The sensitivity of anaerobic digestion metabolism to a wide range of solutes makes it important t... more The sensitivity of anaerobic digestion metabolism to a wide range of solutes makes it important to be able to monitor toxicants in the feed to anaerobic digesters in order to optimize their operation. In this present study, a rapid fluorescence measurement technique based on resazurin reduction using a microplate reader was developed and applied for the detection of toxicants/inhibitors to digesters. A kinetic model was developed to describe the process of resazurin reduced to resorufin, and eventually to dihydroresorufin under anaerobic conditions. By modeling the assay results of resazurin (0.05, 0.1, 0.2 and 0.4 mM) reduction by a pure facultative anaerobic strain, E. faecalis, and fresh mixed anaerobic sludge, with or without 10 mg L(-1) of spiked pentachlorophenol (PCP), it became clear that the pseudo-first-order rate constant for the reduction of resazurin to resorufin, k1, was a good measure of 'toxicity'. With lower biomass density and the optimal resazurin addition...
h i g h l i g h t s S. tabernaemontani showed significant inhibition for ZnO treatment at level o... more h i g h l i g h t s S. tabernaemontani showed significant inhibition for ZnO treatment at level of 1000 mg L À1 .
Desiccated coconut waste sorbent (DCWS), a byproduct of coconut milk processing, was studied as a... more Desiccated coconut waste sorbent (DCWS), a byproduct of coconut milk processing, was studied as a sorbent for Hg(II) sorption. Energy dispersive X-ray analysis indicated that the DCWS mainly contained C, N, and O, while the Fourier transform infrared measurements confirmed the existence of hydroxyl, carboxyl, and amine groups on the DCWS surface. The point of zero charge (pH pzc ) and cation-exchange capacity (CEC) values were 6.05 and 2.02 meq/100g, respectively. The batch equilibrium data were fitted well by the Langmuir isotherm model with a maximum sorption capacity, q max of 500 mg/g, while the kinetic sorption data were found to follow a pseudo-second-order kinetic model. A column sorption study showed that the sorption capacity increased and the breakthrough time decreased with the increase in the initial Hg(II) concentrations. The regeneration studies revealed that the DCWS could be regenerated and reused.
This article provides the methane yield of municipal solid waste and its main constituents using ... more This article provides the methane yield of municipal solid waste and its main constituents using the biochemical methane potential (BMP) test. The methane yield of kitchen waste (KW), paper waste (PW), and garden waste (GW) were 357 ( -24.7), 147 ( -17.1), and 114 ( -0.6) mL CH 4 /g VS, respectively. The hydrolysis constant in the first order kinetic model was 0.25, 0.095, and 0.121 d -1 for KW, PW, and GW, respectively. The effect of the inoculum to substrate (I/S) ratio in the BMP test was investigated. Methane yields of 297.4 ( -18.6), 293.5 ( -33.9), and 378.2 ( -10.3) mL CH 4 /g VS were found at I/S ratios of 1.4, 7.2, and 12.9, respectively, whereas the hydrolysis constants were 0.112, 0.151, and 0.221 d -1 . A new method based on the production of soluble chemical oxygen demand (SCOD) while selectively inhibiting methanogenesis has been used to determine the hydrolysis constant (0.25 d -1 ) according to its true definition, which is the conversion of particulate COD to SCOD, showing that the method based on methane evolution can underestimate the actual value when hydrolysis is not the rate-limiting step.
Journal of Environmental Science and Health, Part A, 2012
Plasticisers are commonly found in landfill leachate and accumulate in the environment. Some of t... more Plasticisers are commonly found in landfill leachate and accumulate in the environment. Some of them are known as disruptive endocrine compound. This manuscript assessed the toxicity of three common plasticisers, including Bis(2-Ethylhexyl)phthalate (DEHP), o-hydroxybiphenyl (HBP) and 2,6-di-tert-butyl-4-(dimethylaminomethyl) phenol (MAMP) on the methanogens during the anaerobic process. It was found that DEHP and MAMP did not impede methanogenesis up to 200 mg/L, but no additional methane could be obtained from their degradation. In contrast, HBP severely inhibited methanogens at 200 mg/L, but after acclimatisation it could be metabolised resulting in a 25% increase in methane production compared to the control.
Journal of Environmental Science and Health, Part A, 2011
In this study, various methods were compared to reduce the Chemical Oxygen Demand (COD) content o... more In this study, various methods were compared to reduce the Chemical Oxygen Demand (COD) content of stabilised leachate from a Submerged Anaerobic Membrane Bioreactor (SAMBR). It was found that Powdered Activated Carbon (PAC) resulted in greater COD removals (84 %) than Granular Activated Carbon (GAC-80 %), an ultrafiltration membrane of 1kDa (75 %), coagulation-flocculation with FeCl(3) and polyelectrolyte (45 %), FeCl(3) alone (32 %), and polymeric adsorbents such as XAD7HP (46 %) and XAD4 (32 %). Results obtained on the <1 kDa fraction showed that PAC and GAC had a similar adsorption efficiency of about 60 % COD removal, followed by XAD7HP (48 %), XAD4 (27 %) and then FeCl(3) (23 %). The post-treatment sequence UF+GAC would result in a final effluent with less than 100 mg COD/L. Size Exclusion Chromatography (SEC) revealed that the extent of adsorption of low MW compounds onto PAC was limited due to low MW hydrophilic compounds, whereas the kinetics of PAC adsorption depended mainly on the adsorption of high MW aromatics.
The digestibility of a starch-polyvinyl alcohol (PVOH) biopolymer insulated cardboard coolbox was... more The digestibility of a starch-polyvinyl alcohol (PVOH) biopolymer insulated cardboard coolbox was investigated under a defined anaerobic digestion (AD) system with key parameters characterized. Laboratory results were combined with industrial operational data to develop a site-specific life cycle assessment (LCA) model. Inoculated with active bacterial trophic groups, the anaerobic biodegradability of three starch-PVOH biopolymers achieved 58-62%. The LCA modeling showed that the environmental burdens of the starch-PVOH biopolymer packaging under AD conditions on acidification, eutrophication, global warming and photochemical oxidation potential were dominated by atmospheric emissions released from substrate degradation and fuel combustion, whereas energy consumption and infrastructure requirements were the causes of abiotic depletion, ozone depletion and toxic impacts. Nevertheless, for this bio-packaging, AD of the starch-PVOH biopolymer combined with recycling of the cardboard emerged as the environmentally superior option and optimization of the energy utilization system could bring further environmental benefits to the AD process.
This study seeks to examine the ability of non-ionic/non-polar Colloidial Liquid Aphrons (CLAs) t... more This study seeks to examine the ability of non-ionic/non-polar Colloidial Liquid Aphrons (CLAs) to preserve enzyme functionality upon immobilization and release. CLAs consisting of micron-sized oil droplets surrounded by a thin aqueous layer stabilized by a mixture of surfactants, were formulated by direct addition (pre-manufacture addition) using 1% Tween 80/ mineral oil and 1% Tween 20 and the enzymes lipase, aprotinin and α-chymotrypsin. The results of activity assays for both lipase and α-chymotrypsin showed that kinetic activity increased upon immobilization by factors of 7 and 5.5, respectively, while aprotinin retained approximately 85% of its native activity. The conformation of the enzymes released through desorption showed no significant alterations compared to their native state. Changes in pH and temperature showed that optimum conditions did not change after immobilization, while analysis of activation energy for the immobilized enzyme showed an increase in activity at ...
The residual COD from anaerobic treatment processes is usually too high to comply with legislativ... more The residual COD from anaerobic treatment processes is usually too high to comply with legislative discharge levels. It has been shown that in well operated systems the majority of the effluent COD originates from soluble microbial products (SMP) produced by the system itself, hence the characteristics of these compounds become important when assessing post-treatment systems to remove the residual COD. The molecular weight (MW) distribution and the identification of SMP in the effluents from three different anaerobic reactors will be presented. It has been found that the bulk of SMP lies in the low MW range, though compounds with MW as high as 300 kDa were also present in all anaerobic effluents. Preliminary results on the identification of such compounds using GC/MS surprisingly revealed the presence of long chain alkenes (C 12 -C 24 ) and alkanes (C 12 -C 16 ), as well as some aromatic compounds. These compounds that likely come from cell lysis and endogenous decay may not be easily biodegradable, hence their presence in the effluent is likely to cause the residual COD.
AbstractÐA review concerning the characterisation, production, modelling, signi®cance and implica... more AbstractÐA review concerning the characterisation, production, modelling, signi®cance and implications of soluble microbial products (SMP) in wastewater treatment is presented. The precise de®nition of SMP is open to debate, but is currently regarded as``the pool of organic compounds that are released into solution from substrate metabolism (usually with biomass growth) and biomass decay'', although for anaerobic systems volatile fatty acids are not included as SMP. Some of the SMP have been identi®ed as humic and fulvic acids, polysaccharides, proteins, nucleic acids, organic acids, amino acids, antibiotics, steroids, exocellular enzymes, siderophores, structural components of cells and products of energy metabolism. Crucially, SMP have been found to comprise the majority of soluble organic material in the euents from biological treatment processes and their presence is, therefore, of particular interest in terms of achieving discharge consent levels for BOD and COD. SMP also exhibit several characteristics, such as toxicity and metal chelating properties, which eect the performance of the treatment system, and their presence has also been shown to adversely aect the kinetic activity and the¯occulating and settling properties of sludge. This review outlines some important discoveries with regard to the MW distribution, biodegradability and treatability of SMP and also the eect of process parameters on their production. It also summarises the attempts at incorporating SMP formation into the modelling of wastewater treatment. However, it concludes that the knowledge regarding SMP is far from complete and that much work is still required to fully understand their contribution to the treatment process; some of these future research areas are then outlined. #
Acetic acid was used in abiotic experiments to adjust the solution pH and investigate its influen... more Acetic acid was used in abiotic experiments to adjust the solution pH and investigate its influence on the chemical hydrolysis of the Organic Fraction of Municipal Solid Waste (OFMSW). Soluble chemical oxygen demand (SCOD) was used to measure the hydrolysis under oxidative conditions (positive oxidation-reduction potential values), and pH 4 allowed for 20% (±2%) of the COD added to be solubilized, whereas only 12% (±1%) was solubilized at pH7. Under reducing conditions (negative oxidation-reduction potential values) and pH 4, 32.3% (±3%) of the OFMSW was solubilized which shows that acidogenesis at pH 4 during the anaerobic digestion of solid waste can result in chemical hydrolysis. In comparison, bacterial hydrolysis resulted in 54% (±6%) solubilization.
This paper focused on the factors affecting the respiration rate of the digestate taken from a co... more This paper focused on the factors affecting the respiration rate of the digestate taken from a continuous anaerobic two-stage process treating the organic fraction of municipal solid waste (OFMSW). The process involved a hydrolytic reactor (HR) that produced a leachate fed to a submerged anaerobic membrane bioreactor (SAMBR). It was found that a volatile solids (VS) removal in the range 40-75% and an operating temperature in the HR between 21 and 35 °C resulted in digestates with similar respiration rates, with all digestates requiring 17 days of aeration before satisfying the British Standard Institution stability threshold of 16 mg CO(2) g VS(-1) day(-1). Sanitization of the digestate at 65 °C for 7 days allowed a mature digestate to be obtained. At 4 g VS L(-1) d(-1) and Solid Retention Times (SRT) greater than 70 days, all the digestates emitted CO(2) at a rate lower than 25 mg CO(2) g VS(-1) d(-1) after 3 days of aeration, while at SRT lower than 20 days all the digestates disp...
The anaerobic baffled reactor (ABR) contains a mixed anaerobic culture segregated into compartmen... more The anaerobic baffled reactor (ABR) contains a mixed anaerobic culture segregated into compartments. During pseudo-steady state runs, formate was detected in the first two or three compartments, thereafter dropping off sharply. Under conditions of shock loading, formate was detected in the reactor effluent, up to peak concentrations of 2500 mg/l. There are indications that formate may play an important role as an intermediate in the anaerobic digestion process, and that its production may contribute significantly to reactor stability.
ABSTRACT The mass transfer characteristics of a non-porous silicone rubber membrane contacting an... more ABSTRACT The mass transfer characteristics of a non-porous silicone rubber membrane contacting an aqueous and an organic phase were determined using a shell and tube mass exchanger. Firstly, the stability of the liquid/membrane interfaces was examined, and when positive aqueous phase transmembrane pressure differentials of up to 2 bar were applied, no bulk transmembrane flow of either liquid was observed. This result was not affected by the addition of surfactants or biomass to the aqueous phase, and therefore it seems that phase breakthrough, common with porous membranes, is avoided. Secondly, the mass transfer characteristics of a range of model solutes were investigated and explained with a resistances in series model. A high membrane/aqueous partition coefficient (Pmemaq) (approximately>25) resulted in the aqueous phase film resistance limiting, whilst a low Pmemaq (approximately<5) resulted in the membrane resistance limiting. In contact with organic solvents the silicone rubber swelled to various degrees, and this was solvent dependent. The degree of swelling, and the relative partitioning of the solute into the swelling solvent, impacted on Pmemaq and the membrane diffusion coefficient. These two parameters could be increased by using a highly swelling solvent (solvent constituting>50% of the swollen membrane volume) with a high organic/aqueous partition coefficient (Porgaq) for the solute. In this way the membrane resistance for some solutes was decreased, and therefore the overall mass transfer coefficient increased. Finally, the effect of the presence of other hydrophobic solutes on the rate of mass transfer was investigated, and in the case of geraniol and citronellol (two chemically similar solutes with low water solubilities, 0.7 and 0.35 g l−1, respectively) the effect was similar to a “salting out” phenomena. This resulted in an increase of Porgaq for both geraniol and citronellol, and therefore a decrease in flux of the solute transferring to the aqueous phase.
Powdered activated carbon (PAC) was added to an effluent from a submerged anaerobic membrane bior... more Powdered activated carbon (PAC) was added to an effluent from a submerged anaerobic membrane bioreactor (SAMBR) treating saline wastewater as a post-treatment method. The adsorption of contaminants was carried out and key Freundlich isotherm parameters were evaluated. The results showed a reduction in dissolved organic carbon (DOC) in the effluent of over 80% after treatment with 1.7 g PAC/L. The composition of the effluent was determined by the use of size exclusion chromatography (SEC) and by GC-MS analysis. Most of the components of the effluent had a MW less than 1 kDa, and these were the hardest to eliminate by PAC adsorption. m-Aminophenylacetylene, cyclohexane 1,2,4 trimethyl and cholestan 3-one were found in the effluent, but could be removed by PAC adsorption. Finally, different methods for using PAC, with or without biomass, revealed that aerobic biomass enhanced the adsorption process resulting in higher DOC removals.
Journal of Chemical Technology & Biotechnology, 2006
A continuous flow flat sheet hybrid membrane aerated biofilm reactor ͑MABR͒ was used to treat a s... more A continuous flow flat sheet hybrid membrane aerated biofilm reactor ͑MABR͒ was used to treat a synthetic wastewater containing perchloroethylene ͑PCE͒; 1.25-2.5 g chemical oxygen demand ͑COD͒/L of glucose was also added to the synthetic wastewater as a source of COD representative of a real wastewater. The reactor was able to biodegrade 70 mg L −1 of PCE in 9 h without the accumulation of any intermediate compounds, resulting in a removal rate of 247 mmol of PCE h −1 m −3 in a reactor with a specific membrane area of 4.048 m 2 m −3 . MABRs have never been used before for PCE degradation, and this rate is one of the highest volumetric PCE degradation rates reported in the literature. COD removal was also good and varied from 85 to 92%. Since very few volatile fatty acids accumulated in the system, most of the residual COD was attributed to soluble microbial products as reported by previous researchers. A mass balance on chloride during this study showed that only 72-81% of it could be accounted for. It is probable that some of the chlorinated ethenes were adsorbed onto the biofilm or that aerobic intermediates of low-chlorinated compounds such as trichloroethanol, dichloroacetyl, and chloroacetaldehyde were produced in the system. Nevertheless the chloride mass balance in this work compares well with the literature. Due to their high PCE and COD removal rates, hybrid MABRs have the potential to be used for a number of refractory organics which require combined anaerobic/aerobic biological treatment for degradation.
The application of many biotransformation processes is limited because the substrates/products ar... more The application of many biotransformation processes is limited because the substrates/products are poorly water soluble, can be further metabolised, or are inhibitory.
The use of enzymes in non-aqueous media is a technique that is now currently being investigated a... more The use of enzymes in non-aqueous media is a technique that is now currently being investigated and commercially exploited. Here we report on the use of a novel immobilisation technique utilising an oil-in-water macroemulsion, termed a colloidal liquid aphron (CLA), to immobilise six different enzymes varying in molecular weight and pI. All enzymes were immobilised to a greater or lesser extent, with greater than 70% of -galactosidase and 90% of -amylase effectively being immobilised over a wide range of pH values (4-10). It was found that in most cases pH had little effect on the degree of immobilisation. The method of immobilisation apperared to be related to the hydrophobicity and adiabatic compressibility of the enzyme, and its molecular weight. These enzymes also exhibited improved activity (superactivity) after immobilisation while the values of the Michaelis-Menten constant were altered. The major factor affecting loss of activity of the immobilised enzymes was found to be the anionic surfactant, sodium dodecyl sulphate, used in the polyaphron preparation. However, SDS also appeared to enhance activity by altering protein conformation.
An emerging technique for the recovery of microbial secondary metabolites, such as antibiotics, i... more An emerging technique for the recovery of microbial secondary metabolites, such as antibiotics, is the use of colloidal liquid aphrons (CLAs) in pre-dispersed solvent extraction (PDSE) processes. Knowledge of the extraction kinetics and the limiting mass transfer resistances will be vital for e$cient process design and operation. In this work, the rates of erythromycin extraction using CLAs and conventional aqueous}organic, two-phase systems have been investigated. The CLAs used were formulated from 1% w/v Softanol 120 in decanol and 0.5% w/v SDS in water. The rate of erythromycin extraction with CLAs dispersed in well-mixed systems was found to be extremely rapid with equilibrium being achieved within 15 s or less. Overall erythromycin mass transfer coe$cients, K M , were typically 6.3;10\ m s\ for extraction experiments, and 1.0;10\ m s\ for stripping experiments. The rapid rates of erythromycin transfer were attributed to the small size of the dispersed CLAs, typically 5 m diameter, and hence the large interfacial area available for mass transfer of around 15;10 m m\. Experiments over a range of Reynolds numbers indicated that both the extraction and stripping processes were probably under mixed control of an interfacial resistance and boundary-layer di!usion. To investigate the in#uence of the surfactants used for aphron formulation on erythromycin extraction, further experiments were performed using aqueous}organic, two-phase systems in a non-dispersive stirred cell. The measured K M values were of the same order of magnitude as in the case of experiments with dispersed CLAs. When present individually, or together with SDS, the non-ionic Softanol surfactant was seen to retard erythromycin extraction rates in all cases. In contrast, the presence of SDS was found to enhance K M values by a factor of 2}4 compared to surfactant-free systems. This may be attributed to a speci"c interaction between individual SDS and erythromycin molecules and/or the generation of interfacial turbulence at a microscopic level. Further investigations are underway to elucidate the mechanism responsible. The concentration of either surfactant was also found to signi"cantly a!ect the measured K M values. The prediction of K M values using existing correlations, and the implications of the experimental results on contactor design and operation are also discussed.
The sensitivity of anaerobic digestion metabolism to a wide range of solutes makes it important t... more The sensitivity of anaerobic digestion metabolism to a wide range of solutes makes it important to be able to monitor toxicants in the feed to anaerobic digesters in order to optimize their operation. In this present study, a rapid fluorescence measurement technique based on resazurin reduction using a microplate reader was developed and applied for the detection of toxicants/inhibitors to digesters. A kinetic model was developed to describe the process of resazurin reduced to resorufin, and eventually to dihydroresorufin under anaerobic conditions. By modeling the assay results of resazurin (0.05, 0.1, 0.2 and 0.4 mM) reduction by a pure facultative anaerobic strain, E. faecalis, and fresh mixed anaerobic sludge, with or without 10 mg L(-1) of spiked pentachlorophenol (PCP), it became clear that the pseudo-first-order rate constant for the reduction of resazurin to resorufin, k1, was a good measure of 'toxicity'. With lower biomass density and the optimal resazurin addition...
h i g h l i g h t s S. tabernaemontani showed significant inhibition for ZnO treatment at level o... more h i g h l i g h t s S. tabernaemontani showed significant inhibition for ZnO treatment at level of 1000 mg L À1 .
Desiccated coconut waste sorbent (DCWS), a byproduct of coconut milk processing, was studied as a... more Desiccated coconut waste sorbent (DCWS), a byproduct of coconut milk processing, was studied as a sorbent for Hg(II) sorption. Energy dispersive X-ray analysis indicated that the DCWS mainly contained C, N, and O, while the Fourier transform infrared measurements confirmed the existence of hydroxyl, carboxyl, and amine groups on the DCWS surface. The point of zero charge (pH pzc ) and cation-exchange capacity (CEC) values were 6.05 and 2.02 meq/100g, respectively. The batch equilibrium data were fitted well by the Langmuir isotherm model with a maximum sorption capacity, q max of 500 mg/g, while the kinetic sorption data were found to follow a pseudo-second-order kinetic model. A column sorption study showed that the sorption capacity increased and the breakthrough time decreased with the increase in the initial Hg(II) concentrations. The regeneration studies revealed that the DCWS could be regenerated and reused.
This article provides the methane yield of municipal solid waste and its main constituents using ... more This article provides the methane yield of municipal solid waste and its main constituents using the biochemical methane potential (BMP) test. The methane yield of kitchen waste (KW), paper waste (PW), and garden waste (GW) were 357 ( -24.7), 147 ( -17.1), and 114 ( -0.6) mL CH 4 /g VS, respectively. The hydrolysis constant in the first order kinetic model was 0.25, 0.095, and 0.121 d -1 for KW, PW, and GW, respectively. The effect of the inoculum to substrate (I/S) ratio in the BMP test was investigated. Methane yields of 297.4 ( -18.6), 293.5 ( -33.9), and 378.2 ( -10.3) mL CH 4 /g VS were found at I/S ratios of 1.4, 7.2, and 12.9, respectively, whereas the hydrolysis constants were 0.112, 0.151, and 0.221 d -1 . A new method based on the production of soluble chemical oxygen demand (SCOD) while selectively inhibiting methanogenesis has been used to determine the hydrolysis constant (0.25 d -1 ) according to its true definition, which is the conversion of particulate COD to SCOD, showing that the method based on methane evolution can underestimate the actual value when hydrolysis is not the rate-limiting step.
Journal of Environmental Science and Health, Part A, 2012
Plasticisers are commonly found in landfill leachate and accumulate in the environment. Some of t... more Plasticisers are commonly found in landfill leachate and accumulate in the environment. Some of them are known as disruptive endocrine compound. This manuscript assessed the toxicity of three common plasticisers, including Bis(2-Ethylhexyl)phthalate (DEHP), o-hydroxybiphenyl (HBP) and 2,6-di-tert-butyl-4-(dimethylaminomethyl) phenol (MAMP) on the methanogens during the anaerobic process. It was found that DEHP and MAMP did not impede methanogenesis up to 200 mg/L, but no additional methane could be obtained from their degradation. In contrast, HBP severely inhibited methanogens at 200 mg/L, but after acclimatisation it could be metabolised resulting in a 25% increase in methane production compared to the control.
Journal of Environmental Science and Health, Part A, 2011
In this study, various methods were compared to reduce the Chemical Oxygen Demand (COD) content o... more In this study, various methods were compared to reduce the Chemical Oxygen Demand (COD) content of stabilised leachate from a Submerged Anaerobic Membrane Bioreactor (SAMBR). It was found that Powdered Activated Carbon (PAC) resulted in greater COD removals (84 %) than Granular Activated Carbon (GAC-80 %), an ultrafiltration membrane of 1kDa (75 %), coagulation-flocculation with FeCl(3) and polyelectrolyte (45 %), FeCl(3) alone (32 %), and polymeric adsorbents such as XAD7HP (46 %) and XAD4 (32 %). Results obtained on the <1 kDa fraction showed that PAC and GAC had a similar adsorption efficiency of about 60 % COD removal, followed by XAD7HP (48 %), XAD4 (27 %) and then FeCl(3) (23 %). The post-treatment sequence UF+GAC would result in a final effluent with less than 100 mg COD/L. Size Exclusion Chromatography (SEC) revealed that the extent of adsorption of low MW compounds onto PAC was limited due to low MW hydrophilic compounds, whereas the kinetics of PAC adsorption depended mainly on the adsorption of high MW aromatics.
The digestibility of a starch-polyvinyl alcohol (PVOH) biopolymer insulated cardboard coolbox was... more The digestibility of a starch-polyvinyl alcohol (PVOH) biopolymer insulated cardboard coolbox was investigated under a defined anaerobic digestion (AD) system with key parameters characterized. Laboratory results were combined with industrial operational data to develop a site-specific life cycle assessment (LCA) model. Inoculated with active bacterial trophic groups, the anaerobic biodegradability of three starch-PVOH biopolymers achieved 58-62%. The LCA modeling showed that the environmental burdens of the starch-PVOH biopolymer packaging under AD conditions on acidification, eutrophication, global warming and photochemical oxidation potential were dominated by atmospheric emissions released from substrate degradation and fuel combustion, whereas energy consumption and infrastructure requirements were the causes of abiotic depletion, ozone depletion and toxic impacts. Nevertheless, for this bio-packaging, AD of the starch-PVOH biopolymer combined with recycling of the cardboard emerged as the environmentally superior option and optimization of the energy utilization system could bring further environmental benefits to the AD process.
This study seeks to examine the ability of non-ionic/non-polar Colloidial Liquid Aphrons (CLAs) t... more This study seeks to examine the ability of non-ionic/non-polar Colloidial Liquid Aphrons (CLAs) to preserve enzyme functionality upon immobilization and release. CLAs consisting of micron-sized oil droplets surrounded by a thin aqueous layer stabilized by a mixture of surfactants, were formulated by direct addition (pre-manufacture addition) using 1% Tween 80/ mineral oil and 1% Tween 20 and the enzymes lipase, aprotinin and α-chymotrypsin. The results of activity assays for both lipase and α-chymotrypsin showed that kinetic activity increased upon immobilization by factors of 7 and 5.5, respectively, while aprotinin retained approximately 85% of its native activity. The conformation of the enzymes released through desorption showed no significant alterations compared to their native state. Changes in pH and temperature showed that optimum conditions did not change after immobilization, while analysis of activation energy for the immobilized enzyme showed an increase in activity at ...
The residual COD from anaerobic treatment processes is usually too high to comply with legislativ... more The residual COD from anaerobic treatment processes is usually too high to comply with legislative discharge levels. It has been shown that in well operated systems the majority of the effluent COD originates from soluble microbial products (SMP) produced by the system itself, hence the characteristics of these compounds become important when assessing post-treatment systems to remove the residual COD. The molecular weight (MW) distribution and the identification of SMP in the effluents from three different anaerobic reactors will be presented. It has been found that the bulk of SMP lies in the low MW range, though compounds with MW as high as 300 kDa were also present in all anaerobic effluents. Preliminary results on the identification of such compounds using GC/MS surprisingly revealed the presence of long chain alkenes (C 12 -C 24 ) and alkanes (C 12 -C 16 ), as well as some aromatic compounds. These compounds that likely come from cell lysis and endogenous decay may not be easily biodegradable, hence their presence in the effluent is likely to cause the residual COD.
AbstractÐA review concerning the characterisation, production, modelling, signi®cance and implica... more AbstractÐA review concerning the characterisation, production, modelling, signi®cance and implications of soluble microbial products (SMP) in wastewater treatment is presented. The precise de®nition of SMP is open to debate, but is currently regarded as``the pool of organic compounds that are released into solution from substrate metabolism (usually with biomass growth) and biomass decay'', although for anaerobic systems volatile fatty acids are not included as SMP. Some of the SMP have been identi®ed as humic and fulvic acids, polysaccharides, proteins, nucleic acids, organic acids, amino acids, antibiotics, steroids, exocellular enzymes, siderophores, structural components of cells and products of energy metabolism. Crucially, SMP have been found to comprise the majority of soluble organic material in the euents from biological treatment processes and their presence is, therefore, of particular interest in terms of achieving discharge consent levels for BOD and COD. SMP also exhibit several characteristics, such as toxicity and metal chelating properties, which eect the performance of the treatment system, and their presence has also been shown to adversely aect the kinetic activity and the¯occulating and settling properties of sludge. This review outlines some important discoveries with regard to the MW distribution, biodegradability and treatability of SMP and also the eect of process parameters on their production. It also summarises the attempts at incorporating SMP formation into the modelling of wastewater treatment. However, it concludes that the knowledge regarding SMP is far from complete and that much work is still required to fully understand their contribution to the treatment process; some of these future research areas are then outlined. #
Acetic acid was used in abiotic experiments to adjust the solution pH and investigate its influen... more Acetic acid was used in abiotic experiments to adjust the solution pH and investigate its influence on the chemical hydrolysis of the Organic Fraction of Municipal Solid Waste (OFMSW). Soluble chemical oxygen demand (SCOD) was used to measure the hydrolysis under oxidative conditions (positive oxidation-reduction potential values), and pH 4 allowed for 20% (±2%) of the COD added to be solubilized, whereas only 12% (±1%) was solubilized at pH7. Under reducing conditions (negative oxidation-reduction potential values) and pH 4, 32.3% (±3%) of the OFMSW was solubilized which shows that acidogenesis at pH 4 during the anaerobic digestion of solid waste can result in chemical hydrolysis. In comparison, bacterial hydrolysis resulted in 54% (±6%) solubilization.
This paper focused on the factors affecting the respiration rate of the digestate taken from a co... more This paper focused on the factors affecting the respiration rate of the digestate taken from a continuous anaerobic two-stage process treating the organic fraction of municipal solid waste (OFMSW). The process involved a hydrolytic reactor (HR) that produced a leachate fed to a submerged anaerobic membrane bioreactor (SAMBR). It was found that a volatile solids (VS) removal in the range 40-75% and an operating temperature in the HR between 21 and 35 °C resulted in digestates with similar respiration rates, with all digestates requiring 17 days of aeration before satisfying the British Standard Institution stability threshold of 16 mg CO(2) g VS(-1) day(-1). Sanitization of the digestate at 65 °C for 7 days allowed a mature digestate to be obtained. At 4 g VS L(-1) d(-1) and Solid Retention Times (SRT) greater than 70 days, all the digestates emitted CO(2) at a rate lower than 25 mg CO(2) g VS(-1) d(-1) after 3 days of aeration, while at SRT lower than 20 days all the digestates disp...
The anaerobic baffled reactor (ABR) contains a mixed anaerobic culture segregated into compartmen... more The anaerobic baffled reactor (ABR) contains a mixed anaerobic culture segregated into compartments. During pseudo-steady state runs, formate was detected in the first two or three compartments, thereafter dropping off sharply. Under conditions of shock loading, formate was detected in the reactor effluent, up to peak concentrations of 2500 mg/l. There are indications that formate may play an important role as an intermediate in the anaerobic digestion process, and that its production may contribute significantly to reactor stability.
ABSTRACT The mass transfer characteristics of a non-porous silicone rubber membrane contacting an... more ABSTRACT The mass transfer characteristics of a non-porous silicone rubber membrane contacting an aqueous and an organic phase were determined using a shell and tube mass exchanger. Firstly, the stability of the liquid/membrane interfaces was examined, and when positive aqueous phase transmembrane pressure differentials of up to 2 bar were applied, no bulk transmembrane flow of either liquid was observed. This result was not affected by the addition of surfactants or biomass to the aqueous phase, and therefore it seems that phase breakthrough, common with porous membranes, is avoided. Secondly, the mass transfer characteristics of a range of model solutes were investigated and explained with a resistances in series model. A high membrane/aqueous partition coefficient (Pmemaq) (approximately>25) resulted in the aqueous phase film resistance limiting, whilst a low Pmemaq (approximately<5) resulted in the membrane resistance limiting. In contact with organic solvents the silicone rubber swelled to various degrees, and this was solvent dependent. The degree of swelling, and the relative partitioning of the solute into the swelling solvent, impacted on Pmemaq and the membrane diffusion coefficient. These two parameters could be increased by using a highly swelling solvent (solvent constituting>50% of the swollen membrane volume) with a high organic/aqueous partition coefficient (Porgaq) for the solute. In this way the membrane resistance for some solutes was decreased, and therefore the overall mass transfer coefficient increased. Finally, the effect of the presence of other hydrophobic solutes on the rate of mass transfer was investigated, and in the case of geraniol and citronellol (two chemically similar solutes with low water solubilities, 0.7 and 0.35 g l−1, respectively) the effect was similar to a “salting out” phenomena. This resulted in an increase of Porgaq for both geraniol and citronellol, and therefore a decrease in flux of the solute transferring to the aqueous phase.
Powdered activated carbon (PAC) was added to an effluent from a submerged anaerobic membrane bior... more Powdered activated carbon (PAC) was added to an effluent from a submerged anaerobic membrane bioreactor (SAMBR) treating saline wastewater as a post-treatment method. The adsorption of contaminants was carried out and key Freundlich isotherm parameters were evaluated. The results showed a reduction in dissolved organic carbon (DOC) in the effluent of over 80% after treatment with 1.7 g PAC/L. The composition of the effluent was determined by the use of size exclusion chromatography (SEC) and by GC-MS analysis. Most of the components of the effluent had a MW less than 1 kDa, and these were the hardest to eliminate by PAC adsorption. m-Aminophenylacetylene, cyclohexane 1,2,4 trimethyl and cholestan 3-one were found in the effluent, but could be removed by PAC adsorption. Finally, different methods for using PAC, with or without biomass, revealed that aerobic biomass enhanced the adsorption process resulting in higher DOC removals.
Journal of Chemical Technology & Biotechnology, 2006
A continuous flow flat sheet hybrid membrane aerated biofilm reactor ͑MABR͒ was used to treat a s... more A continuous flow flat sheet hybrid membrane aerated biofilm reactor ͑MABR͒ was used to treat a synthetic wastewater containing perchloroethylene ͑PCE͒; 1.25-2.5 g chemical oxygen demand ͑COD͒/L of glucose was also added to the synthetic wastewater as a source of COD representative of a real wastewater. The reactor was able to biodegrade 70 mg L −1 of PCE in 9 h without the accumulation of any intermediate compounds, resulting in a removal rate of 247 mmol of PCE h −1 m −3 in a reactor with a specific membrane area of 4.048 m 2 m −3 . MABRs have never been used before for PCE degradation, and this rate is one of the highest volumetric PCE degradation rates reported in the literature. COD removal was also good and varied from 85 to 92%. Since very few volatile fatty acids accumulated in the system, most of the residual COD was attributed to soluble microbial products as reported by previous researchers. A mass balance on chloride during this study showed that only 72-81% of it could be accounted for. It is probable that some of the chlorinated ethenes were adsorbed onto the biofilm or that aerobic intermediates of low-chlorinated compounds such as trichloroethanol, dichloroacetyl, and chloroacetaldehyde were produced in the system. Nevertheless the chloride mass balance in this work compares well with the literature. Due to their high PCE and COD removal rates, hybrid MABRs have the potential to be used for a number of refractory organics which require combined anaerobic/aerobic biological treatment for degradation.
The application of many biotransformation processes is limited because the substrates/products ar... more The application of many biotransformation processes is limited because the substrates/products are poorly water soluble, can be further metabolised, or are inhibitory.
The use of enzymes in non-aqueous media is a technique that is now currently being investigated a... more The use of enzymes in non-aqueous media is a technique that is now currently being investigated and commercially exploited. Here we report on the use of a novel immobilisation technique utilising an oil-in-water macroemulsion, termed a colloidal liquid aphron (CLA), to immobilise six different enzymes varying in molecular weight and pI. All enzymes were immobilised to a greater or lesser extent, with greater than 70% of -galactosidase and 90% of -amylase effectively being immobilised over a wide range of pH values (4-10). It was found that in most cases pH had little effect on the degree of immobilisation. The method of immobilisation apperared to be related to the hydrophobicity and adiabatic compressibility of the enzyme, and its molecular weight. These enzymes also exhibited improved activity (superactivity) after immobilisation while the values of the Michaelis-Menten constant were altered. The major factor affecting loss of activity of the immobilised enzymes was found to be the anionic surfactant, sodium dodecyl sulphate, used in the polyaphron preparation. However, SDS also appeared to enhance activity by altering protein conformation.
An emerging technique for the recovery of microbial secondary metabolites, such as antibiotics, i... more An emerging technique for the recovery of microbial secondary metabolites, such as antibiotics, is the use of colloidal liquid aphrons (CLAs) in pre-dispersed solvent extraction (PDSE) processes. Knowledge of the extraction kinetics and the limiting mass transfer resistances will be vital for e$cient process design and operation. In this work, the rates of erythromycin extraction using CLAs and conventional aqueous}organic, two-phase systems have been investigated. The CLAs used were formulated from 1% w/v Softanol 120 in decanol and 0.5% w/v SDS in water. The rate of erythromycin extraction with CLAs dispersed in well-mixed systems was found to be extremely rapid with equilibrium being achieved within 15 s or less. Overall erythromycin mass transfer coe$cients, K M , were typically 6.3;10\ m s\ for extraction experiments, and 1.0;10\ m s\ for stripping experiments. The rapid rates of erythromycin transfer were attributed to the small size of the dispersed CLAs, typically 5 m diameter, and hence the large interfacial area available for mass transfer of around 15;10 m m\. Experiments over a range of Reynolds numbers indicated that both the extraction and stripping processes were probably under mixed control of an interfacial resistance and boundary-layer di!usion. To investigate the in#uence of the surfactants used for aphron formulation on erythromycin extraction, further experiments were performed using aqueous}organic, two-phase systems in a non-dispersive stirred cell. The measured K M values were of the same order of magnitude as in the case of experiments with dispersed CLAs. When present individually, or together with SDS, the non-ionic Softanol surfactant was seen to retard erythromycin extraction rates in all cases. In contrast, the presence of SDS was found to enhance K M values by a factor of 2}4 compared to surfactant-free systems. This may be attributed to a speci"c interaction between individual SDS and erythromycin molecules and/or the generation of interfacial turbulence at a microscopic level. Further investigations are underway to elucidate the mechanism responsible. The concentration of either surfactant was also found to signi"cantly a!ect the measured K M values. The prediction of K M values using existing correlations, and the implications of the experimental results on contactor design and operation are also discussed.
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Papers by David Stuckey