The reinforcement of sludge-recycling enhanced flocculation by the acid activation of settled sludge

Sludge-recycling enhanced flocculation (SEF) is an effective method for enhancing flocculation. In the conventional SEF process, the settled sludge is recirculated into the flocculation process without any further treatment. However, studies have shown that the efficacy of the SEF process could be improved by pre-treating the sludge. In this work, the acid activation of sludge was performed using a range of pH values (1.0–6.0) and charge states, with and without long-chain bridging. The resulting residual turbidities, floc fractal dimensions and floc morphologies were then analyzed, to examine the effects of sludge activation on the efficacy of SEF. In the absence of long-chain bridging, it was found that flocculation was enhanced by pH values between 2.0 and 5.0 in the electrostatic patch (EP) and near charge neutrality (NCN) states. In the EP state, the optimal pH for SEF enhancement was pH = 2.0; in the NCN state, the optimal pH was pH = 3.0. In terms of floc morphology, pH values between 2.0 and 5.0 resulted in larger average floc sizes and lower floc fractal dimensions than conventional SEF. However, in the presence of long-chain bridging, sludge activation did not enhance flocculation; residual turbidity increased with decreases in pH, in both the EP and NCN states. Based on these results, it may be surmised that the acid activation of sludge is suitable for cases without long-chain bridging.

污泥回流强化絮凝（Sludge-recycling enhanced flocculation, SEF）是一种强化絮凝的有效方法。在传统SEF工艺中，沉降污泥不经任何额外处理即回流至絮凝工序。然而研究表明，对污泥进行预处理可进一步提升SEF工艺的效能。本研究采用一系列pH值（1.0~6.0）及电荷状态，设置有无长链桥接的工况，对污泥开展酸活化处理。随后对所得残余浊度、絮凝体分形维数与絮凝体形貌进行分析，以考察污泥活化对SEF效能的影响。在无长链桥接的工况下，研究发现当处于静电补丁（electrostatic patch, EP）与近电荷中和（near charge neutrality, NCN）状态时，pH值处于2.0~5.0区间可强化絮凝效果。其中EP状态下SEF强化的最优pH为2.0，NCN状态下最优pH为3.0。从絮凝体形貌来看，相较于传统SEF工艺，pH值处于2.0~5.0时所得絮凝体平均粒径更大，分形维数更低。而在存在长链桥接的工况下，污泥活化并未对絮凝起到强化作用；无论EP还是NCN状态，残余浊度均随pH值降低而升高。基于上述结果，可推断污泥酸活化适用于无长链桥接的应用场景。