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- Biological wastewater treatment and bioreactor design: a review
- Biological Wastewater Treatment Systems: Theory and Operation
- Biological and Chemical Wastewater Treatment Processes
- Understanding Laboratory Wastewater Tests: I. ORGANICS (BOD, COD, TOC, O&G)
Wastewater treatment is a process used to remove contaminants from wastewater or sewage and convert it into an effluent that can be returned to the water cycle with acceptable impact on the environment, or reused for various purposes called water reclamation. Pollutants in wastewater are removed, converted or broken down during the treatment process. The treatment of wastewater is part of the overarching field of sanitation. Sanitation also includes the management of human waste and solid waste as well as stormwater drainage management. The processes involved in waste-water treatment include physical processes such as settlement or flotation and biological processes such as aerated lagoons , activated sludge , or bio-films in trickling filters.
Biological wastewater treatment and bioreactor design: a review
Metrics details. Utilization of membrane-based technology and liquid phase oxygen technology in wastewater treatment has also been analyzed. Both aerobic and anaerobic processes have been considered and possibilities of clubbing waste treatment with waste utilization production of valuable products from waste streams have also been surveyed and scrutinized.
Biological wastewater treatment is a biochemical process that is centuries old. Even today, as the quantity of industrial effluents discharged is on the increase and the types of pollutants present in the effluent streams are getting diversified, wastewater treatment processes are being investigated and experimented exorbitantly all over the globe.
It is always desirable to couple wastewater treatment with waste utilization. In such a situation, it becomes invariable to propose and develop renovations in effluent handling and treatment processes to improve their overall economy as well as their energy efficiency. This paper surveys the developments in biological wastewater treatment processes and in the design of bioreactors associated with. Activated sludge process, which involves aerobic treatment of industrial effluents in stirred tank bioreactors, is one among the very old industrial applications of biotechnology.
Still this process is popular in spite of some of its inherent limitations. It is also the process that has been subjected to the maximum number of modifications and diversifications. The conventional activated sludge process employs an aerobic tank which is an agitated vessel stirred tank bioreactor seeded with an inoculum of microbial sludge usually the recycled portion of active sludge.
Here, suspended growth of microbes occur. Air is sparged under high pressure from the bottom to provide sufficient dissolved oxygen in the medium. Since the volume of the aerobic tank is usually quite large and the solubility of atmospheric oxygen in water or aqueous solutions is very low, huge air compressors would have to be deployed to sparge in significant amount of air so as to meet the oxygen requirement of the microbes and that of the aerobic process.
This high operating cost of air compressors forms the major economic limitation of this process, though the system is simple to design and install. Apart from the oxidation of the dissolved organic matter to carbon dioxide and water , nitrification and denitrification processes could also be conducted here. Nitrification is accomplished in the aerobic tank itself simultaneously with carbon removal , during which the dissolved ammonia in wastewater is converted to nitrates.
Denitrification, being an anoxic process, is conducted in a separate bioreactor. During denitrification, the nitrates formed during nitrification are reduced to nitrogen gas and thus is expelled from the bioreactor. Since the process is anoxic in nature, this bioreactor does not need supply of atmospheric air from outside.
As stated earlier, many modifications of activated sludge process have been proposed by different researchers during the past. A comprehensive survey of the same has been presented by Rao and Subramanyam [ 1 ]. Nevertheless, all the schemes employ stirred tank bioreactors. The conventional scheme involves two bioreactors stirred tanks in series, the first one being the aerobic tank in which carbon removal organic matter destruction and nitrification occur, while in the second denitrification is performed anoxically.
The effluent from the denitrification tank is sent to a sedimentation tank for clarification; treated water overflows and the thickened bottom sludge is partially recycled back to the aerobic tank stirred tank — 1. The amount of microbial sludge recycled must be optimized so as to minimize occurrence of endogenous decay of microbes, simultaneously maintaining the degree of biological oxygen demand BOD removal at a higher magnitude.
The so-called Bardenpho scheme [ 2 ] is a modified form of activated sludge process that employs four stirred tank bioreactors in series, the first one being a pre-denitrification bioreactor stirred tank — 1 which is followed by the first aerobic tank stirred tank — 2 and then the second denitrification bioreactor stirred tank — 3 and finally, the second aerobic tank stirred tank — 4.
The effluent from the last bioreactor is sent to the sedimentation tank and the separated sludge is partially recycled to stirred tank — 1. Such a scheme operates at high capacities, provides larger BOD removal, larger degree of denitrification and also larger phosphorus removal, but is more expensive to install, maintain and operate.
Instead of using a single stirred tank bioreactor, it is advisable to use a number of small size stirred tanks in series with the total volume of the cascade remaining the same as the single bioreactor.
Such a scheme, which invariably improves the overall performance of the bioreactor, is achieved in activated sludge process by employing what is called as the step aeration [ 1 , 2 ]. The aerobic tank is divided into a number of compartments and each compartment receives a separate surge of compressed air.
The raw wastewater is fed to the first compartment and the partially treated water flows to the subsequent compartments from one compartment to the other , the product water treated effluent being discharged from the last compartment. The scheme does provide enhanced BOD destruction, though the overall operating cost also gets elevated.
In a single, large volume aerobic tank, dead zones and bypass streams could very well be present and these disturb the degree of back-mixing and adversely affect the performance of the bioreactor. It is further possible to use a series — parallel arrangement of stirred tanks in order to boost the performance of the bioreactor aerobic tank still further [ 3 , 4 ]. In this case also, the aerobic tank is divided into a number of compartments and each compartment receives a part of the raw waste water feed effluent and is also aerated separately.
Both step feeding as well as step aeration are thus employed here. Each compartment, except the first, receives a portion of the fresh feed as well as the partially treated effluent from the previous compartment.
Such a scheme is well-recommended for large capacity installations. Here also, each compartment could perform equivalent to an ideal continuous stirred tank reactor CSTR , providing intimate contacting between the substrate and the biocatalyst microbial cells. The performance equation of each compartment then becomes. If the bioconversion BOD destruction follows Monod-type kinetics and the occurrence of endogenous decay though minimal is taken care of, then.
The performance equation Eq. Though in many cases of aerobic wastewater treatment, Monod-type kinetic equation has been observed to be more or less satisfactory, alternate kinetic models are not rare. For the aerobic synthesis of Xanthan gum from dairy wastes for example, cheese whey using a culture of Xanthomonas campestris , Zabot al [ 5 ]. As stated earlier, the most serious bottleneck associated with aerobic processes employing stirred tank bioreactors is the high operating cost of the air compressors.
A good number of case studies in this connection have been reported in literature discussed subsequently in this paper. LPO technology involves addition of a calculated amount of hydrogen peroxide into the feed water prior to admitting into the bioreactor.
This hydrogen peroxide releases nascent oxygen in solution which, being extremely reactive, meets the entire oxygen requirement of the microbes and that of the process. As a result, no atmospheric air shall be required to be supplied from outside and this eliminates the entire operating cost of huge air compressors. The diffusional resistance encountered during the dissolution of gaseous oxygen into the aqueous substrate becomes absent and no vigorous agitation of the substrate shall be required.
The bioreactor operates essentially in the liquid phase and the two phase gas-liquid nature of reactor operation gets eliminated. The enormously high reactivity of nascent oxygen itself forms the most important safeguard with respect to LPO utilization. Hydrogen peroxide is to be added precisely as per the very calculated amount and any excess even marginal could destroy the microbial cells themselves.
This explains why the commercial adaptation of LPO technology is fairly slow. It is possible and is often advisable to couple Membrane Based Technology with activated sludge process. The wastewater, after pretreatments such as lime addition, coagulation, filtration and clarification , be fed to a reverse osmosis RO unit, from where reusable water is collected as the permeate.
The RO concentrate is further subjected to biological treatment in the aerobic tank and denitrification bioreactor. Smith [ 7 ] has reported a successful case study in this regard and has demonstrated that the BOD removal, phosphorus removal and nitrogen removal can be adequately enhanced by coupling RO with the aerobic process. An economic analysis of such a scheme has been reported by Narayanan [ 8 ].
The operating pressure of the RO unit the transmembrane pressure difference that is required to be maintained and the useful life span of the polymeric membrane are the major considerations that affect the overall economy of RO system. Chances of membrane clogging and fouling are the additional headaches. Narayanan [ 8 ] reported that two-thirds of the wastewater could be recovered in the RO unit and the rest one-third of the total waste be subjected to biological treatment and in that case, the overall cost of production of treated water could go down to three- fourths of the conventional scheme.
This is after including the cost of membrane replacement. Based on their laboratory studies, Thakura et al. The overall economy of the proposal is, nevertheless, to be analyzed keeping in mind the high operating cost of the nanofilters and the large quantity of wastewater that is required to be handled in industrial practices.
As in the case of aerobic treatment of wastes, stirred tank bioreactors are the earliest and still one among the popular ones employed for anaerobic treatment of industrial, domestic and municipal wastes. Large capacity large holdup and ease of installation are the chief reasons for such a choice. The anaerobic digested sludge could be directly used as a low grade nitrogenous biofertiliser or could be used for the manufacture of phosphatic biofertilizer called Phosphate Rich Organic Manure through biochemical pathway [ 10 , 11 ].
The process of anaerobic digestion is however relatively slower. This helps in destroying the pathogens at a faster rate, but there shall be additional cost of installation of heating pipes and supply of heat from outside. The cost of extra energy input often tends to compensate the benefit of faster pathogen kill and increased methane production. Also, thermophilic microbes are relatively slower growing bacteria as compared to mesophilic. Unless waste heat is available such as in Combined Heat and Power systems, thermophilic treatment of wastes shall not be an attractive or beneficial proposition.
A thermophilic pretreatment may, however, be given to the feed slurry in case pathogen destruction is of serious concern [ 3 , 12 ]. Most of the studies reported in literature on anaerobic digestion using mesophilic microbes, are those dealing with the use of alternate, multiple substrates [ 13 , 14 , 15 , 16 , 17 , 18 ].
Most of them have employed laboratory stirred tanks chemostats for conducting the experiments and practically all of them deal with suspended growth of microbes. Momoh and Nwaogazie [ 13 ] have reported increased biogas yield when waste paper is co-digested with water hyacinth and cow dung.
Samson and LeDuy [ 14 ] have demonstrated that addition of microalgae algal mass increases the rate of anaerobic digestion of domestic sewage sludge, peat hydrolysate and spent sulfite liquor and leads to higher biogas yield. Anaerobic co-digestion of microalgae with waste paper has been investigated by Yen and Brune [ 15 ] and with waste activated sludge WAS by Costa et al.
Studies on co-digestion of microalgae with municipal food waste are reported by Krustok al [ 18 ]. In all the cases, addition of algal mass has been found to be beneficial in boosting the rate of digestion and the yield of biogas.
Ajeej et al. Reported kinetic studies on anaerobic digestion [ 12 , 23 ] have indicated that substrate inhibition to microbial growth is not unlikely in these processes, particularly when conducted in stirred tank bioreactors. Accordingly, a Haldane-Andrews type kinetic equation has been found to be most applicable here:.
Endogenous decay of microbes is little reported in these processes. Most probable reason is that the sludge is continuously discharged from the bioreactor almost at the same rate at which the fresh feed is admitted and recycle of microbial sludge is little practiced in these systems.
Graef and Andrews [ 23 ] have presented a detailed parametric analysis of the performance of anaerobic stirred tank bioreactor.
They have however assumed the bioreactor to be equivalent to an ideal CSTR that receives a sterile feed. Though the process involves a complex culture of microbes hydrolytic microbes, acidogens, acetogens, methanogens , the last step of conversion of acetic acid or acetates to methane and carbon dioxide catalyzed by methanogens is reported to be the slowest and thereby the rate controlling step [ 23 ].
As a result, acetic acid is considered as the limiting reactant and the kinetic equation Eq. Based on the ionization constant K a of acetic acid and the equilibrium constant K 1 for carbon dioxide dissolution in the aqueous slurry only CO 2 dissolves in the aqueous phase, all the methane produced gets transferred to the gas phase ,. The net rate of production of carbon dioxide in solution R C shall be the difference between the rate of production of CO 2 by microbial activity and the rate at which CO 2 gas is being transferred to the gas space.
The above Eqs. In spite of the simplifying assumptions involved, the above model proposed by Graef and Andrews [ 23 ] does predict reliable results in specific number of cases. Agitation of the substrate slurry is one of the operational problems encountered in stirred tank bioreactors. Introduction of mechanical impeller is problematic since this could cause leakage of atmospheric air into the bioreactor and escape of biogas produced.
Biological Wastewater Treatment Systems: Theory and Operation
The scope of this comprehensive new edition of Handbook of Biological Wastewater Treatment ranges from the design of the activated sludge system, final settlers, auxiliary units sludge thickeners and digesters to pre-treatment units such as primary settlers and UASB reactors. The core of the book deals with the optimized design of biological and chemical nutrient removal. The book presents the state-of-the-art theory concerning the various aspects of the activated sludge system and develops procedures for optimized cost-based design and operation. It offers a truly integrated cost-based design method that can be easily implemented in spreadsheets and adapted to the particular needs of the user. Handbook of Biological Wastewater Treatment: Second Edition incorporates valuable new material that improves the instructive qualities of the first edition.
Biological and Chemical Wastewater Treatment Processes
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Understanding Laboratory Wastewater Tests: I. ORGANICS (BOD, COD, TOC, O&G)
Wastewater treatment plants WWTP are highly non-linear operations concerned with huge disturbances in flow rate and concentration of pollutants with uncertainties in the composition of influent wastewater. In this work, the activated sludge process model with seven reactor configuration in the ASM3bioP framework is used to achieve simultaneous removal of nitrogen and phosphorus. A total of 8 control approaches are designed and implemented in the advanced simulation framework for assessment of the performance. The performance of the WWTP effluent quality index and global plant performance and the operational costs are also evaluated to compare the control approaches. Additionally, this paper reports a comparison among proportional integral PI control, fuzzy logic control, and model-based predictive control MPC configurations framework. The simulation outcomes indicated that all three control approaches were able to enhance the performance of WWTP when compared with open loop operation. This is a preview of subscription content, access via your institution.
Biological wastewater treatment — which relies on microorganisms to break down organic waste — has a long history, and ranges from simple cesspits to conventional activated sludge plants all the way to technologically advanced solutions like MABR. Biological treatments rely on bacteria, nematodes, or other small organisms to break down organic wastes using normal cellular processes. Wastewater typically contains a buffet of organic matter, such as garbage, wastes, and partially digested foods.
Since the implementation of the Clean Water Act and subsequent creation of the United States Environmental Protection Agency USEPA in the early s, industrial, institutional and commercial entities have been required to continually improve the quality of their process wastewater effluent discharges. At the same time, population and production increases have increased water use, creating a corresponding rise in wastewater quantity. This increased water use and process wastewater generation requires more efficient removal of by-products and pollutants that allows for effluent discharge within established environmental regulatory limits. The determination of wastewater quality set forth in environmental permits has been established since the s in a series of laboratory tests focused on four major categories:. Although wastewater analytical tests are often separated into categories, it is important to understand that these tests are not independent of each other Figure 1.
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Metrics details. Utilization of membrane-based technology and liquid phase oxygen technology in wastewater treatment has also been analyzed. Both aerobic and anaerobic processes have been considered and possibilities of clubbing waste treatment with waste utilization production of valuable products from waste streams have also been surveyed and scrutinized. Biological wastewater treatment is a biochemical process that is centuries old. Even today, as the quantity of industrial effluents discharged is on the increase and the types of pollutants present in the effluent streams are getting diversified, wastewater treatment processes are being investigated and experimented exorbitantly all over the globe.
This chapter elucidates the technologies of biological and chemical wastewater treatment processes. The presented biological wastewater treatment processes include: 1 bioremediation of wastewater that includes aerobic treatment oxidation ponds, aeration lagoons, aerobic bioreactors, activated sludge, percolating or trickling filters, biological filters, rotating biological contactors, biological removal of nutrients and anaerobic treatment anaerobic bioreactors, anaerobic lagoons ; 2 phytoremediation of wastewater that includes constructed wetlands, rhizofiltration, rhizodegradation, phytodegradation, phytoaccumulation, phytotransformation, and hyperaccumulators; and 3 mycoremediation of wastewater. Additionally, this chapter elucidates and illustrates the wastewater treatment plants in terms of plant sizing, plant layout, plant design, and plant location. Wastewater Treatment Engineering. The chapter concerns with wastewater treatment engineering, with focus on the biological and chemical treatment processes.