Abstract

Recent studies have shown that turbidity in construction site runoff can be greatly reduced by chemical turbidity control. This study evaluated the performance of chitosan-based biopolymer (dual polymer system, DPS) vs. anionic polyacrylamide (PAM) for turbidity reduction and characteristics of flocculated sediments using two soils from North Carolina, USA. The soils were Coastal Plain sand (CPS) and Piedmont Sandy loam (PSL), representing smectitic and kaolinitic mineralogy, respectively. A series of jar tests for DPS (charging agent + chitosan) and two commercial PAM products were conducted to find optimal concentration for turbidity reduction in the respective soil suspension (20 g L⁻¹ in soil loading). After determining the optimal flocculant concentrations, the soil suspensions treated with DPS, PAM, and no flocculant (control) were investigated for turbidity change over settling time, floc stability, floc growth, settleable solids through Imhoff cone test, and particle size distribution by a laser diffraction method. Both flocculants were effective in reducing turbidity (> 90%) in PSL suspensions while PAM outperformed DPS in CPS suspension. Settleable solids volumes increased with flocculant treatments by 23–41% relative to untreated soil suspensions (13 mL for CPS and 20 mL for PSL), indicating efficacy of flocculant-assisted particle settlings. PAM-treated particle size was greater (115 µm, median diameter) than DPS (84 µm) in PSL suspension, both being 3–5 times greater than untreated suspension (24 µm). Repeated stirring resulted in floc growth with PAM but not with DPS. Our results suggested that practitioners using flocculants to treat turbid water in construction site need to perform tests with different flocculants to determine the optimal treatment on their project. While PAM has advantage over DPS as a single flocculant treatment, DPS could be an alternative due to its eco-friendly features.

中文翻译：

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聚丙烯酰胺和壳聚糖生物聚合物在土壤悬浮液中的絮凝和降低浊度

摘要

最近的研究表明，通过控制化学浊度可以大大降低施工现场径流中的浊度。这项研究评估了壳聚糖基生物聚合物（双聚合物系统，DPS）与阴离子聚丙烯酰胺（PAM）在使用美国北卡罗莱纳州的两种土壤降低浊度和絮凝沉积物特性方面的性能。土壤为沿海平原砂土（CPS）和皮埃蒙特沙质壤土（PSL），分别代表近晶和高岭土矿物学。进行了一系列针对DPS（充电剂+壳聚糖）和两种市售PAM产品的广口瓶测试，以找到降低各自土壤悬浮液中浊度的最佳浓度（20 g L ^-1在土壤中）。确定最佳絮凝剂浓度后，研究了用DPS，PAM和无絮凝剂（对照）处理的土壤悬浮液在沉降时间内的浊度变化，絮凝稳定性，絮凝物生长，通过Imhoff锥孔试验确定的可沉降固体以及通过激光衍射法。两种絮凝剂均可有效降低PSL悬浮液的浊度（> 90％），而PAM优于CPS悬浮液的DPS。相对于未经处理的土壤悬浮液（CPS为13 mL，PSL为20 mL），絮凝剂处理后可沉降固体量增加了23–41％（表明，絮凝剂辅助颗粒沉降的有效性）。在PSL悬浮液中，PAM处理过的粒径（115微米，中值粒径）大于DPS（84微米），两者均是未处理悬浮液（24微米）的3-5倍。反复搅拌导致絮凝物在PAM中生长，但在DPS中不生长。我们的结果表明，使用絮凝剂在施工现场处理混浊水的从业人员需要对不同的絮凝剂进行测试，以确定其项目的最佳处理方法。虽然PAM作为单一絮凝剂处理剂比DPS具有优势，但由于其具有环保功能，DPS可以替代。