Oil Removal Solution Suitable ...

Oil Removal Solution Suitable for Local Circumstances

Dear Sir,

I suggest the following simple solution that should be sustainable for Sri Lanka.  This treatment concept allows water to cascade, i.e. flow by gravity in series, through three ponds or shallow basins as follows:

1) If free oil exceeds 10 mg/L, use a settling pond sized to allow the free oil to separate from the water and accumulate on the surface for periodic removal by decanting.  Water after free oil separation would exit via an underflow baffle that extends well below the oil level.  This is a very simple yet robust method to remove free oil.  It's possible to enhance removal of emulsified oil by adding emulsion breakers to the feed pipeline, allowing the water to flow through a series of pipe elbows to assure mixing.  However, emulsion chemicals may be an unnecessary expense unless the amount of emulsified oil is very significant.

2) Water would next flow by gravity through a slow sand filter which would remove any remaining free oil by physical filtration by the sand and dissolved oil by biological metabolism by biofilms that will grow on the sand.  Periodically the sand will require replacement and re-ripening (allow new biofilm to grow).  Water would exit via collector pipes at the bottom with 10 cm of gravel above the pipes and another 10-15 cm of filter sand on top of the gravel.

3) Sand filtered water would flow by gravity into a shallow basin or pond configured similarly to the slow sand filter. but would  contain biochar produced from local biomass (wood, coconut shells, etc.) in place of the sand. The biochar would act like activated carbon to adsorb organic contaminants still present after slow sand treatment. There are references online that describe how biochar can be activated to give it adsorption properties so this might take some further development work for your particular application.

 Treated water would flow into a sump for transfer to water users with a sump pump.  Treated water quality can be easily checked on a regular basis by reducing pH of a sample to 2 and evaluating turbidity and color in the sample jar.  The observations of this test should be correlated to lab analyses during development of the process.

I hope this is helpful, and good luck!

Joe Zuback

Global Water Advisors, Inc.