Estimating the Electrical Energy in Different Processes for Nasir Abad Industrial Wastewater Treatment Plant with Emphasis on COD Removal

Document Type : Research Paper

Authors

1 Phd student in Tehran university

2 prof., Dept. of Environmental, Tehran University

3 Assist., Prof., Environmental Eng. Dept., Faculty of civil Eng., Babol Noshirvani University of Technology

Abstract

Introduction
In the wastewater treatment industry, the general attentionis mostly paidto the effluent quality standards. Regardless of energy consumption, the treatment plants have been designed based on experience rather than the latest scientific findings.The treatment plants are considered as a part of energy equipment which largely consumed electrical energy.Thus, electricity is the great part of the costs of plant utilization so that 25% -40% of the total costs of the wastewater treatment process is related to energy supplies. Therefore, energy is regarded as an important factor in treatment plant costs.This has caused designers to adopt new methods to reduce energy consumption. The study in 2010 indicated that 50 – 60% of energyconsumed by treatment plants is related to the aeration process.  Nowadays, due to the rapid population growth along with recent advances in technology and industry, the amount of pollution has been increased. In addition, environmental standards for effluent quality and its recycling process for different utilization have become much stricter. What was mentioned above increases energy consumption. Hence,energy efficiency, effectiveness of the plan and the utilized equipment and technologies, energy recovery processes and effective cost management has been recently considered more seriously. Additionally, enhancement ofenergy efficiency, which means a further reduction in energy consumption, greenhouse gases production and operation costs of wastewater treatment plants,has become more important.The principal concern of the wastewater industry has always been measures to meet water quality standards in order to keep public trust.Thus,wastewater treatment plants (WWTPs) are usually designed to meet certain effluent requirements, without major energy consideration. Wastewater treatment plants are generally very energy-intensive and expensive to operate. WWTPs are hardly designed forenergy efficiency in mind. Their design and operation areoften based on intuition and experience, rather than on optimal trajectories or set points. The amount of energy consumed by treatment plants is counted as a major factor todetermineoptimum performance. Moreover, due to the fact that the treatment plant system of industrial zones is energy consuming. Theenergy subsidies have been cut and water and electricity tariffs have been raised, thus, energy management has become far more important. Todesign treatment plant equipment, it is necessary to adopt approaches which lead to reduce energy consumption and improve efficiency. Knowledge ofthe real operating efficiency of WWPTs is the starting point for any energy saving initiative.
A study was conducted in 2012 in Sweden on WWTPs energy consumption in which aeration was controlled to reduce energy consumption in a treatment plant to employ activated sludge which affected the amount of dissolved oxygen, the efficiency of the aeration process, and equally the results from treatment process. The amount of energy consumed by treatment plants depends on air flow rate and consequently the rate of oxygen consumption. The rate of oxygen consumption in the activated sludge system is changed by changing the concentration of ammonium or ammonia in the effluent. Therefore,reduction inthe amount of ammonium in the effluent, have reduced air flow rate and consequently the rate of oxygen and the amount of electricity consumption. A study in 2011 in Spain performed on the factors affecting the plant energy consumption. The results indicated that the average amount of energy consumed by WWTPs depends on the input quality parameters, treatment technology, effluent quality and the size of the plant. Furthermore, the amount of energy consumed by smaller plants per unit area is higher compared withthe larger plants.
In an article in 2012, the amount of energy consumption was studied in each physical unit. This study found that there is a strong relationship between biological activity and demand for electricity. In 2013, a study conducted to optimize pumps performance and aeration process in treatment plants. The results suggested that the pumping stations and the aeration in activated sludge process are the most energy consuming parts in treatment plants which consume 22% and 42% of electrical energy, respectively. Thus, in order to reduce energy consumption, the pumps performance should be improved and aeration processes should be optimized.
In the present study, the wastewater treatment plant (WWTP) of industrial zone of Nasirabad was studied which works with a combination of Up flow Anaerobic Baffled Reactor (UABR) system and Integrated Fixed Activated Sludge (IFAS).
Material and methods
The aim of this paper is to calculate the electrical energy in different processes for industrial wastewater treatment plants and also to estimate effective electrical energy to remove1 Kg COD. To this end, Nasir Abad industrial wastewater treatment plant was investigated on the basis of energy.The treatment process includes up flow Anaerobic Baffled Reactor(UABR) coupled with Intergraded Fixed/Film Activated Sludge(IFAS) reactors. The present study was conducted using statistical methods and data collectionthrough observation and field study of wastewater treatment plant of industrial town of Nasirabad. Data wereanalyzed through drawing tables and charts in Excel along with making engineering judgment.
 In order to study electrical energy consumption in treatment plant of the industrial zone of Nasirabad, theelectricity bills for different months of 2012 and2013are checked.Theaverage daily electrical energy consumptions per 1cubic meter of wastewater ascalculated during these years were 9.42Kwh and9.73 KWh, respectively. Energy consumption varies at different times of day. Thus, electrical energy falls in three categories namely Peak Load, Medium Load, and Low Load periods. According to the table,thePeak Load was set up by the Electricity Distribution Company of Mazandaran province, Iran. Thus,12 hours out of 24 hours a day is considered to be the Medium Load, 6 hours is considered to be the Low Load, and the remaining 6 hours is considered to be the Peak Load period. However, the beginning and ending time of the each group varies from season to season. The electrical energy consumption relatedto each group (Peak Load, Medium Load, and Low Load periods) is multiplied by the correspondingtimes and the sum is considered as the electrical energy consumption relating to the period.
Results and discussion
 The electromechanical equipment of plant in each unit was examined separately and the energy consumption for each unit was evaluated. The units consist of Pumping station, Grit and grease removal tank, equalization tank, Aeration tank, sand filter, disinfectant system, sludge storage, and filter press. The electrical energy obtained from electrical bills includes the energy consumed by the treatment plant equipment, control room, laboratory, and electrical lighting. In this study, the energy used in the treatment plant units wasconsidered as effective energy and the one used in the sections outside of the units was considered as ineffective energy. For exactspecification ofthe energy consumed by the units (the effective energy) and ineffective energy, the electro mechanic equipment should be examined. Therefore, the field study on the treatment plant of the industrial town of Nasirabad was conducted and different treatment processes were examined. The inflow discharge entered into the treatment plant was approximately 620 m3/day. In order to measure the amount of electrical energy used to remove one kilogram COD, the input and output COD were achieved in mg/lit. The entire procedure of the sampling and testing wasperformed according to the instructions and guidelines provided in the standard methods for examination of water and wastewater. Giventhe fact that the average inflow discharge was in m3/day, the removed COD was defined in Kg/day and the effective energy was in Kwh/ m3, the amount of energy per 1 kilogram COD is in Kw. In this WWTP, about %32 of total electrical energy were used for aeration purposes and about %43 in sludge treatment equipment and %25 in primary treatment, disinfectant system and etc. The influent wasmeasured 620 cubic meter for day and the pump efficiency was assumed %80.The effective daily electrical energy as the energy used in the treatment process was 5.6 Kwh. The non-effective electrical energy that used in other process in Nasirabadindustrial wastewater treatment plant for the years of 2012 and 2013 were calculated 3.82Kwhand4.13kWh. In addition, the amount of electrical energy per 1 kilogram of the removed chemical oxygen demand (COD) was obtained.The use of energy for removing 1 kg COD for the years of 2012 and 2013were equal to 2.68Kwh and 2.5 Kwh.
 
Conclusion
Based onthe obtained results, it can be concluded that energy consumption is not effectively managed in the treatment plant of Nasirabadand that efficientuse ofelectrical energy,make it possible to preserve electrical energy sources as a national asset and also for considerableeconomization. Moreover, the effective aeration optimization of the pumps and blowers performance in the aeration basin is an important tool to minimize energy consumption in WWPTs. This is a tool to control the aeration system for aeration is a costly process and closely linked to energy consumption. Therefore, theefforts to reduce the overall energy use in WWTPs have largely concentrated on improvement of pumping and optimization aeration.The sludge management and reduction should be considered more seriously. The electrical energy consumed in pumps and blowers has a direct relationship with the rate of aeration in the basins and the level of pressure drop. More appropriateoptimization of aeration units, effectivemanagement ofthem and use ofthe methods such as employing ultrasonic waves and sending them to the wastewater treatment system, which can change the chemical structure and the size of the particulate organic matters, will increase the rate of biological treatment process and consequently the wastewater treatment.Furthermore, the rate of aeration and electrical energy consumption will be reduced. Additionally, by using these waves, a huge amount of excess sludge will be reduced and, therefore, less electrical energy will be consumed for sludge equipment. Moreover, if treatment plants designed in a way that the produced electrical energy and sludge treatment in anaerobic sector can be utilized to generate electrical energy, the treatment plants remarkably gain sufficient independence from energy sources. Thus, it can be possible to save more electrical energy. With regard to the importance of energy and its related issues, rising prices and reduction of energy supplies, the effective managerial approaches should be adopted to reduce energy consumption in wastewater treatment plants. Furthermore, experts and designers of wastewater treatment plants should more seriously consider the amount of energy wasted in the processes as well as enhance energy efficiency. Furthermore, improving energy independence in WWTPs can be effective for energy saving. It is concluded that according to usage of energy in plants equipment and increase inenergy prices, management of energy consumption should be considered more seriously.

Keywords

Main Subjects

References

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Journal of Environmental Studies
Volume 42, Issue 1
June 2016
Pages 19-31

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