One of the key success factors for optimal management of anaerobic digestion reactors is to control the volatile fatty acids (VFA)production. This is justified to the extent that at a concentration greater than 3000 mg/l, VFA can inhibit the methanation process. In other words, their concentration is a reliable indicator of reactor stability or stress. Several analysis methods for these VFAhave been developed such as high performance liquid chromatography (HPLC), gas chromatography (GC), colorimetry andvarious titration techniques. The titration technique offers several advantages: it is the simplest, least expensive, fastest, andaccessible to all countries, including developing countries where laboratory equipment’s are generally lacking. The titrationmethod can, therefore, be a useful tool if its reproducibility, precision and interpretation can be improved. The present studyfocused on the development and validation of a new simplified, the improved and accurate titrimetric method for the determination of VFA concentration, sufficiently close to chromatographic methods (GC or HPLC), considered as the goldreference method today. A mathematical model taking into account the main factors affecting the accuracy of VFA concentrationin anaerobic reactors (e.g chemical species, pH, temperature, ion activity coefficients) was developed. Its validation was carriedout using measurements on thirty-three different samples with this new titration method on the one hand and the gas chromatography (GC) method on the other hand. At 99% confidence interval, the VFA concentration determined using this newtitration method/mathematical model were close to those obtained by the GC method with a determination coefficient R2 of 0.97.
Activated sludge model No. 1 (ASM1) and activated sludge model No. 3 (ASM3) can simulate correctly the behaviour of a pilot membrane bioreactor treating old landfill leachates. Both models show similar results, which are consistent with measured data. In this work, a simplified calibration procedure is applied including hydrodynamic and oxygen transfer characterization. The wastewater characterisation was based on a physical–chemical method combined with a BOD analysis for the COD fractions and on standard analysis for nitrogen forms. Default parameters were used for both models; despite this, good simulations were obtained showing the flexibility and accuracy of the well-achieved ASM family models. The sensibility analysis performed allows identification of the most important kinetic, stoichiometric and operational parameters that should be measured to confirm or replace default values. In this specific case, the simulation is most sensitive to heterotrophic yield, particularly under anoxic conditions.
Settling is one of the processes occurring in waste stabilization ponds (WSP). Part of suspended solids (SS) is removed by sedimentation but very often the efficiency of WSP is presented without making a difference between settling and biological processes. In this way the WSP is seen as a black box process. This work presents an experimental approach to the study of the removal of wastewater suspended solids in a test column in order to improve our knowledge of the settling process in ponds. These results show that the settling test in columns can be used to estimate the half removal time (t 50 ) for the study of settling characteristics of suspended solids in wastewater stabilization ponds. The aim of this study was to determine the half removal time (t 50 ) in anaerobic, facultative and maturation ponds, and in the influent to these ponds, at the experimental wastewater treatment plant of CERTE (Recycling and Treatment Center of Wastewater in Tunisia), by a column settling test. The experiments lasted between 15 and 120 min. The column was 2 m high with sampling systems at various depths: 40, 80, 120, 160 and 200 cm. Half-removal suspended solids time t 50 was defined as the time at which 50% of SS was removed. Models derived from the scientific literature were used to interpret the experimental data. The experimental results demonstrated that higher suspended solids concentrations in the influent led to shorter t 50 values and better settling.
Les taux d’accumulation, la distribution spatiale ainsi que les caractéristiques chimiques des sédiments ont été étudiés dans une installation de lagunage composée d’un bassin anaérobie, un bassin facultatif et deux bassins de maturation pour le traitement des eaux usées en Tunisie. Le taux d’accumulation ainsi que la distribution des boues au sein de chaque bassin ont été déterminés par mesure directe de l’épaisseur des sédiments correspondants sur 90 à 105 points (selon un maillage de 11 mètres). En tenant compte du volume total de boue déterminé sur les quatre bassins, le taux d’accumulation de sédiments est de 0,029 m 3 •EH ‑1 •an ‑1 correspondant à un taux d’accumulation de 4,14 kg MS•EH ‑1 •an ‑1 . La distribution des boues est loin d’être homogène; les épaisseurs de sédiments les plus importantes sont enregistrées aux entrées et sorties des bassins. L’étude de la variabilité horizontale des caractéristiques des sédiments a été réalisée en considérant deux sites (entrée et sortie) du bassin facultatif (BI) au niveau desquels cinq réplicats de carottes ont été prélevés. Par contre, l’étude de la variation verticale a été réalisée sur des carottes de sédiments qui, après prélèvement, ont été sectionnées en tronçons. Des paramètres chimiques tels que : carbone total (CT), azote total (NT), phosphore total (PT), matières sèches (MS) et matières volatiles (MV) ont été mesurés sur ces échantillons. Les résultats obtenus ont montré que la teneur en matières sèches dans la couche la plus profonde est supérieure à celle dans la couche de surface. Par contre, les teneurs en CT, NT, PT, MV diminuent en fonction de la profondeur.
Recovering microalgae is one of the main technological and economic concerns in a high-rate algal pond (HRAP) because of their small size and their low density. This paper emphasizes the characterization (identification and assessment of potential flocculation) of chemical compounds involved in microalgae auto-flocculation in a HRAP. First, thermodynamic simulations were performed, using two models (i.e. Visual Minteq and a simplified thermodynamic model) in order to determine the chemical compounds of interest. Experimental tests were then carried out with these compounds for assessing their flocculation ability. Both models revealed that precipitates of calcium phosphates and their substituted forms were the compounds involved in the auto-flocculation. Moreover, experimental tests showed that the stoichiometric neutralization of algal charges by calcium phosphates (i.e. hydroxyapatite (Ca5(PO4)3OH), octacalcium phosphate (Ca4H(PO4)3) and amorphous calcium phosphate (Ca3(PO4)2)), at a pH within the range 7–10 yields 70–82% recovered algal biomass. The optimum ratio required for algae auto-flocculation was 0.33 Ca5(PO4)3OH/g DMalgae at pH 10, 0.11 Ca4H(PO4)3/g DMalgae at pH 7 and 0.23 g Ca3(PO4)2/g DMalgae at pH 9. Auto-flocculation appears as a simple, sustainable and promising method for efficient harvesting of microalgae in a HRAP.
The present investigation was carried out to study the biodegradation of dairy effluent collected from a regional dairy industry, in Tunisia, by using selected aerobic microbial and yeast isolates.The predominant microorganisms: Candida albicans, Candida krusei, Lactobacillus plantarum and Lactobacillus casei isolated from activated sludge pond of the dairy plant were used.Biodegradation tests were performed in batch into Erlenmeyer flasks containing collected dairy wastewater samples.Two sets of experiments were carried out in duplicate.For the first set of experiments, each bacteria and yeast strain was used for the preparation of four inoculums composed of single culture.These inoculums are added separately in the test samples with a concentration of 1% (v/v).For the second set of experiments, three inoculums rate (1, 5 and 10% (v/v)) were tested.A bacteria and yeast mixed culture were added separately in the test samples.A variable amount of COD, proteins and total sugars reduction was observed with individual and mixture isolates after 25 days treatment period.The chemical oxygen demand (COD) has received reduction varying between 51.6 and 71.6% with individual isolates at 1% (v/v) inoculum rate, while bacterial mixed culture and yeast mixed culture showed reduction up to 75.8 and 70.7%, respectively, at 1% (v/v) inoculum rate.Isolates with inoculum rate of 5% (v/v) proved to be most efficient in the treatment of effluent.The highest reduction of total sugar content was obtained by yeast consortium while the highest reduction of protein content was obtained by bacteria consortium.
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