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.

Agricultural Soil Fertilizing Potential of Dry Faecal Sludge from Treatment Plants in Burkina Faso

The dry faecal sludge (DFS) are potential sources of organic fertilizers because of their high content in nutrients and organic matter, critical for plants growth and soil health maintaining. In Burkina Faso, the DFS are processed in faecal treatment plants. However, after drying, the DFS are most often dumped in the nature without any control or directly used as fertilizer without any idea of their potential risks for human health and the environment. This investigation aimed at physico-chemical and toxicological characterization of the DFS from faecal treatment plants according to the duration of their storage. For this purpose, DFS samples were collected in three (3) faecal treatment plants in Ouagadougou and one in Bobo Dioulasso, in Burkina Faso. The measurements were carried out on pH (H2O), organic matter content, major nutrients (N, P, K), trace elements (Na, Ca and Mg) and metallic trace elements. Indifferently to the faecal treatment plants and the duration of the storage, the DFS showed strong acidity (4.85 ± 0.13 et 6.53 ± 0.10) and low content in total elements (Na à40.97% ± 9.99%). Values recorded of the trace metallic elements showed there were no risk of contamination when used as fertilizers: (103.9 ± 2.00 mg/kg < Cu < 137 ± 25.69 mg/kg);(710.13 ± 18.97 mg/kg < Zn < 922.30 ± 7.04 mg/kg);(33.03 ± 1.65 mg/kg < Pb < 152.40 ± 19.40 mg/kg);(1.34 ± 0.17 mg/kg < Cd < 1.76 ± 0.04 mg/kg);(34.34 ± 0.27 mg/kg < Ni < 52.32 ± 3.60 mg/kg) et (771.15 ± 18.36 mg/kg < Cr < 1697.83 ± 55.11 mg/kg). The results indicated a high fertilizer potential of the DFS after addressing the issue of their acidity.

Atmospheric emission characterization of a novel sludge drying and co-combustion system

A novel system combining sludge drying and co-combustion with coal was applied in disposing sludge and its atmospheric emission characteristics were tested. The system was composed of a hollow blade paddle dryer, a thermal drying exhaust gas control system, a 75 tons/hr circulating fluidized bed and a flue gas cleaning system. The emissions of NH3, SO2, CH4 and some other pollutants released from thermal drying, and pollutants such as NOx, SO2 etc. discharged by the incinerator, were all tested. Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans （PCDD/Fs） in the flue gas from the incinerator were investigated as well. The results indicated that the concentrations of NOx and SO2 in the flue gas from the incinerator were 145 and 16 mg/m^3, respectively, and the I-TEQ concentration of 2,3,7,8-substitued PCDD/Fs was 0.023 ng I-TEQ/Nm^3. All these values were greatly lower than the emission standards of China. In addition, there was no obvious odor in the air around the sludge dryer. The results demonstrated that this drying and co-combustion system is efficient in controlling pollutants and is a feasible way for large-scale treatment of industrial sludge and sewage sludge.

Experimental study on agitated drying characteristics of sewage sludge under the effects of different additive agents

Drying experiments of dewatered sewage sludge（DSS） were conducted on a agitated paddle dryer, and the effects of additive agents, i.e., CaO, pulverized coal（PC）, heavy oil（HO）, and dried sludge（＂DS＂ through back mixing） on the agitated drying characteristics of DSS were investigated. The results indicated that CaO can significantly increase the drying rate of DSS.The drying rate at CaO/DSS（mass ratio） = 1/100 was 135% higher than that of CaO/DSS = 0.Pulverized coal has no obvious effect on drying rate, but the increase of PC/DSS can promote breaking up of sludge lump. Heavy oil was found to be slightly effective in improving the drying rate of DSS in the examined experimental range of HO/DSS = 0-1/20. It is also found that HO can reduce the torque of the dryer shaft, due to its lubrication effect. Back mixing of DS was found to be effective in alleviating the unfavorable effect of the lumpy phase by improving the mixing effect of the paddle dryer. There was a marked increase of drying rate with an increase of the DS/DSS in the experimental range of DS/DSS = 0-1/3.

Multifractal characteristics of cylindrical sludge drying

This paper analyzes dewatered sludge drying using the multifractal theory.The drying rates of cylindrical sludge with equal masses but different crosssectional diameters was studied,from which multifractal parameters such as partition function and quality exponent were obtained.The parameters acquired were used to calculate the multifractal singularity spectrum and indicate the presence of multifractal characteristics.The smaller cross-sectional diameters of the sludge were found to be non-homogeneous,and required quantitative methods to analyze.

Research on the treatment of sludge drying gas spray wastewater using discharge free radicals

Wastewater from the spray absorption treatment of sludge drying gas is a kind of refractory wastewater with poor biodegradability.In this study,the free radicals generated from the double dielectric barrier were innovatively used for the degradation of simulated spray wastewater.The effects of residence time,input power,initial pH,aeration rate,and discharge area on the degradation rate and COD(chemical oxygen demand)removal rate were investigated.The optimal conditions were as follows:residence time=120 min,input power=170.0 W,initial pH=5.54,aeration rate=0.9 mL/min,discharge area=10.8 cm^(2),and the initial concentrations of NH_(3),H_(2)S,methanethiol,trimethylamine,benzene and toluene were 250,250,50,50,50 and 100 mg/L,respectively.Meanwhile,it was also found that hydroxyl radical(⋅OH)played an important role in the degradation process.