Influence of sand addition in the early stage retention of fine sludge dewatering by geotextile

Abstract The need to investigate viable methods to facilitate correct disposal of high-water content waste is immediate in the scenario of water source degradation. In this context, Closed Geotextile Systems (CGS) have shown promise for dewatering a variety of high water-content sediments, aiming to reduce the waste final volume, encapsulating particles, and at the same time allowing fluid drainage. Especially in Water Treatment Plants, the geotextiles generally employed in these systems have good tensile strength and rigidity to support mechanical solicitations and hydraulic properties that warrant good drainage conditions. In these applications, the geotextile element should assure the waste confinement and retention of some particles that will form a filter cake which will control internal flow conditions. The present work investigated how small portions of sand influence fine-particle retention. The sludge used consisted of a mixture of filtered water with two well-defined fractions of ground quartz: FG, a silt and CG, a fine sand. The results show that small amounts of sand are capable of leading to the formation of a pre-filter, even if the maximum diameter of the fine particles is much less than the geotextile filtration opening size. The test results indicate that the retention efficiency gradually increases as CG increases in the solution, up to a fraction of CG close to 14%, which represents only 0.7% of the total solution mass. The increase in particle retention was directly proportional to the increase in the GC fraction until reaching the filtration efficiency of approximately 72% where it stabilizes.

摘要：在水源退化的当下，探究高含水率废弃物的合规处置可行方法已是迫在眉睫的需求。在此背景下，闭合土工织物系统（Closed Geotextile Systems, CGS）已展现出对多种高含水率沉积物进行脱水处理的应用潜力，可实现降低废弃物最终体积、包裹固体颗粒并同步完成流体排放的目标。尤其在水处理厂中，此类系统所采用的土工织物通常具备优异的拉伸强度与刚度，可承受机械荷载，同时拥有良好的水力特性以保障理想的排水性能。在这类应用场景中，土工织物组件需确保废弃物被有效约束，并截留部分颗粒以形成滤饼，进而调控内部流体流动状态。本研究探究了少量砂粒对细颗粒截留效果的影响机制。本次实验所用的污泥由过滤水与两种明确分级的磨碎石英颗粒混合而成：其中FG为粉砂级颗粒，CG为细砂级颗粒。实验结果表明，即便细颗粒的最大粒径远小于土工织物的滤孔孔径，少量砂粒仍可形成预过滤层。测试结果显示，随着溶液中CG占比的提升，颗粒截留效率逐步升高，直至CG占比接近14%（该占比仅占溶液总质量的0.7%）。颗粒截留率的提升与CG占比的增加呈正相关，直至过滤效率达到约72%后趋于稳定。