Planted Sludge Drying Beds in Treatment of Faecal Sludge from Ouagadougou: Case of Two Local Plant Species

Management of wastewater is a concern of developing countries. In Burkina Faso, an on-site septic system installed on the property is predominant and those systems product high quantities of faecal sludge which are not treated adequately before discharge. Our country is mainly fed by surface water, while water is the main vector of many diseases. So it is very important to manage efficiently wastewater and faeces. The treatment of faecal sludge by planted beds can use local persistent emergent plants like Andropogon gayanus (LPA) and Cymbopogon nardus (LPN). Those planted beds are compared to a non-planted bed (sludge drying bed) (LT). Treating raw sludge (BB) we got the yield over 90% concerning the biological oxygen demand (BOD5) for the LPA while the two others gave performances of 75% and 76% respectively. Regarding the chemical oxygen demand (COD), LPN gave better yields with 77% of removal against 71% and 69% for LPA and LT respectively. Overall, the pilots assured removal of orthophosphates varying between 77% and 79%, while the Kjeldahl nitrogen is removed by the various beds with respective fields of 94%, 96.5% and 97.5% for LPN, LPA and LT. The microbiological pollution abatement is in the order of 1 log unit on average for all beds.

Influence of the Nature of the Incoming Sludge on the Performance of a Vertical Flow Reed Beds in Dakar-Senegal

This work investigates the influence of the type sludge on drainage, plant development, purification performances and biosolids quality. Drainage properties were measured through the frequency of clogging, the percentage of leachate recovered and the dryness of accumulated sludge. Plant development was measured through the density, the height and the stem diameter. Purification performance was evaluated from the reduction rate. Biosolids quality was measured after 3 months of maturation. The results show that the clogging frequencies were 9.5%;0% and 3.7%;the volume of leachate recovered was 42.2%;20.4% and 24.7% and, the dryness was 33.4%;61.1% and 52.4% for FS-ST, FS-STT and SS respectively. Plants densities were about, with densities 197.1, 171.3 and 178.3 plants/m2 in beds fed respectively with FS-ST, FS-STT and SS. Despite the high removal rates, the concentrations of pollutants in the leachates are above the Senegalese standard NS 05-061 for discharge into the environment. The biosolids are all mature with C/N and NH4+/NO3?ratios lower than 12 and 1 respectively. The biosolids are also rich in organic and mineral elements. The concentrations of Ascaris eggs are higher than the WHO recommendations. These biosolids should be stored for additional time or composted.

Unsaturated Flow Drying Bed(UFDB):An Alternative for Treatment of Septic Tanks Sludge

Unsaturated Flow Drying Bed (UFDB) principles are based on the ones of wastewater treatment by infiltration-percolation on the one hand and septic tanks sludge solar-drying beds on the other hand. With UFDB, sludge charges are split with low heights, leading to the drying of suspended solids in 2 days, and the infiltration of the flow of liquid in unsaturated middle. For average charges reaching 12.5 cm/d, the treatment efficiency of total oxygen demand and Total Kjeldahl Nitrogen, respectively 95 and 96%, correspond to a treatment capacity of 0.5 kg of O2/d/m2 of drying area. Bacteria reductions of 4 Ulog are obtained from filtrates outlet, with average fecal coliforms charges less than 103 CFU/100 ml. Monitoring the hydrodynamic behavior through rates, moisture, organic matter and respiratory activity demonstrates that the clogging of the massifs is linked to a biofilm growth within them. A four week resting period allows biofilm resorption. Thus, the drying of the infiltration surface in two days, the elimination of carbon, nitrogen and bacterial pollutions, as well as the reversibility of clogging show that UFDB is a credible alternative for the treatment of septic tank sludge in the socio-economic context and climate of tropical Africa.

Characteristics of fluidization and dry-beneficiation of a wide-size-range medium-solids fluidized bed

Wide-size-range medium-solids are used in a modularized coal beneficiation demonstration system with a gas-solid fluidized bed. The characteristics of fluidization and dry-beneficiation of the medium solids were studied. The numerical simulation results show that 0.15–0.06 mm fine magnetite powder can decrease the disturbances caused by the bubbles. This is beneficial to the uniformity of the gas-solid interactions and thus to the uniformity and stability of the bed density and height. The experimental results show that, with an increase in the fine coal content in medium solids, both the fluidization quality and the beneficiation performance of the bed decreased gradually. When the fine coal content was no more than 13%, a relatively high superficial gas velocity increased the beneficiation efficiency. When the content was more than 13%, part of the fine coal was separated, leading to product layers. The separation efficiency was therefore gradually decreased. The models for predicting the bed density standard deviation and the probable error, E, value were both proposed. The E value can reach to 0.04–0.07 g/cm^3 under the optimized experimental parameters. This work provides a foundation for the adjustment of the bed density and the separation performance of the modularized 40–60 ton per hour dry coalbeneficiation industrial system.

Characterization and evaluation in vivo of baicalin-nanocrystals prepared by an ultrasonic-homogenization-fluid bed drying method

AIM： To improve the absorption and bioavailability of baicalin using a nanocrystal （or nanosuspension） drug delivery system. METHODS： A tandem, ultrasonic-homogenization-fluid bed drying technology was applied to prepare baicalin-nanocrystal dried powders, and the physicochemical properties of baicalin-nanocrystals were characterized by scanning electron microscopy, photon correlation spectroscopy, powder X-ray diffraction, physical stability, and solubility experiments. Furthermore, in situ intestine single-pass perfusion experiments and pharmacokinetics in rats were performed to make a comparison between the microcrystals of baicalin and pure baicalin in their absorption properties and bioavailability in vivo. RESULTS： The mean particle size of baicalin-nanocrystals was 236 nm, with a polydispersity index of 0.173, and a zeta potential value of-34.8 mV, which provided a guarantee for the stability of the reconstituted nanosuspension. X-Ray diffraction results indicated that the crystallinity of baicalin was decreased through the ultrasonic-homogenization process. Physical stability experiments showed that the prepared baicalin-nanocrystals were sufficiently stable. It was shown that the solubility of baicalin in the form of nanocrystals, at 495 ug·mL-1, was much higher than the baicalin-microcrystals and the physical mixture （135 and 86.4 ug·mL- 1, respectively）. In situ intestine perfusion experiments demonstrated a clear advantage in the dissolution and absorption characteristics for baicalin-nanocrystals compared to the other formulations. In addition, after oral administration to rats, the particle size decrease from the micron to nanometer range exhibited much higher in vivo bioavailability （with the AUC（0-t） value of 206.96 ± 21.23 and 127.95 ± 14.41 mg·L-1·h-1, respectively）. CONCLUSION： The nanocrystal drug delivery system using an ultrasonic-homogenization-fluid bed drying process is able to improve the absorption and in vivo bioavailability of baicalin, compared with pure baicalin coarse powder and micronized baicalin.

Optimizing the drying parameters of a fixed bed with reversing ventilation for peanut using computer simulation

To obtain the optimal operation parameters of fixed-bed reversing ventilation drying of peanuts,a set of partial differential equations indicating the heat and mass transfer relationships between the peanut pods and air during drying was proposed.Then,a series of discretized models were established for simulation,and the time consumed,unevenness,and energy consumption for batch drying were calculated.The results showed that reversing ventilation and segmented drying was helpful to these issues for high drying ability.The optimal operation parameters were determined by uniform design experimentation of mathematical simulation.The result showed that when the moisture content(wet basis)was above 22%,a ventilation velocity of 0.46 m/s was optimal;when the moisture content was between 8%and 22%,a ventilation velocity of 0.20 m/s was optimal.Using the optimal parameters,the computer simulating result was compared with the experimental results.The correlation coefficients between the simulating and the experimental values for the temperature and moisture content were all above 0.98 and the quality of dried peanuts was close to that of natural sun-dried ones,which indicates that the optimization results of the drying parameters are highly reliable.