PetroCare® Process for ballast- and oil polluted water

Biological Oxidation of Hydrogen Sulphide

Oil terminals and oil refineries receive and handle large quantities of ballast water or other oil polluted water, for treatment and oil recovery.

Toxic Hydrogen Sulphide (H₂S) may be formed by the decomposition of organic material in the water, thus causing unpleasant odour and representing a health risk. The H₂S is also very corrosive against metal and concrete. Conventional chemical precipitation of sulphide may produce large quantities of corrosive sludge.

We have developed an environmentally friendly treatment concept for removal of H₂S in water. The PetroCare^®Process will eliminate odour, and reduce health risk and generation of sludge.

Bacteria "eat" the problem
The concept is based on a bacterial break down of sulphide and organic materials under anoxic conditions.

The PetroCare^® Process uses a nitrate salt (PetroCare^® Solution) to stimulate bacteria to oxidize H₂S that has already been formed. At the same time, formation of new sulphide is prevented. The process is based on a biological oxidation, where sulphides and organic materials are converted to non-harmful substances like sulphate, nitrogen gas and carbon dioxide.

One concept, two processes
We propose different solutions on individual conditions and needs:

• Direct oxidation and prevention of H₂S formation using existing storage facilities or pipelines.

Oxidation of H₂S by using a highly effective Biofilm reactor.

Installation of the Biofilm Reactor
In cooperation with Kværner Water Systems a.s, we have developed a new reactor system. This technology is based on oxidation of H₂S using a highly efficient Biofilm reactor. The PetroCare^® Solution is dosed according to sulphide level in the inlet, water composition and water flow, which ensures an optimal biological reaction.

Full scale Biofilm reactor plant
Since May 1994, a full scale Biofilm reactor has been running at the Sture Oil terminal near Bergen, Norway. The reactor was designed to handle an inlet of oil polluted ballast water of 600 m³/h with an H₂S concentration in water up to 130 mg/l.

Process features show that:

• More than 95% of sulphide is oxidized in water containing up to 130 mg/l sulphide concentration
• H₂S emissions to air are reduced to levels at or below odour concentration limit
• Up to 90% reduction in sludge production compared to other chemical treatment methods
• 20 minutes residence time in the Biofilm reactor
• Increased quality of recovered oil
• An environmentally friendly process without toxic chemicals or polluted emissions

Process control and optimization of the PetroCare^® Process
Dosing of PetroCare^® Solution depends on a number of factors, such as the content of organic substances and H₂S in the water, temperature and flow. As the H₂S in the water may vary considerably in the course of the day or "batch", there are special requirements for the dosing of PetroCare^® Solution. For this reason we have developed a special H₂S analyzer and a sampler which measures the content of hydrogen sulphide in the water. These are connected to a microprocessor which provides an optimal dosing of the PetroCare^® Solution, based on a dosing model which takes into account the different variables. Selection of measured data and changes in the dosing model can be made with the aid of a modem.

Adaptation to the individual user
For optimization of the PetroCare^® Process, we depend on close cooperation with our customers. By means of analysis and mutual understanding of the problem, we aim to find the best technological and economic solution for each individual customer site.