Desorption trials and granular stability of chromium loaded aerobic granular sludge from synthetic domestic wastewater treatment

Pb(II) bioremediation using fresh algal-bacterial aerobic granular sludge and its underlying mechanisms highlighting the role of extracellular polymeric substances

Lead (Pb) discharged from rural industries poses a significant threat to the environment and human health. Algal-bacterial aerobic granular sludge (A-B AGS) is a promising alternative for sewage treatment with high efficiency and good settleability. In this study, Pb(II) biosorption using fresh A-B AGS was investigated for the first time. The important role of extracellular polymeric substances (EPS) was revealed with the involved mechanisms being clarified. The desorbents for Pb recovery from Pb-loaded A-B AGS were also screened. Results showed that A-B AGS has an excellent maximum Pb adsorption capacity of 72.4 mg·g^-1 at pH 6.0. EPS plays an important role in keeping microbial activity, Pb bonding, and providing metal ions (Ca, Na and Mg) for Pb ion exchanges. Electrostatic interaction, ion exchange, and bonding to functional groups may occur orderly in the Pb biosorption process and the formation of pyromorphite (Pb₅(PO₄)₃Cl) contributes to Pb biosorption. About 66 % of the adsorbed Pb was accumulated in the A-B AGS microbial cells. Na₂EDTA (0.05 M) can recover 60.3 % of the loaded Pb with the highest microbial activity of granules being remained. All the findings will provide the theoretical basis for the large-scale application of A-B AGS to bioremediate Pb(II)-containing wastewater.

Insight into Cr(VI) biosorption onto algal-bacterial granular sludge: Cr(VI) bioreduction and its intracellular accumulation in addition to the effects of environmental factors

Hexavalent chromium (Cr(VI)) is one of the typical heavy metals that pose a great threat to the environment. As a novel biotechnology, algal-bacterial aerobic granular sludge (AGS) possesses the merits of both bacterial AGS and algae. This study firstly evaluated Cr(VI) removal via biosorption by algal-bacterial AGS under different operation conditions and then some environmental factors. Results show that the highest Cr(VI) reduction (99.3%) and total Cr removal (89.1%) were achieved within 6 h at pH 2 and 6, respectively. The coexisting oxyanions exhibited slight effects, while both tested natural organic matters (humic acid and tannic acid) and carbon sources promoted Cr(VI) reduction at some appropriate concentrations. The coexistence of metal cations favored Cr(VI) reduction, achieving the highest enhancement of 8.1% by Cu²⁺ at 5 mg/L, while the total Cr removal was suppressed to some extent. Salinity > 5 g/L severely inhibited both Cr(VI) reduction and total Cr removal. Moreover, the loaded Cr in algal-bacterial AGS was found to be almost in the form of Cr(III), with 66.8% being contributed by intracellular accumulation. This work suggests that Cr(VI) reduction and intracellular accumulation are the main mechanisms involved in Cr(IV) biosorption onto algal-bacterial AGS.

Adsorption of hydrogen arsenate and dihydrogen arsenate ions from neutral water by UiO-66-NH2

The metal-organic framework (MOF) UiO-66-NH₂ was synthesized with different substrate to solvent ratios and its morphology, surface area, pore distributions, and NMR, XRD, and TGA-FTIR patterns were obtained. Adsorption tests at pH 7 and 25 °C showed that the produced UiO-66-NH₂ has a hydrogen arsenate adsorption capacity of 76.9 mg/g. With the affinity onto Zr clusters, this MOF also can adsorb phosphate ions from water. Treatment with 1-4 M hydrochloric acid (HCl) protonated the amine groups in the MOF. Treatment with 1 M HCl at 25 °C for 6 h maximized the adsorption capacity of UiO-66-NH₂ to 161.3 mg/g, such that the protonated amine groups accounted for 53.7% of the adsorption of arsenate from the water. The use of excessively strong acid at elevated temperature reduced the adsorption capacity.

Performance and microbial protein expression during anaerobic treatment of alkali-decrement wastewater using a strengthened circulation anaerobic reactor

Herein, a strengthened circulation anaerobic (SCA) reactor was employed for the treatment of actual alkali-decrement wastewater. The degradation mechanism of polyester oligomers and the relationship between the treatment performance and microbial community structure were systematically investigated using various advanced techniques. Results suggest that the accumulation of volatile fatty acids has an inhibitory effect on methanogenic activity. Molecular weight distributions suggest that only incomplete degradation of oligomers was achieved, due to acetogenic inhibition in the lower part of the SCA reactor. Meta-proteomic approach analysis revealed that the methanogens containing heterodisulfide reductase were the primary species involved in methane metabolism. Based on these findings, a possible degradation mechanism for alkali-decrement wastewater in the SCA reactor is proposed. This high-performance anaerobic reactor could be further scaled-up and optimized to serve as a promising and effective unit for the treatment of other refractory industrial wastewaters.

Aerobic granular sludge: Cultivation parameters and removal mechanisms

Aerobic granular sludge (AGS) has been the focus of many investigations, and the main parameters responsible for AGS formation are hydrodynamic shear force, short periods and feast-famine cycles. However, some other parameters are associated with AGS maintenance after long periods of operation. This review evaluates the parameters responsible for AGS formation and maintenance and some reference values are proposed. In addition, some discussions are addressed about the main metabolic pathways that AGS uses for the removal of some compounds, such as nutrients, organic matter, dyes, recalcitrant compounds, among others. Finally, the main microbial groups present in the AGS and their respective functions are discussed. It is also highlighted that many parameters that are taken as reference currently for AGS cultivation and maintenance can be optimized for energy savings, implementation costs, among others, as well as a greater recovery of resources during wastewater treatment, within the scope of the biorefinery concept.

Recovery of dehydrated aerobic granules: A comparison

Dehydrated aerobic granules, if can be sufficiently recovered without significant loss of structural stability and biological activities, presents a promising long-time storage option in practical use. This study dehydrated aerobic granules by six protocols: air drying at 25 or 50 °C, freeze-dry, acetone or ethanol dehydration, and microwave heating, and then recovered them in liquid medium, with the measured characteristics being reported. The granule stability has no correlation with measured settleability, hydrophobicity or extracellular polymeric substances compositions; instead, is correlated with the functional strains presented in the recovered granules. Air dry dehydration minimally damage the functional strains including genus Brevundimonas and genus Comamonas and markedly deteriorated structural breaker such as Acinetobacter of Moraxellaceae to lead to stable and tough recovered granules.