The need for new technology in treating municipal wastewater is continuously developing. The newest technology should have advantages in minimizing the required cost for wastewater treatment.
In big cities, the sewerage works are costly compared to other municipalities’ services. Then the cost should be minimized for sewerage works to mobilize this environmental service by municipalities. The construction of small efficient wastewater treatment plants for individual sections of the city will help in reducing the cost of sewerage works.
Technically, ionizing radiation is an advanced form of energy, available for societal use, but feared by many people as being an environmentally dangerous and health hazard. Radiation energy treatment for a clean water supply and wastewater treatment is currently under study in many countries. Greater application of this technology in the treatment of water, wastewater and sludge may help not only for the development of technical processes, but also on greater acceptance of the technology as engineering needs [1
The typical costs for the treatment of wastewater by radiation are found to be favorably comparable with the other advanced wastewater treatment systems [2
The objectives of this study are: To evaluate the applicability of ionizing radiation technology for the removal of biochemical oxygen demand (BOD) and fat, oil, and grease (FOG) from municipal wastewater; to assess the physical and biochemical characteristics of municipal wastewater before and after the irradiation; and to determine the optimum doses for irradiation of wastewater.
Radiation treatment may be defined as the application of ionizing radiation energy to produce a useful change in a material, such as disinfection. The amount of radiation energy absorbed in a material depends on both the chemical and physical state of the material and on the type and energy distribution of the radiation. The respective radiation dose units for biological comparison units are the rem and the sievert (sv) which indicate the physical dose unit multiplied by a radiation quality factor (QF).
The application of radiation energy to water and wastewater treatment needs to achieve a sufficient dose absorbed uniformly at a given flow rate and an economic yield. The involved factors include the type of radiation, its energy distribution, and the penetrability into the water stream, the geometric configuration of the radiation-water interaction volume and the thickness of water normal to the radiation flux [1
There are many types of radiation such as gamma, beta, alpha, X-rays and UV. However, the type of radiation mostly used in the treatment of wastewater is gamma radiation. So in this study, gamma radiation was used in wastewater treatment. Gamma ray, emitted during the decay of radioactive atoms, which is electromagnetic radiation, has relatively high penetrating power. The intensity of a gamma ray source determines the exposure time for a given dosage. Some factors such as the source-to-water geometry and the presence of solids in the water affect the bulk density and irradiator design.
An important characteristic of gamma rays from either Co60 or Cs137 is that it is highly penetrating. For water, the half value and tenth value layer for Co60 gamma ray are 27 and 61 cm respectively. For Cs137 the half value and tenth value gamma ray are 24 and 58 cm, respectively. Therefore, it is clear that with an appropriate mixing to provide homogenous exposure, targets with thickness of 50–60 cm can be readily treated.
Biological Phase Treatment
Although the idea of using ionizing radiation for treatment of sewage waste was conceived almost five decades ago, it is only in recent years that there have been several reports on the potential role of radiation in the treatment of sewage and other wastewater. The rationale for utilizing radiation in treatment of sewage waste rests on number of documented facts [1
Radiation destroys microbial life and this property is considered particularly beneficial, since it will result in the inactivation of pathogenic micro flora;
Radiation is capable of altering the structure of organic molecules, thereby leading to a decrease in Biochemical Oxygen Demand (BOD5) and Chemical Oxygen Demand (COD).
Radiation can bring out physiochemical alteration in suspended solid, leading to the formation of more compact sludge and higher capacity for settling.
It is generally agreed that radiation is an exceptionally effective disinfection method. The sequence of events during radiation exposure includes three periods; latent period; demonstrable effects period, and recovery Period.
Responses of Microorganisms to Irradiation Used in Wastewater Treatment
The responses of microorganisms and parasites to a given dose can be altered in different ways. This is possible because the response depends on:
physical factors (temperature and type of radiation);
chemical factors (sensitizing and protecting agents);
© Biological or physiological factors (growth phase and amount of DNA).
The effect of radiation on microorganisms and parasites can be modified not only by agents present during irradiation, but also by biochemical processes occurring over a much longer period of time. Proper pretreatment of wastewater prior to irradiation offers an advantage in maximizing the lethal effect [3
The treatment of wastewater by irradiation can be optimized to enhance the synergistic inactivation of microorganisms and parasites. The main factors, other than the genotype of the microorganisms that influence, radio sensitivity are oxygen, chemicals present in wastewater and temperature.
Materials and Methods
Samples of wastewater were collected from AL-Rustamia sewage treatment plant for three months: January, February and March (2002) whereBOD5 were estimated as 243mg/L, 309 mg/L and 321mg/L respectively. The samples were collected by using different types of clean containers. Samples were taken from the effluent of the primary settling tank.
The facility used in irradiation is Gamma-cell 220 (Canadian made) supplied with Co60
which has a calculated dose rate of two Mrad/hr and radioactivity of 50 kCi in January 1985. Samples were arranged in the cylindrical irradiation chamber (16 cm in diameter and 20 cm in height). This room moved vertically down to the radiation sources of Co60
as roods rotate around the room to supply a homogenous dose for all samples (Fig 1
All tests in this study were taken as an average of three samples subjected to the same absorbing dose. The doses used were 0, 10, 25, 50, 100, 200, 300, 400, and 500 krad. The dose rate in recent time (i.e. 2002) was approximately 0.2 Mrad/hr (Calculated on the basis that the half-life of Co60 is 5.26 years). The irradiation times for these dosages were 0, 3, 7.5, 15, 30, 60, 90, 120, and 150 min. respectively where:
D = Absorbing dose, (rad): DR = Dose Rate, (rad/min.): and T = Irradiation time, (min).
Physical and Chemical Measurements
The physical and chemical measurement parameters taken for this study were: turbidity, electrical conductivity (EC) and hardness., pH, dissolved oxygen (DO), biochemical oxygen demand (BOD5) and chemical oxygen demand (COD), total suspended solid (TSS ), total dissolved solids (TDS), fat, oil and grease (FOG), and phenolic compounds.