J. (Hans) van Leeuwen

SYNTHESIS, PROPERTIES, AND ENVIRONMENTAL APPLICATIONS OF NANOSCALE IRON-BASED MATERIALS: A REVIEW

Due to their special properties, people have been increasingly interested in studying applications of nanoscale metal materials in environmental engineering. Literature about the current research on the synthesis, properties, and environmental applications of nanoscale iron-based materials is reviewed and summarized in this article. Different physical and chemical methods used for synthesizing nano-iron-based particles with desired size, structure, and surface properties are described. We also emphasize important properties of nano-iron-based particles, including the density and intrinsic reactivity of surface sites. These properties directly influence the chemical behavior of such particles and, consequently, affect their applications in water and wastewater treatment and in air pollution control. Environmental applications of nano-iron particles are discussed in detail, including removal of chlorinated organics, heavy metals, and inorganics.

Ultrasound Applications in Wastewater Sludge Pretreatment: A Review

Municipal wastewater sludge, particularly waste activated sludge (WAS), is more difficult to digest than primary solids due to a rate-limiting cell lysis step. The cell wall and the membrane of prokaryotes are composed of complex organic materials such as peptidoglycan, teichoic acids, and complex polysaccharides, which are not readily biodegradable. Physical pretreatment, particularly ultrasonics, is emerging as a popular method for WAS disintegration. The exposure of the microbial cells to ultrasound energy ruptures the cell wall and membrane and releases the intracellular organics in the bulk solution, which enhances the overall digestibility. This review article summarizes the major findings of ultrasonic application in WAS disintegration, and elucidates the impacts of sonic treatment on both aerobic and anaerobic digestion. This review also touches on some basics of ultrasonics, different methods of quantifying ultrasonic efficacy, and some engineering aspects of ultrasonics as applied to biological sludge disintegration. The review aims to advance the understanding of ultrasound sludge disintegration and outlines the future research direction. There is general agreement that ultrasonic density is more important than sonication time for efficient sludge disintegration. Published studies showed as much as 40% improvement in solubilization of WAS following ultrasonic pretreatment. Based on kinetic models, ultrasonic disintegration was impacted in the order: sludge pH > sludge concentration > ultrasonic intensity > ultrasonic density. Both laboratory and full-scale studies showed that the integration of an ultrasonic system to the anaerobic digester improved the anaerobic digestibility significantly.

Sequential saccharification of corn fiber and ethanol production by the brown rot fungus Gloeophyllum trabeum

Degradation of lignocellulosic biomass to sugars through a purely biological process is a key to sustainable biofuel production. Hydrolysis of the corn wet-milling co-product-corn fiber-to simple sugars by the brown rot fungus Gloeophyllum trabeum was studied in suspended-culture and solid-state fermentations. Suspended-culture experiments were not effective in producing harvestable sugars from the corn fiber. The fungus consumed sugars released by fungal extracellular enzymes. Solid-state fermentation demonstrated up to 40% fiber degradation within 9days. Enzyme activity assays on solid-state fermentation filtrates confirmed the involvement of starch- and cellulose-degrading enzymes. To reduce fungal consumption of sugars and to accelerate enzyme activity, 2- and 3-d solid-state fermentation biomasses (fiber and fungus) were submerged in buffer and incubated at 37 degrees C without shaking. This anaerobic incubation converted up to almost 11% of the corn fiber into harvestable reducing sugars. Sugars released by G. trabeum were fermented to a maximum yield of 3.3g ethanol/100g fiber. This is the first report, to our knowledge, of G. trabeum fermenting sugar to ethanol. The addition of Saccharomyces cerevisiae as a co-culture led to more rapid fermentation to a maximum yield of 4.0g ethanol/100g fiber. The findings demonstrate the potential for this simple fungal process, requiring no pretreatment of the corn fiber, to produce more ethanol by hydrolyzing and fermenting carbohydrates in this lignocellulosic co-product.

Solid-Substrate Fermentation of Corn Fiber by Phanerochaete chrysosporium and Subsequent Fermentation of Hydrolysate into Ethanol

The goal of this study was to develop a fungal process for ethanol production from corn fiber. Laboratory-scale solid-substrate fermentation was performed using the white-rot fungus Phanerochaete chrysosporium in 1 L polypropylene bottles as reactors via incubation at 37 degrees C for up to 3 days. Extracellular enzymes produced in situ by P. chrysosporium degraded lignin and enhanced saccharification of polysaccharides in corn fiber. The percentage biomass weight loss and Klason lignin reduction were 34 and 41%, respectively. Anaerobic incubation at 37 degrees C following 2 day incubation reduced the fungal sugar consumption and enhanced the in situ cellulolytic enzyme activities. Two days of aerobic solid-substrate fermentation of corn fiber with P. chrysosporium, followed by anaerobic static submerged-culture fermentation resulted in 1.7 g of ethanol/100 g of corn fiber in 6 days, whereas yeast ( Saccharomyces cerevisiae) cocultured with P. chrysosporium demonstrated enhanced ethanol production of 3 g of ethanol/100 g of corn fiber. Specific enzyme activity assays suggested starch and hemi/cellulose contribution of fermentable sugar.

A comprehensive pilot plant system for fungal biomass protein production and wastewater reclamation

A comprehensive pilot plant system has been developed for fungal biomass protein (FBP) production and wastewater reclamation from starch processing wastewater (SPW). Consequently, 7.5–9.2 g/l of fungal biomass was produced at 0.65–0.88 g/l per hour in a semi-continuous process by non-aseptic cultivation of Aspergillus oryzae and Rhizopus oligosporus on SPW, without pretreatment and nutrient supplementation. The FBP products contained more than 45% protein and appreciable quantities of essential amino acids, and would be nutritive and edible for animal consumption. The subsequent removal of more than 95% BOD and COD, 75% nitrogen and phosphorus, and total suspended solids make the reclaimed SPW suitable for farm irrigation. The new system appeared to be technically feasible and may be beneficial for food and agricultural industries, with a commercial potential for reclaiming wastewater as a saleable value-added bioproduct.

Ultrasound Pretreatment of Cassava Chip Slurry to Enhance Sugar Release for Subsequent Ethanol Production

The use of ultrasound pretreatment to enhance liquefaction and saccharification of cassava chips was investigated. Cassava chip slurry samples were subjected to sonication for 10–40 s at three power levels of low (2 W/mL), medium (5 W/mL), and high (8 W/mL). The samples were simultaneously exposed to enzymes to convert starch into glucose. The cassava particle size declined nearly 40‐fold following ultrasonic pretreatment at high power input. Scanning electron micrographs of both unsonicated (control) and sonicated samples showed disruption of fibrous material in cassava chips but did not affect the granular structure of starch. Reducing sugar release improved in direct proportion to the power input and sonication time. The reducing sugar increase was as much as 180% with respect to the control groups. The slurry samples with enzyme addition during sonication resulted in better reducing sugar release than the samples with enzyme addition after sonication. The heat generated during sonication below starch gelatinization temperature apparently had no effect on the reducing sugar release. The reducing sugar yield and energy efficiency of ultrasound pretreated samples increased with total solids (TS) contents. The highest reducing sugar yield of 22 g/100 g of sample and efficiency of 323% were obtained for cassava slurry with 25% TS at high power. The reducing sugar yield at the completion of reaction (R∞) were over twofold higher compared to the control groups. The integration of ultrasound into a cassava‐based ethanol plant may significantly improve the overall ethanol yield. Biotechnol. Bioeng. 2008;101: 487–496.

Ultrasound improved ethanol fermentation from cassava chips in cassava-based ethanol plants.

The effects of ultrasound and heat pretreatments on ethanol yields from cassava chips were investigated. Cassava slurries were sonicated for 10 and 30 s at the amplitudes of 80, 160, and 320 microm(pp) (peak to peak amplitude in microm) corresponding to low, medium, and high power levels, respectively. The sonicated and non-sonicated (control) samples were then subjected to simultaneous liquefaction-saccharification and ethanol fermentation. Cassava starch-to-ethanol conversion efficiencies showed that higher ethanol yields were directly related to sonication times, but not to power levels. Significantly higher ethanol yields were observed only for sonicated samples at the high power level. The ethanol yield from the sonicated sample was 2.7-fold higher than yield from the control sample. Starch-to-ethanol conversion rates from sonicated cassava chips were also significantly higher; the fermentation time could be reduced by nearly 24 h for sonicated samples to achieve the same ethanol yield as control samples. Thus, ultrasound pretreatment enhanced both the overall ethanol yield and fermentation rate. When compared to heat-treated samples, the sonicated samples produced nearly 29% more ethanol yield. Combined heat and ultrasound treatment had no significant effect on overall ethanol yields from cassava chips. Ultrasound is also preferable to heat pretreatment because of lower energy requirements, as indicated by energy balances. Integration of ultrasound application in cassava-based ethanol plants can significantly improve ethanol yields and reduce the overall production costs.

Screening and selection of microfungi for microbial biomass protein production and water reclamation from starch processing wastewater

Thirty strains of microfungi and amylolytic yeasts were screened for production of microbial biomass protein (MBP) and water reclamation from starch processing wastewater (SPW). Three species and six strains of microfungi Aspergillus oryzae, Rhizopus oligosporus and Rhizopus arrhizus showing high enzymatic activities on SWP were selected under non-aseptic growth conditions. In 20 h submerged cultivation the selected strains had a high capacity to enzymatically hydrolyse more than 93% of the starch and produce 4.3–5.6 g dm−3 of dry biomass at a specific biomass growth rate from 0.05 to 0.12 h −2. The fungal biomass contained crude protein ranging from 37.5 to 49.8% of dry biomass. The pellet and flocculated biomass products were easily harvested by simple filtration or sedimentation. After these processes, 76–88% of total organic carbon (TOC), 85%–92% of chemical oxygen demand (COD) and 95% suspended solids in SPW were removed, and the treated water was reusable for farm irrigation. Typical pretreatment processes including hydrolysis, sterilisation and nutrient supplementation were unnecessary.

Seawater Ozonation of Bacillus subtilis Spores: Implications for the Use of Ozone in Ballast Water Treatment

The potential of ozone for disinfection of ships’ ballast water was investigated using Bacillus subtilis spores as an indicator. The effects of pH, presence of iron, and bacterial strain on disinfection efficacy in seawater, under simulated ballast conditions, were investigated. Ozone dosages of 9 mg/L (pH 7) and 14 mg/L (pH 8.2) and 24 h contact achieved a 4-log inactivation with the various oxidant residuals formed. Iron surface at a ratio to water of 9 m2/m3 impaired the oxidant residuals and the disinfection of spores. Different strains of B. subtilis resulted in different CT values. Ozone does not seem to be a good choice for the control of spore-forming organisms in ballast water, but may be suitable for the control of other species.

Ultrasonic pretreatment of corn slurry for saccharification: a comparison of batch and continuous systems.

The effects of ultrasound on corn slurry saccharification yield and particle size distribution was studied in both batch and continuous-flow ultrasonic systems operating at a frequency of 20 kHz. Ground corn slurry (28%w/v) was prepared and sonicated in batches at various amplitudes (192-320 microm(peak-to-peak (p-p))) for 20 or 40s using a catenoidal horn. Continuous flow experiments were conducted by pumping corn slurry at various flow rates (10-28 l/min) through an ultrasonic reactor at constant amplitude of 12 microm(p-p). The reactor was equipped with a donut shaped horn. After ultrasonic treatment, commercial alpha- and gluco-amylases (STARGEN 001) were added to the samples, and liquefaction and saccharification proceeded for 3h. The sonicated samples were found to yield 2-3 times more reducing sugars than unsonicated controls. Although the continuous flow treatments released less reducing sugar compared to the batch systems, the continuous flow process was more energy efficient. The reduction of particle size due to sonication was approximately proportional to the dissipated ultrasonic energy regardless of the type of system used. Scanning electron microscopy (SEM) images were also used to observe the disruption of corn particles after sonication. Overall, the study suggests that both batch and continuous ultrasonication enhanced saccharification yields and reduced the particle size of corn slurry. However, due to the large volume involve in full scale processes, an ultrasonic continuous system is recommended.