The oil and gas industry generates significant amounts of wastewater from upstream and downstream activities which must be managed. Produced water and other wastewater sources need to be cleaned and treated before release into the environment as they can be highly polluted. ClearFox has developed a range of modular solutions to deal treat produced water.
Oil and Gas Industry
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The oil and gas sector is listed among the top ten largest water consumers and causes significant water pollution. The oil and gas industry is faced with higher standards for environmental protection and due to the current global market, lower prices. The environmental situation is exacerbated by a lack of water at most drilling sites. At many locations, the wastewater is not adequately treated to comply with local legislation. Wastewater treatment of produced water in oil fields is now considered to be a priority.
The wastewater on oil and gas well fields can be contaminated in different ways. We use our approved-and-tested module system and select the technology used with an evaluation procedure that is always tailored to the specific requirement.
With our modular system, we have experience worldwide in cleaning a wide variety of wastewater types. We are members of the leading professional associations in Germany:
- VDE-Association German Technologies Electrical, electronical and information
- VDI-Association German Engineers
- ATV/DWA- German Waste water association
The wastewater from the oil and gas sector is highly variable in its volume and pollution load. This depends on many factors. So in each case a specific solution must be designed. By utilising our modular process technologies, we can adapt modules to handle any flowrate, any pollution loading and any effluent requirement.
Characteristics of produced water can be described below;
The usual sewage parameters for assessing the water quality or the efficiency of the treatment technology are as follows: (different analyses from Sibiria, USA, South America and Mediterranean Sea)
- pH 4-7
- Oil content can be up to 1 g / l but is mostly removed from the produced water before (since it is the actual valuable substance)
- Salt concentration (salinity) The salinity is an typical characteristic of the water produced. It can contain over 180.00 mg / l. This can usually be seen from the TDS, which essentially consists of sodium chloride. The chloride content is also an important indicator. Many produce water are considered hypersaline, i.e. oversaturated with salt.
- Totally dissolved solids (TDS) up to 300.000 mg/l, mainly caused from NaCl
- Totally suspended solids (TSS) between 50 and 1000 mg/l
- Temperature 15 bis 35 Grad Celsius regional depending
- Hydrocarbons (aliphatic and aromatic)
- Volatile, aromatic hydrocarbons BTEX (sum of Benzene, Toluene, Ethylenbenzene and Xylene) and polycyclic, aromatic hydrocarbons PAH (PAH and alkyl phenols are not so good solable in the waste water, so often they are in the dispersed oil, which are suspended smaller drops oil. Amount depends on pretreatments and the kind of well.)
- Organic acids such as Benzoic acids
- Dispersed hydrocarbons, naphta residues
- Sum parameter for oxygen demand (chemical oxygen demand COD, biological oxygen demand BOD, usually determined in 5 days).
The ratio of these two typical sum parameters gives an indication of the degradability of wastewater. BOD values vary from 500 to 3000 mg / l
COD values vary from 2000 to 20000 mg / l
- Nitrogen, Phosphorus (only seen as traces in relation to carbon, but may contain an excess of nitrogen, which must be removed for some direct discharges)
- Sulphides, depending on injection water
- Heavy metals (Boron, Cadmium, Copper,Mercury, Iron and much more)
- Radioactive materials (NORM, technically enhanced), as already discussed before
- Uranium, thorium, radium with his decay products as well as radon Lead 210, potassium 40, polonium (Partially gaseous, especially concentrated in the sludge and deposits, loads of up to 15000 Bequerel / gram, average waste load 100 Bq / g)
Process technology is a challenge. There is no universal process technology for the purification of produced water from oil and gas fieldsr. Of course Manufacturers always present their own product as if it were a panacea. If one evaluates according to criteria such as cleaning performance, space requirements, operating costs, investment costs, as well as sustainability (further pollution), one comes to the conclusion that different process technologies have to be combined.
Is necessary to remove easily screenable materials from the system and to protect the downstream units. Mostly already included in the pretreatment for the demulsifiers. Sedimentation tanks are simple, but only suspended solids are removed and the space required is high. Screening systems mechanically remove all particles, they are more effective, save space, but require more maintenance.
The goal of oxidation is to bring pure carbon compounds from a dissolved to the suspended condition, in order to make compounds biodegradable, to oxidize heavy metals , to remove organic and inorganic components from the wastewater. Is more or less universally applicable and always suitable. In the typical process, strong oxidizing agents such as ozone, hydrogen peroxide with and without UV light expansion (e.g. Fenton process) are necessary.
In the catalytic wet oxidation, compressed air for the oxidation at high pressure is supersaturated in the water and the temperature is increased. Requires reaction volumes and expensive vessel construction. In both cases, the wastewater has to be post- treated for the subsequent processes, ozone requires high safety regulations, and the electricity requirement is high.
In the electrochemical advanced oxidation / reduction (AEO), a potential is applied between two surface-coated electrodes, no chemicals are added, the process is non-pressure, harmless streichen, ist explosiv, the oxidation takes place on the surface or indirectly through radical formation. The doping of the electrode material must be adapted to the challenge (heavy metals, NORM, COD, AOX, etc.).
The initial invest (e.g. diamond electrode with Boron doping, BDD-electrode) can be large with high-quality doping. Electricity costs are moderate, if the wastewater is highly conductive, the electrical consumption drops. Can be used for almost all contaminants in the waste water produced, up effluent required for direct discharge.
Dissolved Air Flotation (DAF) / with precipitation (DAP)
Flotation (in connection with precipitation and flocculation) has a very high physical separation effect, especially for oils or emulsions that have been splitted before. This is necessary as standard technology, particularly in the case of wastewater produced, to relieve the loads to subsequent process steps. Residues are the removed / precipitated un-dissolved substances that are contained in the wastewater. The investment costs are low, the type of sludge removal determines the operating costs.
Chemical Treatment (precipitation, hydroxide formation)
Adding precipitants to specifically bind substances in-soluble in water (heavy metals, COD, phosphorus) which then have to be removed (flocculation, flotation, filtration). The investment costs are negligible, the technology is simple. With the addition of chemical substances, more and more sludge accumulates, due to the resulting compounds. The cost of the chemicals can increase operating costs extremely. The resulting sludge may contain compounds that are toxic. At high NORM concentrations, the system must be designed without any deposits or chemical sinks inside the system components.
Microfiltration (sand anthracite, filter drums)
Depending on grade of filtration, as filter drums or multilayer sandfilters (anthracite) to remove suspended solids (e.g. from the precipitation). Low investment costs, relatively simple, with high NORM – concentrations sinks must be avoided.
Biological Treatment (aerobic)
Suitable microorganisms oxidize and reduce carbon and nitrogen. These must be in touch with the wastewater long enough under suitable milieu conditions (oxygen, no inhibitors, oxygen present, nutrients). A very high sludge age (high bacterial concentration ) is required for the wastewater produced. This can only be achieved with sessile processes (FBR) or increased sludge concentration, by passing the water through membranes (MBR).
Depending on the salinity, the biological activity drops, the wastewater has to either be diluted or designed larger. Halophilic bacteria reduce BOD and thus the COD load in produced wastewater. Very high space requirement for reaction volumes (only possible in rare cases for offshore). Little residues, very low operating costs, investment costs depending on the container requirements, mostly moderate, can only be used if biodegradable.
Basically, the wastewater produced can be inoculated with specially bred organisms or concentrated bacteria, or the naturally occurring ones in the system can be increased. This takes a long start-up phase, but it is safer and permanent at Zero cost. In any case, however, the BOD must prove before that, the wastewater is degradable, the availability with the TOC and the ratio of the chemically oxidizable to the biologically oxidizable are sufficient for an economic process. Submerged fixed bed reactors (FBR) are very complex to build, but cascaded ones are ideal for treating produced wastewater.
Sequencing Batch (SBR) reactors and MBR reactors are not ideal because the free-floating organisms only build up insufficient EPS and only monocultures. Membrane bioreactors (MBR) are like a combination of activated sludge biology and filtration through membranes. Investment costs are low, but can only be used to a limited extent with wastewater produced and can be used due to the high degree of pre-cleaning. Membrane resistance and good floc formation in biology are the prerequisites for stable operation. Trickling filters are very well suited to the wastewater produced, but only in small quantities, since the space requirement exceeds the costs.
Basically, biological processes for waste water from the oil and gas industry can be favoured, if a high effect is to be achieved with little effort and the biodegradabilty has been checked before. This is usually justified even if the wastewater has to be diluted to lower salt concentrations (up to 40-60,000 mg / l NaCl) in order to provide the right environment for halophilic bacteria
Ultrafiltration, Nanofiltration, Reverse Osmosis
All are used to remove fine suspended particles that have arisen from previous steps or that were already in the wastewater. Ultrafiltration (depending on the cut off of the membrane) competes with simple microfiltration. For each produced water, attention must be paid to the achievable effect and the effort. This must be in proportion. The nanofiltration has high investment costs, the operating costs are increased.
Depending on the process requirements, however, this can be a good option in connection with previous technologies to bring the wastewater to a discharge quality via the direct filtration path. At first glance, reverse osmosis is suitable as a universal separation option for almost all ingredients in the produced water. However, reverse osmosis is usually only worthwhile here if a partial flow is to be prepared for human use.
High salt levels generally reduce the amount. Reverse osmosis requires good pre-treatment (mostly biology + nanofiltration) and is very expensive to invest and operate (chemicals, membranes). In order to keep the flux rates high, chemicals must be added to prevent membrane fouling.
Adsorption and Ion Exchange
For small quantities and when choosing the right materials, a selective removal of many ingredients is possible. Requires good pre-treatment, moderate investment cost, operating costs can be extremely high. Usually only suitable as a partial flow for polishing.
Comparison of process technologies for produced water
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