Inhibition of particle aggregation in fluvial suspended sediment by formaldehyde

Freshwater fluvial suspended sediment particle size characteristics alter temporally when allowed to stand, undergoing continuous aggregation to form larger composite particles (aggregates or flocs) that can settle from the water column and are stable to hand shaking. Treatments to inhibit the spontaneous aggregation of laboratory prepared and fluvial suspended sediments were investigated. A novel method using formaldehyde to fix suspended sediment was developed, which inhibited aggregation of the suspended particles. The formaldehyde-treated particle suspensions formed fragile aggregates on settling, but they were redispersed by hand shaking. When assessed by particle size distribution, photography and turbidity measurements following resuspension, treatments with 2% (v/v) formaldehyde showed little alteration of the initial existing particles or aggregate composition and turbidity. The fixation of fluvial water samples with formaldehyde immediately after collection allowed the transportation and storage of the samples containing suspended sediment for laboratory analysis, weeks after collection.