Ceramic vs polymeric membrane implementation for potable water treatment

The continued technological developments and decreased purchase costs of ceramic membranes have seen increased recent interest in the technology as an alternative to the more widely used polymeric membranes. This paper assesses the relative technical, practical and economic merits of the two membrane materials in the context of potable water production from surface water sources. The work focuses on phenomena of direct technoeconomic significance, namely cleaning efficacy (manifested as permeability recovery), membrane integrity and incurred labour effort. Topics reviewed thus comprise: (a) practical comparison of the two technologies challenged with the same feedwater, (b) comparative technoeconomic analyses, (c) membrane integrity studies of polymeric membranes - incorporating aged samples extracted from operating installations, (d) sludging incidents, and (e) pilot and full-scale data. Available relevant data reveal: (a) bench-scale comparative tests do not indicate a consistent significant difference in the net permeability between the two membranes; (b) polymeric membranes are subject to a decline in both mechanical strength and permeability from the loss of the hydrophilic agent over a period of years from the action of hypochlorite used for cleaning; (c) the decreased mechanical strength with age of polymeric membranes increases the manual repair requirement and shortens membrane life, respectively impacting on labour and membrane replacement costs where the latter is also determined by the permeability; (d) the chemical and mechanical robustness of ceramic membranes permits more aggressive chemical cleaning, which then affects the chemicals consumption cost; and (e) anecdotal evidence suggests that polymeric membranes challenged with pre-coagulated surface waters may be subject to sludging, the agglomeration of solids in the membrane channels, which may also be age-related. Notwithstanding the above, data from published comparative technoeconomic studies indicate a linear relationship between the overall cost benefit and the membrane module cost ratio mitigated by the relative membrane life and operating flux.

The status of potable water reuse implementation

A review of the current status of direct and indirect potable water reuse (DPR/IPR) implementation has been conducted, focusing on the regulatory and practical aspects and with reference to the most recent published literature. The review encompasses (a) the principal contaminant types, their required removal and the methods by which their concentration is monitored, (b) regulatory approaches and stipulations in assessing/ratifying treatment schemes and maintaining treated water quality, and (c) existing full-scale installations. Analytical methods discussed include established in-line monitoring tools, such as turbidity measurement, to more recent polymerase chain reaction (PCR)-based assay methods for microbial detection. The key risk assessment tools of quantitative microbial risk assessment (QMRA) and water safety plans (WSPs) are considered in relation to their use in selecting/ratifying treatment schemes, and the components of the treatment schemes from 40 existing IPR/DPR installations summarised. Five specific schemes are considered in more detail. The review reveals:Whilst there are a number of ongoing projects where RO is not used because of the challenge imposed by disposal of RO concentrate, the prevalence of the sequential RO-UV combination implies the importance of quantifying the impact of process upsets on these unit operations.

Low-pressure membrane technology for potable water filtration: true costs

The overall cost, expressed as the present value (PV), of the construction and operation of low-pressure membrane filtration of inland water for potable water supply has been determined for membrane installations across the UK. The analysis was based on 15 full-scale installations installed with hollow fibre and capillary tube polymeric membranes, for which cost and related data were available. The analysis encompassed labour, in addition to energy, chemicals and critical component replacement. PV data were presented as functions of flow capacity (i.e. as cost curves), delineated as capital (CAPEX), operating (OPEX) and total PV normalised against flow rate (PV') the CAPEX excluding the site-specific civil engineering costs. Captured CAPEX data revealed these to be lower than those previously reported, and with a reduced economy of scale. The OPEX PV exceeded the CAPEX by a factor of 3-6 based on a 20-year life cycle, the difference increasing with decreasing flow capacities. Costs associated with unplanned (or "reactive") maintenance, partly associated with the repair of breached membranes and/or permeability recovery following membrane clogging, were found to make up around half the labour costs. Labour costs as a proportion of the flow increased with decreasing flow, exceeding the CAPEX at flows below 30,000 m³/d. Outcomes indicate labour costs associated with process upsets to contribute significantly to the overall cost of the installation over its life cycle, particularly at flows below ~30,000 m³/d. A clear trade-off exists between supplementary capital investment to allay process upsets and the operational costs associated with such events.

Influence of granular activated carbon media properties on natural organic matter and disinfection by-product precursor removal from drinking water

Operational and financial constraints challenge effective removal of natural organic matter (NOM), and specifically disinfection by-product (DBP) precursors, at remote and/or small sites. Granular activated carbon (GAC) is a widely used treatment option for such locations, due to its relatively low maintenance and process operational simplicity. However, its efficacy is highly dependent on the media capacity for the organic matter, which in turn depends on the media characteristics. The influence of GAC media properties on NOM/DBP precursor removal has been studied using a range of established and emerging media using both batch adsorption tests and rapid small-scale column tests. DBP formation propensity (DBPFP) was measured with reference to trihalomethanes (THMs) and haloacetic acids (HAAs). All GAC media showed no selectivity for specific removal of precursors of regulated DBPs; DBP formation was a simple function of residual dissolved organic carbon (DOC) levels. UV₂₅₄ was found to be a good surrogate measurement of DBPFP for an untreated water source having a high DOC. Due to the much-reduced concentration of DBP precursors, the correlation was significantly poorer for the coagulation/flocculation-pretreateed water source. Breakthrough curves generated from the microcolumn trials revealed DOC removal and consequent DBP reduction to correlate reasonably well with the prevalence pores in the 5-10 nm range. A 3-6 fold increase in capacity was recorded for a 0.005-0.045 cm³/g change in 5-10 nm-sized pore volume density. No corresponding correlation was evident with other media pore size ranges.

Clogging vs. fouling in immersed membrane bioreactors

Whilst the fouling of MBR membrane surfaces has been very extensively explored by the academic community, there is an increasingly widespread recognition by practitioners of the issue of clogging of membrane channels with sludge solids, sometimes termed "sludging". The study undertaken has quantified this phenomenon using a bespoke test cell allowing a flat sheet membrane channel to be viewed directly during operation and the accumulated solids determined by digital image processing. Sludging behaviour has then been correlated both with the sludge properties, from sludge samples taken from both an industrial and municipal MBR, and the permeability decline rate data. The work has revealed the expected trends in fouling propensity, as quantified by the exponent n of the Δp/Δt = m.exp(nJ) correlation from classical flux-step tests. With zero membrane aeration the industrial samples exhibited sludging, the filling of the complete thickness of the membrane channel with sludge solids, whereas for municipal sludge the solids formed a cake layer which did not fill the channel. In the absence of sludging the permeability decline followed the expected pattern of increasing at the elevated soluble COD and capillary suction time values of the industrial sludge, compared with municipal sludge at the same solids concentration range (8-12 g.L^-1). However, there was no evident correlation between fouling (permeability decline without sludging) and sludging: incipient sludging did not appear to influence permeability, though can be assumed to negatively impact on long-term operation, or relate to the sCOD concentration. Sludging instead appeared to depend on the sludge physical properties, and primarily the viscosity: sludge samples at high viscosities were found to exhibit a different air-scour pattern to that at normal MLSS concentrations. Outcomes suggest that sludging is caused by rheological conditions promoting bubble coalescence and bubble stream constriction, reducing the exposure of the membrane surface to scouring air.

Membrane technology costs and me

A reflection of the place cost analysis holds in membrane process technology research and development is provided. The review encompassed two membrane processes and applications: (a) reverse osmosis (RO) for seawater desalination, and (b) membrane bioreactor (MBR) technology for wastewater treatment. The cost analysis undertaken extended to (i) the determination of operating expenditure (OPEX) trends using simple analytical expressions, (ii) the subsequent estimation of the sensitivity of OPEX to individual system parameters, and (iii) published data on CAPEX for individual full-scale installations or from cost analyses. An appraisal of the peer-reviewed literature through a survey of a leading scientific database was also carried out. This bibliometric analysis was based on authors' keywords; it aimed to establish the profile of process cost for each of the two applications when compared with other popular research topics. The OPEX analysis, ostensibly through a consideration of specific energy demand in kWh per m³ permeate, revealed it to relate primarily to hydrodynamics in the case of RO, and to both membrane fouling and air scouring for MBRs. The bibliometric analysis of research trends revealed a marked difference in emphasis on cost aspects between the two research areas, with the focus on cost specifically being 16 times greater for RO desalination of seawater than MBR treatment of wastewater. MBR research appears to be dominated by fouling and foulant characterisation, making up almost a quarter of all studies, notwithstanding evidence from practitioners that other process parameters are as important in determining MBR process OPEX and operability.

THM and HAA formation from NOM in raw and treated surface waters

The disinfection by-product (DBP) formation potential (FP) of natural organic matter (NOM) in surface water sources has been studied with reference to the key water quality determinants (WQDs) of UV absorption (UV₂₅₄), colour, and dissolved organic carbon (DOC) concentration. The data set used encompassed raw and treated water sampled over a 30-month period from 30 water treatment works (WTWs) across Scotland, all employing conventional clarification. Both trihalomethane (THM) and haloacetic acid (HAA) FPs were considered. In addition to the standard bulk WQDs, the DOC content was fractionated and analysed for the hydrophobic (HPO) and hydrophilic (HPI) fractions. Results were quantified in terms of the yield (dDBPFP/dWQD) and the linear regression coefficient R² of the yield trend. The NOM in the raw waters was found to comprise 30-84% (average 66%) of the more reactive HPO material, with this proportion falling to 18-63% (average 50%) in the treated water. Results suggested UV₂₅₄ to be as good an indicator of DBPFP as DOC or HPO for the raw waters, with R² values ranging from 0.79 to 0.82 for THMs and from 0.71 to 0.73 for HAAs for these three determinants. For treated waters the corresponding values were significantly lower at 0.52-0.67 and 0.46-0.47 respectively, reflecting the lower HPO concentration and thus UV₂₅₄ absorption and commensurately reduced precision due to the limit of detection of the analytical instrument. It is concluded that fractionation offers little benefit in attempting to discern or predict chlorinated carbonaceous DBP yield for the waters across the geographical region studied. UV₂₅₄ offered an adequate estimate of DBPFP based on a mean yield of ∼2600 and ∼2800 μg per cm^-1 absorbance for THMFP for the raw and treated waters respectively and ∼3800 and2900 μg cm^-1 for HAAFP, albeit with reduced precision for the treated waters.

Influence of composite particle formation on the performance and economics of grit removal

Grit is routinely removed at the headworks of municipal wastewater treatment works to limit its onerous impact on downstream processes. Grit separation technologies are normally based on sedimentation of a homogeneous material (usually sand). However, in practice inorganic grit particles are likely to be combined with organic matter, such as fats oils and grease (FOG), producing a composite particle whose settling properties vary with the inorganic/organic content. A study of the impact of particle composition on its sedimentation has been conducted encompassing theoretical description (for particle settling in transitional flow), practical measurement and economic analysis. Practical measurement included sedimentation tests of homogeneous and composite particles along with characterisation of accumulated granular material sampled from actual municipal wastewater treatment works. The economic assessment was based on data from full-scale installations in the UK and US pertaining to remedial measures undertaken as a result of grit impacts, primarily accumulation in vessels and channels and damage of mechanical equipment through abrasion. Practical tests revealed coating of the sand grains with a FOG analogue (candlewax) to generate composite particles containing 45% wax by weight. The coated particles were then 30% less dense, 22% larger and 14% less settleable, on average, than the uncoated particles. Samples of accumulated grit taken from anaerobic digesters and aeration lanes from a full-scale plant indicated a FOG content (43%) similar to that of the waxed particles in the bench-scale tests, thus leading to a similar grain retardation of 14% assuming the FOG to be entirely associated with the grit. An assessment of the impact of the consequential breakthrough of grit particles due to buoyancy generated by composite particle formation indicated a $1.1 increase in operating costs per megalitre (ML) wastewater.

Pilot-scale spiral wound membrane assessment for THM precursor rejection from upland waters

The outcomes of a pilot-scale study of the rejection of trihalomethanes (THMs) precursors by commercial ultrafiltration/nanofiltration (UF/NF) spiral-wound membrane elements are presented based on a single surface water source in Scotland. The study revealed the expected trend of increased flux and permeability with increasing pore size for the UF membranes; the NF membranes provided similar fluxes despite the lower nominal pore size. The dissolved organic carbon (DOC) passage decreased with decreasing molecular weight cut-off, with a less than one-third the passage recorded for the NF membranes than for the UF ones.

The yield (weight % total THMs per DOC) varied between 2.5% and 8% across all membranes tested, in reasonable agreement with the literature, with the aromatic polyamide membrane providing both the lowest yield and lowest DOC passage. The proportion of the hydrophobic (HPO) fraction removed was found to increase with decreasing membrane selectivity (increasing pore size), and THM generation correlated closely (R² = 0.98) with the permeate HPO fractional concentration.

Coagulant Recovery from Water Treatment Residuals: A Review of Applicable Technologies

Conventional water treatment consumes large quantities of coagulant and produces even greater volumes of sludge. Coagulant recovery (CR) presents an opportunity to reduce both the sludge quantities and the costs they incur, by regenerating and purifying coagulant before reuse. Recovery and purification must satisfy stringent potable regulations for harmful contaminants, while remaining competitive with commercial coagulants. These challenges have restricted uptake and lead research towards lower-gain, lower-risk alternatives. This review documents the context in which CR must be considered, before comparing the relative efficacies and bottlenecks of potential technologies, expediting identification of the major knowledge gaps and future research requirements.

Biological treatment and thickening with a hollow fibre membrane bioreactor

Aerobic operation of an immersed hollow fibre membrane bioreactor, treating municipal wastewater supplemented with molasses solution, has been studied across mixed liquor suspended solids (MLSS) concentrations between 8 and 32 g L(-1), the higher concentrations being normally associated with thickening operations. Only a marginal loss in membrane permeability was noted between 8 and 18 g L(-1) when operation was conducted without clogging. The sustainable operational flux attainable above 18 g L(-1) was highly dependent upon both the MLSS concentration and the state of the membrane. A temperature-corrected flux of 28 L m(-2) h(-1) (LMH) was sustained for 18 h at an MLSS of 8 g L(-1) using membranes close to initial their virgin-state permeability. This value decreased to around 14 LMH at 20 g L(-1) and 5 LMH at 32 g L(-1) MLSS for an aged membrane whose permeability had been recovered following clogging. Below the threshold flux operation without significant clogging was possible, such that the membrane permeability could be recovered with a chemically enhanced backflush (CEB). Above this flux clogging took place at a rate of around 7-14 g solids per m(2) membrane per m(3) permeate volume passed irrespective of the MLSS concentration. The permeability of the unclogged membrane was depressed and could not be recovered using a standard CEB, indicative of irrecoverable pore clogging. The outcomes corroborated previously reported observations concerning the deleterious long-term impacts of clogging, and confirmed the critical importance of operation at a sustainable flux value.

Biomass properties and permeability in an immersed hollow fibre membrane bioreactor at high sludge concentrations

This study aimed to investigate the influence of biomass properties and high mixed liquor suspended solids (MLSS) concentrations on membrane permeability in a pilot-scale hollow fibre membrane bioreactor treating domestic wastewater. Auxiliary molasses solution was added to maintain system operation at constant food-to-microorganisms ratio (F/M = 0.13). Various physicochemical and biological biomass parameters were measured throughout the trial, comprising pre-thickening, thickening and post-thickening periods with reference to the sludge concentration and with aerobic biotreatment continuing throughout. Correlations between dynamic changes in biomass characteristics and membrane permeability decline as well as permeability recovery were further assessed by statistical analyses. Results showed the MLSS concentration to exert the greatest influence on sustainable membrane permeability, with a weaker correlation with particle size distribution. The strong dependence of absolute recovered permeability on wet accumulated solids (WACS) concentration, or clogging propensity, revealed clogging to deleteriously affect membrane permeability decline and recovery (from mechanical declogging and chemical cleaning), with WACS levels increasing with increasing MLSS. Evidence from the study indicated clogging may permanently reduce membrane permeability post declogging and chemical cleaning, corroborating previously reported findings.

NDMA formation in secondary wastewater effluent

Concern over prospective levels of N-nitrosodimethylamine (NDMA) in waters has increased in recent years due to its disinfection byproduct formation potential from chloramination. It has been mooted that this is promoted by organic precursors from municipal wastewaters, such that there is a more significant risk of excessive levels in water reuse applications. Experiments conducted on chloramination and chlorination of secondary wastewater have confirmed that that significant NDMA formation arises only from chloramination, with its concentration varying with test conditions used. A full factor analysis revealed all parameters studied (temperature, pH, monochloramine dose and contact time), both individually and synergistically, to have a statistically significant impact on NDMA formation with contact time being the most important. At raw water temperatures below 10 °C, the NDMA concentration can be minimised to below the 10 ng L(-1) threshold by not exceeding a monochloramine dose of 2 mg L(-1) as Cl(2). However, at higher water temperatures other measures are required to suppress NDMA formation, such as reducing the contact time (which could prove impractical in most applications) or maintaining a pH below 6. Further trials are required to fully develop the operating envelope to ensure NDMA concentrations do not exceed the 10 ng L(-1) threshold, or else to identify effective pretreatment methods for removing the NDMA precursors.

Granular activated carbon for removal of organic matter and turbidity from secondary wastewater

A range of commercial granular activated carbon (GAC) media have been assessed as pretreatment technologies for a downstream microfiltration (MF) process. Media were assessed on the basis of reduction in both organic matter and turbidity, since these are known to cause fouling in MF membranes. Isotherm adsorption analysis through jar testing with supplementary column trials revealed a wide variation between the different adsorbent materials with regard to organics removal and adsorption kinetics. Comparison with previous work using powdered activated carbon (PAC) revealed that for organic removal above 60% the use of GAC media incurs a significantly lower carbon usage rate than PAC. All GACs tested achieved a minimum of 80% turbidity removal. This combination of turbidity and organic removal suggests that GAC would be expected to provide a significant reduction in fouling of a downstream MF process with improved product water quality.

Precoagulation-microfiltration for wastewater reuse

A range of coagulant chemicals and doses, up to 2 mg/L, were trialled on a microfiltration-based indirect potable reuse (IPR) pilot plant to evaluate their impact on membrane reversible and irreversible fouling. Jar tests revealed these doses to have negligible impact on organic matter removal, whilst scoping pilot trials showed them to have a positive impact on fouling rates. Initial trials carried out over a 6-h period suggested that ferric sulphate was the most promising of the coagulants tested with regards to irreversible fouling. Extended five-day trials using ferric sulphate at 0.5 mg/L were conducted at fluxes of 40-50 l/(m(2)h) (LMH). Operation at 50 LMH without coagulant resulted in rapid fouling and a subsequent shortening of the chemical cleaning interval. The addition of the ferric coagulant resulted in a reduction in both reversible and irreversible fouling to those levels experienced at 40 LMH, enabling sustainable operation. The use of low levels of coagulant thus enables the pilot plant to operate at a 25% increased flux, equating to a 20% reduction in membrane area and overall savings of >0.1 p per m(3) for a seven year membrane life.

Fate and removal of permethrin by conventional activated sludge treatment

The fate and removal of permethrin during conventional wastewater treatment were evaluated at pilot-plant scale at different concentrations of mixed liquor suspended solids (MLSS) and, hence, different solids retention times (SRT). At feed concentrations of 0.26-0.86 microg L(-1), the permethrin was removed by primary treatment at an efficiency rate of 37%, similar to previously reported data, and from 40% to 83% for secondary treatment, decreasing with decreasing SRT. Comparable ranges, from 37% up to 98%, have been reported for micropollutants with similar physicochemical properties to permethrin, such as galaxolide and tonalide. Little difference in removal was noted between the medium and low MLSS concentrations trials, the main difference in treated effluent permethrin concentration arising on changing from high to medium MLSS levels. This was attributed to the limited acclimatization period employed in these two trials, leading to higher levels of soluble organic matter in the treated water, with which the permethrin appeared to be associated.

Screening optimisation for indirect potable reuse

An automatic backflush pre-filter used for pre-treatment for secondary wastewater re-use was evaluated and optimised at two different mesh sizes over an 18 month period. The filter was initially run with a 500 microm rating mesh size, as recommended by the supplier of the downstream membrane filtration process, and then at 100 microm to investigate any change in water quality produced and associated improved membrane performance. With the 500 microm mesh in place, the filter fouling rate was low and a backflush was initiated every 3.5 h. For the 100 microm mesh the fouling rate was extremely rapid. Fouling was found to be caused by reverse side blockage of the pre-filter due to biofilm growth, and not by improved solids capture; there was no improvement in water quality with the smaller mesh size, since particle unloading from the biofilm took place. The pre-filter fouling rate was found to be related to turbidity. At a turbidity of 5 NTU the filter backflushed around 200 times per day, while at 10 NTU this increased to over 300 times. Further analysis enabled the backflush water volume to be decreased by reducing the backflush duration and increasing the backflush cycle time (i.e. the time between backflushes).

Fate and behaviour of copper and zinc in secondary biological wastewater treatment processes: I. Evaluation of biomass adsorption capacity

The current sources of copper and zinc in municipal wastewaters have been considered, and the changes in the concentrations and quantities of these two elements entering sewage treatment works over the last three decades have been calculated. The concentrations and quantities of the heavy metals cadmium, chromium, copper, mercury, nickel, lead and zinc, entering UK sewage treatment works, have been reduced by between 50% and 90% during this period. However, the reductions in copper and zinc appear to be at the lower end of these ranges and thus remain a cause for concern, particularly their concentrations in sewage effluents and their potential environmental impacts on receiving waters. Bench studies have been undertaken to predict removals by three types of biological wastewater treatment plants: trickling filters, conventional activated sludge and membrane bioreactors, to determine if any of these processes are more efficacious for the removal of these metals. These results suggest that, despite membrane bioreactor biomass achieving the lowest effluent suspended solids concentration and having the lowest effluent chemical oxygen demand, which is accepted as a surrogate measure of organic chemical chelating ability of the aqueous phase, they produce the highest effluent values for the two metals in this study (copper and zinc). Removals of zinc and copper in biological wastewater treatment processes are probably primarily determined by those factors influencing metal solubility in the biomass matrix.

Fate and behaviour of copper and zinc in secondary biological wastewater treatment processes: II. Removal at varying sludge age

The mechanisms for the removal of heavy metals during secondary biological treatment of wastewater, with particular emphasis on the activated sludge process, are considered. It is concluded that the predominant mechanism is the entrapment and co-settlement of insoluble metal species in the mixed liquor (biomass). Secondary extracellular polymeric materials, particularly extracellular polysaccharides and other capsule-forming materials, may also play a role. In general, removal of both copper and zinc was superior at the higher sludge ages employed in this study, 4.3 and 8 days, and can in part be attributed to the superior removals of both biochemical oxygen demand and effluent suspended solids achieved at these sludge ages compared with the lowest sludge age studied, 3.6 days. For both copper and zinc there is an increase in soluble metal across the activated sludge process. However, significant removal of both metals occurs as a consequence of the removal of substantial amounts of insoluble metal. The presence of returned sludge liquors, high in settleable solids, to the mixed liquor appears to moderately enhance the percentage removal of copper and zinc. Membranes used in place of secondary sedimentation also enhance removal of both metals by reducing effluent suspended solids. It is concluded that there is potential for maximizing metal removal by optimization of secondary biological treatment in a sustainable manner, without recourse to energy-intensive or chemically-dependent tertiary treatment technologies.

Evaluation of intermittent air sparging in an anoxic denitrification membrane bioreactor

The impact of intermittent air sparging on the operation of an anoxic (dissolved oxygen <0.1 mg l(-1)) immersed membrane bioreactor (iMBR) applied to potable water denitrification is discussed. Air sparge length and specific aeration demand per unit membrane area (SAD(m)) were varied to determine impact on oxygen transfer and membrane fouling. For SAD(m)>0.39 m(3) m(-2) h(-1) with sparge lengths of 10 to 60 seconds, a low dissolved oxygen residual of 0.05 to 0.90 mg O(2) l(-1) was formed which typically inhibited denitrification; oxygen transfer efficiency increased with increasing sparge time. Residual oxygen was rapidly consumed at a rate, r(O(2)), of 0.35 mg O(2) l(-1) min(-1). Once oxygen was depleted, denitrification proceeded. When intermittently sparging at a SAD(m)<0.39 m(3) m(-2) h(-1) for 30 seconds (following 10 minute dead-end filtration cycles in the iMBR), no dissolved oxygen residual was observed and a flux of 21 l m(-2) h(-1) was sustained with fouling rates <0.001 m bar min(-1) recorded. This method provides for effective integration of air sparging into anoxic/anaerobic iMBR environments to simplify process design and delivers a tangible reduction in specific energy demand from 0.19 kWh m(-3) (for constant sparging) to 0.007 kWh m(-3).

Biomass effects on oxygen transfer in membrane bioreactors

Ten biomass samples from both municipal and industrial pilot and full scale submerged membrane bioreactors (MBRs) with mixed liquor suspended solids concentrations (MLSS) ranging from 7.2 to 30.2g L(-1) were studied at six air-flow rates (0.7, 1.3, 2.3, 3, 4.4 and 6m(3)m(-3)h(-1)). Statistical analyses were applied to identify the relative impacts of the various bulk biomass characteristics on oxygen transfer. Of the biomass characteristics studied, only solids concentration (correlated with viscosity), the carbohydrate fraction of the EPS (EPS(c)) and the chemical oxygen demand (COD) concentration of the SMP (SMP(COD)) were found to affect the oxygen transfer parameters k(L)a(20) (the oxygen transfer coefficient) and alpha-factor. The relative influence on k(L)a(20) was MLSS>aeration>EPS(c)>SMP(COD) and on alpha-factor was MLSS>SMP(COD)>EPS(c)>aeration. Both k(L)a(20) and alpha-factor increased with increasing aeration and EPS(c) and decreased with increasing MLSS and SMP(COD). MLSS was found to be the main parameter controlling the oxygen transfer.

Methods for understanding organic fouling in MBRs

The identification and quantification of foulants in membrane bioreactors present a major challenge due to their complexity resulting from biomass heterogeneity. Fouling is normally characterised with respect to the critical flux, this being conventionally viewed as being the flux below which a reduction in membrane permeability does not take place. However, recent studies have revealed that such fouling arises even at very low fluxes. Moreover, fouling rates can differ substantially between different experiments, trials and installations even when operated under apparently similar conditions of biomass and soluble organic carbon concentrations. The methods available for quantifying and analysing fouling are reviewed with specific reference to recent data on sub-critical flux behaviour. It is concluded that HPSEC analysis of extracted biomass fractions may provide the most valuable data towards the determination of differences in fouling propensity between different biomasses, as inferred in conventional flux step analysis.

Pre-coagulation for microfiltration of an upland surface water

The effect of different coagulants on cake formation and hydraulic resistance in membrane filtration of strongly coloured (SUVA> or =4.8) upland surface water has been studied at bench-scale under constant pressure conditions. Coagulants used were aluminium sulphate, polyaluminium chloride, ferric chloride and ferric sulphate. Optimisation of coagulation parameters was carried by conventional jar testing. The R'c (specific cake resistance in m(-2)) values were determined for all coagulants over a range of coagulant doses and slow mixing flocculation periods. Experiments indicated slight differences in cake formation trends between ferric- and aluminium-based coagulants and chloride and sulphate counterions, but that the range of measured R'c values was small (0.9 and 2.6 x 10(18) m(-2)) over the range of doses studied. Greater than 99% UV(254) removal was achieved with every coagulant, whereas dissolved organic carbon (DOC) removal ranged from 78% to 88%. Optimisation of the pre-coagulation-membrane filtration process suggests ferric chloride to be slightly superior for the feedwater matrix studied on the basis of DOC removal, whereas ferric sulphate gave slightly lower filter cake specific resistance values.

The fate of chlorine and organic materials in swimming pools

The fate of organic nitrogen and carbon introduced into a swimming pool by pool users has been studied using a 2.2 m(3) model pool. The study made use of a body fluid analogue (BFA), containing the primary endogenous organic amino compounds, and a soiling analogue represented by humic acid (HA). The system was used to examine the effect of organic loading and organic carbon (OC) sources (i.e. amino or HA) on the levels and speciation of the key chlorinated disinfection by-products of trihalomethanes (THMs) and chloramines under operating conditions representative of those employed on a full-scale pool. Results revealed OC, chloramines and THMs to all attain steady-state levels after 200-500 h of operation, reflecting mineralisation of the dosed OC. Steady-state levels of OC were roughly linearly dependent on dose rate over the range of operational conditions investigated and, as with the chloramine levels recorded, were in reasonable agreement with those reported for full-scale pools. THM levels recorded were somewhat lower than those found in real pools, and were dependent on both on pH carbon source: the THM formation propensity for the soling analogue was around eight times than of the BFA. Of the assayed by-products, only nitrate was found to accumulate, accounting for 4-28% of the dosed amino nitrogen. Contrary to previous postulations based on the application of Henry's Law, only insignificant amounts of the volatile by-products were found to be lost to the atmosphere.

Domestic wastewater treatment by a submerged MBR (membrane bio-reactor) with enhanced air sparging

The air sparging technique has been recognised as an effective way to control membrane fouling. However, its application to a submerged MBR (Membrane Bio-Reactor) has not yet been reported. This paper deals with the performances of air sparging on a submerged MBR for wastewater treatment. Two kinds of air sparging techniques were used respectively. First, air is injected into the membrane tube channels so that mixed liquor can circulate in the bioreactor (air-lift mode). Second, a periodic air-jet into the membrane tube is introduced (air-jet mode). Their applicability was evaluated with a series of lab-scale experiments using domestic wastewater. The flux increased from 23 to 33 l m(-2) h(-1) (43% enhancement) when air was injected for the air-lift module. But further increase of flux was not observed as the gas flow increased. The Rc/(Rc+Rf), ratio of cake resistance (Rc) to sum of Rc and Rf (internal fouling resistance), was 23%, indicating that the Rc is not the predominant resistance unlike other MBR studies. It showed that the cake layer was removed sufficiently due to the air injection. Thus, an increase of airflow could not affect the flux performance. The air-jet module suffered from a clogging problem with accumulated sludge inside the lumen. Because the air-jet module has characteristics of dead end filtration, a periodic air-jet was not enough to blast all the accumulated sludge out. But flux was greater than in the air-lift module if the clogging was prevented by an appropriate cleaning regime such as periodical backwashing.

The effect of obesity on the ratio of type 3 17beta-hydroxysteroid dehydrogenase mRNA to cytochrome P450 aromatase mRNA in subcutaneous abdominal and intra-abdominal adipose tissue of women

OBJECTIVES

To investigate (1) whether type 3 17beta-hydroxysteroid dehydrogenase (17beta-HSD), the enzyme which catalyzes the conversion of androstenedione to testosterone in the testis, is co-expressed with P450aromatase in the preadipocytes of women, and (2) whether the relative expression of type 3 17beta-HSD and aromatase varies in subcutaneous abdominal vs intra-abdominal adipose tissue of women.

SUBJECTS

Subcutaneous abdominal and intra-abdominal adipose tissue was obtained from women undergoing elective abdominal surgery (age 22-78 y, body mass index (BMI) 22.4-52.9 kg/m(2)).

MEASUREMENTS

Expression of type 3 17beta-HSD in adipose cell fractions was determined using RT-PCR. Preadipocyte steroidogenesis was investigated in primary cultures using androstenedione as substrate. Messenger RNA levels for type 3 17beta-HSD and aromatase were measured in adipose tissue from the subcutaneous abdominal and intra-abdominal depots using a quantitative multiplex competitive RT-PCR assay.

RESULTS

Type 3 17beta-HSD is co-expressed with aromatase in the abdominal preadipocytes of women. Cultured preadipocytes from both subcutaneous abdominal (n=5) and intra-abdominal (n=5) sites converted androstenedione to testosterone, and there was minimal conversion of androstenedione to estrone. Consistent with this, the levels of type 3 17beta-HSD mRNA were significantly higher than aromatase mRNA at both sites (P<0.05; n=8 subcutaneous abdominal, n=12 intra-abdominal adipose tissue). The ratio of levels of 17beta-HSD mRNA to aromatase mRNA in intra-abdominal adipose tissue was positively correlated with BMI (n=11, r=0.61, P<0.05) and waist circumference (n=10, r=0.65, P<0.05). The converse was found in subcutaneous abdominal adipose tissue.

CONCLUSION

The intra-abdominal adipose tissue of women may be substantially androgenic, increasingly so with increasing obesity, particularly central obesity. While androgen production by this adipose tissue deposit may not contribute to circulating testosterone levels due to hepatic clearance, it may have hitherto unrecognised local effects in the intra-abdominal adipose tissue and also on the liver via the hepatic portal system. These studies suggest a mechanism linking central obesity with insulin resistance and dyslipidaemia.

Nutrient addition to enhance biological treatment of greywater

This study compares the chemical oxygen demand (COD) removal and respiration rates of a microbial population treating real and synthetic greywaters dosed with nutrient supplements. The nutrient composition of the real and synthetic greywaters was analysed and the dosing regime for nitrogen, phosphorus and a range of trace metals planned accordingly. The doses consisted of eight single additives (macronutrients and trace metals) to the control greywater and six trace metal additions to C: N : P balanced greywater. The COD removal for the control real and synthetic greywater in lab-scale activated sludge systems (0.038 and 0.286 kg COD kg MLSS(-1) d(-1), respectively) confirmed nutrient limitation and the poor degree of greywater treatment. Nutrient dosing increased the COD removal rate and oxygen uptake rate in many cases. The greatest stimulation of microbial activity was observed with zinc additions to C: N: P balanced real greywater (1.291 kg COD kg MLSS(-1) d(-1) over 30 times the control). Inhibitory effects to various extents were rare and limited mainly to the additions of metals to synthetic greywater. The dominance of chemicals effects was observed on addition of some micronutrients; notably iron and aluminium, metals on which many coagulants for use in biotreatment of other wastewaters are based. The data indicate that the impact of understanding microbial processes and the nutrients required for wastewater treatment can only serve to optimise process efficiency for the proposed treatment of greywater.

Optimisation of combined coagulation and microfiltration for water treatment

The effect of upstream coagulant dosing for full-flow microfiltration of an upland-reservoir water has been investigated. The process, run under conditions of constant flux and pH and based on a ferric salt, is compared with a published study of another full-flow process based on alum dosing and operated at constant pressure and coagulant concentration. The current study includes data for the residual deposit remaining following backflushing by reverse flow. Results are presented in terms of the specific-cake resistance (R'o, m(-2)) as a function of pH or coagulant dose. Reasonable correlation with classical cake filtration theory was obtained, such that R' was assumed to be independent of run time and cake thickness. The following trends have been noted: The optimum pH for the alum-based system appears to be between 7.5 and 8 on the basis of cake resistance. The effect of coagulant dose between 18 and 71 microM Fe3+ is much more significant than a change in pH between 5 and 9 for the alum system: a 53-fold increase in specific flux compared with a 7-fold increase with reference to the limiting R'o values at pH 4.8 and 7.7. A low coagulant dose (0.018mM, 1.0 mg l(-1) Fe3+) appears to have a slightly detrimental effect on downstream microfiltration operation. The low coagulant doses apparently cause incomplete aggregation of colloidal particles such that internal fouling of the membrane takes place. The residual (cleaning cycle) deposit resistance followed roughly the same trend as the backflush cycle-cake resistance with coagulant concentration, but with a much reduced value (about 16 times lower, on average). An optimum coagulant dose of 0.055 mM (3.1 mg/l) Fe3+ can be identified on the basis of operational cost based on coagulant cost and cake resistance, all other aspects of the system being substantially unchanged. It is concluded that coagulation with downstream microfiltration offers a cost-effective means of removing natural organic matter, achieving a THMFP removal of around 80% at the optimum dose.

Direct molecular hydrogen sulphide scrubbing with hollowfibre membranes

The emission of hydrogen sulphide is a major problem associated with anaerobic treatment of sulphate and sulphite containing wastewaters. Conventional absorbing processes, such as packed towers, spray towers or bubble columns, are all constrained by factors such as flooding and foaming. Membrane systems, on the other hand, enable independent control of the liquid and gas flow rate and a step change order of magnitude increase in the specific surface area of the contact process. The membrane acts as a gas absorber with a design similar to a shell and tube heat exchanger. On the other hand, they are limited by facets of the membrane such as its resistance to mass transfer and permselectivity, as well as its cost. The work presented in this paper refers to an absorption process based on a non-wetted hollow fibre membrane for the scrubbing of hydrogen sulphide from air, with water as the contact solvent. Results presented describe the performance of the unit in terms of overall transfer and outlet liquid concentration as a function of circulation regime, gas flow rate, liquid flow rate and specific surface area. In particular, results are presented using traditional plots of Sherwood number (Sh) against Graetz (Gr) number for the liquid flowing in the lumens, such that experimental and available empirical descriptions of the process performance are directly compared. Results suggest that, as expected, very efficient mass transfer is obtained. However, the mass transfer was found to reach a maximum value against Gr, contrary to available empirical models.

Advanced biological unit processes for domestic water recycling

The potential of advanced biological unit operations for the recycling of grey and black waters has been evaluated. The membrane bioreactor (MBR) demonstrated the greatest efficacy towards water recycling in terms of all the quality determinants. Both the biologically aerated filter (BAF) and the MBR were able to effectively treat the organic and physical pollutants in all the types of wastewater tested. The main difference was observed in terms of the microbiological quality, measured as total coliforms. The open bed structure of the BAF enabled passage of coliforms whereas the complete barrier of the MBR produced a non detectable level in the effluent. The MBR process complied with commonly adopted water recycling quality standards for the all determinants during the grey water trials and failed only in terms of total coliform counts once black water had been introduced into the feed. The MBR was seen as a particularly suitable advanced biological process as it was very effective at stabilising out the considerable load variations encountered during the trial.

Disturbance of the reproductive axis induced by negative energy balance

Animal reproduction is impaired when intake of energy is so restricted that activities essential to life are threatened; this is seen as a homeostatic adjustment that restricts wasteful energy expenditure. Fasting or exercising to a degree requiring considerable energy expenditure has major effects on the hypothalamus, including activation of corticotrophin-releasing factor (CRF) neurons, suppression of thyrotrophin-releasing hormone synthesis, and increased growth hormone secretion; these are associated with increased concentrations of hypothalamic neuropeptide Y mRNA and are corrected by administration of leptin, an adipose-tissue protein with a tertiary structure similar to the cytokine interleukin-2. This response to fasting results from a disordered pattern of activity in the gonadotrophin-releasing hormone (GnRH) pacemaker, characterized by reduced luteinizing hormone pulsatility, particularly during daytime. Animal studies have suggested that the response depends on an intact afferent vagal system from the stomach and the presence of oestrogen. Noradrenergic neurons forming the A2 group increase the activity of CRF neurons that, in turn, inhibit GnRH pulsatility. Reproductive impairment due to fasting is reversed by leptin, and abnormalities of leptin are described in individuals who fast or who develop exercise-induced amenorrhoea. This paper discusses these changes induced by negative energy balance and speculates on the involvement of leptin as a contributor to these abnormalities.

Expression of types 1, 2, and 3 17 beta-hydroxysteroid dehydrogenase in subcutaneous abdominal and intra-abdominal adipose tissue of women

Human adipose tissue is known to have 17 beta-oxidoreductase activity, interconverting estrone (E1) and estradiol (E2), as well as androstenedione (A) and testosterone (T). We examined both the subcutaneous abdominal and intra-abdominal (visceral) adipose tissue of women for expression of types 1, 2, and 3 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) using ribonuclease (RNase) protection assay and RT-PCR/Southern blotting. Type 1 17 beta-HSD, which encodes the enzyme responsible for the conversion of E1 to E2 in the placenta and ovary, was expressed in the subcutaneous abdominal and intra-abdominal adipose tissue of women, but the messenger RNA transcripts were predominantly incompletely spliced and therefore unlikely to encode an active protein. A pseudogene for type 1 17 beta-HSD was also expressed in these tissues, but messenger RNA transcripts were again unspliced. Type 2 17 beta-HSD, which encodes an enzyme that can catalyze the conversion of T to A and E2 to E1, was expressed in both the subcutaneous abdominal and intra-abdominal adipose tissue of women. Type 3 17 beta-HSD was also expressed in adipose tissue from both sites studied. Type 3 17 beta-HSD encodes the enzyme that catalyzes the conversion of A to T in the testis and also converts E1 to E2. Together with aromatase, which is known to be expressed in adipose tissue, the expression of types 2 and 3 17 beta-HSD indicates that sex steroid production in the adipose tissue of women is a complex process. The association of visceral obesity with the development of insulin resistance and dyslipidaemia raises the question of the role of steroid production in adipose tissue in the pathogenesis of these disorders.

The effect of alprazolam on serum cortisol and luteinizing hormone pulsatility in normal women and in women with stress-related anovulation

Alprazolam, a benzodiazepine derivative, stimulates specific gamma-aminobutyric acidA receptors and has been found to inhibit CRH activity in the brain. This study examined the effect of alprazolam on serum cortisol and LH pulsatility in six women in the early follicular phase (EFP), six women in the midluteal phase (MLP), and six women with stress-related anovulation (SRA) of normal weight, but with a previous history of anorexia nervosa. Subjects were given alprazolam (2 mg, orally) or an identical placebo capsule at 0900 h, and blood samples were collected through an indwelling venous catheter every 10 min for 8 h in the SRA women and 10 h in EFP and MLP women. Women with SRA were also given clomiphene (100 mg/day) for 5 days before a further 8-h blood sampling session. As expected, there was a diurnal decline in serum levels of cortisol, which was significantly less in women with SRA (55 +/- 4%) than those in both EFP (76 +/- 4%) and MLP women (75 +/- 3%; P < 0.005). The food-related rise of cortisol that follows lunch in normal women was absent in women with SRA. Alprazolam accentuated the decline in serum cortisol, and in all three groups, the mean serum cortisol level after alprazolam treatment was significantly less (P < 0.05) than that after placebo. In SRA women, alprazolam restored visible LH pulses in all women and increased the mean LH pulse frequency (P < 0.02) and pulse amplitude (P < 0.05). This was associated with an increase in mean serum LH from 1.3 +/- 0.3 to 3.0 +/- 0.06 IU/L (P < 0.02). In EFP women, alprazolam reduced the frequency of LH pulsatility from a mean of 5.8 +/- 0.7 to 3.2 +/- 0.5 pulses/10 h (P < 0.02) and increased the mean pulse amplitude from 2.4 +/- 0.5 to 5.0 +/- 1.1 IU/L (P < 0.0005). Alprazolam had no significant effect on LH pulsatility or amplitude in MLP women. To explain this variation in response to alprazolam, we propose that alprazolam accelerates the GnRH pacemaker in SRA women by inhibiting excessive CRH activity, which blocks the GnRH pacemaker in these women. In normal women, we hypothesize that tonic inhibition of the GnRH pacemaker by CRH is minimal, and the reduced pulsatility of LH after alprazolam treatment in EFP women results from inhibition of stimulatory noradrenergic neurons. In MLP women, we propose that preexisting opioid inhibition of noradrenergic neurons by progesterone blocks this effect of alprazolam.

Relative diagnostic value of serum non-SHBG-bound testosterone, free androgen index and free testosterone in the assessment of mild to moderate hirsutism

Recent evidence suggests that steroid hormone loosely bound to albumin is available for target-cell entry. Preliminary studies have suggested that a measure of this fraction, non-sex-hormone-binding globulin-bound testosterone (NSB-T), provides the best in vitro diagnostic test for idiopathic hirsutism. We compared the diagnostic value of NSB-T, total testosterone (T), free testosterone (fT), and the free androgen index (FAI) in supporting the clinical diagnosis in 22 pre-menopausal women with hirsutism. NSB-T supported the diagnosis in 50% of cases, compared with 23% for T, 55% for fT by analogue RIA, and 68% for FAI. We conclude that in mild to moderate hirsutism the measurement of NSB-T does not yield diagnostic information addition to that provided by the FAI.

Positive and negative feed-back effect of progesterone on luteinizing hormone secretion in post-menopausal women

Progesterone is known to exert a biphasic feedback effect on luteinizing hormone (LH) secretion in animals and it has been demonstrated that this effect is dependent upon both duration of exposure to progesterone and the dose administered. In this paper we sought to determine whether a similar biphasic effect exists in humans. The pattern of LH secretion was assessed in six healthy oestrogen treated post-menopausal women before and after they were given progesterone (50 mg/day) for 1 and 7 days. Progesterone treatment for 1 day resulted in a significant elevation in the basal serum LH concentration and in individual LH pulse amplitude with no change in LH pulse frequency. In contrast, progesterone treatment for 7 days increased LH pulse amplitude with no change in basal serum LH concentrations and a significant reduction in LH pulse frequency. We concluded that firstly, progesterone does exert a biphasic feedback effect on LH secretion and that the nature of this effect is determined by the duration of exposure to the progesterone stimulus. Secondly, as LH pulsatility has been shown to be an accurate indicator of GnRH pulsatility, that the reduction in LH pulse frequency after a long exposure to progesterone is due to a hypothalamic effect of progesterone whereas the positive feedback effect may be the result of a pituitary or hypothalamic action.

Phase I clinical trial of a World Health Organisation birth control vaccine

A birth control vaccine incorporating a synthetic peptide antigen representing the aminoacid sequence 109-145 of the C-terminal region of the beta subunit of human chorionic gonadotropin (hCG-beta) was submitted to a phase 1 clinical trial. Thirty surgically sterilised female volunteers, divided into five equal groups for different vaccine doses, received two intramuscular injections six weeks apart. Over a six-month follow-up there were no important adverse reactions, and potentially contraceptive levels of antibodies to hCG developed in all subjects. In the highest vaccine dose group, the results gave promise of a contraceptive effect of six months' duration.

Evidence against the involvement of opiate neurons in mediating the effect of clomiphene citrate on gonadotropin-releasing hormone neurons

This study was designed to assess whether the hypothalamic action of clomiphene citrate (CC) on gonadotropin-releasing hormone (GnRH) neurons required activity of opiate neurons. Ten women were studied in two successive cycles. In the first cycle they received infusion of saline or naloxone (2 mg intravenous bolus followed by 1.6 mg/hour) for 9 hours, in random order on days 5 and 6 of the cycle. In the second cycle each woman was treated with CC (100 mg) for 5 days before study on day 6. In each study, blood samples were collected at 15-minute intervals for 9 hours; during the last hour 10 micrograms GnRH was given to test the pituitary response. After CC, luteinizing hormone (LH) pulse frequency was accelerated, and mean serum LH, serum follicle-stimulating hormone, and estradiol increased, but the pituitary response to GnRH was unchanged. These changes are best explained by an increase in activity of GnRH neurons. Conversely, naloxone had no effect on LH pulsatility or the pituitary response to GnRH. This indicates that the action of CC at least during the early follicular phase is exerted primarily at the levels of the hypothalamic GnRH pulse generator and does not depend on the activity of opiate neurons.

Role of endogenous opioids in reducing the frequency of pulsatile luteinizing hormone secretion induced by progesterone in normal women

It is well-established that the frequency of LH pulses varies during the normal menstrual cycle with a significant reduction in frequency in the luteal phase. Previous studies have indicated that both progesterone and opioids are able to reduce the frequency of LH pulses and in this study we sought to clarify the possible interaction between progesterone, endogenous opioids and GnRH neurons. Sixteen normal women in the mid-follicular phase (days 8-12) were randomly allocated to a control or treatment group and LH pulsatility assessed on one or two occasions by taking blood samples at 15 min intervals over 8 h. For the control women, LH pulsatility was assessed on one occasion during a saline infusion. The treated women received progesterone (50-100 mg/d for 7 d) at the end of which LH pulsatility was assessed before and after a naloxone infusion (2 mg/h for 8 h). Mean +/- SEM LH pulse frequency in the control women was 4.9 +/- 0.5 pulses/8 h which was significantly decreased to 3.0 +/- 0.3 pulses/8 h (P less than 0.01) in the progesterone treated women but not different from 5.5 +/- 0.3 pulses/8 h in those also treated with naloxone. Mean +/- SEM LH pulse amplitude in the control women was 2.3 +/- 0.3 IU/l, which was significantly increased to 4.8 +/- 0.7 IU/l (P less than 0.05) in the progesterone treated group, and to 3.7 +/- 0.4 IU/l (P less than 0.05) in the progesterone-treated women after naloxone. We conclude that progesterone slows the frequency of LH pulsatility by increasing endogenous opioid activity in the hypothalamus which may in turn inhibit the firing rate of the GnRH neurons.

Regulation of pulsatile secretion of progesterone during the human luteal phase

This study was designed to evaluate the role of luteinizing hormone (LH) and prolactin (PRL) in regulating pulsatile progesterone secretion in the human. This was done first by correlating the frequency of progesterone, LH and PRL pulses during the mid-luteal phase of normal cycles. Second, by increasing the frequency of LH pulses with naloxone and GnRH injections and examining the impact on progesterone pulse frequency. Third, by abolishing PRL pulsatility with metoclopramide and looking at the effect on progesterone pulsatility. Nine normal subjects in the mid-luteal phase (4-10 days after the initial postovulatory rise in progesterone) were studied for 8 h with blood samples taken at 15 min intervals. Each sample was assayed for progesterone, LH and PRL and the pulse frequency (number of pulses in 8 h) determined for each hormone. The mean pulse frequencies were 2.3 (s.e.m. = 0.4) for progesterone, 1.3 (s.e.m. = 0.4) for LH, and 2.1 (s.e.m. = 0.3) for PRL. Cross-correlation analysis showed that there was no significant synchrony between pulses of progesterone and pulses of LH and PRL. When naloxone was given to six normal subjects in the mid-luteal phase, the mean LH pulse frequency (number of pulses in 6 h) was increased from 2.2 (s.e.m. = 0.3) during a saline infusion to 3.2 (s.e.m. = 0.5) during the naloxone infusion (P less than 0.05). However, the mean pulse frequency for progesterone remained unchanged during the saline and naloxone studies. There was no significant difference between the mean serum LH in the saline and naloxone groups, and the mean serum progesterone concentration was not significantly altered.(ABSTRACT TRUNCATED AT 250 WORDS)

Activity of gonadotropin-releasing hormone neurons during the preovulatory luteinizing hormone surge

We assessed the frequency of luteinizing hormone (LH) pulsatility (reflecting the activity of gonadotropin-releasing hormone [GnRH] neurons in the hypothalamus) in six women during the periovulatory LH surge, in five women during the early follicular phase, and in seven women in the midfollicular phase (MFP) (calculated as being 3 to 8 days before the LH surge). Collection of blood at 5-minute, versus 15-minute, intervals allowed detection of a larger number of LH pulses in both the MFP (16, versus 27) and periovulatory phase (POP) (11, versus 22) groups of women, but it made no difference in the early follicular phase (EFP) (10 pulses with both methods). During the EFP, the mean number of LH pulses per 4 hours (detected by 5-minute sampling) was 2.0 +/- 0.7 (+/- standard deviation [SD]), and the mean LH amplitude (+/- SD) was 1.3 +/- 0.4 IU/l. There was a significant increase in the number of pulses in the MFP group (3.9 +/- 1.3 pulses/4 hours; P less than 0.05) but no significant change in pulse amplitude (1.1 +/- 0.1 IU/l). During the POP, the mean pulse amplitude was increased (8.5 +/- 1.4 IU/l; P less than 0.001), compared with the MFP and EFP groups, but the mean pulse frequency (3.7 +/- 1.2 pulses/4 hours) was not significantly different from the MFP frequency. We conclude that an acceleration of LH pulsatility occurs several days before the LH surge and does not change thereafter. However, there is an increase in LH pulse amplitude during the LH surge; we attribute this to the increase in pituitary sensitivity at this time.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of physiological changes in ovarian steroids on the prolactin response to gonadotrophin releasing factor

This study was designed to assess the effect of an altered level of serum oestrogen and progesterone on the prolactin (PRL) response to gonadotrophin releasing hormone (GnRH). Six normal women were studied in the early follicular phase and the mid-luteal phase of one cycle and five menopausal women were studied before and after treatment with progesterone. Blood samples were collected at 15 min intervals for 6 h after a basal collection period of 30 min. Intravenous boluses of GnRH (1 microgram, 10 micrograms and 50 micrograms) were given at 0, 2 and 4 h. Basal samples were assayed for 17 beta-oestradiol (E2), oestrone (E1) and progesterone (P); LH, FSH and PRL were measured in all samples. Serum PRL was significantly elevated in all groups after 10 micrograms of GnRH with maximum increments (+/- SEM) ranging from 3.9 +/- 1.3 micrograms/l in early follicular phase women to 14.7 +/- 4.7 micrograms/l in progesterone-treated menopausal women. The PRL response to GnRH was significantly greater in the luteal phase and in menopausal women compared to early follicular phase women. There was a significant correlation between the maximum PRL response and the maximum LH response to GnRH in all the women studied (r = 0.7; P less than 0.01). A significant correlation was also found between the maximum PRL response and the basal serum oestrogen concentration in the normal cycling women (r = 0.8; P less than 0.01), but not when the menopausal women were included in the analysis.(ABSTRACT TRUNCATED AT 250 WORDS)