Lars Rehmann

Remediation of PAH contaminated soils: application of a solid-liquid two-phase partitioning bioreactor.

The feasibility of a two-step treatment process has been assessed at laboratory scale for the remediation of soil contaminated with a model mixture of polycyclic aromatic hydrocarbons (PAHs) (phenanthrene, pyrene, and fluoranthene). The initial step of the process involved contacting contaminated soil with thermoplastic, polymeric pellets (polyurethane). The ability of three different mobilizing agents (water, surfactant (Biosolve) and isopropyl alcohol) to enhance recovery of PAHs from soil was investigated and the results were compared to the recovery of PAHs from dry soil. The presence of isopropyl alcohol had the greatest impact on PAH recovery with approximately 80% of the original mass of PAHs in the soil being absorbed by the polymer pellets in 48 h. The second stage of the suggested treatment involved regeneration of the PAH loaded polymers via PAH biodegradation, which was carried out in a solid-liquid two-phase partitioning bioreactor. In addition to the PAH containing polymer pellets, the bioreactor contained a microbial consortium that was pre-selected for its ability to degrade the model PAHs and after a 14 d period approximately 78%, 62% and 36% of phenanthrene, pyrene, and fluoranthene, respectively, had been desorbed from the polymer and degraded. The rate of phenanthrene degradation was shown to be limited by mass transfer of phenanthrene from the polymer pellets. In case of pyrene and fluoranthene a combination of mass transfer and biodegradation rate might have been limiting.

Deep eutectic solvent pretreatment and subsequent saccharification of corncob

Ionic liquid (ILs) pretreatment of lignocellulosic biomass has attracted broad scientific interest, despite high costs, possible toxicity and energy intensive recycling. An alternative group of ionic solvents with similar physicochemical properties are deep eutectic solvents (DESs). Corncob residues were pretreated with three different DES systems: choline chloride and glycerol, choline chloride and imidazole, choline chloride and urea. The pretreated biomass was characterised in terms of lignin content, sugars concentration, enzymatic digestibility and crystallinity index. A reduction of lignin and hemicellulose content resulted in increased crystallinity of the pretreated biomass while the crystallinity of the cellulose fraction could be reduced, depending on DES system and operating conditions. The subsequent enzymatic saccharification was enhanced in terms of rate and extent. A total of 41 g fermentable sugars (27 g glucose and 14 g xylose) could be recovered from 100g corncob, representing 76% (86% and 63%) of the initially available carbohydrates.

Extrusion pretreatment of lignocellulosic biomass: a review.

Bioconversion of lignocellulosic biomass to bioethanol has shown environmental, economic and energetic advantages in comparison to bioethanol produced from sugar or starch. However, the pretreatment process for increasing the enzymatic accessibility and improving the digestibility of cellulose is hindered by many physical-chemical, structural and compositional factors, which make these materials difficult to be used as feedstocks for ethanol production. A wide range of pretreatment methods has been developed to alter or remove structural and compositional impediments to (enzymatic) hydrolysis over the last few decades; however, only a few of them can be used at commercial scale due to economic feasibility. This paper will give an overview of extrusion pretreatment for bioethanol production with a special focus on twin-screw extruders. An economic assessment of this pretreatment is also discussed to determine its feasibility for future industrial cellulosic ethanol plant designs.

Polymer Selection for Biphenyl Degradation in a Solid‐Liquid Two‐Phase Partitioning Bioreactor

The commercially available thermoplastic polymer Hytrel was selected as the delivery phase for the hydrophobic model compound biphenyl in a solid‐liquid two‐phase partitioning bioreactor (TPPB), and 2.9 g biphenyl could successfully be degraded in 1‐L TPPBs by a pure culture of the biphenyl‐degrading bacterium Burkholderia xenovorans LB400 in 50 h and by a mixed microbial consortium isolated from contaminated soil in 45 h. TPPBs consist of an aqueous cell‐containing phase and an immiscible second phase that partitions toxic and/or poorly soluble substrates (in this case biphenyl) on the basis of maintaining a thermodynamic equilibrium. This paper illustrates a rational strategy for selecting a suitable solid polymeric substance for the delivery of the poorly water‐soluble model compound biphenyl. The partitioning of biphenyl between the selected polymers and water was analogous to partitioning of solutes between two immiscible liquid phases. The partitioning coefficients varied between 180 for Nylon 6.6 and 11,000 for Desmopan, where the later numerical value is comparable to biphenyl partitioning coefficients between water and organic solvents. Employing a solid delivery phase enabled the utilization of a surfactant‐producing microbial mixed culture, which could not be cultivated in liquid‐liquid TPPBs and thereby extended the range of biocatalysts that can be employed in TPPBs.

Pyrolysis based bio-refinery for the production of bioethanol from demineralized ligno-cellulosic biomass

This paper evaluates a novel biorefinery approach for the conversion of lignocellulosic biomass from pinewood. A combination of thermochemical and biochemical conversion was chosen with the main product being ethanol. Fast pyrolysis of lignocellulosic biomasss with fractional condensation of the products was used as the thermochemical process to obtain a pyrolysis-oil rich in anhydro-sugars (levoglucosan) and low in inhibitors. After hydrolysis of these anhydro-sugars, glucose was obtained which was successfully fermented, after detoxification, to obtain bioethanol. Ethanol yields comparable to traditional biochemical processing were achieved (41.3% of theoretical yield based on cellulose fraction). Additional benefits of the proposed biorefinery concept comprise valuable by-products of the thermochemical conversion like bio-char, mono-phenols (production of BTX) and pyrolytic lignin as a source of aromatic rich fuel additive. The inhibitory effect of thermochemically derived fermentation substrates was quantified numerically to compare the effects of different process configurations and upgrading steps within the biorefinery approach.

Cellulosic butanol production from alkali-pretreated switchgrass (Panicum virgatum) and phragmites (Phragmites australis).

A potential dedicated energy crop (switchgrass) and an invasive (North America) plant species (phragmites) were compared as potential substrates for acetone butanol ethanol (ABE) fermentation. Both biomass were pretreated with 1% (w/v) NaOH and subjected to enzymatic hydrolysis. Total reducing sugar yields were 365 and 385gkg(-1) raw biomass for switchgrass and phragmites. Fermentation of the hydrolysates resulted in overall ABE yields of 146 and 150gkg(-1) (per kg dry plant material), with a theoretical maximum of 189 and 208gkg(-1), respectively. Though similar overall solvent yields were obtained from both crops, the largest carbon loss in the case of switchgrass occurred during pretreatment, while the largest loss in the case of phragmites occurred to enzymatic hydrolysis. These findings suggest that higher overall yields are achievable and that both crops are suitable feedstocks for butanol fermentation.

Degradation of estrone in water and wastewater by various advanced oxidation processes

A comprehensive study was conducted to determine the relative efficacy of various advanced oxidation processes such as O3, H2O2, UV, and combinations of UV/O3, UV/H2O2 for the removal of estrone (E1) from pure water and secondary effluent. In addition to the parent compound (E1) removal, performance of the advanced oxidation processes was characterized using removal of total organic carbon (TOC), and estrogenicity of the effluent. Although E1 removal was high for all the AOPs, intermediates formed were more difficult to degrade leading to slow TOC removal. Energy calculations and cost analysis indicated that, although UV processes have low electricity cost, ozonation is the least cost option (

On the Use, and Reuse, of Polymers for the Treatment of Hydrocarbon Contaminated Water Via a Solid-liquid Partitioning Bioreactor

0.34/1000 gallons) when both capital and operating costs were taken into account. Ozonation also is superior to the other tested AOPs due to higher removal of TOC and estrogenicity. The rate of E1 removal decreased linearly with the background TOC in water, however, E1 degradation in the secondary effluent from a local wastewater treatment plant was not affected significantly due to the low COD values in the effluent.

Enzymatic hydrolysis of steam exploded corncob residues after pretreatment in a twin-screw extruder

Aqueous environments contaminated with diesel components pose a threat to the native biota due to the intrinsically toxic nature of the many hydrocarbon compounds present. In the event of diesel being released into an aqueous environment it is imperative that the contaminant is recovered in a rapid manner to ensure the safety of aquatic organisms as well as to maintain desired water quality. The research presented in this study investigates the potential of polymeric sorbents to recover diesel from a contaminated aqueous source. Thermoplastic materials, such as styrene butadiene derived polymers, were shown to substantially reduce diesel levels in excess of 98% with 90% of this recoverable fraction being removed in less than 30 min. Recyclable materials, such as used automobile tires, were shown to obtain similar results with added potential benefit including lower cost and reuse of a waste material. The polymeric sorbents were also biologically regenerated and this was accomplished in a solid–liquid two‐phase partitioning bioreactor, in which 65% of the initial diesel contamination was degraded within a 9 day period. The result of this work was the demonstration of a low cost, reusable remediation technology for the recovery, and destruction of diesel from aqueous environments.

Measuring the effect of ionic liquids on laccase activity using a simple, parallel method

A modified twin-screw extruder incorporated with a filtration device was used as a liquid/solid separator for xylose removal from steam exploded corncobs. A face centered central composite design was used to study the combined effects of various enzymatic hydrolysis process variables (enzyme loading, surfactant addition, and hydrolysis time) with two differently extruded corncobs (7% xylose removal, 80% xylose removal) on glucose conversion. The results showed that the extrusion process led to an increase in cellulose crystallinity, while structural changes could also be observed via SEM. A quadratic polynomial model was developed for predicting the glucose conversion and the fitted model provided an adequate approximation of the true response as verified by the analysis of variance (ANOVA).