Anaerobic bioprocessing of organic wastes

Anaerobic digestion of dissolved, suspended and solid organics has rapidly evolved in the last decades but nevertheless still faces several scientific unknowns. In this review, some fundamentals of bacterial conversions and adhesion are addressed initially. It is argued in the light of G-values of reactions, and in view of the minimum energy quantum per mol, that anaerobic syntrophs must have special survival strategies in order to support their existence: redistributing the available energy between the partners, reduced end-product fermentation reactions and special cell-to-cell physiological interactions. In terms of kinetics, it appears that both reaction rates and residual substrate thresholds are strongly related to minimum G-values. These new fundamental insights open perspectives for efficient design and operation of anaerobic bioprocesses. Subsequently, an overview is given of the current anaerobic biotechnology. For treating wastewaters, a novel and high performance new system has been introduced during the last decade; the upflow anaerobic sludge blanket system (UASB). This reactor concept requires anaerobic consortia to grow in a dense and eco-physiologically well-organized way. The microbial principles of such granular sludge growth are presented. Using a thermodynamic approach, the formation of different types of aggregates is explained. The application of this bioprocess in worldwide wastewater treatment is indicated. Due to the long retention times of the active biomass, the UASB is also suitable for the development of bacterial consortia capable of degrading xenobiotics. Operating granular sludge reactors at high upflow velocities (5–6 m/h) in expanded granular sludge bed (EGSB) systems enlarges the application field to very low strength wastewaters (chemical oxygen demand < 1 g/l) and psychrophilic temperatures (10°C). For the treatment of organic suspensions, there is currently a tendency to evolve from the conventional mesophilic continuously stirred tank system to the thermophilic configuration, as the latter permits higher conversion rates and easier sanitation. Integration of ultrafiltration in anaerobic slurry digestion facilitates operation at higher volumetric loading rates and at shorter residence times. With respect to organic solids, the recent trend in society towards source separated collection of biowaste has opened a broad range of new application areas for solid state anaerobic fermentation.W. Verstraete and D. de Beer are with the Center for Environmental Sanitation, University of Gent, Coupure L 653, B-9000 Gent, Belgium; D. de Beer is also with the Max Plank Institut für Marine Mikrobiologie-Microzensor Group, Fahrenstrasse 1, 28359 Bremen, Germany. M. Pena is with the Groupo de Biotechnologia Ambiental, Departamento de Ingenieria Quimica, Universidad de Valladolid, Prado de la Magdalena, 47005 Valladolid, Spain. G. Lettinga is with the Department of Environmental Technology, Wageningen Agricultural University, Bomenweg 2, 6703 HD Wageningen, The Netherlands. P. Lens is with the Environmental Research Unit. Department of Microbiology, University College Galway, Galway, Ireland.     

Tachykinin NK-1 receptor probed with constrained analogues of substance P

The action of rotameric probes introduced either in position 7 or 8 in the sequence of substance P (SP) was investigated, i.e. -tetrahydroisoquinoleic acid (Tic), -fluorenylglycine (Flg), -diphenylalanine (Dip), the diastereoisomers of -1-indanylglycine (Ing) and -benz[ƒ]indanylglycine (Bfi), the Z- and E-isomers of dehydrophenylalanine and dehydronaphthylalanine (Δ^ZPhe, Δ^EPhe, Δ^ZNal, Δ^ENal) and (Dmp). The aim of this study was the topographical characterization of the binding subsites of human NK-1 receptor expressed in CHO cells, especially the S₇ and S₈ subsites, corresponding to residues Phe⁷ and Phe⁸ of substance P. According to the binding potencies of these substituted-SP analogues, the S₇ binding subsite is smaller than the S₈ subsite: the S₇ subsite accepts only one aromatic nucleus, while the S₈ can accommodate three coplanar nuclei altogether. These findings are compatible with the idea that the S₈ binding subsite may reside in the extracellular loops of the hNK-1 receptor. NK-1 agonists bind to human NK-1 receptor and activate the production of both inositol phosphates and cyclic AMP. As already quoted for septide, [pGlu⁶, Pro⁹]SP(6–11), discrepancies are observed between affinity (K_i) and activity (EC₅₀) values for IPs production. While a weak correlation between K_i and EC₅₀ values for IPs production could be found (r = 0.70), an excellent correlation could be demonstrated between their affinities (K_i) and their potencies (EC₅₀) for cAMP production (r = 0.97). The high potency (EC₅₀) observed for ‘septide-like’ molecules on PI hydrolysis, compared to their affinity is not an artefact related to the high level of NK-1 receptors expressed on CHO cells since a good correlation was found between EC₅₀ values obtained for PI hydrolysis and those measured for spasmogenic activity in guinea pig ileum bioassay (r = 0.94).

According to the binding potencies of constrained analogues of phenylalanine, the S₇ binding subsite of human NK-1 receptor is small, whereas the S₈, which can accommodate three coplanar nuclei, might probably reside in the extracellular loop. The discrepancies observed between affinity (K_i) and activity (EC₅₀) values for IPs production are not an artefact of CHO cells since a good correlation was found between EC₅₀ for PI hydrolysis and those measured in guinea pig ileum bioassay.     

里氏木霉液体发酵产纤维素酶的研究

在摇瓶试验基础上,采用里氏木霉(Trichoderma reesei)HC-415菌株进行5L自控罐产纤维素酶深层发酵试验。在通气量为 0.2—0.6vvm、搅拌速度为 400r/min、发酵液pH控制在5.8—6.1的条件下,发酵液的羧甲基纤维素(CMC)酶酶活最高为325.0mg糖/ml,滤纸糖酶(FPA)酶活最高达17.9mg糖/ml。发酵周期为108h。所得冻干纤维素酶粉CMC酶活最高3111IU/g,FPA最高135IU/g ,对发酵液得率平均6.7g/L。酶活总收率CMC酶活平均78.2％,FPA酶活平均73.5％。     

硫酸盐还原一甲烷化两相厌氧消化系统运行工艺条件的研究

以合成废水为基质,研究了采用硫酸盐还原-甲烷化两相厌氧新型工艺处理含高浓度硫酸盐有机废水的系统运行工艺条件.结果表明,酸化-硫酸盐还原反应器的适宜pH为6.5-7.0;500mg/l的S~(2-)使SRB的硫酸盐还原活性下降;208mg/l的[H_2S]_L抑制MPB活性的95.4%;推导出估算气提塔出水回流比R的模型;以得到的工艺条件为依据处理了含19200mg/1的SO_4~(2-)和29400mg/l COD的味精废水.     

黄单胞菌R5产黄原胶的工艺条件研究

本文报道了黄单胞菌（Ｘａｎｔｈｏｍｏｎａｓｃａｍｐｅｓｔｒｉｓ）ＸＣ—８２·５的诱导株Ｒ５发酵生产黄原胶的最适工艺条件。探讨了培养基中不同的碳源、发酵溶氧状况、发酵温度、ｐＨ值、菌龄对产胶水平的影响,向时发现：以菜油替代ＰＰＥ作消泡剂有其独特的优越性;Ｈ２Ｏ２水不能改善溶氧水平。     

Preferred conformation of peptides rich in Ac8c,a medium-ring alicyclic Cα,α-disubstituted glycine

A complete series of terminally blocked, monodispersed homo-oligopeptides (to the pentamer level) from the sterically demanding, medium-ring alicyclic C^α,α-disubstituted glycine 1-aminocyclooctane-1-carb oxylic acid (Ac₈c), and two Ala/Ac₈c tripeptides, were synthesized by solution methods and fully characterized. The preferred conformation of all the oligopeptides was determined in deuterochloroform solution by IR absorption and ¹H-NMR. The molecular structures of the amino acid derivative Z-Ac₈c-OH, the dipeptide pBrBz- (Ac₈c)₂-OH and the tripeptide pBrBz-(Ac₈c)₃-OtBu were assessed in the crystal state by X-ray diffraction. Conformational energy computations were performed on the monopeptide Ac-Ac₈c-NHMe. Taken together, the results obtained strongly support the view that the Ac₈c residue is an effective β-turn and helix former. A comparison is also made with the conformational preferences of α-aminoisobutyric acid, the prototype of C^{α, α}-disubstituted glycines, and of the other members of the family of 1-aminocycloalkane-1-carboxylic acids (Ac_nc, with n=3, 5–7) investigated so far. The implications for the use of the Ac₈c residue in peptide conformational design are considered.     

Development of Media and Automated Liquid Fermentation Methods to Produce Desiccation-Tolerant Propagules ofTrichoderma harzianum

A suitable medium was developed from modified Richard's medium plus V8 juice (RM8) to produce high levels of desiccation-tolerant conidia ofTrichoderma harzianumstrain 1295-22. The addition of 9% (v/v) glycerol to RM8 improved both biomass production and desiccation tolerance of the conidia ofT. harzianum.This medium was then used in a laboratory scale fermenter (1.5 liter) to determine optimal operating conditions. The optimal temperature for conidial production and desiccation tolerance improvement in the fermenter was 32°C when dissolved oxygen was maintained at 50% saturation of air, and the stirring rate was 1000 revolutions per minute. The initial water potential of the medium (with 9% glycerol) was −3.7 MPa, the pH was 6, and neither was controlled during fermentation. Changes in medium pH and dissolved oxygen were associated with the stages of morphological development and conidiation. The pH of the medium decreased concurrently with germ-tube elongation and mycelium development and then increased to 6.0–6.2 at phialide formation. Intensive conidiation occurred at pH 6.3–6.5 and reached its maximal level at 6.9–7.1. Changes in pH values could be used as indicators to monitor the morphological development and conidiation ofT. harzianumduring fermentation. The use of a 48-h-old culture inoculum, rather than conidial inoculum, to start fermentation reduced the time required to complete the shift from vegetative growth to phialide formation. Intensive conidiation occurred immediately after the addition of culture inoculum and reached maximum levels within 68 h of fermentation. Dry weight of biomass increased with the duration of fermentation and was greatest at 96 h. However, no improvements in conidia/gram and CFU/gram were achieved after 72 h of fermentation. The desiccation tolerance of conidia harvested at 72 or 96 h was significantly (P = 0.05) greater than that of conidia harvested at 48 h of fermentation. Results obtained from this study could be used for further scale-up of the fermentation process.     

Cyclic (1 → 2)-β-d-glucans excreted by the glucuronan-producing strain Rhizobium meffloti M5N1CS CS (NCIM B 40472) and by the succinoglycan-producing strain Rhizobium meliloti M5N1

During fermentation, the mutant strain Rhizobium mefliloti M5N1 CS, which induces nodule formation on alfalfa roots, produces a partially acetylated (1 → 4)-β-d-glucuronan. In addition to this exopolysaccharide of high molecular weight, the mutant strain produces oligoglucoronates and cyclic (1 → 2)-β-d-glucans with degrees of polymerization from 17 to 30. Under the conditions applied, magnesium has no effect on cyclic glucan production by the mutant strain, but the succinoglycan production by the wild-type strain Rhizobium meliloti M5N1 increases.     

Kinetic model of disaccharide oxidation by Agrobacterium tumefaciens

Disaccharides were microbaially transformed to their corresponding 3-keto-derivatives by resting cells of Agrobacterium tumefaciens NCPPB 396. The kinetics and yield of this highly specific oxidation depend on several factors. The oxygen concentration especially has a major influence on the production of 3-keto-derivatives and was investigated kinetically with respect to low stationary oxygen concentrations in solution. Experiments showed unconventional results that conflicted with normal Michaelis-Menten kinetics. A kinetic model was developed and the kinetic constants were calculated. The model and experimental data for sucrose, maltose, iso-maltulose (palatinose), and leucrose are in good agreement with each other. Initial reaction rates with different sugars using constant oxygen concentrations resulted in a Michaelis-Mentent type function. The complete kinetics, including the effect of disaccharide and oxygen concentrations, are presented. (c) 1995 John Wiley & Sons, Inc.     

Fermentation and recovery of glutamic acid from palm waste hydrolysate by Ion-exchange resin column

Glutamic acid produced from palm waste hydrolysate by fermentation with Brevibacterium lactofermentum ATCC 13869 is produced with a remarkably high yield compared with that produced from pure glucose as a carbon source. The produce yield is 70 g/L with glucose, wherease, when palm waste hydrolysate is the fermentation medium in the same bioreactor under same conditions, it is 88 g/L. The higher yield may be attributed to the fact that this organism has the ability to convert sugars other than only glucose present in the hydrolysate. Bioreactor conditions most conducive for maximum production are pH 7.5, temperature of 30 degrees rmentation period of 48 h, inoculum size 6%, substrate concentration of 10 g per 100 mL, yeast extract 0.5 g per 100 mL as a suitable N source, and biotin at a concentration of 10 pg/L. Palm waste hydrolysate used in this study was prepared by enzymic saccharification of treated palm press fiber under conditions that yielded a maximum of 30 g/L total reducing sugars. Glutamic acid from fermentation broth was recovered by using a chromatographic column (5cm x 60 cm) packed with a strong ion-exchange resin. The filtered broth containing glutamic acid and other inorganic ions was fed to the fully charged column. The broth was continuously recycled at a flow rate of 50 mL/min (retention time of 55 min) until glutamic acid was fully adsorbed on the column leaving other ions in the effluent. Recovery was done by eluting with urea and sodium hydroxide for total displacement of glutamic acid from the resin. The eluent containing 88 g/L of glutamic acid was concentrated by evaporation to obtain solid crystals of the product. (c) 1995 John Wiley & Sons, Inc.