In situ bioremediation of surface waters by periphytons

A new strategy of using periphyton to simultaneously promote remediation of PAHs-contaminated soil and production of safer crops

Contaminated farmland leads to serious problems for human health through biomagnification in the soil-crop-human chain. In this paper, we have established a new soil remediation strategy using periphyton for the production of safer rice. Four representative polycyclic aromatic hydrocarbons (PAHs), including phenanthrene (Phe), pyrene (Pyr), benzo[b]fluoranthene (BbF), and benzo[a]pyrene (BaP), were chosen to generate artificially contaminated soil. Pot experiments demonstrated that in comparison with rice cultivation in polluted soil with ΣPAHs (50 mg kg-1) but without periphyton, adding periphyton decreased ΣPAHs contents in both rice roots and shoots by 98.98% and 99.76%, respectively, and soil ΣPAHs removal reached 94.19%. Subsequently, risk assessment of ΣPAHs based on toxic equivalent concentration (TEQ), pollution load index (PLI), hazard index (HI), toxic unit for PAHs mixture (TUm), and incremental lifetime cancer risk (ILCR) indicated that periphyton lowered the ecological and carcinogenicity risks of PAHs. Besides, the role of periphyton in enhancing the rice productivity was revealed. The results indicated that periphyton alleviated the oxidative stress of PAHs on rice by reducing malondialdehyde (MDA) content and increasing total antioxidant capacity (T-AOC). Periphyton reduced the toxic stress of PAHs on the soil by promoting soil carbon cycling and metabolic activities as well. Periphyton also improved the soil's physicochemical properties, such as the percentage of soil aggregate, the contents of humic substances (HSs) and nutrients, which increased rice biomass. These findings confirmed that periphyton could improve rice productivity by enhancing soil quality and health. This study provides a new eco-friendly strategy for soil remediation and simultaneously enables the production of safe crops on contaminated land.

Influence of extracellular polymeric substances on arsenic bioaccumulation and biotransformation in biofilms

It is well recognized that biofilms can biosorb and biotransform heavy metals in aquatic environments. However, the effects of extracellular polymeric substance (EPS) on inorganic arsenic (As) bioaccumulation and biotransformation in biofilms are still unrevealed and need to be investigated. In order to explore the above scientific issues, the As accumulation and speciation in EPS-containing or EPS-free biofilms and growth medium under As(V)/As(III) exposure conditions were measured. After the removal of EPS, the amount of As uptake (Asup) and As adsorption (Asad) in biofilms were significantly reduced, no matter whether exposed to As(V) or As(III). FTIR analysis further suggested that the interaction between these functional groups with As was limited after the removal of EPS. In the EPS-containing biofilms, the Asad was mainly As(V) with low toxicity. However, after the removal of EPS, the Asad was mainly As(III) with high fluidity, and no methylated As was found. Moreover, the removal of EPS inhibited As(III) oxidation and methylation by biofilms, resulting in the decrease of As(V) and methylated As in the growth medium. The findings of this study emphasized the essential impact of EPS on the biosorption and biotransformation of As in biofilms. This study provides a unique understanding of the role of biofilms in As biogeochemical cycle, and water quality purification function in water environments.

Sustainable bioremediation technologies for algal toxins and their ecological significance

The emergence of algal toxins in water ecosystems poses a significant ecological and human health concern. These toxins, produced by various algal species, can lead to harmful algal blooms, and have far-reaching consequences on biodiversity, food chains, and water quality. This review explores the types and sources of algal toxins, their ecological impacts, and the associated human health risks. Additionally, the review delves into the potential of bioremediation strategies to mitigate the effects of algal toxins. It discusses the role of microorganisms, enzymes, and algal-bacterial interactions in toxin removal, along with engineering approaches such as advanced oxidation processes and adsorbent utilization. Microbes and enzymes have been studied for their environmentally friendly and biocompatible properties, which make them useful for controlling or removing harmful algae and their toxins. The challenges and limitations of bioremediation are examined, along with case studies highlighting successful toxin control efforts. Finally, the review outlines future prospects, emerging technologies, and the need for continued research to effectively address the complex issue of algal toxins and their ecological significance.

Environmental Biofilms from an Urban Community in Salvador, Brazil, Shelter Previously Uncharacterized Saprophytic Leptospira

Biofilms are complex microecosystems with valuable ecological roles that can shelter a variety of microorganisms. Spirochetes from the genus Leptospira have been observed to form biofilms in vitro, in rural environments, and in the kidneys of reservoir rats. The genus Leptospira is composed of pathogenic and non-pathogenic species, and the description of new species is ongoing due to the advent of whole genome sequencing. Leptospires have increasingly been isolated from water and soil samples. To investigate the presence of Leptospira in environmental biofilms, we collected three distinct samples of biofilms formed in an urban setting with poor sanitation: Pau da Lima, in Salvador, Bahia, Brazil. All biofilm samples were negative for the presence of pathogenic leptospires via conventional PCR, but cultures containing saprophytic Leptospira were identified. Whole genomes were generated and analyzed for twenty isolates obtained from these biofilms. For species identification, we used digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) analysis. The obtained isolates were classified into seven presumptive species from the saprophytic S1 clade. ANI and dDDH analysis suggest that three of those seven species were new. Classical phenotypic tests confirmed the novel isolated bacteria as saprophytic Leptospira. The isolates presented typical morphology and ultrastructure according to scanning electron microscopy and formed biofilms under in vitro conditions. Our data indicate that a diversity of saprophytic Leptospira species survive in the Brazilian poorly sanitized urban environment, in a biofilm lifestyle. We believe our results contribute to a better understanding of Leptospira biology and ecology, considering biofilms as natural environmental reservoirs for leptospires.

Novosphingobium cyanobacteriorum sp. nov., isolated from a eutrophic reservoir during the Microcystis bloom period

A novel Gram-stain-negative, aerobic and rod-shaped bacterial strain, HBC54T, was isolated from periphyton during a Microcystis bloom. Based on the results of the 16S rRNA gene sequence analysis, strain HBC54T was closely related to Novosphingobium aerophilum 4Y4T (98.36 %), Novosphingobium aromaticivorans DSM 12444T (98.08 %), Novosphingobium huizhouense c7T (97.94 %), Novosphingobium percolationis c1T (97.65 %), Novosphingobium subterraneum DSM 12447T (97.58 %), Novosphingobium olei TW-4T (97.58 %) and Novosphingobium flavum UCT-28T (97.37 %). The average nucleotide identity and digital DNA-DNA hybridization values between HBC54T and its related type stains were below 78.97 and 23.7 %, which are lower than the threshold values for species delineation. The major fatty acids (>10.0 %) were identified as C14 : 0 2-OH, summed feature 3 (C16 : 1  ω7c and/or C16 : 1  ω6c) and summed feature 8 (C18 : 1  ω7c and/or C18 : 1  ω6c) and the respiratory quinone was ubiquinone Q-10. The main polar lipids detected in the strain were phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, diphosphatidylglycerol and three unidentified phospholipids. The genomic DNA G+C content was 64.8 mol%. Strain HBC54T is considered to represent a novel species within the genus Novosphingobium, for which the name Novosphingobium cyanobacteriorum sp. nov. is proposed. The type strain is HBC54T (=KCTC 92033T=LMG 32427T).

Fertilizer-induced manganese oxide formation enhances cadmium removal by paddy crusts from irrigation water

Fertilization is a crucial agrological measure for agricultural production that can significantly impact the removal of Cd from irrigation water by paddy crusts (PC). In this study, laboratory and field experiments were conducted to investigate the impact of fertilization at low, medium, and high concentrations on the accumulation of Cadmium (Cd) in PC and the underlying mechanisms involved. The results showed that only low fertilizer concentration could promote the removal of Cd by PC, which reduced the Cd concentration in irrigation water from 19.52 μg/L to 5.35 μg/L. Conversely, medium and high fertilizer concentrations reduced the accumulation of Cd by PC. After fertilizer addition, the proportion of Fe-Mn oxidizable-Cd in PC reached 55 % (with low concentration of fertilizer treatment). The application of low concentration of fertilizer was found to stimulate the growth of filamentous green algae, leading to a significant increase in the relative abundance of sphingomonadaceae (by 1.39 %) and comamonadaceae (by 1.29 %). The XRD, SEM and correlation analysis show that a large amount of manganese oxide is formed on the surface of PC, which increases the fixation of Cd. These findings provide a new perspective for the remediation of heavy metal contamination in paddy fields.

Simulating oligotrophication in a eutrophic shallow lake to assess the effect of periphyton bioreactor on phytoplankton and epipelon

We evaluated the effects of a periphyton bioreactor on phytoplankton by experimentally simulating oligotrophication in a shallow eutrophic system. The experiment had two 50% diluted treatments with and without a periphyton bioreactor. Sampling was performed on days 6, 9, 12, 15, and 20 of the experimental period. The periphyton bioreactor accumulated biomass (chlorophyll-a, AFDM) and TP during the experimental period. Despite the biomass and TP loss due to periphyton detachment from the substrate after community reaching the algal biomass peak, the gains exceeded the losses, and the net rate was positive for all attributes in the bioreactor. Based on the average, our findings suggest that periphyton bioreactors negatively affected the phytoplankton total biovolume. Cyanobacteria were the most abundant phytoplankton group. However, the periphyton bioreactor caused the biomass loss of the Raphidiopsis raciborskii in phytoplankton. Our results suggest that bioreactor influenced the phytoplankton structure, reducing cyanobacterial biomass, especially Raphidiopsis raciborskii. However, the bioreactor did not reflect a significant increase in the epipelon biomass during the experimental period. We conclude that the periphyton bioreactor has the potential to assist in the maintenance of restored shallow lakes and reservoirs, especially in controlling phytoplankton growth.

Effects of the Desiccation Duration on the Dynamic Responses of Biofilm Metabolic Activities to Rewetting

Global climate changes have increased the duration and frequency of river flow interruption, affecting the physical and community structure of benthic biofilms. However, the dynamic responses of biofilm metabolism during the dry-wet transition remain poorly understood. Herein, the dynamic changes in biofilm metabolic activities were investigated through mesocosm experiments under short-term (25 day) and long-term drought (90 day), followed by a 20 day rewetting. The biofilm ecosystem metabolism, as measured by gross primary production and community respiration, was significantly inhibited and turned heterotrophic during the desiccation phase and then recovered, becoming autotrophic during the rewetting period regardless of the desiccation periods due to the high resilience of the autotrophic community. However, long-term drought decreased the recovery rate of the ecosystem metabolism and also caused irreparable damage to the biofilm carbon metabolism, measured using Biolog Eco Plates. Specifically, the recovery of the total carbon metabolic activity is related to the specific carbon source utilized by biofilm microorganisms, such as polymers, carbohydrates, and carboxylic acids. However, the divergent changes of amino acids caused the failure of the total carbon metabolism in long-term drought treatments to recover to the control level even after 20 days of rewetting. This research provides direct evidence that the increased duration of non-flow periods affects biofilm-mediated carbon biogeochemical processes.

The Roles of Different Fractions in Freshwater Biofilms in the Photodegradation of Methyl Orange and Bisphenol A in Aqueous Solutions

Freshwater biofilms play an important role in the migration and transformation of organic pollutants, especially under illumination conditions. Nonetheless, the roles of variable fractions in freshwater biofilms, e.g., extracellular polymeric substances (EPS), microbial cells and original biofilms, in promoting the photodegradation of trace organic pollutants remain largely unclear. In this study, two contaminants, i.e., methyl orange (MO) and bisphenol A (BPA), were selected, and the roles of different fractions in freshwater biofilms in their photodegradation performances were investigated. After dosing 696 mg/L SS biofilm harvested from an effluent-receiving river, the direct photodegradation rate of MO and BPA was increased 8.7 times and 5.6 times, respectively. River biofilm EPS contained more aromatic fractions, chromogenic groups and conjugated structures than biofilm harvested from a less eutrophic pond, which might be responsible for the enhanced photodegradation process. The quenching experiments suggested that when EPS fractions derived from river biofilm were dosed, ³EPS* was the major reactive oxygen species during the photodegradation of MO and BPA. Meanwhile, for EPS derived from the pond biofilm, ·OH/¹O₂ was predominantly responsible for the enhanced photodegradation. Batch experimental results suggested that the cells and EPS in river biofilms could collaboratively interact with each other to enhance the preservation of reactive species and protection of microbes, thus facilitating the photoactivity of biofilms. Our results might suggest that biofilms generated from eutrophic waterbodies, such as effluent-receiving rivers, could play a more important role in the photodegradation processes of contaminants.

Can the carbon metabolic activity of biofilm be regulated by the hydrodynamic conditions in urban rivers?

Hydrodynamic regulation is widely used to improve the water quality of urban rivers. However, it is yet to explore substantially whether hydrodynamics could regulate the metabolic activity of biofilm in such aquatic systems. Herein, the pilot experiment of hydrodynamics in the rotation tanks was designed, including two experiment phases, namely constant flow and adjusting flow for 21 days and 14 days, respectively. In constant flow phase, biofilms grew in five shear stress gradients (R1-R5, 0.0044- 0.12 Pa). The carbon metabolic rate (k) of mature biofilms evaluated by BIOLOG ECO microplates showed a hump-shaped relationship with increasing shear stress, with R3 (0.049 Pa) the highest, while R5 (0.12 Pa) the lowest. To verify whether the metabolic activity of biofilm cultured at constant flow phase can be regulated by shear stress, we initiated the adjusting flow phase, and shear stress in reactors was reset uniformly at 0.049 Pa (with the highest k). Results showed the carbon metabolic activity of biofilm in reactor R4 and R5 increased rapidly by day 3, and there was no significant difference between the carbon metabolic rates among the five treatments by day 14. Meanwhile, the utilization levels of polymers and carbohydrates by biofilms were significantly different among the five treatments after hydrodynamic regulations. These results suggested that the total carbon metabolic activity of biofilm can be regulated by hydrodynamics, while the divergent changes of the specific carbon source category might affect the biofilm-mediated carbon biogeochemical processes, which should be considered for the application of hydrodynamic regulation in river ecological restoration projects.

Nitrogen transformation in slightly polluted surface water by a novel biofilm reactor: Long-term performance and microbial population characteristics

This study proposes a modular floating biofilm reactor (MFBR) for in situ nitrogen removal from slightly polluted water in rivers using enriched indigenous microorganisms. Its main structure is a 60 cm × 60 cm × 90 cm rectangular reactor filled with hackettens. After a 96-day startup, the removal efficiencies of ammonia-N and total N (TN) reached 80% and 25%, respectively, with a hydraulic retention time (HRT) of 10 h, whereas those in a control reactor (without biofilm) were only 4.9% and 0.2%, respectively. The influences of HRT and dissolved oxygen (DO) were also investigated. As a key factor, HRT significantly affected the removal efficiencies of ammonia-N and TN. When HRT was close to the actual value for a river studied (2.4 min), the removal efficiencies of ammonia-N and TN were only 8.7% and 3.1%, respectively. Aeration increased the concentration of DO in water, which enhanced nitrification but inhibited denitrification. When HRT was 2.4 min, aeration intensity was 20 L/min; the ammonia-N and TN removal rates were 9.5 g/(m²·d) and 11.3 g/(m²·d), respectively. The results of microbial community analysis indicated that the microorganisms forming the biofilm were indigenous bacteria. The findings demonstrated a concept-proof of MFBR, which may be evaluated in scaling up investigation for developing a new methodology for nitrogen removal from slightly polluted surface water in plain river networks.

An assessment of the purification performance and resilience of sponge-based aerobic biofilm reactors for treating polluted urban surface waters

Pollutants are continuously released into surface waters, which decrease the dissolved oxygen (DO) concentration and leads to the formation of black-odorous water, especially in slow-flowing urban lakes and enclosed small ponds. In situ treatment by artificial aeration or water cycling, coupled with biofilm, can address this problem without occupying large amounts of land. In this study, we designed a novel sponge-based aerobic biofilm reactor (SABR) and evaluated its performance in purifying urban surface water under different conditions. In the urban lake water treatment, the continuous inflow results revealed that the NH₄⁺-N and NO₂^--N concentrations in the effluent were stable and remained lower than 0.10 mg/L and 0.05 mg/L, respectively. Abrupt increases in the NH₄⁺-N and NO₂^--N concentrations in the influent and sudden increases in the NH₄⁺-N and NO₂^--N concentrations in the effluent were observed, and only 4 to 8 days were required for the concentrations to decline below 0.10 mg/L and 0.05 mg/L, respectively. Increases in the polyurethane sponge filling ratios in the SABRs can reduce the DO concentration but do not affect NH₄⁺-N removal. When no biodegradable organic matter was present in the enclosed surface water, the degradation time of NH₄⁺-N from 14.22 to 0.10 mg/L was only 9 days when SABRs were combined with water cycling, which was shorter than the time needed by water cycling alone (16 days), and most of the NH₄⁺-N was converted to NO₃^--N. When massive amounts of biodegradable organic matter were present in the enclosed surface water, 22 days were required to remove the NH₄⁺-N when SABRs were combined with water cycling. Our results indicated that organic matter could be used as a carbon source to eliminate the produced NO₃^--N in SABRs. Therefore, the newly developed bioreactor provides an effective approach for treating N-polluted urban surface waters.

Different Algicidal Modes of the Two Bacteria Aeromonas bestiarum HYD0802-MK36 and Pseudomonas syringae KACC10292T against Harmful Cyanobacteria Microcystis aeruginosa

Blooms of harmful cyanobacteria Microcystis aeruginosa lead to an adverse effect on freshwater ecosystems, and thus extensive studies on the control of this cyanobacteria’s blooms have been conducted. Throughout this study, we have found that the two bacteria Aeromonas bestiarum HYD0802-MK36 and Pseudomonas syringae KACC10292^T are capable of killing M. aeruginosa. Interestingly, these two bacteria showed different algicidal modes. Based on an algicidal range test using 15 algal species (target and non-target species), HYD0802-MK36 specifically attacked only target cyanobacteria M. aeruginosa, whereas the algicidal activity of KACC10292^T appeared in a relatively broad algicidal range. HYD0802-MK36, as a direct attacker, killed M. aeruginosa cells when direct cell (bacterium)-to-cell (cyanobacteria) contact happens. KACC10292^T, as an indirect attacker, released algicidal substance which is located in cytoplasm. Interestingly, algicidal activity of KACC10292^T was enhanced according to co-cultivation with the host cyanobacteria, suggesting that quantity of algicidal substance released from this bacterium might be increased via interaction with the host cyanobacteria.

Feedback mechanisms of periphytic biofilms to ZnO nanoparticles toxicity at different phosphorus levels

The increasing use of nanoparticles (NPs) has raised concerns about their potential environmental risks. Many researches on NPs focused on the toxicity mechanism to microorganisms, but neglect the toxicity effects in relation to nutritional conditions. Here, we evaluated the interactive effects of zinc oxide (ZnO) NPs and phosphorus (P) levels on the bacterial community and functioning of periphytic biofilms. Results showed that long-term exposure to ZnO NPs significantly reduced alkaline phosphatase activity (APA) of periphytic biofilms just in P-limited conditions. Co-occurrence network analysis indicated that ZnO NPs exposure reduced network complexity between bacterial taxa in P-limited conditions, while the opposite trend was observed in P-replete conditions. Correlation analysis and random forest modeling suggested that excessive Zn²⁺ released and high reactive oxygen species (ROS) production might be mainly responsible for the inhibition of APA induced by ZnO NPs under P-limited conditions, while adjustment of bacterial diversity and improvement of keystone taxa cooperation were the main mechanisms in maintaining APA when subjected to weak toxicity of ZnO NPs in P-replete conditions. Taken together, our results provide insights into the biological feedback mechanism involved in ZnO NPs exposure on the ecological function of periphytic biofilms in different P nutritional conditions.

Influence of a biofilm bioreactor on water quality and microbial communities in a hypereutrophic urban river

Biofilms play an important role in degradation, transformation and assimilation of anthropogenic pollutants in aquatic ecosystems. In this study, we assembled a tubular bioreactor containing a biofilm substrate and aeration device, which was introduced into mesocosms to explore the effects of bioreactor on physicochemical and microbial characteristics of a hypereutrophic urban river. The biofilm bioreactor greatly improved water quality, especially by decreasing dissolved inorganic nitrogen (DIN) concentrations, suggesting that biofilms were the major sites of nitrification and denitrification with an oxygen concentration gradient. The biofilm bioreactor increased the abundance of planktonic bacteria, whereas diversity of the planktonic microbial community decreased. Sequencing revealed that Proteobacteria, Bacteroidetes, Planctomycetes, and Actinobacteria were the four predominant phyla in the planktonic microbial community, and the presence of the biofilm bioreactor increased the relative abundance of Proteobacteria. Variations in microbial communities were most strongly affected by the presence of the biofilm bioreactor, as indicated by principal component analysis (PCA) and redundancy analysis (RDA). This study provides valuable insights into changes in ecological characteristics associated with self-purification processes in hypereutrophic urban rivers, and may be of important for the application of biofilm bioreactor in natural urban river.

Facilitating harmful algae removal in fresh water via joint effects of multi-species algicidal bacteria

Harmful algae blooms posing serious threats to the ecological environment occur frequently across the world. Multi-species algicidal bacteria were enriched by utilizing immobilized carriers in a pilot scale experiment, which significantly promoted the effect of algal control in the reactors. Under the optimal condition, the algicidal ratio and chlorophyll a degradation rate reached 87.69% and 47.00 μg/(L·d), respectively. The growth of Cyanophyta, diatom, Dinoflagellate and Cryptophyta was inhibited significantly by the joint action of algicidal bacteria and light shading of fillers, accounting for 53.74% and 36.47%, respectively. The results of 16S rRNA high-throughput sequencing suggested algicidal bacteria (10.17%) belonging to 13 genera were enriched. Among the algicidal process, Bacillus and Pseudomonas played crucial roles. Fluorescence spectroscopy and UV₂₅₄ were adopted to assess the release of dissolved organic matter (DOM) and the precursors of disinfection by-products (DBPs). Two efficient algicidal strains (C1, C4) were isolated which showed high homology with Enterobacter asburiae JCM6051(T) and Pseudomonas simiae oli(T), respectively. This study provided new insights into the in-situ bioremediation of eutrophication in fresh water.

Distinct microbial metabolic activities of biofilms colonizing microplastics in three freshwater ecosystems

Concerns are growing about the increasing amounts of microplastics (MPs) and their ecological impacts, especially the influences of "plastisphere" in the freshwater ecosystems. Although the microbial structure and composition of biofilms are investigated, knowledge of their microbial functions remains limited. Herein, we investigated the functional diversity of carbon metabolism in biofilms colonizing one inert (glass) and two MPs as polyvinyl chloride (PVC) and polyethylene terephthalate (PET) substrates incubated for 44 days in situ in the Niushoushan River, the Qinhuai River, and Donghu Lake. 2D confocal laser scanning microscopy images visualized distinct micro-structures and biofilm compositions on three substrates. BIOLOG ECO microplates indicated variation on carbon utilization capacities of biofilms of inert and MPs in three freshwater ecosystems. Biofilms on PET showed lower capacities and carbon metabolism rates than those on glass and PVC, indicating the presence of substrate-specific functional diversity. The Shannon-Wiener diversity, Simpson diversity and Shannon evenness indices for the Niushoushan River and Donghu Lake were ordered as glass > PVC > PET. Besides to MPs-specific factors, environmental factors including nutrient (i.e., TN and TP) and turbidity largely shaped biofilm carbon metabolism. Overall findings demonstrated that as specific niches, MPs influenced microbial-mediated carbon cycling in the freshwater ecosystems and MPs-promoted microbial communities posed ecological significance.

Advances in research on petroleum biodegradability in soil

With the increased demand for petroleum and petroleum products from all parts of the society, environmental pollution caused by petroleum development and production processes is becoming increasingly serious. Soil pollution caused by petroleum seriously affects environmental quality in addition to human lives and productivity. At present, petroleum in soil is mainly degraded by biological methods. In their natural state, native bacteria in the soil spontaneously degrade petroleum pollutants that enter the soil; however, when the pollution levels increase, the degradation rates decrease, and it is necessary to add nutrients, dissolved oxygen, biosurfactants and other additives to improve the degradation ability of the native bacteria in the soil. The degradation process can also be enhanced by adding exogenous petroleum-degrading bacteria, microbial immobilization technologies, and microbial fuel cell technologies.

Iron coupling with carbon fiber to stimulate biofilms formation in aerobic biological film systems for improved decentralized wastewater treatment: Performance, mechanisms and implications

Iron coupling with carbon fiber (ICF) as carriers to stimulate the biofilms formation for decentralized wastewater treatment was proposed. The typical pollutants removal was accelerated and enhanced (increased by 13.65% for chemical oxygen demand, 19.68% for ammonia nitrogen and 32.66% for phosphate) in ICF compared with the traditional carbon fiber (CF) system. Mechanism explorations indicated that the iron coupling improved the surface properties of carbon fibers and contributed to the attachment and growth of biomass significantly. The components of biomass were changed with increasing proteins proportion in ICF, which was beneficial to the biofilms formation and stability. The microbial community was altered with the enrichment of functional microorganisms (i.e. Pseudomonas and Thauera). Moreover, the microbial metabolic functions (i.e. enzymatic activities and encoding genes) involved in pollutants removal derived from decentralized wastewater were highly expressed in ICF. This work provided an effective strategy to enhance the decentralized wastewater treatment.

Microbial carbon metabolic functions of biofilms on plastic debris influenced by the substrate types and environmental factors

As an artificial type of microbial carrier, plastic debris has been widely detected in freshwater habitats, and the potential impacts of the plastisphere (biofilms colonized on plastics) in aquatic ecosystems have drawn increasing attention. Distinct community compositions and structures of biofilms in plastic and natural substrates have been recorded in freshwater environments. However, the microbial metabolic functioning of the plastisphere was underestimated, especially in freshwater environments. In this study, the effects of substrate types on the carbon metabolic functions of biofilms were studied by in situ cultivation of biofilms on plastics (polyvinyl chloride, PVC and polyethylene, PE) and natural substrate (cobblestone) for 44 days in two rivers (the Niushoushan River and the Qinhuai River) and two lakes (Donghu Lake and Xuanwu Lake). Biofilms on plastics showed higher biomasses than those on natural substrates in all ecosystems. Variations in the micro-structure and compactness of biofilms developed under different substrates were observed from scanning electron microscope and confocal laser scanning microscope image analyses. The carbon metabolic activities of the biofilms evaluated by BIOLOG EcoPlate were different between plastics (PVC and PE) and natural substrate (cobblestone) in the four freshwater ecosystems. In the Niushoushan River, PE-associated biofilms had different capacity in using carbon sources from cobblestone-associated biofilms as illustrated by the Shannon-Wiener diversity index and Shannon evenness index. Additionally, the metabolic functional diversity profiles of biofilms on PVC were significantly different from those on cobblestone in the other three aquatic ecosystems. Moreover, results from variation partitioning analysis suggested that the impact of environmental factors (contribution: 21%) on microbial carbon metabolic functions was much greater than that of substrate types (contribution: 6%). These findings illustrated distinct microbial functions of biofilms inhabited on plastics, and environmental factors play a decisive role in the differentiation and specificity of carbon metabolism of the plastisphere. This study offers new insights that plastics serving as artificial microbial niches have the ability to affect the microbial-mediated carbon cycling process in aquatic ecosystems.

Pollutant removal from agricultural drainage water using a novel double-layer ditch with biofilm carriers

Agricultural drainage ditches can prevent flooding and mitigate agricultural pollution; however, the performance is unsatisfactory in plateau areas like the Dianchi Lake basin. Thus, a novel double-layer ditch system (DDS) with a fibrous packing as biofilm carriers was developed to form the carrier-attached biofilms and enhance the pollutant removal. The results indicated the DDS performed better than a single-layer ditch system, and annual average removal efficiencies of TN, NO₃^--N, NH₄⁺-N, TP, COD and SS were 18.61%, 17.13%, 7.74%, 11.90%, 11.95% and 23.71%, respectively. High amount and carbon, nitrogen and phosphorus contents of biofilms are favourable to pollutant removal by DDS. Although bacterial diversity of biofilms remained relatively stable throughout the year, the relative abundance of dominant assemblages varied greatly. Denitrifying microorganisms affiliated with Bacteroidetes might contribute to effective NO₃^--N reduction. This study demonstrates DDS performed well and provides a novel method for application of biofilm carriers in drainage ditches.

Kerr P, Ali S, Sultana N, Jia Z. Multifunctional Periphytic Biofilms: Polyethylene Degradation and Cd2+ and Pb2+ Bioremediation under High Methane Scenario

Priority pollutants such as polyethylene (PE) microplastic, lead (Pb²⁺), and cadmium (Cd²⁺) have attracted the interest of environmentalists due to their ubiquitous nature and toxicity to all forms of life. In this study, periphytic biofilms (epiphyton and epixylon) were used to bioremediate heavy metals (HMs) and to biodegrade PE under high (120,000 ppm) methane (CH₄) doses. Both periphytic biofilms were actively involved in methane oxidation, HMs accumulation and PE degradation. Epiphyton and epixylon both completely removed Pb²⁺ and Cd²⁺ at concentrations of 2 mg L⁻¹ and 50 mg L⁻¹, respectively, but only partially removed these HMs at a relatively higher concentration (100 mg L⁻¹). Treatment containing 12% ¹³CH₄ proved to be most effective for biodegradation of PE. A synergistic effect of HMs and PE drastically changed microbial biota and methanotrophic communities. High-throughput 16S rRNA gene sequencing revealed that Cyanobacteria was the most abundant class, followed by Gammaproteobacteria and Alphaproteobacteria in all high-methane-dose treatments. DNA stable-isotope probing was used to label ¹³C in a methanotrophic community. A biomarker for methane-oxidizing bacteria, pmoA gene sequence of a ¹³C-labeled fraction, revealed that Methylobacter was most abundant in all high-methane-dose treatments compared to near atmospheric methane (NAM) treatment, followed by Methylococcus. Methylomonas, Methylocystis, Methylosinus, and Methylocella were also found to be increased by high doses of methane compared to NAM treatment. Overall, Cd⁺² had a more determinantal effect on methanotrophic activity than Pb²⁺. Epiphyton proved to be more effective than epixylon in HMs removal and PE biodegradation. The findings proved that both epiphyton and epixylon can be used to bioremediate HMs and biodegrade PE as an efficient ecofriendly technique under high methane concentrations.

Periphyton has the potential to increase phosphorus use efficiency in paddy fields

The phosphorus (P) supply is mismatched with rice demand in the early and late stages of rice growth, which primarily results in low P use efficiency and high environmental risk. In recent years, the use of the natural periphyton in nutrient regulation in paddy fields has attracted much research interest. However, a mechanistic understanding of the action of periphyton on P biogeochemical cycling during the pivotal stages of rice growth has received little attention. In this study, the influence of periphyton proliferation on the soil surface and its consequential decomposition on P migration and bioavailability were investigated in two paddy soils using two microcosm experiments. The results showed that periphyton rapidly accumulated fertilizer P when it proliferated on the soil surface under favorable light condition, which led to more fertilizer P being stored on the soil surface and less P being fixed by soil particles or transported via runoff into the water bodies. The decomposition of periphyton under unfavorable light condition not only increased soil soluble reactive P, but also increased the amount of easily available P species, such as labile P, AlP, FeP, and mobilized OP. Thus, periphyton colonizing the soil surface in the early stage of rice growth could act as a P sink and decrease the P environmental risk, and its decomposition in the late stage of rice growth could act as a P source and activator. Phosphorus bioavailability regulated by periphyton could be synchronous with rice needs. Thus, periphyton has the potential to increase P use efficiency in paddy fields.

Pollutant removal performance and microbial enhancement mechanism by water-lifting and aeration technology in a drinking water reservoir ecosystem

Here, the performance and mechanism of pollutant removal in the Zhoucun reservoir by water-lifting and aeration systems (WLAs) were explored. The hypolimnion anoxic layer disappeared and the reservoir was mixed after the WLAs were operated for approximately 35 days, providing a suitable environment for pollutant removal. Operation of the system enhanced the metabolic activity of the water microbes and their capacity for purification, which contributed to the removal of nitrogen, organic carbon, Fe, Mn, P, and S. Specifically, the total N concentration decreased from 2.55 to 0.48 mg/L, showing an 81.18% removal rate. Microbial metabolism and the diversity index increased following the operation of the WLAs in the Zhoucun Reservoir. Furthermore, the water reservoir clearly inhibited the performance of Fe, Mn, P, and S through the WLA operation, meeting the requirements for class III based on the Chinese Surface Water Environmental Quality Standard (GB3838-2002). High-throughput sequencing analysis revealed increased levels of indicator and keystone operational taxonomic units belonging to Flavobacterium, hgcI_clade, Rheinheimera, Dechloromonas, Pseudomonas, and Rhodocyclaceae, which are related to the degradation of organic carbon and removal of nitrogen and phosphorus. Moreover, total N, ammonia, total P, dissolved oxygen, temperature, and pH were the principal factors affecting the microbial community based on redundancy analysis and the Mantel test. Furthermore, network analysis showed that symbiotic relationships accounted for the major proportion of the microbial network. Our results provide a theoretical foundation for the efficiency of N removal and essential technical support for improving the self-repair capacity of water in drinking water reservoirs.

Responses of Periphyton Microbial Growth, Activity, and Pollutant Removal Efficiency to Cu Exposure

Periphyton is an effective matrix for the removal of pollutants in wastewater and has been considered a promising method of bioremediation. However, it still needs to be verified whether periphyton can maintain microbial activity and pollutant removal efficiency when dealing with the influence with complex components, and the underlying mechanisms of periphyton need to be revealed further. Herein, this study investigated the microbial growth, activity and functional responses of periphyton after removal of Cu from wastewater. Results showed that the cultivated periphyton was dominated by filamentous algae, and high Cu removal efficiencies by periphyton were obtained after 108 h treatments. Although 2 mg/L Cu²⁺ changed the microalgal growth (decreasing the contents of total chlorophyll-a (Chla), the carbon source utilization and microbial metabolic activity in periphyton were not significantly affected and even increased by 2 mg/L Cu²⁺. Moreover, chemical oxygen demand (COD) removal rates were sustained after 0.5 and 2 mg/L Cu²⁺ treatments. Our work showed that periphyton had strong tolerance and resistance on Cu stress and is environmentally friendly in dealing with wastewater containing heavy metals, as the microbial functions in pollutant removal could be maintained.

Metal distribution and biological diversity of crusts in paddy fields polluted with different levels of cadmium

The paddy-crusts (PCs) play an important pole in the transformation and transfer of heavy metal in paddy. Different PCs were collected from paddy fields whose soils contained cadmium (Cd) at four concentration levels (0.61, 0.71, 1.53, and 7.08 mg/kg) in Hunan Province, China P.R. at Sep 2017. This metal's distribution among and biological community structures of PCs were both measured. Our results indicated that PCs were able to accumulate Cd from irrigation water and soil. With greater Cd levels in paddy fields, the weak EPS-binding Cd fraction decreased whereas the non-EDTA-exchangeable Cd fraction increased. The sorbed Cd fraction was initially enhanced at low-to mid-level Cd concentrations, but then gradually declined. Biomineralization was shown to function as the dominant Cd accumulation mechanism in non-EDTA-exchangeable fractions. The biological diversity of soil microbes decreased with more Cd in soil, and the Proteobacteria, Bacteroidetes, and Cyanobacteria were the dominant phyla in all the sampled PCs. Canonical correspondence analysis (CCA) between the composition of microbial communities and soil chemical variables in the PCs clustered all samples based on the Cd-contaminated level, and demonstrated that Cd, Mn, and Fe all significantly influenced the microbial communities. In particular, the Alphaproteobacteria and Chloroplast classes of bacteria may play a significant role in Cd accumulation via the bio-mineralization process. Taken together, our results provide basic empirical information to better understand the heavy metal speciation transformation mechanisms of PCs upon Cd-contaminated paddy fields.

Reducing the Phytoplankton Biomass to Promote the Growth of Submerged Macrophytes by Introducing Artificial Aquatic Plants in Shallow Eutrophic Waters

Harmful cyanobacterial blooms frequently occur in shallow eutrophic lakes and usually cause the decline of submerged vegetation. Therefore, artificial aquatic plants (AAPs) were introduced into enclosures in the eutrophic Dianchi Lake to investigate whether or not they could reduce cyanobacterial blooms and promote the growth of submerged macrophytes. On the 60th day after the AAPs were installed, the turbidity, total nitrogen (TN), total phosphorous (TP), and the cell density of phytoplankton (especially cyanobacteria) of the treated enclosures were significantly reduced as compared with the control enclosures. The adsorption and absorption of the subsequently formed periphyton biofilms attached to the AAPs effectively decreased nutrient levels in the water. Moreover, the microbial diversity and structure in the water changed with the development of periphyton biofilms, showing that the dominant planktonic algae shifted from Cyanophyta to Chlorophyta. The biodiversity of both planktonic and attached bacterial communities in the periphyton biofilm also gradually increased with time, and were higher than those of the control enclosures. The transplanted submerged macrophyte (Elodea nuttallii) in treated enclosures recovered effectively and reached 50% coverage in one month while those in the control enclosures failed to grow. The application of AAPs with incubated periphyton presents an environmentally-friendly and effective solution for reducing nutrients and controlling the biomass of phytoplankton, thereby promoting the restoration of submerged macrophytes in shallow eutrophic waters.

Functional sustainability of periphytic biofilms in organic matter and Cu2+ removal during prolonged exposure to TiO2 nanoparticles

Responses of microbial communities to nanotoxicity in aquatic ecosystems are largely unknown, particularly with respect to relationship between community dynamics and functions. Here, periphytic biofilms were selected as a model of species-rich microbial communities to elucidate their responses when exposed to titanium dioxide nanoparticles (TiO₂-NPs). Especially, the relationships between the functions (e.g. organic matter and Cu²⁺ removal) and community dynamics after long-term exposure to TiO₂-NPs were assessed systematically. After 5days exposure to TiO₂-NPs (5mgL^-1), periphytic biofilms showed sustainable functions in pollutant removal and strong plasticity in defensing the toxic disturbance of TiO₂-NPs, including photosynthesis and carbon metabolic diversity. The sustainable pollutant removal functions of periphytic biofilms were attributed to their functional redundancy. Specifically, periphytic biofilms altered their composition with cyanobacteria, Sphingobacteriia and Spirochaetes being the newly dominant taxa, and changed the carbon substrate utilization pattern to maintain high photosynthesis and metabolic rates. Moreover, extracellular polymeric substances (EPS) especially proteins were overproduced to bind the NPs and thereby reduce the nanotoxicity. The information obtained in this study may greatly help to understand the interactions between microbial community dynamics and function under NPs exposure conditions and functional redundancy is an important mechanism of periphytic biofilms to maintain sustainable functions.

Advances in the technologies for studying consortia of bacteria and cyanobacteria/microalgae in wastewaters

The excessive generation and discharge of wastewaters have been serious concerns worldwide in the recent past. From an environmental friendly perspective, bacteria, cyanobacteria and microalgae, and the consortia have been largely considered for biological treatment of wastewaters. For efficient use of bacteria‒cyanobacteria/microalgae consortia in wastewater treatment, detailed knowledge on their structure, behavior and interaction is essential. In this direction, specific analytical tools and techniques play a significant role in studying these consortia. This review presents a critical perspective on physical, biochemical and molecular techniques such as microscopy, flow cytometry with cell sorting, nanoSIMS and omics approaches used for systematic investigations of the structure and function, particularly nutrient removal potential of bacteria‒cyanobacteria/microalgae consortia. In particular, the use of specific molecular techniques of genomics, transcriptomics, proteomics metabolomics and genetic engineering to develop more stable consortia of bacteria and cyanobacteria/microalgae with their improved biotechnological capabilities in wastewater treatment has been highlighted.

Augmenting nitrogen removal by periphytic biofilm strengthened via upconversion phosphors (UCPs)

The application of periphytic biofilm in removing nitrogen from water is limited by the fluctuating nitrogen concentration. Here, we delineate a novel approach to enhance periphytic biofilm performance in nitrogen removal via upconversion luminescence of upconversion phosphors (UCPs). Nitrogen removal rates (14 d) in high nitrogen wastewater (26 mg/L) were significantly improved to 58.6% and 61.4% by UCPs doped with Pr³⁺ and Li⁺ and UCPs doped with Pr³⁺, respectively, and to 95.1% and 95.9% in low nitrogen surface water (2 mg/L), respectively. The stimulation of UCPs optimized the microbial community structure in the periphytic biofilms, and also resulted in good acclimation to use different carbon sources. The enhanced synergic action of cyanobacterial biomass, ratio of Gram +ve to Gram -ve bacteria and carbon source metabolic capacity contributed to the improved nitrogen removal. This novel approach is promising in nitrogen removal from wastewater and surface water with fluctuating initial nitrogen concentration.

Water quality in simulated eutrophic shallow lakes in the presence of periphyton under different flow conditions

Although the effects of periphyton on water quality and its relationship with flow conditions have been studied by researchers, our understanding about their combined action in eutrophic shallow lakes is poor. In this research, four aquatic model ecosystems with different water circulation rates and hydraulic conditions were constructed to investigate the effect of periphyton and flow condition on water quality. The concentrations of NH₄⁺, TP, and chlorophyll-a and flow conditions were determined. The results show that, as a result of the rising nutrient level at the early stage and the decline in the lower limit, the presence of periphyton can make the ecosystem adaptable to a wider range of nutrients concentration. In terms of the flow condition, the circulation rate and hydraulic condition are influential factors for aquatic ecosystem. Higher circulation rate in the ecosystem, on one hand, facilitates the metabolism by accelerating nutrient cycling which is beneficial to water quality; on the other hand, high circulation rate leads to the nutrient lower limit rising which is harmful to water quality improvement. At low velocities, slight differences in hydraulic conditions, vertical velocity gradient and turbulence intensity gradient could affect the quantity of phytoplankton. Our study suggests that, considering environmental effect of periphyton, flow conditions and their combined action is essential for water quality improvement and ecological restoration in eutrophic shallow lakes.

Influence of light and temperature on the development and denitrification potential of periphytic biofilms

Periphytic biofilms are microbial aggregates commonly present in submerged aquatic environments and play a significant role in nutrient cycling. In recent years, utilization of natural periphytic biofilms in wastewater treatment and water restoration attracts growing research interests. Light and temperature are two important environmental factors known to affect the development of periphytic biofilms and can be manipulated for the regulation of the biofilm properties. In this work, effects of light and temperature on the development and function (denitrification potential) of periphytic biofilms were investigated using a microcosm experiment. Results showed that thicker periphytic biofilms with higher Chlorophyll a, extracellular polymeric substances (EPS), and total phosphorus contents were developed under higher temperature. Whereas, biomass accumulation was more rapid for periphytic biofilms under higher irradiance. The denitrification potential rate was negatively associated with irradiance, which can be linked to the influence of irradiance on biofilm structure and microbial composition. A relatively lower irradiance is recommended when using periphytic biofilms in nitrogen removal from wastewater.

Cu removal and response mechanisms of periphytic biofilms in a tubular bioreactor

This work studied Cu removal and response mechanisms of periphytic biofilms in a tubular bioreactor. Periphytic biofilms immobilized in a tubular bioreactor were used to remove Cu from wastewater with different Cu concentrations. Results showed that periphytic biofilms had a high removal efficiency (max. 99%) at a hydraulic retention time (HRT) of 12h under initial Cu concentrations of 2.0 and 10.0mgL^-1. Periphyton quickly adapted to Cu stress by regulating the community composition. Species richness, evenness and carbon metabolic diversity of the periphytic community increased when exposed to Cu. Diatoms, green algae, and bacteria (Gammaproteobacteria and Bacteroidia) were the dominant microorganisms and responsible for Cu removal. This study indicates that periphytic biofilms are promising in Cu removal from wastewater due to their strong adaptation capacity to Cu toxicity and also provides valuable information for understanding the relationships between microbial communities and heavy metal stress.

Microorganisms-based methods for harmful algal blooms control: A review

Harmful algal blooms (HABs) are a worldwide problem with numerous negative effects on water systems, which have prompted researchers to study applicable measures to inhibit and control them. This review summarized the current microorganisms-based methods or technologies aimed at controlling HABs. Based on their characteristics, these methods can be divided into two categories: methods based on single-species microorganisms and methods based on microbial aggregates, and four types: methods for rapid decrease of algal cells density (e.g., alga-bacterium and alga-fungus bioflocculation), inhibition of harmful algal growth, lysis of harmful algae (e.g. algicidal bacteria, fungi, and actinomycete), and methods based on microbial aggregates (periphytons and biofilms). An integrative process of "flocculation-lysis-degradation-nutrients regulation" is proposed to control HABs. This review not only offers a systematic understanding of HABs control technologies based on microorganisms but also elicits a re-thinking of HABs control based on microbial aggregates.

Arsenic removal by periphytic biofilm and its application combined with biochar

A biochar and periphyton-based system (BPS) comprising of a biochar column and a periphyton bioreactor was designed to avoid the toxicity issue associated with removing As(III) from wastewater. Results showed that the periphyton can grow when As(III) is less than 5.0mgL^-1. The BPS obtained a high As(III) removal rate (∼90.2-95.4%) at flow rate=1.0mLmin^-1 and initial concentration of As(III)=2.0mgL^-1. About 60% of the As(III) was pre-treated (adsorbed) in the biochar column and the removal of the remaining As(III) was attributed to the periphyton bioreactor. The As(III) removal process by periphytic biofilm in the initial stage fits a pseudo-second-kinetic model. The calcite in the periphytic biofilm surfaces and the OH and CO groups were responsible for the As(III) removal. This study indicates the feasibility of the BPS for As(III) removal in practice.

Removal of nutrients and pharmaceuticals and personal care products from wastewater using periphyton photobioreactors

In this work, periphyton photobioreactors were built and were used for the treatment of synthetic wastewater spiked with PPCPs under different operational conditions. The removal rates of total nitrogen were relatively stable and varied from 39% to 77% overtime in different treatments. However, the removal rates of soluble reactive phosphorus decreased overtime from 42% to 68% on day 2 to 15.8% to 44% on day 22. For the selected PPCPs, only bisphenol A was effectively removed (72%-86.4%), hydrochlorothiazide and ibuprofen were moderately removed (26.2%-48.7%), and carbamazepine and gemfibrozil were poorly removed (6.45%-20.6%). Longer hydraulic retention time enhanced the treatment efficiency but illumination period showed contrasting effects on the removal of the nutrients and the PPCPs.

Phosphorus and Cu2+ removal by periphytic biofilm stimulated by upconversion phosphors doped with Pr3+-Li. BIORESOURCE TECHNOLOGY 2018;248:68-74. [PMID: 28734589 DOI: 10.1016/j.biortech.2017.07.027]

Upconversion phosphors (UCPs) can convert visible light into luminescence, such as UV, which can regulate the growth of microbes. Based on these fundamentals, the community composition of periphytic biofilms stimulated by UCPs doped with Pr³⁺-Li⁺ was proposed to augment the removal of phosphorus (P) and copper (Cu). Results showed that the biofilms with community composition optimized by UCPs doped with Pr³⁺-Li⁺ had high P and Cu²⁺ removal rates. This was partly due to overall bacterial and algal abundance and biomass increases. The synergistic actions of algal, bacterial biomass and carbon metabolic capacity in the Pr-Li stimulated biofilms facilitated the removal of P and Cu²⁺. The results show that the stimulation of periphytic biofilms by lanthanide-doped UCPs is a promising approach for augmenting P and Cu²⁺ removal.

Sustainable pollutant removal by periphytic biofilm via microbial composition shifts induced by uneven distribution of CeO2 nanoparticles

The responses of periphytic biofilm to CeO₂ nanoparticle (CNP) exposure were explored by investigating community shifts and pollutant removal. Results showed that CNPs entered the sensitive microbial cells in the periphytic biofilm, leading to cytomembrane damage and intracellular reactive oxygen species (ROS) generation. The periphytic biofilm communities were, however, able to adapt to the prolonged exposure and maintain their pollutant removal (i.e., phosphorus, nitrogen and copper, organic matter) performance. Observations under synchrotron radiation scanning transmission X-ray microscopy revealed that fewer CNPs were distributed in algal cells compared to bacterial cells, wherein the transformation between Ce(IV) and Ce(III) occurred. High-throughput sequencing further showed that the proportion of algae, such as Leptolyngbya and Nostoc, significantly increased in the periphytic biofilm exposed to CNPs while the proportion of bacteria, such as Bacilli and Gemmatimonadetes, decreased. This change in community composition might be the primary reason for the sustained pollutant removal performance of the periphytic biofilm.

Mechanisms of enhanced inorganic phosphorus accumulation by periphyton in paddy fields as affected by calcium and ferrous ions

The effect of periphyton propagation in paddy fields on phosphorus biogeochemical cycling has received little attention. In this phytotron study, inorganic phosphorus (P_i) accumulation by periphyton was investigated for varying inputs of calcium [Ca(II)] or ferrous‑iron [Fe(II)], and lighting conditions. Results indicated that additions of Ca(II) or Fe(II) enhanced abiotic accumulation of P_i by up to 16 times, and decreased solution P_i concentration by up to 50%, especially under light condition. The enhanced P_i accumulation into periphyton intensified with increasing P_i concentration, and P_i accumulation showed a positive linear relationship with Ca or Fe accumulation. Abiotic accumulation of P_i induced by Ca(II) was mainly through Ca-phosphate precipitation, and co-precipitation of P with carbonates at pH>8. Accumulation with added Fe(II) was mainly considered to be through Fe(III) phosphate precipitation coupled with adsorption of P_i by ferric hydroxides. Moreover, Fe(II) was more effective than Ca(II) in promoting abiotic accumulation of P_i by periphyton. Our results indicate the potential for controlling environmental factors to enhance the role of periphyton in biogeochemical cycling and P-use efficiency in paddy rice fields and to reduce P discharged to neighboring water bodies.

Current research scenario for microcystins biodegradation - A review on fundamental knowledge, application prospects and challenges

Microcystins (MCs) are common cyanotoxins produced by harmful cyanobacterial blooms (HCBs) and severely threaten human and ecosystems health. Biodegradation is an efficient and sustainable biological strategy for MCs removal. Many novel findings in fundamental knowledge and application potential of MC-biodegradation have been documented. Little effort has devoted to summarize and comment recent research progress on MC-biodegradation, and discuss the research problems and gaps. This review deals with current research scenario in aerobic and anaerobic biodegradation for MCs. Diverse organisms capable of degrading MCs are encapsulated. Enzymatic mechanisms and influence factors regulating aerobic and anaerobic MC-biodegradation are summarized and discussed, which are essential for assessing and reducing MC-risks during HCBs episodes. Also, we propose some ideas to solve the challenges and bottleneck problems in practical application of MC-biodegradation, and discuss research gaps and promising research methods which deserve special attention. This review may provide new insights on future direction of MC-biodegradation research, in order to further broaden its application prospects for bioremediation.

Nano-cerium oxide functionalized biochar for phosphate retention: preparation, optimization and rice paddy application

In this study, nano-cerium oxide functionalized maize straw biochar (Ce-MSB) was prepared and utilized to remove P from agricultural wastewater. Response Surface Model was applied to optimize the operating conditions. Moreover, Ce-MSB was applied to actual rice paddy column for the first time. Response Surface Model (RSM) showed higher materials ratio had positive effect on PO₄^3- adsorption capacity, while higher pyrolysis temperature had negative effect. The maximum adsorption capacity of Ce-MSB for PO₄^3- was 78 mg g^-1, implying that Ce-MSB was an effective functionalized adsorbent for P removal. Paddy soil column experiment showed that application of Ce-MSB decreased total phosphorus concentration of surface water by 27.33% and increased total phosphors (TP) content of top soil by 7.22%. Further, Ce-MSB tends to increase rice plant height and leaf area. Therefore, Ce-MSB can be used as a promising functionalized biochar to reduce the risk of phosphorus loss from paddy field surface running water.

Advanced nutrient removal from surface water by a consortium of attached microalgae and bacteria: A review

Innovative and cost-effective technologies for advanced nutrient removal from surface water are urgently needed for improving water quality. Conventional biotechnologies, such as ecological floating beds, or constructed wetlands, are not effective in removing nutrients present at low-concentration. However, microalgae-bacteria consortium is promising for advanced nutrient removal from wastewater. Suspended algal-bacterial systems can easily wash out unless the hydraulic retention time is long, attached microalgae-bacteria consortium is more realistic. This critical review summarizes the fundamentals and status of attached microalgae-bacteria consortium for advanced nutrient removal from surface water. Key advantages are the various nutrient removal pathways, reduction of nutrients to very low concentration, and diversified photobioreactor configurations. Challenges include poor identification of functional species, poor control of the community composition, and long start-up times. Future research should focus on the selection and engineering of robust microbial species, mathematical modelling of the composition and functionality of the consortium, and novel photobioreactor configurations.

Responses of Periphyton to Fe2O3 Nanoparticles: A Physiological and Ecological Basis for Defending Nanotoxicity

The toxic effects of nanoparticles on individual organisms have been widely investigated, while few studies have investigated the effects of nanoparticles on ubiquitous multicommunity microbial aggregates. Here, periphyton as a model of microbial aggregates, was employed to investigate the responses of microbial aggregates exposed continuously to Fe₂O₃ nanoparticles (5.0 mg L^-1) for 30 days. The exposure to Fe₂O₃ nanoparticles results in the chlorophyll (a, b, and c) contents of periphyton increasing and the total antioxidant capacity decreasing. The composition of the periphyton markedly changes in the presence of Fe₂O₃ nanoparticles and the species diversity significantly increases. The changes in the periphyton composition and diversity were due to allelochemicals, such as 3-methylpentane, released by members of the periphyton which inhibit their competitors. The functions of the periphyton represented by metabolic capability and contaminant (organic matter, nitrogen, phosphorus and copper) removal were able to acclimate to the Fe₂O₃ nanoparticles exposure via self-regulation of morphology, species composition and diversity. These findings highlight the importance of both physiological and ecological factors in evaluating the long-term responses of microbial aggregates exposed to nanoparticles.

Evaluating role of immobilized periphyton in bioremediation of azo dye amaranth

The aim of this study was to evaluate the bioremediation capabilities of three kinds of periphyton (i.e. epiphyton, metaphyton and epilithon) immobilized in bioreactors to decolorize and biodegrade the sulphonated azo dye, amaranth. Results showed that periphyton dominated by phyla including Cyanobacteria, Proteobacteria and Bacteroidetes. Complete removal of dye was shown by all the biofilms periphyton (epiphyton showed highest removal efficacy) over a range of initial concentrations (50-500mgL^-1) within 84h at pH 7 and 30°C. Biodegradation of amaranth was confirmed through FTIR and HPLC and the biodegradation pathways were detected by GC-MS/MS analysis. The azo bonds in the amaranth were successfully broken by periphyton and amaranth was converted to non-toxic, aliphatic compounds including isobutene, acetyl acetate and ethyl acetate. The results showed the potential application of immobilized periphyton at industrial scale for the removal of azo dyes from wastewater containing azo dye amaranth.

Removal of parabens and their chlorinated by-products by periphyton: influence of light and temperature

The extensive use of parabens as preservatives in food and pharmaceuticals and personal care products results in frequent detection of their residuals in aquatic environment. In this work, the adsorption and removal of four parabens (methyl-, ethyl-, propyl-, and butyl-paraben) and two chlorinated methyl-parabens (CMPs) by periphyton were studied. Characteristics of the periphyton were identified to explore the possible relationship between paraben removal and periphyton properties. Results showed that linear adsorption coefficients (K _d) vary from 554.4 to 808.6 L kg^-1 for the adsorption parabens and CMPs to autoclaved periphyton. The adsorption strength is positively related to the hydrophobicity of these compounds. Removal of parabens from water by periphyton was efficient with half-life (t _1/2) values estimated using first-order kinetic model ranging from 0.49 to 3.29 days, but CMPs were more persistent with t _1/2 ranging from 1.15 to 25.57 days, and t _1/2 increased with the chlorination degree. Higher incubation temperature accelerated the removal of all tested compounds, while a better removal of CMPs was observed in dark condition. Analysis of periphyton properties suggests that bacteria played a more important role in the removal of CMPs, but no specific relationship between periphyton properties and paraben removal ability can be established.

Periphyton biofilms: A novel and natural biological system for the effective removal of sulphonated azo dye methyl orange by synergistic mechanism

Due to their large scale use, azo dyes are adversely affecting aquatic fauna and flora as well as humans. The persistent nature of sulphonated azo dyes makes them potential ecotoxic hazards. The aim of the present study was to employ a proficient, locally available biomaterial, viz. periphyton (i.e. epiphyton, epilithon or metaphyton), for removal of the azo dye, methyl orange (MO). Results showed that the periphytic biofilms are capable of completely removing comparatively high concentrations (up to 500 mg L^-1) of MO from wastewater. The removal of MO occurs by a synergistic mechanism involving bioadsorption and biodegradation processes. The adsorption of MO by periphyton can be described by pseudo-second order kinetics. Elovich and intraparticle diffusion models as well as Langmuir equations fit well to the MO adsorption process. FTIR analysis of MO and its metabolites demonstrated biotransformation into simpler compounds within 72 h. GC-MS/MS analysis showed the conversion of MO into simpler compounds such as phenol, ethyl acetate and acetyl acetate. The results indicated that periphyton is a promising biomaterial for the complete removal of MO from wastewater and that the treatment process has the potential for in situ removal of MO at contaminated sites.