Checks of Sewage Treatment System and Black Water Reports
- Categoy: Especial Articles
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- 11 January 2013
The biological treatment systems which are commonly used to treat sewage of today’s vessels can cause failures in cleaning and maintenance operations as well as it affects cleanship certificates of the relevant vessel.
If the values in sewage analysis reports, which are prepared as required by the regulations, are out of the desired limits, the cleaning certificate can temporarily be invalidated or punishment operations can come up. Hence, during the class audits of Turkish owner’s vessels, surveys overemphasize the limits of BioChemical Oxygen Demand and Fec. Coliform values because it is too often to face the limit excession problems. Even though the maximum allowable value of BOD is 50 mg/L, it is often measured as over 1000 mg/L and the same problem occurs for Fec. Coliform which is often measured as over 20.000 ems/100 ml despite its maximum allowable value is 250 ems/100 ml. The most important deficiencies result from the lack of information and communication between vessels and laboratories. Cleanship manuals give the required information about relevant experiments and time periods.
It is expected to that the problems will be overcame as a result of an increase in the certified laboratories performing sewage analysis for vessels.
It will be beneficial to give advices and make some explanations about being aware of the relevant maintenance and cleaning operations to avoid the problems mentioned above.
Even though policies of all brands are similar, Aquamar Sewage Treatment Unit is the most preferred brand for our vessels. Its policies are briefly explained as follows:
Air injectors and aerators, which provide oxygen, are put into the tank by utilizing blowers in order to keep the system in biological balance. The black water extracted by vacuum process from toilets is accumulated into the Aeration 1 tank. The inorganic solids are purified and the sewage is transferred to the Aeration 2 tank by utilizing a special overflow method. After purifying the remaining inorganic solids and microorganisms, the sewage is transferred to the Settling tank by utilizing the same overflow method.
Air injectors filter the last sediments out and the sewage is transferred to the Sterilising tank. By the way, the injected sediments are being transferred again to the Aeration 1 tank. A bacteria regulator chemical is injected into the water by a dosage pump in order to provide the recommended values by formations in the released water.
A Sewage Treatment System
The most important factor providing biological balance is oxygen flow. For any reason, if the oxygen flow is interrupted, the biological balance will be corrupted and this will result in harmful bacterial growth. To prevent these consequences, whether the aerators are functioning or not must be controlled annually as indicated in the instruction manual. If there are not any bubbles although the blower is functioning, the aerators and circuits must be cleaned. Besides, whether the air injection system in Settling tank is functioning properly or not must be daily controlled through the transparent return circuit. If the air injection system does not function, the accumulated sediments will transfer into the Sterilising tank.
Also, based on the instruction manual, flushing the Aeration 1 and 2 tanks with freshwater every other month will be beneficial in terms of system cleaning. It is important not to drain both tanks simultaneously.
In addition, whether the level of the chemical injected into the Sterilising tank is decreasing, the dosage pump is functioning, and its nozzle is blocked or not must be controlled daily. If necessary, stroke of dosage pump can be increased. Normally, after deactivation of low level warning and activation of high level warning of the discharge pump, the dosage pump have to inject the required chemicals into the tank. All potential problems affecting the analyses results can be prevented by taking into consideration the topics mentioned above.
Translation By: Umut Celen Arican
