Fermentative production of rhamnosidase from Staphylococcus xylosus MAK 2 in a bioreactor for bio-energy generation

Increasing concern about the environment, food and feed shortages and hike in the price of petroleum have stimulated interest in new ways of producing biofuels. The interest is rapidly increasing towards converting agricultural wastes to commercially valuable products. Biofuels made from waste biomass can offer immediate and sustained greenhouse gas advantages. In this direction, we are focusing on Citrus processing waste, a byproduct of juice manufacture, which contains high amount of flavonoids and polysaccharides. There is a considerable industrial interest in the enzymatic transformation of flavonoids to hydrolysis products; that offers a pathway to bio-energy generation. Rhamnosidase of bacterial origin are very few and thus are potentially subject for research.

Staphylococcus xylosus, Gram positive cocci, a nonpathogenic member of CNS family, isolated from soil was used to produce α-L-rhamnosidase. This new strain, so far unknown for the production of α-L-Rhamnosidase, was identified and characterized as Staphyloccocus sp. through biochemical tests and 16S DNA sequence analysis. Effect of various medium and process parameters like pH, temperature, aeration and agitation rates and inducer concentration were studied. Further, the enzyme activity was enhanced by adding the inducer and divalent metal ion to the optimised fermentation medium. We have recovered important sugars “rhamnose” and “galacturonic acid” from the processed waste which would be utilized for ethanol production. This presentation will summarize current efforts to develop an enzymatic treatment which would facilitate the economical processing of citrus waste for bioenergy generation.

Milk lactate determination with a rotating bioreactor based on an electron transfer mediated by osmium complexes incorporating a continuous-flow/stopped-flow system

The high sensitivity that can be attained using a bienzymatic system and mediated by the redox polymer [Os(bpy)₂ClPyCH₂NHpoly(allylamine)] (Os-PAA), has been verified by on-line interfacing of a rotating bioreactor and continuous-flow/stopped-flow/continuous-flow processing. When the hydrogen peroxide formed by LO_x layer reaches the inner layer, the electronic flow between the immobilized peroxidase and the electrode surface produces a current, proportional to lactate concentration. The determination of lactate was possible with a limit of detection of 5 nmol l⁻¹ in the processing of as many as 30 samples per hour. This arrangement allows working in undiluted milk samples with a good stability and reproducibility. Horseradish peroxidase [EC 1.11.1.7] and Os-PAA were covalently immobilized on the glassy carbon electrode surface (upper cell body), lactate oxidase [EC 1.1.3.x] was immobilized on a disk that can be rotated.

Modelling based design of a pilot-scale membrane bioreactor for combined nutrient removal from domestic wastewater

A three stage-treatment of domestic wastewater including anaerobic, anoxic and aerobic phases is employed in this study while a clarifier unit is replaced with a submerged membrane in the aerobic unit. The effects of operational parameters on the performance of a pilot scale submerged membrane bioreactor (SMBR) namely hydraulic retention time (HRT), ratio of return activated sludge (QRS), ratio of internal recycle (QIR), solid retention time (SRT) and dissolved oxygen (DO) are evaluated by simulations, using a hybrid model composed of TUDP model, oxygen transfer model, biofouling model due to extra-cellular polymeric substances (EPS) and turbulent shear model. The results showed that anaerobic HRT of 3 hours, anoxic HRT of 6 hours, QRS of 20% and QIR of 300 % are satisfactory in obtaining a high removal efficiency (>90%) of COD, NH4-N, P04-P as well as a less sludge production. An increase of sludge production causes an increase in EPS, which fouls the membrane surface and increase the cleaning cycle of membrane. Operation of 5MBR system at 2 mg/I of DO and 30 days of SRT can extend the membrane cleaning cycle dramatically. The membrane cleaning cycle however is strongly dependent on the initial and terminal specific fluxes and displays inverse power relationships to those fluxes.

Removal of ametryn using membrane bioreactor process and its influence on critical flux

Compared to the Conventional Activated Sludge Process (ASP), Membrane Bioreactors (MBRs) have proven their superior performance in wastewater treatment and reuse during the past two decades. Further, MBRs have wide array of applications such as the removal of nutrients, toxic and persistent organic pollutants (POPs), which are impossible or difficult to remove using ASP. However, fouling of membrane is one of the main drawbacks to the widespread application of MBR technology and Extra-cellular Polymeric Substances (EPS) secreted by microbes are considered as one of the major foulants, which will reduce the flux (L/m2/h) through the membrane. Critical flux is defined as the flux above which membrane cake or gel layer formation due to deposition of EPS and other colloids on the membrane surface occurs. Thus, one of the operating strategies to control the fouling of MBRs is to operate those systems below the critical flux (at Sub-Critical flux). This paper discusses the critical flux results, which were obtained from short-term common flux step method, for a lab-scale MBR system treating Ametryn. This study compares the critical flux values that were obtained by operating the MBR system (consisting of a submerged Hollow-Fibre membrane with pore size of 0.4μm and effective area of 0.2m2) at different operating conditions and mixed liquor properties. This study revealed that the critical flux values found after the introduction of Ametryn were significantly lower than those of obtained before adding Ametryn to the synthetic wastewater. It was also revealed that the production of carbohydrates (in SMP) is greater than proteins, subsequent to the introduction of Ametryn and this may have influenced the membrane to foul more. It was also observed that a significant removal (40-60%) of Ametryn from this MBR during the critical flux determination experiments with 40 minutes flux-step duration.

Biodegradation of pentachlorophenol in a membrane bioreactor

Pentachlorophenol (PCP) is a toxic chemical, often used in the formulation of pesticide, herbicide, anti fungal agent, bactericide and wood preservative. This study is aimed at evaluating the potential of membrane bioreactor (MBR) to treat PCP contaminated wastewater. Synthetic wastewater with COD of 600 mg/L was fed into the MBR at varied PCP loading rate of 12–40 mg/m3/d. A PCP removal rate of 99% and a COD removal rate of 95% were achieved at a hydraulic retention time of 12 hs and a mixed liquor suspended solids (MLSS) concentration of 10,000 mg/L. When sodium pentachlorophenol (NaPCP), which has higher solubility in water, was used in the second phase of the study, at loading rates varying from 20 to 200 mg/m3·d, the removal rate of NaPCP was higher than 99% and the removal rate of COD was more than 96%. It was also found that at higher biomass concentrations, biosorption played an important role besides the biodegradation process. Batch experiments conducted in this study revealed that the sorption capacity to be 0.63 (mg PCP/g biomass) and occurred rapidly within 60 min. This phenomenon could enhance the PCP degradation through increased contact between microorganism and PCP. Further, the membrane resistance was low (trans-membrane pressure of 14 kPa) even after more than 100 ds of operation. In addition, the toxic level of PCP in the influent could have induced the microorganisms to secrete more extra-cellular polymeric substances (EPS) for their protection, which in turn must have increased the viscosity of the mixed liquor.

Landfill leachate treatment using thermophilic membrane bioreactor

This study was undertaken to investigate the performance of aerobic thermophilic membrane bioreactor (MBR) treating raw landfill leachate from two landfill sites in Thailand (Pathumthani site and Ram Indra site). The leachates from these sites were mixed in different proportions to produce a BOD/COD ratio of 0.39, 0.57, and 0.65, which was investigated in 3 experimental runs. The COD, ammonia, and TKN composition of the mixed leachate was 12,000, 1700 and 1900 mg/L, respectively. BOD was supplemented with glucose and soy protein. The system was operated at 45 degrees C and at a hydraulic retention time (HRT) of 24 hrs. The membrane used was a ceramic membrane with an ‘‘outside-in’’ flow mode and consisted of 22 open fibres with an inner diameter of approximately 2 mm. The COD removal rate increased from an average value of 62–79% while ammonia removal efficiency decreased from 75 to 60% with gradual increase in BOD. Furthermore, a high BOD removal efficiency (97–99%) was also observed. This clearly indicates that thermophilic system is highly suitable for COD and BOD removal especially at elevated organic loading. However, the system does not favor high nitrogen content wastewaters as the ammonia removal efficiency dropped with increasing BOD/COD ratio. Similar trends were found in TKN analysis as well. However, this system could serve as a pretreatment in removing ammonia. The concentrations of soluble and bound extra-cellular polymeric substances (EPS) found in thermophilic MBR were higher when compared to the corresponding concentrations in a mesophilic MBR, which led to a higher rate of fouling in the thermophilic membrane.

Pretreatment of seawater for biodegradable organic content removal using membrane bioreactor

Reverse osmosis (RO) is currently one of the most prevalent methods used for seawater desalination. During the past four decades, the research anddevelopment has reduced the energy consumption from about 20 to 4 kWh/m3, while improvements in membrane science has led to a 20-fold increase in the specific membrane flux. Nevertheless, research is still underway to reduce the operation and maintenance problems and thus improve the performance of RO systems. The most important maintenance problem associated with RO operation is the membrane fouling, especially biological fouling (biofouling). This work focuses on the aspects to eliminate biofouling in RO membranes, by adopting a proper pretreatment system. The experimental results revealed that fluidized bed biological granular activated carbon, at 15 min empty bed contact time (with dissolved organic carbon, DOC concentration of 6–8 mg/L) can be utilized effectively to remove nearly 100% biodegradable DOC from seawater. Continuous experiments of membrane bioreactor (MBR) have been conducted concomitantly to gain insight into the long-term effects of MBR on biodegradable organic content removal and biofouling control. The results show that MBR system produced better effluent with 78% DOC removal and quasi-total biodegradable DOC removal. Dissolved oxygen was not a limiting factor for the DOC degradation. Short-term experimental runs were conducted with RO membrane using both pretreated and non-pretreated seawater. The results showed that filtrate from MBR yielded the highest permeate flux improvement, which was approximately 300% compared with non-pretreated seawater.

Biological treatment of oily wastewater from gas stations by membrane bioreactor

In many Asian countries, rapid industrialization and urbanization has led to an increased number of cars, making wastewater from gas stations an important issue of concern in urban environment. This wastewater is characterized by high concentration of oil-water emulsion, which cannot be effectively removed by a conventional gravity separator. An experimental investigation on the treatability of oily wastewater from gas stations using a membrane bioreactor (MBR) system revealed that MBR system could achieve good removal efficiency with stability against shock loading. Optimum operating conditions were found to be at a hydraulic retention time of 4 h and an oil-loading rate of 1.8 kg oil m^sup -3^.d^sup -1^. It was anticipated that adding powdered activated carbon (PAC) in the MBR could help to adsorb the oils. However, operating the MBR with only microbial flocs has an advantage over adding PAC particles into the MBR, since the former condition could provide a prolonged cycle of filtration with a relatively lesser increase in transmembrane pressure.