Thermomechanical Properties of Nontoxic Plasticizers for Polyvinyl Chloride Predicted from Molecular Dynamics Simulations.

Environmental and toxicity concerns dictate replacement of di(2-ethylhexyl) phthalate (DEHP) plasticizer used to impart flexibility and thermal stability to polyvinyl chloride (PVC). Potential alternatives to DEHP in PVC include diheptyl succinate (DHS), diethyl adipate (DEA), 1,4-butanediol dibenzoate (1,4-BDB), and dibutyl sebacate (DBS). To examine whether that these bio-based plasticizers can compete with DEHP, we need to compare their tensile, mechanical, and diffusional properties. This work focuses on predicting the effect these plasticizers have on Tg, Young's modulus, shear modulus, fractional free volume, and diffusion for PVC-plasticizer systems. Where data was available, the results from this study are in good agreement with the experiment; we conclude that DBS and DHS are most promising green plasticizers for PVC, since they have properties comparable to DEHP but not the environmental and toxicity concerns.

Optimization of carbon dioxide supply in raceway reactors: Influence of carbon dioxide molar fraction and gas flow rate.

Influence of CO2 composition and gas flow rate to control pH in a pilot-scale raceway producing Scenedesmus sp. was studied. Light and temperature determined the biomass productivity whereas neither the CO2 molar fraction nor the gas flow rate used influenced it; because pH was always controlled and carbon limitation did not take place. The CO2 molar fraction and the gas flow rate influenced carbon loss in the system. At low CO2 molar fraction (2-6%) or gas flow rate (75-100l·min(-1)) the carbon efficiency in the sump was higher than 95%, 85% of the injected carbon being transformed into biomass. Conversely, at high CO2 molar fraction (14%) or gas flow rate (150l·min(-1)) the carbon efficiency in the sump was lower than 67%, 32% of the carbon being fixed as biomass. Analysis here reported allows the pH control to be optimized and production costs to be reduced by optimizing CO2 efficiency.

Hip arthroscopy in the setting of hip arthroplasty.

PURPOSE: Hip arthroscopy has traditionally been viewed as a hip preservation procedure performed in patients with native joint pathology. However, as the list of indications for arthroscopic hip intervention grows, further advances are expanding its use. The purpose of this systematic review was to examine existing evidence supporting the use of hip arthroscopy in the setting of hip arthroplasty. METHODS: Using predetermined inclusion criteria, EMBASE, MEDLINE and PubMed were searched for articles addressing arthroscopic hip surgery performed in hips containing joint replacement arthroplasties. Inclusion criteria limited our search to human and English language studies addressing articles where clear surgical indications are described. Article screening was conducted in duplicate. RESULTS: Seven-hundred and forty-three studies were retrieved before duplicate screening, and 18 satisfied inclusion criteria. Eleven case series, six case reports and one prospective cohort study are included. In total, 171 patients underwent hip arthroscopy following previous arthroplasty. Indications for arthroscopy included iliopsoas tendinopathy (35.8%), symptomatic hips with no clear diagnosis despite extensive investigation (24.6%), periprosthetic infection (6.4%) and intra-articular loose bodies (3.5%). Almost all patients who underwent hip arthroscopy experienced positive outcomes from the procedure. CONCLUSION: Hip arthroscopy after hip arthroplasty is supported by our systematic review for a variety of indications. Hip arthroscopy can be a safe and effective method of treating hip arthroplasty patients with iliopsoas tendinopathy. Hip arthroscopy also has utility in patients with symptomatic hip arthroplasty despite exhaustion of other diagnostic avenues. LEVEL OF EVIDENCE: A systematic review of level IV studies.

Biogas stripping of ammonia from fresh digestate from a food waste digester.

The efficiency of ammonia removal from fresh source-segregated domestic food waste digestate using biogas as a stripping agent was studied in batch experiments at 35, 55 and 70°C, at gas flow rates of 0.125 and 0.250Lbiogasmin(-1)L(-1)digestate with and without pH adjustment. Higher temperatures and alkaline conditions were required for effective ammonia removal, and at 35°C with or without pH adjustment or 55°C with unadjusted pH there was little or no removal. Results were compared to those from earlier studies with digestate that had been stored prior to stripping and showed that ammonia removal from fresh digestate was more difficult, with time constants 1.6-5.7 times higher than those previously reported. This has implications for the design of large-scale systems where continuous stripping of fresh digestate is likely to be the normal operating mode. A mass balance approach showed that thermal-alkaline stripping improved hydrolysis.

Modelling fuel consumption in kerbside source segregated food waste collection: separate collection and co-collection.

Source separated food waste is a valuable feedstock for renewable energy production through anaerobic digestion, and a variety of collection schemes for this material have recently been introduced. The aim of this study was to identify options that maximize collection efficiency and reduce fuel consumption as part of the overall energy balance. A mechanistic model was developed to calculate the fuel consumption of kerbside collection of source segregated food waste, co-mingled dry recyclables and residual waste. A hypothetical city of 20,000 households was considered and nine scenarios were tested with different combinations of collection frequencies, vehicle types and waste types. The results showed that the potential fuel savings from weekly and fortnightly co-collection of household waste range from 7.4% to 22.4% and 1.8% to 26.6%, respectively, when compared to separate collection. A compartmentalized vehicle split 30:70 always performed better than one with two compartments of equal size. Weekly food waste collection with alternate weekly collection of the recyclables and residual waste by two-compartment collection vehicles was the best option to reduce the overall fuel consumption.

Evaluation of carbon dioxide mass transfer in raceway reactors for microalgae culture using flue gases.

Mass transfer of CO2 from flue gas was quantified in a 100m(2) raceway. The carbonation sump was operated with and without a baffle at different liquid/gas ratios, with the latter having the greatest influence on CO2 recovery from the flue gas. A rate of mass transfer sufficient to meet the demands of an actively growing algal culture was best achieved by maintaining pH at ∼8. Full optimisation of the process required both pH control and selection of the best liquid/gas flow ratio. A carbon transfer rate of 10gCmin(-1) supporting an algal productivity of 17gm(-2)day(-1) was achieved with only 4% direct loss of CO2 in the sump. 66% of the carbon was incorporated into biomass, while 6% was lost by outgassing and the remainder as dissolved carbon in the liquid phase. Use of a sump baffle required additional power without significantly improving carbon mass transfer.

Ammonia removal in food waste anaerobic digestion using a side-stream stripping process.

Three 35-L anaerobic digesters fed on source segregated food waste were coupled to side-stream ammonia stripping columns and operated semi-continuously over 300 days, with results in terms of performance and stability compared to those of a control digester without stripping. Biogas was used as the stripping medium, and the columns were operated under different conditions of temperature (55, 70, 85 °C), pH (unadjusted and pH 10), and RT (2-5 days). To reduce digester TAN concentrations to a useful level a high temperature (≥70 °C) and a pH of 10 were needed; under these conditions 48% of the TAN was removed over a 138-day period without any detrimental effects on digester performance. Other effects of the stripping process were an overall reduction in digestate organic nitrogen-containing fraction compared to the control and a recovery in the acetoclastic pathway when TAN concentration was 1770±20 mg kg(-1).

Oxygen transfer and evolution in microalgal culture in open raceways.

The mass transfer characteristics of all sections of a 100 m(2) raceway were evaluated. The efficiency of different diffusers was determined dynamically and the most effective was used for steady state system characterisation at water depth 0.2 m and velocity 0.22 m s(-1). Mass transfer coefficients at a gas flow rate of 6 m(3) h(-1) were 164.50, 63.66, 0.87 and 0.94 h(-1) for the paddlewheel, sump, straight and curved channel sections, with associated oxygen transfer rates of 106, 172, 27 and 39 g h(-1). Oxygen supersaturation during algal cultivation led to a reduction in biomass productivity, which was more severe with pure CO2 than flue gas. Simulations showed the energy required to increase mass transfer and reduce oxygen concentrations was more than compensated for by increased biomass and potential energy yields. Oxygen removal is likely to be a critical criterion, and maintenance of mass transfer by sparging may be necessary even when CO2 is not required.

Operation and recovery of a seasonally-loaded UK waste stabilisation pond system.

An intermittent discharge waste stabilisation pond system was trialled for treatment of a seasonal wastewater load from a campsite. The system showed rapid acclimatisation to incoming load, with chlorophyll-a exceeding 700 mg l(-1) within 2 weeks and filtered and unfiltered effluent biochemical oxygen demand below 20 and 30 mg l(-1) respectively. Good performance continued for some weeks, after which photosynthetic oxygenation capacity in the first pond was seriously impaired by a shock loading believed to include fatty material. Inflow to the system was suspended and a surface film was broken up, after which the pond recovered within an 8-day period. Laboratory experiments indicated that interventions such as artificial aeration and dilution with effluent had no beneficial effect although mixing may have increased the rate of recovery.

Assessment of the potential for biogas production from wheat straw leachate in upflow anaerobic sludge blanket digesters.

Wheat straw is a major potential source of waste biomass for renewable energy production, but its high salt content causes problems in combustion. The salts can be removed by washing, but this process also removes a proportion of the organic material which could potentially be recovered by anaerobic digestion of the washwater leachate. This approach would maximise the overall energy yield in an integrated process in which washwater could be recycled after further desalting. Leachate from cold water washing with a chemical oxygen demand (COD) of 1.2 g l⁻¹ was fed to mesophilic upflow anaerobic sludge blanket (UASB) digesters at a loading rate of 1 g COD l⁻¹ day⁻¹ to determine the energy yield and any detrimental effects of the leached salts on the process. The specific methane production was 0.29 l CH4 g⁻¹ COD(added), corresponding to a COD removal rate of 84%. Light metal cations in the leachate, especially potassium, were found to accumulate in the digesters and appeared to have a synergistic effect up to a concentration of ∼6.5 mg K g⁻¹ wet weight of the granular sludge, but further accumulation caused inhibition of methanogenesis. It was shown that gas production in the inhibited digesters could be restored within 12 days by switching the feed to a synthetic sewage, which washed the accumulated K out of the digesters.

Effect of increasing the organic loading rate on the co-digestion and mono-digestion of cattle slurry and maize.

Co-digestion of cattle slurry and maize has been shown to have benefits for both, improving the biogas yield of the slurry and stability of digestion of the maize. The effect of increasing the total loading rate from 3 to 6 g VS l(-1) day(-1) on the co-digestion of cattle slurry and maize, mixed at equal volatile solids volumes, was investigated in laboratory-scale continuously stirred digesters. These were compared with similar digesters evaluating the increase of 1.5 to 3 g VS l(-1) day(-1) loading rates of slurry and maize digested separately. Compared with mono-digestion of the substrates, where the digestion of maize failed at loading rates greater than 2.5 g VS l(-1) day(-1), the co-digestion of cattle slurry and maize was feasible at all the loading rates tested with an increase in the volumetric methane yield occurring with loading rate. Even at the lowest rate of loading, the addition of equal amounts of volatile solids of maize to slurry leads to an increase in volumetric methane yield of 219%.

Seasonally loaded waste stabilisation ponds: a novel application for intermittent discharge.

This research examined the use of a single facultative pond for treatment of an intermittent discharge from a UK campsite. The system was monitored over an 11-month period to determine the optimum time for discharge in terms of quality standards. The results showed that based on organic strength, discharge was possible in winter between November and March but February was the optimum to meet nutrient and suspended solids requirements. The pond showed rapid acclimatisation to the influent wastewater, with biochemical oxygen demand removal rates during the filling period of around 60 kg ha(-1) day(-1) and removal efficiencies of ∼95% after maturation. The system proved simple to operate. A major design factor is the requirement for storage of net incoming precipitation, which may provide dilution of residual pollutants but requires additional system capacity.

Calibration of a simple model for waste stabilisation pond performance in seasonal climates.

The paper describes the calibration of a model for waste stabilisation pond (WSP) performance in seasonal climates, based on the use of readily available climate data sets. Calibration data were taken from a wide geographical area of Canada and the USA, including coastal and moderately seasonal sites. Good agreement with measured values was shown using a biochemical oxygen demand (BOD) decay constant of 0.3 day(-1) for facultative ponds and 0.07-0.1 day(-1) for storage/maturation ponds with a temperature-related Arrhenius constant of 1.05, and a fixed BOD decay constant of 0.007 day(-1) at water temperatures below 0 °C. The results suggested that such models could potentially be used as the basis for WSP design guidelines tailored to a wide range of climatic conditions.

Reducing the environmental impact of methane emissions from dairy farms by anaerobic digestion of cattle waste.

Four dairy cattle farms considered representative of Northern Spain milk production were studied. Cattle waste was characterised and energy consumption in the farms was inventoried. Methane emissions due to slurry/manure management and fuel consumption on the farms were calculated. The possibility of applying anaerobic digestion to the slurry to minimise emissions and of using the biogas produced to replace fossil fuels on the farm was considered. Methane emissions due to slurry management (storage and use as fertiliser) ranged from 34 to 66kg CH(4)cow(-1)year(-1) for dairy cows and from 13 to 25kg CH(4)cow(-1)year(-1) for suckler calves. Cattle on these farms are housed for most of the year, and the contribution from emissions from manure dropped in pastures is insignificant due to the very low methane conversion factors. If anaerobic digestion were implemented on the farms, the potential GHG emissions savings per livestock unit would range from 978 to 1776kg CO(2)eq year(-1), with the main savings due to avoided methane emissions during slurry management. The methane produced would be sufficient to supply digester heating needs (35-55% of the total methane produced) and on-farm fuel energy requirements.

Two-stage anaerobic digestion of biodegradable municipal solid waste using a rotating drum mesh filter bioreactor and anaerobic filter.

A rotating drum mesh filter bioreactor (RDMFBR) with a 100 microm mesh coupled to an anaerobic filter was used for the anaerobic digestion of biodegradable municipal solid waste (BMW). Duplicate systems were operated for 72 days at an organic loading rate (OLR) of 7.5 g VS l(-1) d(-1). Early in the experiment most of the methane was produced in the 2nd stage. This situation gradually reversed as methanogenesis became established in the 1st stage digester, which eventually produced 86-87% of the total system methane. The total methane production was 0.2 l g(-1) VS(added) with 60-62% volatile solids destruction. No fouling was experienced during the experiment at a transmembrane flux rate of 3.5 l m(-2) h(-1). The system proved to be robust and stably adjusted to a shock loading increase to 15 g VS l(-1) d(-1), although this reduced the overall methane production to 0.15 l g(-1) VS(added).

Development of a coarse membrane bioreactor for two-stage anaerobic digestion of biodegradable municipal solid waste.

A laboratory-scale coarse membrane bioreactor was developed to test its potential for the enhanced degradation of biodegradable municipal (solid) waste. The purpose of the mesh was to retain solid substrate and biomass in the reactor, promoting optimal degradation while also allowing intermediate soluble compounds to be removed and degraded in a second reactor. Three reactors with nylon woven mesh membranes of pore sizes 30, 100 and 140 mum were operated at a solid and liquid retention time of 20 and 1.5 days respectively and fed at an organic loading rate of 3.75 gVS l(-1) d(-1). Liquid effluent was fed to an anaerobic filter reactor. The total methane production for the two stage systems was very similar at 0.21-0.22 l g(-1) VS added (c.f. 0.26 l g(-1) VS added for BMP). The effect of increasing the pore size of the mesh was to reduce the methane production in the first stage and transfer more of this to the filter reactor, with the proportion of the total methane produced in the first stage changing from 72% to 49% between 30 and 140 mum meshes. The VS content of the first stage effluent also increased with pore size so it is likely that the mechanism for the differences in methane production is one of solids/biomass retention. The 30 mum pore size is recommended for further work since it transmitted a lower solid and soluble loading to the anaerobic filter. Solids accumulation in the second stage, although causing no problems in the 85-day operational period of this trial, could lead to blocking of the anaerobic filter, which is undesirable on a large scale.

Effect of solid and liquid retention times on hydrolysis of maize.

First stage hydrolysis/acidification, using maize as the substrate, was carried out both in single pass (SP) reactors at different hydraulic retention times (HRT) and in hydraulic flush (HF) reactors in which the solids and liquid retention time were uncoupled. The HF reactors were operated at two different loadings (2 and 4 g VS l(-1) d(-1)) and at liquid retention times between 2-16 days with solids held for 20 days. The volatile solids destruction (VS(destroyed) d(-1)) and specific methane potential (l CH(4) g VS(added) d(-1)) of the intermediate products formed in the SP reactors both decreased with increasing retention and showed a maximum VS destruction of 55.6% at a 2-day HRT. The HF reactors showed a slightly lower VS destruction at the same loading but the methane potential was slightly higher as the intermediate COD produced had a greater proportion of volatile fatty acids (VFA) present. At the loading used it was necessary to operate the HF reactors at a HRT of less than 8 days to have any benefit over the SP reactors.

Anaerobic digestion of maize in coupled leach-bed and anaerobic filter reactors.

The methane potential of a leach bed reactor (LBR) coupled to an anaerobic filter (AF) was assessed using energy maize (Zea mays) as substrate. Four LBRs were used operated as pairs, with and without leachate recirculation, over two feed cycles with retention times of 14 and 28 days. Performance was estimated from the total solids destruction in the LBR, and the volatile fatty acid (VFA) and soluble chemical oxygen demand (SCOD) in the leachate. Overall conversion of fresh substrate added to the combined system was good although the organic loading rate (OLR) was limited. The coupled LBR demonstrated improved hydrolysis performance promoted by good buffering, and the AF showed rapid conversion of leachate SCOD into methane with possible further hydrolysis and acidification. Theoretical estimation of the methane potential showed that between 20-40% of the methane was formed in the LBR and was not captured in this trial.

Influence of annual climate variability on design and operation of waste stabilisation ponds for continental climates.

WSPs are widely used in North America, and offer huge potential for other continental climate regions. The standard design and operating protocol is robust even at high latitudes, but may be conservative elsewhere. A simple model based on first-order kinetics for biochemical oxygen demand (BOD) is used to consider some alternative design and operating protocols, using long-term daily climate records for cities across continental central Asia. Options include changing the discharge period; retaining treated water in the pond over the winter; and changing the facultative pond loading. Annual variability in climate parameters has a major effect, in particular on the date at which treated wastewater meets appropriate standards for discharge or re-use: the earlier the discharge, the greater the variability in effluent quality. Skilful management of these systems may therefore be required to maximise their performance. While current models require development, it is clear modelling could provide tools and guidelines that would allow the design of continental climate WSP to be tailored to specific regional and local climate conditions.

The potential for facilitating spring discharge from continental climate waste stabilisation ponds by carry-over of treated wastewater: concepts and experimental findings.

The research investigated some factors influencing the rate of stabilisation of wastewater in the spring period in continental climate waste stabilisation ponds, and in particular the potential for bringing forward the discharge date by optimising storage capacity and dilution. Experiments using pilot and modelscale ponds were set up in Almaty, Kazakhstan. These simulated operating regimes for a facultative and storage/maturation pond system subject to ice cover from late November until late March. Two pilot-scale facultative ponds were operated at hydraulic retention times (HRT) of 20 and 30 days, with surface loading rates of 100 and 67 kg BOD ha(-1) day(-1). Effluent from the 20-day HRT facultative pond was then fed to two pilot-scale storage/maturation ponds which had been partially emptied and allowed to refill over the winter period with no removal of effluent. The paper discusses the results of the experiments with respect to selection of an operating regime to make treated wastewater available early in the spring. Preliminary results indicate that there may be potential for alternative operating protocols designed to maximise their performance and economic potential.