SLUDGE CHARACTERIZATION OF KHARTOUM PETROLEUM REFINING WASTEWATER TREATMENT PLANT- KHARTOUM-SUDAN

Clearance of sludge has made a major task in latest periods. In the current study sludge from KPRWTP were investigated concerning physicochemical characteristics & disposal options. Organic content of petroleum sludge & clay soil was 0.23 ±0.09% and 0.186±0.1%, respectively. Metals average concentration: Chromium: 130.95±27.32 mg/kg; Arsenic: 0.899±0.434 mg/kg; lead: 47.83±21.44 mg/kg; Cadmium: 18.33±9.04 mg/kg; Copper: 209±31.18 mg/kg; Zinc: Nickel:


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Disposed of petroleum sludge to the surroundings, generate riskassociated with physicochemical characteristics of the adjacent environment, causingalteration in the morphological properties (Robertson et al., 2007).Thus, subsequent deficiency in vegetation growth and receiving nutrient uptake was noticed (Al-Mutairi et al., 2008).
Generation of huge quantities of sludge from the wastewater treatment, had the capacity to pollute soil, groundwater, &surface water and cause a risk to the natural resources and environment as a whole, because it contains detrimental level of contaminants including heavy metals (Stylianouet al., 2007). Disposal of metals is a greatworry due to their being non-decomposable and their affinity to bioaccumulation. Thus, they can influence the health of living things andthe quality of environment (Nair et al., 2008).
However, there are different technologies that concentrated sludge, and thendecrease the bulks that we finally must disposedof. Moreover, sludge can be handled &stabilized, which can impart a low, but none-the-less marketable value to this waste. These technologies and practices do indeed constitute pollution prevention and waste minimization programs within water treatment plant operations. This driving us to a group of technologies that emphasis on: (A) thickening of sludge, (B) stabilization of sludge, (C) treatment and disposal of sludge. Therefore, sludge treatment is one of the most vitaltasks in management of wastewater (Fytili and Zabaniotou, 2008).There are numeroustechniquesfor treatment of sludge, each with benefits and disadvantages such as utilization of land (Shirani et

Study Area
The studied Khartoum Refinery Company limited (KRC) located at Al Gaili town, about 80 Km, from Khartoum the Capital of Sudan,12 Km from river Nile, 6 km from Altahdi high way , and beside the rail way. Wastewater of petroleum industry from the investigate area has been collected and pretreated, the treated water will be discharge into the oxidation pond and KRC Parks. The generated sludge has been collected from the tank of sedimentation and dumped outside the study area. The key treatment technology that been used is Cyclic Activated Sludge System (CASS) which is consist of the following stages.

Pre-treatment stage (Grid):
It's a mechanical stage for blocking the suspended substances in sewage it put before wastewater collection point and adjustment pond to hold up the big solid in order to avoid the bad influence to following treatment process.

Adjustment Stage:
It is a pond used for the adjusting the un-regular discharge and water quality of wastewater collection by settingthe balance of water quality, and make the wastewater enter biological treatment stage with design capacity.

Biological treatment:
The biological treatment process of the system will be performed by Cyclic Activated Sludge System ponds, which have different function of primary sedimentation, aeration, secondary sedimentation all as one unit. It is an intermittent reaction system. In this pond active sludge process is running repeatedly between aeration and un aeration period, the bio-chemical reaction and sludge water separation process will be also finished in the pond.

Materials and Methods:-Sampling
Samples of sludge petroleum were obtained from refining plant of treatment wastewater (PRWWTP) in Northern part of Khartoum-Sudan (Fig. 1), 20 sludge samples were collected on weekly base in period from June -November 2014 from secondary sedimentation tank of the Cyclic Activated Sludge System ponds process. Standard of procedures for Water and Wastewater Examination was applied during transporting and storage of samples (APHA,2005).

Characterization of sludge
Samples of petroleum sludge were obtained from refining wastewater treatment plant of Khartoum Refinery Company limited (KRC), secondary sedimentation tank (unit 3), Khartoum, Sudan. This Companyhiresa unit of chemical and biological treatment and utilize CaCO 3 and Fe 2 SO 4 as coagulant. Sludge moisture and organic contents were determined,pH (781 pH meter, Metrohm, Switzerland), electrical conductivity (712 Conduct meter, Metrohm, Switzerland), were determined by APHA method(APHA, 2012).Regarding the heavy metal determination , five gramsfrom sieved ground dried sludge sample was reacted with a blend of concentrated HCL and HNO 3 (1:3) for one day (24 hours) on a hot plate , then to make a 500 ml solution a volume of distilled water (500 ml) was boiled with the sample for two and half hours. Lastly, the obtained mixture was passed through 0.45 filter paper then the collected filtrate was used to evaluate the content of Chromium, Arsenic, Lead, Cadmium, Nickel, copper, and Zinc by using Atomic Absorption Spectrophotometer (AAS) (Shimadzu AA 6800) (Raposo et al., 2009;Juel et al., 2015;Saha and Hossain, 2011).

Statistical analysis
All samples analyses were repeated three times. The means and standard deviation (±SD) were done according to SAS program (SAS, 1989). The different parameters of heavy metals and soil solution composition were explored using correlation. Table 1displaysmetal content &physicochemical characteristics of the sample frompetroleum sludge and soil of Khartoum Refinery Company. The petroleum sludge and clay soilmoisture content were75 ± 8.34% &15.06± 3.56%, respectively. Organic content of both sludge and soilwere0.23 ±0.09% and 0.186±0.1%, respectively. Most oilfield waters and refinery have pH between 4.0 and 8.0 while in Sudan where this study was carried it fluctuated from 7.o to 8.0 (Ali et al., 2017). It is well known that calcium and iron mixtures solubility is approximately high dependent on pH of the medium, and the tendency of water to form scales is reduced at lower levels of pH, therefore, the calcium and iron precipitation in pipelines of Sudanese oil industry is predicted to be in high level (Nuha, 2013).The investigated sludge pH was slightly alkaline (8.65±0.45). Electrical conductivity of the investigated petroleum sludge was high compared with other studies reported by some researchers (4, 15, and 16). It is well known that high electrical conductivity means that high salinity which create condition of incompatibility of sludge for application in land.Average concentration of the metals were: Chromium: 130.95±27.32 mg/ kg; Arsenic: 0.899±0.434 mg/kg; lead: 47.83±21.44 mg/kg; Cadmium: 18.33±9.04 mg/kg; Copper:209±31.18 mg/kg; Zinc: 631±159.57 mg/kg; Nickel:6.6±2.44 mg/kg; cobalt: 35.54±10.08 mg/kg; manganese:35.54±10.08 mg/kg: iron: 501±5490.04 mg/kg: titanium: 108.3±18.33 mg/kg, and zirconium: 2.54±0.246 mg/kg respectively (Table 1).Also this table shows the sequence of metals investigated in the petroleum sludge as: Zinc ˃Iron˃ Copper˃ Chromium˃ Titanium ˃ lead˃ Cobalt ˃Cadmium˃ Manganese ˃Nickel ˃Zirconium ˃Arsenic, we noticed that the content of iron in the sludge approximately was high this attributed to the utilization of ferric chloride (FeCl 3 ) and ferrous sulphate (FeSO 4 ) during wastewater treatment processes as coagulant-flocculants and co-oxidation elements respectively.Sludge compositionmaydiffer from company to company reliant on the types of treatment proceduresinvolved and chemicals used. Nevertheless, these metals had been the prevalentingredient in the sludge of petroleum as reported in other research work. Previous studies showed that Chromium, Cadmium, and lead contents were high compared to the content of Nickel, Zinc, and Copper which were low and this due to the characteristics of the produced sludge (Wang el al., 2005).

Sludge characterization
Petroleum sludge and soil exhibit distribution of particle size and chemical composition as a ratio of available oxides are explained respectively in Tables 2 and 3. Sludge of petroleum was made up of elements atoms of a slightly bigger bulkportioncompared to the soil (sludge: clay and silt 58.9%, sand 41.1%;soil: clay and silt 76%, sand 34%). The core constituents of sludge of petroleum were Fe 2 O 3 (38.45%), SiO 2 (8.55%), CaO (30.35%), MgO (0.85%). The soil components (clay) that are used for manufacturing of brick was made up of comparable constituents that exist in the sludge of petroleum but in altered amounts. Consequently soil (clay) can be somewhat substituted by sludge of petroleum as raw substances for manufacture of constriction materials.

Applications of sludge of wastewater treatment plant Application of sludge in Industrial, Residential, and Nonresidential utilizations:
Wastewater treatment plant generated Enormousquantity of sludge daily, which is upturnthe worries over their disposal and related costs.  (FLDEP,2006).According to standards of (NJDEPSCC) As, Cd, Cu,Pb, Ni, andZnhave significantly lower concentration in sludgewith regards to guideline assigned for residential and nonresidential land usages. On the other hand chromium represent the exception metals since was significantly have higher concentration ofCr guideline assigned for residential and nonresidential land usage. In case of using this metals for industrial application both copper and zinc were significantly higher than the assigned guidelines for industrial utilization so were restricted for this application (Table 4).
On the other hand comparing our study results with Florida Department of Environmental Protection Soil Cleanup Target Levels (FDEPSCTLs) it showed that Cu and Zn were only metals in sludge that significantlyhave high concentration regarding guideline assigned for residential applications only.Other metal factors have lower contentsrelated with FDEPCTLs guidelines for direct contact of soil in both nonresidential and industrial utilizations.Therefore,all other investigated metals were suitable for utilization for nonresidential and industrial application since they have concentration significantly lower than that guidelines assigned for application.

Application of sludge in Building and construction utilization
Waste stabilization can be applied as a building substance providing that the substanceowns the essential engineering characteristics and leakslethalcontaminants to an adequatelevel (Hassan et  The sludge of the current studied has a good potential for utilizing as a raw substance for manufacture of building materials. However, the present of heavy metals, which was above the required level, can limit its use for this determination. On other hand the FloridaDepartment of Environmental Protection guidance provided a blending techniques, so that sludge can be blended with unpolluted clay soil to decrease the possible health risks from exposure to the sludge, providing that the subsequentblendwassuitable for valuableutilization. To assess the suitablecombinedpercentage (percentage of combinedsubstance to sludge) for dropping the pollutantsenclosed in the sludge.FloridaDepartment of Environmental Protection (FDEP)endorses the following equivalence(FLDEP,2006): Ratio of blending = A-B (1) (FLDEP,2006).

B-C Where,
A ≡ amount of contaminant in the sludge, mg/kg, B≡ target amount of the blended material, mg/kg, C≡ amount of contaminant in the material used for blending, mg/kg. Some of researchers found that small percentage of fine sludge from steel was useful to ceramic building out of the consideration of the content of heavy metals (Vieiraet al., 2006). On the other hand, the technology of stabilization and solidification was used to improve the properties of the sludge from electroplating activities by producing substances which is beneficial for concrete block building .

Application of sludge in wastewater treatment plant
Utilization of sludge in the wastewater treatment plants should be well-thought-out under precaution given to investigation ofnature of chemicals (compositions), sludge volume, and loading of solids which required to be taken in the accountsince it maydisturb the capacity ofwastewater solid items &risethe costs of operational and maintenance.Previous studies highlighted application of sludge as adsorbent materials for removal of contaminants, metals like phosphorus, and heavy metals (e.g., Pb and Cu) in the wastewater, in addition to that sludge give brilliant removal results when used as coagulant substances in refinery of wastewater from vegetable oil and can be comparable with aluminum sulfate and ferric chloride in its removal efficiencies (Basibuyuk and Kalat, 2004;Yang et al., 2006;Georgantas and Grigoropoulou, 2005;Wu CHet al., 2004).Also, there is some experience in applying sludge in removal of dyestuff substances from wastewater of both tannery and textile industries (Chu, 2001). with suggested level of content should be functionalin land. Previously some researchers reported the potentiality of sludge from food industry in improving the productivity of soil by combined the vermin composting 30% cow manure (Yadav and Garg, 2009).They found that iron content was increased significantly in the final compost, while the contents of copper, manganese, and zinc in the mixture was in a decreasing rate (Yadav and Garg, 2009).

Application of sludge in Land use
In the current research work, as stated before, in comparison with the limits of international standards such as New Jersey Department of Environmental Protection Soil Cleanup Criteria (NJDEPSCC) and Florida Department of Environmental Protection Soil Cleanup Target Levels (FDEPSCTLs) for residential &nonresidential for utilization in land, Chromium, copper and zinccontents in the investigated sludge was greater which create inappropriatesituation for land use.

Sludge dumping
This the final step in waste management which is to dispose the sludge in the dumping allocated area. Since such sludge usually contain hazards materials, which can generatesevere environmental harms in groundwater, it is essential to protect the under part of landfill with the suitable impermeable substances, such as clay or plastic liner (UNEP, 2002). Leaching can be evaluated by the toxicity characteristic leaching procedure (TCLP) which stated that if the pollutant content in toxicity characteristic leaching method was above the recommended scheduled in the Land Disposal Restrictions (LDR) of Resource Conservation and Recovery Act (RCRA), then the sludge is categorized as hazardous (USEPA, 2011). Figure 3 shows that the heavy metals under investigation were significantly lesser than the quantities controlled by toxicity characteristic leaching procedure (TCLP) of Resource Conservation and Recovery Act (RCRA), with exception for chromium content that was expressively great in the investigated sludge. Therefore, the considered sludge under this research work must be disposed in a Resource Conservation and Recovery Act subtitle C class landfill, which indicates that current practice of dumping sludge should be abandoned. Khartoum refinery company in Sudan adopt currently practice of management of the studied petroleum wastewater sludge is to release it, in the form of dry solid materials, in lined evaporation ponds in the site. In such case of disposal method, sludge cannot add to landfill leachate, to cause groundwater pollution, so the leachate cannot interfere with the food chain and cause health risk. These lined evaporated ponds could be utilized as an economic and harmlesstechnique for the liquid from industries and disposal of sludge in dry environments (Al Yaqout, 2003).

Conclusions:-
The current research work investigated the physicochemical characteristic of petroleum sludge derived from Khartoum Refining Wastewater Treatment Plant in Sudan. Torecognize their performanceindiverse condition with an objective to decide their appropriateness as a possiblebuildingsolid for residential, nonresidential, and industries. The arrangement of the investigated metals in the sludge of petroleum was as follows: Zinc ˃Iron˃ Copper˃ Chromium˃ Titanium ˃ lead˃ Cobalt ˃Cadmium˃ Manganese ˃Nickel ˃Zirconium ˃Arsenic, we noticed that the content of iron in the sludge approximately was high, this attributed to the utilization of ferric chloride (FeCl 3 ) and ferrous sulphate (FeSO 4 ) during wastewater treatment processes as coagulant-flocculants and co-oxidation elements respectively. The Petroleum sludge was made up of units of a slightly bigger bulkportioncompare to the soil (sludge: clay and silt 58.9%, sand 41.1%; soil: clay and silt 76%, sand 34%). The core constituents of petroleum sludge were Fe 2 O 3 (38.45%), SiO 2 (8.55%), CaO (30.35%), MgO (0.85%). According to standards of (NJDEPSCC) As, Cd, Cu, Pb, Ni, and Zn have significantly lower concentration in sludge with regards to guideline assigned for residential and nonresidential land utilization. On the other hand, comparing our study results with FDEPSCTLs itshowed that Cuand Zn were only metals in sludge that significantly have high concentration regarding guideline assigned for residential applications only. The study also shows that the heavy metals under investigation were significantly lesser than the quantities controlled by (TCLP) of (RCRA), with exception for chromium content that was expressively great in the investigated sludge. Therefore, the considered sludge under this research work must be disposed in a subtitle C class landfill of Resource Conservation and Recovery Act, which indicates that presentmethod of sludge dumping must be discarded.