Potential of hydrolyzed polyacrylamide biodegradation to final products through regulating its own nitrogen transformation in different dissolved oxygen systems

Characterization and degradation mechanism of a newly isolated hydrolyzed polyacrylamide-degrading bacterium Alcaligenes faecalis EPDB-5 from the oilfield sludge

Hydrolyzed polyacrylamide (HPAM) is posing serious threats to ecosystems. However, biodegradation is an effective method to remove HPAM owing to its low cost and environmental friendliness. In this study, Alcaligenes faecalis EPDB-5 was isolated as a highly efficient HPAM degrading strain from sludge contaminated with polymerized produced water from Daqing oilfield. Under the optimal conditions, the strain EPDB-5 demonstrated an impressive HPAM degradation rate of 86.05%, the total nitrogen (TN) removal of 71.96% and chemical oxygen demand (COD) removal of 67.98%. Meanwhile, it can maintain a stable degradation rate higher than 75% under different pH and temperature conditions. 27 genes that play a key role in HPAM degradation were annotated by metagenomics sequencing. The key genes were involved in multiple KEGG pathways, including biofilm formation, biosynthesis secondary metabolites, and metabolic pathways. SEM, GPC, and FTIR analyses revealed that the structure of HPAM after biodegradation showed pores, a significant decrease in molecular weight, -NH2 detachment, and carbon chain breakage. Particularly, we propose a possible mechanism of biofilm formation - HPAM degradation - biofilm disappearance and reorganization. Moreover, the degradation rate of strain EPDB-5 on real wastewater containing HPAM was 29.97% in only three days. This work expands our knowledge boundary about the HPAM degradation mechanism at the functional gene level, and supports the potential of strain EPDB-5 as a novel auxiliary microbial resource for the practical application of HPAM.

Binding of Anionic Polyacrylamide with Amidase and Laccase under 298, 303, and 308 K: Docking and Molecular Dynamics Simulation Studies Combined with Experiments

Amidase and laccase play a key role in the degradation process of anionic polyacrylamide (HPAM). However, the largest challenge of HPAM enzymatic degradation is whether the enzyme can bind with a substrate for a period of time. Here, the most suitable complexes, namely, Rh Amidase-HPAM-2 and Bacillus subtilis (B. subtilis) laccase-HPAM-3, were obtained by docking, and they were carried out for molecular dynamics simulation (MDS) under 298, 303, and 308 K. MDS result analysis showed that Rh Amidase-HPAM-2 was the most stable at 298 K mainly due to a salt bridge and a hydrogen bond, and B. subtilis laccase-HPAM-3 was the most stable at 298 K mainly due to two electrostatic and hydrogen bonds. The LYS96 in Rh Amidase-HPAM-2 and LYS135 in B. subtilis laccase-HPAM-3 had been the most important in their binding process. The binding of Rh Amidase-HPAM-2 and B. subtilis laccase-HPAM-3 was optimal at 303 and 298 K, respectively. HPAM was degraded by mixed bacteria, and the optimal conditions were determined to be 308 K, initial pH = 7, and an inoculated dosage of 2 mL. Under these conditions, the degradation ratio reached 39.24%. The effect of parameters on the HPAM degradation ratio followed a decreasing order of temperature > initial pH > inoculated dosage. The HPAM codegradation mechanism was supposed by mixed bacteria according to test data. The mixed bacteria secreted both amidase and laccase, and they interacted jointly with HPAM. These results lay a theoretical foundation to design and modify the enzyme through mutation experiments in the future.

Study on potential microbial community to the waste water treatment from bauxite desilication process

Discharging waste water from the bauxite desilication process will bring potential environmental risk from the residual ions and organic compounds, especially hydrolyzed polyacrylamide. Characterization of the microbial community diversity in waste water plays an important role in the biological treatment of waste water. In this study, eight waste water samples from five flotation plants in China were investigated. The microbial community and functional profiles within the waste water were analyzed by a metagenomic sequencing method and associated with geochemical properties. The results revealed that Proteobacteria and Firmicutes were the dominant bacterial phyla. Both phylogenetical and clusters of orthologous groups' analyses indicated that Tepidicella, Paracoccus, Pseudomonas, and Exiguobacterium could be the dominant bacterial genera in the waste water from bauxite desilication process for their abilities to biodegrade complex organic compounds. The results of the microbial community diversity and functional gene compositions analyses provided a beneficial orientation for the biotreatment of waste water, as well as regenerative using of water resources. Besides, this study revealed that waste water from bauxite desilication process was an ideal ecosystem to find novel microorganisms, such as efficient strains for bio-desilication and bio-desulfurization of bauxite.

Hydrolyzed polyacrylamide biotransformation during the formation of anode biofilm in microbial fuel cell biosystem: Bioelectricity, metabolites and functional microorganisms

The anode biofilm serves as the core dominating the performance of microbial fuel cell (MFC) biosystem. This research provides new insights into hydrolyzed polyacrylamide (HPAM) biotransformation during the formation of anode biofilm. The current density, coulombic efficiency, voltage, power density, volatile fatty acid (VFA) production and total nitrogen (TN) removal enhanced with the thickening of biofilm (1-6 cm), and the maximums achieved 146 mA·m^-2, 47.3%, 8.76 V, 1.28 W·m^-2, 184 mg·L^-1 and 84.6%, respectively. HPAM concentration descended from 508 mg·L^-1 to 83.3 mg·L^-1 after 60 days. HPAM was metabolized into VFAs, N₂, NO₂^--N and NO₃^--N, thereby releasing electrons. Laccase and tyrosine/tryptophan protein induced HPAM metabolism and bioelectricity production. The microbial functions involving HPAM biotransformation and bioelectricity generation were clarified. The alternative resource recovery, techno-economic comparison and development direction of MFC biosystem were discussed to achieve the synchronization of HPAM-containing wastewater treatment and bioelectricity generation based on MFC biosystem.

Spotlight on the Life Cycle of Acrylamide-Based Polymers Supporting Reductions in Environmental Footprint: Review and Recent Advances

Humankind is facing a climate and energy crisis which demands global and prompt actions to minimize the negative impacts on the environment and on the lives of millions of people. Among all the disciplines which have an important role to play, chemistry has a chance to rethink the way molecules are made and find innovations to decrease the overall anthropic footprint on the environment. In this paper, we will provide a review of the existing knowledge but also recent advances on the manufacturing and end uses of acrylamide-based polymers following the "green chemistry" concept and 100 years after the revolutionary publication of Staudinger on macromolecules. After a review of raw material sourcing options (fossil derivatives vs. biobased), we will discuss the improvements in monomer manufacturing followed by a second part dealing with polymer manufacturing processes and the paths followed to reduce energy consumption and CO2 emissions. In the following section, we will see how the polyacrylamides help reduce the environmental footprint of end users in various fields such as agriculture or wastewater treatment and discuss in more detail the fate of these molecules in the environment by looking at the existing literature, the regulations in place and the procedures used to assess the overall biodegradability. In the last section, we will review macromolecular engineering principles which could help enhance the degradability of said polymers when they reach the end of their life cycle.

Elucidate microbial characteristics in a full-scale treatment plant for offshore oil produced wastewater

Oil-produced wastewater treatment plants, especially those involving biological treatment processes, harbor rich and diverse microbes. However, knowledge of microbial ecology and microbial interactions determining the efficiency of plants for oil-produced wastewater is limited. Here, we performed 16S rDNA amplicon sequencing to elucidate the microbial composition and potential microbial functions in a full-scale well-worked offshore oil-produced wastewater treatment plant. Results showed that microbes that inhabited the plant were diverse and originated from oil and marine associated environments. The upstream physical and chemical treatments resulted in low microbial diversity. Organic pollutants were digested in the anaerobic baffled reactor (ABR) dominantly through fermentation combined with sulfur compounds respiration. Three aerobic parallel reactors (APRs) harbored different microbial groups that performed similar potential functions, such as hydrocarbon degradation, acidogenesis, photosynthetic assimilation, and nitrogen removal. Microbial characteristics were important to the performance of oil-produced wastewater treatment plants with biological processes.

Treatment of polyacrylamide-polluted wastewater using a revolving algae biofilm reactor: Pollutant removal performance and microbial community characterization

Industries such as oil mining face challenges in the treatment of polyacrylamide (PAM)-containing wastewater produced during petroleum extraction. The feasibility of using revolving algae biofilm (RAB) reactors to treat PAM-contaminated wastewater for simultaneous removal of carbon and nitrogen was evaluated. The presence or absence of external nitrogen sources had a significant impact on the treatment effect of the RAB system. With the additional N source, the PAM, COD, TOC, and TN removal rates were 64.1 ± 2.0, 58 ± 1.5, 34.5 ± 1.5, and 85 ± 6.0%, respectively. High-throughput sequencing showed that the biofilms on RAB reactors contained a variety of bacteria, cyanobacteria, and green algae, degrading PAM through various mechanisms. The results of infrared spectroscopy analysis indicate that the product of these processes was carboxylic acid. Based on these results, it was concluded that RAB systems can be effectively applied to the treatment of polymer-containing wastewater.

Simultaneous removal of nitrogen and dimethyl phthalate from low-carbon wastewaters by using intermittently-aerated constructed wetlands

Phthalic acid esters (PAEs) such as dimethyl phthalate (DMP) have been widely used as a plasticizer in society, which pose severe harm to human health. In this study, the potential of DMP elimination and nitrogen removal from low-carbon wastewaters by intermittently-aerated subsurface flow constructed wetlands (SSFCWs) was evaluated, and the effect of the influent DMP concentrations on nitrogen removal was also investigated. The results showed a better removal of DMP (88.5-97.8%) was obtained in CWs under different influent DMP concentrations, and the high removal of COD (86.7-95.0%) and NH₄⁺-N (95.5-98.7%) was also achieved simultaneously. The maximum TN removal (48.7%) was observed at an influent DMP concentration of 10 mg L^-1. Furthermore, the TN removal and DMP reduction had a good fitting relationship (R² = 0.71) in CWs under different influent DMP concentrations. The analysis of DMP decomposition processes demonstrated that DMP was degraded into some smaller molecular fractions, and DMP degradation intermediates mainly including monomethyl phthalate (MMP) and phthalate (PA), which might provide a potential carbon source for the denitrification processes in CWs. These findings could contribute to a better understanding of DMP removal mechanism and provide useful guidance for the practical application of CWs for treating wastewater containing phthalates.

Acidic pretreatment as a chemical approach for enhanced Photorhabdus temperata bioinsecticide production from industrial wastewater

The chemical treatment of the wastewater used for the bioinsecticide production by the bacterium Photorhabdus temperata was investigated in this study. An improvement of the volatile suspended solids (VSS) solubilization along with an increase in protein, carbohydrate, reducing sugar and nitrogen concentrations were demonstrated after alkali and thermo-alkali hydrolysis. In contrast, the application of acidic and thermo-acidic pretreatments reduced the organic matter hydrolysis. Compared to untreated wastewater, the chemical oxygen demand (COD) solubilization and the heavy metal concentration, except manganese, were enhanced in all the chemically pretreated wastewaters. Although its low contribution in the solubilization of the wastewater organic matter, the acidic-pretreated wastewater showed the highest performance in supporting P. temperata biopesticide production. Indeed, using the acidic-pretreated wastewater as a fermentation medium decreased the lag phase, enhanced the growth of the strain K122 to reach a final biomass production of 20 × 10⁸ cells/mL, increased culturable cell count to 262 × 10⁶ cells/mL and improved oral toxicity against Ephestia kuehniella larvae by 68.4%. Among chemical pretreatments performed, the acidic hydrolysis was demonstrated to be the unique promising one for P. temperata bioinsecticide production due to its ability to reduce aromatic compounds as shown by Gas Chromatography-Mass Spectrometry (GC-MS) analysis.

Biodegradation of anionic polyacrylamide mediated by laccase and amidase: docking, virtual mutation based on affinity and DFT study

The aim of this work was to document the elucidation of a mechanism as a reference.

Parametric Study of Polymer-Nanoparticles-Assisted Injectivity Performance for Axisymmetric Two-Phase Flow in EOR Processes

Among a wide range of enhanced oil-recovery techniques, polymer flooding has been selected by petroleum industries due to the simplicity and lower cost of operational performances. The reason for this selection is due to the mobility-reduction of the water phase, facilitating the forward-movement of oil. The objective of this comprehensive study is to develop a mathematical model for simultaneous injection of polymer-assisted nanoparticles migration to calculate an oil-recovery factor. Then, a sensitivity analysis is provided to consider the significant influence of formation rheological characteristics as type curves. To achieve this, we concentrated on the driving mathematical equations for the recovery factor and compare each parameter significantly to nurture the differences explicitly. Consequently, due to the results of this extensive study, it is evident that a higher value of mobility ratio, higher polymer concentration and higher formation-damage coefficient leads to a higher recovery factor. The reason for this is that the external filter cake is being made in this period and the subsequent injection of polymer solution administered a higher sweep efficiency and higher recovery factor.

Key role of different levels of dissolved oxygen in hydrolyzed polyacrylamide bioconversion: Focusing on metabolic products, key enzymes and functional microorganisms

Dissolved oxygen (DO) played a short board effect on nitrogen biotransformation and pollutant metabolism. This study for the first time explored the key role of different levels of DO (covering anaerobic, anoxic and aerobic) on hydrolyzed polyacrylamide (HPAM) bioconversion. HPAM was metabolized to intermediates with different chain length. Volatile fatty acid (VFA) production rose first and then descended with DO concentration (0-2 mg·L-1), and the maximum reached 92.5 mg·L-1 when DO was 0.5 mg·L-1. Total nitrogen (TN) removal increased first and then dropped with DO concentration, and the maximum (61.4%) occurred at 0.5 mg·L-1 DO. NH4+-N dipped from 42.8 to 0 mg·L-1 and NO3--N rose from 0 to 32.8 mg·L-1 with DO concentration. The changes of enzyme activities were consistent with those of VFA production and TN removal, which were related to HPAM metabolism and N bioconversion. Microbial function was correlated to HPAM metabolism, N bioconversion and key enzyme.

Insights into the effect of different levels of crude oil on hydrolyzed polyacrylamide biotransformation in aerobic and anoxic biosystems: Bioresource production, enzymatic activity, and microbial function

The differences of crude oil recovery ratio resulted in different levels of crude oil in actual hydrolyzed polyacrylamide (HPAM)-containing wastewater. The effect of crude oil on HPAM biotransformation was explored from bioresource production, enzymatic activity and microbial function. In aerobic biosystems, the highest polyhydroxyalkanoate (PHA) yield (19.6%-40.2%) and dehydrogenase (DH) activity (4.06-8.32 mg·g^-1 VSS) occurred in the 48th hour, and increased with crude oil concentration (0-400 mg·L^-1). In anoxic biosystems, the highest PHA yield (24.5%-50.5%) and DH activity (3.24-6.69 mg·g^-1 VSS) occurred in the 72nd hour, and increased with crude oil concentration. The higher substrate removal (38.5%-65.7%) occurred in aerobic biosystems, while the higher PHA accumulation occurred in anoxic biosystems. PHA yield, DH activity and HPAM removal were related. Microbial function related to HPAM biodegradation and PHA synthesis was discussed. The main function of Pseudomonas and Bacillus in aerobic biosystems was to degrade HPAM, and in anoxic biosystems was to synthesize PHA.

Biohydrogen and polyhydroxyalkanoate production from original hydrolyzed polyacrylamide-containing wastewater

This work aimed to study biohydrogen (H₂) and polyhydroxyalkanoate (PHA) production from original hydrolyzed polyacrylamide (HPAM)-containing wastewater. NH₄⁺-N from HPAM hydrolysis was removed efficiently through short-cut nitrification and anoxic ammonia oxidation (anammox). Carbon/Nitrogen (C/N) ratios of effluent reached 51-97, and TOC decreased only 2%-4%, providing potential for subsequent H₂ and PHA production. The maximum yields of H₂ (0.833 mL·mg^-1_substrate) and Volatile Fatty Acid (VFA) (465 mg·L^-1) occurred at influent C/N ratio of 51. Substrate removal increased linearly with the activities of dehydrogenase and hydrogenase (R² ≥ 0.990), and H₂ yield rose exponentially with enzyme activities (R² ≥ 0.989). The maximum PHA yield (54.2% VSS) occurred at the 42nd hour and influent C/N ratio of 97. PHA yield was positively correlated with substrate uptake. The change of H₂-producing, PHA-accumulating and HPAM-degradating bacteria indicated that those functional microorganisms had synergistic effects on H₂ production and substrate uptake, as well as PHA accumulation and substrate uptake.

Rapid removal of polyacrylamide from wastewater by plasma in the gas-liquid interface

Due to the severe restrictions imposed by legislative frameworks, the removal of polyacrylamide (PAM) rapidly and effectively from produced wastewater in offshore oilfields before discharge is becoming an urgent challenge. In this study, a novel advanced oxidation process based on plasma operated in the gas-liquid interface was used to rapidly decompose PAM, and multiple methods including viscometry, flow field-flow fractionation multi-angle light scattering, UV-visible spectroscopy, and attenuated total reflectance-Fourier transform infrared spectroscopy were used to characterize the changes of PAM. Under a discharge voltage of 25 kV and pH 7.0, the PAM concentration decreased from 100 to 0 mg/L within 20 min and the total organic carbon (TOC) decreased from 49.57 to 1.23 mg/L within 240 min, following zero-order reaction kinetics. Even in the presence of background TOC as high as 152.2 mg/L, complete removal of PAM (100 mg/L) was also achieved within 30 min. The biodegradability of PAM improved following plasma treatment for 120 min. Active species (such as O₃ and H₂O₂) were produced in the plasma. Hydroxyl radical was demonstrated to play an important role in the degradation of PAM due to the inhibitory effect observed after the addition of an ·OH scavenger, Na₂CO₃. Meanwhile, the release of ammonia and nitrate nitrogen confirmed the cleavage of the acylamino group. The results of this study demonstrated that plasma, with its high efficiency and chemical-free features, is a promising technology for the rapid removal of PAM.

Biodegradability enhancement of hydrolyzed polyacrylamide wastewater by a combined Fenton-SBR treatment process

An efficient way to solve the environmental pollution deriving from hydrolyzed polyacrylamide (HPAM)-containing drilling wastewater is urgent. This work adopted a novel method coupling Fenton oxidation with sequencing batch reactor (SBR) to treat gas-field drilling wastewater successively. This Fenton-SBR process reduced COD, HPAM, NH₄⁺-N and total phosphorus (TP) concentrations of drilling wastewater by 98.35%, 87.58%, 94.50% and 93.52%, respectively. While simulated HPAM wastewater with similar HPAM concentration to Fenton-oxidized drilling wastewater was treated only by biological process, and the COD and HPAM removal efficiencies reached 78.26% and 62.95%. The result indicates that the biodegradability of the drilling wastewater was enhanced after Fenton oxidation. Moreover, the analysis on microbial community structure indicates the dominant bacteria in treated drilling wastewater were different from that in treated simulated-wastewater. It can be considered the Fenton-SBR process possesses potential to be applied to treating the drilling wastewater.

Preparation of Superhydrophilic Adsorbents with 3DOM Structure by Water-Soluble Colloidal Crystal Templates for Boron Removal from Natural Seawater

Three-dimensionally ordered macroporous cross-linked poly(glycidyl methacrylate) (3DOM) was constructed by water-soluble colloidal crystal templates and further functionalized with N-methyl-d-glucamine (NMDG) to prepare superhydrophilic adsorbents for boron removal from natural seawater. 3DOM adsorbents possess features of interconnected macropore structure, ultrathin pore wall, and superhydrophilicity, making efficient adsorption possible. The effect of cross-linking degree on the adsorption capacity toward boron was investigated. The NMDG-modified 3DOM adsorbent with rich vicinal diol functional groups showed superhydrophilicity and outstanding performance of adsorption. Significantly, its adsorption effect in boron removal from natural seawater indicated that the concentration of boron in natural seawater could decline to 0.16 from 4.24 mg·L^-1 when the adsorbent dosage was 1 g·L^-1, whereas the boron rejection reached 96.2%. After 10 regeneration-adsorption cycles, the adsorption capacity of 3DOM adsorbent remained over 85% of the initial value and the ordered structure was hardly changed. Additionally, 3DOM adsorbent could be directly and quickly separated from the seawater by a filter mesh of 16 mesh number. Research shows that the 3DOM adsorbent exhibits an adsorption performance for practical applications in boron removal from natural seawater.