Biodegradation of hydrolyzed polyacrylamide by a Bacillus megaterium strain SZK-5: Functional enzymes and antioxidant defense mechanism

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.

Acceleration of the biodegradation of cationic polyacrylamide by the coupling effect of thermophilic microorganisms and high temperature in hyperthermophilic composting

As a flocculant of sewage sludge, cationic polyacrylamide (CPAM) enters the environment with sludge and exists for a long time, posing serious threats to the environment. Due to the environmental friendliness and high efficiency in the process of organic solid waste treatment, hyperthermophilic composting (HTC) has received increasing attention. However, it is still unclear whether the HTC process can effectively remove CPAM from sludge. In this study, the effects of HTC and conventional thermophilic composting (CTC) on CPAM in sludge were compared and analyzed. At the end of HTC and CTC, the concentrations of CPAM were 278.96 mg kg-1 and 533.89 mg kg-1, respectively, and the removal rates were 72.17% and 46.61%, respectively. The coupling effect of thermophilic microorganisms and high temperature improved the efficiency of HTC and accelerated the biodegradation of CPAM. The diversity and composition of microbial community changed dramatically during HTC. Geobacillus, Thermobispora, Pseudomonas, Brevundimonas, and Bacillus were the dominant bacteria responsible for the high HTC efficiency. To our knowledge, this is the first study in which CPAM-containing sludge is treated using HTC. The ideal performance and the presence of key microorganisms revealed that HTC is feasible for the treatment of CPAM-containing sludge.

Acidovorax PSJ13, a novel, efficient polyacrylamide-degrading bacterium by cleaving the main carbon chain skeleton without the production of acrylamide

Given the environmental challenge caused by the wide use of polyacrylamide (PAM), an environmental-friendly treatment method is required. This study demonstrates the role of Acidovorax sp. strain PSJ13 isolated from dewatered sludge in efficiently degrading PAM. To be specific, the strain PSJ13 can degrade 51.67% of PAM in 96 h (2.39 mg/(L h)) at 35 °C, pH 7.5 and 5% inoculation amount. Besides, scanning electron microscope, X-ray photoelectron spectroscopy, liquid chromatography-mass spectrometry and high-performance liquid chromatography were employed to analyze samples, and the nitrogen present in the degradation products was investigated. The results showed that the degradation of PAM by PSJ13 started from the side chain and then mainly the -C-C- main chain, which produced no acrylamide monomers. As the first study to report the role of Acidovorax in efficiently degrading PAM, this work may provide a solution for industries that require PAM management.

Biotransformation of sulfamethoxazole by newly isolated surfactant-producing strain Proteus mirabilis sp. ZXY4: Removal efficiency, pathways, and mechanisms

In this study, the SMX degrading strain Proteus mirabilis sp. ZXY4 with surfactant manufacturing potential was isolated from sludge utilizing blood agar and CTAB agar plate. FTIR analysis indicated that the biosurfactant generated by strain ZXY4 was glycolipid. 3D-EEM demonstrated that SMX biodegradation was strongly connected to biosurfactants, the synergistic effect of biodegradation and biosurfactant made strain ZXY4 have excellent SMX degradation performance. Under the optimal conditions of inoculation dosage of 15%, temperature of 30 ℃, pH of 7 and initial SMX concentration of 5 mg L^-1, strain ZXY4 could completely degrade SMX within 24 h. SMX biodegrades at low concentrations (less than5 mg L^-1) followed by the zero-order kinetic model, high concentration (>5 mg L^-1) is more consistent with the first-order kinetic model. LC-MS analysis revealed 14 SMX degradation intermediates, and five potential biodegradation mechanisms were postulated. The findings provide new insights into the biodegradation of SMX.

Efficiency and microbial community characteristics of strong alkali ASP flooding produced water treated by composite biofilm system

Strong alkali alkali-surfactant-polymer (ASP) flooding produced water is a by-product of oil recovery, and it is a stable system composed of petroleum, polyacrylamide, surfactant, and inorganic salts. Efficient, green, and safe ASP produced water treatment technology is essential for oilfield exploitation and environmental protection. In this study, an anaerobic/anoxic/moving bed biofilm reactor with a microfiltration membrane was established and assessed for the real strong alkali ASP flooding produced water (pH 10.1-10.4) treatment. The results show that the average removal rates of COD, petroleum, suspended solids, polymers and surfactants in this process are 57, 99, 66, 40, and 44%, respectively. GC-MS results show that most of the organic compounds such as alkanes and olefins in the strong alkali ASP produced water are degraded. Microfiltration membrane can significantly improve the efficiency and stability of sewage treatment system. Paracoccus (AN), Synergistaceae (ANO) and Trichococcus (MBBR) are the main microorganisms involved in the degradation of pollutants. This study reveals the potential and adaptability of composite biofilm system in treating the produced water of strong alkali ASP produced water.

The capability of chloramphenicol biotransformation of Klebsiella sp. YB1 under cadmium stress and its genome analysis

Co-contamination by antibiotics and heavy metal is common in the environment, however, there is scarce information about antibiotics biodegradation under heavy metals stress. In this study, Klebsiella sp. Strain YB1 was isolated which is capable of biodegrading chloramphenicol (CAP) with a biodegradation efficiency of 22.41% at an initial CAP of 10 mg L^-1 within 2 days. CAP biodegradation which fitted well with the first-order kinetics. YB1 still degrades CAP under Cd stress, however 10 mg L^-1 Cd inhibited CAP biodegradation by 15.1%. Biotransformation pathways remained the same under Cd stress, but two new products (Cmpd 19 and Cmpd 20) were identified. Five parallel metabolism pathways of CAP were proposed with/without Cd stress, including one novel pathway (pathway 5) that has not been reported before. In pathway 5, the initial reaction was oxidation of CAP by disruption of C-C bond at the side chain of C1 and C2 with the formation of 4-nitrobenzyl alcohol and CY7, then these intermediates were oxidized into p-nitrobenzoic acid and CY1, respectively. CAP acetyltransferase and nitroreductase and 2,3/4,5-dioxygenase may play an important role in CAP biodegradation through genome analysis and prediction. This study deepens our understanding of mechanism of antibiotic degradation under heavy metal stress in the environment.

Biological oxidation methods for the removal of organic and inorganic contaminants from wastewater: A comprehensive review

Enzyme-based bioremediation is a simple, cost-effective, and environmentally friendly method for isolating and removing a wide range of environmental pollutants. This study is a comprehensive review of recent studies on the oxidation of pollutants by biological oxidation methods, performed individually or in combination with other methods. The main bio-oxidants capable of removing all types of pollutants, such as organic and inorganic molecules, from fungi, bacteria, algae, and plants, and different types of enzymes, as well as the removal mechanisms, were investigated. The use of mediators and modification methods to improve the performance of microorganisms and their resistance under harsh real wastewater conditions was discussed, and numerous case studies were presented and compared. The advantages and disadvantages of conventional and novel immobilization methods, and the development of enzyme engineering to adjust the content and properties of the desired enzymes, were also explained. The optimal operating parameters such as temperature and pH, which usually lead to the best performance, were presented. A detailed overview of the different combination processes was also given, including bio-oxidation in coincident or consecutive combination with adsorption, advanced oxidation processes, and membrane separation. One of the most important issues that this study has addressed is the removal of both organic and inorganic contaminants, taking into account the actual wastewaters and the economic aspect.

Partially hydrolyzed polyacrylamide: enhanced oil recovery applications, oil-field produced water pollution, and possible solutions

Polymers, such as partially hydrolyzed polyacrylamide (HPAM), are widely used in oil fields to enhance or improve the recovery of crude oil from the reservoirs. It works by increasing the viscosity of the injected water, thus improving its mobility and oil recovery. However, during such enhanced oil recovery (EOR) operations, it also produces a huge quantity of water alongside oil. Depending on the age and the stage of the oil reserve, the oil field produces ~ 7-10 times more water than oil. Such water contains various types of toxic components, such as traces of crude oil, heavy metals, and different types of chemicals (used during EOR operations such as HPAM). Thus, a huge quantity of HPAM containing produced water generated worldwide requires proper treatment and usage. The possible toxicity of HPAM is still ambiguous, but its natural decomposition product, acrylamide, threatens humans' health and ecological environments. Therefore, the main challenge is the removal or degradation of HPAM in an environmentally safe manner from the produced water before proper disposal. Several chemical and thermal techniques are employed for the removal of HPAM, but they are not so environmentally friendly and somewhat expensive. Among different types of treatments, biodegradation with the aid of individual or mixed microbes (as biofilms) is touted to be an efficient and environmentally friendly way to solve the problem without harmful side effects. Many researchers have explored and reported the potential of such bioremediation technology with a variable removal efficiency of HPAM from the oil field produced water, both in lab scale and field scale studies. The current review is in line with United Nations Sustainability Goals, related to water security-UNSDG 6. It highlights the scale of such HPAM-based EOR applications, the challenge of produced water treatment, current possible solutions, and future possibilities to reuse such treated water sources for other applications.

Biodegradation of Polymers Used in Oil and Gas Operations: Towards Enzyme Biotechnology Development and Field Application

Linear and crosslinked polymers are commonly used in the oil and gas industry. Guar-derived polymers have been extensively utilized in hydraulic fracturing processes, and recently polyacrylamide and cellulose-based polymers have also found utility. As these polymers are used during various phases of the hydraulic fracturing process, they can accumulate at formation fracture faces, resulting in undesired filter cakes that impede oil and gas recovery. Although acids and chemical oxidizers are often added in the fracturing fluids to degrade or ‘break’ polymer filter cakes, the constant use of these chemicals can be hazardous and can result in formation damage and corrosion of infrastructure. Alternately, the use of enzymes is an attractive and environmentally friendly technology that can be used to treat polymer accumulations. While guar-linkage-specific enzyme breakers isolated from bacteria have been shown to successfully cleave guar-based polymers and decrease their molecular weight and viscosity at reservoir conditions, new enzymes that target a broader range of polymers currently used in hydraulic fracturing operations still require research and development for effective application. This review article describes the current state-of-knowledge on the mechanisms and enzymes involved in biodegradation of guar gum, polyacrylamide (and hydrolyzed polyacrylamide), and carboxymethyl cellulose polymers. In addition, advantages and challenges in the development and application of enzyme breaker technologies are discussed.

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.

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.

Green remediation of toxic metals contaminated mining soil using bacterial consortium and Brassica juncea

Microorganism-assisted phytoremediation is being developed as an efficient green approach for management of toxic metals contaminated soils and mitigating the potential human health risk. The capability of plant growth promoting Actinobacteria (Streptomyces pactum Act12 - ACT) and Firmicutes (Bacillus subtilis and Bacillus licheniformis - BC) in mono- and co-applications (consortium) to improve soil properties and enhance phytoextraction of Cd, Cu, Pb, and Zn by Brassica juncea (L.) Czern. was studied here for the first time in both incubation and pot experiments. The predominant microbial taxa were Proteobacteria, Actinobacteria and Bacteroidetes, which are important lineages for maintaining soil ecological activities. The consortium improved the levels of alkaline phosphatase, β-D glucosidase, dehydrogenase, sucrase and urease (up to 33%) as compared to the control. The bacterial inoculum also triggered increases in plant fresh weight, pigments and antioxidants. The consortium application enhanced significantly the metals bioavailability (DTPA extractable) and mobilization (acid soluble fraction), relative to those in the unamended soil; therefore, significantly improved the metals uptake by roots and shoots. The phytoextraction indices indicated that B. juncea is an efficient accumulator of Cd and Zn. Overall, co-application of ACT and BC can be an effective solution for enhancing phytoremediation potential and thus reducing the potential human health risk from smelter-contaminated soil. Field studies may further credit the understanding of consortium interactions with soil and different plant systems in remediating multi-metal contaminated environments.

Enhanced removal of Congo red dye from aqueous solution by surface modified activated carbon with bacteria

AIMS

The adsorption behaviour and mechanisms of the surface modified activated carbon with bacteria was evaluated.

METHODS AND RESULTS

16S rRNA was employed to identify the hydrocarbon-degrading bacteria. The bacteria was characterized by TEM and electron microscope. The surface modified activated carbon with bacteria was characterized by SEM. The adsorption behaviour was tested by static adsorption and dynamic adsorption.

CONCLUSION

The adsorption efficiency of the modified activated carbon was high when pH was weak acidic, and the adsorption capacity increased with the increase of temperature ranging from 20 to 35°C. The adsorption capacity peaked at 234·6 mg g^-1 at 25°C, which was sixfold higher than that of activated carbon. The pseudo-first-order kinetic can more accurately assess Congo red adsorption on the two adsorbents. The adsorption of Congo red by bacteria surface modified activated carbon fitted well with the Langmuir's model. The adsorption process was endothermic, and the biological floccules were formed during the adsorption. The physical adsorption is the main driving force.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results indicate that the bacteria surface-modified activated carbon can be used effectively as an adsorbent to eliminate Congo red from aqueous solutions.

Hydrolyzed polyacrylamide-containing wastewater treatment using ozone reactor-upflow anaerobic sludge blanket reactor-aerobic biofilm reactor multistage treatment system

Polymer flooding is one of the most important enhanced oil recovery techniques. However, a large amount of hydrolyzed polyacrylamide (HPAM)-containing wastewater is produced in the process of polymer flooding, and this poses a potential threat to the environment. In this study, the treatment of HPAM-containing wastewater was analyzed in an ozonic-anaerobic-aerobic multistage treatment process involving an ozone reactor (OR), an upflow anaerobic sludge blanket reactor (UASBR), and an aerobic biofilm reactor (ABR). At an HPAM concentration of 500 mg L^-1 and an ozone dose of 25 g O₃/g TOC, the HPAM removal rate reached 85.06%. With fracturing of the carbon chain, high-molecular-weight HPAM was degraded into low-molecular-weight compounds. Microbial communities in bioreactors were investigated via high-throughput sequencing, which revealed that norank_c_Bacteroidetes_vadinHA17, norank_f_Cytophagaceae, and Meiothermus were the dominant bacterial groups, and that Methanobacterium, norank_c_WCHA1-57, and Methanosaeta were the key archaeal genera. To the best of our knowledge, this is the first study in which HPAM-containing wastewater is treated using an ozonic-anaerobic-aerobic multistage treatment system. The ideal degradation performance and the presence of keystone microorganisms confirmed that the multistage treatment process is feasible for treatment of HPAM-containing wastewater.

Current status on the biodegradability of acrylic polymers: microorganisms, enzymes and metabolic pathways involved

Abstract

Acrylic polymers (AP) are a diverse group of materials with broad applications, frequent use, and increasing demand. Some of the most used AP are polyacrylamide, polyacrylic acid, polymethyl methacrylates, and polyacrylonitrile. Although no information for the production of all AP types is published, data for the most used AP is around 9 MT/year, which gives an idea of the amount of waste that can be generated after products’ lifecycles. After its lifecycle ends, the fate of an AP product will depend on its chemical structure, the environmental setting where it was used, and the regulations for plastic waste management existing in the different countries. Even though recycling is the best fate for plastic polymer wastes, few AP can be recycled, and most of them end up in landfills. Because of the pollution crisis the planet is immersed, setting regulations and developing technological strategies for plastic waste management are urgent. In this regard, biotechnological approaches, where microbial activity is involved, could be attractive eco-friendly strategies. This mini-review describes the broad AP diversity, their properties and uses, and the factors affecting their biodegradability, underlining the importance of standardizing biodegradation quantification techniques. We also describe the enzymes and metabolic pathways that microorganisms display to attack AP chemical structure and predict some biochemical reactions that could account for quaternary carbon-containing AP biodegradation. Finally, we analyze strategies to increase AP biodegradability and stress the need for more studies on AP biodegradation and developing stricter legislation for AP use and waste control.

Key points

• Acrylic polymers (AP) are a diverse and extensively used group of compounds.

• The environmental fates and health effects of AP waste are not completely known.

• Microorganisms and enzymes involved in AP degradation have been identified.

• More biodegradation studies are needed to develop AP biotechnological treatments.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-020-11073-1.

Unlocking the potential of plant growth-promoting rhizobacteria on soil health and the sustainability of agricultural systems

The concept of soil health refers to specific soil properties and the ability to support and sustain crop growth and productivity, while maintaining long-term environmental quality. The key components of healthy soil are high populations of organisms that promote plant growth, such as the plant growth promoting rhizobacteria (PGPR). PGPR plays multiple beneficial and ecological roles in the rhizosphere soil. Among the roles of PGPR in agroecosystems are the nutrient cycling and uptake, inhibition of potential phytopathogens growth, stimulation of plant innate immunity, and direct enhancement of plant growth by producing phytohormones or other metabolites. Other important roles of PGPR are their environmental cleanup capacities (soil bioremediation). In this work, we review recent literature concerning the diverse mechanisms of PGPR in maintaining healthy conditions of agricultural soils, thus reducing (or eliminating) the toxic agrochemicals dependence. In conclusion, this review provides comprehensive knowledge on the current PGPR basic mechanisms and applications as biocontrol agents, plant growth stimulators and soil rhizoremediators, with the final goal of having more agroecological practices for sustainable agriculture.

Bioremediation of tetracycline antibiotics-contaminated soil by bioaugmentation

Bioaugmentation using specific microbial strains or consortia was deemed to be a useful bioremediation technology for increasing bioremediation efficiency. The present study confirmed the effectiveness and feasibility of bioaugmentation capability of the bacterium BC immobilized on sugarcane bagasse (SCB) for degradation of tetracycline antibiotics (TCAs) in soil. It was found that an inoculation dose of 15% (v/w), 28–43 °C, slightly acidic pH (4.5–6.5), and the addition of oxytetracycline (OTC, from 80 mg kg⁻¹ to 160 mg kg⁻¹) favored the bioaugmentation capability of the bacterium BC, indicating its strong tolerance to high temperature, pH, and high substrate concentrations. Moreover, SCB-immobilized bacterium BC system exhibited strong tolerance to heavy metal ions, such as Pb²⁺ and Cd²⁺, and could fit into the simulated soil environment very well. In addition, the bioaugmentation and metabolism of the co-culture with various microbes was a complicated process, and was closely related to various species of bacteria. Finally, in the dual-substrate co-biodegradation system, the presence of TC at low concentrations contributed to substantial biomass growth but simultaneously led to a decline in OTC biodegradation efficiency by the SCB-immobilized bacterium BC. As the total antibiotic concentration was increased, the OTC degradation efficiency decreased gradually, while the TC degradation efficiency still exhibited a slow rise tendency. Moreover, the TC was preferentially consumed and degraded by continuous introduction of OTC into the system during the bioremediation treatment. Therefore, we propose that the SCB-immobilized bacterium BC exhibits great potential in the bioremediation of TCAs-contaminated environments.

Bioaugmentation using specific microbial strains or consortia was deemed to be a useful bioremediation technology for increasing bioremediation efficiency.

Enhanced hydrolyzed polyacrylamide removal from water by an aerobic biofilm reactor-ozone reactor-aerobic biofilm reactor hybrid treatment system: Performance, key enzymes and functional microorganisms

Degradation of hydrolyzed polyacrylamide-containing (HPAM-containing) wastewater was investigated in a lab-scale aerobic-ozonic-aerobic hybrid treatment system. When the HPAM concentration was 500 mg L^-1 and the ozone dose was 25 g O₃/g TOC, the HPAM removal rate reached 90.79%. Experimental results obtained from gel permeation chromatography (GPC) and rheometer indicated that the refractory HPAM was decomposed into small-molecule compounds. High performance liquid chromatography (HPLC) analysis showed that there was no acrylamide (AM) in the effluent of the system. Microbial communities in two aerobic biofilm reactors (ABRs) were analyzed by Illumina MiSeq Sequencing, which indicated that norank_f_Cytophagaceae, Meiothermus, Bacillus, etc. were keystone functional bacterial genera and Methanobacterium, norank_p_Bathyarchaeota, norank_c_Marine_Group_Ⅰ, etc. were dominant functional archaeal groups. To our knowledge, this is the first study to treat HPAM-containing wastewater using an aerobic-ozonic-aerobic hybrid process. Good removal efficiencies and presence of functional microorganisms demonstrated that the hybrid treatment system was practical for treating HPAM-containing wastewater.