Solvent extraction of phosphoric acid

This work investigated the purification of phosphoric acid using a suitable organic solvent, followed by re-extraction of the acid from the solvent using water. The work consisted of practical batch and continuous studies and the economics and design of a full scale plant, based on the experimental data. A comprehensive literature survey on the purification of wet process phosphoric acid by organic solvents is presented and the literature describing the design and operation of mixer-settlers has also been reviewed. In batch studies, the equilibrium and distribution curves for the systems water-phosphoric acid-solvent for Benzaldehyde, Cyclohexanol and Methylisobutylketone (MIBK) were determined together with hydrodynamic characteristics for both pure and impure systems. The settling time increased with acid concentration, but power input had no effect. Drop size was found to reduce with acid concentration and power input. For the continuous studies a novel horizontal mixer~settler cascade was designed, constructed and operated using pure and impure acid with MIBK as the solvent. The cascade incorporates three air turbine agitated, cylindrical 900 ml mixers, and three cylindrical 200 ml settlers with air-lift solvent interstage transfer. Mean drop size in the fully baffled mixer was correlated. Drop size distributions were log-normal and size decreased with acid concentration and power input and increased with dispersed phase hold-up. Phase inversion studies showed that the width of the ambivalent region depended upon rotor speed, hold-up and acid concentration. Settler characteristics were investigated by measuring wedge length. Distribution coefficients of impurities and acid were also investigated. The following optimum extraction conditions were found: initial acid concentration 63%, phase ratio of solvent to acid 1:1 (v/v), impeller speed recommended 900 r.p.m. In the washing step the maximum phase ratio of solvent to water was 8:1 (v/v). Work on phosphoric acid concentration involved constructing distillation equipment consisting of a 10& spherical still. A 100 T/d scale detailed process design including capital cost, operating cost and profitability was also completed. A profit model for phosphoric acid extraction was developed and maximised. Recommendations are made for both the application of the results to a practical design and for extensions of the study.

Modelling of wastewater treatment plants:how far shall we go with sophisticated modelling tools?

Several levels of complexity are available for modelling of wastewater treatment plants. Modelling local effects rely on computational fluid dynamics (CFD) approaches whereas activated sludge models (ASM) represent the global methodology. By applying both modelling approaches to pilot plant and full scale systems, this paper evaluates the value of each method and especially their potential combination. Model structure identification for ASM is discussed based on a full-scale closed loop oxidation ditch modelling. It is illustrated how and for what circumstances information obtained via CFD (computational fluid dynamics) analysis, residence time distribution (RTD) and other experimental means can be used. Furthermore, CFD analysis of the multiphase flow mechanisms is employed to obtain a correct description of the oxygenation capacity of the system studied, including an easy implementation of this information in the classical ASM modelling (e.g. oxygen transfer). The combination of CFD and activated sludge modelling of wastewater treatment processes is applied to three reactor configurations, a perfectly mixed reactor, a pilot scale activated sludge basin (ASB) and a real scale ASB. The application of the biological models to the CFD model is validated against experimentation for the pilot scale ASB and against a classical global ASM model response. A first step in the evaluation of the potential of the combined CFD-ASM model is performed using a full scale oxidation ditch system as testing scenario.

Caracterización de bacterias filamentosas en el funcionamiento de un reactor aerobio de la planta de tratamiento de aguas residuales de origen cervecero

La actividad industrial y el desarrollo material y económico, han traído como consecuencia la contaminación del aire, agua y el suelo; lo que ocasiona modificaciones físicas químicas y biológicas que han producido un deterioro en la calidad del agua, dando como resultado problemas de contaminación que afectan tanto la productividad de los sistemas como la salud humana. A las aguas de composición variada provenientes de uso municipal, industrial, comercial, agrícola, pecuario, o de cualquier otra índole, ya sea privada o pública que han sufrido una degradación o alteración en su calidad original se le conoce como agua residual. Este trabajo tiene como objetivo “Caracterizar las bacterias filamentosas en el funcionamiento de un reactor aerobio de la planta de tratamiento de aguas residuales de origen cervecero” para ello se estudió durante varios meses los parámetros físico-químicos y biológicos para poder así controlar de las bacterias filamentosas y así evitar en un futuro problemas de operación o poder controlar su crecimiento y por ende, ecológicos dentro del sistema de lodos activados. La identificación se realizó tomando muestras en el reactor aerobio y realizándole la tinción de Gram para posteriormente ser vistos en un microscopio de una resolución de 100x; luego se caracterizaron las bacterias juntas con los parámetros de operación del tanque de lodos por muestra y los resultados encontrados fueron la presencia de filamentos Microtrix Parvicella, Tipo 021N, y Sp1 (llamada así por no ser identificada, ni encontrada en la literatura), esta es una nueva especie encontrada, ya que es propia de este reactor aerobio y crecen principalmente en aguas cerveceras y por deficiencia de nutrientes en el sistema. Este trabajo nos permitió conocer la dinámica que existe entre los parámetros fisicoquímicos y los microorganismos que se encuentran en un biorreactor Aerobio. Esto nos llevó a comprender mejor el funcionamiento de estos sistemas dentro de plantas de aguas residuales de tipo industrial. ABSTRACT Industrial activity and the physical and economic development have resulted in contamination of air, water and soil, causing physical chemical and biological changes that have produced deterioration in water quality, resulting in pollution problems affects the productivity of the systems and human health. A varied composition waters from municipal, industrial, commercial, agricultural, livestock, or any other use, whether private or public who have suffered a degradation or alteration in their original quality is known as residual water. This work aims to "characterize filamentous bacteria in the operation of an aerobic reactor plant wastewater treatment brewer origin" for this physicochemical and biological parameters were studied for several months to thereby control bacteria stringy and avoid future problems in operation or to control their growth and thus ecological This work aims to "characterize filamentous bacteria in the operation of an aerobic reactor plant wastewater treatment brewer origin" for this physicochemical and biological parameters were studied for several months to thereby control bacteria stringy and avoid future problems in operation or to control their growth and thus ecological within the activated sludge system. This work allowed us to understand the dynamics between physicochemical parameters and microorganisms found in an aerobic bioreactor. This led us to better understand the operation of these systems within plants industrial wastewater.

Waste recovery into activated carbon for water purification from heavy metals

Dissertação apresentada para obtenção do Grau de Doutor em Engenharia Química Pela Universidade Nova de Lisboa,Faculdade de Ciências e Tecn

Feasibility of ASH DEC‐ process in treating sewage sludge and manure ash in Finland

In Finland the thermal treatment of sewage sludge has been moderate in 21th century. The reason has been the high moisture content of sludge. During 2005-2008, 97-99% of sewage sludge was utilized in landscaping and agriculture. However agricultural use has been during 2005-2007 less than 3 %. The aim of national waste management plan is that by 2016 100% of sludge is used either as soil amendment or energy. The most popular utilization method for manure is spreading it on arable land. The dry manures such as poultry manure and horse manure could also be used in incineration. The ashes could be used as fertilizers and while it is not suitable as a starter fertilizer, it is suitable in maintaining P levels in the soil. One of the main drivers for more efficient nutrient management is the eutrophication in lakes and the Baltic See. ASH DEC process can be used in concentrating phosphorus rich ashes while separating the heavy metals that could be included. ASH DEC process uses thermochemical treatment to produce renewable phosphate for fertilizer production. The process includes mixing of ashes and chlorine donors and subsequent treatment in rotary kiln for 20 min in temperature of 900 – 1 050 oC. The heavy metals evaporate and P-rich product is obtained. The toxic substances are retained in air pollution control system in form of mixed metal hydroxides. The aim of conducting this study is to estimate the potential of ASH DEC process in treating phosphorus rich ashes in Finland. The masses considered in are sewage sludge, dry manure from horses, and poultry and liquid pig manure. To date the usual treatment method for sewage sludge in Finland is composting or anaerobic digestion. Part of the amount of produced sewage sludge (800 kt/a fresh mass and 160 kt/a TS) could also be incinerated and the residual ashes used in ASH DEC process. Incinerating only manure can be economically difficult to manage because the incineration of manure is in Finland considered as waste incineration. Getting a permit for waste incineration is difficult and also small scale waste incineration is too expensive. The manure could act as an additional feedstock in counties with high density of animal husbandry where the land area might not be enough for spreading of manure. Now when the manure acts as a supplementary feedstock beside sludge, the ash can’t be used directly as fertilizer. Then it could be used in ASH DEC process. The perquisite is that the manure producers could pay for the incineration, which might prove problematic.

A sewage sludge co-composting process using respirometric monitoring method in hermetic rotary reactor

This paper has the objective of monitoring the biological activity of composting process of sewage sludge, sugarcane bagasse and ground coffee in a hermetic rotary reactor using the respirometric method in laboratory scale, in order to obtain parameters and system design for large scale projects. Another particularity of this study is the use of a hermetic reactor with gas purging cycles. Purging was performed when the percentage of oxygen reached less than 5%, thus eliminating the gaseous mixture (with elevated CO2 ratio) and the introduction of environmental air with around 21% of O2, successively until the compost was stabilized. The average purge intervals obtained were 29 h and 2 min with reactor rotation frequency of 15 min. The time of the compost stabilization was optimized in 60% if compared to the 90 days in the traditional method. The results obtained can be used to design the process in industrial scale using a simple O2 gas analyzer.

Carbon dioxide adsorption in chemically activated carbon from sewage sludge

In this work, sewage sludge was used as precursor in the production of activated carbon by means of chemical activation with KOH and NaOH. The sludge-based activated carbons were investigated for their gaseous adsorption characteristics using CO2 as adsorbate. Although both chemicals were effective in the development of the adsorption capacity, the best results were obtained with solid NaOH (SBAT16). Adsorption results were modeled according to the Langmuir and Freundlich models, with resulting CO2 adsorption capacities about 56 mg/g. The SBAT16 was characterized for its surface and pore characteristics using continuous volumetric nitrogen gas adsorption and mercury porosimetry. The results informed about the mesoporous character of the SBAT16 (average pore diameter of 56.5 Å). The Brunauer-Emmett-Teller (BET) surface area of the SBAT16 was low (179 m2/g) in comparison with a commercial activated carbon (Airpel 10; 1020 m2/g) and was mainly composed of mesopores and macropores. On the other hand, the SBAT16 adsorption capacity was higher than that of Airpel 10, which can be explained by the formation of basic surface sites in the SBAT16 where CO2 experienced chemisorption. According to these results, it can be concluded that the use of sewage-sludge-based activated carbons is a promising option for the capture of CO2. Implications: Adsorption methods are one of the current ways to reduce CO2 emissions. Taking this into account, sewage-sludge-based activated carbons were produced to study their CO2 adsorption capacity. Specifically, chemical activation with KOH and NaOH of previously pyrolyzed sewage sludge was carried out. The results obtained show that even with a low BET surface area, the adsorption capacity of these materials was comparable to that of a commercial activated carbon. As a consequence, the use of sewage-sludge-based activated carbons is a promising option for the capture of CO2 and an interesting application for this waste.

Composting sewage sludge by high-rate suction aeration techniques : the process as conducted at Bangor, Maine, and some guides of general applicability /

Mode of access: Internet.

Life Cycle Assessment (LCA) Applied to the Design of an Innovative Drying Process for Sewage Sludge

Most adverse environmental impacts result from design decisions made long before manufacturing or usage. In order to prevent this situation, several authors have proposed the application of life cycle assessment (LCA) at the very first phases of the design of a process, a product or a service. The study in this paper presents an innovative thermal drying process for sewage sludge called fry-drying, in which dewatered sludge is directly contacted in the dryer with hot recycled cooking oils (RCO) as the heat medium. Considering the practical difficulties for the disposal of these two wastes, fry-drying presents a potentially convenient method for their combined elimination by incineration of the final fry-dried sludge. An analytical comparison between a conventional drying process and the new proposed fry-drying process is reported, with reference to some environmental impact categories. The results of this study, applied at the earliest stages of the design of the process, assist evaluation of the feasibility of such system compared to a current disposal process for the drying and incineration of sewage sludge.

Yield and nutrition of sunflower fertilized with sewage sludge stabilized by different processes

The different methods of sewage sludge stabilization modify their physical chemical and biological properties, altering its efficiency when applied in agriculture. The objective of this study was to evaluate the nutrient levels in soil and the yield of sunflower fertilized with sewage sludge stabilized by different processes. The experiment was conducted in Cambisol, with the treatments: control (without fertilization), fertilization with sewage sludge solarized, composted, vermicomposted, limed and chemical fertilizer recommended for sunflower crop. The experimental design a randomized block with four replications. The different methods of sewage sludge treatment did not affect the yield; however, the application of sewage sludge, regardless the stabilization process adopted, was more effective than chemical fertilizer and the control treatment. Overall, fertilization with limed sewage sludge provided higher soil nutrients concentrations, while treatments with composted and vermicomposted sewage sludge showed higher levels of nutrients in the plant.

Optimization of the electrodialytic phosphorus recovery from sewage sludge ash

Phosphorus (P) is becoming a scarce element due to the decreasing availability of primary sources. Therefore, recover P from secondary sources, e.g. waste streams, have become extremely important. Sewage sludge ash (SSA) is a reliable secondary source of P. The use of SSAs as a direct fertilizer has very restricted legislation due to the presence of inorganic contaminants. Furthermore, the P present in SSAs is not in a plant-available form. The electrodialytic (ED) process is one of the methods under development to recover P and simultaneously remove heavy metals. The present work aimed to optimize the P recovery through a 2 compartment electrodialytic cell. The research was divided in three independent phases. In the first phase, ED experiments were carried out for two SSAs from different seasons, varying the duration of the ED process (2, 4, 6 and 9 days). During the ED treatment the SSA was suspended in distilled water in the anolyte, which was separated from the catholyte by a cation exchange membrane. From both ashes 90% of P was successfully extracted after 6 days of treatment. Regarding the heavy metals removal, one of the SSAs had a better removal than the other. Therefore, it was possible to conclude that SSAs from different seasons can be submitted to ED process under the same parameters. In the second phase, the two SSAs were exposed to humidity and air prior to ED, in order to carbonate them. Although this procedure was not successful, ED experiments were carried out varying the duration of the treatment (2 and 6 days) and the period of air exposure that SSAs were submitted to (7, 14 and 30 days). After 6 days of treatment and 30 days of air exposure, 90% of phosphorus was successfully extracted from both ashes. No differences were identified between carbonated and non-carbonated SSAs. Thus, SSAs that were exposed to the air and humidity, e.g. SSAs stored for 30 days in an open deposit, can be treated under the same parameters as the SSAs directly collected from the incineration process. In the third phase, ED experiments were carried out during 6 days varying the stirring time (0, 1, 2 and 4 h/day) in order to investigate if energy can be saved on the stirring process. After 6 days of treatment and 4 h/day stirring, 80% and 90% of P was successfully extracted from SSA-A and SSA-B, respectively. This value is very similar to the one obtained for 6 days of treatment stirring 24 h/day.

Electrodialytic recovery of phosphorus and organic contaminants removal from sewage sludge

Phosphorus is a macronutrient essential to life which comes from phosphate rock, a non-renewable resource. Sewage sludge from wastewater treatment plants (WWTP) is a secondary resource rich in phosphorus that can be valorized. However, organic compounds are detected in sewage sludge, due to its non-polar and hydrophobic character, being considered an environmental risk. The present dissertation aims to study the efficiency of the electrodialytic process (ED) when applied to sewage sludge aiming phosphorus recovery and organic contaminants removal. Four organic compounds were analyzed: 17α-ethynylestradiol (EE2), bisphenol A (BPA), caffeine (Caf) and oxybenzone (MBPh). The experiments took place in an ED cell with two compartments and an anion exchange membrane, with the sludge in the cathode compartment. The experiments were carried out for three days with spiked sewage sludge (six assays). One control experiment was done without current, three experiments were carried out applying a constant current of 50, 75, and 100 mA and two experiments were carried out applying sequential currents: 50 mA, 75 mA and 100 mA and the opposite (100-75-50 mA). A qualitative and quantitative analysis of microorganisms existing in the samples was also done. At the end, the pH increased in the sewage sludge favoring phosphorus recovery. In terms of phosphorus, the highest recovery was achieved in the experiment run with 100 mA, where 70.3±2.0% of total phosphorus was recovered in the electrolyte. Generally, compounds degradation was favored by the current. Caf and MBPh achieved degradation percentages of 96.2±0.2% and 84.8±1.3%, respectively, in 100 mA assay. EE2 (83.1±1.7%) and BPA (91.8±4.6%) degradations were favored by 50 mA current. A total of 35 taxa from four different groups were identified, totalizing between 81,600-273,000 individuals per gram of initial sludges. After ED, microbial community population decreased between 47-98%. Arcella gibbosa represented 61% of the total observed organisms and revealed to be more tolerant to medium changes.

Evaluation of sample processing methods for the polar contaminant analysis of sewage sludge using liquid chromatography - mass spectrometry (LC/MS)

Monitoring of sewage sludge has proved the presence of many polar anthropogenic pollutants since LC/MS techniques came into routine use. While advanced techniques may improve characterizations, flawed sample processing procedures, however, may disturb or disguise the presence and fate of many target compounds present in this type of complex matrix before analytical process starts. Freeze-drying or oven-drying, in combination with centrifugation or filtration as sample processing techniques were performed followed by visual pattern recognition of target compounds for assessment of pretreatment processes. The results shown that oven-drying affected the sludge characterization, while freeze-drying led to less analytical misinterpretations.