Treatment and Disposal of Excess Sludge in Wastewater Treatment - Term Paper Example

Treatment and Disposal of Excess Sludge in Wastewater Treatment Affiliation This paper analyzes various wastewater treatment methods with a view of reaching at a method that achieves low operation cost and low production of sludge. The paper focuses on modification of conventional methods of wastewater treatment in an attempt to minimize the amount of sludge produced. Excessive amount of sludge is found to increase the overall operational cost of running a wastewater treatment plant. This perception calls for the need to reduce the amount of sludge produced in order to cut down the cost of disposing the sludge as an additional cost. The modification of conventional methods is the main principle that underlies the research project in this case. The use of combined anaerobic biofilm-aerobic membrane is chosen as an alternative. The process is dived into two key phases that would ensure the reduction of excess yielding of sludge. The process proves to be environmentally friendly and cost-effective. 1.0 Introduction Efforts to maintain a healthy environment have been in place for a long time. Various activities have been initiated to promote a healthy environment. Among the most important activities, wastewater treatment stands out to be a key activity in managing the environment. With this regard, the wastewater treatment process involves the removal of organic matter, which is contained in the biological unit for water treatment plant. Usually, various microbes including bacteria are considered critical in the wastewater treatment process (Monclus et al., 2010). The play a major role in degrading the solid waste under highly controlled conditions. Such conditions include a predetermined level of oxygen and temperature. Typically, wastewater treatment process is meant to provide a meaningful solution to the various challenges facing the environment due to contaminated water, but this comes with some adverse environmental problems as well. Ideally, clear and safe water is obtained as the intended product, but a large quantity of sludge is created at the end of it all. This sludge results from various causes such as the biological procedure resulting from the biomass of sludge or it could emerge from the primary unit of treatment procedures (Rosal et al. 2010). Often, the sludge is treated further before it is disposed, but it leads to the increment of operating costs for the plant, usually by a significant percentage. The best option of dealing with the escalating costs resulting from sludge disposal process is to structure ways of reducing the sludge during wastewater treatment. Studies have been conducted in an attempt to investigate the ways in which excessive sludge could be avoided during the treatment of wastewater using biological methods. Most of these studies were prompted by the discovery of the problem faced in treating the excess sludge during wastewater treatment processes. Generally, it always seem that the treatment costs count in the entire running costs and given that the treatment costs are always increasing, the operating costs are known to increase as well. In order to come up with proper ways of handling the cumulative cost that seem to be elevated by increasing sludge treatment cost, several strategies have been implemented. Most of the strategies in this case focus on reducing the production of sludge in which various mechanisms have been applied. Some of the most successful mechanisms include uncoupling of bacteria, predation of bacteria, maintaining metabolism, and lysis-cryptic growth. Results obtained through a study on the same strategies pointed oligochaetes sludge reduction method as the best strategy because it is the most cost effective technique. Again, the results pointed out that all strategies used in reducing the production of sludge had some significant impact on the microbial community. This impact is mainly realized in the course biological treatment of the wastewater. Besides, the impact caused on the microbial community is found to adversely influence sludge characteristics and the quality of effluent according to Monclus et al. (2010). 2.0 Methodology This section stipulates the techniques, tools, and methods used in the actual research. The study made use of the MBR process, which combined anaerobic biofilm-aerobic membrane bioreactor. MBR in this case had been proposed as an alternative method for the conventional activated sludge process. MBR as the process of choice was considered because it has the capability of maintaining a high level of mixed liquor volatile suspended solids (MLVSS) in the reactor. This method is advantageous because it controls the retention time for biomass for the longest time possible as compared to many other options. The result of this lengthy retention of biomass is the creation of conditions that favor normal growth of certain bacterial species like nitrifiers, which typically have low growth rates. The system is found to have high possibilities of allowing simultaneous nitrification and de-nitrification that are occasioned by its high concentration of MLVSS. This in turn makes it easy to form both anoxic and aerobic zones in one reactor (Andrade, Motta & Amaral, 2013). The system here produces better effluent that is more reliable in terms of its quality that other conventional processes. The process therefore is able to eliminate any requirements for post-treatment. The system used was not only compact but also easy to control due to automation mechanisms. The system was used with core aim of minimizing excess sludge production through combined anaerobic biofilm using the aerobic MBR process. A part of the biomass within the MBR was treated with ozone after which, the ozonated sludge was returned to the anaerobic inlet. This was later mixed with influent for continued biological treatment. The treatment process was used in this research given the emphasis laid down in when the research was being proposed. The proposition was made because anaerobic process has been considered effective in the removal of organics. This translates to a reduced production of excess sludge as well as a reduction in the consumption of energy. The excessive sludge, which was ozonated, was returned into the anaerobic tank for degradation and stabilization (Andrade, Motta & Amaral, 2013). The aerobic MBR was used to maintain a high concentration in the sludge in order to ease the implementation of simultaneous de-nitrification and nitrification in one reactor under low dissolved oxygen conditions. The idea in this case was to reduce the growth in net biomass under cryptic conditions. In this case, the use of the organic carbon within the microorganism as a substrate of the metabolism process resulted to the reduction of sludge production. Under this situation, it was assumed that ozone could be used as a cell lysis agent because it is a strong oxidation agent and could promote the cell’s biodegradation (Andrade, Motta & Amaral, 2013). The excess sludge that was treated was then returned to the biological treatment unit that ensured that there was a minimal production of net excess sludge. Generally, the treatment system consisted of a biological unit and an ozonation unit. A pilot project was first structured in order to represent the main project. The test project was divided into two stages in which case the biological treatment unit was structure in such as way that it could run for more than two months with controlled conditions meant to achieve a steady state in two distinct phases. Anaerobic phase was the first phase. This phase targeted on improving the BOD5/COD ratio for the creation of a good condition for the post-positioned aerobic process (Chen & Saby, 2000)). With this regard, suspended organic matters were hydrolyzed to a soluble state with the hydrolysis of bacteria. Biodegradation of the large molecule organics into smaller ones was initiated as well as other activities such as improvement of the conventional system. Within the first phase, existence of a bio-carrier ensured that most of the bacteria lived in an attached state. This was meant to facilitate the biodegradation process for the minimization of excess sludge production, if possible to almost zero. Within the same phase, the dissolved oxygen was kept at minimal levels for the facilitation of effective removal of COD. This action further led to the improvement of the BOD5/COD ratio. Within the aerobic MBR, it was projected that the presence of highly concentrated MLSS was to reduce excess sludge yield to minimum levels (Andrade, Motta & Amaral, 2013). The ozonation unit marked the second phase and was structured for the excess sludge. This second phase entailed simultaneous processes for the wastewater treatment as well as sludge digestion within the same system. The processes in this phase were ozonation and biodegradation processes. These two processes performed distinct, but coordinated activities. The ozonation process was initiated to enhance a biological process for degradability of the sludge. The sludge decomposed in subsequent biological treatments within this second phase. A portion of the biomass was mineralized using ozonation through a biological treatment. The reactor was expected to produce a small to negligible quantity of excess sludge. A schematic diagram was used to present the two-phase process as shown in figure 1 below. The test project was structured to run for at least four months. The entire test program had a budget of $15,000 whereby $10,000 was for the first phase and $5,000 for the second phase. This budget could only cater for a domestic wastewater treatment plant a test program for large-scale wastewater treatment plants. Figure 1: A Schematic Diagram for the 2-Phase Process 3.0 Discussion and Conclusion Generally, the test project gave a clear picture of the techniques suitable for larger plants as well as possible ways of projecting budget allocation for large-scale projects. The project showed that conventional treatment plans for wastewater lead to large volumes of bio-solid formations. The consequences of such volumes of bio-solid formations include high operating costs as well as huge capital outlays. These effects arise during the separation, dewatering, treatment, and disposition of the excess sludge. Typically, satisfactory wastewater treatment depends on the choices made in terms of method selection for the task. The major considerations here are costs of operation, efficiency/effectiveness, and further impact on the environment. The ultimate goal in all the processes is to ensure a health living environment that is free of wastewater related hazards. This notion follows the fact that the disposal of wastewater becomes satisfactory only after its treatment prior to the disposal (He et al., 2003). Adequate treatment is a key aspect to avoid the contamination of other waters such as river water to a point of making such waters loses their initial importance. This requirement has been a major aspect pushing for the initiation of the test project using a domestic wastewater treatment plant. Previous studies conducted by various researchers have depicted the same aspect, but major concentrations are in the cost of operations and efficiencies as determined by the choice of wastewater treatment method. Various results all leading to the same conclusion exist about waste water treatment. In a study conducted by Jiang et al. (2009), for example, a two-chambered cell for microbial was used along with an electronic acceptor. The study by Jiang et al. (2009) was meant to degrade sewage and generate electricity at the same time. In this method, up to 46.4 per cent of sludge reduction was achieved. Generation of power by the cell was highly associated with the sledge’s “Soluble Chemical Oxygen Demand (SCOD. From the study, it was established that the sludge pretreatment process, which untrasonic contributed to the enhancement of the level of dissolution of the sludge’s organic matter component. Similarly, the process is applicable in wastewater treatment in both generating power and in enhancing the reduction process of the sludge according to Jiang et al. (2009). Still in a similar study, it was established that sonication could effectively reduce activated water sludge. Again, it was found out that sonication can reduce waste-activated sludge as well as enhancing the synthesis of biomass. The use of the same technique can as well improve the organic mineralization of sewage. High waste activated sludge reduction is often realized in urban areas as opposed to artificial wastewater. This kind of sludge on the centrally has been found to have a low chemical oxygen demand rate. The intense power of sonification especially in liquid sludge is disrupted long before the cell materials are released into water. Zhanng et al. (2009), points out that SCOD increase by at least ten times in this case. The processes of coagulation–flocculation and flotation also contribute to the enhanced pre-treatment of wastewater. This happens mainly in hospital. In such as case, using flotation cells helps to remove all suspended solid materials that may soak and sink thereby increasing the quantity of sledge within material designated for the water treatment plant. Other important methods found to achieve success in sludge reduction is the nozzle-cavitation treatment technique, which has been found to disintegrate sludge thereby reducing its production significantly. In this case, sodium hydrate is added before the sludge is returned to the membrane bioreactor (MBR). Up to 80 per cent of sludge, production is reduced in centrally to the case where sludge disintegration hardly occurs. Often, ozonation does not interfere with the efficient removal of organics although it may influence the removal of Ammoniacal nitrogen within the aerobic MBR process. Generally, Biological treatment and ozonation are considered effective methods of treating wastewater because they lead to the minimization of excess production of sludge according to Rosal et al. (2010). Minimizing the amount of sludge produced as seen in previous studies and in this project is mainly driven by the need to reduce the cost of operation. New technologies in all sectors are meant to improve efficiency, reduce energy, and above all, cut down operational costs. The same ideology is used in wastewater treatment with the focus being on reducing the amount of sludge produced because it was take extra cost to dispose it. In the recent past, restrictions regarding the disposal of sludge have increased. Besides, cost of disposing the sludge has also been increase (Silva, & Urbain, 1998). The combination of these two forces has called for the application of the most effective wastewater treatment methods that not only lower the initial operating cost but also ensure a lower production of sludge. Conventional processes require fast modification as stipulated in this research paper. References Andrade, L. H., Motta, G. E., & Amaral, M. C. S. (2013). Treatment of dairy wastewater with a membrane bioreactor. Brazilian Journal of Chemical Engineering, 30(4), 759-770. Chen, G. H., Mo, H. K., and Saby, S. et al. (2000). Minimization of activated sludge production by chemically stimulated energy spilling. Journal of water Science Technology, 42(12): 189-200 Dos Santos Salazar, R. F., Sanches Carrocci, J., & Izário Filho, H. J. (2011). Employment of factorial design to evaluate the organic loading and aeration of biological systems in the degradation of dairy wastewater. Revista Ambiente e Água, 6(3). He, S. B., Wang, B. Z., Wang, L., Jiang, Y. F., & Zhang, L. Q. (2003). A novel approach to treat combined domestic wastewater and excess sludge in MBR. Journal of Environmental Sciences, 15(5), 674-679. Jiang, J., Zhao, Q., Zhang, J., Zhang, G., & Lee, D. J. (2009). Electricity generation from bio-treatment of sewage sludge with microbial fuel cell. Bioresource technology, 100(23), 5808-5812. Monclús, H., Sipma, J., Ferrero, G., Rodriguez-Roda, I., & Comas, J. (2010). Biological nutrient removal in an MBR treating municipal wastewater with special focus on biological phosphorus removal. Bioresource technology, 101(11), 3984-3991. Rosal, R., Rodríguez, A., Perdigón-Melón, J. A., Petre, A., García-Calvo, E., Gómez, M. J., ... & Fernández-Alba, A. R. (2010). Occurrence of emerging pollutants in urban wastewater and their removal through biological treatment followed by ozonation. Water Research, 44(2), 578-588. Silva, D. G., Urbain, V., et al. (1998). Advanced analysis of membrane-bioreactor performance with aerobic-anoxic cycling. Journal of water Science Technology, 38(4-5): 505-512 Zhang, G., He, J., Zhang, P., & Zhang, J. (2009). Ultrasonic reduction of excess sludge from activated sludge system II: Urban sewage treatment. Journal of hazardous materials, 164(2), 1105-1109. Read More