Showing papers in "Process Biochemistry in 2005"

Application of biosorption for the removal of organic pollutants: a review

Abstract: In modern society, an increasing number of hazardous organic compounds are being discharged into the environment. Most are degraded or detoxificated by physical, chemical and biological treatments before released into the environment. Although the biological treatments are a removal process for some organic compounds, their products of biodegradation may also be hazardous. Moreover, some nondegradable compounds discharged into the environment along with the treated compounds can cause problems because they usually come back to humanbeings through the several channels such as bioaccumulation. As a result, organic molecules that are not biodegradable, can still be removed from the wastewater by the microbial biomass via the process of biosorption. Biosorption is also becoming a promising alternative to replace or supplement the present removal processes of organic pollutants from wastewaters. Among these pollutants, dyes, phenolics and pesticides have recently been of great concern because of the extreme toxicity and/or persistency in the environment. Biosorption of these type of hazardous organics by selected live and dead microoganisms has been investigated by various workers. This review examines a wide variety of microorganisms (fungi, yeasts, bacteria, etc.), which are capable of uptake of organic pollutants, discusses various mechanisms involved in biosorption, discusses the effects of various parameters such as pH, temperature, concentrations of organic pollutant, other ions, and biomass in solution, pretreatment method, etc. on biosorption, reports some elution and regeneration methods for biomass; summarizes the equilibrium and kinetic models used in batch and continuous biosorption systems which are important to determine the biosorption capacity of microorganism and to design of treatment processes.

Microbial pectinolytic enzymes: A review

Abstract: Pectinases or petinolytic enzymes, hydrolyze pectic substances. They have a share of 25% in the global sales of food enzymes. Pectinases are one of the most widely distributed enzymes in bacteria, fungi and plants. Protopectinases, polygalacturonases, lyases and pectin esterases are among the extensively studied pectinolytic enzymes. Protopectinases catalyze the solubilization of protopectin. Polygalacturonases hydrolyze the polygalacturonic acid chain by addition of water and are the most abundant among all the pectinolytic enzymes. Lyases catalyze the trans-eliminative cleavage of the galacturonic acid polymer. Pectinesterases liberate pectins and methanol by de-esterifying the methyl ester linkages of the pectin backbone. Pectinolytic enzymes are of significant importance in the current biotechnological era with their all-embracing applications in fruit juice extraction and its clarification, scouring of cotton, degumming of plant fibers, waste water treatment, vegetable oil extraction, tea and coffee fermentations, bleaching of paper, in poultry feed additives and in the alcoholic beverages and food industries. The present review mainly contemplates on the types and structure of pectic substances, the classification of pectinolytic enzymes, their assay methods, physicochemical and biological properties and a bird's eye view of their industrial applications.

Bubble column reactors

Abstract: Bubble columns are intensively used as multiphase contactors and reactors in chemical, biochemical and petrochemical industries. They provide several advantages during operation and maintenance such as high heat and mass transfer rates, compactness and low operating and maintenance costs. Three-phase bubble column reactors are widely employed in reaction engineering, i.e. in the presence of a catalyst and in biochemical applications where microorganisms are utilized as solid suspensions in order to manufacture industrially valuable bioproducts. Investigation of design parameters characterizing the operation and transport phenomena of bubble columns have led to better understanding of the hydrodynamic properties, heat and mass transfer mechanisms and flow regime characteristics ongoing during the operation. Moreover, experimental studies are supported with computational fluid dynamics (CFDs) simulations and developed mathematical models to describe better the phenomena taking place in a bubble column reactor. This review focuses on bubble column reactors, their description, design and operation, application areas, fluid dynamics and regime analysis encountered and parameters characterizing the operation are presented together with the findings of published studies.

Dilute acid pretreatment, enzymatic saccharification and fermentation of wheat straw to ethanol

Abstract: Wheat straw consists of 48.57 ± 0.30% cellulose and 27.70 ± 0.12% hemicellulose on dry solid (DS) basis and has the potential to serve as a low cost feedstock for production of ethanol. Dilute acid pretreatment at varied temperature and enzymatic saccharification were evaluated for conversion of wheat straw cellulose and hemicellulose to monomeric sugars. The maximum yield of monomeric sugars from wheat straw (7.83%, w/v, DS) by dilute H2SO4 (0.75%, v/v) pretreatment and enzymatic saccharification (45 °C, pH 5.0, 72 h) using cellulase, β-glucosidase, xylanase and esterase was 565 ± 10 mg/g. Under this condition, no measurable quantities of furfural and hydroxymethyl furfural were produced. The yield of ethanol (per litre) from acid pretreated enzyme saccharified wheat straw (78.3 g) hydrolyzate by recombinant Escherichia coli strain FBR5 was 19 ± 1 g with a yield of 0.24 g/g DS. Detoxification of the acid and enzyme treated wheat straw hydrolyzate by overliming reduced the fermentation time from 118 to 39 h in the case of separate hydrolysis and fermentation (35 °C, pH 6.5), and increased the ethanol yield from 13 ± 2 to 17 ± 0 g/l and decreased the fermentation time from 136 to 112 h in the case of simultaneous saccharification and fermentation (35 °C, pH 6.0).

Omega-3/6 fatty acids: Alternative sources of production

Abstract: Polyunsaturated fatty acids (PUFAs) are essential components of higher eukaryotes. Single cell oils (SCO) are now widely accepted in the market place and there is a growing awareness of the health benefits of PUFAs, such as γ-linolenic acid (GLA), arachidonic acid (ARA), docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). ARA and DHA have also been used for fortification of infant formulae in many parts of the world. Fish oils are rich sources of DHA and EPA and a limited number of plant oilseeds are good sources of other PUFAs. Marine protists and dinoflagellates, such as species of Thraustochytrium, Schizochytrium and Crypthecodinium are the rich sources of DHA, whereas microalgae like Phaeodactylum and Monodus are good sources of EPA. Species of lower fungi Mortierella accumulate a high percentage of ARA in the lipid fraction. In this paper, various microbiological and enzymatic methods for synthesis of PUFAs are discussed.

Recent advances in microbial polyhydroxyalkanoates

Abstract: Polyhydroxyalkanoates (PHAs) are polyesters of hydroxyalkanoates (HAs) synthesised by numerous bacteria as an intracellular carbon and energy storage compound. These are accumulated in the cytoplasm of cells. A number of bacteria including Alcaligenes, Pseudomonas, recombinant Escherichia coli and methylotrophs have been used for the production of PHAs and high productivities have been achieved. Production of PHA by transgenic plants has been demonstrated on a laboratory-scale and large-scale production will be feasible in the near future. By controlling the monomer composition of PHA, it has been indicated that the physical properties of polymers can be regulated to a great extent. Even though PHAs have been recognised as a good candidate for biodegradable polymers, their high production cost limits their industrial application. It is hoped that with improvement in fermentation and downstream processing techniques, development of new recombinant strains and large-scale production by transgenic plants will reduce the cost of production of PHAs thereby making them competitive with conventional plastics.

Bioreactor performance in anaerobic digestion of fruit and vegetable wastes

Abstract: This work reviews the potential of anaerobic digestion for material recovery and energy production from fruit and vegetable wastes (FVW). These wastes contain 8–18% total solids (TS), with a total volatile solids (VS) content of 86–92%. The organic fraction includes about 75% easy biodegradable matter (sugars and hemicellulose), 9% cellulose and 5% lignin. Anaerobic digestion of FVW was studied under different operating conditions using different types of bioreactors. It permits the conversion of 70–95% of organic matter to methane, with a volumetric organic loading rate (OLR) o f 1–6.8 g versatile solids (VS)/l day. A major limitation of anaerobic digestion of FVW is a rapid acidification of these wastes decreasing the pH in the reactor, and a larger volatile fatty acids production (VFA), which stress and inhibit the activity of methanogenic bacteria. Continuous two-phase systems appear as more highly efficient technologies for anaerobic digestion of FVW. Their greatest advantage lies in the buffering of the organic loading rate taking place in the first stage, allowing a more constant feeding rate of the methanogenic second stage. Using a two-stage system involving a thermophilic liquefaction reactor and a mesophilic anaerobic filter, over 95% volatile solids were converted to methane at a volumetric loading rate of 5.65 g VS/l d. The average methane production yield was about 420 l/kg added VS.

Anaerobic treatment of dairy wastewaters: a review

Abstract: Anaerobic treatment is often reported to be an effective method for treating dairy effluents. The objective of this paper is to summarize recent research efforts and case studies in anaerobic treatment of dairy wastewaters. The main characteristics of industrial dairy waste streams are identified and the anaerobic degradation mechanisms of the primary constituents in dairy wastewaters, namely carbohydrates (mainly lactose), proteins and lipids are described. Primary attention is then focused on bench–pilot–full-scale anaerobic treatment efforts for dairy waste effluents. Combined (anaerobic–aerobic) treatment methods are also discussed. Finally, areas where further research and attention are required are identified.

Biosorption of reactive dyes on the green alga Chlorella vulgaris

Abstract: Biosorption of three vinyl sulphone type reactive dyes (Remazol Black B (RB), Remazol Red RR (RR) and Remazol Golden Yellow RNL (RGY)) onto dried Chlorella vulgaris , a green alga was investigated in a batch system. The algal biomass exhibited the highest dye uptake capacity at the initial pH value of 2.0 for all dyes. The effect of temperature on equilibrium sorption capacity indicated that maximum capacity was obtained at 35 °C for RB biosorption and at 25 °C for RR and RGY biosorptions. Biosorption capacity of alga increased with increasing initial dye concentration up to 800 mg l −1 for RB and RR dyes, and up to 200 mg l −1 for RGY dye. Among the three dyes, RB was adsorbed most effectively by the biosorbent to a maximum of approximately 419.5 mg g −1 . The Freundlich, Langmuir, Redlich–Peterson and Koble–Corrigan adsorption models were used for the mathematical description of the biosorption equilibrium and isotherm constants were evaluated at different temperatures. Equilibrium data of RB biosorption fitted very well to all models except that the Langmuir model, while this model was found most suitable for describing the biosorptions of RR and RGY dyes in the studied concentration and temperature ranges. The pseudo first- and second-order and saturation type kinetic models were also applied to the experimental data assuming that the external mas transfer limitations in the system can be neglected. The results indicated that the dye uptake process followed the pseudo second-order and saturation type rate expressions for each dye- C. vulgaris system.

The effect of volatile fatty acid additions on the anaerobic digestion of cellulose and glucose in batch reactors

Abstract: Batch anaerobic reactor experiments were set up in which the degradation of the primary substrates cellulose and glucose was assayed when dosed with a concentration range from 1 to 20 g l −1 of a synthetic mixture of volatile fatty acids (VFA). Biogas production from the VFA mix and from reactors without VFA additions was used as a baseline control against which the results were compared and interpreted. The 1-l mesophilic (35 °C) reactors were seeded with an actively digesting sludge of sewage origin and monitored for biogas production, gas composition, volatile fatty acid concentration, glucose content and the cellulolytic enzymes carboxymethylcellulase and avicelase. Cellulose reduction was measured from initial and final samples of the reaction mix in each case. VFA caused inhibition of the cellulolytic activity at concentrations ≥2 g l −1 , and therefore of the rate of cellulose hydrolysis. The fermentation of glucose was slightly inhibited at VFA concentrations above 4 g l −1 . The inhibitory effect on the production of biogas and also on the methane to carbon dioxide ratio was evident above 6 g l −1 VFA in the initial mixture when used as the sole substrate. In combination with paper as primary substrate, biogas production due to the paper was more than halved above 1 g l −1 initial VFA, indicating inhibition of the hydrolysis process. Where glucose was the primary substrate biogas production was more than halved above 8 g l −1 which indicated that the fermentation was less sensitive to inhibition caused by VFA.

Polychlorinated biphenyls and their biodegradation

Abstract: Polychlorinated biphenyls (PCBs) are stable organic molecules that were widely used during 1930s and 1940s. Because of their widespread use, PCBs have entered the environment through both legal and illegal use and disposal and are persistent in the environment contaminating various environmental matrices worldwide. The environmental persistence of PCBs results primarily from the inability of natural aquatic and soil biota to metabolize the compound at a considerable rate. Several studies have been conducted on PCBs biodegradation to determine how the degradation rate can be improved. This paper is a review of literature and studies on the biodegradation of PCBs. Studies show that there are two biologically mediated PCBs degradation processes: anaerobic and aerobic. The anaerobic process removes chlorine atoms of highly chlorinated PCBs, which are then mineralized under aerobic condition. The degradation route is dependent on the complexity of the PCB congener coupled with the type of microorganism employed and the interaction among the microorganisms.

Removal of basic dye from aqueous solution using tree fern as a biosorbent

Abstract: A batch sorption system using tree fern as biosorbent was investigated to remove Basic Red 13 from aqueous solutions. The system variables studied include sorbent particle size and temperature and results revealed the potential of tree fern, an agriculture product, as a low-cost sorbent. The Langmuir isotherm was found to represent the measured sorption data well. The dye sorption capacity of tree fern increased as the sorbent particle size decreased. Maximum saturated monolayer sorption capacity of tree fern for Basic Red 13 was 408 mg/g. Various thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated indicating that this system was a spontaneous and endothermic process.

Optimization of α-amylase production by Bacillus sp. using response surface methodology

Abstract: The combined effects of macronutrients of media on α-amylase production by Bacillus sp. were studied using response surface methodology. A 22 full-factorial central composite design was chosen to explain four medium constituents, viz. starch, glycerol, yeast extract (YE) and peptone, and to analysis of the results. This procedure limited the number of actual experiments performed while allowing for possible interactions between four components. The P-value of the coefficient for quadratic effect of glycerin concentration was <0.0001, suggesting that this was the principal experimental variable having the greatest effect on the production of α-amylase. It was found that YE had no effect on α-amylase production. The optimal combinations of media constituents for maximum α-amylase production were determined as 17.58 g/l starch, 12.37% (v/v) glycerin, 8.77 g/l peptone and 0.00 g/l YE.

Comparative evaluation of neutral protease production by Aspergillus oryzae in submerged and solid-state fermentation

Abstract: A comparative study was carried out on the production of neutral protease using agro-industrial residues as substrate in solid-state fermentation (SSF) and submerged fermentation (SmF). Seven fungal cultures, viz. three strains of Aspergillus oryzae and four strains belonging to Penicillium sp, P . funiculosum , P . funiculosum, P. pinophilum , P . aculeatum were evaluated using a plate assay for enzyme production, which showed a strain of A. oryzae NRRL 1808 as the most useful culture. Several agro-industrial residues (wheat bran, rice husk, rice bran, spent brewing grain, coconut oil cake, palm kernel cake, sesame oil cake, jackfruit seed powder and olive oil cake) were screened for neutral protease production in SmF and SSF. In both systems, wheat bran was the best substrate. Best results in SSF were obtained in a medium having an initial moisture content of 43.6%, when inoculated with 1 ml of spore suspension (8 × 10 8 spores) and incubated at 30 °C for 72 h (31.2 U enzyme per gram of fermented substrate – U/gds). SmF medium (pH 7.5) containing 2% (w/v) wheat bran, when inoculated with 3 ml of spore suspension and incubated at 30 °C and 180 rpm for 72 h gave maximum enzyme yield of 8.7 U/gds. A comparative evaluation of protease yield by the two fermentation systems showed 3.5-fold more enzyme production in SSF, clearly demonstrating the superiority of SSF over SmF.

Phenolic antioxidants from clonal oregano (Origanum vulgare) with antimicrobial activity against Helicobacter pylori

Abstract: Phenolic phytochemicals consumed via our diet are good sources of natural antioxidants. These phenolic metabolites have beneficial effects on human health, including inhibition of mutagenesis and carcinogenesis. In addition some phenolic phytochemicals have also been shown to have antimicrobial and antifungal activity. Oregano ( Origanum vulgare L.) is an important Mediterranean herb rich in phenolic compounds with antioxidant and antimicrobial activity. Using tissue culture techniques several high phenolics and rosmarinic acid-containing oregano clonal lines have been isolated with high antioxidant activity with antimicrobial potential. In this investigation the antioxidant activity of phenolic-enriched clonal oregano extracts, and their antimicrobial activity against ulcer-associated Helicobacter pylori have been evaluated. In all cases clonal extracts were compared to commercial oregano from heterogeneous sources. Total phenolics were the highest in 60% ethanol extracts of clonal oregano. Antioxidant activity based on 1,1-diphenyl-2-picrylhydrazyl-2-radical (DPPH) scavenging activity depended on the physiochemical nature of phenolic phytochemical and percentage inhibition activity based on 3-ethyl benzthiazoline-6-sulphonic acid (ABTS + ) assay correlated to the amount of total phenolics. Thiobarbutyric acid reactive substances (TBARS) and antioxidant protection factor (APF) method using β-carotene linoleic acid system were correlated to lipophilic phenolic phytochemicals. Antimicrobial activity against H. pylori was tested by the standard agar diffusion method. Phenolic profiles in oregano extracts were analyzed using HPLC. The differences in physico-chemical properties of phenolic acids consisting of C 6 -C 1 -COOH, and C 6 -C 3 -COOH structures were hypothesized to play a role in growth inhibition of H. pylori .

Removal of copper(II) ions from aqueous solution by biosorption onto agricultural waste sugar beet pulp

Abstract: Dried sugar beet pulp, an agricultural solid waste by-product, was used as an biosorbent for the removal of copper(II) from aqueous solution. A series of experiments were conducted in a batch system to assess the effect of the system variables, i.e. initial pH, temperature and initial metal ion concentration. The results indicated that at 250 mg l−1 initial copper(II) concentration dried sugar beet pulp exhibited the highest copper(II) uptake capacity of 28.5 mg g−1 at 25 °C and at an initial pH value of 4.0. The equilibrium data were analyzed using the Freundlich, Langmuir, Redlich–Peterson and Koble–Corrigan isotherm models depending on temperature. The Langmuir model was found to best describe the data in the concentration and temperature ranges studied. Simple mass transfer and kinetic models were applied to the experimental data to examine the mechanisms of biosorption and potential rate-controlling steps such as external mass transfer, intraparticle diffusion and biosorption process. It was found that the intraparticle diffusion played an important role in the biosorption mechanisms of copper(II), and biosorption kinetics followed pseudo first- and pseudo second-order kinetic models rather than the saturation type kinetic model for all temperatures studied. The activation energy of biosorption (EA) was determined as −58.47 kJ mol−1 using the Arrhenius equation. Using the thermodynamic equilibrium coefficients obtained at different temperatures, the thermodynamic constants of biosorption (ΔG°, ΔH° and ΔS°) were also evaluated.

Effects of high free ammonia concentrations on the performances of anaerobic bioreactors

Abstract: UASB reactors inoculated with different seed sludges were operated for 450 days under high ammonia concentrations to investigate inhibition effects. Reactors were fed with synthetic wastewater providing an organic loading of about 1.2 kg COD m3/day and having total ammonia nitrogen (TAN) concentrations gradually increasing from 1000 to 6000 mg/l. As, corresponding free ammonia nitrogen (FAN) concentrations elevated up to 800 mg/l, COD removal efficiencies in the range of 78–96% were determined. High removal efficiencies revealed that seed sludges taken from anaerobic reactors treating considerably low ammonia containing wastewaters have adapted to elevated free ammonia concentrations successfully. However, propionate accumulation in some reactors and decrease in eubacterial signals detected by fluorescent in situ hybridization (FISH) indicated that propionate degrading acetogenic bacteria are more sensitive than methanogenic archaea to free ammonia. Differences in the efficiencies of reactors were correlated with the quantity of resistant and sensitive microorganisms dominated in the reactors.

Mesophilic anaerobic digestion of waste activated sludge: influence of the solid retention time in the wastewater treatment process

Abstract: The performance of mesophilic anaerobic digesters of four large Italian wastewater treatment plants without primary sedimentation were studied. Only the waste activated sludge is stabilised by means of the mesophilic (35‐37 8C) anaerobic digestion process. The anaerobic digesters generally worked with a hydraulic retention time in a range of 20‐40 days and an organic loading rate of some 1 kg VS/m 3 day. The solids content of the sludge fed to the digesters was in the range 2.6‐3.9% and the gas produced per kilogram of volatile solids added was in the range 0.07‐0.18 m 3 /kg VSfed. The specific gas production per kilogram of volatile solids destroyed was in the range 0.5‐0.9 m 3 / kg VSdestroyed and the reduction of the volatile solids concentration was in the range 13‐27% (average 18%). These figures are particularly significant when designing anaerobic digesters for the treatment of waste activated sludge as single substrate. Moreover, it was observed that the higher the applied solid retention time in the activated sludge process for wastewater treatment, the lower the gas production. In particular, the specific gas production decreased from 0.18 to 0.07 m 3 /kg VSfed when increasing the solid retention time in the wastewater treatment line from 8 to 35 days. Finally, a mathematical model for the prediction of biogas production on the solid retention time applied in the wastewater treatment process was developed. # 2004 Elsevier Ltd. All rights reserved.

A kinetic study of metal complex dye sorption onto pine sawdust

Abstract: The removal of metal complex dyes, Metal Complex Blue (MCB) and Metal Complex Yellow (MCY), from aqueous solutions by pine sawdust has been studied in single component sorption systems. The aim of this study was to understand the mechanisms that govern metal complex dyes removal and find a appropriate model for the kinetics of removal in a batch reactor. In order to investigate the mechanism of sorption and potential rate controlling steps, pseuso first- and second-order equations, intraparticle diffusion equation and the Elovich equation have been used to test experimental data. Kinetic analysis of the four models has been carried out for system variables—particle size and mass of sawdust, pH and initial dye concentration. The rate constants for the four models have been determined and the correlation coefficients have been calculated in order to assess which model provides the best fit predicted data with experimental results. Both pseudo second-order equation and the Elovich equation provide the best fit to experimental data.

Optimization of lipase entrapment in Ca-alginate gel beads

Abstract: Lipase from Candida rugosa was entrapped by drop-wise addition of an aqueous mixture of sodium alginate and the biocatalyst to a hardening solution of a Ca 2+ salt. Effects of immobilization conditions such as alginate concentration, CaCl 2 concentration, ratio by weight of enzyme to alginate (E/A) and bead size on loading efficiency (percent of total enzyme entrapped) and immobilization yield (specific activity ratio of entrapped lipase to free lipase) were investigated. An increase in alginate concentration raised loading efficiency, but decreased immobilization yield. CaCl 2 concentration was expected to have a similar effect on loading efficiency and immobilization yield, but the effect was small in the tested range of 50–300 mM. With increasing bead size, immobilization yield decreased due to mass transfer resistance, but loading efficiency was unchanged. In order to prevent enzyme from leaking out of the gel beads, beads were coated with chitosan and silicate. Compared to non-coated beads, coated alginate beads showed the higher re-usability, illustrating the effectiveness of the coating method. When coated with silicate, lipase-entrapped beads retained the highest catalytic activity.

Characterization of cellulases and hemicellulases produced by Trichoderma reesei on various carbon sources

Abstract: Cellulase and hemicellulase enzymes were produced by Trichoderma reesei RUT C30 on steam pretreated spruce, willow, corn stover and delignified lignocellulose (Solka Floc), as a reference The enzymes produced were characterized by protein and various enzyme activity measurements On steam pretreated corn stover higher cellulolytic enzyme activities were reached than on Solka Floc, while the activities obtained on steam pretreated spruce and willow were considerably lower The produced and two commercial cellulases (Celluclast 15 L and Econase CE) were compared by determining specific activities There were minor differences among the enzymes corresponding to their specific cellulase activities In contrast, within hemicellulase and β-glucosidase activities, the differences were found to be more significant It should be also noted that commercial cellulases had considerably higher specific acetyl xylan esterase activities than the produced enzymes According to subsequent hydrolysis experiments, performed to characterize the produced enzyme complexes to evaluate their applicability for hydrolysis and enzyme production, it seems that the application of the enzyme that was produced on the same substrate as was used for hydrolysis can be advantageous in the case of some substrates As a result, these experiments demonstrated that pretreated corn stover is a good substrate both for enzyme production and hydrolysis, since high cellulolytic activities could be reached using it as carbon source Moreover, high sugar yields could be obtained in the hydrolysis by the enzyme produced on steam pretreated corn stover

Pretreatment by microwave/alkali of rice straw and its enzymic hydrolysis

Abstract: Combination pretreatment of rice straw using microwave and alkali and its enzymic hydrolysis were investigated and compared with the alkali-alone pretreated process. First, the effect of microwave power and pretreatment time on the weight loss and composition of rice straw was examined. The results show that higher microwave power with shorter pretreatment time and the lower microwave power with longer pretreatment time had almost the same effect on the weight loss and composition at the same energy consumption. The comparison was then made between the effect of the microwave/alkali pretreatment and the alkali-alone one on the weight loss and composition of rice straw. The rice straw had a weight loss of 44.6% and composition cellulose 69.2%, lignin 4.9% and hemicellulose 10.2% after 30-min microwave/alkali pretreatment at 700 W while it only had a weight loss of 41.5% and composition cellulose 65.4%, lignin 6.0% and hemicellulose 14.3% after 70-min alkali-alone pretreatment. It may be that microwave/alkali pretreatment could remove more lignin and hemicellulose from rice straw with shorter pretreatment time compared with the alkali-alone one. Finally, the enzymic hydrolysis of pretreated rice straw (substrate concentration 50 g l −1 , enzyme loading 20 mg g −1 substrate) was also investigated and the results indicate that rice straw pretreated by microwave/alkali had a higher hydrolysis rate and glucose content in the hydrolysate in comparison with the one by alkali alone.

Camparison for biosorption modeling of heavy metals (Cr (III), Cu (II), Zn (II)) adsorption from wastewater by carrot residues

Abstract: The removal of chromium (III), copper (II) and zinc (II) from aqueous solution by adsorption on carrot residues (CR) was studied. Biosorption of chromium (III), copper (II) and zinc (II) on CR were compared. It was shown that CR has high metal removal efficiency. The Freundlich and Langmuir model can describe the adsorption equilibrium of chromium (III), copper (II) and zinc (II) on CR. The Freundlich and Langmuir constants for biosorption of chromium (III), copper (II) and zinc (II) on CR were determined. The effect of solution pH on biosorption was studied.

Equilibrium studies for the sorption of chromium and nickel from aqueous solutions using raw rice bran

Abstract: The capacity of raw rice bran for chromium and nickel removal from aqueous solutions was investigated. The Langmuir and Freundlich adsorption models, which are in common use for describing sorption equilibrium for wastewater-treatment applications, were used to represent the experimental data and equilibrium data fitted well to the Freundlich isotherm model. The negative value of ΔG° for Cr(III) indicates the spontaneous nature of sorption, but positive values were determined for Cr(VI) and Ni(II). Indeed, Cr(VI) and Ni(II) are sorbed due to the strong interactions with the active sites of the sorbent. The kinetics data for chromium and nickel sorption onto rice bran were studied according mass transfer and intraparticle diffusion models in order to increase sorption process understanding. A very good correlation coefficient was obtained using the pseudo-second-order kinetic model, suggesting that chromium and nickel sorption process onto rice bran particles tend to follow second-order kinetics.

Ammonia removal from anaerobically digested dairy manure by struvite precipitation

Abstract: Ammonia is one of the most important contaminants impairing the quality of water resources. When this is considered along with the fact that the global demand for nitrogenous fertilizers is in constant rise, the need for recovery as well as removal of nitrogen is well justified. Crystallization of N and P in the form of struvite (MgNH 4 PO 4 ·6H 2 O), which is a slow releasing and valuable fertilizer, is one possible technique for this purpose. This study investigated the removal of NH 4 + through struvite precipitation from the effluents of one- (R1) and two-phase (R2) anaerobic reactors digesting dairy manure. To force the formation of struvite in the anaerobic reactor effluents, Mg 2+ ion was added by using both Mg(OH) 2 and MgCl 2 ·6H 2 O. To prevent the effect of different total phosphorus (TP) concentration in the effluents of R1 and R2, as well as to not limit the formation of struvite, an excess amount of PO 4 3− (0.14 M) was added in the form of Na 2 HPO 4 . Different stoichiometric Mg 2+ :NH 4 + :PO 4 3− ratios were tested to determine the required Mg 2+ concentrations for maximum NH 4 + removal by keeping NH 4 + :PO 4 3− ratio constant for the effluents of reactors R1 and R2. The results revealed that very high NH 4 + removal efficiencies (above 95%) were possible by adding Mg 2+ ions higher than 0.06 M concentration in the effluents from reactors R1 and R2. It was also observed that the initial pH adjustment to 8.50 using NaOH did not result in any significant increase in the removal of NH 4 + and the removal of NH 4 + in the reactors treated with MgCl 2 ·6H 2 O was higher than those treated with Mg(OH) 2 for the same Mg 2+ concentration.

Production of astaxanthin by the green microalga Chlorella zofingiensis in the dark

Abstract: Dark-heterotrophic growth of microalgae eliminates the requirement for light and therefore, facilitates large-scale cultivation of microalgae, especially in denser cultures [Trends Biotechnol. 14 (1996) 421]. In this study, the heterotrophic production potential of the secondary carotenoid astaxanthin by the green microalga Chlorella zofingiensis was investigated. The alga showed excellent growth on glucose-supplemented media in batch culture. The maximum specific growth rate and astaxanthin yield were 0.031 h−1 and 10.3 mg l−1, respectively obtained at glucose concentrations of 20 and 50 g l−1, which were the highest ever reported in heterotrophic algal cultures. In the absence of light, formation of secondary carotenoids was mostly dependent on the initial carbon and nitrogen balance in the medium; enhanced biosynthesis of secondary carotenoids including astaxanthin was found in the medium with a high C/N ratio (i.e. C/N ratio=180). The light-independent astaxanthin-producing ability of C. zofingiensis suggested that the alga might be potentially employed for commercial production of astaxanthin on a large-scale.

Adsorption of malachite green onto Pithophora sp., a fresh water algae: Equilibrium and kinetic modelling

Abstract: Batch biosorption experiments were carried out for the removal of malachite green a cationic dye from its aqueous solution using raw and thermally activated Pithophora sp., a fresh water algae as biosorbent. The operating variables studied are initial malachite green concentration, biomass concentration and solution pH. Pithophora sp. activated at 300 °C for 50 min posses a maximum sorption capacity for the range of initial dye concentrations studied (20–100 mg/L). The sorption kinetics were analysed using reversible first order kinetics, pseudo-first order, pseudo-second order model and the sorption data tend to fit very well in pseudo-second order model for the entire sorption time. The average pseudo-second order rate constant, K II and initial sorption rate h were determined to be 3.46 × 10 −3 and 7.97 × 10 2 mg/g h. Equilibrium data are very well represented by Redlich Peterson isotherm model followed by Freundlich and Langmuir isotherm model. The maximum sorption capacity was 117.647 mg/g at 30 °C. The negative value of free energy change (−8.585 kJ/mol) indicates the spontaneous nature of adsorption.

Two-phase anaerobic digestion of unscreened dairy manure

Abstract: Concentrated animal feeding operations along with a corresponding absence of suitable manure disposal methods have been shown to cause significant environmental and public health problems, including odors and nutrient enrichment and pathogen contamination of surface and ground waters. Anaerobic digestion (AD) of manure can offer substantial benefits, both economic and intangible, to animal feeding operators and surrounding communities, such as on-site energy generation, production of stable, liquid fertilizer and high quality solid soil amendment, reduction in odors, and reduction in ground and surface water contaminations. The two-phase AD has several advantages over conventional one-phase processes, such as selection and enrichment of different bacteria in each phase, increased stability of the process, and higher organic loading rates (OLR) and shorter hydraulic retention times (HRT). Even though several aspects of two-phase configuration might be very significant for efficient AD of dairy manure, its application has been limited to screened dairy manure only. Therefore, this study investigated possible exploitation of the advantages of two-phase AD for unscreened dairy manure. The results indicated that the use of a two-phase reactor at a SRT/HRT of 10 days (2 days acidogenic and 8 days methanogenic) for AD of dairy manure resulted in 50 and 67% higher biogas production at OLRs of 5 and 6 g VS/L day, respectively, relative to a conventional one-phase configuration with SRT/HRT of 20 days. Furthermore, the phased configuration could tolerate an elevated OLR of 12.6 g VS/L day, which was not achievable with a conventional one-phase configuration.

Carotenoids production by the yeast Rhodotorula mucilaginosa: Use of agricultural wastes as a carbon source

Abstract: The effects of pH, temperature, aeration rate, initial sugar and ammonium sulphate concentrations, and activator (cotton seed oil and Tween 80) addition on the growth and carotenoids production properties of Rhodotorula mucilaginosa, a soil yeast was investigated in a batch system. Optimum pH and temperature for total carotenoids production were determined as 7.0 and 30 °C, respectively. Total carotenoids concentration and carotenoids production yield were significantly increased with increasing aeration rate up to 2.4 vvm. An initial ammonium sulphate concentration of 2 g l−1 gave the maximum carotenoids production. Only cotton seed oil enhanced the carotenoid productivity at a lower glucose concentration. Glucose, molasses sucrose and whey lactose sugars were chosen as the carbon sources in this study. In general, the increase in sugar concentration increased the growth of yeast and total carotenoids production. The highest carotenoid concentration (89.0 mg total carotenoids per liter of fermentation broth) was obtained when 20 g l−1 molasses sucrose was used as the carbon source while the highest product yield (35.0 mg total carotenoids per gram of dry cells) was achieved when 13.2 g l−1 whey lactose was the carbon source in the broth.

Equilibrium sorption isotherms for of Cu2+ on rice bran

Abstract: A new sorbent (rice bran) for removing Cu 2+ from aqueous solution has been investigated. The experimental results were fitted to the Langmuir, Freundlich, Temkin and Redlich–Peterson isotherms to obtain the characteristic parameters of each model. Langmuir, Temkin and Redlich–Peterson isotherms were found to represent the measured sorption data. The maximum sorption capacity of Cu 2+ on the rice bran was 33.58 mg/g according to the evaluation of using the Langmuir equation.