Alternatives for the detection of residual polyacrylamide in geotextile tube dewatering-streaming current detection and china clay settling rate methods

The use of polyacrylamide (PAM)-based flocculants has become an essential component of most geotextile tube dewatering projects. Although knowledge of the residual flocculant concentration in geotextile tube supernatant and effluent is essential to the safe use of PAM-based flocculants, residual flocculant concentration is not commonly measured in geotextile tube dewatering operations. Furthermore, there is no ASTM standard test method for measuring residual flocculant concentrations in water. This paper presents a comparative study of two different methods that are commonly used to measure residual flocculant concentrations in water: the Streaming Current Detection (SCD) method and the China Clay Settling Rate (CCSR) method, to evaluate their applicability to the geotextile tube industry. The comparison is based on an analysis of measured residual PAM concentrations obtained for five different cationic PAM polymers used to flocculate Tully fines soil. Optimum flocculant doses for the Tully fines soil were determined using the jar test (ASTM D2035-08) for three different solids concentrations by mass (5, 15, and 33 %). The SCD and CCSR methods were performed on the supernatants of Tully fines that were conditioned at their optimum doses and at concentrations 50 % above their optimum dose. Laboratory test results showed that both the SCD and CCSR methods produced similar residual PAM concentration results for the polymer/soil combinations tested. The SCD method, however, produced more consistent and repeatable results in comparison to the CCSR method. The SCD method was also easier to use and could be performed in shorter amounts of time than the CCSR method. Based on the results, it is recommended that the SCD method be standardized and used to measure residual PAM-based flocculant concentrations in geotextile tube supernatant and effluent.