Coagulation–flocculation is a process commonly applied to treat many types of industrial wastewater. However, chemicals used in a wastewater treatment plant, including coagulants/flocculants, are costly. This study evaluated the feasibility of recycling the chemical sludge of the Mobarakeh Steel Complex (MSC), and using it as a coagulant aid in the process of wastewater treatment. The experiments were conducted in a jar test apparatus in consecutive cycles by adding a fraction of the settled sludge to samples. The response surface methodology (RSM) was employed to design the experiments and optimize the process. The response in the RSM model was residual turbidity, and the factors affecting the response included the sludge recycle ratio and return sludge cycle number. The sludge volume index (SVI) of the chemical sludge was also examined in each cycle of the tests to assess the sludge quality. The results revealed that recycling the sludge reduced the use of chemicals up to 60%. Finally, it was concluded that flocculation sludge could be considered as an alternative to chemicals, without adversely affecting the removal efficiency. Furthermore, SVI results showed that an increase in the number of cycles led to a decrease in SVI in each cycle, resulting in sludge volume reduction, better dewatering, and decreased sludge treatment costs.

混凝-絮凝是通常用于处理多种类型工业废水的过程。但是，废水处理厂中使用的化学品（包括凝结剂/絮凝剂）价格昂贵。这项研究评估了回收Mobarakeh钢厂（MSC）的化学污泥并将其用作废水处理过程中的助凝剂的可行性。通过将一部分沉淀的污泥添加到样品中，在广口瓶试验设备中以连续循环进行实验。响应面方法（RSM）用于设计实验和优化过程。RSM模型中的响应为残留浊度，影响响应的因素包括污泥再循环率和返回污泥循环次数。在每个测试周期中还检查化学污泥的污泥体积指数（SVI），以评估污泥质量。结果表明，回收污泥可减少多达60％的化学品使用。最后，得出的结论是，絮凝污泥可被视为化学品的替代品，而不会不利地影响去除效率。此外，SVI结果表明，循环数的增加导致每个循环中SVI的减少，从而导致污泥量减少，脱水效果更好，污泥处理成本降低。不会对去除效率产生不利影响。此外，SVI结果表明，循环数的增加导致每个循环中SVI的减少，从而导致污泥量减少，脱水效果更好，污泥处理成本降低。不会对去除效率产生不利影响。此外，SVI结果表明，循环次数的增加导致每个循环中SVI的减少，从而导致污泥量减少，脱水效果更好，污泥处理成本降低。