Comparative Study of Different Technologies for Treating Municipal Wastewater- A Review

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1 IJIRST International Journal for Innovative Research in Science & Technology Volume 2 Issue 11 April 2016 ISSN (online): Comparative Study of Different Technologies for Treating Municipal Wastewater- A Review Ankit Kumar Singh Department of Civil Engineering Madan Mohan Malaviya University of Technology, Gorakhpur Govind Pandey Department of Civil Engineering Madan Mohan Malaviya University of Technology, Gorakhpur Abstract Municipal Wastewater Treatment aims to the production of large amount of sewage sludge, which requires proper and environmentally accepted management before disposal. The main objective of this paper is to outline the current situation and discuss future perspectives for sludge treatment and disposal management. A great variety of wastewater treatment technologies are used in the world, while differences are observed between aerobic and anaerobic digestion are the most popular methods. This paper reviews treatment process, advantages and disadvantages of various technologies present in India. Keywords: Wastewater, Sequential Batch Reactor (SBR), Biological Filtration and Oxygenated Reactor (BIOFOR), Membrane Bio Reactor (MBR) I. INTRODUCTION Municipal wastewater is mainly generated from domestic sources and usually contains high content of various organic and inorganic compounds which are easily utilized by different type of microorganisms (Bentzen et al., 1995). Wastewater is very complex microbiological system including a great number of microorganisms divided into specific class that exist in bulk water phase, biofilms and sewer sediments (Hvitved-Jacobsen et al., 1999). Recently, the following technologies such as Sequencing Batch Reactor(SBR) and Membrane Bio Reactor (MBR)/ Fluidized Aerobic Bioreactor have been approved under JNNURM projects due to their advantages such as less requirement of land, high effluent quality etc. Membrane Bio Reactor (MBR) Sequencing Batch Reactor (SBR) Bio-Tower Technology BIOFOR Technology (Biological Filtration and Oxygenated Reactor) Fixed Bed Biofilm Activated Sludge Process (FBAS) II. TECHNOLOGIES ANALYSED Membrane Bio-Reactor (MBR) This technology combines the aeration and secondary clarifier in one and the same tank by sucking out the aerated mixed liquor through membranes instead of settling in a separate downstream tank and to that extent, it does yield a treated sewage with practically no BOD and suspended solids and hence being clear and virtually transparent besides its claimed ability to hold and sustain mixed liquor suspended solids (MLSS) of three to four times than what is possible in the conventional aeration tanks which in turn offers minimization of the footprint of the treatment plant. Diffused aeration is of course needed. The membrane is a matter of proprietorship and the throughput per membrane module offered by various vendors are different and also each vendor advocates various shapes of the membranes as flat sheet, cross flow, dead end flow, which makes it difficult for common validated standard design criteria. Schematic flow diagram of Submerged Membrane Bioreactor process is presented in Fig. 1. All rights reserved by 80

2 Fig. 1: Schematic Flow Process of Membrane Bio Reactor (MBR) Sequential Batch Reactor (SBR) This variant of ASP technology is essentially a batch treatment by combining, primary settling, aeration, secondary settling and decanting the treated sewage in a series of sequenced and or simultaneous reactions in the same basin on a time deferred cycle. Thus, multiple basins are used whereby when one basin is in one part of the cycle such as aeration, another tank will be settling and discharging the treated sewage in a cyclically repeated operation. High efficiency fine bubble non-clog membrane diffused aeration is preferred. As different from the well-known reaction kinetics of continuous flow steady state ASP for our sewage characteristics, the bio-kinetic reaction rate in this non-steady state batch process needs to be evaluated for its higher rate or otherwise. Schematic diagram of Sequencing Batch Reactor process is presented in Fig. 2. Fig. 2: Schematic diagram of Sequencing Batch Reactor (SBR) process Bio-Tower Technology The principle of Bio-Tower is very simple and logical. The Bio-Tower pertains to the attached growth type of treatment. On the Bio-Tower waste is fed from the top, the microorganism within the wastewater gradually develops a colony over the surface of plastic media, which provide stability and higher surface area. In this process temperature within Bio-Tower goes above the ambient temperature and the hot air within the Bio-Tower is released from top (because it is light). Obviously to substantiate air loss within Bio-Tower, fresh air rushes from bottom of Bio-Tower and therefore a cycle of air movement is formed, which air requirement of Bio-Tower to the great extent. Thus as stated above, there are several methods for removing BOD in respective units of particular technology adopted for treating the wastewater, However, The detail study / survey of Bio-Tower with Forced Aeration for removal of BOD in attached growth technology Bio-Tower/s with natural draft or with forced aeration from bottom may be available but Bio-Tower with powerless forced aerators installed on top of tower is new concept which we have developed. By adopting Forced Aeration in Bio-Tower Technology, limitations due to natural air draft will be removed and plant will operate at better performance without spending any amount on power for aeration within Bio-tower. According to this invention a Forced Aeration technique in Bio-Tower Technology is introduced by providing a non-conventional and eco-friendly wind-operated air exhaust mechanism at the top of the Bio-Tower. Because of the normal wind speed the wind-operated air exhaust mechanism rotates and removes air inside the Bio-Tower, allowing fresh air to enter from the bottom of the Bio-Tower. Thus, introducing a wind operated air exhaust mechanism at the top, forced aeration is achieved and oxygen from fresh air supplied is used to remove the BOD. The above process is achieved by providing Cover and Forced Aeration through wind operated air exhaust mechanism on the top of conventional Bio-Tower, which is operated by wind speed thereby increasing All rights reserved by 81

3 circulation of air and also resulting in improving the quality of effluents, which is better than the conventional Bio-Tower. No additional power is required for the movement of the air as this is achieved by wind operated air exhaust mechanism at the top. Fig. 3: Schematic Diagram of Bio-Tower Technology Fixed Bed Biofilm Activated Sludge Process The FBAS process is an essentially an activated sludge attached growth process where the plant roots provide the area for the biofilm to develop and grow. The aeration system is divided into a series of biological reactors where fixed biofilm is maintained in every stage of the process. Biodegradation of influent contaminants takes place mainly with the help of fixed biological cultures, where plant roots are used as biofilm carriers; additional textile media is used in the reactors as additional biofilm carriers. As a standard feature of the technology the reactors are covered by a shading structure or a greenhouse. As the influent travels through the cascade, the available nutrient quantity is consumed and as a result, the composition of the ecosystem fixed in the biofilm changes from reactor to reactor, gradually adapting itself to the decreasing nutrient concentration. In each cascade stage a specially adapted ecosystem will form, thus maximizing the decomposition of contaminants. As reported, some plants with such technologies have been set up in different countries including Hungary, China and France etc in last 10 years. However, it will be useful to demonstrate this project under Indian conditions Fig. 4: Schematic Diagram of FBAS BIOFOR Technology Biological Filtration and Oxygenated Reactor is one of the patented technologies of M/s Degremont Ltd. Which include Intensified Aerobic treatment with Dense-Deg & BIOFOR. BIOFOR filters are aerobic biological reactor that use attached growth technology. BIOFOR employs a proprietary dense granular support media that acts as a biological contactor as well as a filter, thus eliminating the need for a separate clarification step. Both the influent wastewater and process air required, flows into the system from the bottom of the unit in an upward direction. Process air provides the necessary oxygen for aerobic biological activity and is introduced in the media through a network of diffusers located at the base of the reactor. Exceptionally high oxygen transfer is achieved the media due to the up-flow pattern of air bubbles. The biological filtration process is of the submerged bed type. The effluent to be treated enters continuously from the bottom of the reactor and is distributed over the All rights reserved by 82

4 entire filter surface area by the nozzle under drain. Co-current up-flows of air and water allow for the finest particles to pass to the upper reaches of the Biolite filter support media; suspended matter becomes attached through the full height of the media which allows for long filter runs. Carbonaceous and nitrogenous pollution is eliminated through the high concentration of fixedfilm biomass which is retained on the filter media during the filtration cycle. Process air is introduced continuously into the lower part of the reactor by air diffusers. According to the full scale experiences, the oxygen transfer in the BIOFOR depends on the nature of the filter material. The biological filtration can be described as a system of three phases with a) A solid phase - the filter material attached with biomass b) A liquid phase - the wastewater that passes through filter material c) A Gas phase - the oxygen to assure oxidative process or the gaseous nitrogen at denitrification. Fig. 5: Process Flow Diagram of Bio-Tower III. ADVANTAGES AND DISADVANTAGES OF VARIOUS TECHNOLOGIES Table - 1 Technologies/Features Advantages Disadvantages Membrane Bio Reactor (MBR) Sequential Batch Reactor (SBR) Bio-Tower Technology BIOFOR Technology FBAS Technology High quality effluent for reuse without separate nutrient removal and fine filtration. Higher stability to organic shocks /upsets due to higher MLSS concentration. Compact system, reduces plant footprint by 25-40% compared to a conventional STP. Can remove N and P concurrent with BOD. Absence of odour and corrosive gases. Less manpower Required due to automatic control and easy to operate and to maintain. No skilled staff is required. The need for a buried central feed pipe in large central feed clarifiers is avoided. Due to cross flow configuration, The liquid has about 4 times higher detention time. High quality effluent for reuse without separate nutrient removal and fine filtration. Absence of corrosive gases in the area. Effluent suitable for UV disinfection without filtration. Can be adopted for nutrient removal such as P and N. The process requires much lesser land area than conventional activated sludge. The process is odourless and hence the plants can be easily built in urban area with no negative impact on the value of adjoining areas. High reliance on energy input in the absence of biomethanation. It is not possible to cannibalize the system between different manufacturers. Detailed evaluation of existing plants required either by IITs, CPCB or NEERI. No provision of primary treatment to moderate pollution load variation. Requires at least semi-skilled manpower. No provision for sludge management. The sludge suction arrangement if it gets into repair necessitates the emptying of the clarifier for repairs. Foaming occurs. NA Continuous and high chemical dosing in primary clarification. Undigested sludge from primary clarification requiring post treatment. Large sludge generation due to the addition of chemicals. The technology requires more qualified operators than in other technologies. Because of higher automation the technology is not attractive for smaller sizes of plants. In colder climates where the temperature drops to sub normal, the plants have to be protected with a greenhouse otherwise the biota may freeze up. All rights reserved by 83

5 IV. CONCLUSION The ultimate goal of wastewater management is the protection of the environment in a manner commensurate with public health and socio-economic concerns. Based on the nature of wastewater, it is suggested whether primary, secondary and tertiary treatment will be carried out before final disposal. Understanding the nature of wastewater is fundamental to design appropriate wastewater treatment process, to adopt an appropriate procedure, determination of acceptable criteria for the residues, determination of a degree of evaluation required to validate the procedure and decision on the residues to be tested based on toxicity therefore, it is necessary to ensure the safety, efficiency and quality of the treated wastewater. REFERENCES [1] Bhat Hemant Nagesh, 2004, Indian patent for An Improved Bio-Tower for Wastewater treatment [2] Metcalf and Eddy Inc., 2003, Wastewater Engineering, 4 th Edition, Tata Mc Graw Hill Publishing C. Ltd., New Delhi. [3] Frank R. Spellman., 2014, Handbook of Water and Wastewater Treatment Plant operations, 3 rd Edition, CRC Press., New York. [4] D.G. Rao., 2013, Wastewater treatment: Advance Process and Technologies, CRC Press., New York. [5] Niraj.S, 2011, Wastewater treatment technologies: A Review, Sci. Revs. Chem. Commun. [6] H. Zhou and D. W. Smith, 2002, Advanced Technologies in Water and Wastewater Treatment, J. Environ. Eng. Sci. [7] Charu Sharma, 2013, Performance Evaluation of Sewage Treatment Plant Based on Advanced Aerobic BIOFOR Technology, IJESIT. [8] T. J. McGhee, 1991, Water Supply and Sewerage, McGraw-Hill, New York. All rights reserved by 84