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Abstract Conditioning can drastically improve the dewaterability of sewage sludge and thus it is widely practiced in most wastewater treatment plants (WWTPs). In WWTPs, various antibiotic resistance genes (ARGs) present in sewage are concentrated in the sewage sludge, but the effect of sludge conditioning on ARGs in sewage sludge remains unclear. Here, we evaluated and compared the effectiveness of four sludge conditioning methods (namely chemical conditioning with polyacrylamide (PAM), chemical conditioning with Fe[III]/CaO, bioleaching conditioning, and chemical acidification conditioning) and an aerobic incubation control in removing 46 target ARGs and intI1 from a municipal sewage sludge. The damage of sludge microbial cells and the change in the sludge bacterial community during the various sludge conditioning treatments were also characterized. The results suggested that the chemical conditioning with PAM and aerobic incubation treatment did not remove ARGs and intI1 from the sewage sludge. The chemical acidification reduced the absolute abundances of most ARGs and intI1 , but increased their relative abundances. However, the chemical conditioning with Fe[III]/CaO and bioleaching conditioning reduced both the absolute and relative abundances of most ARGs and removed a majority of extracellular ARGs in the sludge. During sludge conditioning treatments, the sludge microbial cells were severely damaged to decrease the total bacterial biomass in sludge, and accordingly the bacterial hosts carrying ARGs and intI were effectively damaged to reduce the absolute abundances of most ARGs and intI1. In addition, the sludge bacterial community in conditioned sludge determined the relative abundances of residual ARGs. Our findings suggest that sludge conditioning can be an important sludge treatment process in attenuating antibiotic resistance in sewage sludge, and bioleaching and chemical conditioning with Fe[III]/CaO can be employed as effective conditioning ways to reduce ARGs in sewage sludge, potentially limiting their release to the environment. Graphical abstract Image 1 Highlights • Conditioning is an important process to attenuate antibiotic resistance in sludge. • Chemical conditioning with Fe[III]/CaO and bioleaching reduced most ARG abundances. • Chemical conditioning with Fe[III]/CaO and bioleaching removed extracellular ARGs. • Sludge microbial cells were damaged to reduce the absolute abundances of most ARGs. • The sludge bacterial community determined the relative abundances of residual ARGs. [ABSTRACT FROM AUTHOR]

Utilization of the filamentous fungus Mucor circinelloides ZG-3 in improving sludge dewaterability during sludge bioleaching was evaluated in the present study. The degradation of sludge dissolved organic matter (DOM) by M. circinelloides ZG-3 shortened the period of complete oxidation of Fe 2+ by Acidithiobacillus ferrooxidans LX5 from 11 days to only 4 days, and the inoculation of M. circinelloides ZG-3 into sludge improved the sludge dewaterability by 8.1 times. The sequential inoculation of M. circinelloides ZG-3 and A. ferrooxidans LX5 on day 0 and the end of day 1, respectively, was associated with a 25.9% lower sludge specific resistance to filtration (SRF) than that achieved using conventional bioleaching with A. ferrooxidans LX5 alone. In sludge bioleaching with the sequential inoculation of filamentous fungus M. circinelloides ZG-3 and A. ferrooxidans LX5, M. circinelloides ZG-3 acted to improve sludge dewaterability and decrease sludge DOM related toxicity to A. ferrooxidans LX5 by degrading toxic sludge DOM, and then A. ferrooxidans LX5 that was not negatively affected by sludge DOM toxicity could better improve sludge dewaterability. The filamentous fungus M. circinelloides ZG-3 was more efficacious than sludge DOM-degrading yeast strains such as Rhodotorula mucilaginosa R30 in enhancing sludge dewaterability during bioleaching. [ABSTRACT FROM AUTHOR]

It is well documented that bioleaching with the co-inoculation ofAcidithiobacillus ferrooxidansandAcidithiobacillus thiooxidanscan drastically enhance sludge dewaterability under ambient temperature condition, but little information on low temperature effect on bioleached sludge dewaterability is available. In this study, the optimum sludge retention time of bioleaching treatment and the mechanisms responsible for the dewaterability enhancement of bioleached sludge were studied in two bioleaching systems conducted at a low temperature of 10°C and a normal temperature of 28°C, respectively. Results showed thatAcidithiobacillusbacteria involved in the bioleaching were still active at 10°C, and sludge capillary suction time (CST) decreased in the first 3 days of bioleaching. Nevertheless, the degree of sludge dewaterability enhancement by bioleaching was much lower at 10°C than that at 28°C. The only slight decreases in the sludge pH value and relative high contents of extracellular polymeric substances (EPS) and bound water at a low temperature were responsible for the relatively lower dewaterability enhancement of bioleached sludge compared to that at the normal temperature. Moreover, statistical results showed that sludge CST had significant positive correlations with the sludge pH value, and EPS and bound water contents in the optimum bioleaching process (from day 0 to day 3). Therefore, reducing medium pH, and/or removing EPS from bioleaching bacteria and bound water of bioleached sludge through forced physical–chemical approaches prior to mechanical dewatering might be a good method to greatly improve sludge dewatering at a low temperature. [ABSTRACT FROM PUBLISHER]

Abstract: This study sought to elucidate the effect and mechanism of Galactomyces sp. Z3 in improving the bioleaching of heavy metals from sludge. Results showed that co-inoculation of Galactomyces sp. Z3 and two Acidithiobacillus strains (Acidithiobacillus ferrooxidans LX5 and Acidithiobacillus thiooxidans TS6) reduced the period required for sludge bioleaching by 4.5days compared to Acidithiobacillus alone. Further, removal efficiencies of Cu, Zn and oxidation rate of Fe2+ and S0 were higher in co-inoculation system than the Acidithiobacillus alone. Galactomyces sp. Z3 consumed the acetate, propionate, iso-butyrate, butyrate, and iso-valerate in sludge from the initial concentrations of 109.50, 28.80, 7.70, 34.30, and 18.40mg/L to 10.20, 0.61, 0.63, 19.40 and 1.30mg/L, respectively, after 12h in the co-inoculation system, significantly lower than the concentrations observed in the Acidithiobacillus alone. Meanwhile, the surfactant properties of the extracellular polymeric substances produced by the Galactomyces accelerated the rate of sulfur oxidization by A. thiooxidans. [Copyright &y& Elsevier]

The feasibility of removing heavy metals and eliminating pathogens from pig slurry through bioleaching involving the fungusGalactomycessp. Z3 and two acidophilic thiobacillus (A. ferrooxidansLX5 andA. thiooxidansTS6) was investigated. It was found that the isolated pig slurry dissolved organic matter (DOM) degrader Z3 was identified asGalactomycessp. Z3, which could grow well at pH 2.5–7 and degrade pig slurry DOM from 1973 to 942 mg/l within 48 h. During the successive multi-batch bioleaching systems, the co-inoculation of pig slurry degraderGalactomycessp. Z3 and the twoAcidithiobacillusspecies could improve pig slurry bioleaching efficiency compared to the single system withoutGalactomycessp. Z3. The removal efficiency of Zn and Cu exceeded 94% and 85%, respectively. In addition, the elimination efficiencies of pathogens, including both total coliform and faecal coliform counts, exceeded 99% after bioleaching treatment. However, the counts ofGalactomycessp. Z3 decreased with the fall of pH and did not restore to the initial level during successive multi-batch bioleaching systems, and it is necessary to re-inoculateGalactomycessp. Z3 cells into the bioleaching system to maintain its role in degrading pig slurry DOM. Therefore, a bioleaching technique involving bothGalactomycessp. Z3 andAcidithiobacillusspecies is an efficient method for removing heavy metals and eliminating pathogens from pig slurry. [ABSTRACT FROM PUBLISHER]

Abstract: Four inorganic mineral nutrients including , K+, Mg2+ and soluble inorganic phosphate (Pi) were investigated to reveal the potential limiting nutrients for tannery sludge bioleaching process driven by Acidithiobacillus species, and the feasibility of supplementing the limiting nutrients to accelerate tannery sludge bioleaching was studied in the present study. It was found that the concentration of Pi was lower than 3.5 mg/L throughout the whole bioleaching process, which is the most probable restricting nutrient for tannery sludge bioleaching. Further experiments revealed that the deficiency of Pi could seriously influence the growth of Acidithiobacillus thiooxidans and lower its oxidization capacity for S0, and the limiting concentration of Pi for the growth of A. thiooxidans was 6 mg/L. The low concentration of soluble Pi in sludge matrix was resulted from the extremely strong sorbing/binding capacity of tannery sludge for phosphate. The supplementation of more than 1.6 g/L KH2PO4 into tannery sludge bioleaching system could effectively stimulate the growth of Acidithiobacillus species, enhance Cr removal rate and further shorten tannery sludge bioleaching period from 10 days to 7 days. Therefore, inorganic phosphate supplementation is an effective and feasible method to accelerate tannery sludge bioleaching process, and the optimum dosage of KH2PO4 was 1.6 g/L for tannery sludge with 5.1% of total solids. [Copyright &y& Elsevier]

Abstract: The introduction of acid-tolerant heterotrophic microorganisms into sludge bioleaching systems has been proven effective in improving sludge bioleaching processes, and such positive effect is mainly attributed to the biodegradation of low molecular weight organic acids or sludge dissolved organic matter (DOM) toxic to Acidithiobacillus species by the heterotrophic microorganisms introduced. Here we report that elevated dissolved CO2 concentration and resulting extracellular polymeric substances (EPS) in bioleach solution due to the incorporation of heterotrophic microorganisms also play important roles in improving sludge bioleaching. It was found that in tannery sludge bioleaching system coinoculated with Rhodotorula mucilaginosa R30 and Acidithiobacillus species, dissolved CO2 concentration in bioleach solution can be elevated from 0.23–0.54 mg/L to 0.76–1.01 mg/L compared to the control inoculated only with Acidithiobacillus species. Correspondingly, the distinct degradation of sludge DOM was also observed in this experiment. It was experimentally demonstrated that the accumulation of CO2 did greatly enhance the growth of Acidithiobacillus thiooxidans and the decrease rate of pH in the medium. In addition, EPS derived from R. mucilaginosa R30 could bind readily Fe3+ in bioleach solution with maximum binding capacity (MBC) of 0.82 mg Fe3+ by per mg DOC of EPS secreted and the oxidization activity of EPS-bound Fe3+ was decreased but not totally inhibited, indicating that the formation of soluble EPS-Fe(III) complexes enhances, to a certain extent, bioleaching efficiency due to maintaining Fe3+ level in solution by inhibiting Fe precipitation occurrence. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bioleaching conditioning mitigated ARGs in sludge compost products. • Bioleaching conditioning led to the lowest abundances of ARG-associated bacteria. • ARGs Shift during bioleached sludge composting can be ascribed to potential hosts. • Pre-removal of ARGs is crucial for the ARGs reduction in bioleached sludge compost. • Possible limited horizontal transfer of ARGs also contributed to their reduction. Conditioning can drastically improve the dewaterability of sewage sludge and is widely practiced in most wastewater treatment plants (WWTPs). Sludge conditioning was also reported as a crucial step in sludge treatment to attenuate antibiotic resistance, but it remains unclear whether the attenuated antibiotic resistance by conditioning treatments would guarantee low abundance of antibiotic resistance genes (ARGs) in the compost products of municipal sewage sludge. Herein, the impacts of three conditioning treatments, including bioleaching and chemical conditioning using Fe[III]/CaO or polyacrylamide (PAM), on the abundances of 20 ARGs and 4 mobile genetic elements (MGEs) during conventional aerobic composting of dewatered sludge were investigated. It was found that the absolute and relative abundances of total ARGs in compost product of bioleached sludge accounted for only 13.8%-28.8% of that in compost products of un-conditioned, Fe[III]/CaO-conditioned, or PAM-conditioned sludges. Besides, bioleaching conditioning resulted in the lowest abundances of ARG subtypes and ARG-associated bacteria in the sludge compost product. The shift of ARG profiles in the bioleached sludge composting can be mainly ascribed to the ARG-associated bacteria, while the MGEs drove the ARG profiles during conventional composting of un-conditioned sludge and the two chemically conditioned sludge. Thus, bioleaching conditioning is superior to the chemical conditioning using Fe[III]/CaO or PAM in mitigating antibiotic resistance in sludge compost products, which was contributed by the pre-removal of ARGs prior to composting treatment and the potential limitation of ARGs transfer during conventional composting. [ABSTRACT FROM AUTHOR]