Introduction

The Sewage Treatment Plant (STP) is employed to treat sewage water for irrigation utilities and also for the Oman Gulf disposal. The sewage treatment plant and its auxiliaries are provided to satisfy and achieve the required quality of water to be valid for irrigation NOT for drinking. CORODEX INDUSTRIES supplies plant equipment with high quality to ensure the product water facilities required for irrigation qualitatively and quantitatively. Moreover; great qualities of product water disposed to Oman Gulf matches the required water quality for disposal by Environment Groups due to high performance and experience of design and proposal.

Sewage water contains many harmful contents, chemically, physically, and biologically. The bacteria content in sewage causes a lot of diseases if not drained from the society usage of water. Also, ammonia and hydrogen sulfide contents are harmful and hazardous where problems of odor and toxicity can cause healthy problems. Furthermore, amount of ammonia and nitrates disposed in Oman Gulf causes the higher rate growth of plants in sea waters, but the animals in sea water will die due to dissolved oxygen consumption from plants. Additional to previous, nitrates are harmful to human and can cause ‘blue baby disease’. Moreover, large solids disposed within sewage water cause a lot of physical problems where problems of environment take place due to dirty large solids that may cause problems in plants irrigation and form layer of wastes in which oxygen cannot be dissolved into sea water. In addition, sewage water contains oils, fats, and grease where thick layer of fat, oil, and grease is formed in which the problem of this layer causes the difficulty of mass transfer between gases through sea water surface.

Due to the reasons mentioned above, CORODEX INDUSTRIES supplies the sewage treatment plant, as per Sharjah Municipality demand, to ensure the treatment of sewage while matching the quality and quantity of the product.

Scope of Work

The sewage treatment plant, proposed by Corodex Industries, will reduce the chemical content of the raw sewage water using multi techniques and processes; thus, the final product water quality will meet the irrigation water specifications.

Corodex scope of work for this project includes engineering, manufacturing, supply, and supervision of installation and commissioning of the MBR raw sewage treatment plant with a capacity of 7,000 m3/day and 10,000 m3/day extension. The plant will be located at Dibba Al – Hisn, Sharjah , UAE.

CORODEX INDUSTRIES provided the plant to treat water from the following: bacteria, ammonia, nitrate, total nitrogen content, hydrogen sulfide, biological oxygen demand (BOD), fats, oil and grease (FOG), chemical oxygen demand (COD), and decreases turbidity. Consequently, this STP helps environment to keep clean and safe from dangerous wastes and benefited in reusing water for irrigation to reduce water consumption.

STP includes stages which are employed to satisfy the process. Raw sewage is pumped by lifting station pumps to the plant to be treated by six stages. These stages are: Screening to remove large solids, Break Tanks to equalize the process and keep constant transfer, ANOXIC Tank where nitrogen is removed by nitrification and de-nitrification processes, respectively, Aeration Tanks to activate bacteria for the next stage by aeration of the raw sewage, Membrane Bio – Reactor (MBR) tanks where highly qualified pure water is produced, and finally the product water is disinfected by UV – System to be ready after disinfection for irrigation and disposal to Oman Gulf.

The technology of this plant is the newest sewage treatment technology which is called MBR that depends on the membrane technology for water purification. In this technology the permeate water through membrane (product water) has a quality better than the quality of other classical techniques based on CORODEX INDUSTRIES experience. STP will reduce about more than 98 % of BOD during the process. Another facility of this technology is that- the technology does not require further treatment such as further settling tanks of filtration. Moreover, the area space of the plant depending on this technology will be reduced as a comparison to other technologies due to the presence of membranes. Furthermore, the quality of water produced due to MBR technology can be treated more to be valid for drinking using post-treatment such as Nano – filtration and Reverse Osmosis system.

Process Flow Description

3.2.1. Lifting Station

STP is designed to remove and overcome all these problems. The municipal sewage water is collected in the lifting station which is not provided by CORODEX INDUSTRIES. From the lifting station, sewage is pumped to the plant through submersible pumps working at a peak factor 2.7. Meaning, the pumps’ capacity is 2.7 times the designed capacity and it is operating even 2.7 times the capacity or it is not working, depending on the liquid level of balancing tanks and aeration tanks (to be shown on the next page).

3.2.2. Automatic Screens

Sewage will be transferred from the lifting station to the plant. Sewage major line will be divided into two lines (three lines in the future after extension). To elaborate, STP is divided into twp lanes (three lanes in the future). The first equipment that each line of sewage will pass through are the screens. Each lane of sewage will be screened by two stages. The first stage is the screening of sewage to remove 6mm solids or larger. After that, the screened water will pass through the second screen to remove Fat, Oil, and Grease (FOG) and grit having a particle size of 3mm or higher. The removed solids, dirt, FOG, and grit are collected by drum and then delivered periodically and manually to the sludge holding tank.

3.2.3. Break Tank

The screened sewage water will be transferred to the break tank by gravity. CORODEX INDUSTRIES has supplied only one break tank. This tank is provided by eight air diffusers to activate bacteria for growth. The discussion and description of the aeration will be mentioned later on with aeration tank. This tank (break tank) serves as an intermediate tank.

3.2.4. ANOXIC Tank

The most important goal of this process is to remove nitrates (NO3-) by the de – nitrification process. It is similar to the anaerobic process. In this process, oxygen is absent. The following reaction shows the removal of nitrates by de – nitrification.

NO3- + ORGANIC MATTER ==> N2 (GAS) + CO2 + H2O

It must be noted that in this process (ANOXIC TANK), air is not supplied and sewage is not aerated.

3.2.5. Aeration Tank

In the aeration tank, air is supplied by air blowers. Air contains about 21 % of oxygen which is essential for bacteria to grow. Bacteria can be considered as catalyst of reactions of oxygen with bio-organic materials. In addition, bacteria are known for having much requirement for food and air. Bacteria breathe oxygen (absorb oxygen) and eat organic matters which are dissolved in water releasing carbon dioxide (CO2), water (H2O), other gases released, and large numbers of bacteria formed with the following reaction:

Consequently, due to aeration, the Total Suspended Solids (TSS) will increase. Sewage in the tank is delivered to the next stage by submersible pumps to the Membrane Bio – Reactor (MBR) Tank.

3.2.6. MBR Tank

This tank or process is the most important and most sensitive in STP. In the tank, membrane sheets are submersible. Also, air is supplied for aeration to enhance bacterial growth. However, TSS of this tank is too high that problems can occur. CORODEX INDUSTRIES has supplied this STP with 42 membrane frames. Each frame contains membrane sheets.

The process of aeration has the following aims:

bacterial growth
Preventing membrane sheets to be plugged from bacteria and sludge.
Keep the sludge fluidized continuously.

Membranes only permeate pure water and some dissolved ions. These membranes are not selective as R.O membranes, but they are selective to permeate pure water and dissolved salts and also to reject bacteria, biomass, dissolved and non – dissolved organic matters, and suspended solids.

The overflow of the MBR Tank is supplied by CORODEX INDUSTRIES in order to re-circulate the aerated sewage water to the ANOXIC Tank to enhance the treatment process, decreasing equipment size, activate bacteria to enhance, and achieve possibly the de – nitrification process in ANOXIC zone.

Purified water is delivered using self priming pumps system in which vacuum is created on the head of the membranes, so pure water will be forced to pass through the membrane to delete the vacuum of the membrane head to the next final stage, which is UV Disinfection System.

UV Disinfection System

The product water from self priming pump (permeate pump) is pumped to the UV System, where any small bacterial content is disinfected and die by Ultra – Violet lamp.

4. Functional Blocks

The proposed plant for producing irrigation, reuse, and disposal water will be based on Membrane Bio – Reactor (MBR) technology as the treatment unit will undergo proper pre & post treatment processes in order to achieve the desired quality as irrigation, reuse, and disposal water.

The MBR system will significantly reduce total biological oxygen demand (BOD). However, more than 3mm suspended solids are not acceptable to pass through the membranes because they may damage the membranes.

The illustration below shows the functional processes proposed by Corodex Industries which will act along with the MBR system as one complete process.

Pre – Treatment Process Stage

Raw Sewage Water

From Lifting

Station

Disinfection:

Disinfection by UV System

Product water can be used for irrigation, disposal, reuse and advanced treatment

Post Treatment Process Stage

Figure 4.1 Functional Blocks for the proposed sewage water treatment

4.1 Screening

In this stage as discussed, the sewage water is clarified by two stages followed in series.

These stages are:

Ø 6 mm Automatic screen

This equipment is supplied in order to remove the large solids, rages, and debris larger than 6mm. a manual by pass screen (16 mm) will be in operation in case of malfunctioning of the automatic screen.

Ø 3 mm Automatic screen

This equipment is supplied in order to remove the large solids, rags, and debris larger than 3mm, grit and FOG (fat, oil and grease). This extra screen is provided by CORODEX INDUSTRIES in order to ensure safe operation of membranes sheets.

4.2 Sewage Breaking

In this stage, sewage water will reside in this tank to be ready for further processes. This tank can be considered as an intermediate tank and the second lifting station where the liquid level is increasing each time matching up to the high level switch and then the submersible pumps of the lifting stations will be switched OFF automatically. After that, due to the operation of break tank submersible pumps, the liquid level of the break tank will decrease gradually to match the low level switch and then, the lifting station submersible pumps will switch ON and the operation of this sequence will be periodical and frequent. The break tank can be described as a new lifting station for further processes of STP. In the submersible tank, as it is appearing, there are submersible pumps. These submersible pumps are provided to deliver the sewage water to the next stage, which is called an ANOXIC process.

4.3 ANOXIC Process (De – Nitrification Process)

In this process, any content of nitrates (NO3-) will be converted to nitrogen gas, even if the nitrate source is from the raw sewage water or from MBR Tank recirculation, after ammonia oxidation in MBR and aeration tanks. This tank should neither be aerated, nor exposed to oxygen in order to satisfy the reduction reaction (de – nitrification) as the following chemical reduction reaction:

NO3- + ORGANIC MATTER ==> N2 (GAS) + CO2 + H2O

4.4 Aerobic Process

Ø Aeration Process

This process mainly aims to reduce BOD as possible, where air is diffused through the sewage water. Organic materials are catalytically oxidized by bacteria. Due to aeration ammonium ions (NH4+), dissolved hydrogen sulfides (H2S) and sulfide ions (HS- or S-2) will be oxidized and removed from the sewage water, where energy, carbon dioxide (CO2), and vapor water will be released, then bacteria will grow as their number will amplify so that the typical TSS of this tank’s process will reach 10,000 mg/L.

Ø MBR Process

After the sewage is pumped from the aeration tank to MBR Tank by submersible pumps submerged in aeration tank, the sewage water will pass through this tank as previously in the aeration tank under air diffusion, where the oxidation reactions mentioned in the aeration process also take place. However in this process, there is submerged membrane where sewage water passes through and pure product water, salts, and any matter having the molecular size smaller than 0.2 µm will permeate. In contrary, biomass, bacteria, suspended solids, and any matter having the size more than 0.2 µm will be rejected. Moreover, the air bubbles diffusing through the MBR Tank from the bottom of the MBR frame will service the membrane sheets to avoid plugging of suspended solids, biomass, bacteria, and microorganisms on the membrane sheet.

4.5 UV Disinfection System

This is the final stage wherein any microorganism that permeates through the membrane sheets will die and the product water will be purified. In this system, ultra violet rays with high frequency will be used to kill the bacteria and other present microorganisms.

~ scribbled for CCG