Thermal properties and crystallization behavior of fractionated blocky and random polyhydroxyalkanoate copolymers from mixed microbial cultures

This study represents the first detailed analysis of the thermal, morphological, and crystallization properties of the blend components within a range of mixed‐culture polyhydroxyalkanoates (PHAs), with 3‐hydroxyvalerate content in the as‐produced materials and in the fractions ranging from low (12 mol %) to high (91 mol %). Both coarse and fine fractionation of the as‐produced copolymers confirmed that they were blends of nominally blocky and/or random copolymers of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate), with very broad compositional distributions as governed by the PHA accumulation strategy. The crystallization kinetics and thermal properties of the fractions were found to be very significantly different from each other, consistent with the hypothesis that the overall mechanical properties were primarily controlled by the more rapidly crystallizing components. Two materials produced using an alternating feeding strategy demonstrated unique crystallization and thermal properties in their fractions, which are considered to have contributed to distinctly more elastic mechanical properties in these particular samples. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40836.     

Solids characterisation in an anaerobic migrating bed reactor (AMBR) sewage treatment system

The aim of this work was to characterise the solids in an anaerobic sewage treatment process. Hindered settling velocity, particle size distributions (PSD), influent and effluent COD(P)/SS and discrete settling velocity distributions were all measured. The anaerobic migrating bed reactor (AMBR) solids were mainly flocculent and had a settling rate equivalent to a good settling activated sludge ( approximately SSVI=60 mL/g). The PSD of the anaerobic solids were very different to PSD for activated sludge flocs, with the anaerobic solids having a modal size an order of magnitude smaller than activated sludge, but a range of particle sizes being two orders of magnitude larger. There was a far greater range in size and structure in the anaerobic solids. The anaerobic process solids were primarily feed solids undergoing VSS destruction (hydrolysis). The biological mass was small. The solids seemed to retain their size as the volatiles were degraded and the density decreased ('skeletons' of the influent particulates). The small fraction of slowly settling solids, which have been identified to have a similar modal size but lower density than the mixed solids in the reactor, pose a solids retention time (SRT) control problem when relying on settling alone for solids retention.     

The connection between water and energy in cities: a review

We have only rudimentary understanding of the complex and pervasive connections between water and energy in cities. As water security now threatens energy and economic security, this is a major omission. Understanding the water-energy nexus is necessary if we want to contribute to solving water and energy issues simultaneously; if we want to stop moving problems from one resource dimension to another. This is particularly relevant in the Australian context where energy use for water supplies is forecast to rapidly escalate, growing around 300% from 2007 levels, by 2030. This paper presents a literature review with an aim of characterising the research to date with a particular focus on cities, the major centres of consumption and growth. It systematically analyses a wide range of papers and summarises the diverse objectives, dimensions, and scale of the research to-date together with knowledge gaps. There are many major gaps. These include energy use associated with water in industrial and commercial operations as well as socio-political perspectives. A major gap is the lack of a unifying theoretical framework and consistent methodology for analysis. This is considered a prerequisite for quantitative trans-city comparisons.     

Estimating spatial variations in soil organic carbon using satellite hyperspectral data and map algebra

This study evaluated the effectiveness of using Hyperion hyperspectral data in improving existing remote-sensing methodologies for estimating soil organic carbon (SOC) content on farmland. The study area is Big Creek Watershed in Southern Illinois, USA. Several data-mining techniques were tested to calibrate and validate models that could be used for predicting SOC content using Hyperion bands as predictors. A combined model of stepwise regression followed by a five hidden nodes artificial neural network was selected as the best model, with a calibration coefficient of determination (R ²) of 78.9% and a root mean square error (RMSE) of 3.3 tonnes per hectare (t ha^?1). The validation RMSE, however, was found to be 11.3 t ha^?1. Map algebra was implemented to extrapolate this model and produce a SOC map for the watershed. Hyperspectral data improved marginally the predictability of SOC compared to multispectral data under natural field conditions. They could not capture small annual variations in SOC, but could measure decadal variations with moderate error. Satellite-based hyperspectral data combined with map algebra can measure total SOC pools in various ecosystem or soil types to within a few per cent error.     

Fossil organic carbon in wastewater and its fate in treatment plants

This study reports the presence of fossil organic carbon in wastewater and its fate in wastewater treatment plants. The findings pinpoint the inaccuracy of current greenhouse gas accounting guidelines which defines all organic carbon in wastewater to be of biogenic origin. Stable and radiocarbon isotopes (¹³C and ¹⁴C) were measured throughout the process train in four municipal wastewater treatment plants equipped with secondary activated sludge treatment. Isotopic mass balance analyses indicate that 4–14% of influent total organic carbon (TOC) is of fossil origin with concentrations between 6 and 35 mg/L; 88–98% of this is removed from the wastewater. The TOC mass balance analysis suggests that 39–65% of the fossil organic carbon from the influent is incorporated into the activated sludge through adsorption or from cell assimilation while 29–50% is likely transformed to carbon dioxide (CO₂) during secondary treatment. The fossil organic carbon fraction in the sludge undergoes further biodegradation during anaerobic digestion with a 12% decrease in mass. 1.4–6.3% of the influent TOC consists of both biogenic and fossil carbon is estimated to be emitted as fossil CO₂ from activated sludge treatment alone. The results suggest that current greenhouse gas accounting guidelines, which assume that all CO₂ emission from wastewater is biogenic may lead to underestimation of emissions.     

Decreasing activated sludge thermal hydrolysis temperature reduces product colour, without decreasing degradability

Activated sludges are becoming more difficult to degrade in anaerobic digesters, due to the implementation of stricter nitrogen limits, longer sludge ages, and removal of primary sedimentation units. Thermal hydrolysis is a popular method to enhance degradability of long-age activated sludge, and involves pressure and heat treatment of the process fluid (150-160 degrees C saturated steam). However, as documented in this study, in a full-scale system, the use of thermal hydrolysis produces coloured, recalcitrant compounds that can have downstream impacts (e.g., failure of UV disinfection, and increased effluent nitrogen). The coloured compound formed during thermal hydrolysis was found to be melanoidins. These are coloured recalcitrant compounds produced by polymerisation of low molecular weight intermediates, such as carbohydrates and amino compounds at elevated temperature (Maillard reaction). By decreasing the THP operating temperature from 165 degrees C to 140 degrees C, THP effluent colour decreased from 12,677 mg-PtCo L(-1) to 3837 mg-PtCo L(-1). The change in THP operating temperature from 165 degrees C to 140 degrees C was shown to have no significant impact on anaerobic biodegradability of the sludge. The rate and extent of COD biodegradation remained largely unaffected by the temperature change with an average first order hydrolysis rate of 0.19 d(-1) and conversion extent of 0.43 g-COD(CH4)g-COD(-1).     

The effect of pH on N2O production under aerobic conditions in a partial nitritation system

Ammonia-oxidising bacteria (AOB) are a major contributor to nitrous oxide (N₂O) emissions during nitrogen transformation. N₂O production was observed under both anoxic and aerobic conditions in a lab-scale partial nitritation system operated as a sequencing batch reactor (SBR). The system achieved 55 ± 5% conversion of the 1 g NH₄⁺-N/L contained in a synthetic anaerobic digester liquor to nitrite. The N₂O emission factor was 1.0 ± 0.1% of the ammonium converted. pH was shown to have a major impact on the N₂O production rate of the AOB enriched culture. In the investigated pH range of 6.0-8.5, the specific N₂O production was the lowest between pH 6.0 and 7.0 at a rate of 0.15 ± 0.01 mg N₂O-N/h/g VSS, but increased with pH to a maximum of 0.53 ± 0.04 mg N₂O-N/h/g VSS at pH 8.0. The same trend was also observed for the specific ammonium oxidation rate (AOR) with the maximum AOR reached at pH 8.0. A linear relationship between the N₂O production rate and AOR was observed suggesting that increased ammonium oxidation activity may have promoted N₂O production. The N₂O production rate was constant across free ammonia (FA) and free nitrous acid (FNA) concentrations of 5-78 mg NH₃-N/L and 0.15-4.6 mg HNO₂-N/L, respectively, indicating that the observed pH effect was not due to changes in FA or FNA concentrations.     

Microbial community analysis during continuous fermentation of thermally hydrolysed waste activated sludge

Acidogenic fermentation of thermally hydrolysed waste activated sludge was carried out at laboratory scale in two reactors operated under different hydraulic retention times (HRT). Process performance was assessed in terms of volatile fatty acid (VFA) composition and yield. The diversity of the microbial population was investigated by constructing a 16S rRNA gene library and subsequent phylogenetic analysis of clones. Fluorescence in situ hybridization (FISH) was used to assess the relative abundance of different bacterial groups. Bacteroidetes and Firmicutes were the dominant taxonomic groups representing 93% of the total sequences obtained in the reactor with 4 d HRT. A similar VFA yield (0.4-0.5 g VFA(COD) g SCOD(-1)) was obtained for the HRTs tested (1-4 d), indicating that extended retention times were not useful. Within Firmicutes, Clostridia was the major group detected in the clone sequences. These had close affiliation to Sporanaerobacter acetigenes, suggesting organisms of this group were important for hydrolysis of the protein fraction of the substrate. However, FISH analysis failed to detect the major portion of the bacteria, and this is most likely due to the lack of appropriate probes. This work emphasizes the diversity of fermentative communities, and indicates that more work is needed to identify and detect the important members.     

Phosphorus recovery from centralised municipal water recycling plants

Depletion of world phosphorus reserves is driving research into options to recover and recycle this essential, non-renewable resource. Phosphate (PO₄³⁻) recovery at centralised wastewater treatment plants can be achieved through biosolids reuse or sidestream precipitation though the PO₄³⁻ levels are low compared with decentralised systems based on source separation. However, the recent growth in membrane based water recycling projects, where reverse osmosis is used to produce high quality water has resulted in the production of liquid waste streams with elevated concentrations of PO₄³⁻. Four recycling scenarios using different membrane processes and anaerobic treatment were compared and the potential PO₄³⁻ recovery via struvite (magnesium ammonium phosphate) from membrane concentrate examined. By incorporating an anaerobic reactor in the process we have been able to investigate the possibility of cogeneration of electricity from methane. Modelling of struvite recovery from membrane concentrate with co-generation indicates a net power requirement of 260 kWh/kg P recovered compared with 510 kWh/kg P for a system without cogeneration at a water consumption level of 250 L/p/d. When water consumption is limited to 80 L/p/d, this scenario compares favourably with literature values for recovery from source separated urine which range from 18 to 43 kWh/kg P.