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

ABSTRACT

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.

KEYWORDS:

• Settled sludge
• enhanced flocculation
• acid activation

Disclosure statement

No potential conflict of interest was reported by the author(s).

Conflicts of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability statement

Data sharing is not applicable to this article as no new data were created or analyzed in this study.

Additional information

Funding

This research was funded by the Project of National Key Research and Development Program (NO.2019YFC0408505); Natural Science Foundation of Anhui Universities, China (NO. KJ2019A0756); Research Project Fund of Anhui Jianzhu University, Hefei, China (NO.2018QD08) and Anhui Provincial Natural Science Foundation, China (NO. 1908085QE249).