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In this study, oxidation-reduction potential (ORP) was employed to regulate oxygen dosing for online sulfide toxicity control during anaerobic treatment of high sulfate wastewater. The experiment was conducted in an upflow anaerobic filter, which was operated at a constant influent total organic carbon of 6,740 mg/L [equivalent to a chemical oxygen demand (COD) of 18,000 mg/L], but with different influent sulfates of 1,000, 3,000, and 6,000 mg/L. The reactor was initially run at natural ORP (the system’s ORP without oxygenation) of about —290 to —300 mV and then was followed by oxygenation to raise ORP by +25 mV above the natural level for each influent sulfate level. At 6,000 mg/L sulfate under the natural ORP, methanogenesis was severely inhibited due to sulfide toxicity, and the anaerobic process was almost totally upset. Upon oxygenation by raising ORP to —265 mV, the dissolved sulfide was quickly reduced to 12.2 mg S/L with a concomitant improvement in methane yield by 45.9%. If oxygen was not totally used up by sulfide oxidation, the excess oxygen was consumed by facultative bacteria which had been found to stabilize about 13.5% of the influent COD. Both sulfide oxidation and facultative activity acted as a shield to protect the anaerobes from an excessive oxygen exposure. This study showed that direct oxygenation of the recirculated biogas was effective to oxidize sulfide, and the use of ORP to regulate the oxygen dosing was practical and reliable during anaerobic treatment of high sulfate wastewater.

In this study, oxidation-reduction potential (ORP) was used as a controlling parameter to regulate oxygen dosing to the recycled biogas for online sulfide oxidation in an upflow anaerobic filter (UAF) system. The UAF was operated with a constant influent COD of 18,000 mg/L, but with different influent sulfates of 1000, 3000 and 6000 mg/L. The reactor was initially operated under a natural ORP of -290 mV (without oxygen injection), and was then followed by oxygenation to raise its ORP by 25 mV above the natural level for each influent sulfate condition. At 6,000 mg/L sulfate without oxygen injection, the dissolved sulfide reached 733.8 mg S/L with a corresponding free sulfide of 250.3 mg S/L, thus showing a considerable inhibition to methanogens. Upon oxygenation to raise its ORP to -265 mV (i.e., a 25 mV increase), the dissolved sulfide was reduced by more than 98.5% with a concomitant 45.9% increase of the methane yield. Under lower influent sulfate levels of 1,000 and 3,000 mg/L, the levels of sulfides produced, even under the natural ORP, did not impose any noticeable toxicity to methanogens. Upon oxygenation to raise the ORP by +25 mV, the corresponding methane yields were actually reduced by 15.5% and 6.2%, respectively. However, such reductions were not due to the adverse impact of the elevated ORP; instead, they were due to a diversion of some organic carbon to support the facultative activities inside the reactor as a result of excessive oxygenation. In other words, to achieve satisfactory sulfide oxidation for the lower influent sulfate conditions, it was not necessary to raise the ORP by as much as +25 mV. The ORP increase actually needed depended on both the influent sulfate and also actual wastewater characteristics. This study had proved that the ORP controlled oxygenation was reliable for achieving consistent online sulfide control.

The compositional changes of Napier grass (Pennisetum purpureum) with respect to maturity (namely, 2, 4, 6, and 8 months age), and its effect on anaerobic digestion was examined under three sieving regimes (6, 10, and 20 mm). Significant changes in plant composition were observed with crop maturity. The highest methane yields of 219 ± 4.9 NmL/g VS added was found for biomass harvested at 2 months old compared to 189 ± 7.3, 131 ± 4.7, and 104 ± 2.3 NmL of methane/g VS added, respectively, for 4, 6, and 8 months old biomass. For all ages, feedstock passed through a 6 mm sieve resulted in significantly higher methane yields compared to biomass passed through 10 and 20 mm sieves. Additionally, 2 months old biomass exhibited the highest digestibility of cellulose and hemicellulose, whereas digestibility of cellulose and hemicellulose were lowest for the biomass harvested at 8 months of maturity.

Pot studies as well as field experiments with sunflower (Pacific ‐ 33) and grass (Zoysia matrella) were conducted to investigate the suitability of Bangkok sewage and nightsoil sludges in agricultural application with respect to potentially toxic elements. Pots with pure nightsoil sludge showed highly promising results, however no plants grew‐up voluntarily in pure sewage sludge. Turf application of sewage and nightsoil sludges gave a significantly good yield but no significant differences were found with application rate of 0.50 and 0.25 cm in respect of PTEs accumulation. Field experiment with sunflower depicted that high concentration of Zn, Mn and Cu was accumulated in sunflower leaves. None of these metal concentrations exceeded the intolerable limit of plant. The application of sludges to agricultural land exhibited positive response to plant growth and yield.

Aquaculture is one of the fastest-growing segments of the food economy in modern times. It is also being considered as an important source of greenhouse gas (GHG) emissions. To date, limited studies have been conducted on GHG emissions from aquaculture system. In this study, daily addition of fish feed and soluble starch at a carbon-to-nitrogen (C/N) ratio of 16:1 (w/w) was used to examine the effects of carbohydrate addition on nitrogen transformations and GHG emissions in a zero-water exchange intensive aquaculture system. The addition of soluble starch stimulated heterotrophic bacterial growth and denitrification, which led to lower total ammonia nitrogen, nitrite and nitrate concentrations in aqueous phase. About 76.2% of the nitrogen output was emitted in the form of gaseous nitrogen (i.e., N2 and N2O) in the treatment tank (i.e., aquaculture tank with soluble starch addition), while gaseous nitrogen accounted for 33.3% of the nitrogen output in the control tank (i.e., aquaculture tank without soluble starch addition). Although soluble starch addition reduced daily N2O emissions by 83.4%, it resulted in an increase of daily carbon dioxide (CO2) emissions by 91.1%. Overall, starch addition did not contribute to controlling the GHG emissions from the aquaculture system.

The potential for large-scale production of an edible fungus, Rhizopus oligosporus, on a liquid residue from sugar-to-ethanol production, vinasse, was investigated. An airlift bioreactor (2.5-L working volume) was used for cultivating the fungus on 75% (v/v) vinasse with nutrient supplementation (nitrogen and phosphorus) at 37°C and pH 5.0. Aeration rates were varied from 0.5, 1.0, 1.5 to 2.0 volume(air)/volume(liquid)/min (vvm). The fungal biomass yield depended on the aeration rate, and the highest fungal biomass obtained was 8.04±0.80 (g(biomass increase)/g(initial biomass)) at 1.5vvm. The observed reductions in organic content by 80% (as soluble chemical oxygen demand) suggest the potential of recycling treated effluent as process water for in-plant use or for land applications. The fungal biomass contained ~50% crude protein and the essential amino acids contents were comparable to commercial protein sources for aquatic feeds (fishmeal and soybean meal), with the exception of methionine and phenylalanine.

This study examines the effects of household detergent on anaerobic methane fermentation of wastewater from food waste disposers (FWDs). Anaerobic toxicity assay (ATA) demonstrated that methane production substantially decreased at a higher detergent concentration. The Gompertz three-parameter model fitted well with the ATA results, and both the extent of methane production (M) and methane production rate (R(m)) obtained from the model were strongly affected by the concentration of the detergent. The 50% inhibitory concentration (IC(50)) of the detergent was 603 mg/L based on R(m). Results from fatty acid methyl esters (FAMEs) analysis of microbial culture revealed that deterioration of methane fermentation was attributed to impaired structure of anaerobic microbial membrane due to detergent. This study suggests that wastewater from FWD could be used for methane production, but it is necessary to reduce the concentration of detergent prior to anaerobic fermentation.

The potential of ultrasonics to replace hydrocooking in corn-to-ethanol plants was examined in this study. Batch and continuous experiments were conducted on corn slurry with sonication at a frequency of 20 kHz. Batch mode used a catenoidal horn operated at an amplitude of 144 μm peak-to-peak (p–p) for 90 s. Continuous experiments used a donut horn operating at inner radius amplitude of 12 μm p–p. Jet-cooked samples from the same ethanol plant were compared with ultrasonicated samples. The highest starch-to-ethanol conversion was obtained by the jet-cooked samples with a yield of 74% of the theoretical yield. Batch and continuous sonication achieved 71.2% and 68% conversion, respectively, however, statistical analysis showed no significant difference between the jet cooking and ultrasonication. On the basis of the similar performance, an economic analysis was conducted comparing jet cooking and ultrasonic pretreatment. The analysis showed that the capital cost for the ultrasonics system was ~10 times higher compared to the capital cost of a hydrocooker. However,due to the large energy requirements of hydrocookers, the analysis showed lower total overall costs for continuous ultrasonication than that for jet cooking, assuming the current energy prices. Because of the high utility cost calculated for jet cooking, it is concluded that ultrasonication poses as a more economical option than jet cooking. Overall, the study shows that ultrasonics is a technically and economically viable alternative to jet cooking in dry-grind corn ethanol plant.

In this study, the volumetric mass transfer coefficients (Ka) for CO were examined in a composite hollow fiber (CHF) membrane bioreactor. The mass transfer experiments were conducted at various inlet gas pressures (from 5 to 30 psig (34.5-206.8 kPa(g))) and recirculation flow rates (300, 600, 900, 1200 and 1500 mL/min) through CHF module. The highest Ka value of 946.6 1/h was observed at a recirculation rate of 1500 mL/min and at an inlet gas pressure of 30 psig(206.8 kPa(g)). The findings of this study confirm that the use of CHF membranes is effective and improves the efficiency CO mass transfer into the aqueous phase.

Net ethanol production per unit mass of corn kernel can be significantly improved by utilizing fibrous co-products to produce cellulosic ethanol. Corn fiber is a good cellulosic feedstock to produce second-generation biofuel. A biorefinery concept is introduced to convert fibrous residue, corn fiber, into fermentable sugars at a lower temperature with minimal use of chemicals. Laboratory-scale consolidated fermentation system comprised of on-site fungal enzyme production system and simultaneous saccharification and fermentation (SSF) yielded 7.1, 8.6 and 4.1 g ethanol per 100 g corn fiber when saccharified with the white-, brown-, and soft-rot fungi, respectively. The highest corn-to-ethanol yield (8.6 g ethanol/100 g corn fiber) was equivalent to 42% of the theoretical ethanol yield from starch and cellulose in corn fiber. This is equivalent to 120 l of ethanol per metric ton of corn fiber. With process optimization, conversion of over 70% of corn fiber carbohydrate content into ethanol can generate as much as 13x109 l of ethanol per year, which is equivalent to 25% of the current annual ethanol production (52x109 l) in the US, additional $8.65 billion annual revenue and reduction in corn acreage by 3 mha. It is also possible to convert the carbohydrates to a fuel oil using a secondary oleaginous fungal process. The residual fiber enriched with fungal protein can still be utilized as animal feed without unbalancing the feed market/supply.

Volatile oil prices and an increasing world demand for energy exemplifies the critical need for renewable sources of energy, particularly in the transportation sector, which can displace a significant fraction of fossil fuels imports. Following a shift in focus from first generation starch- and sugar-based feedstocks to second generation lignocellulosic biomass, a multitude of biomass pretreatment techniques and processes has been developed to facilitate the bioconversion of plant structural carbohydrates to fermentable sugars (for biofuels production). The state-of-the-art advancements to date in the pretreatment of second generation feedstocks have been considered, with an emphasis on the maximum yields and barriers of each technology. A brief discussion on the biorefinery concept, its applications, and the potential future of biofuels has also been included.

Publisher Summary The syngas can be converted into liquid biofuels through Fischer-Tropsch (FT) synthesis (using metal catalysts) or direct microbial fermentation knownas syngas fermentation (using microbial catalysts). The FT synthesis usually utilizes metal catalysts such as cobalt (Co), ferrous (Fe), copper (Cu), aluminum (Al), zinc (Zn), molybdenum (Mo), nickel (Ni), rubidium (Ru), and ruthenium (Rh). The major drawbacks of FT synthesis are the high costs of the metal catalyst, a fixed H2:CO ratio (2:1), catalyst poisoning due to inert gases and contaminants containing sulfur, and high operating temperature and pressure. Syngas fermentation via biocatalysts (such as Clostridium ljungdahlii, C. autoethanogenum, C. carboxydivorans, Butyribacterium methylotrophicum, Methanosarcina barkeri, and Rhodospirillum rubrum) produces liquid/gaseous biofuels, and offers several advantages over the biochemical approach and the FT process. Some of the merits of syngas fermentation are the elimination of the need of expensive metal catalysts, a higher specificity of the biocatalysts, the independence of theH2:CO ratio for bioconversion, the operation of bioreactors at ambient conditions, and the elimination of issues concerning noble metal poisoning Biomass-derived syngas fermentation to biofuels is identified as a sustainable alternative for the fast depleting fossil-derived fuels. The process has several advantages including higher availability, low feedstock cost, and no competition with food and feed. The commercialization of syngas fermentation to biofuels is often plagued by the gas-to-liquid mass transfer limitations and low product yield. Innovative reactors designs and metabolic engineering aspects are being studied extensively in recent literature focusing on higher product yields. Use of CHFM (composite hollow fiber membrane) in syngas fermentation is at its infant stage and needs extensive research to prove its economic and scale-up feasibilities. Similarly, research efforts should also be directed toward production of other biofuel such as butanol and gaseous fuel, methane.

Lignocellulosic biomasses are non-food energy resources, the worldwide terrestrial availability of which is estimated to be around 200 x 10 kg (220 billion ton) annually (Foust et al., 2008). A USDA and USDOE report estimates that the United States has the potential of producing 1.3 billion dry tons of biomass annually after meeting food, feed and fiber demands, and exports (USDA and USDOE joint report, 2005), which could theoretically substitute more than 30% of the nation’s petroleum consumption. Thus, biomass may play an important role in the domestic bio-based economy through production of a variety of biofuel and biomolecules. Major lignocellulosic biomass sources include forest and woody products along with agricultural residues, agricultural processing byproducts, and energy crops. Broadly, there are two major pathways for producing biofuels from lignocellulosic feedstocks: biochemical conversion and thermochemical conversion. The biological route to obtain ethanol from lignocellulosic biomass is based on microbial fermentation of sugars derived from saccharification of cellulose biomass. A simplified process overview of ethanol production from lignocellulosic biomass via the biochemical route is shown in Figure 10.1. As cellulose is protected by lignin and intertwining hemicellulose and pectin, it is not easily accessible to the enzymes for saccharification, thus necessitating pretreatment. Pretreatment is the first operation in lignocellulosic ethanol production, which essentially prepares biomass to enzyme hydrolysis. Various forms of pretreatment are: physical, e.g. mechanical comminution, extrusion; physical-chemical, e.g. steam explosion, ammonia fiber explosion, CO2 explosion; chemical, e.g. ozonolysis, high temperature acid treatment, alkali hydrolysis, organosolv; and biological pretreatment, e.g. fungal treatments of biomass. They are well reviewed by several researchers (See Chapter 9 on Biomass Pretreatment). Depending on the type of pretreatment, the following can be accomplished: lignin breakup and crystallinity reduction in cellulose (mechanical), hemicellulose removal (acid treatment), delignification (alkaline, oxidative delignification, biological), breakup of internal lignin and hemicelluloses bonds (organosolv), size reduction (comminution), or the generation of high shear, high pressure (extrusion) conditions. In all cases, pretreatment prepares the biomass for

Biomass preprocessing is one of the primary operations in the feedstock supply system. Preprocessing essentially prepares biomass into a form suitable for transportation, storage and handling prior to its conversion to biofuel and other biobased products (Wright et al., 2006). The importance of biomass preprocessing to the overall bio-based industry lies on its influence on critical cost and quality barriers associated with bulk biomass handling, transportation, and variability in quality. The harvesting window of biomass depends on geographical locations and prevailing weather conditions like rain, snow, extreme temperatures, and relative humidity among others. In addition, the physical and compositional characteristics of biomass vary significantly. The harvested biomass has low bulk density, high moisture content, and varying composition in addition to different shape and size (USDOE, 2003). Conversion of non-preprocessed biomass to biofuels or other biobased chemicals is uneconomical due to high delivery costs and greater risk of variability in feedstock quality. The orderly flow of biomass from field to conversion facilities has the following major requirements

The effect of mild alkali and steam pretreatments on fungal saccharification and sequential simultaneous-saccharification and fermentation (SSF) of corn fiber to ethanol was studied. The corn fiber was pretreated with: (i) 2% NaOH (w/w) at 30 degrees C for 2h and (ii) steaming at 100 degrees C for 2h. Ethanol yields were 2.6g, 2.9g and 5.5g ethanol/100g of corn fiber, respectively, for Phanerochaete chrysosporium, Gloeophyllum trabeum and Trichoderma reesei saccharification and sequential SSFs. SSF with commercial cellulase enzyme - Spezyme-CP had 7.7g ethanol/100g corn fiber. Mild alkali pretreatment resulted in higher glucose yields following fungal saccharification of corn fiber. However, the ethanol yields were comparatively similar for untreated and mild alkali pretreated corn fiber. Solid-substrate fermentation of corn fiber with fungi can be improved to either eliminate or reduce the dosage of commercial cellulase enzymes during SSF.

The conversion of biomass-derived synthesis gas (or syngas in brief) into biofuels by microbial catalysts (such as Clostridium ljungdahlii, Clostridium autoethanogenum, Acetobacterium woodii, Clostridium carboxidivorans and Peptostreptococcus productus) has gained considerable attention as a promising alternative for biofuel production in the recent past. The utilization of the whole biomass, including lignin, irrespective of biomass quality, the elimination of complex pre-treatment steps and costly enzymes, a higher specificity of biocatalysts, an independence of the H(2):CO ratio for bioconversion, bioreactor operation at ambient conditions, and no issue of noble metal poisoning are among the major advantages of this process. Poor mass transfer properties of the gaseous substrates (mainly CO and H(2)) and low ethanol yield of biocatalysts are the biggest challenges preventing the commercialization of syngas fermentation technology. This paper critically reviews the existing literature in biomass-derived syngas fermentation into biofuels, specifically, different biocatalysts, factors affecting syngas fermentation, and mass transfer. The paper also outlines the major challenges of syngas fermentation, key performance index and technology road map, and discusses the further research needs.

We are convinced...that socially compatible and environmentally sound economic develop-ment is possible only by charting a course that makes full use of environmentally advantageoustechnologies. By this, we mean technologies that utilize resources as efficiently as possible andminimize environmental harm while increasing industrial productivity and improving qualityof life (United States National Research Council Committee, 1995).

The effects of ultrasonication of corn slurry, on particle size distribution and enzymatic hydrolysis was studied for the dry-grind mill ethanol industry. Two independent ultrasonic experiments were conducted at a frequency of 20 kHz; in batch and continuous systems. The ground corn slurry (33% m/v) was pumped at flow rates 10-28 L/min in continuous flow experiments, and sonicated at constant amplitude (20µmpeak-to-peak(p-p)). Ultrasonic batch experiments were conducted at varying amplitudes of 192-320µmp-p. After ultrasonication, StargenTM001 enzyme was added to the samples and a short 3h hydrolysis followed. The treated samples were found to yield 2-3 times more reducing sugar compared to the control (untreated) samples. In terms of energy density, the batch ultrasonic system was found to deliver 25-times more energy than the continuous flow systems. Although the experiments conducted in continuous system released less reducing sugar than the batch system, the continuous system was more energy efficient. The particle size of the sonicated corn slurry (both batch and continuous) was reduced relative to the controls (without treatment). The reduction of particle size was directly proportional to the energy input during sonication. The study suggests that both batch and continuous flow ultrasonic systems enhances enzymatic hydrolysis yield, reduces particle size of corn slurry and could be a potential effective pretreatment for corn slurry.

The potential application of ultrasonics as a pretreatment process to enhance saccharification of starch in corn-to-ethanol plants is evaluated in this paper. Due to energy intensive use of steam in hydro-cooking, ultrasonics poses a promising alternative as a pretreatment method. Two independent ultrasonic experiments were conducted at a frequency of 20 kHz; batch and continuous flow treatment. Corn slurry was obtained from a nearby ethanol plant and sonicated in batch mode at amplitude of 144µmpeak-to-peak (p-p) for 90 s using a catenoidal horn with a 10 mm diameter face. In the continuous flow treatment, corn slurry was pumped through a reactor equipped with a Branson Ultrasonics “donut horn”. Jet-cooked samples were obtained from the same ethanol plant and analyzed for comparison in fermentation yield. Ethanol yields in sonicated samples were comparable to jet-cooked samples. The glucose levels decreased with consumption during the initial stage of the fermentation and suddenly dropped after 6 h as the ethanol increased. An economic comparison was also conducted on jet cooking and ultrasonics pretreatment methods. The analysis showed that capital cost for the ultrasonics system was higher compared to the capital cost of hydrocooking. However, due to the relatively large energy demand of jet cookers, the operating costs of the hydrocooker suggest that it is cost effective to use ultrasonics.

Anaerobic biotechnology for bioenergy production , Anaerobic biotechnology for bioenergy production , کتابخانه مرکزی دانشگاه علوم پزشکی تهران

Rhizopus microsporus was grown in an attached growth system using corn wet-milling effluent as a growth medium. This strain was chosen due to its ability to effectively degrade organic matter in corn wet-milling effluent and for its properties to produce significant levels of protein, chitin and chitosan. Fungal growth and organic removal efficiency were examined under both aseptic and non-aseptic conditions with and without nutrient supplementation. Plastic composite support (PCS) tubes, composed of 50% (w/w) polypropylene (PP) and 50% (w/w) agricultural products were used as support media. Significantly higher organic removal measured as chemical oxygen demand (COD) and biomass yield were observed in the bioreactor with PCS tubes than in two control bioreactors; that is with PP tubes alone and suspended growth (without support media). This confirmed that the PCS support medium with agricultural components enhanced fungal growth and organic removal. The results showed that supplementation of nutrients (e.g., mineral salts) under aseptic conditions enhanced the COD removal from 50% to 55% and observed biomass yield from 0.11 to 0.16 g (dry-weight)/g CODremoved (i.e., from 0.10 to 0.14 g volatile solids (VS)/g CODremoved approximately). Non-aseptic operation without nutrient supplementation resulted in an observed biomass yield of 0.32 g volatile suspended solids (VSS)/g CODremoved with no significant improvement in COD removal (∼53%); whereas with nutrient supplementation, the observed biomass yield increased to 0.56 g VSS/g CODremoved and COD removal improved to 85%. The fungal system was able to degrade the organic matter with concomitant production of high-value fungal biomass. This is the first study that examined the conversion of corn milling waste stream into high value fungal protein. Biotechnol. Bioeng. © 2008 Wiley Periodicals, Inc.

This study investigates the potential application of high powered ultrasonics as a liquefaction pretreatment of sugary-2 corn slurry. Ground sugary-2 corn (Zea Mays L.) slurry was treated with ultrasonics at 20kHz and amplitudes of 192-320µmpp (peak-to-peak) for 5, 10, 15, 20 and 40 seconds. After sonication, enzymes (StargenTM001) were added to the samples to hydrolyze the starch into fermentable sugars. It was found that the reducing sugar released in the treated samples were 6-fold higher than in the non-treated samples. Scanning electron microscopy images revealed that the sugary starch was partially gelatinized during sonication. This observation was confirmed by polarized-light microscopic images, where deformed “Maltese crosses” were found. The swelling rate of sonicated samples was nearly 66 times higher than when applying conventional heating. This result confirms better gelatinization capability of ultrasonics compared to conventional heating. The maximum relative net energy gain (additional chemically released energy) of the sonicated samples was at 5s of sonication time with a power setting between 248-330W. The findings in this study indicated ultrasonics as a promising pretreatment step in sugary-2 corn hydrolysis.

Soy protein recovery from hexane-defatted soybean flakes using conventional methods is generally low. Importantly, some tightly-bound sugar in the soy flakes ends up in soy protein, thereby deteriorating the usefulness and quality of soy protein as a food ingredient. This research investigated the use of high-power ultrasound prior to soy protein extraction to simultaneously enhance protein yield and facilitate more sugar release in soy whey. The nutrient-rich soy whey was then used as a cheap growth medium to produce high-value nisin using Lactococcus lactis subsp. lactis. A nisin sensitive organism Micrococcus luteus was used as an indicator organism for international unit determination of nisin production as compared to standard. Soy flakes and water was mixed at the ratio of 1:10 (w/w). The slurry was then sonicated for 15, 30, 60 and 120 sec at a frequency of 20 kHz. The ultrasonic amplitude was maintained at 84 µmpp (peak to peak amplitude in µm) for all sonication durations. The results showed that with ultrasound pretreatment, the protein yield improved as much as by 46% in soy extract and sugar release by 50% with respect to nonsonicated samples (control). To maximize nisin production from soy whey, different parameters, such as aeration/agitation and incubation period were optimized. Nisin production from standard medium, DeMan, Rogosa and Sharpe (MRS) and soy whey was tested and compared. Maximum nisin production was achieved in stationary conditions and showed a continuous increase in yield till 48h of incubation (incubation period beyond that was not tested). Maximum nisin yield of 1.78 g/L of soy whey was obtained at 30°C and pH of 4.5 as opposed to 2.96 g/L of nisin with MRS medium

Dry grind corn milling does not reach full efficiency of starch conversion to sugars and subsequently to ethanol because of limitations in the milling process. This paper examines the use of high-power ultrasonics to enhance the release of fermentable sugars from milled dry corn. In this work, 20 kHz ultrasonic energy was used to pretreat corn mash prior to enzymatic conversion of corn starch to glucose in a batch-mode. The ultrasonic amplitude was varied from 0, 191 to 320 µmpp. The corn mash was sonicated for 0 (control), 20 and 40 seconds. Other experimental variables that were studied included the effect of temperature and pretreatment sequencing, e.g., ultrasonic pretreatment before and after enzyme addition. It was found that the reaction rate kinetics of the enzymatic reactions increased threefold for sonicated samples. Energy balance (efficiency) analysis indicated that ultrasound pretreatment released twice as much energy (as sugar) when introduced during pretreatment. Based on scanning electron microscopy examination and particle size analysis, the enhancement of the conversion was primarily attributed to particle size reduction, resulting in an increase in the surface area to volume ratio, which in turn increased the available enzymatic reaction sites. One of the most striking findings was that enzymes were not degraded by low level ultrasonication. In addition, the most significant increase in sugar yield was seen when the enzymes were added before ultrasonic pretreatment. Ultrasound has the potential to enhance the ethanol yield from cornstarch and reduce the production cost significantly in commercial dry corn milling ethanol plants.

Conventional dry-grind corn ethanol plants generate considerable amounts of low-value thin stillage. Thin stillage is currently concentrated by flash evaporation, an energy-intensive process, to produce syrup, which is blended with distillers dried grains (DDG) to produce DDGS. The condensate is recycled as process water. Thin stillage is generated in pasteurized condition and is rich in organic compounds and other nutrients, with a chemical oxygen demand (COD) of 90 g/L. The low initial pH of 4 and high nutrient levels make it an ideal medium for fungal cultivation. In this research, the fungus Rhizopus oligosporus was cultivated on thin stillage obtained from a local dry-grind ethanol plant. Preliminary batch tests in a 1.75-L reactor showed proliferous fungal growth under non-sterile conditions and COD removal of up to 86%. Suspended solids decreased from an initial 2 to 3% to as low as 0.03%, with partial removal by attachment to the fungal biomass. The effluent was well-clarified with a light yellow tint. Solids separation is very important, and the effluent from the fungal process could potentially be recycled as process water with minimal further treatment. The fungal biomass is high in lysine (corn protein is low) making it a nutritionally beneficial livestock feed; if fungal cell walls are disrupted, it can be co-fed with DDG to monogastrics. The ability to feed more of the byproducts to hogs and chickens would help resolve the anticipated corn grain shortfall created by the booming ethanol industry. The fungal biomass could also be used to extract chitin/chitosan.

Corn processing wastewater was treated in an attached growth system of Rhizopus oligosporus fungi. The effects of hydraulic retention time (HRT) and plant-based components in the support media were evaluated in 1 L reactors under non-aseptic conditions. Plastic composite support (PCS) tubes, composed of 50% (w/w) polypropylene (PP) and 50% (w/w) agricultural products were used as support media or, as a test, PP only. A maximum chemical oxygen demand (COD) removal of 78% was achieved at a 5 h HRT with a biomass yield of 0.44 gVSS/gCODremoved. The biomass yield increased to 0.48 gVSS/gCODremoved while COD removal reduced to 70% at a 2.5 h HRT. Competitive bacterial growth was reduced at the shorter HRT. A lower HRT of 1.25 h led to biomass wash out from the reactor. Significantly lower COD removal of 28% and biomass yield of 0.19 gVSS/gCODremoved were observed in a biofilm reactor with PP tubes alone, indicating that the agricultural components in PCS media were essential for better biofilm formation and organic removal.

Anaerobically digested swine manure (ADSM) generally contains high concentrations of zinc (Zn) and copper (Cu). These metals levels exceed the land application regulations of municipal biosolids of many European countries and are on the borderline of exceptional quality in the U.S. Environmental Protection Agency (U.S. EPA) 40 CFR part 503 standards. From this perspective, a series of batch tests were conducted to evaluate the feasibility of bioleaching of Zn and Cu from ADSM so that the produced biosolids could safely be applied to land. The effect of different substrate levels (sulfur) and total solids content (as high as 9%) on metal solubilization was investigated. The results showed that metal solubilization efficiency for both Zn and Cu declined significantly with an increase in total solids from 3 to 6% and then to 9% at the same substrate level. Metal solubilization increased proportionately with increases in substrate concentration up to 6% of total solids content. However, at 9% total solids content, metal solubilization was insignificant at all substrate levels tested. At a 6% total solids level and 10 000 mg/L of substrate, 94% of Zn and 72% of Cu were solubilized. Bioleaching was also found to be effective in destruction of pathogens with approximately 2.5 log-scale reduction. The residual biosolid was found to meet the Class A biosolids standands of U.S. EPA 40 CFR part 503.

A laboratory-scale study was conducted using a completely mixed reactor with a constant influent-total-organic carbon (TOC) of 3750 mg/L to evaluate the effect of increasing influent-sulfate levels on anaerobic-treatment performance. The sulfate levels were increased stepwise from 333 to 666, 1000, 1333 and 1666 mg S/L. The results showed that an elevation of influent sulfate actually increased the TOC removal efficiency as long as the produced sulfide level did not induce toxicity. At 1333 mg S/L influent sulfate, the produced dissolved sulfide was 613 mg S/L (free sulfide = 228 mg S/L), which started to impose toxicity to the methane-producing bacteria (MPB). It was also found that the percent electron flow to the sulfate-reducing pathway increased with the increasing influent sulfate, but the direction toward the methanogenesis was correspondingly reduced. Nevertheless, under the experimental conditions tested, the majority of the influent organics was still degraded through the methanogenic pathway. Through this study, an oxidation-reduction-potential (ORP)-based oxygenation process was developed for online oxidation of sulfide in recirculating biogas. With controlled oxygen injection to raise the reactor's ORP by 25 mV, the residual sulfide in the reactor was almost totally eliminated. In case of over oxygenation, any excess oxygen was quickly consumed by the facultative organisms in the reactor, thereby imposing no toxicity to the MPB.

A series of batch tests were conducted to investigate the effects of pH and intermediate products on biological hydrogen production. The tests were run in serum bottles to determine the optimal operating conditions to maximize hydrogen production using sucrose and starch as organic substrates. Apart from hydrogen, variations in pH, volatile fatty acids, and solvent concentrations were also monitored. Initial pH was found to have a profound effect on both hydrogen production potential and hydrogen production rate. A mixed microbial culture was involved in the fermentation process with H2, propionate, acetate, butyrate, and CO2 as major products. The lowest initial pH of 4.5 gave the highest specific hydrogen production potentials of 214.0 ml H2/g chemical oxygen demand (COD) and 125.0 ml H2/g COD for sucrose and starch respectively, but with the lowest specific hydrogen production rate. Although hydrogen production started earlier with the high production rate at a higher initial pH, the duration of the production was shorter. The rapid pH depletion could have caused a metabolic alteration of the microorganisms involved in hydrogen production, thereby resulting in the shift of intermediates production pathway [variation of the acetate/butyrate (HAc/HBu) ratio] and a consequent decrease in hydrogen production. The specific hydrogen production rate was highest for the pH range of 5.5–5.7. For the optimum pH range, the HAc/HBu ratio was in the range of 3–4 for both sucrose and starch. The findings of this study can be applied in the design of a high rate hydrogen bioreactor.

A series of chemostat studies were conducted at a constant influent total organic carbon of 3750 mg/L (equivalent chemical oxygen demand (COD) of 10,000mg/L) but at different influent sulfates of 1000, 3000 and 5000 mg/L in order to investigate the feasibility of online sulfide toxicity control through periodic oxygenation to the recycled biogas stream. The oxygen dosing for sulfide oxidation was regulated by using oxidation–reduction potential (ORP) as a controlling parameter. During oxygenation at elevated ORPs of −230 and −180 mV (50 and 100 mV above natural ORP of −280 mV, respectively), the dissolved and gaseous sulfides were completely eliminated which resulted in a concomitant improvement in methane yield by 56.3% at 5000 mg/L influent sulfate. However, at influent sulfates of 1000 and 3000 mg/L, both methane generation rate and sulfate removal efficiency were dropped appreciably at elevated ORPs. Facultative heterotrophs were found to consume as high as 66.3% of the influent COD during oxygenation. For effective sulfide oxidation at lower sulfate levels, it was no longer required to raise the ORP by as much as 50 or 100 mV. The actual needed ORP increase depended on the influent sulfate. This study had proven that the ORP-controlled oxygenation was reliable for achieving consistent online sulfide control during anaerobic treatment of high-sulfate wastewater.