Wastewater Treatment and Disposal Study

Objective

The wastewater treatment and disposal study shall encompass the following:

• Identify sources and quantity effluent & identify all the overboard discharges streams from the study scope and estimation of volumes.
• Evaluate wastewater treatment and disposal options implemented in study scope for best available options and compliance.
• Identify monitoring requirements for overboard discharge streams.
• Provide information of the approximate sewage effluent from different sources during normal and emergency scenarios.
• Identify all the discharges for both normal and emergency response.

Methodology:

The wastewater treatment and disposal study, using Best Practical Environmental Option (BPEO) is performed to provide assurance that the design minimizes as far as practical environmental impacts throughout all phases of the study scope. This includes ensuring all environmental impacts are identified, managed and controlled as appropriate to regulatory and industry standards.

A quantitative assessment of discharges is performed to calculate the cumulative impact of the study scope’s operations on local water quality as described in the Best Practical Environmental Option (BPEO). The BPEO assessments performed shall investigate opportunities to reduce the local impact of discharges on water quality through the selection of discharge handling systems and equipment, which shall include Screening of Alternatives, Evaluation and Selection.

Project activities will generate liquid and semi-solid wastses that will need to be disposed of safely without causing harm to the environment or personnel. To minimize effluent discharged to the marine environment, options towards water recycling and reuse initiatives needs to be implemented. Potential wastewater sources are:

• Produced Water
• Deck drainage water
• Sewage
• Cooling water
• Produced Sand

Each of the above sources have distinctive methods of treatment and disposal which is studied under the Wastewater treatment and disposal study.

Produced Water Management:

Produced water is the largest volume of wastewater generated during oil and gas recovery operations. It is a complex mixture of dissolved and particulate inorganic and organic matters ranging from near freshwater quality to concentrated saline brine. The management of produced water has been the main focus of oil and gas industry in view of the stringent legislations on the discharge of produced water the environment. It is the main source of oil discharged from routine production operations and contains naturally occurring hazardous substances such as heavy metals, polycyclic aromatic hydrocarbons, alkyl phenols and radionuclides.

The disposal of untreated oil and gas produced water containing many hazardous materials can interfere with the environmental quality of the receiving environment. The characteristics, chemical and physical composition of produced water must be known to provide an appropriate way of reducing the content of any hazardous substances in the produced water to a permissible level prior to disposal.

Drain water Management

Deck drainage includes all effluents resulting from rain, deck washings, tank cleaning operations and run off from curbs, gutters and drains, including drip pans in work areas.

It is not allowed to discharge any deck drainage that would cause a sheen on the water surface or an emulsion beneath the water surface.

Generally, the drain system is divided as follows:

• Non-hazardous open drain: collects the drainage from the drains from the non-hazardous areas i.e. deck areas and equipment drip trays.
• Hazardous open drain: collects the drainage from the drains of hazardous areas i.e. the deck areas, equipment drip trays, sampling connections etc
• Closed drain: collects the drains from the pressure vessels and piping containing hydrocarbons.

Cooling Water Management

Cooling water management involved the monitoring of residual chlorine, amount of Fresh water used as the cooling medium and temperature of sea water supplied. Proper disposal of cooling water discharge must be monitored to be within the discharge quality limits.

Produced Sand Management

Sand is produced from the reservoir. Produced sand can contain hydrocarbons, and the hydrocarbon content can vary substantially, depending on location, depth, and reservoir characteristics.

Sand is recovered topside through the strainers and in the vessels using sand removal units. When removed, the sand is disposed.