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 industry's wastewater by reed beds as a tertiary treatment method is quite effective.

Inhibition kinetics of phenolic compounds in aerobic degradation of organic wastewaters.

This study proposed a kinetic model for the aerobic degradation of high strength organic wastewaters with high concentrations of phenolic compounds. The model was based on the conventional Monod kinetic equation incorporating phenols' inhibition. Furthermore, a methodology for determining biokinetic constants was proposed. Olive-mill wastewater (OMWW) was used for the case study. The model and proposed methodology were fitted on the experimental data and it was proved that the aerobic degradation of OMWW was described satisfactorily. The following kinetic constants were determined: maximum specific substrate removal rate, 1.35 h(-1); minimum microorganisms decay rate, 0.01 h(-1); inhibition coefficient of phenolic compounds, 373 mg L(-1); half-saturation concentration in carbon units, 1004 mg L(-1); and decay acceleration coefficient of phenolic compounds, 231 mg L(-1). Finally, the biomass yield coefficient was found to be equal to 0.36. Thus, it was determined that the proposed methodology would be a useful tool for determining biokinetic constants of similar substrates.

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.

Determination of granule size distribution in a UASB reactor.

Granular sludge is the key factor for an efficient operation of an upflow anaerobic sludge blanket (UASB) reactor. In order to monitor the granularity of anaerobic sludge, the determination of the granule size distribution is of vital importance. For this reason, several techniques have been proposed; however, they are either tedious, imprecise or expensive and hardly applicable in full-scale treatment plants. There was then the need for a simple and low-cost technique. This technique involves the determination of the settling velocities of a sludge sample and of extrapolating the corresponding diameters using a mathematical algorithm. In the proposed algorithm, the granules density was calculated, the flow regime was examined and finally the granule size distribution was obtained. Two very important correlations were suggested by the experimental results. The granule density and diameter were strongly correlated with the VSS/TSS ratio.

Effect of ferrous ion on the biological activity in a UASB reactor: mathematical modeling and verification.

The effect of ferrous ion on the biological activity in a upflow anaerobic sludge blanket (UASB) reactor was studied. A mathematical model was developed and validated in order to simulate the dynamic behavior of a UASB reactor. This model took into consideration of all the biological and physicochemical reactions. The model was able to simulate the accumulation of iron in the sludge bed and its effect on the biological activity of the anaerobic sludge. A significant increase in the maximum uptake rate of methanogens and acidogens was revealed when iron was supplemented to the UASB reactor. The addition of ferrous iron induced a stable and excellent COD conversion rate. The model can be a useful tool for the prediction of process performance in the future and can be used to assist in the operation of biogas plants. The ferrous ion addition proved to enhance the biological activity of UASB sludge. Thus, the model can be used for the design of treatment plants that will take advantage of the benefits of iron addition.

Electrochemical detoxification of four phosphorothioate obsolete pesticides stocks.

The phosphorothioate pesticides are widely used for crop production and fruit tree treatment, but their disposal causes serious environmental problems. Four commercial phosphorothioate pesticides (Demeton-S-methyl, Metamidophos, Fenthion and Diazinon) 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 Fenthion the achieved reduction was over 60%, while for Demeton-S-methyl, Metamidophos and Diazinon was more than 50%. Diazinon had the lowest energy demand. The COD/BOD5 ratio was improved considerably after electrolysis for all four pesticides examined. As a conclusion, electrochemical oxidation could be used as a pretreatment method of the pesticides detoxification.

Degradation of methylparathion in aqueous solution by electrochemical oxidation.

The electrochemical degradation of methylparathion has been investigated by using Ti/Pt as anode, Stainless Steel 304 as cathode, and sodium chloride as electrolyte. The pesticide is rapidly degraded, but full mineralization is not observed. Degradation products have been monitored through gas chromatography and mass spectrometry, and the overall degradation process has been monitored through dissolved and particulate organic carbon, sulfur, and phosphorus measurements. Several intermediates have been identified, and oxalic, formic, and acetic acids as well as tetraphosphorus trisulfide have been recognized as final products of the degradation process. A proposed mechanism of the process is presented.