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

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

Influence of sludge characteristics on pressure-driven electro-dewatering of stabilized sewage sludge

The feasibility of the pressure-driven electro-dewatering (EDW) on aerobically and anaerobically stabilised sludge samples, taken from four different wastewater treatment plants around the metropolitan area of Milan (Italy), has been assessed. First, sewage sludges were characterized by measuring DS content, VS/DS ratio, pH, conductivity, zeta potential and capillary suction time (CST) of the liquid fraction. Then, after a preliminary centrifugation of the sludge samples in the laboratory, pressure-driven EDW tests have been performed in a lab-scale device, under the application of 300 kPa of pressure and an applied voltage of 15 V. The DS content increased up to 18.4-31.1%, (with an increase of 8.6% to 23.0% from the initial DS value) depending on the characteristics of the sludge samples and the polymer dosage. If compared with EDW tests, the increase due to the sole effect of pressure ranged from 3 to 10% and strictly depended on polymer dosage. The characteristics of sludge that affect the increase of the DS content were investigated during both the pressure-driven stage and the EDW stage. Polyelectrolyte addition (4 and 8 g/kgDS) mainly affected the pressure-driven phase of the tests. However, the VS/DS ratio was the main factor affecting the pressure-driven stage on the unconditioned aerobically stabilised samples. CST values could also reliably predict the efficiency of this stage during experiments

Diferencias estacionales entre tropopausas térmicas calculadas usando perfiles verticales de temperatura a partir de niveles significativos y estándar de radiosondeos para la red aerológica de Sudamérica

Se llevó a cabo un estudio de diferencias entre dos tropopausas térmicas sobre 59 estaciones aerológicas de Sudamérica. La tropopausa térmica primigenia, llamada lapse rate tropopause (LRT) y obtenida de perfiles verticales de temperatura en niveles significativos incluidos en los radiosondeos siguiendo la definición de la Organización Meteorológica Mundial (World Meteorological Organization, WMO), fue comparada con la tropopausa estimada de los niveles estándar (LRTM) con un algoritmo que está de acuerdo con la definición de la WMO. El período de estudio comprende enero 1973‒diciembre 2019. Las comparaciones entre la LRT y la LRTM se llevaron a cabo de manera estacional para presión, altura y temperatura. Los resultados fueron organizados en bandas latitudinales de 5º de ancho. Por bandas zonales la LRTM está, en promedio, por debajo o por encima de la LRT dependiendo de la banda, y en general ambas tropopausas son estadísticamente distintas. Con el objetivo de estimar si existe una relación entre ellas se calculó el coeficiente de correlación de Spearman entre las mismas variables de LRTM y LRT, los cuales resultaron positivos por lo que las variables correlacionadas pueden vincularse a través de funciones monótonas crecientes. Se escogió una función lineal y las pendientes y ordenadas al origen fueron obtenidas para cada banda de latitud. Las variables de la LRTM tomadas como predictores permiten así conocer las correspondientes a la LRT estimada (LRT*). La discrepancia entre LRT* y LRT fueron cuantificadas con el error cuadrático medio, cuya maximización tiene lugar en la región de influencia del jet subtropical.An analysis on the differences between two thermal tropopauses at 59 South American upper-air stations was carried out. The original lapse rate tropopause (LRT) derived from significant-level radiosonde temperature profiles following the World Meteorological Organization (WMO) definition was compared with the tropopause estimated from radiosonde mandatory levels (LRTM) with a WMO-compliant algorithm. The study period encompasses January 1973–December 2019. The comparisons between the LRT and the LRTM were performed on a seasonal basis for pressure, height and temperature and the results were organized into latitudinal bands of 5° width. On average, the LRTM locates below or above the LRT, depending on the band considered, and in general the both tropopauses are statistically different. The Spearman’s correlation coefficients between the same LRTM and LRT variables were calculated in order to estimate whether there exists a relation between them. The coefficients resulted positive so the correlated variables can be related through monotonic increasing functions. A linear function was selected and the slopes and the intercepts for this relation were provided at each latitudinal band. Taking the LRTM variables as predictors enables the obtention of the corresponding LRT variables. The matching between the LRT and the LRTM-derived LRT was addressed through root mean squares, whose maximization occurs in the subtropical jet’s region of influence.Asociación Argentina de Geofísicos y Geodesta

Pressure-driven electro-dewatering applied for sludge: Economic & environmental life cycle assessment

Dewatering plays an important role in sludge minimization and reuse. In this study, pressure-driven electro-dewatering (EDW) was investigated using a lab device and various operating parameters were optimised. Furthermore, the EDW system’s economic and environmental performances were evaluated using Life Cycle Assessment. These results can be interesting for the stakeholders within the WWTP industry who are considering upgrading from the conventional mechanical dewatering to the EDW

La disidratazione elettro-assistita dei fanghi: influenza del dosaggio di polielettrolita e dei parametri operativi

In questa ricerca è stato studiato a scala di laboratorio il processo di disidratazione elettroassistita (Electro Dewatering, EDW) dei fanghi di depurazione. I campioni di fango, stabilizzati aerobicamente o anaerobicamente, sono stati prelevati da quattro impianti di depurazione intorno all’area metropolitana di Milano. Per le prove EDW sono state utilizzate due tipologie di campioni: (i) fango liquido ispessito (LI), prelevato prima del condizionamento, e (ii) fango disidratato meccanicamente (DM). Le prove EDW su fango LI hanno consentito la disidratazione dei campioni fino ad un contenuto di solido secco (SS) del 18,4-31,1%, corrispondente a un aumento compreso tra il 2,0% e il 12,7% rispetto alla disidratazione meccanica convenzionale utilizzata nei quattro impianti. In aggiunta all’aumento del tenore di secco finale, il processo ha consentito una riduzione del dosaggio di polielettrolita rispetto a quello utilizzato negli impianti. Nelle prove su fango DM si sono raggiunti valori di SS compresi tra 30,1-41,0%. Si è dimostrato che le condizioni operative, come il potenziale elettrico applicato e lo spessore iniziale del fango trattato nel dispositivo, hanno notevole influenza sull’efficienza del processo EDW, sia su fango LI, sia su fango DM. Infine, il costo del polielettrolita, il consumo di energia elettrica e il costo dello smaltimento dei fanghi associati al processo EDW sono stati confrontati con la disidratazione convenzionale utilizzata nei quattro impianti. Si è constatato che l’utilizzo del processo EDW consentirebbe di ridurre i costi di gestione dei fanghi fino al 37% all’anno per fango LI e fino al 50% per fango DM.In this research the process of electrodewatering (EDW) of sewage sludge has been studied. The sludge samples, aerobically or anaerobically stabilized, have been taken from four wastewater treatment plants (WWTPs) around the metropolitan area of Milan. For the EDW tests two types of samples have been used: (i) thickened sludge (LI), taken before conditioning and (ii) mechanically dewatered sludge (DM). The EDW tests on LI sludge allowed the dewatering of the samples up to a dry solid content (SS) of 18.4-31.1%, equal to an increase of 2.0-12.7% compared to the conventional mechanical dewatering treatments used in the four WWTPs. Together with the final DS increase, the EDW process allowed to reduce the polyelectrolyte dosage with respect to that used in the WWTPs. The tests on DM sludge achieved DS values between 30.1-41.0%. It has been shown that the operating conditions, such as electrical potential and cake thickness, have considerable influence on the efficiency of the EDW process, both on LI and DM sludge. The cost of the polyelectrolyte, the consumption of electric energy and the cost of sludge disposal associated to the EDW process have been compared to conventional dewatering used in the four WWTPs. It was found that the use of the EDW process would reduce sludge management costs by up to 37% per year for LI samples and up to 50% for DM samples

Early 21st century cyclone climatology: a 3D perspective. Basic characterization

Extratropical cyclones are a relevant feature in the climate at middle and high latitudes. Despite their relevance, most of studies typically focus on cyclones identified at a single atmospheric level and on events close to the surface. This paper provides a new perspective on the Southern Hemisphere cyclone events based on the multilevel cyclone tracking algorithm STACKER. The algorithm, using relative vorticity, detects the raw tracks at single levels and objectively combine them to provide the 3D events and their evolutionary timeline. As result, 3D cyclone climatology, based on ECMWF Reanalysis ERA-I data from 12 pressure levels in the troposphere and lowermost stratosphere is presented. To the best of our knowledge this is the first analysis carried out throughout the troposphere and the lowermost extratropical/subpolar stratosphere in order to give a comprehensive picture of the cyclone events as physical entities throughout their lifetime. Cyclone properties analysed are track densities, translational velocity, vorticity and lifetimes. For the subtropical and extrattropical SH, results support many previous ideas about cyclone characteristics, but new insights are also obtained. A total of 58231 multilevel cyclone events lasting at least 2 days were detected, with vertical structures spanning two or more levels. This means an average of 303 cyclone events of all types per month, between 2001 and 2017, disregarding seasonality. Results shows that the lowermost level of cyclones are most frequently detected at 925 and 700 hPa, Considering that cyclonic systems can be grouped into families, results per month on average, show that shallow systems are the most frequent events with approximately 248 systems detected, followed by 43 intermediates and 11 deep events. Shallow and deep systems have a large percentage of events with genesis at 925 and 700hPa. Density statistics show that shallow events are present at all latitude ranges mostly poleward 30ºS with high and medium intensities, while intermediate ones are mostly restricted to mid-latitudes and deep events are mostly confined to sub-polar and polar latitudes. Cyclones over Antarctica seems to be mostly intermediates and deeps, with longer lifetimes and lower velocities

Wine tourist valuation of information sources: the role of prior travel

Purpose: The purpose of this study is to examine winery visitors’ use of information sources in making decisions regarding the choice of wineries to visit. Enrichment theory is used as a framework for determining how previous experience influences the decision on how much and what type of information individuals will use when planning a trip using wine tourism as the context for the research. Design/methodology/approach: A visitor study was conducted at 23 wineries in the US Southeast. Data were collected from winery visitors using a structured self-administered questionnaire. Findings: Results from 832 consumers indicate that an individual’s previous travel systematically influences the number and type of information sources that they will seek out when making future consumer decisions. Findings confirmed the hypothesized expectations about wine tourist information search behavior and help to partially explain the nature of bounded rationality in the case of tourists’ winery visit decisions. Research limitations/implications: Because the study focused only on winery visitors in the US Southeast, the research results may lack generalizability. Practical implications: These findings can assist winery owners and destinations with wineries in their promotional efforts. Of major importance is the finding that increases in experiential knowledge from prior travel are monotonically associated with increases in the number of information sources marked to be valuable in selecting a winery. The influence of experience is particularly dramatic in that the mean number of information sources marked to be valuable moves from a low of 2.5 to a high of 10.0 out of 16 as travel experience increases. Originality/value: The study contributed significant and useful findings that advance the application of enrichment theory to wine tourism. Enrichment theory does not currently differentiate between types of knowledge that enrich a consumer’s ability to more easily encode and use new information. The current study confirms that experiential knowledge is an important knowledge construct in models of bounded rationality