International INTERNATIONAL Journal of Civil JOURNAL Engineering and OF Technology CIVIL ENGINEERING (IJCIET), ISSN 0976 AND 6308 TECHNOLOGY (IJCIET) ISSN 0976 6308 (Print) ISSN 0976 6316(Online) Volume 4, Issue 6, November December, pp. 230-238 IAEME: www.iaeme.com/ijciet.asp Journal Impact Factor (2013): 5.3277 (Calculated by GISI) www.jifactor.com IJCIET IAEME COMPARISON BETWEEN RAPID SAND FILTER AND DYNA SAND FILTER IN WASTEWATER TERTIARY TREATMENT Mostafa. H. 1 & Aly. O.H.I. 2 1 Assistant Professor of Sanitary & Environmental Engineering, Public works, ASU, Faculty of Engineering, Cairo, Egypt 2 Assistant Professor of Sanitary & Environmental Engineering, Higher Institute of Engineering, Shorouk City, Cairo, Egypt ABSTRACT Tertiary treatment is any treatment process added to the flow scheme following conventional secondary treatment. The general target for this study is to evaluate and compare between the performance of the Dyna sand filter and the rapid sand filter as tertiary treatment method for wastewater to be able to enhance the characteristics of effluent wastewater. The samples for analysis were taken from 15th of May City wastewater treatment plant during the study period. The samples were collected after the final sedimentation tanks. The secondary treatment applied in this wastewater treatment plant is the aeration tanks. Then samples were collected after the tertiary treatment, which was Rapid Sand Filters. These filters were later replaced by Dynamic up flow Sand Filters. The samples were collected after the Dyna sand filter for evaluation and comparison between both filters efficiencies. The Dynamic up flow sand filter showed high removal efficiency in the removal of the total suspended solids, while for BOD & COD the removal efficiency was similar compared to that of the Rapid sand filter. However the removal efficiency in case of Dyna Sand was steady, although in the rapid sand filter there were great fluctuations in the results, which in return will cause further problems in the case of the Rapid Sand Filter. INTRODUCTION Nowadays, Egypt development are growing quickly especially in cities like Cairo, Alexandria etc. These developments suffer from several problems as level of utilities service available, the air pollution, the wastewater drainage & disposal and the shortage of potable water required for human usage in such developed cities. The potable water shortage is mainly due to the high costs required for water treatment due to area need, operation techniques difficulties and low investments in such field with the absence of its developing. To overcome such problems it has been found that it is necessary to resort to fast processing techniques. The developing for the filtration 230
techniques to increase filtration production per square meter area became a need for this case to solve the filtration problems as the used area, water quality and operation and maintenance economy. One of these problems is the need for repeated cleaning by back wash. This led to establish new technique for the filter cleaning. Among the new techniques of filtration, Dyna sand filtration system which has been effectively used in treating several varieties of water resources to produce potable water around the world (such as England, Sweden, Holland) had succeeded in producing good results.(1) Tertiary treatment may be defined as any treatment process in which unit operations are added to the flow scheme following conventional secondary treatment. Additions to conventional secondary treatment could be as simple as the addition of a filter for many unit processes for organic, suspended solids, nitrogen and phosphorus removal. Primary and Secondary treatment remove the majority of BOD and suspended solids found in waste waters. However, in an increasing number of cases this level of treatment has proved to be insufficient to protect the receiving waters or to provide reusable water for industrial or domestic recycle. Thus, additional treatment steps have been added to waste water treatment plants to provide for further organic and solids removals or to provide for removal of nutrients and toxic metals, according to London School of Hygiene, 1999.(2) The purpose of tertiary treatment is to provide a final treatment stage to raise the effluent quality before it is discharged to the receiving environment (sea, river, lake, ground, etc...). More than one tertiary treatment process may be used at any treatment plant. If disinfection is practiced, it is always the final process. It is also called effluent polishing. The main purpose can be identified in the additional removal of organic and suspended solids removal, nitrogenous oxygen demand removal, toxic and nutrient removal.(3) The problem in the treatment of wastewater is that the Governments are giving high attention nowadays to the quality of wastewater effluent to reuse the wastewater in several applications. Filtration is considered the cheapest method for tertiary treatment of wastewater. Several researches & applications were done for the application of Dyna Sand in Industrial Wastewater. The general target for this study is to evaluate and compare between the performance of the Dyna sand filter and the rapid sand filter as tertiary treatment method for wastewater to be able to enhance the characteristics of effluent wastewater. LITERATURE REVIEW They are different methods of Tertiary treatment applied all over the world. From these techniques is Filtration, lagooning, Nutrient Removal and Disinfection. The Sand Filtration removes much of the residual suspended matter. Filtration over activated carbon, also called carbon adsorption, removes residual toxins. Granular media filtration removes those suspended and colloidal solids, which are carried over from previous unit processes is a common unit process in advanced waste water treatment. Effluents of less than 10 mg/l BOD and 5 mg/l suspended solids are not uncommon for effluents from biological treatment processes after filtration. Gravity filters similar to rapid sand filters are sometimes used. Often a combination of filter media, such as anthracite coal and sand are used to provide coarse combination of filter Medias, such as anthracite coal and sand are used to provide coarse to fine filtration as the water passes through the filter. The water passes through the filter media and support gravel and is then collected by the under drain system. As filtration proceeds, the head loss through the filter increase until it reaches an unacceptable level or until solids breakthrough occurs and the effluent becomes unacceptable. When either the head loss becomes excessive or solids break through occurs, the filter is backwashed. Ideally, filters are designed to have the solids in the effluent and the head loss reaches their allowable levels at the same time. (4) Lagooning is one of the methods of tertiary treatment of wastewater, which provide settlement and further biological improvement through storage in large man made ponds or lagoons. 231
These lagoons are highly aerobic and colonization by native macrophysics, especially reeds, is often encouraged, small filter feeding invertebrates such as Daphria and species of Rotifer greatly assist in treatment by removing fine particulates, referring to Ballater, 2010.(5) Also another application of tertiary treatment is Nutrient Removal. Waste water may contain high levels of the nutrients nitrogen and phosphorus. Excessive release to the environment can lead to a buildup of nutrients, called eutrophication, which in turn can encourage the over growth of weeds, algae, and cyanobacteria (blue green algae). This may cause an algal bloom, a rapid growth in the population of algae, the algae numbers are unsustainable and eventually most of them die. The decomposition of the algae by bacteria uses up so much of oxygen in the water that most or all of the animals die, which creates more organic matter for the bacteria to decompose. In addition to causing deoxygenating, some algal species produce toxins that contaminate drinking water supplies. Different treatment processes are required to remove nitrogen and phosphorus. Disinfection is one of the methods used in tertiary treatment of wastewater. The purpose of disinfection in the treatment of waste water is to substantially reduce the number of microorganisms in the water to be discharged back into the environment for the later use of drinking, bathing, irrigation, etc. The effectiveness of disinfection depends on the quality of the water being treated (e.g. cloudiness, ph, etc...) and other environmental variables. Common methods of disinfection include ozone, chloride, ultraviolet light or sodium hypochlorite. Chloramine, which is used for drinking water, is not used in waste water treatment because of its persistence. After multiple steps of disinfection, the treated water is ready to be released back into the water cycle by means of the nearest body of water or agriculture. Afterwards, the water can be transferred to reserves for everyday human use.(6) In October/November 2001, Holmen Braviken of Sweden benefited from improved water supply at its paper mill. Braviken met its requirements of good quality water with the installation of 20 Dynasand filters. The filters provided a continuous sand cleaning process and eliminate the problem of downtime for back washing. These filters also provided additional benefits such as light maintenance and reduction in the quantity of polymer required for retaining fines on the paper.(7) In October/November 2001, Minett and Jonsson found in its use for water treatment that the filters provide a continuous sand clearing process, eliminate the problem of down time backwashing, light maintenance and reduction in the quantity of polymer required for retaining fines. (8) In December 2006, Abdel Azeem, M.M studied the Evaluation of The performance of Dynamic Sand Filtration under Real Working Conditions. In 2007 Ahmed, H. studied the Dyna sand Filter Application in Water Treatment. In 2013 Aly, O.H.I., studied the optimization of design and operating parameters for dynamic up flow sand filter.(9) MATERIALS AND METHODS The samples for analysis were taken from 15 th of May City wastewater treatment plant during the study period. The samples were collected after the final sedimentation tanks. The secondary treatment applied in this wastewater treatment plant is the aeration tanks. Then samples were collected after the tertiary treatment, which was Rapid Sand Filters. These filters were later replaced by Dynamic up flow Sand Filters. The samples were collected after the Dyna sand filter for evaluation and comparison between both filters efficiencies. The following tables show the sizing and units of the wastewater treatment plant in 15 th of May City. The number of Rapid Sand Filter units in 15th of May Wastewater treatment plants is 12, the depth of water is 1.95m, the area of one unit is 54.48 m 2, while the volume per unit is 106.23 m 3 and the total Capacity is 1274.83 m 3. The specification of the pilot unit for the dynamic up flow sand filter is as follows: Diameter = 0.95 m, area = 0.7 m2, height = 3m and effective bed height is 2m. 232
Figure (1): The Pilot Unit of the Dyna Sand RESULTS AND DISCUSSION Samples were collected and examined for the Rapid Sand Filter. These samples were tested to point out the concentration in the Influent to both types of filters. The influent samples were examined after the secondary treatment. On the other hand, to evaluate the Dyna sand filter samples were taken from the effluent of the filter and the parameters were tested. The following figures show the concentration of Suspended Solids, Bio chemical Oxygen Demand and Chemical Oxygen Demand in the Influent and both effluents. Figure (2): The SS concentration 233
The Suspended solids concentration after the secondary treatment ranged between 30 to 40 mg/l, while after the tertiary treatment using the rapid sand filter it was found to be between 10 to 20 mg/l. Finally after the Dyna sand it ranged between 3 to 6 mg/l. Figure (3): The BOD concentration The BOD concentration after the secondary treatment ranged between 25 to 40 mg/l, while after the tertiary treatment using the rapid sand filter it was found to be between 10 to 18mg/l. Finally after the Dyna sand it ranged between 10to 16 mg/l. Figure (4): The COD concentration The COD concentration after the secondary treatment ranged between 30 to 48 mg/l, while after the tertiary treatment using the rapid sand filter it was found to be between 11 to 25mg/l. Finally after the Dyna sand it ranged between 10to 17 mg/l. 234
The removal efficiency for the three parameters, the suspended solids, the BOD and the COD was derived between the influent and the effluent of the Rapid sand filters and the Dyna Sand. The removal efficiency for the three parameters id illustrated in tables (4) and (5). Figures 5, 6 and 7 show the removal efficiency for the three parameters. Table (4) Effluent of Rapid Sand Filter and the Removal efficiency Sample No BOD RR BOD COD RR COD SS RR SS 1 18 50 25 38 19 42 2 10 72 12 71 12 67 3 12 60 15 63 12 66 4 10 60 12 61 11 63 5 12 68 15 69 12 68 6 11 73 12 73 13 68 7 10 74 12 74 12 68 8 16 56 20 57 16 54 9 12 70 12 73 12 68 10 12 69 19 61 12 70 11 12 69 18 62 12 67 12 11 72 16 66 10 72 Table (5) Effluent of Dyna Sand Filter and the Removal efficiency Sample No BOD RR COD RR SS RR 1 14 61 14 65 6 82 2 14 61 15 64 4 89 3 12 60 14 65 4 89 4 10 60 11 65 3 90 5 15 61 17 65 4 89 6 16 60 16 64 4 90 7 15 61 16.5 65 4 89 8 14 61 16 65 4 89 9 16 60 15.5 65 5 87 10 15 62 17 65 4.5 89 11 15 62 16.5 65 4 89 12 15 62 16.5 65 4 89 235
Figure (5): The SS removal efficiency The removal efficiency of the Rapid sand filter in the removal of Suspended Solids ranged between 43 t0 70%, while for the Dyna Sand it was found to be between 82 to 90%. The Dyna Sand Filter showed very high removal efficiency and proved that it is very successful in SS removal. Figure (6): The BOD removal efficiency The removal efficiency of the Rapid sand filter in the removal of BOD ranged between 50 t0 75%, while for the Dyna Sand it was found to be around 60%. 236
Figure (7): The COD removal efficiency The removal efficiency of the Rapid sand filter in the removal of COD ranged between 38 t0 75%, while for the Dyna Sand it was found to be around 65%. CONCLUSION AND RECOMMENDATIONS The Dynamic up flow sand filter showed high removal efficiency in the removal of the total suspended solids, while for BOD & COD the removal efficiency was similar compared to that of the Rapid sand filter. However the removal efficiency in case of Dyna Sand was steady, although in the rapid sand filter there were great fluctuations in the results, which in return will cause further problems in the case of the Rapid Sand Filter. From the economic point view, the results of the Dyna Sand were obtained with one pilot unit, although in case of Rapid Sand Filter there was 12 filters. According to the previous results, the following conclusion can be driven: 1. The removal ratio of COD was ranging from 38 % to 75 % for the Rapid Sand Filter, while for the Dyna Sand it was around 65%. 2. The removal ratio of BOD was ranging from 50 % to 75% for the Rapid Sand Filter, when for the Dyna Sand it was around 60%. 3. The removal ratio of TSS was ranging from 43 % to 70 % in case of Rapid Sand Filter, while for the Dyna Sand it showed high efficiency 82% to 90%. Therefore, it is recommendedd to use Dynamic up flow sand filter (Dyna Sand) in the removal of Suspended solids in wastewater. However for the removal of BOD and COD their removal was almost the same for both filters, although the steady removal efficiency of Dyna Sand gives it great advantage. The effluent from both filters can be used in the irrigation of tress and the crops that are cooked before eating according to the Environmental Laws. 237
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