A biofilm reactor was designed with flat ceramic substrates to remove Co(II), Ni(II) and Zn(II) from industrial wastewater. The ceramics were made of clay and nano-rubber with high mechanical resistance. The surface of the ceramic substrate was modified with neutral fiber and nano-hydroxyapatite. A uniform and stable biofilm mass of 320 g with 2 mm of thickness was produced on the modified ceramic after 3 d. The micro-organisms were identified in the biofilm by polymerase chain reaction (PCR) method. Functional groups of biofilms were identified with a Fourier transform infrared spectrometer (FT-IR). Experiments were designed by central composite design (CCD) using the responsive surface method (RSM). The biosorption process was optimized at pH = 5.8, temperature = 22 °C, feed flux of heavy metal wastewater = 225 ml, substrate flow = 30 ml, and retention time = 7.825 h. The kinetic data was analyzed by pseudo first-order and pseudo second-order kinetic models. Isotherm models and thermodynamic parameters were applied to describe the biosorption equilibrium data of the metal ions on the biofilm-ceramic. The maximum biosorption efficiency and capacity of heavy metal ions were about 72% and 57.21 mg, respectively.

The quality of freshwater undoubtedly reflects the health of our surrounding environment, society, and economy, as these are supported by various freshwater ecosystems. Monitoring efforts have therefore been considered a vital means of ensuring the ecological health of freshwater environments. Nevertheless, most aquatic environmental monitoring strategies largely focus on bulk water sampling for analysis of physicochemical and key biological indicators, which for the most part do not consider pollution events that occur at any time between sampling events. Because benthic biofilms are ubiquitous in aquatic environments, pollution released during sporadic events may be absorbed by these biofilms, which can act as repositories of pollutants. The aim of this study was to assess whether benthic biofilm monitoring could provide an efficient way of properly characterizing the extent of pollution in aquatic environments. Here, bulk water and benthic biofilms were sampled from three Hong Kong streams having various pollution profiles, and subsequently compared via high-resolution microscopy, metagenomic analysis, and analytical chemistry. The results indicated that biofilms were, indeed, reservoirs of environmental pollutants, having different profiles compared with that of the corresponding bulk water samples. Moreover, the results also suggested that biofilms sampled in polluted areas were characterized by a higher species richness. While the analytical testing of benthic biofilms still needs further development, the integration of chemical-pollutant profiles and biofilm sequencing data in future studies may provide unique perspectives for understanding and identifying pollution-related biofilm biomarkers.

Development of low-cost cathode materials for Plant-Sediment Microbial Fuel Cells (P-SMFCs) has gained increasing interest, due to improved performance levels in terms of power and pollutant removal. A novel low cost three-dimensional cathode prepared by simple three-step strategy with growth of Co₃O₄ in-situ biofilm was successfully prepared. Different cathodes were applied to the six parallel P-SMFCs systems (reactor: R1-R6), such as graphite felt (GF), Pt/C, GF@Co₃O₄ (non-bonding Co₃O₄ nanowires on GF), GF@SG-Co₃O₄ (using argon as shielding gas (SG)). Its performances (R1, R2: control groups) were evaluated by electricity generation and Cr(VI) reduction at initial cadmium concentrations (4.97, 10.29 and 21.16 mg L⁻¹). A significant Cr(VI) removal efficiency of 99.76%, maximum power density of 75.12 ± 2.90 mW m⁻² and Cr(VI) adsorption capacity of 1.67 mg g⁻¹ were obtained at initial Cr(VI) concentration of 21.16 mg L⁻¹ with non-bonding GF@Co₃O₄ and bio-GF@SG-Co₃O₄ as cathodes. This indicated that these two materials were better than others (GF, Pt/C and GF@Co₃O₄) as cathodes. Characterization analysis including scanning electron microscope (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), Polarization curve, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) showed that high current generation Cr(VI) removal mainly attributed to transportation of plants, adsorption of bio-cathode, formation of a relatively high concentration region and abundant oxygen vacancies of GF@SG-Co₃O₄. The results show that P-SMFCs with GF@SG-Co₃O₄ cathode may be a potentially novel approach for remediating Cr(VI) contaminated waster or soil.

The present study investigated the physiological responses, photosynthetic activity, and microbial community structure of leaf-associated biofilms on the microphyte Vallisneria natans during a harmful algal bloom. Results of the physiological and photosynthetic indices (Fᵥ/Fₘ ratios [maximum quantum yield of photosystem II (PSII)]; malondialdehyde content; total chlorophyll; and activities of superoxide dismutase, catalase and peroxidase) indicated that algal blooms could cause inhibition of photosynthesis, oxidative stress and an antioxidant system stress response in Vallisneria natans leaf-associated biofilms. Multifractal analysis suggested that allelochemicals or algal organic matter released by cyanobacteria could reduce the surface roughness of the leaf. Microbial diversity analysis of the biofilms showed that algal blooms slightly altered the microbial community structure while the richness and evenness of the microbial composition remained stable. This study provided useful information to better understand the adverse effects of algal blooms on submerged macrophytes.

The widespread application of commercial TiO₂ NPs inevitably leads to their release into environmental waters through various ways. TiO₂ NPs released into water might be absorbed by and react with periphytic biofilms, which are a kind of aquatic environmental media of important ecological significance, and influence the physiological activity and ecological function of periphytic biofilms. This study investigated the effects of exposure to 1 mg/L and 5 mg/L of TiO₂ NPs on periphytic biofilms cultured indoors. After a 10-day exposure to TiO₂ NPs, the growth (measured by chlorophyll-a content) of microalgal community was inhibited greatly (more than 60%); however, the primary production (indicated by quantum yield) of periphytic biofilms maintained changeless. As for bacteria, TiO₂ NP-exposure increased the bacterial diversity and altered the composition structure. Significant changes were observed in the bacterial communities at the class level, mainly including Alphaproteobacteria, Gammaproteobacteria, Cytophagia, Flavobacteriia, Sphingobacteriia, Synechococcophycideae and Oscillatoriophycideae. The enhancement of metabolic activities (the production of extracellular polymeric substances, especially proteins content increased by 48.51%) of periphytic biofilms was a resistance mechanism to toxicity of NPs. As for extracellular enzyme activities of periphytic biofilms, alkaline phosphatase activity was inhibited (22.43%) after exposed to 5 mg/L of TiO₂ NPs, which posed a threat to phosphorus metabolism of periphytic biofilms. Overall, this study demonstrated that 1 mg/L and 5 mg/L of TiO₂ NPs negatively influenced physiological activities and ecological functions of periphytic biofilms, highlighting that the ecological risks of TiO₂ NPs should be paid attention to.

Bacterial antibiotic resistance (BAR) is profoundly important to human health, but the environmental reservoirs of resistance determinants are poorly understood. BAR of biofilm and tap water were analyzed by using a water distribution simulator where different doses of chlorine and chloramine were used in this study. The results revealed that the disinfectants (≥2 mg/L) suppressed antibiotic resistant bacteria (ARB) in tap water and biofilms, while disinfected water and biofilms had a high relative abundance of ARB. The difference of ARB concentration and ARB percentage between the samples obtained from a disinfected pipeline and a non-disinfected pipeline became smaller over time. Because the water supply system is a unidirectional process, it is unclear how planktonic bacteria in water transfer BAR over time, although biofilm is suspected to play a role in this process. Compared with the biofilm samples without disinfectant, the disinfected biofilm had lower ICC and HPC/ICC percentage, lower AOC and AOC/TOC percentage, indicating that the disinfectant inhibited the bacteria growth in biofilm, and the disinfected biofilm had high proportion of non-culturable bacteria and low biodegradability, which affected BAR in biofilms. High throughput sequencing showed that in biofilms, the relative abundance of genera (uncultured_f_Rhodocyclaceae, Brevundimonas, and Brevibacillus in chlorinated systems, and Brevundimonas, Brevibacillus in chloraminated systems) with multiple antibiotic resistance and high abundance (up to 78.5%), were positively associated with disinfectant concentration and ARB percentage. The major prevalent genera in biofilms were also detected in tap water, suggesting that biofilm growth or biofilm detachment caused by external environmental factors will allow the movement of biofilm clusters with higher ARB concentration and percentage into bulk water, thereby increasing the antibiotic resistance of bacteria in tap water.

Methyl tert-butyl ether (MTBE) degradation technologies based on two-phase partitioning systems such as extractive membrane biofilm reactors (EMBFR) permit separation of biological and contaminant compartments, thus allowing optimization of the biological section. In this study, we set-up an EMBFR with three MTBE-degrading and cooperating strains (termed social biofilm: Agrobacterium sp. MS2, Paenibacillus etheri SH7ᵀ and Rhodococcus ruber EE6). The removal efficiency of the social-biofilm EMBFR was 80%, and functional stability was observed in the reactor, i.e. more efficient than previous studies (single-strain inoculated EMBFR, <50% removal efficiency and unstable function). Metabolite tert-butyl alcohol was not observed, and the EC₅₀ values were higher than those observed in single-strain EMBFRs. Comparative analysis of the MTBE enzymatic pathway and the social-biofilm was performed, where the mechanism of cooperation observed within the social-biofilm is likely due to enzymatic redundancy. Functional outcomes were equal to previous batch tests, hence 100% scalability was obtained. Overall, higher functional and stability outcomes are obtained with the use of the social-biofilm in an MTBE-EMBFR.

Integrated systems with appropriate bio-filters can be used to treat aquaculture effluents. However, the information on bio-filters that alters the ecological functions of the bacterioplankton community (BC) in biodegradation of the aquaculture effluents remains controversial. In this study, we implemented a comprehensive restoration technology combined with bio-filters [biofilm, clam (Tegillarca granosa), and macrophytes (Spartina anglica)] to investigate their influence on the stability of the BC and nutrient removal. We found that the diversity of BC was linked with biogeochemical factors in processing and upcycling nitrogen-rich effluents into high-value biomass. The BC exhibited significant distinct patterns in the bio-filter areas. Potential biomarkers for constrained harmfully algae-bacteria (Nitriliruptoraceae, Bacillales, and Rhodobacteraceae) and nutrient removal were significantly higher in the bio-filters areas. The bio-filters significantly promoted the restoration effects of N and P balance by reducing 82.34% of total nitrogen (TN) and 81.64% of total phosphorus (TP) loads at the water interface. The main mechanisms for TN and TP removal and nutrient transformation were achieved by assimilation and absorption by the emergent macrophytes (Spartina anglica). The bio-filters significantly influenced the biodegradability and resolvability of particulate organic matter through ammonification, nitrification, and denitrification of microbes, which meliorated the nutrient removal. Beside bio-filter effects, the BC was significantly controlled by abiotic factors [nitrate (NO₃⁻-N), dissolved oxygen (DO), total nitrogen (TN), and water temperature (WT)], and biotic factors (chlorophyll ɑ and green algae). Our study revealed that the co-existence system with bio-filters may greatly improve our understanding on the ecological functions of the BC in aquaculture systems. Overall, combined bio-filters provide an opportunity for the development of efficient and optimized aquaculture wastewater treatment technology.

Bioelectrochemical systems (BESs) have been widely investigated for recalcitrant waste treatment mainly because of their waste removal effectiveness. Electroactive microbes (EMs) have long been thought to contribute to the high effectiveness by interacting with electrodes via electron chains. However, this work demonstrated the dispensable role of EMs for enhanced recalcitrant contamination degradation in BESs. We revealed enhanced p-fluoronitrobenzene (p-FNB) degradation in a BES by observing a defluorination efficiency that was three times higher than that in biodegradation or electrochemical processes. Such an improvement was achieved by the collaborative roles of electrode biofilms and planktonic microbes, as their individual contributions to p-FNB degradation were found to be similarly stimulated by electricity. However, no bioelectrochemical activity was found in either the electrode biofilms or the planktonic microbes during stimulated p-FNB degradation; because no biocatalytically reductive or oxidative turnovers were observed on cyclic voltammetry curves. The non-involvement of EMs was further proven by the similar microbial community evolution for biofilms and planktonic microbes. In summary, we proposed a mechanism for indirect electrical stimulation of microbial metabolism by electrochemically generating the active mediator p-fluoroaniline (p-FA) and further degradation by a sequential combination of electrochemical p-FNB reduction and biological p-FA oxidation by non-EMs.

This study investigated the potential of biochar filters as a replacement for, or complement to, sand filters for removal of per- and polyfluoroalkyl substances (PFASs) from wastewater in on-site wastewater treatment systems (OWTSs). Concentrations and removal of nine perfluoroalkyl carboxylates (PFCAs; C₃₋₁₁) and three perfluoroalkane sulfonates (PFSAs; C₄, ₆, ₈) and one perfluorooctanesulfonamide (FOSA; C₈) were investigated over 22 weeks in four treatments with column filters: biochar (BC) without biofilm (BC-no-biofilm), biochar with active biofilm (BC-active-biofilm), biochar with inactive biofilm (BC-inactive-biofilm) and sand with active biofilm (Sand-active-biofilm). The filters were operated under hydraulic loading (50 L m⁻² day⁻¹) to mimic the loading rate in on-site filtration beds. The initial concentrations of the ΣPFASs in the influent were in the range of 1500–4900 ng L⁻¹. In BC-no-biofilm, the removal efficiency (20–60%) and adsorption capacity (0–88 ng ΣPFASs g⁻¹ BC) of short-chain PFCAs (C₃₋₆) and PFSA (C₄) was low, whereas the removal efficiency (90–99%) and the adsorption capacity (73–168 ng g⁻¹) was high for C₇-C₁₁ PFCAs, C₆, C₈ PFSAs and FOSA. The relative removal was generally lower for C₃₋₉ PFCAs and C₄, C₆, C₈ PFSAs using BC-active-biofilm and BC-inactive-biofilm compared with BC-no-biofilm. This can be explained by the presence of biofilm and solids in BC-active-biofilm and the presence of wastewater solids in BC-inactive-biofilm, which decreased the availability and number of adsorption sites for PFASs compared with BC-no-biofilm. On the other hand, inactivation of the biofilm resulted in lower removal efficiencies for C₅₋₁₁ PFCAs, C₄, C₆, C₈ PFSAs and FOSA, probably because the biofilm degraded organic matter and thus increased the availability and number of adsorption sites compared with BC-inactive-biofilm. Sand-active-biofilm showed poor removal (0–70%) for all PFASs except FOSA (90%) and its adsorption capacity was low (0.0–7.5 ng g⁻¹). In general, for all biochar treatments, shorter-chain PFASs were more resistant to removal than longer-chain PFASs. In addition, C₄, C₆ and C₈ PFSAs showed 10–30%, 10–50% and 20–30% higher average removal efficiency, respectively, than PFCAs with corresponding perfluoroalkyl chain length. In conclusion, biochar is a promising filter medium for removal of PFASs in OWTSs, especially for PFASs with a perfluorocarbon chain longer than C₆.