Sofia Mai

An integrated mathematical model for co-composting of agricultural solid wastes with industrial wastewater.

An integrated model for the composting process was developed. The structure of the model is such that it can be implemented in any mixture of different substrates, even in the case of co-composting of a solid waste with industrial wastewater. This paper presents a mathematical formulation of the physicochemical and biological principles that govern the composting process. The model of the co-composting ecosystem included mass transfer, heat transfer and biological processes. The biological processes included in the model were hydrolysis of particulate substrates, microbial growth and death. Two microbial populations (bacteria and fungi) were selected using Monod kinetics. Growth limiting functions of inhibitory factors, moisture and dissolved oxygen were added in the Monod kinetics. The bacteria were considered to utilise the easy biodegradable carbon hydrolysis product, fungi the difficult one, while both could degrade the carbon of wastewater. The mass balances of the most important nutrients, nitrogen and phosphorous, were also included in this approach. Model computer simulations provided results that fitted satisfactory the experimental data. Conclusively, the model could be a useful tool for the prediction of the co-composting process performance in the future and could be used to assist in the operation of co-composting plants.

Granulation mechanism of a UASB reactor supplemented with iron

The aim of this paper was to propose a granulation mechanism in order to interpret all the experimental observations that arose during experiments on two UASB reactors, where one was supplemented with ferrous iron at a dose of 0.01 g Fe(2+) per g COD feed. This supplementation with ferrous iron allowed COD removal of more than 98% at a loading rate of 9 g COD/L per day, which was 24% higher than for the reactor not receiving the ferrous iron. Moreover, in the Fe(2+)-dosed reactor, a higher increase of the granule diameter was observed. Indeed, the granule diameter in the Fe(2+)-dosed reactor at the end of the experiments was 56% greater than that of the control reactor. This mechanism describes the course of anaerobic granule growth. The formation of the inorganic precipitate of ferrous sulphide constitutes the inert nuclei around which the biomass is attached. This initiates the formation of new granules.

Electrochemical oxidation of two organophosphoric obsolete pesticide stocks

Organophosphoric pesticides are widely used for crop and fruit tree treatment, but their disposal causes serious environmental problems. Two commercial organophosphoric pesticides (Monocrotophos and Phosphamidon) were treated by an electrolysis system using Ti/Pt as anode and stainless steel 304 as cathode. A number of experiments were run in a laboratory scale pilot plant and the results are presented. For Monocrotophos, the achieved reduction was over 28%, while for Phosphamidon it was nearly 26%. Phosphamidon had a higher energy demand than Monocrotophos. The COD/BOD5 ratio was improved considerably after electrolysis for both pesticides examined. Therefore, electrochemical oxidation could be used as a pretreatment method for their detoxification.

Implementation of Fenton process on wastewater from a cheese-making factory

Abstract In this work, the performance of Fenton oxidation on whey, the high strength fraction of cheese-dairy wastewater, was studied. For this reason, factorial experimental design was used to study the main variables affecting the Fenton process, as well as their interactions. A 24 factorial design was performed in order to estimate the effects of the following parameters: the ratio FeSO4·7H2O/H2O2 (X 1), the hydraulic retention time (X 2), the pH (X 3), and the temperature (X4). The oxidation was carried out batch wise in an agitated, temperature- and pH-controlled glass reactor. At the end of the experiment, samples were taken from the effluent of the reactor and were analyzed in terms of COD, TOC, total Kjeldahl Nitrogen (TKN), total phosphorous, and fats and oils. The highest percentage of TOC efficiency measured was 33% in the experimental point (X 1, X 2, X 3, X 4) = (2/3, 1, 3.4, 20). Concentration of fats presented high reduction that reached 57%. Phosphorous removal was also high in all experi...

Influence of vegetation and gravel mesh on the tertiary treatment of wastewater from a cosmetics industry

To estimate the influence of gravel mesh (fine and coarse) and vegetation (Phragmites and Arundo) on the efficiency of a reed bed, a pilot plant was included after the wastewater treatment plant of a cosmetic industry treatment system according to a 22 factorial experimental design. The maximum biochemical oxygen demand (BOD5), chemical oxygen demand (COD) and total phosphorous (TP) reduction was observed in the reactor, where Phragmites and fine gravel were used. In the reactor with Phragmites and coarse gravel, the maximum total Kjeldahl nitrogen (TKN) and total suspended solids (TSS) reduction was observed. The maximum total solids reduction was measured in the reed bed, which was filled with Arundo and coarse gravel. Conclusively, the treatment of a cosmetic industrys wastewater by reed beds as a tertiary treatment method is quite effective.

Kinetics of Air Absorption by Water in Sparged Agitated Pressure Vessels

In this work, the transfer rate of air to water in a sparged agitated pressure vessel was studied. The mass-transfer coefficient of air was proved to depend on the mixing energy per liquid volume (Pg/V), the air flow rate per liquid volume (Qa/V) as well as the vessels pressure and temperature. The derived equation, which correlates these parameters with the mass-transfer coefficient, can be used for the design of a pressure vessel included in a dissolved air flotation process.