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

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.

Photocatalytic synergistic biofilms enhance tetracycline degradation and conversion

Tetracyclines are refractory pollutants that cause persistent harm to the environment and human health. Therefore, it is urgently necessary to develop methods to promote the efficient degradation and conversion of tetracyclines in wastewater. This report proposes a photobiocatalytic synergistic system involving the coupling of GeO₂/Zn-doped phosphotungstic acid hydrate/TiO₂ (GeO₂/Zn-HPW/TiO₂)-loaded photocatalytic optical hollow fibers (POHFs) and an algal-bacterial biofilm. The GeO₂/Zn-HPW/TiO₂ photocatalyst exhibits a broad absorption edge extending to 1000 nm, as well as high-efficiency photoelectric conversion and electron transfer, which allow the GeO₂/Zn-HPW/TiO₂-coated POHFs to provide high light intensity to promote biofilm growth. The resulting high photocatalytic activity rapidly and stably reduces the toxicity and increases the biodegradability of tetracycline-containing wastewater. The biofilm enriched with Salinarimonas, Coelastrella sp., and Rhizobium, maintains its activity for the rapid photocatalytic degradation and biotransformation of intermediates to generate the O₂ required for photocatalysis. Overall, the synergistic photocatalytic biofilm system developed herein provides an effective and efficient approach for the rapid degradation and conversion of water containing high concentrations of tetracycline.

Mechanism analysis of hydroxypropyl guar gum degradation in fracture flowback fluid by homogeneous sono-Fenton process

An effective hybrid system was applied as the first report for the successful treatment of key pollutants (hydroxypropyl guar gum, HPG) in fracturing flowback fluid, and the synergistic index of the hybrid system was 20.45. In this regard, chemical oxygen demand (COD) removal ratio was evaluated with various influencing operating factors including reaction time, H₂O₂ concentration, Fe²⁺ concentration, ultrasonic power, initial pH, and temperature. The optimal operating parameters by single-factor analysis method were: the pH of 3.0, the H₂O₂ concentration of 80 mM, the Fe²⁺ concentration of 5 mM, the ultrasonic power of 180 W, the ultrasonic frequency of 20-25 kHz, the temperature of 39 ℃, the reaction time of 30 min, and the COD removal rate reached 81.15 %, which was permissible to discharge surface water sources based on the environmental standards. A possible mechanism for HPG degradation and the generation of reactive species was proposed. Results of quenching tests showed that various impacts of the decomposition rate by addition of scavengers had followed the order of EDTA-2Na < BQ < t-BuOH, therefore OH radicals had a dominant role in destructing the HPG. Based on the kinetic study, it was concluded that Chan Kinetic Model was more appropriate to describe the degradation of HPG. Identification of intermediates by GC-MS showed that a wide range of recalcitrant compounds was removed and/or degraded into small molecular compounds effectively after treatment. Under the optimal conditions, the sono-Fenton system was used to treat the fracturing flowback fluid with the initial COD value of 675.21 mg/L, and the COD value decreased to 80.83 mg/L after 60 min treatment, which was in line with the marine sewage discharge standard. In conclusion, sono-Fenton system can be introduced as a successful advanced treatment process for the efficient remediation of fracture flowback fluid.

Biodegradability enhancement of phenolic wastewater using hydrothermal pretreatment

A novel hydrothermal pretreatment was applied for the biochemical treatment of phenolic wastewater with high concentrations of phenolic substances. The results demonstrated that 250 °C was the reaction temperature dividing point for complete oxidation, hydrothermal gasification, and amino release from carbonaceous organics in phenolic wastewater. Before the dividing point reached, some of the large molecules were hydrolyzed into small molecules of volatile phenolic substances that were easily adsorbed by the activated sludge. After the integrated hydrothermal pretreatment and anaerobic/aeration process, the removal rate of volatile phenolswas respectively reached by 97 % and 88 % with hydrothermal temperature of 250 °C and without pretreatment. Functional microorganisms (i.e., Chloroflexi) responsible for aromatic compounds degradation were enriched, thus the dioxygenases, dehydrogenase reactions, and meta-cleavage of catechol were enhanced. This work provided an innovative approach to remove phenolic substances from phenolic wastewater, and in-depth understandings of microbial responses in biochemical systems.

Biodegradation of anionic polyacrylamide by manganese peroxidase: docking, virtual mutation based on affinity, QM/MM calculation and molecular dynamics simulation

Manganese peroxidase (Mn P) is capable of effectively degrading anionic polyacrylamide (HPAM). However, the interaction of Mn P with HPAM at molecular level is lacking until now. Here, the HPAM model compounds, HPAM-2, HPAM-3, HPAM-4, and HPAM-5, were selected to reveal their binding mechanisms with Mn P. The results showed that the most suitable substrate for Mn P was HPAM-5, and the main reason for MnP-HPAM-5 with maximal affinity was strong hydrogen bond. LYS96 was the important key residue in all complexes, and the number of key residue was largest in MnP-HPAM-5. The optimal THR27ILE mutant may enhance the affinity of Mn P to HPAM-4. The stability of Mn P binding to HPAM-4 was the optimal. These results were helpful in designing highly efficient Mn P against HPAM to protect the ecological environment.

Effectiveness of sodium sulfite as an electron acceptor for bioenhanced treatment of salt-containing water produced from ASP flooding

The wastewater produced from alkaline-surfactant-polymer (ASP) flooding is a complex multiphase mixture that contains oil, polymers, surfactants and other pollutants and is thus a salt-containing industrial waste recalcitrant to treatments. Through laboratory tests, this study assessed the effectiveness of using sodium sulfite as an electron acceptor for a modified anaerobic baffled reactor (ABR) for removing oil, suspended solids, polymers and surfactants from salt-containing wastewater produced from ASP flooding. During the 90-day operation, the method established in this study successively removed 52.8%, 98.6%, 77.0%, 21.2% and 21.5% of the chemical oxygen demand (COD), oil, suspended solids, polymers and surfactants, respectively, from the wastewater. The changes in organic compounds in the reactor during the treatment were monitored through gas chromatography-mass spectrometry (GC-MS), and the results showed that the established method was very effective in removing alkanes, alkenes, cycloalkanes, aromatic hydrocarbons and esters, and the organic macromolecules in the wastewater were degraded to small molecules. The main bacterial species and microbial communities in the reactor were characterized using molecular biological techniques, and the results indicated that under the stress of high pH and salts, Halomonas sp. gradually dominated and played a major role in degrading hydrocarbons. The findings of this study can aid the development of a cost-effective biological system to treat the water produced from ASP flooding.

Advanced treatment of secondary effluent organic matters (EfOM) from an industrial park wastewater treatment plant by Fenton oxidation combining with biological aerated filter

This study investigated the advanced treatment of secondary effluent organic matters (EfOM) from an industrial park wastewater treatment plant (IPWTP) by Fenton oxidation process and its combination with biological aerated filter (BAF). The constituents of EfOM were characterized by using fluorescence excitation-emission matrix, and the results showed that the major components included aromatic proteins, soluble microbial products, humic and fulvic acid-like substances, and compounds associated with fluorescent region of Ex 250-300 nm/Em 600-700 nm. The EfOM was strongly resistant to biodegradation (biochemical oxygen demand (BOD₅):chemical oxygen demand (COD) ratio at 0.11), resulting in less than 15% dissolved organic carbon (DOC) removal efficiency by the BAF reactor. The advanced treatment of EfOM by Fenton oxidation process led to maximum ~50% mineralization efficiency of EfOM under the optimal conditions of 2.0 mM Fe^II, 10 mM H₂O₂, pH 3.0 and 3.0 h of the reaction time. Particularly, Fenton oxidation treatment effectively improved the biodegradability of EfOM in the IPWTP secondary effluents, e.g., increasing the BOD₅:COD ratio from 0.11 to 0.42. A synergistic combination of Fenton oxidation process with the BAF reactor offered desirable mineralization efficiencies of EfOM (>70%) at lower dosages of Fenton's reagents. The present results suggest that Fenton oxidation process combining with the BAF reactor can be a promising strategy for the advanced treatment of EfOM in IPWTP secondary effluents. This study provides guidance for the characterization and advanced treatment of EfOM in IPWTP secondary effluents for practical purpose.

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.

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.

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.

Semiconductor-Microbial Mechanism of Selective Dissolution of Chalcocite in Bioleaching

Chalcocite-dominant secondary copper ore with a high pyrite content had a rapidly increased iron concentration in the middle and later periods of bioleaching, which increased the difficulty of separating copper and iron ions in the leaching solution. In the two aspects of microbial community succession and energy band theory, the selective dissolution mechanism of chalcocite in this type of copper ore was analyzed and illustrated using experiments and first-principles calculations. The results showed that controlling the solution potential at a lower level was beneficial to the selective leaching of chalcocite, while bacteria promoted the leaching of pyrite and chalcocite simultaneously by oxidizing Fe²⁺ to Fe³⁺ in the solution. Below 700 mV of solution potential, the bacterial community, mainly consisting of Acidithiobacillus and Sulfobacillus, had a stronger promotion on the selective dissolution of chalcocite. The solution energy level of bioleaching was higher than ideal pyrite but lower than ideal chalcocite, which resulted in the accumulation of electrons on the surface of pyrite and the formation of holes at the top of the chalcocite valence band. When bacteria assisted the oxidation of Fe²⁺ to Fe³⁺ and caused the raise of the solution potential, the difference between the solution energy level and the top of the pyrite valence band would be smaller than the width of the pyrite energy gap. Below 700 mV, the assistance of Acidithiobacillus and Sulfobacillus on the oxidation of Fe²⁺ was weak. Chalcocite would be selectively dissolved by oxygen and a small amount of Fe³⁺ in the solution. Because of the existence of Fe, Cu, and S vacancies in real minerals, the atomic activity in the Cu-S bond and the Fe-S bond enhanced, and the reaction difficulty between chalcocite, pyrite, and electron acceptors in the solution reduced. The solution potential should be controlled at 600 mV or less to ensure the selective dissolution of chalcocite.

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

Hydrolyzed polyacrylamide (HPAM) is the most widely used water-soluble linear polymer with high molecular weight in polymer flooding. Microbiological degradation is an environment-friendly and effective method of treating HPAM-containing oilfield produced water. In this study, a strain SZK-5 that could degrade HPAM was isolated from soil contaminated by oilfield produced water. Based on morphological, biochemical characteristics and 16S rDNA sequence homology analysis, the strain was identified as Bacillus megaterium. The biodegradation capability of strain SZK-5 was determined by incubation in a mineral salt medium (MSM) containing HPAM under different environmental conditions, showing 55.93% of the HPAM removed after 7 d of incubation under the optimum conditions ((NH₄)₂SO₄ = 1667.9 mg L^-1, temperature = 24.05 °C and pH = 8.19). Cytochrome P450 (CYP) and urease (URE) played significant roles in biological carbon and nitrogen removal, respectively. The strain SZK-5 could resist the damages caused by oxidative stress given by crude oil and HPAM. To our knowledge, this is the first report about the biodegradation of HPAM by B. megaterium. These results suggest that strain SZK-5 might be a new auxiliary microbiological resource for the biodegradation of HPAM residue in wastewater and soil.