Youssouf Djibril Soubaneh

Waste Water Treatment in Chemical Industries: The Concept and Current Technologies

The world’s chemical industries face formidable environmental regulatory challenges in treating their wastewater effluents. The present work aims at highlighting the various industrial wastewater treatment technologies currently available including physico-chemical and biological processes as well as constructed wetland and conventional or advanced oxidation processes. Activated carbon prepared from low cost material, Agricultural by-product materials or modified natural polymers, which is considerably efficient for removal of direct dyes from wastewater, is also discussed. Combinations of anaerobic and aerobic treatment processes are found to be efficient in the removal of soluble biodegradable organic pollutants. The use of membrane in final stage of industrial wastewater treatments is increasing. The chemical oxidation techniques to treat wastewater, classical chemical treatment and advanced oxidation processes, is discussed.

Sorption and competition of two persistent organic pesticides onto marine sediments: Relevance to their distribution in aquatic system

Sorption is a key process in the distribution of substances between environmental compartments in marine ecosystems. Two persistent organic pesticides, also known as toxaphene congeners, namely B8-1413 (P26) and B9-1679 (P50), are of special interest because they are not detected in sediments while relatively concentrated in marine mammals. Sorption-desorption, entrapment and competition behaviors of these pesticides onto marine sediments were studied to explain their environmental distribution. Data obtained under marine experimental conditions were fitted to sorption models to evaluate sorption coefficients and to assess the degree of B8-1413/B9-1679 entrapment of the two toxaphene congeners in sediments. Carbon normalized sorption coefficients (Koc) of both congeners were similar under in cold (2°C) marine (30 psu) conditions with high values ranging from 1.53×10(5) to 3.28×10(5) mL g(-1)indicative of a strong affinity to marine sediments However, the sorption-desorption investigations indicate that B8-1413/B9-1679 were on average 2.5 times less entrapped in sediments compared to B7-1450, a toxaphene congener known to accumulate predominantly in sediments. These results suggest that the low entrapment of B8-1413 and B9-1679 favor their availability and transfer to biological matrices.

Sorption of Pesticides on Natural Geosorbents

Pesticides are chemicals used to manage pest organisms in both agricultural and non-agricultural environments. They include important classes of compounds such as herbicides, insecticides, fungicides, and biocides (Table 1). Their dispersion into agricultural environments occurs through a variety of methods including air and ground spraying. Relatively few pesticide applications are made directly and exclusively to a target pest, and most application methods rely on the use of an appreciable quantity of pesticides to the environment so that exposure to the pest species reaches effective levels. Estimates for some scenarios indicate that less than 0.1% of the applied materials reach the target pest (Pimentel & Levitan, 1986), the other important fraction of the discharged pesticide is dispersed in the environment. Considering the inherent toxicity and the possible deleterious effects of pesticides, it is of paramount importance to study the pathway and behaviour of excess pesticides released into the environment. Soils and sediments, also called geosorbents, are important sinks for pesticides because of their tremendous quantities and their ability to accumulate, or sorb, large amounts of harmful compounds. How long does a pesticide remain in soils or in sediments depends on how fast it is volatilized, solubilized or degraded, but also on how strongly it is bound by soils or sediment components (Arias-Estevez et al., 2008). Increasing amounts of research reveal that sorption is a key process for deciding the ultimate transport, persistence, bioactivity, and risk exposition of organisms to pesticides in the environment. The extent of sorption is related to structural and chemical characteristics of the pesticides (Table 1) that control some environmentally important physicochemical parameters such as volatility, water solubility, and octanol-water partition coefficient. Moreover, various soil or sediment properties including organic matter content, type and amount of clay content, ion exchange capacity and pH also modulate the magnitude of the sorption on geosorbents. A way to describe the subtle interactions of pesticides with natural geosorbents is to discuss their compositions and the interactions involved in the sorption process and the key equations that describe the sorption in an environmental perspective. The main objective of this brief review is to examine the processes of sorption on natural solids, the geosorbents, which strongly determine the persistence, mobility and bioavailability of pesticides in the environment.

Investigations on the sorption of a toxaphene model congener, the B7-1450, on marine sediments

Sorption is a natural process that takes place in sediments or soils and changes the mobility and availability of hydrophobic organic compounds, such as toxaphene pesticide in the environment. The sorption of the 2-exo,3-endo,5-exo,8,9,10,10-heptachlorobornane (B7-1450), used as a model compound of the toxaphene heptachlorobornane congeners found in sediments, was investigated for the first time through a series of batch sorption experiments. The losses of B7-1450 due to adsorption onto glass walls and to evaporation occurring during analytical treatment steps were corrected. The study showed that these specific losses ranged from 2% to 3.5% for the glass walls adsorption and can be as high as 15% for the evaporation treatment. The sorption coefficients, K(d) and K(oc), of B7-1450 could be overestimated by >30%, particularly for low-concentration samples, if the losses were not corrected. Loss correction equations were established, validated and applied to determine sorption coefficients for the B7-1450 congener. The K(oc) values for B7-1450 determined over a gradient of concentrations ranged from 3.5x10(4) to 6.5x10(4)mlg(-1), revealing a strong affinity of B7-1450 for marine sediments.

Sorption behaviors of a persistent toxaphene congener on marine sediments under different physicochemical conditions

Sorptive processes are important parameters affecting the mobility, availability and fate of persistent organic pollutants (POPs), such as toxaphene, in aquatic systems. The sorption and desorption behaviors of the B7-1450, a stable toxaphene congener in environment, on marine sediment was studied under different temperature and salinity conditions to better understand the B-1450 distribution in estuarine systems. The data were fitted to different sorption models to characterize sorption behaviors by evaluating sorption coefficients and sequestrated fraction of B7-1450 on sediments. High carbon-normalized sorption coefficients (Koc) of the B7-1450 were observed with values ranging from 3.2×104 to 6.0×104 mL g(-1) under experimental conditions. The data showed an increase of B7-1450 sorption coefficients with the salinity and a decrease with temperature. These investigations indicate that B7-1450 is three times more sequestred on sediments in cold (2°C, 30 psu) than in warm marine conditions (20°C, 30 psu). These results suggest that the mobility and bioavailable of B7-1450 or other POPs from the sediments could be less important in cold marine comparatively in warm marine and warm freshwater media. As a result of climate changes, the warming of mid and high latitudes coastal waters could enhance the mobility of POPs.

Impact of Human Activity on Marine and Coastal Environment in the Gulf of Tadjourah

Extensive research with the aim of establishing seawater quality monitoring is considered essential of any integrated coastal management program. The present study reports for the first time the republic of Djibouti costal water quality. The state of the sixteen stations’ seawater quality was assessed on the basis of determination of temporal and spatial variability of inorganic nutrients with physicochemical variables. The samples were collected seasonally from different areas such as harbor and important touristic area in the Gulf of Tadjourah for three years (2008, 2009 and 2012). The seawater temperatures, pH or Chlorophyll a of sampling sites were evaluated and compared to those of the Gulf of Tadjourah or Red Sea waters. Relatively high concentrations of nutrients (for some sites) and very low chlorophyll a concentrations (0.006 to 0.06 μg.l-1) were observed at sampling sites. The seawater concentrations of trace metals in ten stations across the Doraleh coast, where is located the main port of Djibouti, were also investigated in 20012 and the values were compared to the normal range of concentrations for seawater. The levels of microbial concentrations were also determined for the main beaches of Djibouti-city and showed relatively higher concentrations for stations beaches close to sewage outfall.

Wastewater reclamation using discarded reverse osmosis membranes for reuse in irrigation in Djibouti, an arid country.

The purpose of this paper is to establish the feasibility of recovering discarded reverse osmosis (RO) membranes in order to reduce the salinity of domestic treated wastewater. This study shows that the reuse of RO membranes is of particular interest for arid countries having naturally high mineralized water such as Djibouti. The pilot desalination unit reduces the electrical conductivity, the turbidity and the total dissolved salt respectively at 75-85, 96.7 and 95.4%. The water produced with this desalination unit contains an average of 254 cfu/100 mL total coliforms and 87 cfu/100 mL fecal coliforms. This effluent meets the World Health Organization standards for treated wastewater reuse for agricultural purposes. The annual cost of the desalination unit was evaluated as US

The geothermal resources of the Republic of Djibouti — II: Geochemical study of the Lake Abhe geothermal field

/m(3) 0.82, indicating the relatively high cost of this process. Nevertheless, such processes are required to produce an effluent, with a high reuse potential.