Classification of hemispheric monthly mean stratospheric potential vorticity fields

International audienceMonthly mean NCEP reanalysis potential vorticity fields at the 650 K isentropic level over the Northern and Southern Hemispheres between 1979 and 1997 were studied using multivariate analysis tools. Principal component analysis in the T-mode was applied to demonstrate the validity of such statistical techniques for the study of stratospheric dynamics and climatology. The method, complementarily applied to both the raw and anomaly fields, was useful in determining and classifying the characteristics of winter and summer PV fields on both hemispheres, in particular, the well-known differences in the behaviour and persistence of the polar vortices. It was possible to identify such features as sudden warming events in the Northern Hemisphere and final warming dates in both hemispheres. The stratospheric impact of other atmospheric processes, such as volcanic eruptions, also identified though the results, must be viewed at this stage as tentative. An interesting change in behaviour around 1990 was detected over both hemispheres

Manometric monitoring of biological denitrification

A simple, automated manometric method is here discussed and applied to perform batch experiments for the stoichiometric and kinetic characterization of biological denitrification. The main strength of the proposed methodology is that it requires simple instrumentation, which is usually available in wastewater treatment plant laboratories, being it used in BOD and in BMP tests. The experimental setup consists of a glass bottle, a mixing and termostated system and a manometric bottle-head which can measure and log the overpressure that is caused by denitrified N2. At first, tests were conducted to determine the repeatability of the method; they were performed under low Food-to-Biomass ratio and with both endogenous and externally dosed carbon sources. Later, experimental procedures were performed to assess (1) the anoxic growth yield, (2) the endogenous anoxic decay rate; (3) the anoxic growth rate on acetate; (4) the fraction of anoxic active biomass in the sludge sample. Sludge samples for all these tests were taken from two WWTPs and 6 to 10 replicates were performed each time. Results indicated that the testing procedures is well repeatable and reliable and resulting estimates were within reported literature values

EVALUATION OF ELECTRODE SURFACE TREATMENTS IN SLUDGE ELECTRO-OSMOSIS DEWATERING”

The drying of sludge produced by Wastewater Treatment Plants (WWTPs) is a very hard process due to the presence of the colloid fraction. Electro-osmosis could be a suitable technique to reduce the water content of the final sludge. Electrical fields of 10 V/cm, 15 V/cm and 20 V/cm have been studied for electro-osmosis tests in a static or dynamic apparatus, obtaining a dry solids content up to 40-45%, with respect to 25-30% obtained by mechanical methods. In order to optimise the apparatus, the corrosion behaviour of the anodic material appears the main critical aspect, due to the high circulating current density. Moreover, wear may be detrimental for the surface of rotating electrodes. We then investigated the behaviour of materials used as electrodes mainly by evaluating the efficiency of the process and their surface aspect after treatment. The full understanding of the electrochemical reactions developed at the anode are a key factor for the material choice. We compared the efficiency and the corrosion resistance of anodes made of titanium MMO with respect to bare stainless steel (AISI 304) and stainless steel coated by PVD technique with TiN, AlTiN and DLC. Characterization of the anodes samples by roughness tests and by AFM show that corrosion resistance of the DSA was the most suitable for our application. However, efficiencies of the electro-osmosis process for all the materials used have been found comparable, in terms of developed current densities and total energy consumptions, for low-test duration

Nitrogen removal in fixed-bed submerged biofilters without backwashing

The paper reports the findings of four years of pilot-scale research on nitrogen removal in fixed-bed biofilters fed on real raw municipal wastewater. The plant was made of two fixed-bed biofilm reactors in series with an intermediate settling tank from which excess biomass from the first stage was discharged. The first filter was used for carbon removal either with oxygen or nitrates. The second filter was used for nitrification. The average nitrification rate at 20°C was 0.84 gNH 4 + -N m −2 d −1 with 5 mg l −1 dissolved oxygen in the bulk liquid. Temperature dependence was calculated (r n = r n,20° 1,05 T-20 ). The influent organic load strongly affected ammonia oxidation. If the organic loading exceeded 2.5 gCOD m −2 d −1 nitrification rate was reduced by 50%. Denitrification was performed by recycling nitrates back from the second filter and by using sewage itself as carbon source. Denitrification rate showed to be strongly dependent on temperature (r d = r d,20° 1.11 T-20 ) and on the recycle rate. Hydrolysis of the colloidal COD fraction showed a similar dependence on both temperature and recycle rate. Therefore, it has been concluded that the hydrolysis of finely dispersed COD particles can be the limiting step of denitrification in the biofilter when real sewage is used as carbon source

Treatability of digested piggery/poultry manure by anammox bacteria

The liquid fraction of digested material is rich in ammonium and may require nitrogen removal. The aim of this research was to evaluate the applicability of the anammox process for the biological N removal from a supernatant coming from the anaerobic digestion of a mixture of piggery manure, poultry manure, and of agro-wastes. The supernatant was pre-treated in a partial nitritation pilot-scale reactor located at the farm. A batch procedure for testing the short term effect of high-strength wastewaters on anammox activity is presented. The anammox process was successfully applied for the first time to undiluted digestate, and the average N removal efficiency achieved during 350 days of experimentation in a SBR lab-scale reactor was 91%

Phosphorus recovery from a pilot-scale grate furnace: influencing factors beyond wet chemical leaching conditions

Phosphorus is a non-renewable resource going to exhaustion in the future. Sewage sludge ash is a promising secondary raw material due to its high phosphorus content. In this work, the distribution of 19 elements in bottom and cyclone ashes from pilot-scale grate furnace have been monitored to determine the suitability for the phosphorus acid extraction. Moreover, the influence of some parameters beyond wet chemical leaching conditions were investigated. Experimental results showed that bottom ash presented lower contamination in comparison to cyclone ash and low co-dissolution of heavy metals (especially Cr, Pb and Ni), while high phosphorus extraction efficiencies (76-86%) were achieved. High Al content in the bottom ash (9.4%) negatively affected the phosphorus extraction efficiency as well as loss on ignition, while the particle size reduction was necessary for ensuring a suitable contact surface. The typology of precipitating agents did not strongly affect the phosphorus precipitation, while pH was the key parameter. At pH 3.5-5, phosphorus precipitation efficiencies higher than 90% were achieved, with a mean phosphorus content in the recovered material equal to 16-17%, comparable to commercial fertilizers. Instead, the co-precipitation of Fe and Al had a detrimental effect on the recovered material, indicating the need for additional treatments

LTE transmission exploiting pulse width modulation in fibre optic links

Recently it has been demonstrated that pulse width modulation (PWM) can represent a viable solution for the analog optical fronthaul alternative to standard radio over fibre, which still avoids the bandwidth expansion of the digital fronthaul. The PWM encodes the analog samples at the transmitter onto the duration of the on/off keyed optical signal, splitting the sampling and quantization of the radio signal between remote radio units (RRUs) and baseband units (BBUs). In particular in this contribution we demonstrate the capabilities of optical PWM for the transport of LTE signals to support the centralized access network (C-RAN) fronthaul in fibre optic link up to 10-km of standard single mode fibre. The generation and analysis of the radio signals is provided by software modules compliant with the LTE standard which allowed to analyse performance results for the different LTE carriers, channels and services. The PWM optical signal connecting RRUs to BBUs is generated by either directly modulating a DFB laser or an externally seeded reflective semiconductor optical amplifier (RSOA). Both devices could be exploited inside a wavelength division multiplexed passive optical network (WDM PON) architecture where the various RRU-to-BBU links are pooled through virtual point-to-point connections at different wavelengths

Giant Aneurysm of the Extracranial Carotid Artery: Case Report

AbstractWe report a case of giant extracranial carotid aneurysm treated by carotid aneurysmectomy. A 70-year-old female was referred with a palpable swelling on left lateral region of the neck, associated with dizziness and dysarthria. Spiral-CT scan showed a 5-cm aneurysm of the internal carotid artery (ICA), kinking of ICA and increased flow in the right vertebral artery. Angiography showed, a fusiform ICA aneurysm, with lengthening and tortuosity of intracranial vessels. An aneurysmectomy was performed with end-to-end repair of ICA. The patient was discharged on the 12 post-operative day. Twelve months after the operation, the patient showed a complete recovery from the neurological deficit and patency of ICA. We recommend surgical treatment in order to avoid rupture, thromboembolism and cerebrovascular insufficiency

ELECTRO-OSMOTIC DEWATERING OF SEWAGE SLUDGE: PRELIMINARY RESULTS

About half of the organic pollution load treated by the activated sludge process is oxidised and converted into water and carbon dioxide, while the remaining is converted into biomass, called “excess biological sludge” or “waste sludge”. At present, this technique is the cheapest way to remove colloidal and soluble organic pollutants from sewage, but it produces a huge amount of liquid waste sludge, with a dry solid (DS) content of less than 2%, rich in organic substances, mostly biodegradable. Therefore, it needs further processes to reduce its volume, by reducing its water content, and to reduce its polluting potential, due to its high content of biodegradable organic matter. However, sludge produced by Wastewater Treatment Plants (WWTPs) usually has a poor dewaterability. Industrially, mechanical dewatering is the method employed to increase the dry solids (DS) of sewage sludge. The aim of dewatering is the decrease of transport and disposal costs, but the efficiency of the mechanical dehydration methods is low. Electro-osmosis could be a suitable technique to reduce water content of the final sludge by the application of an electric field. Studies about electro-dewatering reported that the DS could increase to values around 40-45%, with respect to 25-30% obtained by mechanical methods, such as centrifuge, filter press and belt press. Aim Here, we investigated the parameters affecting pressure-driven electro-dewatering, with a static and a dynamic device, starting from types of sludge mechanically pre-dehydrated. We focused on the optimization of operating conditions to achieve the best results in terms of solids percentage at the minimum energy consumption. Methods Experiments have been performed by means of a lab-scale device able to produce both a mechanical pressure and an electric field. The use of both these systems could be efficient to increase the amount of dry solids in the final sludge. This device, as illustrated in Figure 1, consists of: • Cylindrical glass vessel (h=176 mm, Ø=80 mm) • Cooling water-jacket • Compressed air system (1-4.5 bar) • Double effect cylinder (200 mm stroke) SMC-CP96 (piston) • DC power supply (30 V-5 A) • Anode: DSA Ti (MMO), fixed to the piston • Cathode: stainless steel mesh (AISI 304) • Cloth: PTT (polytrimethyleneterephthalate) Figure 1-Equipment schematic of electro-dewatering device. Main Results The applied voltage has been set at 10 V, 15 V and 20 V and pressures at 3 bar. The results confirmed values of final DS around 40%. Initial DS and sludge conductivity, together with the applied electric field, are the key factors of electro-osmosis tests. The rotating piston highlighted that a mixing of sludge during the potential application could slightly increase the sludge conductivity, but cakes must be kept under 1.5 cm of thickness in order to achieve a good dewatering. In conclusion, in this paper we assess the feasibility of the electro-osmosis dewatering. It is a promising technique to remove water from sewage sludge, since it is able to increase DS of 15% on average with respect industrial mechanical dewatering. Moreover, this work proved that the treatment of a high DS cake is more difficult than a non-dewatered sludge due to a lower conductivity during the process