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.

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.

Surface flow constructed wetland with composite plant bed for pretreatment of micro-polluted Yellow River raw water in China

In order to investigate the feasibility of pretreating the micro-polluted Yellow River raw water by constructed wetland, an experiment was conducted using a surface flow constructed wetland with composite plant bed. The contamination removal efficiency and their trends in the wetland treatment system were studied under different hydraulic loading rates(HLR). The contamination removal efficiencies were compared according to the seasonal change under optimum HLR. The result shows that in the same season, under different hydraulic loadings ranging from 2 to 6 m3/(m2·d) at the same period, the best HLR is 4 m3/(m2·d) in the experimental system. The average removal rates of COD, TN, ammoniacal nitrogen(NH4+-N), and TP in the constructed wetland are 38.37%, 45.97%, 39.86% and 41.69%, respectively. According to China Standard for Surface Water Resources (GB3838-2002), mean effluent of COD, TN, NH4+-N and TP can nearly reach Grade Ⅲ, GradeⅤ, GradeⅠand GradeⅠ, respectively. Furthermore, treatment efficiency of the system in summer is obvious higher than that in other seasons. The expenditure of constructing the constructed wetland with the average treating capacity of 176 m3/d and lifetime of 20 years is 17075.00 RMB. The average disposal cost is summed up to 0.17 RMB/m3, which shows that the pretreatment of the micro-polluted Yellow River raw water by constructed wetland is feasible.

Increasing yield and agronomic efficiency of boro rice(Oryza sativa)by fertigation with bed planting compared with conventional planting

The fertigation technique with raised bed planting for transplanted boro(winter,irrigated)rice production is a research focus nowadays.A field experiment compared two cultivation methods:the fertigation technique within raised bed planting on boro rice,and fertilizer broadcasting in the conventional planting method.Compared to conventional fertilizer broadcasting,results showed that the new fertigation technique in raised bed planting increased grain yield of transplanted boro rice by up to 17.04%.It yielded a greater number of panicles per square meter,a greater number of grains per panicle,higher 1000-grains weight,and better plant growth attributes.Sterility percentage and weed infestation were lower.Thirty six percent of irrigation water and time for application could be saved.Water use efficiency for grain and biomass production was higher.The agronomic efficiency of nitrogen(N)fertilizer was significantly higher.This study concluded that fertigation in raised bed planting for transplanted boro rice is a new approach with higher yield and higher fertilizer and water use efficiency than the existing agronomic practice in Bangladesh.

Restoration of hyper-eutrophic water with a modularized and air adjustable constructed submerged plant bed

A modularized and air adjustable constructed submerged plant bed(CSPB)which can be used to restore the eutrophic water is introduced in this paper.This plant bed helps hydrophyte grow under poor conditions such as frequently changed water depth,impaired water transparency,algae bloom and substantial duckweed in summer,which are not naturally suitable for growing hydrophyte.This pilot study in Waihuan River of Tianjin,China,revealed that reduction of Chemical Oxygen Demand(COD),Total Nitrogen(TN)and Total Phosphorus(TP)by the use of CSPB could be reached 30%-35%,35%-40%,30%-40%respectively in the growing season(from March to October)and 5%-10%,5%-15%,7%-20%respectively in the winter(from November to February)when the detention time was 6 d.The relationships between the concentration of COD,TN,TP and the detention time fit the first-order kinetic equation well and the coefficients of determination(R^(2))were all above 0.9.The attenuation coefficients k of the kinetic equation were a function of the water temperature.When the water temperature was quite low or quite high,k was not significantly changed with increasing or decreasing water temperature.While when the temperature was in a moderate range,an increase or decrease of water temperature would lead to a rapid increase or decrease in k.