypsum. In soils from the Coastal Plain, there was a positive combined gypsum and PAM effect at all PAM concentrations. However, APS 705 alone was more effective at reducing turbidity than other PAMs combined with gypsum. PAM effectively decreased turbidity of most soil suspensions and could be very useful in reducing construction site runoff turbidity to meet water quality standards.
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sediment, polyacrylamide, flocculation, erosion, soil suspension
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MS
Discipline
Soil Science
