The application of purple non-sulfur bacteria for microbial mixed culture polyhydroxyalkanoates production

Reviews in Environmental Science and Bio/Technology - Polyhydroxyalkanoates (PHA) are a group of biopolymers produced naturally by microorganisms with properties similar to various petroleum-based...     

Aeration conditions affecting growth of purple nonsulfur bacteria in an organic wastewater treatment process

Effects of aeration on purple nonsulfur bacteria (PnSB) were studied in photobioreactors. Bacterial community changes were analyzed by denaturing gradient gel electrophoresis (DGGE) and fluorescence in situ hybridization (FISH). DGGE band pattern change was small and only few prominent bands were obtained at non-aeration condition. Sequencing results of the prominent DGGE bands obtained at this condition revealed that they represented mainly the PnSB, Rhodobacter sphaeroides and Rhodopseudomonas palustris. On the other hand, under aerated condition, some prominent bands originated from heterotrophs appeared but no proliferation of PnSB was observed. FISH was applied to detect PnSB and their population was quantified. Maximum PnSB ratio (up to 80%) was obtained both at non-aeration condition and at constant ORPs less than -200 mV. In the presence of DO, Rps. palustris was more competitive to chemoheterotrophs than Rb. sphaeroides.     

Optimization of sulphide production in an anaerobic continuous biofilm process with sulphate reducing bacteria

Different biofilm reactors for sulphide production by sulphate reducing bacteria were compared in a packed bed reactor and in two suspended carrier biofilm reactors. Lactate was used as carbon source in the experiments. The process was reversibly inhibited by free sulphide at 14 mM. The packed bed reactor was more efficient and less sensitive to changes. The maximum load in the system was 5.3 g sulphate/l.d.     

Thermophilic mixed culture of bacteria utilizing methanol for growth

A thermophilic mixed population of bacteria, capable of utilizing methanol as its sole carbon-energy source at temperatures up to 65 C, was selected by enrichment and studied. A maximal cellular yield of 0.42 g per g of methanol was observed at 50 to 56 C. The maximal specific growth rate of the mixed population in continuous culture at 56 C was greater than 0.32 per h. The amino acid profile of the mixed culture indicated that a high quality protein was produced and the protein content was 71%. The properties of this culture and its ability to grow at elevated temperatures are discussed in terms of single-cell protein production and the treatment of industrial waste.     

Screening of facultative anaerobic bacteria utilizing D-xylose for xylitol production

Seventeen cultures belonging to three genera of facultative bacteria ( Serratia, Cellulomonas, and Corynebacterium) were screened for the production of xylitol, a sugar alcohol used as a sweetener in the pharmaceutical and food industries. The bacterial strains that utilized D-xylose for growth were investigated for xylitol production. A chromogenic assay of both solid and liquid cultures showed that ten of the 17 bacteria screened could grow on D-xylose and produce detectable quantities of xylitol during 24-96 h of fermentation. Among the screened cultures, Corynebacterium sp. B-4247 produced the highest amount of xylitol. In addition, the ten bacterial cultures that initially produced xylitol were studied for the effect of the environmental factors, such as temperature, concentration of D-xylose and aeration, on xylitol production.     

Optimization of sulfide production by an indigenous consortium of sulfate-reducing bacteria for the treatment of lead-contaminated wastewater

Bioprocess and Biosystems Engineering - Biological treatment with sulfate-reducing bacteria (SRB) is considered to be an excellent option to remove heavy metals from wastewater. In this study, the...     

Biological treatment of wastewater containing an azo dye using mixed culture in alternating anaerobic/aerobic sequencing batch reactors

The performance of one stage anaerobic/aerobic processes for the biological treatment of synthetic wastewaters containing Acid Red 18 was studied. In addition, a method for evaluating dye mineralization using lumped parameters was investigated. The selected initial dye concentrations were 0, 35, 70, 140, and 280 mg/L, in reactors R1 ～ R5, respectively. This study showed that average COD removal was not lower than 85% while the remaining COD originated from Acid Red 18 and its degradation products. The majority of the dye removal occurred in the anaerobic phases and the aerobic phase contributions were insignificant. The kinetics data of dye removal showed that the increase in initial dye concentration (35 ～ 280 mg/L) caused a decrease in first-order kinetic rate constants (0.0593 ～ 0.0384/h). The overall mineralization of AR 18 dye was at least 44, 35, 13, and 0% in R2 ～ R5, respectively. Increase in initial dye concentrations had no significant effect on sludge characteristics.     

Effect of various pretreatment methods on anaerobic mixed microflora to enhance biohydrogen production utilizing dairy wastewater as substrate

Influence of different pretreatment methods applied on anaerobic mixed inoculum was evaluated for selectively enriching the hydrogen (H(2)) producing mixed culture using dairy wastewater as substrate. The experimental data showed the feasibility of molecular biohydrogen generation utilizing dairy wastewater as primary carbon source through metabolic participation. However, the efficiency of H(2) evolution and substrate removal efficiency were found to be dependent on the type of pretreatment procedure adopted on the parent inoculum. Among the studied pretreatment methods, chemical pretreatment (2-bromoethane sulphonic acid sodium salt (0.2 g/l); 24 h) procedure enabled higher H(2) yield along with concurrent substrate removal efficiency. On the contrary, heat-shock pretreatment (100 degrees C; 1 h) procedure resulted in relatively low H(2) yield. Compared to control experiments all the adopted pretreatment methods documented higher H(2) generation efficiency. In the case of combination experiments, integration of pH (pH 3; adjusted with ortho-phosphoric acid; 24 h) and chemical pretreatment evidenced higher H(2) production. Data envelopment analysis (DEA), a frontier analysis technique model was successfully applied to enumerate the relative efficiency of different pretreatment methods studied by considered pretreatment procedures as input and cumulative H(2) production rate and substrate degradation rate as corresponding two outputs.     

Dynamical model development and parameter identification for an anaerobic wastewater treatment process.

This paper deals with the development and the parameter identification of an anaerobic digestion process model. A two-step (acidogenesis-methanization) mass-balance model has been considered. The model incorporates electrochemical equilibria in order to include the alkalinity, which has to play a central role in the related monitoring and control strategy of a treatment plant. The identification is based on a set of dynamical experiments designed to cover a wide spectrum of operating conditions that are likely to take place in the practical operation of the plant. A step by step identification procedure to estimate the model parameters is presented. The results of 70 days of experiments in a 1-m(3) fermenter are then used to validate the model.     

A one-step process for the production of single-cell protein and amyloglucosidase

Summary A new Rhizopus species was isolated from traditional Indonesian food, tempeh. The newly isolated species was similar in its morphological characteristics to Rhizopus oligosporus UQM 145F, but grew faster on potato-dextrose agar as well as in submerged culture. The new isolate was found to convert ground cassava tuber directly into single cell protein without pretreatment due to its high amyloglucosidase formation.From 100 g ground tuber, a dry biomass of 33.75 g containing 26.48% true protein together with 60 ml of highly active amyloglucosidase (282 units) was obtained in 12 h. The amyloglucosidase was recovered by ultrafiltration, releasing 26.226 millimol glucose/l/min from soluble starch. The crude enzyme exhibited a pH optimum between 4.6 and 5.0, a temperature optimum between 55 and 60° C and an apparent Km of 3.125 g/l. High substrate concentrations and ammonium sulphate are inhibitory to the enzyme.     

Engineering application of anaerobic ammonium oxidation process in wastewater treatment

Anaerobic ammonium oxidation (Anammox), a promising biological nitrogen removal process, has been verified as an efficient, sustainable and cost-effective alternative to conventional nitrification and denitrification processes. To date, more than 110 full-scale anammox plants have been installed and are in operation, treating industrial NH₄ ⁺-rich wastewater worldwide, and anammox-based technologies are flourishing. This review the current state of the art for engineering applications of the anammox process, including various anammox-based technologies, reactor selection and attempts to apply it at different wastewater plants. Process control and implementation for stable performance are discussed as well as some remaining issues concerning engineering application are exposed, including the start-up period, process disturbances, greenhouse gas emissions and especially mainstream anammox applications. Finally, further development of the anammox engineering application is proposed in this review.     

A mixed yeast-bacteria process for the aerobic conversion of poultry waste into single-cell protein

Summary A mixed yeast-bacteria process was developed to convert poultry waste into a high protein feedstuff. A uricase producing strain ofCandida utilis was utilized with the, natural flora of the poultry manure. Molasses was used as carbon source. Variation of C/N consumed ratio with dilution rate was investigated and the product quality was compared with the other feedstuffs.     

Mutualistic interaction between dichloromethane‐ and chloromethane‐degrading bacteria in an anaerobic mixed culture

The microbial mixed culture RM grows with dichloromethane (DCM) as the sole energy source generating acetate, methane, chloride and biomass as products. Chloromethane (CM) was not an intermediate during DCM utilization consistent with the observation that CM could not replace DCM as a growth substrate. Interestingly, cultures that received DCM and CM together degraded both compounds concomitantly. Transient hydrogen (H₂) formation reaching a maximum concentration of 205 ± 13 ppmv was observed in cultures growing with DCM, and the addition of exogenous H₂ at concentrations exceeding 3000 ppmv impeded DCM degradation. In contrast, CM degradation in culture RM had a strict requirement for H₂. Following five consecutive transfers on CM and H₂, Acetobacterium 16S rRNA gene sequences dominated the culture and the DCM‐degrader Candidatus Dichloromethanomonas elyunquensis was eliminated, consistent with the observation that the culture lost the ability to degrade DCM. These findings demonstrate that culture RM harbours different populations responsible for anaerobic DCM and CM metabolism, and further imply that the DCM and CM degradation pathways are mechanistically distinct. H₂ generated during DCM degradation is consumed by the hydrogenotrophic CM degrader, or may fuel other hydrogenotrophic processes, including organohalide respiration, methanogenesis and H₂/CO₂ reductive acetogenesis.     

Development of an improved anaerobic filter for municipal wastewater treatment

Development of an improved reactor configuration of anaerobic filter was carried out for the elimination of clogging of filter media. The experiments over different hydraulic retention times (HRTs) indicated that the HRT of 12 h was the most appropriate one for the system studied while treating the municipal wastewater, which resulted 90% and 95% BOD and COD reduction, respectively. Reduction up to 95% in suspended solids concentration could be achieved without any pretreatment. The specific biogas yield obtained was 0.35 m(3) CH(4)/kgCODr with 70% of CH(4) content in the biogas generated from the system at the HRT of 12 h. Operational problems such as clogging of filter media were not observed throughout the period of study over 600 d.     

Limitations of thermophilic anaerobic wastewater treatment and the consequences for process design

Thermophilic anaerobic digestion offers an attractive alternative for the treatment of medium- and high-strength wastewaters. However, literature reports reveal that thermophilic wastewater treatment systems are often more sensitive to environmental changes than the well-defined high-rate reactors at the mesophilic temperature range. Also, in many cases a poorer effluent quality is experienced while the carry over of suspended solids in the effluent is relatively high. In this paper recent achievements are discussed regarding the process stability of thermophilic anaerobic wastewater treatment systems. Laboratory experiments reveal a relatively low sensitivity to temperature changes if high-rate reactors with immobilized biomass are used. Other results show that if a staged process is applied, thermophilic reactors can be operated for prolonged periods of time under extreme loading conditions (80–100 kg chemical oxygen demand.m^-3.day^-1), while the concentrations of volatile fatty acids in the effluent remain at a low level.     

An integrated electrocoagulation-phytoremediation process for the treatment of mixed industrial wastewater

The elimination of organic contaminants in highly complex wastewater was tested using a combination of the techniques: electrocoagulation with aluminum electrodes and phytoremediation with Myriophyllum aquaticum. Under optimal operating conditions at a pH of 8 and a current density of 45.45 A m(-2), the electrochemical method produces partial elimination of contaminants, which was improved using phytoremediation as a polishing technique. The combined treatment reduced chemical oxygen demand (COD) by 91%, color by 97% and turbidity by 98%. Initial and final values of contaminants in wastewaters were monitored using UV-vis spectrometry and cyclic voltammetry. Finally, the morphology and the elemental composition of the biomass were characterized with using scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS). The presence of Al in the roots of plants in the system indicates that the aluminum present in the test solution could be absorbed.     

Physiological characteristics of four methylotrophic bacteria and their potential use in single-cell protein production

Summary Four methylotrophic bacteria, isolated at the Kuwait Institute for Scientific Research, were able to grow on methanol as the only carbon source at a maximum temperature of 44°C. An optimized medium composition was obtained through intensive chemostat studies varying both macro- and micro-element concentrations. Various batch and chemostat experiments were carried out at different pH, temperature, dilution rate and methanol concentrations. The results showed optimum pH around 6.8, at temperatures of 37 to 40°C, dilution rate 0.2–0.3 h^–1 and methanol was found to be inhibitory at concentrations above 20 g l^–1. The performance of all four bacteria under chemostat conditions was similar. Chemostat fermentation experiments using the optimized medium at 40°C, pH 6.8, dilution 0.2 h^–1 and 10 g methanol/l in the feed gave a biomass yield coefficient of 0.42–0.44 g/g methanol, 78–79% crude protein content, 58–62% total amino acid content and 10–11.5% nucleic acid content. In conclusion all four methylotrophic strains has good potential for use in the production of single-cell protein.

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Caractéristiques physiologiques de quatre bactéries méthylotrophes et leur emploi potentiel dans la production de protéine uni-celluliare

Résumé Quatre bactéries méthylotrophes, isolées à l'Institut pour la Recherche Scientifique du Kuweit, se sont révélées capables de croître sur méthanol comme seule source de carbone à une température maximum de 44°C. Des études intensives en chémostat de variation des concentrations tant en macro-qu'en micro-éléments, ont permis d'obtenir une composition optimum du milieu. Diverses expériences en milieu non renouvelé et en chémostat ont été effectuées à différents pH, températures, taux de dilution et concentration en méthanol. Les résultats ont montré un optimum de pH vers 6.8, de température entre 37 et 40°C, de taux de dilution de 0.2 à 0.3 h^–1. Le méthanol s'est révélé inhibiteur aux concentrations supérieures à 20 g l^–1. La performance des quatres bactéries dans les conditions du chémostat se sont révélées très semblables. Les expériences de fermentátion en chémostat, utilisant le milieu optimum à 40°C, pH 6.8, taux de dilution de 0.2 h^–1 et à 10 g de méthanol par litre dans l'alimentation ont produit un coefficient de rendement en biomasse de 0.42 à 0.44 g de cellules par g de méthanol contenant de 78 à 79% de protéines, de 58 à 62% d'acides aminés totaux et de 10 à 11.5% d'acides nucléiques. En conclusion, les quatre bactéries méthylotrophes présentent une bonne potentialité pour être utilisées dans la production de protéine uni-cellulaire.