Assessment of The Quality of Treated Sewage Sludge (Doha, Qatar)

This study aims at evaluating the quality of currently produced sewage sludge in Doha, State of Qatar. Doha urban areas are currently served by two tertiary wastewater treatment plants at Al-Neaaga (Doha south plant) and Al-Sailiyah (Doha west plant). Industrial areas around Doha are getting wastewater treatment facilities where extra amounts of sludge will be generated. Sludge is composed of primary and secondary sludge and sedimented sand filters backwash. It undergoes further treatment by drying beds for Doha south plant and centrifugation for Doha west plant. Doha south plant produced 190 m/d sludge, Doha west plant produced 110 m/d sludge, and industrial region plant produced 16 m/d sludge. Samples were collected weekly for two months before and after drying beds from Doha south plant, after centrifuge and after storage from Doha west plant, and from industrial region plant. Samples were analyzed chemically and microbiologically. The results revealed that sludge produced by the three plants had heavy metals concentration way below the EPA ceiling limits for land application. On the other hand, the microbiological characterization of the product classified it as class B sludge according to EPA classification which requires significantly reduction of pathogen. Ascaris lombricoides and Toxocara cati were the most dominant ova detected. The sludge produced needs monitoring and further treatment before its application on land. INTRODUCTION Sewage sludge is the solid, semisolid, or liquid residue generated during treatment of domestic sewage.(1) Sludge, also known as biosolids, is composed mostly of human waste that is treated to reduce the prevalence of disease-causing bacteria.(2) The use and disposal of biosolids is always preceded with treatments to ensure regulatory requirements are met, public health and the environment are being protected, to facilitate handling and to reduce costs.(3) The use of sewage sludge as soil amendments or for land reclamation has been increased to reduce the 602 Bull High Inst Public Health Vol.37 No.3 [2007] volume of sewage sludge that must be landfilled, incinerated, or disposed of at surface sites.(1) The sludge treatment processes focus on the removal of water and the destruction of pathogens. The treatment processes prepare biosolids specifically for intended methods of use or disposal.(3) The best practical environmental option for the management of sewage sludge is its beneficial application to agricultural land.(4) Biosolids are applied to agriculture and non-agriculture lands as soil amendments, because they can improve the chemical and physical properties of soils and they contain nutrients and trace elements important for plant growth.(1,5) Sewage sludge, if applied inappropriately can also be potentially harmful to the water and soil environment and human and animal health.(4) However, careful use of sewage sludge is necessary to ensure pathogenic, nutrients, and heavy metals do not contaminate ground water.(6) Care should always be taken when applying sewage sludge to land to prevent any forms of adverse environmental impacts. Sludge application rates must be adjusted and under certain circumstances, spreading might have to be discontinued.(7) Qatar mediates coast of the Arab Gulf, which is a peninsula extending to the north in the Gulf waters. The total area of islands, including 11493 Km2. It is divided administratively into ten municipalities. Doha is the most important city, the capital, is the potential and commercial center for state of Qatar .Abd-Elaty et al., 603 and is located in the mid-eastern Coast of the peninsula of Qatar. The population of Qatar is 743 thousand people, 80% are concentrated in Doha. Its climate is desert moderate, characterized by long hot summer with temperature range of 25-460C and winter short little rain.(8,9) Doha urban areas are currently served by two tertiary wastewater treatment plants at Al-Neaaga and AlSailiyah. Industrial areas around Doha are getting wastewater treatment facilities where extra amounts of sludge will be generated. Sludge is composed of primary sludge, secondary sludge, and sand filters backwashing liquid sedimentation. It undergoes further treatment by drying beds for Doha south plant and centrifugation for Doha west plant. Doha south plant produced 190 m3/d sludge with solid concentration of 16%, Doha west plant produced 110 m3/d sludge with solid concentration of 70%, and industrial region plant produced 16 m3/d sludge with no treatment. This study aims at evaluating the quality of currently produced sewage sludge in Doha, state of Qatar. MATERIAL AND METHODS Samples were collected weekly for two months before and after drying beds from Doha south plant, after centrifugation and after storage from Doha west plant, and from industrial region plant. Samples were analyzed physicochemically and microbiologically at Environmental Studies Center Laboratories, Qatar University according to listed references from 10 to 17 as presented in table (1). 604 Bull High Inst Public Health Vol.37 No.3 [2007] RESULTS AND DISCUSSION Doha west plant: The primary sludge (generated from primary sedimentation tank) which contains 3-7% solids and secondary sludge (generated from secondary biological treatment processes) which contains 0.5-2% solids are mixed and thickened by adding polymer and using air at the Dissolved Air Flotation (DAF) unites. Then it is sent to sludge consolidation tank. The settled sludge is pumped from this tank to anaerobic digesters. Finally, sludge from secondary digesters is fed to drying beds. The sludge samples were collected before and after drying beds. 1Before drying beds Table (2) represented the Physicochemical characterization of sludge samples taken before drying beds. The water content ranged between 84.5888.76%, nitrite average was 0.0002%, nitrate was 0.0011%, and ammonia average was 0.0039%. Phosphorus average was 17.93%. The average value of TOC was 25.05 % and Calcium was 5926 ppm. The application of liquid or dewatered sludge on land is one of the most effective and attractive methods because it has a relatively high content of nutritive elements such as Ca, Mg, P, N, and organic carbon. However, there is a risk that toxic consituents in sludge, such as trace metals and chlorinated hydrocarbons, may accumulate in soil and contaminate ground water, crops, and enter the food chains. (18) Sewage sludge may contain appreciable amounts of chlorinated hydrocarbons. The samples were analyzed for TPHs and PCBs; they were detected in a concentration ranging .Abd-Elaty et al., 605 between 543-1264 ppm for TPHs and 0.0-0.138 ppb for PCBs. The trace metals measurements in sludge samples collected before drying beds recorded the following order for the highest values: Iron (13116 ppm)> Selenium (2195 ppm)> Copper (1031 ppm) and this order for the lowest values: Mercury (1.71 ppm)< Arsenic (7.64 ppm)< Molybdenum (17.88 ppm). All measured metals were in compliance with the EPA exceptional quality for unrestricted land application except Selenium which recorded a relatively high value as presented in table (2a). A large number of enteric bacteria and viral pathogens may be excreted by infected individuals and may therefore be present in untreated sewage. Since a large number of these pathogens become associated with wastewater solids, many are not completely removed during sewage treatment processes and are merely transferred to wastewater sludge. The latter are further digested anaerobically or aerobically to stabilize sludge solids.(19,20) the anaerobic biological reactions are carried out by microorganisms. Both anaerobic and facultative bacteria degrade the organic solids by converting them into soluble substances and gaseous products.(21) It is well established that anaerobic digestion of sludge does not completely remove bacterial or viral pathogens. Table (2b) presented the microbiological characterization of sewage sludge samples collected before drying beds. It was noticed that total coliform average was 1.56E+09 MPN/gds, fecal coliform average was 1.55E+09 MPN/gds and total Nematoda ova average was 4.11E+05 ova/4gds. 606 Bull High Inst Public Health Vol.37 No.3 [2007] Total coliform value was approximately the same of the fecal coliform value, because sewage sludge is composed mostly of human waste and fecal coliform associated with feces from warm blooded vertebrates. These values were higher than the EPA permissible limits (class A and B) for reuse in agriculture. The examination of samples for the Nematoda species eggs showed that Ascaris lombricoides, Toxocara cati and Hymenolopis nana were the most dominant which were detected in all samples collected, while Hymenolopis diminuta and hookworms were detected in 75% of samples. On the other hand, Fasciola hepatica and Taenia saginata were detected in 50% only from samples. It was noticed that the following descending order was detected for the highest values: Ascaris lombricoides (9.63E+04 ova/4gds)> Taenia saginata (4.91E+04 ova/4gds)> Toxocara cati (4.51E+04 ova/4gds)> Hymenolopis diminuta (4.47E+04 ova/4gds)> hookworms (4.39E+04 ova/4gds)> Hymenolopis nana 4.03E+04 ova/4gds)> Fasciola hepatica (1.47E+04 ova/4gds). The lowest values were detected in the following ascending order: Echinostoma (1.68E+03 ova/4gds) < Paragonium westermani (3.23E+03 ova/4gds) < Trichuris trichura (3.75E+03 ova/4gds) as shown in figure (1). Black et al.,(23) stated that some Ascaris eggs (23%) were destroyed during anaerobic digestion, Trichuris and Toxocara eggs were not destroyed. The total nematode count was far higher than EPA limits class A, where no limits were stated for class B. .Abd-Elaty et al., 607 2After drying beds Sludge drying beds, the most widely used method of sludge dewatering, rely on natural evaporation and percolation to dewater the solids.(24) As presented in table (3), the water content ranged between 7.88-37.45% with an average of 2


INTRODUCTION
Sewage sludge is the solid, semisolid, or liquid residue generated during treatment of domestic sewage. (1) Sludge, also known as biosolids, is composed mostly of human waste that is treated to reduce the prevalence of disease-causing bacteria. (2) The use and disposal of biosolids is always preceded with treatments to ensure regulatory requirements are met, public health and the environment are being protected, to facilitate handling and to reduce costs. (3) The use of sewage sludge as soil amendments or for land reclamation has been increased to reduce the volume of sewage sludge that must be landfilled, incinerated, or disposed of at surface sites. (1) The sludge treatment processes focus on the removal of water and the destruction of pathogens. The treatment processes prepare biosolids specifically for intended methods of use or disposal. (3) The best practical environmental option for the management of sewage sludge is its beneficial application to agricultural land. (4) Biosolids are applied to agriculture and non-agriculture lands as soil amendments, because they can improve the chemical and physical properties of soils and they contain nutrients and trace elements important for plant growth. (1,5) Sewage sludge, if applied inappropriately can also be potentially harmful to the water and soil environment and human and animal health. (4) However, careful use of sewage

RECOMMENDATIONS
The reuse of such sludge in land application must be subjected to the 618 Bull High Inst Public Health Vol.37 No.3 [2007] following considerations: Environmental protection: • Care should always be taken when applying on land to prevent any adverse environmental impacts, • Vehicles used in sludge transfer should be carefully selected for their local suitability and routes chosen so as to minimize inconvenience to the public, • Enclosed tankers should be used for transporting to control odor, • Sludge should be used in accordance with the requirements of the pollution control authority as well as of good farming practice.

Monitoring requirements:
• Prior to application onto land, it is to be analyzed for the metals and the level of pathogenic organisms as specified by EPA, • Composite soil samples to be collected from the land and analyzed also for metals, • All of the drinking water wells located within 500 meters from the land boundary shall be monitored, • Records related to the quantity of sludge applied onto the land, application rate, results of sludge, soil, and water quality analysis shall be maintained, • The monitoring requirements adjusted based on the frequency of sludge application onto land.

Application requirements:
• Legal description of the land to be used, together with plans showing topography, watercourses, general soil classification, water wells within one kilometer, radius of the land, residences, and other buildings, • The quantity that will be applied onto land and application rate, .Abd-Elaty et al.,

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• Application should not take place during or immediately after a rainfall, • Animals shall not be grazed on the land for 30 days after application, • It must apply below the surface of the land, • Restrictions are placed on the site where it is applied to prevent exposure to it.

Further treatment:
Alternative processes to significantly reduce pathogens: • Air drying or storage for a period of at least 3-monthes.
• Composting with temperatures greater than 40 degrees for five days.
• Lime stabilization to a pH greater than 12 for two hours.

Acknowledgment
Authors would like to thank all the participates of the project from public workers authorities and Qatar university, state of Qatar.   * US EPA Limits for using sewage sludge in agriculture, A stands for: Exceptional quality limits for un-restricted land application, B stands for: Ceiling limit for land application Un-restricted use indicates the sludge up to the listed limits could be used for beneficial use considering the accumulation application rates should not be exceeded.