Treatment of Contaminated Collected Wastwater at Petroleum Fuel Filling Stations for Using as Make Up Water for Cooling Tower in Petroleum Refineries

The collection of washing wastewater (oily water) in petroleum service stations represents an environmental problem particularly after the introducing of cars washing stations to the petroleum station site. The generated water from washing and maintenance of the petroleum stations, rain water is collected in the storage tank. This water contains hydrocarbons and suspended solids with high organic load. Discarding this type of water to the water bodies like rivers without treatment causes increasing of pollution. This study aims to manage generated wastewater in petroleum service stations successfully by using methods keeping the source of water and protect the environment from the pollution. Alsmood and Alnaher petroleum stations which are located at the east of Baghdad were taken as case study. A mixed sample of wastewater from both two stations was prepared. The sample was fully tested to study the expected specifications of water.The mixed samle was underwent to many treatement stages(oil skimming,coagulation-flocculation, sand filteration).The oil concentration of the raw smixed sample was decreased from (5% , 50000mg/L) to 1mg/L . The turbidity value was reduced after filteration from 175 to 1.4 NTU and also the total suspended solids(TSS) was decreased from 272 mg/L to 4 mg/L. The chemical oxygen demand (COD) underwent reduction during wastewater treatment from 730 to 44 mg O2 /L . Badse on the research fndings,the proposed scenario to manage the watstewater is installing a wastewater (oily water) treatment plant with 100m3/day capacity next to Aldura refinery in Baghdad to treat the water for reusing application as a make-up water for the cooling towers.


Introduction:
Fuel filling stations are essential community facility in modern societies, also they are a potential pollutant to the stormwater drain system.The pollutants in fuel filling stations come out in daily basis from different activities, such as mechanical workshop, car washing, refueling and the use of petroleum products, oils, grease, solvents and detergents.These pollutants are transported and discharged into stormwater drains by using clean water.These pollutants result from.[1]  Leakage of fuel from storage tanks, especially from single-walled underground tanks.
 spillage of fuel, lubricants, engine coolant and hydraulic.
 Disposal of vehicle wash facilities wastewater.
 Inadequate disposal of wastes car parts, batteries, tires and fluids derived from mechanical servicing.
Currently, the available conventional treatment technologies for fuel filling station wastewater comprise a physical, chemical and biological methods, despite that, some soluble organic compounds remain untreated, that cause an increased level of pollutants in the treated water effluent.However, there is no single technology to meet all the requirements due to the variable nature of the wastewater.[2] Various technologies are used for oil and Total Suspended Solids removing from oil contaminated water.For oil removing, corrugted plate interceptor (CPI) separator is oil-water gravity separator, developed by the oil company shell for oily wastewater treatment.CPI oil separator enables gravity separation with high efficiency by using corrugated plates that provide excellent treatment for high flow rates.the simple structure of the CPI reduces the construction cost and simplifies the maintenance process.The mechanism of CPI in removing oil from wastewater depends on gravity, and it does not need energy to operate [3].Tilted Plate Interceptor (TPI) Separator is a general term used for such type of separators.The separator when used in liquid-liquid separation (mostly free oil removing from water) is called a TPI or CPI separator [4].A high -effect centrifuge is another process for oil-water separation.The centrifuge is often used for low pressure water streams due to the device is motor driven, and this type of equipment has high energy demand and high maintenance [5].An American Petroleum Institute (API) Separator is a separation device depends on gravity, designed by finding velocity of oil droplets rising that depends on the density and size of oil droplets.The design of API is based on density difference between oil and wastewater, and because that difference is much smaller than density difference between suspended solids and water, most suspended solids settle in the separator basin bottom as sediment layer, and the oil rise to the separator top, the wastewater then will be in the middle layer between the oil and the suspended solids.The oil layer is usually skimmed off and re-processed or disposed of subsequently, and a chain and flight scraper (or equivalent device) and a sludge pump extract the bottom sediment layer.The water layer shall be sent for further treatment consisting, as a general rule, of a Dissolved Air Flotation (DAF) unit for further removal of any residual oil and, subsequently, of a certain type of biological treatment unit for removal of undesirable dissolved chemical compounds.The API technology is highly efficient and low-cost; therefore, it has been chosen for oil removing from contaminated water in this research [6].Coagulation and Flocculation is the process by which colloidal particles and very fine solid suspensions initially present in a wastewater are combined into larger agglomerates [7].
Dissolved Air Flotation (DAF) is a process in which fine gas bubbles are used to separate small, suspended particles that are difficult to separate by settling or sedimentation.Gas is injected into the water to be treated, and particulates and oil droplets suspended in the water are attached to the air bubbles, and they both rise to the surface.As a result, foam develops on the surface, which is commonly removed by skimming.The dissolved gas can be air, nitrogen, or another type of inert gas.The efficiency of the flotation process depends on the density differences of liquid and contaminants to be removed.It also depends on the oil droplet size and temperature.Minimizing gas bubble size and achieving an even gas bubble distribution are critical to removal efficiency [8].A hydrocyclone separator improved treatment methods have resulted from the continuous demand for higher treatment capacity in very limited space.The benefits of this type of equipment are high reliability (no moving parts), low maintenance, very little space needed, and a better separation effect and high capacity [9].

The problem statement and suggest proposal treatment of case study.
Most of fuel stations in Iraq have an underground water tank with 1.5 to 2 m3 capacity.This tank is called slope tank.The washing water, gasoline spills, gas oil spills, spent lubricants, and dust are drained to the slope tank.The only management of this type of contaminated water is discarding it outside the station and it may cause some environmental problems for air, soil and ground water.
The philosophy of this scenario depends on installing of a central small-scale plant for treatment of transferred oily water from different fuel stations in Baghdad.The design capacity of the plant is assumed 100 m 3 /day.

Fig. (1): Process flow diagram (PFD) for Oily Water Treatment
The target parameters of water to be treated are oil and total suspended solids (TSS).Generally, the obtained specifications of treated water led to use it safely in cooling tower.

Collecting oily sample wastewater
Two equalization tanks (5 x 4 x 2.5m + 0.5m freeboard) with 50 m 3 volume of each one will receive water from vehicles.

Oil Removing
The removing of oil from the mixed sample was conducted in the lab by using rotary belt as explained in Figure (2).136 API technology will be adopted in this study for oil recovery in the proposed oily water treatment plant for using as make up water in Al-Dura refinery cooling tower, and because of the high efficiency and low cost of this technology, it has been chosen for oil removing from the contaminated water.

Total suspended solids Removing by Coagulation and Flocculation process
In this step, the fine particle size of the suspended particles is removed by Coagulation -Flocculation process.A Jar test method was conducted in the lab.It is considered a simulation method of clarification of water used in any full-scale treatment plant.A jar test conditions were, 150 rpm, 1 min for high-speed mixing (coagulation) and 150 rpm,5 min for low speed (flocculation).
Poly aluminum chloride (PAC) was used as a coagulant [10] to destabilize the water colloidal system and a cationic modified polyacryl amide (EBAGROS®A-158C) was used as a flocculant to gather the flocs.The other solutions used for pH adjustment are hydrochloric acid and sodium hydroxide.
Some specifications of the chemicals used in Jar Test as in Table (2) and the results obtained by using Jar Test method for the mixed contaminated water are illustrated in Tables (3, 4, 5 and 6) with different concentrations of PAC:

Sand Filtration
A lab scale gravity flow vertical filter was designed, it consists of two separated layers (Anthracite, and Sand respectively), as shown in Figure (4).The particle size of the materials is shown in Table (7).

Results of the sand filtration in the lab
After passing the treated water from clarification process across the designed and assembled sand filter, the laboratory results of tested treated water show good specifications to use the water as a makeup source for cooling tower Table (8).As the quantities of the water that treated by this scenario is relatively low, so the water recommended to be mixed with treated water produced by Reverse Osmoses process in the refinery.In this case the treated water will be diluted and the final specifications of water will meet the required specification of raw water used in cooling towers Table (1).In addition, it can be noticed that the turbidity of coagulation\flocuulation effluent has been reduced form 3.4 NTU to 1.4 NTU.However, this reduction is considered to be low, as the highest reduction 98 % has been acheived earlier.

Treated Water Storage Tanks
Two tanks (2 x 10 m 3 ) for receiving treated water are including in the oily water treatment plant.

Sequences processes of oily water treatment
The simplified stages of treatment are explained in Figure (5), the general expected form of the oily water treatment plant is illustrated in Figure (6).

2.1 Treatment of Case study 2.1.1 Characterization of oily wastewater Two
(1)ples of contaminated water at the waste water tanks of fuel stations were sampled, and analyzed after mixing the two samples with 1:1 ratio.The fuel stations that selected for water sampling were Alsmood Station and Alnaher Station located in the east of Baghdad.The laboratory analyzing of the mixed sample showed the specifications explained in Table(1)below: