Factors influencing the enzymatic hydrolysis of soy molasses into fermentation feedstock.

Soybean processing generates huge amounts of soy molasses that can support biorefinery but require development of waste-to-value conversion technologies. Here, soy molasses processing by Aspergillus niger enzymes was studied to optimize the conversion of oligosaccharides to monomeric sugars as ready fermentation feedstock. The effects of pH and temperature were first investigated using fixed enzyme composition and loading. pH, in the tested 3.0-6.5 range, significantly affected hydrolysis particularly in galactose release. The hydrolysis was fastest at pH 4.8 and 60 °C although the 48-h sugar (glucose, fructose, and galactose) yields were similar at pH 4.8 and 5.7, and 50 and 60 °C. Study was next made at these favorable pH and temperatures using different enzyme compositions and loadings. Glucose and fructose were effectively released, reaching ∼100 % yields in 24-48 h by most of the enzymes and loadings evaluated. Galactose production was less effective and varied significantly with the pH-temperature condition and enzyme loading and composition. Mechanistic evaluation suggested formation and accumulation of galactose disaccharide, whose slow hydrolysis was rate-limiting in the systems with complete glucose and fructose releases but low galactose yields. Model equations were developed to describe the kinetic sugar-release profiles and make technoeconomic analysis, which showed that a process of lower enzyme loading, while requiring longer duration, is more economical within the analyzed range of 5-50 (U α-galactosidase/g molasses). With 5 (U/g) loading, the total cost is about 30 % lower at 60 °C-pH 5.7 than 50 °C-pH 4.8. The α-galactosidase-to-sucrase ratio plays a less significant role in affecting the overall process cost.

Advanced strategies for production of soy-processing enzyme.

Enzyme production is critical and often costly for biorefinery. It is challenging to produce enzymes with not only high titers but also proper combinations of all required activities in a single fermentation. This work aimed at improving productivity and composition of the multiple enzyme activities required for hydrolysis of complex soybean carbohydrate in a single fermentation. A previously selected Aspergillus niger strain was used for its high carbohydrases and low protease production. Strategies of fed-batch substrate addition and programmed pH-decrease rates were evaluated. Cheap soybean hull (SH) was confirmed to induce production of all necessary carbohydrases. Surprisingly, fed-batch SH addition, originally thought to sustain substrate-inducer availability and reduce feedback repression by sugars, did not increase pectinase and cellulase production significantly and even lowered the α-galactosidase production, when compared with batch fermentation having the same total SH amount (all added initially). On the other hand, the pH-decrease rate could be effectively optimized for production of complex enzyme mixtures. The best fermentation was programmed to lower pH from 7 to 4 in 84 h, at a drop rate of .0357 per h. It produced the highest pectinase (19.1 ± .04 U/mL), α-galactosidase (15.7 ± .4 U/mL), and cellulase (.88 ± .06 FPU/mL). Producing these high enzyme activities in a single fermentation significantly improves the effectiveness and economics of enzymatic soy processing, which, e.g., can hydrolyze the 30%-35% carbohydrate in soybean meal to sugars, with minimal protein degradation, to generate high-value protein-rich products and a hydrolysate as fermentation feedstock.

Application of phagotrophic algae in waste activated sludge conversion and stabilization.

Phagotrophic algae can consume bacteria that are the predominant microorganisms present in the waste activated sludge (WAS) generated from municipal wastewater treatment processes. In this study, we developed a combined ultrasonication-phagotrophic algal process for WAS conversion. The ultrasonic pretreatment released small volatile solids (VS) including bacteria from WAS flocs. A phagotrophic alga Ochromonas danica then grew by consuming more than 80% of the released VS, with approximately 30% (w/w) algal cell yield. The process reduced the overall WAS VS by 42.4% in 1 day, comparing very favorably with the 27% reduction in 10 days by aerobic digestion. For stabilizing the solids remaining from the ultrasonic step, the total oxygen uptake required was 65%-92% lower than that for the original WAS, indicating substantially reduced aeration cost. Overall, this novel process enhanced the WAS digestion at lower energy requirements and produced microalgae for other potential uses. © 2021 Water Environment Federation PRACTITIONER POINTS: At least 80% of released VS from WAS can be processed by phagotrophic algae. Significant amounts of algae can be produced from WAS. Ultrasonication-phagotrophic algal process can make sludge management more sustainable.

Aspergillus niger production of pectinase and α-galactosidase for enzymatic soy processing.

Soybean is a most promising sustainable protein source for feed and food to help meet the protein demand of the rapidly rising global population. To enrich soy protein, the environment-friendly enzymatic processing requires multiple carbohydrases including cellulase, xylanase, pectinase, α-galactosidase and sucrase. Besides enriched protein, the processing adds value by generating monosaccharides that are ready feedstock for biofuel/bioproducts. Aspergillus could produce the required carbohydrases, but with deficient pectinase and α-galactosidase. Here we address this critical technological gap by focused evaluation of the suboptimal productivity of pectinase and α-galactosidase. A carbohydrases-productive strain A. niger (NRRL 322) was used with soybean hull as inducing substrate. Temperatures at 20 °C, 25 °C and 30 °C were found to affect cell growth on sucrose with an Arrhenius-law activation energy of 28.7 kcal/mol. The 30 °C promoted the fastest cell growth (doubling time = 2.1 h) and earliest enzyme production, but it gave lower final enzyme yield due to earlier carbon-source exhaustion. The 25 °C gave the highest enzyme yield. pH conditions also strongly affected enzyme production. Fermentations made with initial pH of 6 or 7 were most productive, e.g., giving 1.9- to 2.3-fold higher pectinase and 2.2- to 2.3-fold higher α-galactosidase after 72 h, compared to the fermentation with a constant pH 4. Further, pH must be kept above 2.6 to avoid limitation in pectinase production and, in the later substrate-limiting stage, kept below 5.5 to avoid pectinase degradation. α-Galactosidase production always followed the pectinase production with a 16-24 h lag; presumably, the former relied on pectin hydrolysis for inducers generation. Optimal enzyme production requires controlling the transient availability of inducers.

Eco-friendly rhamnolipid based fungicides for protection of soybeans from Phytophthora sojae.

BACKGROUND: Excessive use of chemical fungicides over the years for plant pathogen control has caused unwanted damage to non-target organisms and resistance buildup in the target organisms. These harmful effects have prompted the industry to look for more sustainable and eco-friendly solutions. Rhamnolipid is a naturally occurring surfactant that is biodegradable, relatively innocuous to non-target species and can effectively lyse zoospores, the life form responsible for the spread of Phytophthora. In this study, rhamnolipid based coatings were developed and evaluated for protection of soybeans from P. sojae zoospores. RESULTS: Pure (acidic) rhamnolipid, when coated on the soybeans, affects the germination negatively. However, sodium and calcium complexed rhamnolipids do not interfere with germination. Seeds coated with 15-20 mg of developed formulation were planted in soil pots and then subjected to P. sojae infection by simulating flooding conditions and zoospore inoculation. Statistical analysis showed that sodium rhamnolipid based coating significantly improved the germination in presence of P. sojae from 42% to 73% (P = 0.017) while the germination of stress-free control was 85% (statistically similar to coated seeds, P = 1). CONCLUSION: Neutralized rhamnolipid can protect soybeans from P. sojae without any negative effect on germination. This work illustrates the strategy to use rhamnolipid as effective fungicide. © 2019 Society of Chemical Industry.

Conversion of wastewater-originated waste grease to polyunsaturated fatty acid-rich algae with phagotrophic capability.

Grease balls collected from a municipal wastewater treatment plant were melt-screened and used for cultivation of microalga Ochromonas danica, which could phagocytize droplets and particles as food. After autoclaving, the waste grease (WG) separated into two (upper and lower) phases. O. danica grew well on both, accumulating 48-79% (w/w) intracellular lipids. Initial WG contained approximately 50:50 triglycerides and free fatty acids (FFAs); over time, almost only FFAs remained in the extracellular WG presumably due to hydrolysis by algal lipase. PUFAs, mainly C18:2n6, C18:3n3, C18:3n6, C20:4n6, and C22:5n6, were synthesized and enriched to up to 67% of intracellular FAs, from the original 15% PUFA content in WG. The study showed feasibility of converting wastewater-originated WG to PUFA-rich O. danica algae culture, possibly as aquaculture/animal feed. WG dispersion was identified as a major processing factor to further improve for optimal WG conversion rate and cell and FA yields.

Reclamation of wastewater organics via two-stage growth of bacteria-then-oleaginous phagotrophic algae.

A substantial amount of organic matter is wasted in current wastewater treatment processes. To reclaim the value of organic matter, a two-stage continuous-flow open process has been developed by utilizing the capability of phagotrophic algae in ingesting bacterial cells. In this process, wastewater is first pumped into a bacteria tank to grow bacterial cells, and then the effluent containing grown bacteria cells is fed to an algae tank to grow phagotrophic algae. The operation conditions such as dilution rate, pH, and dissolved oxygen level were comprehensively investigated and optimized with long-term tests. Results show that phagotrophic algae can be stably cultivated with wastewater organics through this open process without costly chemical/physical sterilization. The produced phagotrophic algae had high lipid content and can be potentially used as biofuel feedstock.

Phagotrophic microalgae production from waste activated sludge under non-sterile conditions.

In this study waste activated sludge (WAS) was sonicated to release bacteria-sized volatile solids (VS) from flocs, after initial pH adjustment to 10 for higher energy efficiency. The released VS supported growth of phagotrophic alga Ochromonas danica. Initial-rate growth experiments confirmed the Monod-type kinetics but the specific cell growth rate, µ, correlated with the prey-to-predator ratio, i.e., the ratio of (fed VS concentration)-to-(initial O. danica concentration), significantly better than with the VS alone, as the typical Monod dependency on soluble substrates. The best-fit kinetics had the following parameters: µmax = 0.198 h-1 and KM = 1.056 (g-VS/g-algae). Post-sonication reflocculation could render particles too large to ingest by O. danica; therefore, pH and VS effects on reflocculation were investigated. Batch cultivations were then conducted in fermentors at pH 5, under nonsterile conditions. Algae number reached 8.86 × 1010 L-1 after 20 h, corresponding to ∼2.3 g/L dry-weight and volumetric algae productivity of 2.8 g/L-day. VS reduction was 38%, giving an O. danica VS yield of 44.5%. The ultrasonication-algae process can be used to produce algae while achieving at least partial WAS treatment.

Energy-efficient ultrasonic release of bacteria and particulates to facilitate ingestion by phagotrophic algae for waste sludge treatment and algal biomass and lipid production.

Wastewater treatment generates large amounts of waste activated sludge (WAS) that contains concentrated bacteria and particulate organics and requires costly treatment prior to disposal. This study develops an approach to harness the unique capability of oleaginous phagotrophic microalgae for treating WAS and producing algal biomass and lipids. WAS ultrasonication is studied for releasing particulates and bacteria suitable for direct ingestion by phagotrophic microalgae, without bacterial destruction/lysis, and thus minimizing energy requirement. Particle release into supernatant was followed by optical density at 610 nm (OD610) and volatile solid concentration (VS); OD610 correlated well with micron-size particle count rates measured by dynamic light scattering. Microalgae (Ochromonas danica) grew with a 7.6-h doubling time in sonication-generated WAS supernatant alone, giving approximately 66% (w/w) cell yield from consumed VS and ∼30% intracellular lipids. Effects of sonication power (P in W), WAS volume (V in mL) and sonication duration (t in s) were studied with a 3 × 3 × 6 factorial design. Supernatant OD610 increased with increasing P and t and decreasing V. Multiple linear regression gave the following equation with only significant terms: OD610TS=-0.0536+0.000592P-0.000213t+0.000003P×t+0.000274P×tV (R2 = 0.94). Sonicating 500-mL WAS at 180 W for 240 s was selected for giving high particulate release (∼29% VS) with maximal energy efficiency, corresponding to a specific energy input of 4320 kJ (kg TS)-1, which was much lower than the range (15,000-250,000 kJ (kg TS)-1) reported previously for WAS ultrasonication. The results supported development of new ultrasonication-phagotrophic algae processes for WAS treatment and algae production.

High monomeric sugar yields from enzymatic hydrolysis of soybean meal and effects of mild heat pretreatments with chelators.

Defatted soybean meal has 30-35% oligo-/polymeric carbohydrates and approximately 50% proteins. Enzymatic carbohydrate monomerization enables easy separation to enrich protein content, reduces indigestibility concerns, and facilitates use of carbohydrate as fermentation feedstock. Among soybean carbohydrates, pectin and glucan are more recalcitrant to hydrolyze. To destabilize Ca2+-bridged junctures in pectin, effects of 3 chelators ethylenediaminetetraacetic acid (EDTA), sodium hexametaphosphate (HMP) and citric acid under 2-h 90 °C pretreatments were investigated here. Citric acid was the most effective while EDTA decreased enzymatic hydrolysis. In a 3-factor 2-level factorial study, heat (90 °C, 2 h) and citric acid (10 g/L) pretreatments and cellulase supplementation (10 FPU/g) were found to increase yields of all monosaccharides, to 86.8 ±â€¯5.2% glucose, 98.1 ±â€¯1.6% xylose, 87.5 ±â€¯5.2% galactose, 83.6 ±â€¯1.6% arabinose, and 91.4 ±â€¯3.1% fructose + mannose. The largest percentage improvements were for arabinose (382%), mannose (113%) and glucose (51%). Achieving high monosaccharide yields greatly increases value of soybean carbohydrate as fermentation feedstock.

Maximize rhamnolipid production with low foaming and high yield.

Rhamnolipids are well-known microbial surfactants with many potential applications. Their production cost, however, remains high due to the severe foaming tendency in aerobic fermentation and the relatively low productivity and yield. In this study, we assessed the boundaries set by these constraints after optimization of basic parameters such as dissolved oxygen concentration (DO), pH and carbon sources. DO 10% and pH 5.5-5.7 were found optimal; cell growth and/or rhamnolipid production were slower at lower DO (5%) or pH (5.0) while foaming became hard to control at higher DO (30%) or pH (6.0 and 6.5). Although the Pseudomonas aeruginosa strain used was selected for its high rhamnolipid production from glycerol as substrate, soybean oil was still found to be a better substrate that increased specific rhamnolipid productivity to 25.8mg/g cells-h from the glycerol-supported maximum of 8.9mg/g cells-h. In addition, the foam volume was approximately halved by using soybean oil instead of glycerol as substrate. Analysis by liquid chromatography coupled with mass spectrometry revealed that rhamnolipid compositions from the two carbon sources were also very different, with primarily (82%) monorhamnolipids from soybean oil and more (64%) dirhamnolipids from glycerol. The optimized fermentation produced 42g/l rhamnolipids at a yield of approximately 47% and a volumetric productivity of 220mg/l-h. These values are among the highest reported.

Minimization of fermentation inhibitor generation by carbon dioxide-water based pretreatment and enzyme hydrolysis of guayule biomass.

Guayule rubber production leaves >80% biomass as ground bagasse, which can be hydrolyzed to release sugars but also fermentation inhibitors. Here inhibitor generation and sugar conversion by the CO2-H2O pretreatment and enzyme hydrolysis were studied. Different pretreatment conditions: 550-4900 psi, 160-195 °C, 10-60 min and fixed 66.7% water, generated widely varying amounts of inhibitors (per dry-bagasse mass): 0.014-0.252% hydroxymethylfurfural, 0.012-0.794% furfural and 0.17-8.02% acetic acid. The condition (195 °C/3400 psi/30 min) giving highest reducing sugar (86.9 ±â€¯1.5%) and cellulose (99.2 ±â€¯1.3%) conversions generated more inhibitors. Kluyveromyces marxianus fermentation showed complete growth and ethanol production inhibition at ≥14 g/L combined inhibitors. Considering both sugars and inhibitors, the optimum condition was 180 °C, 1800 psi and 30 min, enabling 82.8 ±â€¯2.8% reducing sugar, 74.8 ±â€¯4.8% cellulose and 88.5 ±â€¯6.9% hemicellulose conversions with low levels of hydroxymethylfurfural (0.07%), furfural (0.25%) and acetic acid (3.0%). The optimized CO2-H2O pretreatment gave much lower inhibitor formation and higher sugar conversion than other pretreatment methods.

Production of arabitol from enzymatic hydrolysate of soybean flour by Debaryomyces hansenii fermentation.

Arabitol is a low-calorie sugar alcohol with anti-cariogenic properties. Enzymatic hydrolysate of soybean flour is a new renewable biorefinery feedstock containing hexose, pentose, and organic nitrogen sources. Arabitol production by Debaryomyces hansenii using soybean flour hydrolysate was investigated. Effects of medium composition, operating conditions, and culture stage (growing or stationary phase) were studied. Production was also compared at different culture volumes to understand the effect of dissolved oxygen concentration (DO). Main factors examined for medium composition effects were the carbon to nitrogen concentration ratio (C/N), inorganic (ammonium) to organic nitrogen ratio (I/O-N), and sugar composition. Arabitol yield increased with increasing C/N ratio and a high I/O-N (0.8-1.0), suggesting higher yield at stationary phase of low pH (3.5-4.5). Catabolite repression was observed, with the following order of consumption: glucose > fructose > galactose > xylose > arabinose. Arabitol production also favored hexoses and, among hexoses, glucose. DO condition was of critical importance to arabitol production and cell metabolism. The yeast consumed pentoses (xylose and arabinose) only at more favorable DO conditions. Finally, arabitol was produced in fermentors using mixed hydrolysates of soy flour and hulls. The process gave an arabitol yield of 54%, volumetric productivity of 0.90 g/L-h, and specific productivity of 0.031 g/g-h.

CO2-H2O based pretreatment and enzyme hydrolysis of soybean hulls.

The high carbohydrate content of soybean hull makes it an attractive biorefinery resource. But hydrolyzing its complex structure requires concerted enzyme activities, at least cellulase, xylanase, pectinase and α-galactosidase. Effective pretreatment that generates minimal inhibitory products is important to facilitate enzymatic hydrolysis. Combined CO2-H2O pretreatment and enzymatic hydrolysis by Aspergillus niger and Trichoderma reesei enzyme broths was studied here. The pretreatment was evaluated at 80°C-180°C temperature and 750psi-1800psi pressure, with fixed moisture content (66.7%) and pretreatment time (30min). Ground hulls without and with different pretreatments were hydrolyzed by enzyme at 50°C and pH 4.8 and compared for glucose, xylose, galactose, arabinose, mannose and total reducing sugar release. CO2-H2O pretreatment at 1250psi and 130°C was found to be optimal. Compared to the unpretreated hulls hydrolyzed with 2.5-fold more enzyme, this pretreatment improved glucose, xylose, galactose, arabinose and mannose releases by 55%, 35%, 105%, 683% and 52%, respectively. Conversions of 97% for glucose, 98% for xylose, 41% for galactose, 59% for arabinose, 87% for mannose and 89% for total reducing sugar were achieved with Spezyme CP at 18FPU/g hull. Monomerization of all carbohydrate types was demonstrated. At the optimum pretreatment condition, generation of inhibitors acetic acid, furfural and hydroxymethylfurfural (HMF) was negligible, 1.5mg/g hull in total. The results confirmed the effective CO2-H2O pretreatment of soybean hulls at much lower pressure and temperature than those reported for biomass of higher lignin contents. The lower pressure requirement reduces the reactor cost and makes this new pretreatment method more practical and economical.

Enzyme-based processing of soybean carbohydrate: Recent developments and future prospects.

Soybean is well known for its high-value oil and protein. Carbohydrate is, however, an underutilized major component, representing almost 26-30% (w/w) of the dried bean. The complex soybean carbohydrate is not easily hydrolyzable and can cause indigestibility when included in food and feed. Enzymes can be used to hydrolyze the carbohydrate for improving soybean processing and value of soybean products. Here the enzyme-based processing developed for the following purposes is reviewed: hydrolysis of different carbohydrate-rich by/products from soybean processing, improvement of soybean oil extraction, and increase of nutritional value of soybean-based food and animal feed. Once hydrolyzed into fermentable sugars, soybean carbohydrate can find more value-added applications and further improve the overall economics of soybean processing.

Enzyme recycle and fed-batch addition for high-productivity soybean flour processing to produce enriched soy protein and concentrated hydrolysate of fermentable sugars.

Despite having high protein and carbohydrate, soybean flour utilization is limited to partial replacement of animal feed to date. Enzymatic process can be exploited to increase its value by enriching protein content and separating carbohydrate for utilization as fermentation feedstock. Enzyme hydrolysis with fed-batch and recycle designs were evaluated here for achieving this goal with high productivities. Fed-batch process improved carbohydrate conversion, particularly at high substrate loadings of 250-375g/L. In recycle process, hydrolysate retained a significant portion of the limiting enzyme α-galactosidase to accelerate carbohydrate monomerization rate. At single-pass retention time of 6h and recycle rate of 62.5%, reducing sugar concentration reached up to 120g/L using 4ml/g enzyme. When compared with batch and fed-batch processes, the recycle process increased the volumetric productivity of reducing sugar by 36% (vs. fed-batch) to 57% (vs. batch) and that of protein product by 280% (vs. fed-batch) to 300% (vs. batch).

Soybean hull induced production of carbohydrases and protease among Aspergillus and their effectiveness in soy flour carbohydrate and protein separation.

Soybean hull consists mainly of three major plant carbohydrates, i.e., cellulose, hemicellulose and pectin. It is inexpensive and a good potential substrate for carbohydrase production because it is capable of inducing a complete spectrum of activities to hydrolyze complex biomass. Aspergillus is known for carbohydrase production but no studies have evaluated and compared, among Aspergillus species and strains, the soybean hull induced production of various carbohydrases. In this study, A. aculeatus, A. cinnamomeus, A. foetidus, A. phoenicis and 11 A. niger strains were examined together with T. reesei Rut C30, another known carbohydrase producer. The carbohydrases evaluated included pectinase, polygalacturonase, xylanase, cellulase, α-galactosidase and sucrase. Growth morphology and pH profiles were also followed. Among Aspergillus strains, morphology was found to correlate with both carbohydrase production and pH decrease profile. Filamentous strains gave higher carbohydrase production while causing slower pH decrease. The enzyme broths produced were also tested for separation of soy flour carbohydrate and protein. Defatted soy flour contains about 53% protein and 32% carbohydrate. The enzymatic treatment can increase protein content and remove indigestible oligo-/poly-saccharides, and improve use of soy flour in feed and food. Protease production by different strains was therefore also compared for minimizing protein degradation. A. niger NRRL 322 and A. foetidus NRRL 341 were found to be the most potent strains that produced maximal carbohydrases and minimal protease under soybean hull induction.

Soybean bio-refinery platform: enzymatic process for production of soy protein concentrate, soy protein isolate and fermentable sugar syrup.

Soybean carbohydrate is often found to limit the use of protein in soy flour as food and animal feed due to its indigestibility to monogastric animal. In the current study, an enzymatic process was developed to produce not only soy protein concentrate and soy protein isolate without indigestible carbohydrate but also soluble reducing sugar as potential fermentation feedstock. For increasing protein content in the product and maximizing protein recovery, the process was optimized to include the following steps: hydrolysis of soy flour using an Aspergillus niger enzyme system; separation of the solid and liquid by centrifugation (10 min at 7500×g); an optional step of washing to remove entrapped hydrolysate from the protein-rich wet solid stream by ethanol (at an ethanol-to-wet-solid ratio (v/w) of 10, resulting in a liquid phase of approximately 60 % ethanol); and a final precipitation of residual protein from the sugar-rich liquid stream by heat treatment (30 min at 95 °C). Starting from 100 g soy flour, this process would produce approximately 54 g soy protein concentrate with 70 % protein (or, including the optional solid wash, 43 g with 80 % protein), 9 g soy protein isolate with 89 % protein, and 280 ml syrup of 60 g/l reducing sugar. The amino acid composition of the soy protein concentrate produced was comparable to that of the starting soy flour. Enzymes produced by three fungal species, A. niger, Trichoderma reesei, and Aspergillus aculeatus, were also evaluated for effectiveness to use in this process.

Rhamnolipid Adsorption in Soil: Factors, Unique Features, and Considerations for Use as Green Antizoosporic Agents.

In aqueous solutions, rhamnolipids effectively kill the motile zoospores responsible for spreading many pathogens, including soy-infecting Phytophthora sojae. For use in soil, adsorption properties need to be considered. Having low critical micelle concentrations, rhamnolipids tend to form micelles/aggregates with unknown effects on soil adsorption. Effects of soil pH, rhamnolipid congener structure, and concentration were examined. Congeners were identified and each quantitated for adsorptive partitioning. The adsorption isotherm at pH 6.5 showed a multi-stage profile plateauing at 1700 µg/g of soil. Less hydrophilic congeners adsorbed preferentially: R-C10-C12 > R-C10-C12:1 > RR-C10-C12:1 > RR-C10-C12 > R-C10-C10 > RR-C10-C10 > R-C8-C10 > RR-C8-C10 (where R is rhamnose and C# is the carbon number of ß-hydroxy fatty acid). Adsorptive selectivity among congeners was very clear in dilute solutions but diminished with increasing concentrations. Results were interpreted with aggregate formation in solutions and on the soil surface. The cost estimate made accordingly supported the economic feasibility of rhamnolipid antizoosporic uses in soil.

Additive-free harvesting of oleaginous phagotrophic microalga by oil and air flotation.

A unique oleaginous phagotrophic microalga Ochromonas danica is poised for effective lipid production from waste. Cell harvesting and dewatering are major costs in making algae-based products. In this work an effective additive-free harvesting method was developed, taking advantage of O. danica's comparatively more hydrophobic surface and larger size. The algal cells' partitioning to oil/water interface was evaluated. Recovery by flotation with waste cooking oil was optimized using an L-9 Taguchi orthogonal-array design. Further, additive-free cell collection and concentrating by air flotation was studied for the effects of both physical factors (column dimension, air-stone pore size, sample-to-column volume ratio) and culture properties (pH, culture growth stage, cell concentration, and pure versus impure cultures). The optimized process consistently achieved >90 % recovery in a single stage. 98+ % recovery could be achieved when starting concentrations were >10(8) cells/ml, or potentially using a two- or multi-stage process for diluter cultures.