Abstract
Bioleaching is of increasing interest because of its high efficiency in improving sludge dewaterability and removing heavy metals from sewage sludge. However, in traditional single-phase bioleaching, a high-efficiency level cannot be maintained continuously, wherein the microbial synergistic effect is disrupted at a low pH environment. Therefore, in this study, a series of multi-compartment-baffled flow trials were performed to assess the effects of phase separation on sludge bioleaching by comparing a two-phase trial with two single-phase trials. Energy substrate and part of the bioleached sludge were introduced separately into two compartments to form two phases, namely selection phase and bioleaching phase. The results show that phase separation apparently shortened the start-up duration of sludge bioleaching from 7 days in a single-phase bioleaching to 4 days in two-phase bioleaching. The dewaterability of bioleached sludge was also enhanced by phase separation with relative decreases of 25.0-33.3% for specific resistance to filtration and 14.2% for capillary suction time, which was attributed to lower pH values, zeta potential closer to zero, and less dissolved organic matter in bioleached sludge after two-phase bioleaching. Phase separation generally increased the removal ratios of heavy metals during sludge bioleaching by -0.79 to 2.60%, 11.06 to 15.04%, 4.45 to 11.03%, 17.98 to 23.46%, 7.20 to 9.28%, -9.22 to -2.46%, and -6.72 to -10.68% for As, Cd, Cr, Cu, Ni, Pb, and Zn, respectively. Phase separation also enriched the Acidithiobacillus spp. and reduced the inactivation of acid-tolerant fungi, which can be conducive to better synergistic effect, and therefore maintain long-term stable state in the bioleaching phase of the two-phase bioleaching process.
Highlights
The production of sewage sludge has increased rapidly with improvement of sewage treatment capacity in China (Li et al 2013)
The dewaterability improvement of bioleached sludge was enhanced by phase separation with the relative decreases of 25.0 ‒ 33.3% for specific resistance to filtration (SRF) and 14.2% for capillary suction time (CST), which was attributed to lower pH values, zeta potentials of closer to zero and less dissolved organic matter (DOM) of bioleached sludge after the twophase bioleaching
Since the blue spot was excited by alive A. ferrooxidans (Fig. 3), more spots in sludge meant a larger amount of A. ferrooxidans in high activity
Summary
The production of sewage sludge has increased rapidly with improvement of sewage treatment capacity in China (Li et al 2013). There are three classes of conditioning methods to enhance dewaterability of sludge: physical methods, chemical methods such as advanced oxidation (Masihi and Gholikandi 2018), and biological methods including microbial flocculants, and bioleaching (Liu et al 2012, Lu et al 2019) Among those methods, bioleaching is of increasing interest because of a low cost and high efficiency to promote sludge dewaterability. Even though sewage sludge can be effectively conditioned to improve its dewaterability under those optimal ranges of factors for single-phase bioleaching, it cannot be continuously operated at a stable and high-efficiency status, which is due to a destruction of the synergistic effect caused by growth inhibition of acid-tolerant heterotrophic microbes at a long-time lowpH environment. It was used to evaluate the feasibility of phase separation on sludge bioleaching via investigating its effects on physicochemical properties, dewaterability improvement and of heavy-metals removal sludge, and microbial community
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