Efficient Separation
1. Avoid Emulsions: Emulsions are formed when the interfacial tension between two liquids is reduced by certain means sufficiently to allow droplets of one liquid to disperse in another. Mechanical agitation, shearing forces, solvents, chemicals, surfactants, and the presence of particulate matter can all reduce interfacial tension and result in the formation of an emulsion.
2. Avoid Chemical emulsions: The chemical emulsion is formed by the addition of some chemicals in the water. These chemicals act as surfactants and they hold the oil drops together in the emulsified state. The surfactants may be the detergents used for cleaning, alkaline chemicals used for boiler cleaning and conditioning, etc.
3. Avoid secondary dispersion: Mechanical emulsions are of primary and secondary types. The primary emulsions are larger drops of oil dispersed in water and are generally separated within 24 hours. The secondary emulsions are fine droplets of oil that are thermodynamically stable and do not separate. The secondary dispersion is caused by turbulent conditions.
4. Avoid suspended solids: Suspended solids cause stabilization of emulsion and cause problems in the separation of the oil from the bilge water. Suspended solids can be mud, boiler soot and cargo residues sucked from the blowers. The suspended solids get coated with oil and stabilize the emulsion. Neutrally buoyant solids that neither rise nor fall is most troublesome as it is difficult to remove them. They also generate a high ppm alarm.
5. Avoid Turbulence: OWS needs laminar flow to operate optimally as per their design. Avoid using OWS in times of heavy rolling and keep all line valves fully open to avoid generating turbulence. Rolling motion, retrofitting on old pipelines, and inadequate opening of the suction line valves can lead to turbulent flow inside the OWS resulting fall in OWS capacity due to the formation of an emulsion.
Sometimes due to turbulence some of the oil droplets become less than 8 microns and are affected by the random motion of the water particles. This random motion is called Brownian motion and it nullifies the forces of buoyancy and the oil drops fail to rise.
6. Avoid Particulate Matter: Fine particulate matter like soot, rust, microbial contamination of bilge water, etc. also acts as an emulsifying agent. Although most of the soot of the boiler washing settles down in the bilge holding tank, fine soot particles (1μm or less) will give the bilge water a blackish appearance.
This particulate matter will not only fool the ppm meter into activating the high ppm alarm but will also physically act as an emulsifying agent
7. Optimal use of Chemicals: Sometimes it is required to use special chemicals called emulsion breakers to separate the oil from the water and release free oil. If an emulsion breaker chemical is used, care should be taken that it is used as per the instructions given by the manufacturer so the emulsion doesn’t go worse. Sometimes putting in more than the recommended amount can worsen the problem.
8. Restrict Drainage of Chemicals: A lot of many chemicals are used in the engine room for special purposes such as water conditioning, corrosion inhibition, rust removal, cleaning, degreasing, etc.
However, care should be taken to collect these chemicals and dispose of them properly. Allowing all kinds of chemicals to run free into the bilges is not good housekeeping. Moreover, the pH of water above 10 and below 4 can cause chemical emulsification.
9. Detergent Disposal: Detergents are used for mopping and soap-washing bulkheads and such areas. Generally, these are the same detergents we use at home or ashore.
These detergents act as surfactants and cause the emulsion of oil in water. Disposing of mop water separately or using quick break detergents would help significantly towards better separation.
10. Avoid prolonged storage: Prolonged storage of the bilge water causes modification in the nature of free oil. Normally oil-water mixture when allowed to stand for some time (say 24 hours) separates into a layer of oil on top of water called free oil.
This free oil is easy to remove but long retention of the bilge water can cause modification in the properties of free oil due to oxidation and microbial action. If this modification occurs then it is difficult to remove the oil.
11. Do Proper Filtration: If there is a large number of solid particles, floating media, jute, etc. in the bilge water, it should be properly removed using strainers to avoid fouling of the filter media.
12. Collect leakages: Ensure that a minimum of oil reaches the bilge wells and if the oil quantity is more in a mixture (of oil and water) put it in the separated oil tank. Always remember that the Oily Water Separator is not a purifier.
13. Heat the influent: Heating the influent reduces the viscosity of the continuous media causing better separation.
14. Segregation of Wastes: Do not mix sludge and bilges. Even a bit of sludge can contaminate a large amount of bilge water. In some ports, even discharge of treated sewage is not permitted due to local regulations, and therefore in absence of dedicated sewage holding tank, treated sewage is put in a bilge holding tank. This should be avoided as it would be impossible to run the Oily Water Separator thereafter without cleaning the tank.
15. Fill up OWS prior to use: Prior to operating the OWS and allowing the bilge water to enter always ensure that it is filled up with clean water and that all air pockets have been removed. This is important as air pockets can confuse the capacitive sensors and can make automation go haywire.
16. Back Flush: Backflushing of the OWS should be done as per the recommended frequency given by the manufacturer if there is a provision for doing so as increases the life of the filter media.
17. Clean Sensors: Frequent cleaning of the electronic interface sensors would ensure the correct operation, proper oil removal, and sharp cutting off ensuring less discharge of water to the separated oil tank.
18. Remove Accumulated Oil: Apart from the automated oil removal, any other accumulated oil should be removed from the OWS chambers regularly.
19. Proper Operating Procedure: Make sure that the operating procedure of OWS is followed in a proper step-by-step and systematic procedure.
20. Proper OWS Maintenance: Needless to say proper maintenance of the OWS as per the instructions of the manufacturer would keep its ship shape.
