Blue valorization of lignin-derived monomers via reprogramming marine bacterium Roseovarius nubinhibens.

Biological valorization of lignin, the second most abundant biopolymer on Earth, is an indispensable sector to build a circular economy and net-zero future. However, lignin is recalcitrant to bioupcycling, demanding innovative solutions. We report here the biological valorization of lignin-derived aromatic carbon to value-added chemicals without requesting extra organic carbon and freshwater via reprogramming the marine Roseobacter clade bacterium Roseovarius nubinhibens. We discovered the unusual advantages of this strain for the oxidation of lignin monomers and implemented a CRISPR interference (CRISPRi) system with the lacI-Ptrc inducible module, nuclease-deactivated Cas9, and programmable gRNAs. This is the first CRISPR-based regulatory system in R. nubinhibens, enabling precise and efficient repression of genes of interest. By deploying the customized CRISPRi, we reprogrammed the carbon flux from a lignin monomer, 4-hydroxybenzoate, to achieve the maximum production of protocatechuate, a pharmaceutical compound with antibacterial, antioxidant, and anticancer properties, with minimal carbon to maintain cell growth and drive biocatalysis. As a result, we achieved a 4.89-fold increase in protocatechuate yield with a dual-targeting CRISPRi system, and the system was demonstrated with real seawater. Our work underscores the power of CRISPRi in exploiting novel microbial chassis and will accelerate the development of marine synthetic biology. Meanwhile, the introduction of a new-to-the-field lineage of marine bacteria unveils the potential of blue biotechnology leveraging resources from the ocean.IMPORTANCEOne often overlooked sector in carbon-conservative biotechnology is the water resource that sustains these enabling technologies. Similar to the "food-versus-fuel" debate, the competition of freshwater between human demands and bioproduction is another controversial issue, especially under global water scarcity. Here, we bring a new-to-the-field lineage of marine bacteria with unusual advantages to the stage of engineering biology for simultaneous carbon and water conservation. We report the valorization of lignin monomers to pharmaceutical compounds without requesting extra organic substrate (e.g., glucose) or freshwater by reprogramming the marine bacterium Roseovarius nubinhibens with a multiplex CRISPR interference system. Beyond the blue lignin valorization, we present a proof-of-principle of leveraging marine bacteria and engineering biology for a sustainable future.

Qualitatively and quantitatively assessing the aggregation ability of sludge during aerobic granulation process combined XDLVO theory with physicochemical properties.

Inexact mechanism of aerobic granulation still impedes optimization and application of aerobic granules. In this study, the extended Derjaguin, Landau, Verwey, and Overbeek (XDLVO) theory and physicochemical properties were combined to assess the aggregation ability of sludge during aerobic granulation process qualitatively and quantitatively. Results show that relative hydrophobicity of sludge and polysaccharide content of extracellular polymeric substances (EPS) increased, while electronegativity of sludge decreased during acclimation phase. After 20days' acclimation, small granules began to form due to high aggregation ability of sludge. Since then, coexisted flocs and granules possessed distinct physicochemical properties during granulation and maturation phase. The relative hydrophobicity decreased while electronegativity increased for flocs, whereas that for granules presented reverse trend. Through analyzing the interaction energy using the XDLVO theory, small granules tended to self-grow rather than self-aggregate or attach of flocs due to poor aggregation ability between flocs and granules during the granulation phase. Besides, remaining flocs were unlikely to self-aggregate owing to poor aggregation ability, low hydrophobicity and high electronegativity.

Establishing a high-performance anti-fouling PEI-ZIF-PAA membrane with improved Lewis acid-base interactions and hydrophilicity.

Membrane fouling and the trade-off between membrane permeability and selectivity restrict the potential applications of membrane filtration for water treatment. ZIF-8 was found having great permeability and antibiofouling performance, but with issue on particle aggregation makes it difficult to achieve high ZIFs loading and fabricate a defect-free molecular sieving membrane in previous research. In this study, we formed a scalable antibiofouling surface with improved permeability and fouling resistance on a PEI-ZIF-PAA membrane using a layer-by-layer assembly technique. The synergistic effects of being sandwiched between two different polyelectrolyte layers with opposite charges endowed the ZIF nanoparticles with improved stability and scalability for membrane modification. The PEI-ZIF-PAA membrane exhibited a satisfactory water flux of 120.78 LMH, which was 46.97% higher than that of the pristine PES membrane. The normalized water flux loss was serious in the absence of ZIF-8, and the flux increased with the ZIF-8 concentration. Antifouling tests suggested that the PEI-ZIF-PAA membrane possessed good antifouling performance due to the much higher surface hydrophilicity and positive Lewis acid-base interactions with foulants. The HA rejection increased with the ZIF-8 concentration and reached a maximum of 92.1% in the presence of 1.00% (w/v) ZIF-8. The membrane regeneration was tested under physical and chemical cleaning with flux recovery rates of about 85% and 95%. XDLVO analysis showed that the total interaction energy between HA and the PEI-ZIF-8-PAA membrane was 26.45 mJ/m2, and the superior antifouling performance was mainly attributed to Lewis acid-base interactions. This study indicates that ZIF-8 nanocrystals are promising materials for fabricating novel membranes for sewage treatment.

Chlorine disinfection elevates the toxicity of polystyrene microplastics to human cells by inducing mitochondria-dependent apoptosis.

Microplastics (MPs) are ubiquitous in drinking water and pose potential threats to human health. Despite increasingly attentions on the toxicity of MPs, the deleterious effects of MPs after chlorine disinfection, which might be a more accessible form of MPs, has rarely been considered. Here, we first treated pristine polystyrene microplastics (PS-MPs) with chlorine to simulate the reactions that occur during drinking water treatment, and investigated and compared the cytotoxicity of chlorinated PS-MPs to those of pristine PS-MPs. Chlorine disinfection did not change the size of pristine PS-MPs, but increased the surface roughness. In addition, abundant carbon-chlorine bonds and persistent free radicals were generated on the surface of chlorinated PS-MPs. Compared with pristine PS-MPs, chlorinated PS-MPs markedly inhibited the cell proliferation, changed cellular morphology, destroyed cell membrane integrity, induced cell inflammatory response and apoptosis. Proteomics confirmed the difference in interactions with intracellular proteins between these particles. Furthermore, we found that the regulation of PI3K/AKT and Bcl-2/Bax pathways, oxidative stress-triggered mitochondrial depolarization, and the activation of caspase cascade were identified as the underlying mechanisms for the enhanced apoptosis ratio in GES-1 cells when exposed to chlorinated PS-MPs. This exacerbated cytotoxicity could be explained by the enhanced surface roughness and changed surface chemistry of these PS-MPs after chlorine disinfection. This work discloses the impacts of chlorine disinfection on the cytotoxicity of PS-MPs, which provides new insights for a more systematic risk assessment of MPs.

AOPs enhance the migration of polystyrene nanoparticles in saturated quartz sand.

Wastewater treatment plants are suspected to be significant point sources of microplastic and nanoplastic particles (NPs) in the environment. As one of the main wastewater treatment processes, advanced oxidation processes (AOPs) may change the physicochemical properties of NPs and further affect their migration. However, limited information is known about the environmental fate of NPs after AOP treatment. In this study, polystyrene nanoparticles were treated using two representative AOPs, Fenton and persulfate treatments, and the migration of the NPs in quartz sand was investigated via column transport experiments. FTIR and XPS analysis indicated that a large number of oxygen-containing groups were generated on the NP surface after AOP treatment leading to lower hydrophobicity and a higher negative charge. Besides, the C/O ratio after Fenton and persulfate treatments was increased from 10.98 to 7.25 and 8.68. Moreover, the NPs after AOP treatment exhibited higher mobility in quartz sand in both ultrapure water and 10 mM NaCl solution. It was more obvious in 10 mM NaCl solution with breakthrough percentages of 79.73% for P-PS, 90.97% for F-PS and 95.67% for N-PS, respectively. These results could be explained by the roles of generated oxygen-containing functional groups; first, the higher negative charge enhanced the electrostatic repulsion between treated NPs and sand; second, lower hydrophobicity improved the binding with water molecules in background solution. This work is helpful in understanding the changes of nanoplastics in AOP treatment and their migration in the natural environment, which has far-reaching influence on the environmental fate and behavior of nanoplastics.

Forward osmosis membranes for high-efficiency desalination with Nano-MoS2 composite substrates.

Attractive membranes are critical for improving efficiencies of forward osmosis (FO) desalination process. In this study, a novel FO-PES-MoS2 thin film composite (TFC) membrane was assembled using the phase transfer method through merging MoS2 nanosheets into substrate casting solution. A sequence of characterization techniques was applied to test microstructures and physicochemical properties of the membranes and modification mechanisms based on MoS2 concentrations. Desalination efficiencies of the fabricated membranes were assessed by three NaCl draw solutions. Compared to the blank membrane, the MoS2-contained membranes had a thinner active layer, more upright and open pore structure, higher porosity, and lower surface roughness. 1 wt% MoS2 content was the optimal modification condition, and water flux increased by 35.01% under this condition. Simultaneously, reverse salt flux of the FO-PES-1-MoS2 membrane declined by 29.15% under 1 M NaCl draw solution, indicating increased salt ion rejection performance of the modified membranes. Moreover, Js/Jv ratio indicated that MoS2 nanosheets helped stabilize the desalination performance of the membranes. This study demonstrated that the novel FO-PES-MoS2 TFC membranes possessed improved performances and showed promising properties for saline water desalination.

Insights on the inhibition of anaerobic digestion performances under short-term exposure of metal-doped nanoplastics via Methanosarcina acetivorans.

Anaerobic digestion is an attractive waste treatment technology, achieving both pollution control and energy recovery. Though the inhibition of polystyrene nanoplastics in anaerobic granular sludge is well studied, no direct evidence has been found on the interaction of methanogens and nanoplastics. In this study, to characterize the location of nanoplastics, Pd-doped polystyrene nanoplastics (Pd-PS) were used to explore the inhibition mechanism of anaerobic sludge through short-term exposure to Methanosarcina acetivorans C2A. The results showed that Pd-PS inhibited the methanogenesis of the anaerobic sludge, and the methane production decreased as the Pd-PS increased, with a 14.29% reduction at the Pd-PS concentration of 2.36 × 1010 particles/mL. Also, Pd-PS interacted with the protein in the extracellular polymeric substances (EPS). Furthermore, Pd-PS inhibited the methanogenesis of M. acetivorans C2A without exhibiting an evident reduction in the growth. The inhibition of Pd-PS on methane was due to the inhibition of methane production related genes, MtaA and mcrA. These results provide potential explication for the inhibition of nanoplastics on the methanogens, which will fulfill the knowledge on the stability of methanogens under the short-term exposure of nanoplastics.

Effects of long-term addition of Cu(II) and Ni(II) on the biochemical properties of aerobic granules in sequencing batch reactors.

Copper (Cu(II)) and nickel (Ni(II)) are often encountered in wastewaters. This study investigated the individual toxic effects of long-term addition of Cu(II) and Ni(II) on the biochemical properties of aerobic granules in sequencing batch reactors (SBRs). The biochemical properties of aerobic granules were characterized by extracellular polymeric substances (EPS) content, dehydrogenase activity, microbial community biodiversity, and SBR performance. One SBR was used as a control system, while another two received respective concentration of Cu(II) and Ni(II) equal to 5 mg/L initially and increased to 15 mg/L on day 27. Results showed that the addition of Cu(II) drastically reduced the biomass concentration, bioactivity, and biodiversity of aerobic granules, and certainly deteriorated the treatment performance. The toxic effect of Ni(II) on the biodiversity of aerobic granules was milder and the aerobic granular system elevated the level of Ni(II) toxicity tolerance. Even at a concentration of 15 mg/L, Ni(II) still stimulated the biomass yield and bioactivity of aerobic granules to some extent. The elevated tolerance seemed to be owed to the concentration gradient developed within granules, increased biomass concentration, and promoted EPS production in aerobic granular systems.

Behavior of tetracycline and polystyrene nanoparticles in estuaries and their joint toxicity on marine microalgae Skeletonema costatum.

Polystyrene nanoplastics (PS NPs), which are newly emerging as particulate pollutants, are one of the most abundant plastic types in marine debris. Although there has been extensive research on microplastics, the sorption behavior of PS NPs in surface waters remains unknown. In addition, in the previous joint toxicity studies, the concentration of organic pollutant in the joint system was based on the EC50 of this pollutant, rather than the actually amount of this pollutant adsorbed on nanoplastics (NPs). In this study, the sorption behavior of PS NPs with different surface charges in the surface water of estuaries and joint toxicity of that absorbed tetracycline antibiotic in equilibrium were investigated for the first time. Because of the electrostatic repulsion, salting-out effect, and partition function, the sorption capacity of tetracycline antibiotic by differently charged PS NPs was enhanced with increasing salinity. The biological effects of exposure to tetracycline-saturated PS NPs were complicated, which can be attributed to the surface characteristics of mixtures such as hydrophobicity and charges. Thus, the role of NPs in the natural environment as a carrier of antibiotics may provide an alternative for antibiotic inputs from inland water to coastal marine water, which would not only change the environmental fate and ecotoxicology of antibiotics and NPs, but also pose challenges to the safety of coastal aquaculture and marine ecosystem.

Differentially charged nanoplastics demonstrate distinct accumulation in Arabidopsis thaliana.

Although the fates of microplastics (0.1-5 mm in size) and nanoplastics (<100 nm) in marine environments are being increasingly well studied1,2, little is known about the behaviour of nanoplastics in terrestrial environments3-6, especially agricultural soils7. Previous studies have evaluated the consequences of nanoplastic accumulation in aquatic plants, but there is no direct evidence for the internalization of nanoplastics in terrestrial plants. Here, we show that both positively and negatively charged nanoplastics can accumulate in Arabidopsis thaliana. The aggregation promoted by the growth medium and root exudates limited the uptake of amino-modified polystyrene nanoplastics with positive surface charges. Thus, positively charged nanoplastics accumulated at relatively low levels in the root tips, but these nanoplastics induced a higher accumulation of reactive oxygen species and inhibited plant growth and seedling development more strongly than negatively charged sulfonic-acid-modified nanoplastics. By contrast, the negatively charged nanoplastics were observed frequently in the apoplast and xylem. Our findings provide direct evidence that nanoplastics can accumulate in plants, depending on their surface charge. Plant accumulation of nanoplastics can have both direct ecological effects and implications for agricultural sustainability and food safety.

Enhanced removal of ciprofloxacin using humic acid modified hydrogel beads.

In this study, humic acid coated biochar (HA-BC) and chitosan were combined to prepare an adsorbent with enhanced reactivity for the removal of ciprofloxacin (CIP). With initial CIP concentrations of 250 mg/L, the maximum adsorbed amount was 154.89 mg/g. Removal rates reached equilibrium after 12 h, obeying the pseudo second-order kinetic model. Adsorption isotherm data was better fitted to the Langmuir isotherm model. The sorption capacity of humic acid-biochar/chitosan hydrogel beads (HBCB) decreased by 11.42%, 6.66%, 9.32%, and 23.92% in the presence of NaCl, NaNO3, Na2SO4, and Na3PO4, respectively. A complex mechanism was found to be responsible for the adsorptive removal of CIP including, hydrogen bonding, π-π electron donor-acceptor (EDA) interactions and hydrophobic interactions. After four regeneration steps, sorption capacity remained sufficient (61.23 mg/g). These removal results indicate that HBCB is durable and effective for long term CIP removal.

Joint toxicity of microplastics with triclosan to marine microalgae Skeletonema costatum.

Toxicity of single microplastics on organisms has been reported widely, however, their joint toxicity with other contaminants on phytoplankton is rarely investigated. Here, we studied the toxicity of triclosan (TCS) with four kinds of microplastics namely polyethylene (PE, 74 µm), polystyrene (PS, 74 µm), polyvinyl chloride (PVC, 74 µm), and PVC800 (1 µm) on microalgae Skeletonema costatum. Both growth inhibition and oxidative stress including superoxide dismutase (SOD) and malondialdehyde (MDA) were determined. We found that TCS had obvious inhibition effect on microalgae growth within the test concentrations, and single microplastics also had significant inhibition effect which followed the order of PVC800 > PVC > PS > PE. However, the joint toxicity of PVC and PVC800 in combination with TCS decreased more than that of PE and PS. The higher adsorption capacity of TCS on PVC and PVC800 was one possible reason for the greater reduction of their toxicity. The joint toxicity of PVC800 was still most significant (PE < PVC < PS < PVC800) because of the minimum particle size. According to the independent action model, the joint toxicity systems were all antagonism. Moreover, the reduction of SOD was higher than MDA which revealed that the physical damage was more serious than intracellular damage. SEM images revealed that the aggregation of microplastics and physical damage on algae was obvious. Collectively, the present research provides evidences that the existence of organic pollutants is capable of influencing the effects of microplastics, and the further research on the joint toxicity of microplastics with different pollutants is urgent.

Membrane biofouling retardation by zwitterionic peptide and its impact on the bacterial adhesion.

Nanofiltration polyamide membranes naturally tend towards biofouling, due to their surface physicochemistries. Nisin, a type of short cationic amphiphilic peptide with antimicrobial properties, has been recognized as a safe antimicrobial for food biopreservation and biomedical applications. This study investigates the impact of nisin on the initial bacterial attachment to membranes, its anti-biofouling properties, and characterizes a non-monotonic correlation between nisin concentration and biofilm inhibition. Nisin was found to inhibit B. subtilis (G+) and P. aeruginosa (G-) attachment to both the nanofiltration membrane and the PES membrane. To determine the mechanism of action, we investigated the polysaccharides, protein, and eDNA as target components. We found that the quantities of polysaccharides and eDNA were significantly changed, resulting in bacterial death and anti-adhesion to membrane. However, there were no discernable impacts on protein. We postulated that nisin could prevent irreversible biofouling by decreasing adhesion, killing bacteria, and reducing biofilm formation. We examined membrane flux behavior through bench-scale cross-flow experiments at a set concentration of nisin (100 µg mL-1), with membrane behavior being confirmed using CLSM images. Results showed that nisin could enhance anti-biofouling properties through both anti-adhesive and anti-bacterial effects, and therefore could be a novel strategy against biofouling of membranes.

Bioflocculant production by culture of Serratia ficaria and its application in wastewater treatment.

A bioflocculant-producing bacterium was isolated from soil and identified as Serratia ficaria. Using optimized culture conditions a flocculating activity of 95.4% was obtained. It was found to be effective for flocculation of a kaolin suspension over weakly acidic pH (5-7); divalent cations (Ca2+ and Mg2+) enhanced the flocculating activity, while the co-presence of Al3+ and Fe3+ resulted the negative effect. Measurements of zeta potential revealed that charge neutralization played an important role in the flocculation. It could flocculate a variety of real wastewaters, including river water, brewery wastewater, meat processing wastewater and soy sauce brewing wastewater. The bioflocculant was also used to treat pulp effluent, and the removal rate of color and chemical oxygen demand (COD) were up to 99.9% and 72.1%, respectively, which were better than traditional chemical flocculants.

Low-level concentrations of aminoglycoside antibiotics induce the aggregation of cyanobacteria.

The interactions between antibiotics and microorganisms have attracted enormous research attentions. In this study, we investigated the effects of two typical aminoglycoside antibiotics on the aggregation of the model cyanobacterium, Synechococcus elongatus, and the dominating strain in algal blooms, Microcystis aeruginosa, via the analysis of zeta potentials, hydrophobicity, and extracellular polymeric substances (EPS) secretion. The results showed that low-level antibiotics promoted the aggregation of S. elongatus and M. aeruginosa by 40 and 18% under 0.10 and 0.02 µg/mL of kanamycin, respectively, which was mainly attributed to the combined effects of increased zeta potentials and the ratio between extracellular proteins and polysaccharides. Tobramycin exerted similar effects. Additionally, we discovered that at low pH (pH 5) and ionic strength (1 mM Na+ and 2 mM Mg2+), the inducing effects of antibiotics would be even larger than those with higher pH and ionic strength. As aggregation is important to cyanobacteria in either the basic physiology of biofilm formation or the algal bloom, our study demonstrated that low-level antibiotics exert ecological impacts via interfered aggregation. We believe this study will shed light on the mechanisms underlying antibiotic-induced biofilm formation and help with the evaluation of the environmental and ecological risks of antibiotics and other emerging pollutants.

Role of extracellular polymeric substances in the acute inhibition of activated sludge by polystyrene nanoparticles.

Microplastics and nanoplastics in aquatic systems have become a global concern because of their persistence and adverse consequences to ecosystems and potentially human health. Though wastewater treatment plants (WWTPs) are considered a potential source of microplastics in the environment, the role of extracellular polymeric substances (EPS) of activated sludge on the fate of nanoplastics is not clear. In this study, the role of EPS in the influence of polystyrene nanoparticles (PS-NPs) on the endogenous respiration of activated sludge was investigated for the first time. The results showed that the acute inhibition of activated sludge by PS-NPs was enhanced with increasing PS-NPs concentration. X-ray photoelectron spectroscopy (XPS) results indicate that the functional groups involved in the interactions between PS-NPs and EPS were carbonyl and amide groups and the side chains of lipids or amino acids. Furthermore, the Fourier transform infrared (FTIR) spectroscopy results show that the protein secondary structures in EPS were changed by PS-NPs and lead to the bioflocculation of activated sludge, which provides a better understanding on the fate of nanoplastics in WWTPs.

Mitigation of membrane biofouling by d-amino acids: Effect of bacterial cell-wall property and d-amino acid type.

Development of novel approaches for biofouling mitigation is of crucial importance for membrane-based technologies. d-amino acids (d-AAs) have been proposed as a potential strategy to mitigate biofouling. However, the effect of bacterial cell-wall properties and d-AAs type on biofouling mitigation remains unclear. This study assesses the effect of d-AAs type on membrane biofouling control, towards Gram positive (G+) and Gram negative (G-) bacteria. Three kinds of d-AAs were found to inhibit both G+ and G- bacterial attachment in short-term attachment and dead-end filtration experiments. The existence of d-AAs reduces extracellular polysaccharides and proteins on the membrane, which may decrease membrane biofouling. Cross-flow filtration tests further indicated that d-AAs could effectively reduce membrane biofouling. The permeate flux recovery post chemical cleaning, improved for both P. aeruginosa and B. subtilis treated with d-AAs. The results obtained from this study enable better understanding of the role of d-AAs species on bacterial adhesion and biofilm formation. This may provide a new way to regulate biofilm formation by manipulating the species of d-AAs membrane systems.

Influences of D-tyrosine on the stability of activated sludge flocs.

The sludge floc stability is essential for the solid/liquid separation in biological wastewater treatment. In this study, the effect of an exogenous d-tyrosine on the shear stability and surface characteristics of activated sludge flocs was investigated. Sludge flocs were found to be less stable in the addition of d-tyrosine. d-Tyrosine inhibited the production of extracellular polymeric substances (EPS) especially for the proteins. A high correlation coefficient was observed between the composition of EPS fraction and d-tyrosine content. In addition, the hydrophobicity of sludge flocs was reduced and the zeta potential was more negative with the content of d-tyrosine increased. A linear relationship between the extracellular polymeric substances and surface characteristics for sludge flocs indicated that the inhibited EPS production may be responsible for the instability of sludge upon the addition of d-tyrosine.

Enhancement of acidic dye biosorption capacity on poly(ethylenimine) grafted anaerobic granular sludge.

Developing a novel biosorbent with high capacity is crucial to remove dyes from waters in an efficient way. This study demonstrated that porous anaerobic granular sludge could be grafted with polyethylenimine (PEI), which definitely improved the sorption capacity towards Acid Red 18 (AR18) removal. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) study revealed that the PEI modification introduced a large number of amino groups on the surface of sludge, and the amino groups played an important role in the adsorption of dye molecule. Analysis of sorption data using a Boyd plot confirms the film diffusion was the rate-limiting step. The equilibrium data were well fitted Langmuir model, with a maximum AR18 uptake of 520.52 mg/g. Removal of AR18 decreased with the increasing pH and the maximum color removal was observed at pH 2.0. The sorption energy calculated from Dubinin-Radushkevich isotherm was found to be less than 8 for the biosorption of AR 18, which suggested that the biosorption processes of dye molecule onto modified anaerobic granules could be taken place by physical adsorption. Various thermodynamic parameters, such as ΔG(0), ΔH(0) and ΔS(0), were also calculated, which indicated that the present system was spontaneous and endothermic process.

Enhanced Cu(II) and Cr(VI) biosorption capacity on poly(ethylenimine) grafted aerobic granular sludge.

The biosorption characteristics of cations and anions from aqueous solution using polyethylenimine (PEI) modified aerobic granules were investigated. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis exhibit the presence of PEI on the granule surface. Compared with the raw granule, the modified aerobic granules with PEI showed a significant increase in sorption capacity for both metal ions. The monolayer biosorption capacity of granules for Cu(II) and Cr(VI) ions was found to be 71.239 and 348.125mg/g. The optimum solution pH for adsorption of Cu(II) and Cr(VI) from aqueous solutions was found to be 6 and 5.2, respectively. The biosorption data fitted better with the Redlich-Peterson isotherm model. FTIR showed chemical interactions occurred between the metal ions and the amide groups of PEI on the biomass surface. XPS results verified the presence of Cr(III) on the biomass surface, suggesting that some Cr(VI) anions were reduced to Cr(III) during the sorption.