CHEMICAL ENGINNERING

A strategy for adaptive control and energetic optimization of aerobic fermentors was implemented, with both air flow and agitation speed as manipulated variables. This strategy is separable in its components: control, optimization, estimation. We optimized parameter’s estimation (from the usual KLa correlation) using sinusoidal excitation of air flow and agitation speed. We have implemented parameter’s estimation trough recursive least squares algorithm with forgetting factor. We carried separate essays on control, optimization and estimation algorithms. We carried our essays using an original computational simulation environment, with noise and delay generating facilities for data sampling and filtering.

Our results show the convergence and robustness of the estimation algorithm used, improved with use of both forgetting factor and KLa dead-band facilities. Control algorithm used in our work compares favorably with PID using the integrated area criteria for deviation between oxygen molarity and critical molarity (set point). Optimization algorithm clearly reduces energetic consumption, respecting critical molarity. Integration of control, optimization and adaptive algorithms was implemented, but future work is needed for stability. Methods were defined and implemented for stability improvement. We have implemented data acquisition and computer manipulation of air flow and agitation speed for actual fermentors.

Environmental concerns, generated by the use of fossil fuels, has made countries look for energy-efficient alternatives in order to supply the energy demand in a sustainable way. In this context, wastes generated by agricultural and industrial sectors, which generally do not have economic value, can represent an important energy source. The recovery of these residues can be performed through a thermochemical conversion process such as pyrolysis. The pyrolysis products are gas, liquid and/or solid compounds that it can be used as an energy source or Raw material for chemical industry. However, to obtain a higher efficiency of pyrolytic conversion reactors, it is necessary to know the physicochemical characteristics, the thermal behavior and the kinetic parameters of the chemical reactions. Thus, the main aim of this work is to evaluate the kinetic parameters (activation energy, pre-exponential factor and reaction model) of the pyrolysis process of sugarcane bagasse, besides observing the physicochemical properties and thermal behavior of this residue. The physicochemical characterization was performed through proximate analysis, ultimate analysis, high heating value calculation, X-ray fluorescence (XRF) and Fourier transform infrared spectroscopy (FTIR). The thermogravimetric behavior of the sugarcane bagasse pyrolysis process was observed through thermogravimetric analysis based on variation of parameters of mass, particle diameter, chemical composition and atmosphere. For kinetic parameters evaluate of sugarcane bagasse pyrolysis were used weight loss data at five different heating rates (2, 5, 10, 20 and 30 ºC min-1) under gas flow of nitrogen (99.997%), where the isoconversional methods of Friedman Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) were initially applied to obtain activation energy values. The pre-exponential factor and reaction model were obtained through the effect of compensation and masterplot, respectively. From the results of the physicochemical characteristics, it can be observed that the sugarcane bagasse presents a satisfactory applicability at pyrolytic system, due to its low moisture and ash content, and with a significant potassium composition between the inorganic compounds. Different thermal behavior could be observed by variation of parameters of mass, particle diameter, chemical composition and atmosphere. The kinetic parameters evaluated from the isoconversional methods showed that the KAS method presents better application, among the three methods used, due to the results of the kinetic parameters present a smaller difference between experimental results.

This study considers the kinetics of snail shells demineralization process using acetic acid. It was washed, sundried then ground into four different particle sizes. The ranges of particle sizes are 6.3-4.75 mm, 4.75-2 mm, 2-1 mm, and 600-300 μm. The shells were first deproteinized with sodium hydroxide solution thereafter they were demineralized using 1.2 M acetic acid solution. Kinetics of demineralization of the snail shells was performed by XRF analysis of the chitin produced at 5, 10, 15, 20, 25, 30, and 35 min. The kinetic results show that mechanism of chitin formation from snail shell occurs through the chemical reaction controlled (CRC) model of the shrinking core model for particle sizes between 6.3-4.75 mm, 4.75-2 mm, and 2-1 mm particle sizes while Fluid Film Diffusion (FFD) model was observed for the smaller range of 600-300 μm particle sizes. The surface morphology and the FTIR analysis of the synthesized chitin were typical of those obtained for earlier studies.

Most of the wastewater treatment systems in small rural communities of the Cova da Beira region (Portugal) consist of constructed wetlands (CW) with horizontal subsurface flow (HSSF). It is believed that those systems allow the compliance of discharge standards as well as the production of final effluents with suitability for reuse. Results obtained in a nine-month campaign in an HSSF bed pointed out that COD and TSS removal were lower than expected. A discrete sampling also showed that removal of TC, FC and HE was not enough to fulfill international irrigation goals. However, the bed had a very good response to variation of incoming nitrogen loads presenting high removal of nitrogen forms. A good correlation between mass load and mass removal rate was observed for BOD5, COD, TN, NH4-N, TP and TSS, which shows a satisfactory response of the bed to the variable incoming loads. The entrance of excessive loads of organic matter and solids contributed for the decrease of the effective volume for pollutant uptake and therefore, may have negatively influenced the treatment capability. Primary treatment should be improved in order to decrease the variation of incoming organic and solid loads and to improve the removal of COD, solids and pathogenic. The final effluent presented good physical–chemical quality to be reused for irrigation, which is the most likely application in the area.

Similarly to most of Mediterranean EU member states, Portugal regularly experience severe water supply and demand imbalances, particularly in the summer months.
Tourism is a very important economic activity in Portugal and is pushing water demand particularly in regions suffering occasional water deficit, like the southern half part of Portugal mainland. Golf courses are an important tourist factor contributing to water demand rising. A number of golf courses are installed in tourist areas and need high amount of water for irrigation.
Water reuse is a very important management strategy in situations of water scarcity. Portugal badly needs to include treated wastewater as a dependable resource in the nation water resources management. Sustainable water reuse requires technical guidelines to ensure the public health and environmental protection but the economic sustainability is crucial for the success of water reuse projects as a strategy of water conservation. This paper briefly presents Portuguese guidelines on water reuse focusing mainly on the aspects to be taken into account in the assessment of the economic viability of water reuse projects, such as the model of tariff structure, the costs to internalise, share of costs among users and recovery of investment costs.

A submerged biologicalaeratedfilter (BAF) partiallyaerated was used to study the removal of lowconcentrations of ammonia nitrogen (0.3 g N/m3 to 30.5 g N/m3) typically found in nutrient enriched river and lake waters, and treated effluents. Four series of experiments were performed with a synthetic wastewater at ammonia loading rates between 6 g N/m3 d and 903 g N/m3 d and C/N ratios from 2 to 20. The results showed that ammonia removal rates reached higher values (172 g N/m3 d to 564 g N/m3 d) for C/N = 2 and lower values (13.6 g N/m3 d to 34.6 g N/m3 d) for C/N = 20. Between 50% and 70% of the ammonia was removed in the upper section of the BAF, where the dissolved oxygen (DO) concentration was over 2.1 g O2/m3 and the biofilm depth ranged from 0.4 to 0.6 mm. At the bottom section of the reactor, simultaneous removal of ammonia and nitrate was observed at the DO concentrations in the range 0.4 g O2/m3 to 0.8 g O2/m3. There was no removal of ammonia nitrogen for loads below 15 g N/m3.d. The results indicate that the removal of nitrogen in partiallyaerated BAF may not only be explained by the conventional mechanisms of nitrification/denitrification.

We present a numerical solution for the dead zone model which describes the solute transport in a subsurface and horizontal flow constructed wetland. This model is a system of two mass balance equations for two conceptual areas: the main channel and the storage zone. We use finite difference schemes to determine the numerical solution of the system and we study its convergence by presenting properties related to the stability and accuracy of the schemes. Concerning the experimental results, the magnitude of the longitudinal dispersion and the extension of dead volumes is estimated for clean conditions and after a certain operating period under organic loading conditions. The results showed a considerable amount of longitudinal dispersion through the bed, which was very strong near the feeding point, indicating the occurrence of mixing and significant presence of dead zones and short-circuiting.