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

Effects of pressure on the biogeochemical and geotechnical behavior of treated oil sands tailings in a pit lake scenario

Reclamation options for oil sands fluid fine tailings (FFT) are limited due to its challenging geotechnical properties, which include high water and clay contents and low shear strength. A feasible reclamation option for tailings with these properties is water capped FFT deposits (pit lakes). A relatively new proposal is to deposit FFT that has been treated with alum and polyacrylamide in pit lakes. Though over 65 Mm3 of alum/polyacrylamide treated FFT has been deposited to date, there is limited publicly available information on the biogeochemical and geotechnical behavior of this treated FFT. Further, the effects of pressure from overlying tailings on microbial activity and biogeochemical cycling in oil sands tailings has not been previously investigated. Twelve 5.5 L columns were designed to mimic alum/polyacrylamide treated FFT deposited beneath a water cap. A 2x2 factorial design was used to apply pressure and hydrocarbon amendments to the tailings. Pressure (0.3-5.1 kPa) was applied incrementally and columns were monitored for 360 d. Pressure significantly enhanced consolidation and microbial activity in treated FFT. Columns with pressure generated significantly more CH4(g) and CO2(g) and had significant increases in dissolved organic carbon and chemical oxygen demand in the FFT and water caps. The enhanced microbial activity in columns with pressure indicates that pressure increased the solubility of microbial substrates and metabolites in the tailings, thereby increasing the bioavailability of these compounds. Ammonium generation was significantly higher in columns with pressure, suggesting that microorganisms utilized polyacrylamide and/or N2 fixation as a nitrogen source to meet enhanced nutrient demands. Pressure also impacted microbial community structure, shifting methanogenic communities from hydrogenotrophic methanogens to predominately acetoclastic methanogens. This study also revealed the importance of sulfur cycling in treated FFT. Extensive sulfate reduction occurred in all columns, generating dissolved sulfides and H2S(g), and this was accelerated by hydrocarbon amendments.

On the Response to Aging of OPEFB/Acrylic Composites: A Fungal Degradation Perspective

Biological agents and their metabolic activity produce significant changes over the microstructure and properties of composites reinforced with natural fibers. In the present investigation, oil palm empty fruit bunch (OPEFB) fiber-reinforced acrylic thermoplastic composites were elaborated at three processing temperatures and subjected to water immersion, Prohesion cycle, and continuous salt-fog aging testing. After exposition, microbiological identification was accomplished in terms of fungal colonization. The characterization was complemented by weight loss, mechanical, infrared, and thermogravimetric analysis, as well as scanning electron microscopy. As a result of aging, fungal colonization was observed exclusively after continuous salt fog treatment, particularly by different species of Aspergillus spp. genus. Furthermore, salt spray promoted filamentous fungi growth producing hydrolyzing enzymes capable of degrading the cell walls of OPEFB fibers. In parallel, these fibers swelled due to humidity, which accelerated fungal growth, increased stress, and caused micro-cracks on the surface of composites. This produced the fragility of the composites, increasing Young's modulus, and decreasing both elongation at break and toughness. The infrared spectra showed changes in the intensity and appearance of bands associated with functional groups. Thermogravimetric results confirmed fungal action as the main cause of the deterioration.

Assessing the enhanced reduction effect with the addition of sulfate based P inactivating material during algal bloom sedimentation

The typical harm effect of algal bloom sedimentation is to increase sulfides level in surroundings, threatening aquatic organisms and human health; whereas, P inactivating materials containing sulfate are commonly attempted to be used to immobilize reactive P or to flocculate excessive algae in water columns for eutrophication control. In this study, variations in sulfate reduction during algal bloom sedimentation with the addition of sulfate based inactivating materials was comprehensively assessed based on using Al₂(SO₄)₃ with comparison to AlCl₃. The results showed that addition of Al₂(SO₄)₃ had more substantial effect on overlying water and sediment properties compared to those of ACl₃. Al₂(SO₄)₃ can enhance sulfate reduction, resulting in temporary increase of sulfides (p < 0.01) and quick decrease of various Fe (p < 0.01) in overlying water and then promoting the formation of FeS and FeS₂ (determined by EXAFS analysis) in sediments. Most importantly, the increased sulfides, as well as the physical barrier on sediment formed due to Al₂(SO₄)₃ addition, enhanced the transformation of sulfides to odorous contaminants, increasing odorous contaminants (especially methyl thiols) production by approximately one order of magnitude in overlying water. Furthermore, the increased sulfides facilitated to the enrichment of microorganisms related to S cycles (Thiobacillu with relative abundance of 23.8%) and even promoted to enrich bacterial genus potentially with pathogenicity (Treponema) in sediments. The impacts of sulfate tended to be regulated by algae concentration; however, careful management was recommended for sulfate based inactivating materials application to control eutrophication with algal blooms.

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.

Organic matter stabilized Fe in drinking water treatment residue with implications for environmental remediation

Fe-based materials used to adsorb P are commonly considered to be limited by the increased Fe lability, while Fe in drinking water treatment residue (DWTR) shows stable P adsorption abilities. Accordingly, this study aimed to gain insight into Fe lability in DWTR as compared to FeCl₃ and Fe₂(SO₄)₃ using Fe fractionation, EXAFS, and high-throughput sequencing technologies. The results showed that compared to Fe₂(SO₄)₃ and FeCl₃, Fe was relatively stable in the DWTR under the effects of organic matter, sulfides, and anaerobic conditions. Typically, the addition of FeCl₃ and Fe₂(SO₄)₃ enhanced Fe mobility in sediment and overlying water, promoting the formation of Fe-humin acid and ferrous sulfides (FeS and FeS₂). However, the addition of DWTR, even at relatively high doses of Fe, has limited impact on Fe mobility. The addition remarkably increased oxidizable Fe in sediment (by approximately 63%), causing Fe to be dominated by oxidizable and residual fractions (like those in raw DWTR); EXAFS analysis also suggested that Fe-humin acid increased substantially with the addition of DWTR, becoming the main Fe species in sediment (with a relative abundance of 50.1%). Importantly, the Fe distributions were stable in sediment with DWTR added, which demonstrated that organic matter stabilized the Fe in the DWTR. Further analysis indicated that all materials promoted the enrichment of bacterial genera potentially related to Fe metabolism (e.g., Bacteroides, Dok59, and Methanosarcina). Fe₂O₃ in the FeCl₃ and Fe₂(SO₄)₃ groups and Fe-HA in the DWTR group were the key species affecting the microbial communities. Overall, the stabilizing effect of organic matter on Fe in DWTR could be used to develop Fe-based materials to enhance Fe stability for environmental remediation.