Proceedings of National Conference on ...

Proceedings of National Conference on Advancements and Futuristic Trends in Mechanical Engineering; Department of Mechanical Engineering, PEC University of Technology, Chandigarh on 17th-18th Oct. 2014

ROLE OF SBR TECHNIQUE IN WASTE WATER TREATMENT PLANTS: A REVIEW

Navdeep Kaur1; D. R. Prajapati2; S. K. Sharma3 PG student, Department of Production and Industrial Engineering, PEC University of Technology, Chandigarh, India 2 Assistant Professor, Department of Mechanical Engineering, PEC University of Technology, Chandigarh, India 3 Associate Professor, Department of Civil Engineering, PEC University of Technology, Chandigarh, India 1 E-mail: [email protected]; 2E-mail ID: [email protected]; 3 E-mail ID: [email protected]

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ABSTRACT The overall analysis of water resources indicates that in coming years, there will be a twin edged problem to deal with reduced fresh water availability and increased waste water generation due to increased population and industrialization. In class-I cities, oxidation pond or Activated sludge process is the most commonly employed technology, covering 59.5% of total installed capacity. Domestic waste water is difficult to treat using conventional Activated Sludge Process, without having very large tanks and long hydraulic retention time to degrade the waste. Although Activated sludge Process has been a proven alternative, it is not possible to install the same due to limitation of space. Activated sludge is the most widely used biological waste water treatment process in the developed world, treating both sewage and a variety of Industrial waste water. This paper deals with the advantages of SBR technology along with some previous research work done by the researchers. Keywords: Sequential Batch reactor, water treatment, BOD, COD and TSS

Nomenclature: Sr. No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Abbreviation BOD SBR ASP MBBR UASB EAS MLSS DO TN TP mg/l CPHEEO CPCB STP EPA MOEF IIT BCM

Full Form Biochemical Oxygen Demand Sequential Batch Reactor Activated Sludge Process Moving Bed Biofilm Reactor Upflow Anaerobic Sludge Blanket Extended Aeration System Mixed Liquor Suspended Solids Dissolved Oxygen Total Nitrogen Total Phosphorus milligram per litre Centre for Public Health and Environmental Engineering Organization Central Pollution Control Board Sewage Treatment Plant Environmental Protection Agency Ministry of Environment and Forests Indian Institute of Technology Billion cubic meters

Navdeep Kaur; D. R. Prajapati; S. K. Sharma

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Proceedings of National Conference on Advancements and Futuristic Trends in Mechanical Engineering; Department of Mechanical Engineering, PEC University of Technology, Chandigarh on 17th-18th Oct. 2014

1. Introduction India accounts for 2.45% of land area and 4% of water resources of the world but represents 16% of the world population. Total utilizable water resource in the country has been estimated to be about 1123 BCM (690 BCM from surface and 433 BCM from ground), which is just 28% of the water derived from precipitation (Kaur et al). Insufficient capacity of waste water treatment and increasing sewage generation pose big question of disposal of waste water. As a result, at present, significant portion of waste water being bypassed in STPs and sold to the nearby farmers on charge basis by the Water and Sewerage Board or most of the untreated waste water end up into river basins and indirectly used for irrigation. It has been reported that irrigation with sewage or sewage mixed with industrial effluents results in saving of 25 to 50 per cent of N and P fertilizer and leads to 15-27 % higher crop productivity, over the normal waters (Anonymous, 2004). In India, there are 234 Sewage Water Treatment plants (STPs). Most of these were developed under various river action plans (from 1978-79 onwards) and are located in (just 5% of) cities/ towns along the banks of major rivers (CPCB, 2005a). Batch Operation of the activated sludge process is nothing new. During the early development of the activated sludge process in the United Kingdom by Arden and Lockett around 1914, plants were operated using fill-and-draw or batch feed methods. These researchers firmly established the concept of operating a single reactor basin using repetitive cycles of aeration, settlement and discharged of treated effluent. Around 1956, during the development of oxidation ditch technology, Pasveer incorporated interrupted and continuously fed batch treatment principles. Further advancements to the oxidation ditch fed-batch treatment then took place by incorporating a rectangular basin configuration.

1.1 Sequential Batch Reactor (SBR) Sequential batch reactor is a type of biological treatment system in which stabilization of organic matter, flocculation of generated cells and settling of cells occur in a safe tank. In its operations, the cycle processes FILL-REACT, REACT, SETTLE DRAW are controlled by time to achieve the objectives of the operation. Each process is associated with particular reactor conditions (turbulent/Quiescent, Aerobic/Anaerobic) that promote selected changes in the chemical and physical nature of the waste water. These changes lead ultimately to a fully treated effluent.


1.1.1 Process Description A treatment plant utilizing the SBR concepts has only one type of process unit, the batch reactor tank. It is possible and even preferable in many cases, to link several identical reactors in a multiple tank configuration, to limit the size of Individual units and increased flexibility. There are no units dedicated to a single process, such as equalizing basin, aeration chambers, and clarifiers, as continuous flow systems. In its simplest form, a batch reactor consists of single tank equipped with an inlet for raw waste water; air diffusers, with associated compressors and piping for aeration; a sludge draw off mechanism at the bottom of waste sludge; a decant mechanism to remove the supernatant after settling; and a control mechanism to time and sequence the processes. Various suppliers of SBR systems include different modifications to the basic system, such as the installation of a baffle near the inlet to provide a pre react chamber separated from the aerated portion of the basin. Many decant structures are marketed with features designed to limit the discharge of floating solids and settled sludge. Air diffuser design and construction also varies among suppliers, but many SRBs use jet aerators or mechanical aeration to accomplish aeration and/or mixing with a single device. The heart of the SBR system is the control unit and automatic switches and valves that sequence and time the different operations. The advent of reliable microprocessors at reasonable cost, used in conjunction with modern limit/level switches and automatic valves, has been a major factor in the recent development of SBR technology. The ability to control the processes in time rather than space is crucial in SBR Concept.

1.1.2 BOD, Nitrogen and Phosphorus Removal Mechanism More than 95% removal of BOD is noted in SBR. An important advantage of the SBR system is the control the operator can maintain over microorganism selection. Within a complete treatment cycle, the microorganism selection pressures are highly variable and severe. These pressures include oxygen availability, which ranges from anaerobic through anoxic to high DO conditions, and substrate availability, which ranges from famine to feast conditions. While certain of these selection pressures can occur in some conventional continuous flow systems, the SBR system provides the ability to easily select and extend or limit preferred conditions through time, allowing the preferential growth of desirable microorganisms. Two observations have been documented that illustrate the beneficial effects of this control ability. Firstly, in an SBR system more microorganisms are capable of processing a greater quantity of substrate at a

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Proceedings of National Conference on Advancements and Futuristic Trends in Mechanical Engineering; Department of Mechanical Engineering, PEC University of Technology, Chandigarh on 17th-18th Oct. 2014 greater rate than in a conventional system. Secondly, it has been reported that a properly selected aeration

strategy can result in the minimizing of the growth of filamentous microorganisms. These microorganisms,

whose presence in quantity leads to problems with sludge bulking and foaming, are undesirable in the activated sludge floc in excessive numbers, and their control is an asset to system performance. Nitrogen removal can be achieved in the SBR system without additional equipment or chemicals. Nitrogen enters the system in the raw waste water in the form of organic nitrogen and ammonia (NH4). It is removed from the system in the form of organic nitrogen gas. Phosphorus removal by microbiological methods in SBR systems is well documented. The additional of chemical coagulant to the reactor that precipitates phosphorus into the sludge is a common phosphorus removal process applicable to both conventional continuous flow and SBR systems. The microbiological removal of phosphorus first requires an anaerobic period (absence of dissolved Oxygen and Oxidation nitrogen) during which substrate (raw waste) is present. This period should be followed by an aerobic period (high DO) that promotes the uptake of excess phosphorus by the sludge mass. Excess sludge should be removed from the reactor in suitable quantities before the onset of next anaerobic period. In term of SBR operation anaerobic conditions and aeration must be available during FILLREACT period for phosphorus release and uptake by biomass. These conditions can also available in selector by recirculation of sludge. Fig.1 shows a Typical SBR Cycle for BOD, SS and COD, SS, T-N and T-P Removal.

1.1.3 Design Requirement SBR plants typically consist of a minimum two reactors in a plant. When one unit of reactors is in the fill mode, the other reactor(s) may be in the stage of react, settle, decant or idle. In the reaction stage, the oxygen supplied to the system within the time frame of reaction cycle. This generally requires higher oxygen capacity than a continuous flow system. All SBR plant must be designed to cater for peak flows. A minimum of a two (2) tank system is required. Proven control system in the form of Programmable Logic Controller with complete instruction is provided. All SBR systems musts must be preceded with complete preliminary works.

1.1.4 Performance Comparisons The performance of SBRs is typically better to conventional activated sludge system and depends on system design and site specific criteria. Depending on their mode of operation, SBRs can achieve good BOD and nutrient removal. For SBRs the BOD removal efficiency is generally 85 to 95 percent. SBR manufactures will typically provide a process guarantee to produce an effluent of less than: (i) 10 mg/L Biochemical Oxygen Demand (ii) 10 mg/L Total Suspended Solids (iii) 5-8 mg/L Total Nitrogen (iv) 1-2 mg/L Total Phosphorus(EPA, 1995). The advantages of Sequential Batch Reactor over conventional system are:

Fig. 1: Typical SBR Cycle


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Control system provides high flexibility. The control system automatically coordinates equipment operation through various phase of SBR cycle. This feature offers a high degree of flexibility allowing adaptation of the process cycle to meet the changing influent conditions through simple changes in control set points.

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No primary and secondary settling tanks, no return sludge pumping, hence lesser area requirement and ease in operation & maintenance.

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It is a proven process, which enhances the standard system through strategic cost, operating and biological advantage.

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Improved effluent quality: extended aeration mode, a special ability to handle extremely high organic and hydraulic shock loads, no washout of biomass,

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Proceedings of National Conference on Advancements and Futuristic Trends in Mechanical Engineering; Department of Mechanical Engineering, PEC University of Technology, Chandigarh on 17th-18th Oct. 2014 reliable performance. More than 95% BOD removal, advantage aeration processes. 

The process is also recommended for small-scale sewage treatment in CPHEEO manual, but due to the advancement in technology in last decade, these plants are very favourable for medium and largescale sewage treatment applications. It is a proven process all over the world for sewage treatment. Many large-scale plants working efficiently around the globe.

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Nitrified effluent (no ammonia is present), doesn’t consume further oxygen for nitrification and much beneficial for irrigation and fisheries.

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Expansion potential: Simplified expansion- Each unit forms a modular treatment unit. All basins have been built with common wall construction. This can be achieved by maintaining the same length for all tanks and increasing the width appropriately. The blower equipment is also sized proportionally to the capacity of each basin such that the same blowers are used before and after expansion.

Surrounding environment conditions and advantages for specific site requirement as shown in Table 1.

Fig. 2 Comparative cost between conventional activated sludge process and SBR

2. Literature Review

1.1.5 Cost Factor Moreover, US Environmental Protection Agency (EPA) did extensive study on construction cost comparison of SBR and conventional activated sludge process and found that SBR are much more promising than conventional activated sludge process for municipal sewage treatment. As shown in below that the differences between Sequential Batch Reactor and continuous flow Activated Sludge Processes are drastic. However, this comparison should only be used as an indication of the relative construction costs of SBRs and continuous flow ASPs. Clearly, the lack of need of a primary and secondary clarifier and return sludge pumping system offers potential saving in construction cost. Fig.2 shows comparative cost between conventional activated sludge process and SBR.

1.2 Comparison of Sequential Batch Reactor with existing Waste Water Technologies Based on extensive data collection and field surveys by IIT Roorkee on various sewage treatment plants in India (CPCB & NRCD, MOEF sponsored Projects), the following technologies are compared and recommended on the parameters of land price, Effluent Quality,


The previous important work of the various authors is summarized in this section. Mohamed and Saed (1995) studied SBR efficiency in the treatment of waste water from a dairy plant. The SBR is utilized for 30-minutes aeration feed, 12-hours reaction with O2, 1-hour settling period without O2, 30-minutes draw without O2, and 15-minutes idle phase. The removal of 96.7% of NH3-N, 94% of COD, and 96% of SS were achieved. Sirianuntapiboon (2002) studied application of Granular Activated Carbon- Sequencing Batch Reactor (GAC-SBR) system for treating pulp and paper industry waste water by utilizing six reactors of 10 litres capacity made up of 5 mm thick acrylic plastic with l8 cm in diameter and 40 cm in height, working volume was 7.5 litres, operated at 60 r.p.m. fed by paper and pulp industry waste water. GAC showed the COD and color adsorption under jar test conditions as 127.00 mg/g of GAC and 248'00 Pt-Co/g of GAC, respectively. Debsarkar et al. (2004) studied sequencing batch reactor treatment for simultaneous organic carbon and nitrogen removal in a laboratory study, by using a reactor made in 5 mm thick Perspex sheet, having effective volume 20.0 litres, operated at combination 1 - 4 hour aerobic react period and 4 hours anoxic react period, combination 2 - 5 hours aerobic react period and 3

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Proceedings of National Conference on Advancements and Futuristic Trends in Mechanical Engineering; Department of Mechanical Engineering, PEC University of Technology, Chandigarh on 17th-18th Oct. 2014 hours anoxic react period, combination 3 - 3 hours aerobic react period and 5 hours anoxic react period in aerobic-anoxic sequence, fed by synthetic waste water having soluble chemical oxygen demand 1000±100 mg/l, ammonia nitrogen of 40-90 mg/l. The removal Process Technol ogy Type Waste Stabilization Pond (WSP)

Land Price

Effluent Quality

Less Than Rs 700/sqm

Up flo w Anaerobic Sludge Blanket Final Polishing Unit (UASB+FPU) Up flo w Anaerobic Sludge Blanket +Extended Aeration System (UASB+EAS) Activated Sludge Process: Conventional (ASP)

Rs. 7003000/sqm

BOD:30-50 mg/ L SS: 75-125 mg/ L Fecal Coliforms: 4 Log-5 Log units Color: Green ish BOD:30-40 mg/ L SS:75-100 mg/ L Fecal Co liforms 4 Log-5 Log units Color: Green ish

Sequencing Batch Reactor (SBR)

Greater than Rs 3500/sqm

Moving Bed Biofilm Reactor (MBBR)

Membrane Bioreactor (MBR)

Surroundi ng Environment Conditi ons Odor in winter months, mosquito problems.

Distinct Advantage

Less nuisance compared to WSP

Less operation & maintenance cost. Energy Recovery.

Very easy operation & Maintenance

Rs. 13002500/sqm

BOD:30 mg/L SS: 75-100mg/ L Fecal Coliforms: 3 Log-5 Log units Color: less

Less odor or vector nuisance compared to UASB+FPU

Less operation & maintenance cost

Rs. 5002000/sqm

BOD:10-20 mg/ L SS: 20-50 mg/ L Fecal Co liforms. 4 Log-5 Log units Color: Co lorless BOD: 5-10 mg/ L SS: 10-30 mg/ L Fecal Co liforms. 3 Log-4 Log units Color: Co lorless

Less odor or vector nuisance compared to UASB+EAS.

Less capital cost compared to recent advanced technologies

No odor or vector problem, Aesthetic sense. Modular Units

Excellent effluent quality Less Area requirement Less moving Parts

More than Rs 355/sqm

BOD:20-40 mg/ L SS: 30-80 mg/ L Fecal Co liforms3 Log-4 Log units Color: Less Colo r

Require equalization tank Inferior quality effluent compared to SBR

Less area requirement compared to ASP but more than SBR

More than Rs 10,000/sqm

BOD