Abstract:
A potential environmental impact associated with horizontal directional drilling is the
inadvertent return of bentonite-based drilling fluid to the surface via naturally occurring fractures
or fissures. This study investigated a range of flocculants consisting of water-soluble linear
polyacrylamides (PAMs) differing in charge (anionic, neutral, and cationic), biopolymer
(chitosan) and gypsum for treating the bentonite suspension that might release with runoff or into
stream water. Laboratory jar test were conducted with a 0.4 % (w/v) bentonite suspension having
an average initial turbidity of 1,217 nephelometric turbidity units (NTU). None of the PAMs by
themselves were effective in flocculating bentonite suspension (> 690 NTU), but adding gypsum
in a combination with anionic PAM enhanced the flocculation reaction (< 120 NTU). The
biopolymer performed better than the PAMs alone by lowering turbidity to 437 NTU. A simple,
passive dosing system was tested in which bentonite-laden turbid water was pumped into a
length of pipe with a jute lining treated with the chemical and passed through a geotextile
dewatering bag. Both the biopolymer and the combination of gypsum and anionic PAM were
effective, reducing turbidity by 86-95 % relative to influent bentonite suspension (1,188 NTU).
These results suggest that simple, inexpensive flocculation systems can be deployed to reduce
turbidity caused by bentonite spills. |
