SEQUENTIAL BATCH REACTORS: TAKING PACKAGED WASTEWATER TREATMENT TO NEW HEIGHTS - A REVIEW

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1 INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND TECHNOLOGY (IJCIET) International Journal of Civil Engineering and Technology (IJCIET), ISSN (Print), ISSN (Print) ISSN (Online) Volume 5, Issue 10, October (2014), pp IAEME: Journal Impact Factor (2014): (Calculated by GISI) IJCIET IAEME SEQUENTIAL BATCH REACTORS: TAKING PACKAGED WASTEWATER TREATMENT TO NEW HEIGHTS - A REVIEW Er. Devendra Dohare 1, Er. Parth Bochare 2 1 Assistant Professor, Department of Civil Engineering and Applied Mechanics, SGSITS, 23, Park Road, Indore, Madhya Pradesh (452001), India 2 Student M.Tech Environmental Engineering, Department of Civil Engineering and Applied Mechanics, SGSITS, 23, Park Road, Indore, Madhya Pradesh(452001), India ABSTRACT SBR is undoubtedly the new black in today s era of packaged wastewater treatment. SBR is an ASP operating in a single vessel which operates in time rather than space. SBR has gained worldwide attention because it can treat different kinds of effluents such as municipal, domestic, saline, tannery, brewery, and dairy wastewater, landfill leachates, etc. under different conditions. SBR is also considered as a promising technology for areas where sewage treatment is to be decentralized. It requires less area to function, easy to operate, and is very cost effective even on small scales. Hence, developing SBR is considered to be the heartbeat of Packaged STP s. In a country like India, struggling environmentally SBR Packaged STP s will be a boon to its ever deteriorating rivers/water bodies. Keywords: Decentralization of STPs, Heartbeat of Packaged STPs, Industrial/ Municipal Waste Water Treatment, Packaged STP, Sequential Batch Reactor(SBR), The new black. 1. INTRODUCTION There is abundant literature on full scale applications of SBR in terms of treatment performance, operation, and costs (Wilderer et al., 2001; Keller, 2005). Advantages of SBR process for municipal and high strength industrial effluents has been highlighted in these new literatures. All in all SBR technology has earned lot of attention from environmental companies for fabricating decentralized packaged STPs. In this technology, there is a single reactor or number of reactors working in parallel batches, hence the name- sequencing batch reactor, works on both the principles either intermittent or continuous. Presently more popular is intermittent. Sequencing batch reactor is 131

2 a fill and draw type reactor. SBR performs equalization, neutralization, biological treatments and secondary clarification in a single tank using timed control sequence and also eliminates the need of primary clarification. (USEPA, Wastewater Technology Factsheet SBR, 1999). Sequencing batch reactor consists of single tank equipped with an inlet- for wastewater, air diffuser with compressor and piping- for aeration, sludge drawing mechanism- for draining sludge, decant mechanism- for drawing supernatant, stirrer- for inducing aeration and control mechanism- for operation control with respect to time and sequence. (USEPA, Summary Report SBR, 1986) SBR operation system has five basic operating modes - Fill, React, Settle, Decant and Idle. 2. SBR PROCESS DESCRIPTION 2.1 FILL The influent to SBR may either be raw wastewater (screened and degritted) or primary effluent. Considerable decrease in tank volume is observed due to quiescent conditions as the aeration tank acts as a primary clarifier in this step. The influent may either be pumped in or allowed to flow in by gravity. The time of Fill depends upon the volume of each tank, the number of parallel tanks in operation, and the extent of diurnal variations in the wastewater flow rate though in general it covers 20-25% of total time cycle. The following variations are used for the Fill step namely: Static fill, Mixed fill, Aerated fill. Static fill is characterized by no mixing or aeration, meaning there will be a high substrate (food) concentration when mixing begins. A high food to microorganisms (F/M) ratio creates an environment favorable to floc forming organisms versus filamentous organisms, which provide good settling characteristics for the bio solids. Additionally, static fill conditions favor organisms that produce internal storage products during high substrate conditions, a requirement for biological phosphorus removal. Mixed fill is classified by mixing influent organics with the biomass, which initiates biological reactions. During mixed fill, bacteria biologically degrade the organics and use residual oxygen/alternative electron acceptors, such as nitrate-nitrogen Mixed fill is comparable to the anaerobic zone used for denitrification Aerated fill is classified by aerating the contents of the reactor to begin the aerobic reactions initially and thereby reducing the time of react step considerably. Level sensing devices/timers/in-tank probes (for measuring DO and ammonia nitrogen) can be used to switch aerators on/off as desired. 2.2 REACT This phase is categorized by aeration where aerators/blowers impart DO and mixing to the filled wastewater. Time dedicated to react can be as high as 50% or more of the total time cycle but is generally around 35 %. The biological reactions are completed in the React step, in which mixed react and aerated react modes are available. During aerated react, the aerobic reactions initialized during aerated fill are completed and nitrification can be achieved. Nitrification is the conversion of ammonia-nitrogen to nitrite-nitrogen and ultimately to nitrate-nitrogen. If the mixed react mode is selected, anoxic conditions can be attained to achieve denitrification. Anaerobic conditions can also be achieved in the mixed react mode for phosphorus removal.in this step, no influent flow into SBR is allowed & no sludge could be wasted (Surampalli et al., 1997 ;). Most of the carbonaceous BOD is polished in this step. 2.3 SETTLE In SBR, solids separation takes place under no inflow/outflow conditions. This helps to achieve considerable decrease in the clarifier volume which the reacts acts in this step. This major advantage in the clarification process results from the fact that entire aeration tank now serves as a secondary clarifier in this step. The activated sludge tends to settle as a flocculent mass, forming a distinctive interface with the clear supernatant. It covers 20-25% of the total cycle time. 132

3 2.4 DECANT During this step a decanter is used to remove the clear supernatant effluent. There are floating and fixed arm decanters. Floating decanters maintain the inlet orifice slightly below the water surface to minimize the removal of solids in the effluent removed during the decant step. They offer the flexibility to vary fill and draw volumes. On the other hand fixed arm decanters are cost effective but does not allow to vary the volume of decanted effluent. The vertical distance from the decanter to the bottom of the tank should be maximized to avoid disturbing the settled bio solids. The time dedicated to this step is around 15% of the total cycle time. The most important aspect to the decanter design is to ensure that effluent is withdrawn uniformly from within the tank. Point discharges suffer from scouring suspended solids from the settled sludge blanket and have no flexibility for process changes, e.g. higher sludge blanket through increased tank solids concentration. Decanter designs usually incorporate guard mechanisms to prevent scum and other floating material from causing deterioration in effluent quality. 2.5 IDLE The period between Draw and Fill is termed as Idle. This step is classified as sludge wasting. In SBR wasting of sludge can be as infrequent as once every 2 to 3 months. It covers 5% of the total cycle time and covers 35 to 25% of total volume. It occurs between draw step of one cycle and fill step of successive cycle. (USEPA, Wastewater Technology Factsheet SBR, 1999). (Refer to Fig 1) 3. WHY PACKAGED TREATMENT PLANTS Sewage treatment has always been treated as a project- it requires lengthy analysis, detailed design, cumbersome construction, difficult installation and long lead times. It need not be so. A standardized range of sewage treatment plants helps to make the selection, supply and execution of the customer s requirement much easier. As in the ongoing market the manufacturers are using new technologies to make every solution more standardized and user friendly by the day, sewage treatment is the new foray. Though the packaged solution of an STP is a relatively new concept, yet the demand for it has already caught up. This is because packaged wastewater treatment system has a few noticeable advantages over a conventionally built one. Firstly, it reduces the time of construction drastically from few months to about a week. Secondly, its aesthetic design is backed by its operational and maintenance friendly nature. Lastly, its compact size takes care of the space required, which has become major concern for most builders today. To sum up, a packaged STP has now turned out to be a total package for Sewage treatment solutions. Thus the view of the above technological innovation, at the present time one can look at packaged STP as a boon and dream come true to the current sewage treatment gaps in growing towns and cities where centralized plant is a farfetched possibility. (Refer to Fig 2) 4. SBR: THE HEART OF PACKAGED STP What is it that SBR is the most used technology in packaged STP s and decentralized wastewater treatment plants? It was observed that a packaged STP must be easy to use with minimum monitoring, efficient in BOD, Nitrogen, Phosphorus removal, economic, low area consuming and most importantly should have least operation and maintenance issues as Package STP s are generally used by normal public with least knowledge of STP working. SBR has the following features which make it the best choice for Packaged STPs 133

4 4.1 Simplicity in construction and operation 4.2 As the process is entirely aerobic, primary settling of wastewater and the anaerobic digestion of the sludge are omitted. 4.3 Aeration and secondary settling are carried out tin batches, thus mineralizing the sludge solids sufficiently so that they can be dewatered without any digestion. This in turn will improve the overall efficiency and simplify the whole operation. 4.4 The BOD removal efficiency is higher than any conventional Activated Sludge Process; even to the range of 97-98% which itself is very good by any standards. In Case for further treating the liquid by tertiary treatment large amount can be saved due to very less impurities in inlet water to tertiary treatment unit, which makes it especially desirable to use where it is to be followed by Tertiary Treatment for reuse. The supernatant from the SBR reactor is then pumped into tertiary filtration unit after on line chlorination. 4.5 The space requirement is comparatively less than any other conventional treatment. 4.6 The plant as constructed / fabricated will be fully automatic in nature will result in easy operation ensuring high efficiency and minimum manpower requirement. 5. FIGURES AND TABLES Fig 1-Source: 134

5 Fig 2-Source: ryalitechnologies.com/wp-content/uploads/2014/06/modular_stp.jpg TABLE I: KEY DESIGN PARAMETERS FOR A CONVENTIONAL LOAD PARAMETER MUNICIPAL INDUSTRIAL F/M RATIO,/DAY CYCLE DURATION, HOURS TYPICALLY LOW WATER LEVEL MIXED LIQUOR SUSPENDED SOLIDS, MG/L 2,000-2,500 2,000-4,000 HYDRAULIC REETENTION TIME, HOURS 6-14 VARIES SOURCE: AQUA SBR DESIGN MANUAL,

6 TABLE II: EFFLUENT CHARECTERISTICS IN PACKAGED SBR WITHOUT TERTIARY TREATMENT FOR MUNICIPAL SEWAGE S.NO. PARAMETER VALUE 1. BOD 5,mg/L <10 2. TSS,mg/L <10 3. Faecal coliform removal, log unit up to 3<4 4. TOTAL NITROGEN, mg/l <10 5. TOTAL PHOSPHORUS, mg/l <2 6. OIL AND GREASE, mg/l <5 7. ph Table source: SBR, Premier Tech Aqua, Packaged SBR manufacturing TABLE III: EFFLUENT CHARECTERISTICS IN PACKAGED SBR WITH TERTIARY TREATMENT FOR MUNICIPAL SEWAGE S.NO. PARAMETER VALUE 1. BOD 5,mg/L <10 2. TSS,mg/L <5 3. Total coliforms, MPN/100mL TOTAL NITROGEN mg/l <5 5. TOTAL PHOSPHORUS, mg/l < OIL AND GREASE, mg/l <2 7. ph Table source: SBR, Premier Tech Aqua, Packaged SBR manufacturing TABLE IV: SBR COST ANALYSIS S.NO. PARAMETER VALUE 1. Average Capital Cost (Secondary Treatment), Lacs/MLD Average Capital Cost (Tertiary Treatment), Lacs/MLD Civil Works Yearly Power Costs, Lacs/MLD Yearly Repair Costs, Lacs/MLD Yearly Chemical Cost Yearly Salary+Benefits TOTAL, Lacs/MLD Table Source: Report Code: 003_GBP_IIT_EQP_S&R_02_Ver 1_Dec

7 TABLE V: DECENTRALIZED PACKAGED SBR STP IN INDIA S.NO. CITY CAPACITY 1 Surat 30 KLD 2 Ahmedabad 100 KLD 3 Indore 100 KLD 4 Mumbai 50 KLD 5 Haryana 10 KLD 6 Jabalpur 20 KLD 7 Raigarh 20 KLD 8 Bangalore 70 KLD 9 Chhattisgarh 4no.sx10KLD 10 Kolkata 100 KLD Table source: Source: Packaged sewage treatment plants for medium/large applications Sintex industries Limited FLOW (MGD) TABLE VI: SBR REQUIREMENTS REACTORS BLOWERS NO. SIZE (FEET) VOLUME(MG) NO SIZE (H.P) X X X X X X X X X SOURCE: EPA 832-F SEPTEMBER 1999 WASTEWATER TECHNOLOGY FACT SHEET SEQUENCING BATCH REACTORS 137

8 6. CONCLUSION So, it is evident that SBR technology has changed the way people used to perceive waste water treatment. The advantages of SBR as discussed in the paper, has undoubtedly proved to be the treatment technology which can be used by common man through packaged STPs. So to conclude SBR technology is promising since its being and more research and field work in this field will lead us to new levels of waste water treatment. 7. REFERENCES [1] Arora, Madan L. Technical Evaluation of Sequencing Batch Reactors. Prepared for U.S. EPA. U.S. EPA Contract No [2] Altaf, M. S. and Ali, T. A. (2010). Wastewater treatment using sequential batch reactor and development of microbiological method for the analysis of relative toxicity, Pakistan Journal of Nutrition, 9 (6), ( ) [3] AquaSBR Design Manual. Mikkelson, K.A. of Aqua-Aerobic Systems. Copyright [4] EPA 932-F (Sept 1999) Wastewater Technology Fact Sheet, Sequencing Batch Reactors. Wilderer, Irvine, and Goronszy. [5] Irvine, Robert L. Technology Assessment of Sequencing Batch Reactors. Prepared for U.S. EPA. U.S. EPA Contract No [6] Manufacturers Information. Aqua-Aerobics, Babcock King-Wilkinson, L.P., Fluidyne, and Jet Tech Systems, [7] Metcalf & Eddy, Inc. Wastewater Engineering: Treatment, Disposal, Reuse.3rd edition. New York: McGraw Hill. [8] M. Young, The Technical Writer s Handbook. Mill Valley, CA: University Science, [9] N. Artan and D. Orhon, Mechanism and Design of Sequencing Batch Reactors for Nutrient Removal, IWA Publishing, Hove, UK (2005). [10] Norcross, K.L., Sequencing Batch Reactors- An Overview. Technical Paper published in the IAWPRC 1992 ( /92).Wat. Sci. Tech., Vol. 26, No. 9-11, pp [11] Peavy, Rowe, and Tchobanoglous: Environmental Engineering. New York: McGraw-Hill, Inc. [12] Sequencing Batch Reactor Technology; Scientific and Technical Report No. 10, IWA Publishing. [13] Sewage Treatment in Class I Towns:Recommendations and Guidelines. Report Code: 003_GBP_IIT_EQP_S&R_02_Ver 1_Dec 2010 [14] United States Environmental Protection Agency, (1986) An emerging technology SBR a project assessment. U.S. Environmental Protection Agency, Washington, D. C. [15] U.S. EPA. Innovative and Alternative Technology Assessment Manual, EPA/430/ Cincinnati, Ohio, [16] U.S. EPA. EPA Design Manual, Summary Report Sequencing Batch Reactors. EPA/625/8-86/011, August [17] Mostafa. H. and Aly. O.H.I., Comparison Between Rapid Sand Filter and Dyna Sand Filter in Wastewater Tertiary Treatment, International Journal of Civil Engineering & Technology (IJCIET), Volume 4, Issue 6, 2013, pp , ISSN Print: , ISSN Online: [18] R Radhakrishanan and A Praveen, Sustainability Perceptions on Wastewater Treatment Operations in Urban Areas of Developing World, International Journal of Civil Engineering & Technology (IJCIET), Volume 3, Issue 1, 2012, pp , ISSN Print: , ISSN Online: