Raw Phosphate Research Articles

Analysis of the settling process to improve the quality of phosphate products of the Djebel Onk deposit

The object of the study is the phosphates of the Djebel Onk region, which are part of a vast group of phosphate deposits formed in the Late Cretaceous-Eocene period on the South and Southeast Mediterranean shores. These concentrations of economic interest are operated near the town of Bir El Ater (Tebessa, Algeria). The mining industry based on the extraction and processing of different minerals while respecting the environmental framework plays an important role in the economy of a country. The economic potential of each country will be determined based on the level of production of metals and various mineral substances. In the case of the Djebel Onk phosphate ore, the most dominant mineral in addition to P2O5 is calcium carbonate CaCO3 with more than 50 % in the all-mineral content. In addition, phosphate concentrate contains harmful elements which reduce the value of the market product. Therefore, this study aims to recover the enriched product efficiently and profitably with a minimum of deleterious elements. This work aims to develop a treatment technology with a minimum rejection rate, which allows for achieving production goals and reducing environmental impacts. For this purpose, we proposed an enrichment of these phosphate discharges from the settling process utilizing pneumatic selection (Turbo Separator Ventilate – TSV). The results of the chemical analyses confirm the significant difference in useful and major elements (P2O5) and the minor and harmful elements (MgO). According to the granulochemical analysis of each slice, it is possible to note that the P2O5 content is similar to the various particle-size slices. It is therefore necessary to treat the mass of waste if we want to recover as much phosphate as possible. The obtained X-ray diffractograms highlighted appreciable differences between the raw phosphates and the concentrates, in fact, the qualitative and quantitative variation of the mineralogical species, particularly the calcite, quartz, dolomite, and apatite. TSV is a process used to improve the quality and quantity of phosphate and to eliminate the layer below 0.8 mm. Corresponding to the analyses it was appeared that the P2O5 content 29.5–30 % of the settled product increases to 30.2–31 % after dust removal. Then it is possible to achieve an increase in the quality of phosphate from 63/65 % TPL to 66/68 % TPL.

Elevating Sorghum Prosperity: Unveiling Growth Trends through Phosphate-Solubilizing Bacteria and Arbuscular Mycorrhizal Fungi Inoculation in Phosphate-Enriched Substrates

This study aimed to elucidate the impact of phosphate-solubilizing bacteria (PSB) and arbuscular mycorrhizal fungi (AMF) inoculation on sorghum growth within substrates derived from phosphate solid sludge, with the overarching objective of repurposing phosphate sludge to be a viable agricultural substrate. Four PSB strains (Serratia rubidaea, Enterobacter bugandensis, Pantoea agglomerans, Pseudomonas sp.) were meticulously selected from phosphate solid sludge, along with two AMF strains (Rhizophagus intraradices and Funneliformis mosseae), constituting the experimental inocula. Phosphate solid sludge was judiciously blended with peat at varying volumetric proportions (0%, 10%, 20%, 40%, and 60%), providing the matrix for sorghum cultivation, and concomitantly subjected to inoculation with PSB and AMF. Following a meticulously monitored two-month duration, a comprehensive evaluation of diverse morphological parameters, biomass accrual, nitrogen content, total phosphorus concentration, potassium levels, calcium content, and root colonization in sorghum plants was conducted. The empirical findings underscored a discernible decline in the assessed parameters with escalating concentrations of phosphate solid sludge. Particularly noteworthy was the pronounced amelioration observed in plants inoculated with AMF in comparison to both the control and PSB-inoculated counterparts. In conclusion, the application of raw phosphate solid sludge as an agricultural substrate is deemed unsuitable, prompting the imperative need for further in-depth investigations to ascertain the nuanced intricacies underlying these outcomes.

Development of organic phosphorus vermicompost from raw phosphate rock using microorganisms and enzymes and its effect on tomato yield

Chemical phosphorus and other chemical fertilizers undergo certain changes in the soil. These changes cause crop yield loss because of changes in soil pH and EC. In addition, other toxic compounds accumulate. They also lead to serious soil contamination and threaten the environment. In this study, vermicompost was developed from raw phosphate rock by using microorganisms and phosphorus solubilizing enzymes (protease, lipase, dehydrogénase, hydrolase, urea, nitrogenesis, cellulose) to eliminate phosphorus deficiency in soil. Two-year greenhouse trials were conducted to determine the effectiveness of the organic phosphorus humus produced after six months of mineralization, and tomato plants were grown. As a result of these experiments, the effects on yield and physicochemical properties of the tomato plant were studied. Earthworm fertilizer at a rate of 4500 kg ha−1 increased the tomato yield of 22.12% compared to the control application, in the two-years means. In addition, the effect on nutrient content of tomato plants resulted in statistically significant increases (p < 0.05). When the macronutrient concentrations in the leaves of the plant were examined, they were considered to have reached the level of sufficiency. It was also found that the content of amino acids, chlorophyll and antioxidants in the tomato plant reached the highest levels compared to the control application. Based on our results, it was concluded that this organic fertilizer will contribute to higher crop yields in plants of cultural and commercial importance and to other plant growth parameters.

Chemical characterization of phosphogypsum produced from raw phosphate rock from the phosphoric acid manufacturing process

Chemical characterization of phosphogypsum produced from raw phosphate rock from the phosphoric acid manufacturing process

Global sensitivity analysis for phosphate slurry flow in pipelines using generalized polynomial chaos

Slurry transportation via pipelines has garnered growing attention across various industries worldwide, thanks to its efficiency and environmental friendliness. It has emerged as a vital tool for conveying significant volumes of raw phosphate material from extraction points to industrial plants, where it is processed into fertilizers. Yet, optimal and secure pipeline operations necessitate the careful calibration of several physical parameters and their interplay to minimize energy losses. A thorough exploration of the flow pressure drop and the various factors that influence it constitutes a crucial step in attaining this goal. The computational fluid dynamics techniques required to simulate three-dimensional slurry pipe flows pose formidable challenges, primarily due to their high computational costs. Furthermore, numerical solutions for slurry flows are frequently subject to uncertainties arising from the initial and boundary conditions in the mathematical models employed. In this study, we propose the use of polynomial chaos expansions to estimate the uncertainty inherent in the desired slurry flow and perform a sensitivity analysis of flow energy efficiency. In this framework, five parameters are considered as random variables with a given probability distribution over a prescribed range of investigation. The uncertainty is then propagated through the two-phase flow model to statistically quantify their effect on the results. Our findings reveal that variations in slurry velocity and particle size play a pivotal role in determining energy efficiency. Therefore, controlling these factors represents a critical step in ensuring the efficient and safe transportation of slurry through pipelines.

Manufacture of simple superphosphate from Tahoua rock phosphate

In this work, we used the rock phosphate Tahoua sample. It underwent several processing steps before obtaining the raw phosphate powder. However it presents a weak solubility and this weakness is due to the presence of metal oxides in the phosphate. Indeed, rock phosphate is the raw material of the fertilizer industry and it is rarely used directly as is, because of its low assimilability by plants. To solve this problem, we have transformed merchantable phosphate into phosphate fertilizers directly and easily assimilated. The objective of this work is to manufacture a simple superphosphate fertilizer (SSP) and study its solubility in perchloric acid and water. We manufactured a simple superphosphate based on crushed and ground Tahoua merchant phosphate. The studied granulometries are: (inferior to 63µm; 63µm; 100µm; 160µm). The attack was made with sulfuric acid (H2SO4) with a variation of temperatures (40°C; 60°C and 80°C) in order to determine the effects of the granulometrys and temperatures. The results obtained for granulometries (inferior to 63µm; 63µm; 100µm; 160µm) with ripening times (5th day, 12 days) and at these different temperatures are respectively 40°C (15.79%; 14.77%; 17.35%; 15.93%); 60°C (18.58% ; 8.32%; 8.32%; 12.67%); 80°C (16.40%; 19.73%; 16.54%; 21.56%) in the perchloric acid solution and 40°C (5.74%; 8.32%; 8.32%; 12.67%); 60°C (7.64%; 8.32%; 8.73%; 7.91%); 80°C (11.86%; 12.67%; 11.04%; 6.55%) in water These results allowed us to conclude that Tahoua rock phosphate is suitable for the manufacture of simple superphosphate fertilizer at 80°C (total P2O5 equals 21.54%) and at 60°C (and a soluble P2O5 equal to 12.87%) for a particle size of 160µm.

Self‑Cleaning TiO2/Phosphate Photocatalytic Degradation of Organic Dyes in Aqueous Solution

In this study, a new reactor was carried out to recover UV solar radiation to degrade the methylene blue (MB) and methyl orange (MO) dyes using the raw phosphate doped by TiO2. The raw phosphate (Pht), TiO2, and TiO2/doped phosphate (TiO2/Pht) were characterized by several techniques to determine their physicochemical properties. The performance of MB and MO photocatalytic degradation was very high around 88% for MO and 99% for MB using 1 g of TiO2/Pht at midday. This new process is capable of degrading the high concentrations of dyes in water, especially the azo dyes which are hard to treat.

Mechanical and thermal characterization of natural phosphate: Clogging understanding (Part 1)

In mining, particularly for phosphates, extraction is a crucial step. This phase presents several problems that must be treated to optimize ore flow. Among those constraints we find clogging of phosphate ore on different metal supports. It is therefore necessary to understand the factors behind this phenomenon to control it. We focused, in this paper, on the mechanical and thermal characterization of natural phosphate under different conditions of pressure, temperature and humidity. First, we evaluated the compressive strength of raw phosphate, to determine the threshold pressure, which lead to a compact solid phase. We also measured its different limits of friability. Secondly, we studied the structural properties of phosphate ore as a function of temperature and water content. This study was carried out using heating and water adsorption protocols. The results show that phosphate ore compacts easily when subjected to high pressures. In addition, it becomes easily friable when the mass handled is high. Furthermore, the source of phosphate, as well as external conditions, play an important role in its ability to lose moisture, which is the main reason for agglutination.

Geochemical Assessment and Mobility of Undesired Elements in the Sludge of the Phosphate Industry of Gafsa-Metlaoui Basin, (Southern Tunisia)

The raw phosphates in the Gafsa-Metlaoui phosphate basin are valorized by wet processes that are performed in the laundries of the Gafsa Phosphates Company (CPG, Gafsa, Tunisia) to reach market grades (&gt;28% P2O5). This enrichment process allows the increase of P2O5 content by the elimination of the coarse (&gt;2 mm) and fine (&lt;71 µm) fractions. Mineralogical analysis has shown that all the investigated materials (raw phosphate, marketable phosphate, coarse waste, and fine waste) from the laundries of M’Dhilla-Zone L and Redeyef are both composed of carbonate fluorapatite, carbonates, quartz, gypsum, clays, and clinoptilolite. Chemical analysis shows that Cr, Cd, Zn, Pb, and U are concentrated in the fine wastes and associated with the clay–phosphate fraction. The rare earth elements are more concentrated in both raw and marketable phosphates. Drilling and sludge-water analysis, along with leaching tests conducted on the fine wastes, showed that, due to phosphate industry, cadmium, fluorine, and sulfate contributing to the pollution of water resources in the region, pollution is more conspicuous at M’Dhilla.

A Water-Energy-Food Nexus approach for conducting trade-off analysis: Morocco's phosphate industry in the Khouribga region

Abstract. The study objective was to develop and use the Water-Energy-Food Nexus Phosphate (WEF-P) Tool to evaluate the impact of Morocco's phosphate industry on water, energy, and food sectors of Khouribga, which is the representative phosphate mining region of Morocco. The developed WEF-P Tool enabled a trade-off analysis based on integrating supply-chain processes, transportation, and water–energy footprints of the region. Field data from the mining to transportation processes were collected and applied to possible supply-chain scenarios in accordance with the type of product (phosphate rock and slurry). The potential impacts of the scenarios were considered in terms of the water supply in the agricultural areas. The analysis of the positive impacts of dynamic management suggests that seasonal management of phosphate production (less during the irrigated season, more during wetter or rainier seasons) is more effective. Additionally, while the transport of raw phosphate slurry through a pipeline increased the total water required to 34.6×106 m3, which is an increase of 76 % over the “business as usual” (BAU) scenario, it also resulted in an energy savings of nearly 80 % over BAU: slurry transport requires only 40.5×106 L of fossil fuel instead of the 204×106 L required to transport rocks. During the dry or “water-scarce” irrigation season (May to July), total groundwater use decreased from 5.8×106 to 5.2×106 m3. Dynamic management of the phosphate industry can also save 143 MWh (megawatt-hour) of electricity annually and can bring a reduction of 117 t of CO2 emissions. Making water available at the correct season and location requires analysis of complex scientific, technical, socioeconomic, regulatory, and political issues. The WEF-P Tool can assist by assessing user-created scenarios; thus, it is an effective management-decision aid for ensuring more sustainable use of limited resources and increased reliability of water resources for both agricultural and industrial use. This study on the applications of WEF Nexus to the phosphate industry offers a roadmap for other industrial application for which trade-offs between the primary resources must be considered.

Characterization of crude and calcined phosphates of Kef Essennoun (Djebel Onk, Algeria)

Rock phosphate is the fundamental component for the manufacture of phosphoric acid and phosphate fertilizers. The aim of this study is to predict how sample preparation of Kef Essennoun phosphate responds to heat treatment and to estimate the purity of the raw and calcined phosphates. The influence of temperature (600–900 °C) was evaluated. The evolution of thermal treatment and the characterization of the Kef Essennoun ore (Djebel Onk mine, Algeria) were carried out by various analytical techniques including X-ray diffraction (XRD), wavelength-dispersive X-ray fluorescence, Fourier-transform infrared spectroscopy, thermogravimetric analysis/differential thermal analysis, and scanning electron microscopy (SEM). The results showed that the raw phosphate is a mixture of six phases, of which carbonate hydroxyapatite [Ca10(PO4)3(CO3)3(OH)2] is the dominant phase. With heat treatment, at 700 °C, a fluorapatite [Ca5(PO4)3F] phase appeared, as confirmed by XRD analysis, with good crystallization indicated by SEM. The P2O5 content was increased from 28.389% in raw phosphate to 31.085% in the calcined product. The dissolution of the calcined phosphate at 900 °C was completed by HNO3 acid attack, and occurred rapidly at ambient temperature. The results show that the production of phosphoric acid by Ca5(PO4)3F was more easily achieved with optimized consumption of the acid attack.

Impact of Phosphate Industry on Natural Radioactivity in Sediment, Seawater, and Coastal Marine Fauna of El Jadida Province, Morocco

This study aims to investigate the radiological impact of phosphogypsum (PG) discharge on the marine environment along the coast of the province of El Jadida (Morocco). The specific activity of the main radionuclides present in the raw phosphates, PG, and coastal sands will be measured using gamma spectrometry. The volume activities of radon in samples of sand, seawater, and mussel type Mytilus galloprovincialis will be evaluated using passive alpha dosimetry based on the use of LR115 detectors. The analysis shows that the radioactivity of the raw phosphates was mainly attributed to the radionuclides of the uranium (238U) family that has a specific activity of approximately 1,264 Bq/kg. The results revealed that the production of phosphoric acid (H3PO4)using the wet process has caused a dramatic radioactive imbalance in the 238U family presented in the formed PG. This disequilibrium was due to a reduction in the amount of 238U radionuclides by 84% with a quantitative release of radium (226Ra) radionuclides (845 Bq/kg). Therefore, the discharge of PG into the high seas has caused the contamination of natural beach sand by 226Ra and 238U radionuclides. The specific activity of 226Ra in beach sand increased from 16 to 217 Bq/kg when approaching the industrial discharge point of the phosphates. A large variation was noticed in the volume activities of radon measured in different samples of sand, seawater, and mussel, from 174 to 7,287 Bq/m3, 11 to 354 Bq/m3, and 18 to 497 Bq/m3, respectively. This marine radioactive contamination is spreading over a large area around the PG discharge points, which has a diameter of 10 km. This radioactive pollution could damage marine and coastal ecosystems and harm the livelihood of entire communities.

The Effect of Organomineral on pH, Nitrogen Content, Organic-C Content and Yield of Upland Rice (Oryza sativa L.) on Inceptisols, West Java Indonesia

Generally, Inceptisols has low to moderate fertility characteristics. This condition can make a problem on the development of upland rice production caused by poor soil quality. Upland rice is one of the cultivated plants that is cultivated on dry land. This research was aimed to find the perfect combination of organomineral including humic acid, zeolite, natural phosphate, and dolomite on soil and yield of upland rice in Inceptisols. This research was conducted at Ciparanje, Faculty of Agriculture, Universitas Padjadjaran from July 2017 to February 2018. This experiment applied a Randomize Block Design (RBD) consisted of 10 treatments and three repetitions with the combination of humic acid (6; 8; 10 kg/ha); zeolite (150; 200; 250 kg/ha); dolomite (100; 150; 200 kg/ha) and natural phosphate (250; 300; 350 kg/ha). The result of this experiment showed that there was a significant effect of the organomineral on pH, Organic-C and yield of upland rice but no for total N. However the combination of humic acid 10 kg / ha + zeolite 150 kg / ha + dolomite 100 kg / ha + raw phosphate 250 kg / ha is the best doses compared to other combinations.

Enhanced Phosphorus Release from Phosphate Rock Activated with Lignite by Mechanical Microcrystallization: Effects of Several Typical Grinding Parameters

Recently, microcrystallization technology has gained much interest because of the enhanced dissolution of the target sample and promotion of the sustainable development of agriculture. Phosphorus (P) is one of the most important nutrients for increasing crop yield; the increase in effective P ratio directly from raw phosphate rock (PR) powder by mechanical grinding to increase its microcrystallinity is believed to be the best choice for this purpose. This study reports the improvement in the activation property of PR powder with different lignite ratios (1%, 2%, 3%, and 5%), particularly the relationship between particle-size distribution, specific surface area, granule morphology, and the citric acid-soluble P. It was found that a 3% lignite addition was the optimal treatment for increasing the release of citric acid-soluble P. The maximum total amount of dry matter from rapeseed cultivation and the available P after the test increased by 56.1% and 89.6%, respectively, with direct use of PR and microcrystallized PR powder (PR2), compared with the control test without any addition of phosphate minerals.

The Beneficiation Processes of Low-Grade Sedimentary Phosphates of Tozeur-Nefta Deposit (Gafsa-Metlaoui Basin: South of Tunisia)

The enrichment of the low-grade-phosphate ore of the Tozeur-Nefta deposit was investigated using scrubbing-attrition, ball grinding and anionic/cationic reverse flotation in order to separate phosphate-rich particles from their gangue. The choice of the beneficiation process was based on the petrographic, mineralogical and chemical analyses. The petrographic and mineralogical studies have revealed the abundance of phosphatic (carbonate-fluorapatite-CFA) particles) coupled with carbonates (calcite, dolomite,) and silicates (quartz, illite, kaolonite) that constitute the (endo/exo) gangue of these ores. Chemical analysis has demonstrated that the raw phosphate sample contains low amounts of P2O5 (12.0%) and MgO (4.9%) and high amounts of CaO (40.7%) and SiO2 (20.5%). Microscopic observation/counting has shown that the release mesh occurs in the 71–315 μm size. Scrubbing-attrition, grinding and reverse flotation methods were applied to the +71μm fraction. Scrubbing-attrition tests of the 71–315 μm fraction have helped to improve the P2O5 grade to 15.5%. Ball-grinding tests were used to reduce the coarse fraction +315 μm. Grounded materials were sieved to 71–315 μm and combined with the scrubbed fraction in the flotation feed. Reverse-flotation tests of the phosphate-rich fraction (71–315 μm) have helped to improve the P2O5 grade to 27.1%, with a recovery rate of 92.4%.

Scientific basis of effective energy resource use and environmentally safe processing of phosphorus-containing manufacturing waste of ore-dressing barrows and processing enterprises

Waste barrows of ore-dressing and processing enterprises have a special role among anthropogenic deposits where fine finders are stored, intensifying their amenability to wind and water erosion. Rock barrows occupy much larger territories than factory lands, leading to environmental pollution. Herein, we create a fundamental physical and chemical basis for the effective use of energy resources and environmentally safe processing of ore-dressing waste products, which allows for transformation of raw fine finders stored in tailing dumps into competitive products and decreases the amount of resources aimed toward ground disposal. It will also assure the extermination of tailing dumps and grounds. This can also minimize negative environmental impact and stabilize further development. For this purpose, a mathematical model of a complex chemical energy technological system (CETS) aimed at manufacturing phosphorite pellets has been developed. Large-scale models of multistage chemical energy technological processes of baking and coking moving dense multilayer masses of phosphorite pellets, which differ in their raw material physical, chemical, and granulometric characteristics, have also been developed. Additionally, special multilayer algorithms for formulating making decisions concerning optimal energy resource effectiveness management of CETS manufacturing phosphorite pellets have been developed. They differ in the quality ratings of the prepared pellets in the characteristics of raw phosphate materials. These calculations also consider the impact of controlling the actions of temperature and speed of gas supply for the exchange of having a dynamic dense multilayer pellets mass, which allows for using an available potential of increased effectiveness to maximize energy resources of CETS.

Addition of low-grade phosphate rock for improvement of soil fertility on plant models: A preliminary case study

To sustain food production in the course of time and for efficient utilization of available resources, it is essential to approach improved methodologies and techniques for enhancing crop productivity. Commercial agricultural production has achieved this through the external application of synthetic inorganic fertilizers which has some detrimental effects on the soil structure, composition, microflora and additional characteristic properties of soil. The mining and industrial waste is an unwanted by-product of mining. Reusing and recycling of these wastes is possible therefore recovery and recycling is the most excellent environmental resolution to save raw resources and to diminish the number of industrialized waste materials produced, and also control the contamination of the environment. In the present study, an attempt has been made to utilize low-grade phosphate rock as a fertilizer and its effects on soil fertility. The raw phosphate rock samples are subjected to physicochemical test followed by elemental analysis by EDXRF (Energy Dispersive X-ray Fluorescence). The tests confirmed that it is possible to use this raw phosphate rock as fertilizer for plant growth in a simple process. Different soil and plant parameters were measured. Data on pot experiment revealed higher plant growth is in PR amended soil than normal soil. The greatest positive effect on growth was recorded in the treatments that received phosphate rock (8g) per kg of soil. Thus, observations indicated that direct application of this PR could be an alternative, promising technology for simultaneous waste minimization, waste utilization, and improved resource-use efficiency.

Assessing stress response of Stylophora pistillata towards oil and phosphate pollution in the Gulf of Aqaba, using molecular and biochemical markers

ABSTRACTCrude oil (from oil terminal) and raw phosphate (from phosphate port) pollution are responsible for the lowered health conditions of coral reefs at their vicinity in the Jordanian coast of the Gulf of Aqaba. Both in situ incubations and ex situ laboratory exposure experiments were used to study the effects of those pollutants on corals, by using molecular and biochemical biomarkers in the coral Stylophora pistillata. For ex situ part of the experiment, crude oil and raw phosphate were added to a final concentration of 500 ppm for both pollutants. The DNA damage was assessed by Comet assay, while biochemical stress markers were reassessed by lipid peroxidation (LPO) test. Although the corals looked healthy from outside, the use of stress biomarkers indicated that they are under high pressure at the cellular level. The corals incubated with oil and phosphate had more DNA damage and LPO in comparison with the control samples. The results obtained suggest that the use of stress biomarkers can be used as important prognostic tools for examining the sub-lethal stress on corals before their death.

Effect of phosphorus solubilizing bacteria on some soil properties, wheat yield and nutrient contents

Application of chemical fertilizers besides economic concerns has been a reason of environmental and ecosystem degradation, so sustainable organic agriculture is becoming popular in researches and among farming communities. Phosphorus holds second position after nitrogen among macronutrients required for better plant growth and is needed in higher amounts. Meeting this high phosphorus input for better crop yields causes environmental problems like eutrophication, so phosphorus solubilizing bacteria (PSB) and plant growth promoting rhizobacteria (PGPR) are being emphasized to utilize phosphorus fixed in soil layers. This study was carried out to evaluate the effect of PSB on plant growth, soil biological properties including enzymes and soil respiration. Treatments including control, 50 mg kg -1 nitrogen, 50 mg kg -1 nitrogen and 12 mg kg -1 phosphorus applications reduced dosage of nitrogen 25 mg kg -1 with PGPR and 25 mg kg -1 nitrogen along with 0.12 g raw phosphate and PGPR. Results indicated that plant parameters like above and below ground plant biomasses (fresh and dry weight), plant nitrogen and phosphorus content were significantly enhanced in all the treatments when compared with the control. While soil pH in rhizosphere significantly increased with the treatments, bulk soil pH decreased with PGPR treatments when compared with all other treatments. EC values in rhizosphere and bulk soils were not significantly influenced with the treatments. Rhizospheric and bulk soil showed high amount of N, P and organic matter in PGPR treatments. Alkaline phosphatase and β-glucosidase activities were found significantly higher in the last treatment than the other treatments. Basal soil respiration was interestingly found higher in control soil but did not differ statistically from the other treatments. Concluding, application of PGPR with lower amounts of chemical fertilizers can reduce the use of chemical fertilizers and has also potential of improving soil health in long term aspects.

Removal of odorous sulphur compounds from industrial gases by biotrickling filters

A pilot plant for the treatment of Sulphur-based odorous gases was installed in a line of a phosphoric acid plant located in Skhira, Tunisia. The air pollution control system train consisted of a first stage, including a chemical scrubber operating with an alkaline solution containing caustic soda, followed by a two-stage biotrickling filter (BTF) filled with Mytilus edulis shells. This study evaluated the performance of the dual-stage BTF in removing hydrogen sulphide (H2S), sulphur dioxide (SO2) and dimethyl sulphide (DMS) from the phosphoric acid reactor’s exhaust air current. Concentrations of H2S, SO2 and DMS at the inlet of the two-stage BTF were 10-30 ppm, &lt; 1-20 ppm and 16-30 ppm, respectively. All of the respective concentrations at the outlet of the biological step were &lt; 1 ppm, except for the H2S in the outlet during the first day of operation (10 ppm). Removal efficiencies were generally higher than 95% for all compounds, and remained high even with an increase of the off-gas flow rate. Mass-removal capacity was at least 2.0 g m-3 h-1, 0.5 g m-3 h-1 and 6.2 g m-3 h-1, for H2S, SO2 and DMS, respectively. The removal efficiencies of the process were satisfactory, especially considering the already low inlet concentrations, due to the high quality of the raw phosphate used.