Hydrolyzed polyacrylamide biodegradation and mechanism in sequencing batch biofilm reactor

Molecular and microbial insights towards anaerobic biodegradation of anionic polyacrylamide in oil sands tailings

Anionic polyacrylamide (A-PAM) is widely used as a flocculant in the management of oil sands tailings. Nevertheless, apprehensions arise regarding its potential biodegradation and environmental consequences within the context of oil sands tailings. Consequently, it is imperative to delve into the anaerobic biodegradation of A-PAM in oil sands tailings to gain a comprehensive understanding of its influence on tailings water quality. This work explored the dynamics of A-PAM biodegradation across concentrations: 50, 100, 250, 500, 1000, and 2000 mg/kg TS. The results showed a significant decrease in A-PAM concentration and molecular weight at lower concentrations (50 and 100 mg/kg TS) compared to higher ones, suggesting enhanced degradation efficiency. Likewise, the organic transformation and methane production exhibited dependency on A-PAM concentrations. The peak concentrations observed were 20.0 mg/L for volatile fatty acids (VFAs), 0.07 mg/L for acrylamide (AMD), and 8.9 mL for methane yield, with these maxima being recorded at 50 mg/kg TS. The biodegradation efficiency diminishes at higher concentrations of A-PAM, potentially due to the inhibitory effects of polyacrylic acid accumulation. A-PAM biodegradation under anaerobic condition did not contribute to acute toxicity or genotoxicity. SEM-EDS, FT-IR and XRD analyses further revealed that higher concentrations of A-PAM inhibited the biodegradation by altering floc structure and composition, thereby restricting the microbial activity. Major microorganisms, including Smithella, Candidatus_Cloacimonas, W5, XBB1006, and DMER64 were identified, highlighting A-PAM's dual role as a source of carbon and nitrogen under anaerobic conditions. The above findings from this research not only significantly advance understanding of A-PAM's environmental behavior but also contribute to the effective management practices in oil sands tailings.

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.

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.

Efficiency and bacterial diversity of an improved anaerobic baffled reactor for the remediation of wastewater from alkaline-surfactant-polymer (ASP) flooding technology

Alkaline-surfactant-polymer (ASP) flooding technology is used to maximize crude oil recovery. However, the extensive use of alkaline materials makes it difficult to treat the water used. Here, an improved multi-zone anaerobic baffled reactor (ABR) using FeSO₄ as electron acceptor was employed to treat the wastewater from ASP flooding technology, and the effects on major pollutants (hydrolyzed polyacrylamide, petroleum substances, surfactants suspended solids) and associated parameters (chemical oxygen demand, viscosity) were evaluated. Gas chromatography-mass spectrometry (GC-MS) was used to follow the degradation and evolution of organic compounds while high-throughput DNA sequencing was used to determine the bacterial diversity in the ABR. The results obtained after 90 d of operation showed decreases in all parameters measured and the highest mean removal rates were obtained for petroleum substances (98.8%) and suspended solids (77.0%). Amounts of petroleum substances in the ABR effluent could meet the requirements of a national standard for oilfield reinjection water. GC-MS analysis showed that a wide range of chemicals (e.g. aromatic hydrocarbons, esters, alcohols, ketones) could be sequentially removed from the influent by each zone of ABR. The high-throughput DNA sequencing showed that the bacteria Micropruina, Saccharibacteria and Synergistaceae were involved in the degradation of pollutants in the anaerobic and anoxic reaction zones, while Rhodobacteraceae and Aliihoeflea were the main functional microorganisms in the aerobic reaction zones. The results demonstrated that the improved ABR reactor had the potential for the treatment of wastewater from ASP flooding technology.

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.

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.

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.

Combination of biochar and immobilized bacteria accelerates polyacrylamide biodegradation in soil by both bio-augmentation and bio-stimulation strategies

Polyacrylamide (PAM) has been used extensively due to its well-known stable chemical properties, but limited information is available on the biodegradation of soil-containing PAM. In this work, sufficient degradation of PAM was achieved via the addition of the Klebsiella sp. PCX-biochar composite to PAM-containing soil, due to the synergic effect of bio-augmentation and bio-stimulation. The optimal degradation rate of 69.1% over 30-day period was observed under the following conditions: the addition of immobilized bacteria at 0.07 g/g, pH 6.6, and temperature at 38.0 °C. In this study, we showed that PAM was successfully hydrolyzed by amidase, and ammonia in the hydrolysis product was then oxidized by the nitrifying bacteria. The decrease of water-extractable organic carbon (WEOC) also demonstrated the chain cleavage in PAM. PAM was utilized as a carbon source not only by Klebsiella sp. PCX but also by some taxa from indigenous bacteria. Last but not least, it was shown in this study that biochar, even though immobilized with exogenous microorganisms, actually enhanced bacterial diversity and stimulated the growth of some indigenous PAM-degrading taxa. Based on the above observations, we concluded that PAM biodegradation via the addition of bacteria-immobilized biochar was a synergy of both bio-augmentation and bio-stimulation strategies.

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.

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.

Biodegradation of low molecular weight polyacrylamide under aerobic and anaerobic conditions: effect of the molecular weight

The biodegradation of polyacrylamide (PAM) includes the hydrolysis of amino groups and cleavage of the carbon chain; however, the effect of molecular weight on the biodegradation needs further investigations. In this study, biodegradation of low molecular weight PAM (1.6 × 10⁶ Da) was evaluated in two aerobic (25 °C and 40 °C) and two anaerobic (35 °C and 55 °C) reactors over 100 days. The removal of the low molecular weight PAM (52.0-52.6%) through the hydrolysis of amino groups by anaerobic treatment (35 °C and 55 °C) was much higher than that of the high molecular weight (2.2 × 10⁷ Da, 11.2-17.0%) observed under the same conditions. The molecular weight was reduced from 1.6 × 10⁶ to 6.45-7.42 × 10⁵ Da for the low molecular weight PAM, while the high molecular weight PAM declined from 2.2 × 10⁷ to 3.76-5.87 × 10⁶ Da. The results showed that the amino hydrolysis of low molecular weight PAM is easier than that of the high molecular weight one, while the cleavage of its carbon chain is still difficult. The molecular weights of PAM in the effluents from the two aerobic reactors (25 °C and 40 °C) were further reduced to 4.31 × 10⁵ and 5.68 × 10⁵ Da by the biofilm treatment, respectively. The results would be useful for the management of wastewater containing PAM.

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.

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.

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.

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.

High temperature utilization of PAM and HPAM by microbial communities enriched from oilfield produced water and activated sludge

Non-hydrolyzed polyacrylamide (PAM) and partially hydrolyzed polyacrylamide (HPAM) are commonly used polymers in various industrial applications, including in oil and gas production operations. Understanding the microbial utilization of such polymers can contribute to improved recovery processes and help to develop technologies for polymer remediation. Microbial communities enriched from oilfield produced water (PW) and activated sludge from Alberta, Canada were assessed for their ability to utilize PAM and HPAM as nitrogen and carbon sources at 50 °C. Microbial growth was determined by measuring CO₂ production, and viscosity changes and amide concentrations were used to determine microbial utilization of the polymers. The highest CO₂ production was observed in incubations wherein HPAM was added as a nitrogen source for sludge-derived enrichments. Our results showed that partial deamination of PAM and HPAM occurred in both PW and sludge microbial cultures after 34 days of incubation. Whereas viscosity changes were not observed in cultures when HPAM or PAM was provided as the only carbon source, sludge enrichment cultures amended with HPAM and glucose showed significant decreases in viscosity. 16S rRNA gene sequencing analysis indicated that microbial members from the family Xanthomonadaceae were enriched in both PW and sludge cultures amended with HPAM or PAM as a nitrogen source, suggesting the importance of this microbial taxon in the bio-utilization of these polymers. Overall, our results demonstrate that PAM and HPAM can serve as nitrogen sources for microbial communities under the thermophilic conditions commonly found in environments such as oil and gas reservoirs.

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.

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

Potential of hydrolyzed polyacrylamide (HPAM) biodegradation to final products was studied through regulating its own nitrogen transformation. Under the conditions of 2, 3 and 4 mg/L of DO, HPAM removal ratio reached 16.92%, 24.51% and 30.78% and the corresponding removal ratio reached 49.15%, 60.25% and 76.44% after anaerobic biodegradation. NO₃^--N concentration was 9.43, 14.10 and 17.99 mg/L in aerobic stages and the corresponding concentration was 0.17, 0.07 and 0.008 mg/L after anaerobic biodegradation. Oxygen as electron acceptors stimulated the activities of nitrification bacteria and other functional bacteria, thus further enhanced nitrification and HPAM biodegradation. NO₃^- (from HPAM oxidation) as electron acceptors stimulated the activities of nitrate-reducing, acetate-producing and methanogenic microorganisms and they could form a synergistic effect on denitrification and methanogenesis. Thermodynamic opportunity window revealed that NO_x^- could accelerate anaerobic HPAM bioconversion to methane. Aerobic and anaerobic growth-process equations of cells verified that the metabolism on HPAM was feasible.

Effects of different electron acceptors on the methanogenesis of hydrolyzed polyacrylamide biodegradation in anaerobic activated sludge systems

The type of electron acceptor was a crucial factor in regulating the methanogenic process of anaerobic hydrolyzed polyacrylamide (HPAM) degradation. The combined methods of biodegradation experiments and thermodynamic calculations were applied to explore the effects of different electron acceptors on methanogenic HPAM degradation. Under the conditions of without electron acceptor, SO₄^2-, Fe³⁺, SO₄^2- and Fe³⁺ as electron acceptors, HPAM biodegradation ratio reached 31.56%, 41.48%, 49.4% and 61.1%, acetate production reached 0.0532, 28.28, 112.7 and 141.95mg·L^-1, CH₄ production reached 0.024, 0.3015, 9.446 and 11.78mg·L^-1, respectively. The synergistic effect of SO₄^2- and Fe³⁺ further promoted methanogenic HPAM biotransformation. Archaeal community analysis revealed that Methanobacteriales, Methanomicrobiales and Methanosarcinales were dominant. Thermodynamic opportunity windows of methanogenesis with Fe³⁺ as electron acceptor are 35 times larger than that with SO₄^2- as electron acceptor. It indicated that acetoclastic methanogenesis was dominant and hydrogenotrophic methanogenesis was inhibited in the methane-producing process of anaerobic HPAM degradation.

Kinetics and thermodynamics of biodegradation of hydrolyzed polyacrylamide under anaerobic and aerobic conditions

Kinetics and thermodynamics of hydrolyzed polyacrylamide (HPAM) biodegradation in anaerobic and aerobic activated sludge biochemical treatment systems were explored to determine the maximum rate and feasibility of HPAM biodegradation. The optimal nutrient proportions for HPAM biodegradation were determined to be 0.08g·L(-1) C6H12O6, 1.00g·L(-1) NH4Cl, 0.36g·L(-1) NaH2PO4 and 3.00g·L(-1) K2HPO4 using response surface methodology (RSM). Based on the kinetics, the maximum HPAM biodegradation rates were 16.43385mg·L(-1)·d(-1) and 2.463mg·L(-1)·d(-1) in aerobic and anaerobic conditions, respectively. The activation energy (Ea) of the aerobic biodegradation was 48.9897kJ·mol(-1). Entropy changes (ΔS) of biochemical treatment system decreased from 216.21J·K(-1) to 2.39J·K(-1). Thermodynamic windows of opportunity for HPAM biodegradation were drawn. And it demonstrated HPAM was biodegraded into acetic acid and CO2 under laboratory conditions. Growth-process equations for functional bacteria anaerobically grown on polyacrylic acid were constructed and it confirmed electron equivalence between substrate and product.