Household mixed plastic waste derived adsorbents for CO2 capture: A feasibility study

The feasibility of producing activated carbon (AC) from real Household Mixed Plastic Waste (HMPW) comprising of LDPE, HDPE, PP, PS, and PET for carbon capture via direct carbonisation followed by microwave-assisted or conventional thermally assisted chemical activation was investigated. A microwave-assisted activation procedure was adopted to assess the impact on the CO2 capture capacity of the resulting AC using both a lower temperature (400 °C vs. 700 °C) and a shorter duration (5 vs. 120 mins) than that required for conventional activation. The results obtained showed that the AC yield was 71 and 78% for the conventional and microwave-assisted samples, respectively. Microwave activation consumed five-fold less energy (0.19 kWh) than the conventional activation (0.98 kWh). Thermal stability results indicated total weight loss of 10.0 and 8.3 wt%, respectively, for conventional and microwave-activated samples over the temperature range of 25-1000 °C, with ACs from both activation routes displaying a type 1 nitrogen isotherm. The dynamic CO2 uptake capacity at 1 bar and 25 °C was 1.53 mmol/g, with maximum equilibrium uptake ranging between 1.32 and 2.39 mmol/g at temperatures (0-50 °C) and 1 bar for the conventionally activated AC. The analogous microwave-activated sample showed a higher dynamic CO2 uptake of 1.62 mmol/g and equilibrium uptake in the range 1.58-2.88 mmol/g under equivalent conditions. The results therefore indicate that microwave activation results in enhanced carbon capture potential. To the best of our knowledge, this is the first-time microwave heating has been employed to convert household mixed plastic wastes directly into ACs for carbon capture applications. This report therefore demonstrates that the management of mixed plastics could lead to the development of a circular economy through the conversion of waste into value-added materials.

Research ReportDiurnal global ocean surface pCO2 and air-sea CO2 flux reconstructed from spaceborne LiDAR data

The ocean absorbs a significant amount of carbon dioxide (CO2) from the atmosphere, helping regulate Earth's climate. However, our knowledge of ocean CO2 sink levels remains limited. This research focused on assessing daily changes in ocean CO2 sink levels and air-sea CO2 exchange, using a new technique. We used LiDAR technology, which provides continuous measurements during day and night, to estimate global ocean CO2 absorption over 23 years. Our model successfully reproduced sea surface partial pressure of CO2 data. The results suggest the total amount of CO2 absorbed by oceans is higher at night than during the day. This difference arises from a combination of factors like temperatures, winds, photosynthesis, and respiration. Understanding these daily fluctuations can improve predictions of ocean CO2 uptake. It may also help explain why current carbon budget calculations are not fully balanced-an issue scientists have grappled with. Overall, this pioneering study highlights the value of LiDAR's unique day-night ocean data coverage. The findings advance knowledge of ocean carbon cycles and their role in climate regulation. They underscore the need to incorporate day-night variability when assessing the ocean's carbon sink capacity.

Atmospheric Thermodynamic Profiling through the Use of a Micro-Pulse Raman Lidar System: Introducing the Compact Raman Lidar MARCO

It was for a long time believed that lidar systems based on the use of high-repetition micro-pulse lasers could be effectively used to only stimulate atmospheric elastic backscatter echoes, and thus were only exploited in elastic backscatter lidar systems. Their application to stimulate rotational and roto-vibrational Raman echoes, and consequently, their exploitation in atmospheric thermodynamic profiling, was considered not feasible based on the technical specifications possessed by these laser sources until a few years ago. However, recent technological advances in the design and development of micro-pulse lasers, presently achieving high UV average powers (1-5 W) and small divergences (0.3-0.5 mrad), in combination with the use of large aperture telescopes (0.3-0.4 m diameter primary mirrors), allow one to presently develop micro-pulse laser-based Raman lidars capable of measuring the vertical profiles of atmospheric thermodynamic parameters, namely water vapor and temperature, both in the daytime and night-time. This paper is aimed at demonstrating the feasibility of these measurements and at illustrating and discussing the high achievable performance level, with a specific focus on water vapor profile measurements. The technical solutions identified in the design of the lidar system and their technological implementation within the experimental setup of the lidar prototype are also carefully illustrated and discussed.

Investigating the challenges of biogas provision in water limited environments through laboratory scale biodigesters

The potential for biogas provision through household-scale anaerobic digestion in rural sub-Saharan Africa is limited due to perceived water shortages. The most common substrate is animal dung diluted 1:1 with water. Two experimental methods tested the potential of reducing water demand. The first experiment compared the chemical oxygen demand (COD) and volatile solid removal of four cow dung dilutions ranging from 3.5-10.6% total solids. In the second experiment, bioslurry filtrate was recirculated back into the fresh substrate at different concentrations. The highest COD removal rate of 28.3% was obtained from mixing equal volumes of dung with filtrate (mean total solids 7.4%) while the highest methane production rate of 0.40 g/L/day, calculated from COD balance, was obtained from undiluted cow dung (total solids 10.6%). Results suggest the potential for a 75-100% reduction in water demand.

Comprehensive, Continuous, and Vertical Measurements of Seawater Constituents with Triple-Field-of-View High-Spectral-Resolution Lidar

Measuring the characteristics of seawater constituent is in great demand for studies of marine ecosystems and biogeochemistry. However, existing techniques based on remote sensing or in situ samplings present various tradeoffs with regard to the diversity, synchronism, temporal-spatial resolution, and depth-resolved capacity of their data products. Here, we demonstrate a novel oceanic triple-field-of-view (FOV) high-spectral-resolution lidar (HSRL) with an iterative retrieval approach. This technique provides, for the first time, comprehensive, continuous, and vertical measurements of seawater absorption coefficient, scattering coefficient, and slope of particle size distribution, which are validated by simulations and field experiments. Furthermore, it depicts valuable application potentials in the accuracy improvement of seawater classification and the continuous estimation of depth-resolved particulate organic carbon export. The triple-FOV HSRL with high performance could greatly increase the knowledge of seawater constituents and promote the understanding of marine ecosystems and biogeochemistry.

Shipborne oceanic high-spectral-resolution lidar for accurate estimation of seawater depth-resolved optical properties

Lidar techniques present a distinctive ability to resolve vertical structure of optical properties within the upper water column at both day- and night-time. However, accuracy challenges remain for existing lidar instruments due to the ill-posed nature of elastic backscatter lidar retrievals and multiple scattering. Here we demonstrate the high performance of, to the best of our knowledge, the first shipborne oceanic high-spectral-resolution lidar (HSRL) and illustrate a multiple scattering correction algorithm to rigorously address the above challenges in estimating the depth-resolved diffuse attenuation coefficient K_d and the particulate backscattering coefficient b_bp at 532 nm. HSRL data were collected during day- and night-time within the coastal areas of East China Sea and South China Sea, which are connected by the Taiwan Strait. Results include vertical profiles from open ocean waters to moderate turbid waters and first lidar continuous observation of diel vertical distribution of thin layers at a fixed station. The root-mean-square relative differences between the HSRL and coincident in situ measurements are 5.6% and 9.1% for K_d and b_bp, respectively, corresponding to an improvement of 2.7-13.5 and 4.9-44.1 times, respectively, with respect to elastic backscatter lidar methods. Shipborne oceanic HSRLs with high performance are expected to be of paramount importance for the construction of 3D map of ocean ecosystem.

CO2 Profiling by Space-Borne Raman Lidar

As clearly reported in the IPCC fifth Assessment Report, CO2 emissions are already producing destructive effects to the plant ecosystem through the alteration of soil-atmosphere interaction mechanisms.

Although the space and ground network for CO2 monitoring has regularly expanded over the past 50 years, it does not guarantee the necessary spatial and temporal resolution needed for a quantitative analysis of sources and sinks. For the purpose of estimating forests’ carbon capturing capabilities, accurate measurements of CO2 gradients between the forest floor and the top of the canopy, which ultimately translates into the capability to measure CO2 concentration profiles. Space sensors provide CO2 measurements above forest canopies, which do not allow to properly estimate Gross Primary Production (GPP).

These observational gaps could be addressed with an active remote sensing system in space based on the vibrational Raman lidar technique. CO2 profile measurements are possible, together with simultaneous measurements of the temperature and water vapour mixing ratio profile and a variety of additional variables (aerosol backscatter profile, aerosol extinction profile, PBL depth, cloud top and base heights, cloud optical depth). An assessment of the expected performance of the system has been performed based on the application of an analytical simulation model developed at University of Basilicata.

Particulate Optical Properties in the Mediterranean and Black Seas Through Calipso Spaceborne Lidar Measurements

New applications on global-scale plankton retrievals using the CALIOP (Cloud-Aerosol Lidar with orthogonal Polarization) lidar measurements on the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) satellite recently suggested that space-based lidars could provide information about the depth distribution of optical scattering. Assessing the oceanic surface layer’s optical properties through CALIOP is one of the reasons of the extension of the CALIOP mission for another 3 years (2018-2020). The objective of this work is the evaluation of the potential CALIOP ocean products in the Mediterranean and Black seas using the ocean color products provided by the Copernicus Marine Environment Monitoring Systems (CMEMS).

Water vapor and aerosol lidar measurements within an atmospheric instrumental super site to study the aerosols and the tropospheric trace gases in rome

A joint instrumental Super Site, combining observation in urban (“Sapienza” University) and semi-rural (ESA-ESRIN and CNR-ISAC) environment, for atmospheric studies and satellites Cal/Val activities, has been set-up in the Rome area (Italy). Ground based active and passive remote sensing instruments located in both sites are operating in synergy, offering information for a wide range of atmospheric parameters. In this work, a comparison of aerosol and water vapor measurements derived by the Rayleigh-Mie-Raman (RMR) lidars, operating simultaneously in both experimental sites, is presented.

Feasibility study to measure HDO/H2O atmospheric profiles through a raman lidar

The Raman lidar technique as currently applied for the retrieval of WV mixing ratio profiles allows, in theory, to estimate HDO/H2O atmospheric profiles. The objective of this study is to develop a lidar simulator and to study the feasibility of the groundbased Raman lidar HDO measurement. Thus, the characteristics of a realistic lidar system for the estimation of HDO/H2O atmospheric profiles are investigated through a set of numerical simulations.

Earlinet validation of CATS L2 product

The Cloud-Aerosol Transport System (CATS) onboard the International Space Station (ISS), is a lidar system providing vertically resolved aerosol and cloud profiles since February 2015. In this study, the CATS aerosol product is validated against the aerosol profiles provided by the European Aerosol Research Lidar Network (EARLINET). This validation activity is based on collocated CATS-EARLINET measurements and the comparison of the particle backscatter coefficient at 1064nm.

Quantification of hydrocarbon species on surfaces by combined microbalance-FTIR

Absorption coefficients for the asymmetric stretching modes of CH₃ and CH₂ groups formed by adsorbing alkyl chained species from the vapour phase onto two different adsorbents; a γ-alumina support material and a supported metal catalyst have been determined using a custom made thermogravimetric-infrared cell. Results show that despite variations in the individually calculated absorption coefficients (ca. ±20%), the ratio of the absorption coefficients (CH₂:CH₃) remained consistent despite employing adsorbates of varying chain length and functionality, and despite the choice of adsorbents which exhibited different surface areas and light scattering characteristics. The use of this absorption coefficient ratio has been shown to be applicable in the quantification of the average chain length of multiple adsorbed species of differing chain length. The potential for applying this to scenarios where reactions on surfaces are monitored is discussed.

Experimental investigation of a new process for treatment and valorisation of pot ale wastewaters

This study investigated an innovative process for the treatment and valorisation of pot ale wastewater. The first phase was to balance the pH to precipitate nitrogen, phosphorus and magnesium, recovering them as fertiliser; the second phase investigated the evaporation of water, reducing the volume of liquid to be transported to an anaerobic digester. In the pH balancing phase we investigated the effect of the final pH, in the range 8-11, on the removal of calcium, magnesium, ammonia, phosphorus and copper. We observed that, for all the species, most of the precipitation occurred when pH was increased from 8 to 9. By pH balancing, a removal from the liquid phase of up to 65% of ammonia and 60% of total phosphorus was obtained. Calcium and magnesium also precipitated from the liquid phase, giving solids with the following composition, calculated from liquid phase measurements: 24-27% magnesium, 4-5% nitrogen, 16-18% phosphorus. We investigated the evaporation process at pH 6 and 10 and at atmospheric pressure and under vacuum. The results showed that only a few % of the chemical oxygen demand (COD) evaporates, indicating very little loss of organic substance for anaerobic digestion. Mass balances for this process in a medium-size whisky distillery were also carried out.

LIDAR developments at Clermont-Ferrand--France for atmospheric observation

We present a Rayleigh-Mie-Raman LIDAR system in operation at Clermont-Ferrand (France) since 2008. The system provides continuous vertical tropospheric profiles of aerosols, cirrus optical properties and water vapour mixing ratio. Located in proximity to the high altitude Puy de Dôme station, labelled as the GAW global station PUY since August 2014, it is a useful tool to describe the boundary layer dynamics and hence interpret in situ measurements. This LIDAR has been upgraded with specific hardware/software developments and laboratory calibrations in order to improve the quality of the profiles, calibrate the depolarization ratio, and increase the automation of operation. As a result, we provide a climatological water vapour profile analysis for the 2009-2013 period, showing an annual cycle with a winter minimum and a summer maximum, consistent with in-situ observations at the PUY station. An overview of a preliminary climatology of cirrus clouds frequency shows that in 2014, more than 30% of days present cirrus events. Finally, the backscatter coefficient profile observed on 27 September 2014 shows the capacity of the system to detect cirrus clouds at 13 km altitude, in presence of aerosols below the 5 km altitude.

Operation of fill-and-draw reactors fed with bisphenol A as sole carbon and energy source

While there is ample evidence in the literature that many organic xenobiotics can be biodegraded as sole carbon and energy source by pure batch cultures of selected microorganisms, the same evidence is very limited for continuous or semi-continuous mixed-culture processes simulating biological wastewater treatment plants. This study investigates for the first time whether Bisphenol A (BPA) can be removed and used as sole carbon and energy source by mixed microbial cultures in a semi-continuous process. Four fill and draw bioreactors were inoculated with unacclimated soil and operated at various hydraulic retention times (HRT), in the range of 1.7-4.2 d, using a feed composed solely of BPA (115 mg/l), and mineral salts. At steady-state, the BPA removal in the four reactors varied in the range 7.5-19% and did not show a significant trend with the HRT. The maximum growth rate on BPA was measured in the range 0.29-1.54 d-1.

Metabolic analysis of the removal of formic acid by unacclimated activated sludge

This paper investigates the removal of formic acid by unacclimated biomass from a municipal activated sludge wastewater treatment plant. The biomass was initially able to remove formic acid, but its removal rate and Oxygen Uptake Rate (OUR) decreased with time, until formic acid removal stopped before the formic acid had been exhausted. Formaldehyde was removed in a similar way, whereas the same biomass was simultaneously able to grow and store PHAs when acetic acid was used as substrate. Batch tests with glycine and (13)C NMR analysis were performed, showing that unacclimated biomass was not able to synthesize all the metabolic intermediates from formic acid alone. At least glycine needed to be externally supplemented, in order to activate the serine synthesis pathway. A small amount of formic acid removal in the absence of growth was also possible through formaldehyde formation and its further conversion to formalin (1,2-formaldehyde dimer), whereas no PHAs were formed.

High-rate anaerobic treatment of Fischer-Tropsch wastewater in a packed-bed biofilm reactor

This study investigates the anaerobic treatment of an industrial wastewater from a Fischer-Tropsch (FT) process in a continuous-flow packed-bed biofilm reactor operated under mesophilic conditions (35 degrees C). The considered synthetic wastewater has an overall chemical oxygen demand (COD) concentration of around 28g/L, mainly due to alcohols. A gradual increase of the organic load rate (OLR), from 3.4gCOD/L/d up to 20gCOD/L/d, was adopted in order to overcome potential inhibitory effects due to long-chain alcohols (>C6). At the highest applied OLR (i.e., 20gCOD/L/d) and a hydraulic retention time of 1.4d, the COD removal was 96% with nearly complete conversion of the removed COD into methane. By considering a potential of 200tCOD/d to be treated, this would correspond to a net production of electric energy of about 8x10(7)kWh/year. During stable reactor operation, a COD balance and batch tests showed that about 80% of the converted COD was directly metabolized through H(2)(-) and acetate-releasing reactions, which proceeded in close syntrophic cooperation with hydrogenotrophic and acetoclastic methanogenesis (contributing to about 33% and 54% of overall methane production, respectively). Finally, energetic considerations indicated that propionic acid oxidation was the metabolic conversion step most dependent on the syntrophic partnership of hydrogenotrophic methanogens and accordingly the most susceptible to variations of the applied OLR or toxicity effects.

Mechanisms of heavy-metal removal by activated sludge

This paper investigates the chemical mechanisms operating in cadmium and lead removal by activated sludge in sequencing batch reactors. Selective extraction and acid digestion of sludge samples denoted that both Cd and Pb are mainly present as surface-bound metals. Characterisation of sludge samples by potentiometric titrations and IR spectra suggested that carboxylic and amino groups are the main active sites responsible for the binding properties of the biomass. Simulation of metal speciation implemented with complexation constants determined in biosorption tests, showed that cadmium predominates as biosorbed species, while lead was mainly removed by precipitation.

Role of biomass adaptation in the removal of formic acid in sequencing batch reactors

This study deals with formic acid removal in activated sludge processes, in particular in the processes carried out in sequencing batch reactors (SBRs). Formic acid removal has been investigated in a SBR fed with acetic and formic acids at equimolar concentrations. Biomass performance in the reactor has been investigated both by the analysis of the removal of the two substrates and by batch tests. Regarding SBR process, the obtained results show that a relevant difference occurred between formic and acetic acid profiles. Acetic acid was never found in the effluent and was always completely removed during the reaction phase. On the other hand, formic acid removal was determined by biomass acclimation, which is in turn determined by sludge age imposed to the system. Batch tests confirmed that formic acid removal occurs only if biomass is acclimated. It has been shown that the minimal sludge age to obtain complete formic acid removal is much higher than those predictable with the classical models of microbial growth in wastewater treatment processes. The advantages of SBRs over continuous-flow systems in the removal of formic acid have also been highlighted.

Effect of the Length of the Cycle on Biodegradable Polymer Production and Microbial Community Selection in a Sequencing Batch Reactor

The effect of the length of the cycle on the enrichment and selection of mixed cultures in sequencing batch reactors (SBRs) has been studied, with the aim of biodegradable polymers (namely, polyhydroxyalkanoates (PHAs)) production from organic wastes. At a fixed feed concentration (20 gCOD/L) and organic loading rate (20 gCOD/L/day), the SBR was operated at different lengths of the cycle, in the range 1-8 h. Process performance was measured by considering the rates and yields of polymer storage and of the competing phenomenon of growth. The selected biomass was enriched with microorganisms that were able to store PHAs at high rates and yields only when the length of the cycle was 2 or 4 h, even though in these conditions the process was unstable. On the other hand, when the length of the cycle was 1 or 8 h, the dynamic response of the selected microorganisms was dominated by growth. The best process performance was characterized by storage rates in the range 500-600 mgCOD/gCOD/h and storage yields of 0.45-0.55 COD/COD. The corresponding productivity of the process was in the range 0.25-0.30 gPHA/L/h, the highest values obtained until now for mixed cultures. The microbial composition of the selected biomasses was analyzed through denaturing gradient gel electrophoresis (DGGE) and reverse-transcriptase denaturing gradient gel electrophoresis (RT-DGGE). The instability of the runs characterized by high storage rate was associated with a higher microbial heterogeneity compared to the runs with a stable growth response.

Effect of periodic feeding on substrate uptake and storage rates by a pure culture of Thiothrix (CT3 strain)

A pure culture of Thiothrix strain CT3 has been aerobically cultured under periodic acetate feeding in a Sequencing Batch Reactor (SBR) at volumetric organic load rate of 0.12gCODL(-1)d(-1). Two different culture residence times (12d or 20d) were adopted as well as two different feed frequencies (1 and 4d(-1), for each culture residence time), the volumetric organic load rate being the same under all conditions. The transient response of the microorganism to the periodic acetate feed was investigated through batch tests with biomass withdrawn from the SBR, as function of the different SBR operating conditions. In all tested conditions, a quick transient response to the acetate spike was observed with fast increase of acetate uptake rate (ranging from 71 to 247mgCODgCOD(-1)h(-1)). This transient response was mainly due to acetate storage in form of poly-hydroxybutyrate (ranging from 45% to 64% of the observed yield) whereas the growth response (i.e. increase of production rate of active biomass) generally played a minor role (ranging from 21% to 38% of the observed yield). Apart from this general trend, culture residence time as well as feed frequency had a strong impact on transient behaviour of cultured cells. The overall transient response (i.e. maximum specific substrate removal rate) increased as culture residence time decreased or as feed frequency increased. Moreover, the ratio of storage response and growth response increased as the overall transient response decreased, i.e. the storage response was preferentially maintained when cells presented a lower transient response. The ability of the cells to increase their growth rate with respect to SBR average value was the lowest under the most unfavourable conditions (residence time 20d, feed frequency 1d(-1)) and increased with the increase in maximum substrate uptake rate.

Effect of feed length on settleability, substrate uptake and storage in a sequencing batch reactor treating an industrial wastewater

The paper compares the performance of two Sequencing Batch Reactors (SBRs) treating the same industrial wastewater (composed of formic acid, ethylene glycol and methanol) operated at two different lengths of the feed. The two SBRs were operated in parallel under the same conditions of organic load (0.85 gCOD l(-1) d(-1)) and sludge age (about 10 d), the only difference being the length of the feed: less than 1 min vs. 5 h. In this way the conditions of a plug flow reactor and of a completely mixed reactor were simulated. The two systems were compared on sludge settleability (related to filaments abundance and floc morphology), substrate uptake rates and polyhydroxyalkanoates (PHAs) storage rates. The main difference between the two systems was in the settling properties of the sludge: both SVI and effluent solids were higher in the system with slow feed. With regard to filamentous microorganisms, even though both reactors were inoculated with the same sludge with high concentration of filaments, they were rapidly washed out from both systems. Microscopic observations showed that the reason for the different settling properties of the two sludges was in the floc structure, which was more compact in the system operated with fast feed. These data support the theory of the role of diffusion inside the flocs in determining the settling properties of the sludge. The maximum substrate uptake rates and PHA storage rates were similar in the two systems, showing that also the microorganisms grown at a constant and low substrate concentration were able to quickly increase their activity and to store PHAs when in the presence of a sudden change in substrate concentration.

Enrichment of activated sludge in a sequencing batch reactor for polyhydroxyalkanoate production

The paper describes the start up of a process for the production of polyhydroxyalkanoates (PHAs) from activated sludge. The excess sludge from a wastewater treatment plant was inoculated in a lab-scale sequencing batch reactor (SBR) to be enriched under aerobic conditions through intermittent feeding with a mixture of organic acids. Enriching of activated sludge was monitored through the measurement of polymer concentrations either in the mixed liquor or in the microbial biomass. The bacterial population dynamics during the SBR start up was followed through denaturing gradient gel electrophoresis and the main species present at the steady state were identified. All the measured parameters significantly changed in the SBR during first two weeks after the inoculum was seeded into the reactor, they then stabilized. At the steady state, the SBR produced 2.6 gVSSl(-1) d(-1), with a PHA content of 11% (on a COD basis). The enriched microbial biomass was then transferred into a batch reactor where the bacterial polymer content was increased through a new feeding. In the final batch stage, maximum storage rate and maximum polymer content in the biomass were 405 mgCOD gCOD(-1) h(-1) and 44% (on a COD basis), respectively. The PHA storage from the enriched microbial biomass was about 20 times faster and the PHA content was about 4 times higher than that of the inoculated activated sludge. Observations by fluorescence microscopy showed that the majority of microorganisms in the enriched biomass could be stored. Among the numerically most representative genera in the enriched biomass, Thauera, Candidatus Meganema perideroedes, and Flavobacterium were identified.

Olive oil mill effluents as a feedstock for production of biodegradable polymers

The aim of the present paper was to study the feasibility of using olive oil mill effluents (OMEs) as a substrate in biodegradable polymer production. OMEs were anaerobically fermented to obtain volatile fatty acids (VFAs), which are the most highly used substrate for polyhydroxyalkanotes (PHAs) production. The anaerobic fermentation step was studied both without pretreatment and with different pretreatments (i.e., centrifugation, bentonite addition, and bentonite addition followed by centrifugation) and at various concentrations (28.5, 36.7 and 70.4 g CODL(-1)). During fermentation, VFA concentration was determined (7-16 g CODL(-1)) as well as the corresponding yield with respect to initial COD (22-44%). At all initial concentrations, centrifugation pretreatment (with or without previous addition of bentonite) significantly increased the final VFA concentration and yield, whereas the addition of bentonite alone had no influence. Moreover, centrifugation pretreatment led to a different acid distribution, which affected the hydroxyvalerate (HV) content within the obtained copolymer poly beta-(hydroxybutyrate-hydroxyvalerate) [P(HB-HV)]. OMEs were tested for PHA production by using a mixed culture from an aerobic SBR. Centrifuged OMEs, both with or without fermentation, were tested. PHAs were produced from both matrices, but with fermented OMEs PHA production was much higher, because of the higher VFA concentration. The initial specific rate of PHA production obtained with fermented OMEs was approximately 420 mg COD g COD(-1)h(-1) and the maximum HV content within the copolymer was about 11% (on a molar basis). The HV monomer was produced only until propionic acid remained present in the medium.

Effect of the applied organic load rate on biodegradable polymer production by mixed microbial cultures in a sequencing batch reactor

This article studies the operation of a new process for the production of biopolymers (polyhydroxyalkanoates, PHAs) at different applied organic load rates (OLRs). The process is based on the aerobic enrichment of activated sludge to obtain mixed cultures able to store PHAs at high rates and yields. A mixture of acetic, lactic, and propionic acids at different concentrations (in the range 8.5-31.25 gCOD/L) was fed every 2 h in a sequencing batch reactor (SBR). The resulting applied OLR was in the range 8.5-31.25 gCOD/L/day. Even though, as expected, the increase in the OLR caused an increase in biomass concentration (up to about 8.7 g COD/L), it also caused a relevant decrease of maximal polymer production rate. This decrease in polymer production rate was related to the different extent of "feast and famine" conditions, as function of the applied OLR and of the start-up conditions. As a consequence the best performance of the process was obtained at an intermediate OLR (20 gCOD/L/day) where both biomass productivity and PHA storage were high enough. However, at this high OLR the process was unstable and sudden decrease of performance was also observed. The sludge characterized by the highest PHA storage response was investigated by 16S rDNA clone library. The clone library contained sequences mostly from PHA producers (e.g., Alcaligenes and Comamonas genera); however many genera and among them, one of the dominant (Thauera), were never described before in relation to PHA storage response.

Biodegradable polymers from organic acids by using activated sludge enriched by aerobic periodic feeding

This article describes a new process for the production of biopolymers (polyhydroxyalkanoates, PHAs) based on the aerobic enrichment of activated sludge to obtain mixed cultures able to store PHAs at high rates and yields. Enrichment was obtained through the selective pressure established by feeding the carbon source in a periodic mode (feast and famine regime) in a sequencing batch reactor. A concentrated mixture of acetic, lactic, and propionic acids (overall concentration of 8.5 gCOD L(-1)) was fed every 2 h at 1 day(-1) overall dilution rate. Even at such high organic load (8.5 gCOD L(-1) day(-1)), the selective pressure due to periodic feeding was effective in obtaining a biomass with a storage ability much higher than activated sludges. The immediate biomass response to substrate excess (as determined thorough short-term batch tests) was characterized by a storage rate and yield of 649 mgPHA (as COD) g biomass (as COD)(-1) h(-1) and 0.45 mgPHA (as COD) mg removed substrates (as COD(-1)), respectively. When the substrate excess was present for more than 2 h (long-term batch tests), the storage rate and yield decreased, whereas growth rate and yield significantly increased due to biomass adaptation. A maximum polymer fraction in the biomass was therefore obtained at about 50% (on COD basis). As for the PHA composition, the copolymer poly(beta-hydroxybutyrate/beta-hydroxyvalerate) with 31% of hydroxyvalerate monomer was produced from the substrate mixture. Comparison of the tests with individual and mixed substrates seemed to indicate that, on removing the substrate mixture for copolymer production, propionic acid was fully utilized to produce propionylCoA, whereas the acetylCoA was fully provided by acetic and lactic acid.

Storage of substrate mixtures by activated sludges under dynamic conditions in anoxic or aerobic environments

In spite of the fact that in most activated sludge plants substrate complex mixtures are removed under alternating anoxic and aerobic conditions, most studies on the dynamic response of biomass are limited to feeding a single substrate (acetate or glucose) under a single redox condition (aerobic or anoxic). In this study, the dynamic response of biomass in a sequencing batch reactor is described in terms of substrate removal and related storage as internal polymers, as functions of single or simultaneous feed of several substrates (acetate, glucose, glutamic acid and ethanol) and of anoxic vs. aerobic conditions. Under anoxic conditions, the four substrates were simultaneously removed at a significantly greater nitrate removal rate than when single substrates were present, so showing that the simultaneous removal was partially due to independent metabolic activities. On the other hand, the removal of every substrate was affected (positively or negatively) by the presence of the others, demonstrating that the substrates can be also used by the same metabolism. As an exception, acetate removal was not affected by the presence of other substrates. As for the comparison of aerobic and anoxic conditions, the acetate uptake rate almost doubled moving from anoxic to aerobic conditions, whereas other substrates were only slightly affected. This difference was probably due to the additional presence of aerobic denitrification, which was much more important for acetate. This also confirmed that acetate removal was independent from other substrates. In all cases, storage was the main mechanism of solids formation, so confirming the general importance of such phenomenon under dynamic conditions, independently from feed complexity and redox conditions.

Glutamic acid removal and PHB storage in the activated sludge process under dynamic conditions

Glutamic acid removal in the activated sludge process is studied herein, primarily the formation of storage polymers under dynamic conditions. The activated sludge process was operated by using a sequencing batch reactor (sludge age of 6 d) fed with a synthetic mixture of readily available carbon sources, including glutamic acid. Removal of glutamic acid as the only carbon sources was studied in batch tests, along with oxygen consumption, ammonia uptake-release, and formation of storage polymers. It was found that poly-3-hydroxybutyrate (PHB) was stored and that the storage also occurred simultaneously to biomass growth. PHB storage accounted for 16% of the overall solids that were formed from glutamic acid, as the average value of nine batch tests. Neither other Polyhydroxyalkanoates nor polyglutamic acid were detected. Nuclear magnetic resonance analysis, performed on biomass extracts, allowed us to clarify the main metabolic pathways involved in glutamic acid removal and, in particular, the pathways involved in PHB storage. It was found that glutamic acid enters the Krebs cycle as alpha-ketoglutaric acid and exits to form pyruvic acid and then acetyl-CoA, which is the starting point of PHB production pathway.

Effect of periodic feeding in sequencing batch reactor on substrate uptake and storage rates by a pure culture of Amaricoccus kaplicensis

A pure culture of Amaricoccus kaplicensis was aerobically cultured at a long culture residence time (Theta(C)>12d), under periodic acetate feeding in a sequencing batch reactor (SBR). The cycle length and, correspondingly, the volumetric organic load rate (vOLR) were varied in the range 4-24h and 0.76-0.12gCODl(-1)d(-1), respectively. The transient response of the microorganism to the acetate spike was investigated throughout batch tests, as a function of SBR cycle length and vOLR. In all tested conditions, a rapid transient response was observed, mainly due to acetate storage in the form of polyhydroxybutyrate, since growth (production of active biomass) played a minor role. Apart from this general trend, the maximum rates under transient conditions increased as the cycle length increased from 4 to 24h. In the SBR, the longest cycle also caused a decrease in floc size and settleability as well as an increase in the observed yield. The observed effect of SBR operating conditions on the physiological state of cells and their related transient response may have great significance on the performance of full scale activated sludge processes.

Gas chromatographic analysis of polyhydroxybutyrate in activated sludge: a round-robin test

Polyhydroxyalkanoates (PHA) and poly-beta-hydroxybutyrate (PHB) in particular have become compounds which is routinely investigated in wastewater research. The PHB analysis method has only recently been applied to activated sludge samples where PHA contents might be relatively low. This urges the need to investigate the reproducibility of the gas chromatographic method for PHB analysis. This was evaluated in a round-robin test in 5 European laboratories with samples from lab-scale and full-scale enhanced biological phosphorus removal systems. It was shown that the standard deviation of measurements in each lab and the reproducibility between the labs was very good. Experimental results obtained by different laboratories using this analysis method can be compared. Sludge samples with PHB contents varying between 0.3 and 22.5 mg PHB/mg sludge were analysed. The gas chromatographic method allows for PHV, PH2MB and PH2MV analysis as well.

Effect of different carbon sources on aerobic storage by activated sludge

A study of substrate removal by real activated sludge with several synthetic substrates (acetate, ethanol, glutamic acid) and wastewater (raw and filtered) was carried out. Substrate, stored compounds (polyhydroxyalkanoates, PHA and internal carbohydrates), ammonia and oxygen uptake rate (OUR) were analytically determined. Polyhydroxybutyrate (PHB) was stored when the substrate was acetate or ethanol, while no appreciable formation of storage compound was detected using glutamic acid. A low amount of PHB was also formed in tests with raw and filtered wastewater which was probably mainly due to its acetate content. As far as the sum of storage and growth (indirectly estimated through ammonia consumption) did not match the overall solids formation, other unidentified mechanisms of substrate removal were likely to occur (biosorption, accumulation and/or storage of unidentified compounds). ASM3 and two derived models were used in the interpretation of experimental data with reference to synthetic substrates. With reference to synthetic substrates ASM3 can well describe the experimental data only assuming a stored product formation much higher than the analytically detected one, whereas the model that assumes a parallel growth and storage on the substrate can well describe the observed stored product profile only assuming a direct contribution of growth much higher than estimated from ammonia consumption. The model that assumes an accumulation/biosorption stage as first step of substrate removal can better describe the whole experimentally observed behaviour. However as well as in ASM3 this implies that some fraction of removed COD is still unidentified. With reference to real wastewater where the different phenomena were mixed up due to the presence of several substrates, the different models gave similar results.

PHA storage from several substrates by different morphological types in an anoxic/aerobic SBR

An activated sludge was cultivated on a mixture of several soluble substrates (acetate, ethanol, glucose, glutamic acid, peptone, Tween 80, starch, yeast extract) in an anoxic/aerobic SBR. Highly dynamic conditions in the SBR (feast famine regime) caused fast removal of most COD in the anoxic phase (in particular acetate, ethanol, glutamic acid and glucose were totally removed) and relevant contribution of storage. In spite of that, filament abundance was always high, as is typical of bulking sludges. Filaments which developed in the reactor were characterized on a morphological basis and on the basis of their ability to grow and to store polyhydroxyalkanoates (PHAs). Three main filaments prevailed in the biocenosis, whose relative abundance was varyng with time: Nostocoida limicola II, (two different morphological types), Haliscomenobacter hydrossis and an unidentified one. It was found that maximum growth rate was higher for flocformers than for filaments on each of the tested substrates. Epifluorescence showed that storage ability was more widespread among flocformers than in the filaments. Only one type of Nostocoida limicola II was able to store PHAs. The obtained data show that aerobic growth on the little residual fraction of COD from the anoxic phase was enough to support high abundance of filamentous microorganisms.

Aerobic storage by activated sludge on real wastewater

Activated sludge processes are often operated under dynamic conditions, where the microbial response can include, besides of growth, several COD removal mechanisms, and particularly the storage in form of polymers. While abundant evidence of aerobic storage under dynamic conditions with synthetic substrates can be found (Majone et al., Water Sci. Technol. 39(1) (1999) 61), there is still little knowledge about COD removal mechanisms with real activated sludge and wastewater. The aim of the present paper is therefore to give a direct evidence of storage phenomena occurring when a real sludge is mixed with influent wastewater and of their influence onto OUR profiles in typical respirometric batch tests. For this purpose, respirometric batch tests were performed on the same sludge by using acetate, filtered wastewater and raw wastewater as carbon source along with determination of acetate uptake and storage polymer formation. Comparison of results obtained has shown that poly-3-hydroxybutyrate (PHB) storage gives always the main contribution to acetate removal and that in the case of wastewater PHB is also formed from other substrates. PHB formation clearly occurs during the high-rate RBCOD-phase, however for wastewater it accounts for only a fraction (18-22%) of overall RBCOD removal, so calling for other unidentified storage compounds or other non-storage phenomena. In the low-rate SBCOD phase of respirogram PHB is clearly utilised in tests with acetate as internal reserve material once the acetate is depleted. In tests with filtered and raw wastewater the PHB concentration decreases much slower, probably because more PHB is formed due to the availability of external SBCOD (soluble and not). Moreover, reported OUR in the SBCOD-phase from filtered or raw wastewater are quite higher than those reported in batch tests with acetate, so confirming a main contribution of external SBCOD. However, the respective contributions for utilisation of previously stored compounds and of external SBCOD cannot be easily separated by the comparison of tests on filtered and raw wastewater, because both substrates are simultaneously present also in tests with the filtered wastewater. As a side consequence, the chemical-physical method for evaluation of true soluble and biodegradable COD tends to overestimate the respirometry-based RBCOD, at least for the wastewater under observation. Even though modelling by ASM3 (Gujer et al., Water Sci. Technol. 39(1) (1999) 183) makes it possible to well describe the whole experimental behaviour, it requires that much more storage compounds are formed than the experimentally observed PHB. These compounds have still to be identified and quantified in order to confirm the conceptual structure of ASM3.

The storage of acetate under anoxic conditions

Till now the role of storage in activated sludge processes under transient conditions has been deeply investigated under anaerobic (EBPR processes) or aerobic (bulking control) environments. Little attention has been given to the role of storage in processes including anoxic environments. Hence, the aim of the present work was to investigate the anoxic storage along with other substrate removal mechanisms under transient conditions. Several mixed culture were ad hoc selected under anoxic environment and periodic feeding (acetate as carbon source) at different organic load rate (OLR) and feed length; then their transient response to substrate spike was investigated by batch tests under both anoxic and aerobic conditions. The relative role of different mechanisms in the substrate removal was established on the basis of COD balance assuming that the acetate COD removed from the liquid phase could be oxidised for energy needs or recovered into solids as poly-3-hydroxybutyric acid (PHB) (storage), other internal precursors or intermediates (accumulation) and active biomass (growth, as estimated by ammonium uptake). In all tested conditions, growth response was very little while PHB storage was prevailing. In some operating conditions, indirect evidence of accumulation (in forms still to be identified) was also found. The transient response was not affected by the presence of free amino acids, at least for the unacclimated mixed culture under observation. Transient response under aerobic condition was quite similar to the anoxic one.

Role of storage phenomena on removal of different substrates during pre-denitrification

Removal mechanisms of different substrates during the pre-denitrification step of an anoxic/aerobic sequencing process are studied. Biomass was cultivated in an anoxic/aerobic SBR and fed with a mixture of low and high molecular weight compounds. Substrate removal mechanisms are studied by means of batch tests, performed under anoxic conditions. The dynamic response to a spike of four different substrates (acetate, glucose, glutamic acid and ethanol) is described by simultaneously considering substrate and electron acceptor removal, and PHB and carbohydrates storage. PHB storage is a relevant mechanism during the removal of acetate and ethanol, while glucose is removed mainly by carbohydrate storage.

[Recent progress in the stimulation of the histiocyte system and the anti-infection defences. Research into the effect of stanozolol treatment on the phagocyte activity of human macrophages]

A group of patients was treated with stanozolol. A modified version of Roebuck's skin window technique was used to obtain macrophages. These were then fixed in vitro with a suspension of Paracolonbacter aerogenoides. Comparison with a group of control subjects showed that the macrophages from the treated patients appeared to take up and destroy germs more effectively and that this could be potentiated by prior opsonisation with serum from the treated subjects. These results are seen as an expression of functional activation of the macrophages and an increase in serum opsonin content.