Integrated physicochemical and biological treatment process for fluoride and phosphorus removal from fertilizer plant wastewater.

The phosphate fertilizer industry produces highly hazardous and acidic wastewaters. This study was undertaken to develop an integrated approach for the treatment of wastewaters from the phosphate industry. Effluent samples were collected from a local phosphate fertilizer producer and were characterized by their high fluoride and phosphate content. First, the samples were pretreated by precipitation of phosphate and fluoride ions using hydrated lime. The resulting low- fluoride and phosphorus effluent was then treated with the enhanced biological phosphorus removal (EBPR) process to monitor the simultaneous removal of carbon, nitrogen, and phosphorus. Phosphorus removal included a two-stage anaerobic/aerobic system operating under continuous flow. Pretreated wastewater was added to the activated sludge and operated for 160 days in the reactor. The operating strategy included increasing the organic loading rate (OLR) from 0.3 to 1.2 g chemical oxygen demand (COD)/L.d. The stable and high removal rates of COD, NH4(+)-N, and PO4(3-)-P were then recorded. The mean concentrations of the influent were approximately 3600 mg COD/L, 60 mg N/L, and 14 mg P/L, which corresponded to removal efficiencies of approximately 98%, 86%, and 92%, respectively.

Bioassay and use in irrigation of untreated and treated wastewaters from phosphate fertilizer industry.

Wastewater from phosphate fertilizer industry that contains essentially a significant amount of both fluoride and phosphate was treated by separative precipitation of fluoride ions with hydrated lime. Thus, a phosphate-rich effluent with low content of fluoride was obtained. The microtoxicity of the treated wastewater was then monitored by LUMIStox and its phytotoxicity was investigated on tomato (Lycopersicon esculentum), wheat (Triticum aestivum), maize (Zea mays), ryegrass (Lolium perenne), and alfalfa (Medicago sativa) seed germination and plant growth. The cress (Lepidium sativum) was used as a standard species for the germination index and phytotoxicity evaluation. Seedlings of four species (namely wheat, maize, ryegrass, and alfalfa) were grown in pots, which were irrigated with untreated wastewater, treated wastewater, aqueous solution of triple superphosphate fertilizer (TSP) or with tap water as control. LUMIStox tests showed that lime treatment allowed a significant toxicity removal. The treated water displayed beneficial fertilizing effect on plants. An increase in the germination index from 100% to 119% was observed. However, the untreated wastewater inhibited the species germination even when diluted 10 times. Neither plants mortality nor growth inhibition was observed after 90 days of treated wastewater application. Moreover, an improvement in plant growth, leaf number and a root development were noticed in these plants when compared with those irrigated with tap water or with fertilizer. In contrast, leaf necrosis and growth inhibition were observed in plants amended with raw wastewater. The irrigation with treated wastewater also improved soil labile P content. Indeed, soils amended with treated wastewater had more a double labile P concentration (38.15 mg kg(-1)) in comparison with control soil (15.53 mg kg(-1)).

Adsorption of a textile dye "Indanthrene Blue RS (C.I. Vat Blue 4)" from aqueous solutions onto smectite-rich clayey rock.

The adsorption of a textile dye, namely, Indanthrene Blue RS (C.I. Vat Blue 4) onto smectite-rich clayey rock (AYD) and its sulphuric acid-activated products (AYDS) in aqueous solution was studied in a batch system with respect to contact time, pH, and temperature. The adsorbents employed were characterized by X-ray diffraction, infrared spectroscopy and specific surface area, cation exchange capacity and point of zero charge were also estimated. The effect of contact time on dye adsorption showed that the equilibrium was reached after a contact time of 40 min for the both adsorbents. The optimum pH for dye retention was found 6.0 for AYDS and 7.3 for AYD. The equilibrium adsorption data were analysed using the Langmuir and Freundlich isotherms. The adsorption capacities (Q(m)) for AYD and AYDS were found 13.92 mg/g and 17.85 mg/g, respectively. The effect of temperature on the adsorption was also investigated; adsorption of Indanthrene Blue RS is an endothermic process. This study demonstrates that all the considered adsorbents can be used as an alternative emerging technology for water treatment.

Separative recovery with lime of phosphate and fluoride from an acidic effluent containing H3PO4, HF and/or H2SiF6.

Fluoride content and flow-rate of fertilizer plant wastewater from phosphoric acid and/or triple superphosphate (TSP) production lead to the discharge of several thousand tons of fluoride (F(-)) per year and even more for phosphate (PO4(3-)). Since sustainability is an important environmental concern, the removal methods should allow phosphorus and fluoride to be recycled as a sustainable products for use as raw materials either in agricultural or industrial applications. In the present work, separative recovery with lime of these two target species was investigated. A preliminary speciation study, carried out on the crude effluent, showed that two forms of fluoride: HF and H2SiF6 are present in a highly acidic medium (pH approximately 2). Evidence that fluoride is present under both free (HF) and combined (H2SiF6) forms, in the phosphate-containing effluent, was provided by comparing potentiometric titration curves of a crude wastewater sample and synthetic acid mixtures containing H3PO4, HF and H2SiF6. In a second step synthetic effluent containing mixtures of the following acids: HF, H2SiF6 and H3PO4, were treated with lime. The behaviour of these compounds under lime treatment was analysed. The data showed that fluoride has a beneficial effect on phosphate removal. Moreover, by acting on the precipitation pH, a "selective" recovery of fluoride and phosphate ions was possible either from phosphoric acid/hydrofluoric acid or phosphoric acid/hexafluorosilicic acid mixtures. Indeed, the first stage of the separative recovery, led to a fluoride removal efficiency of 97-98% from phosphoric acid/hydrofluoric acid mixture. It was of 93-95% from phosphoric acid/hexafluorosilicic acid mixture. During the second stage, the phosphate precipitation reached 99.8% from both acidic mixtures whereas it did not exceed 82% from a solution containing H3PO4 alone. The XRD and IR analyses showed that during lime treatment, a H2SiF6 hydrolysis occurred, instead of CaSiF6 solid formation, leading to CaF2 precipitate. Calcium fluoride and calcium phosphate based-by-products resulting from the two-step treatment process can be used as raw materials in several industrial sectors, such as ceramic and phosphate fertilizer industries.

Electrochemical oxidation post-treatment of landfill leachates treated with membrane bioreactor.

Integration of membrane bioreactor (MBR) with electrochemical process was investigated as treatment of stabilized landfill leachates, collected from Djebel Chekir (Tunisia). Results showed that at optimum conditions for the membrane and with organic loading rates of 1.9 and 2.7g COD L(-1)d(-1), MBR treated effluent is still colouring and contains high COD and ammonia concentrations. In order to reduce these high pollutant concentrations, electrochemical oxidation process using Ti/Pt, graphite and PbO(2) electrodes, was tested as effluent post-treatment. Ti/Pt electrodes showed the best performance. COD, ammonia and colours removals were affected by the current density (J) and treatment time (t). At optimal operational conditions (t=1h, J=4Adm(-2)), the final COD and total kjeldahl nitrogen concentrations (TKN) were 1000 and 86mgL(-1), respectively. The final treated wastewater COD, TKN, colours, pH meet the discharge standards in the sewer. The combination of MBR treatment process with electrochemical oxidation can be a technical suitable solution for stabilized landfill leachates treatment with an efficient reduction of different parameters, essentially COD (85%), TKN (94%), and colour(436) (99%).

Lead removal from aqueous solutions by a Tunisian smectitic clay.

The adsorption of Pb(2+) ions onto Tunisian smectite-rich clay in aqueous solution was studied in a batch system. Four samples of clay (AYD, AYDh, AYDs, AYDc) were used. The raw AYD clay was sampled in the Coniacian-Early Campanian of Jebel Aïdoudi in El Hamma area (South of Tunisia). AYDh and AYDs corresponds to AYD activated by 2.5 mol/l hydrochloric acid and 2.5 mol/l sulphuric acid, respectively. AYDc corresponds to AYD calcined at different temperatures (100, 200, 300, 400, 500 and 600 degrees C). The raw AYD clay was characterized by X-ray diffraction, chemical analysis, infrared spectroscopy and coupled DTA-TGA. Specific surface area of all the clay samples was determined from nitrogen adsorption isotherms. Preliminary adsorption tests showed that sulphuric acid and hydrochloric acid activation of raw AYD clay enhanced its adsorption capacity for Pb(2+) ions. However, the uptake of Pb(2+) by AYDs was very high compared to that by AYDh. This fact was attributed to the greater solubility of clay minerals in sulphuric acid compared to hydrochloric acid. Thermic activation of AYD clay reduced the Pb(2+) uptake as soon as calcination temperature reaches 200 degrees C. All these preliminary results were well correlated to the variation of the specific surface area of the clay samples. The ability of AYDs sample to remove Pb(2+) from aqueous solutions has been studied at different operating conditions: contact time, adsorbent amount, metal ion concentration and pH. Kinetic experiments showed that the sorption of lead ions on AYDs was very fast and the equilibrium was practically reached after only 20 min. The results revealed also that the adsorption of lead increases with an increase in the solution pH from 1 to 4.5 and then decreases, slightly between pH 4.5 and 6, and rapidly at pH 6.5 due to the precipitation of some Pb(2+) ions. The equilibrium data were analysed using Langmuir isotherm model. The maximum adsorption capacity (Q(0)) increased from 25 to 25.44 mg/g with increasing temperature from 25 to 40 degrees C. Comparative study between sulphuric acid activated clay (AYDs) and powder activated carbon (PAC) for the adsorption of lead was also conducted. The results showed that sulphuric acid activated clay is more efficient than PAC.