What is the working principle of a marine wastewater treatment plant?

This device utilizes activated sludge, contact oxidation, and membrane bioreactor (MBR) treatment principles to decompose organic pollutants in wastewater. MBR achieves efficient, thorough, and clean wastewater treatment, ensuring effluent meets new IMO standards and other more stringent requirements. The treatment process is as follows:

In the primary aeration tank, activated sludge flocs, primarily composed of aerobic bacteria, form cotton-like, sticky flocs that adsorb organic matter. Under oxygenated conditions, these organic matter is decomposed into harmless carbon dioxide and water. Simultaneously, the activated sludge multiplies. As the organic pollutants that serve as nutrients for the flocs decrease, the bacteria become starved and die. These dead cells become food for protozoa and metazoa attached to the activated sludge. Over 95% of the fecal wastewater consists of easily decomposable organic matter, which is completely oxidized.

In the secondary contact oxidation tank, flexible biofilm packing is suspended. This biofilm, with its function of adsorbing and decomposing organic matter, floats freely in the water. Most protozoa reside within the fibrous biofilm. Again, due to oxygenation, organic matter further contacts and oxidizes the biofilm. If the system is shut down for a period and then restarted, the start-up time is much faster than with conventional aeration methods because bacterial spores still survive within the biofilm. Meanwhile, the soft packing material, like cotton bolls, expands when there is an excess of nutrients, absorbing excess sludge; when there is a deficiency in nutrients, it slowly digests itself, a process known as "endogenous respiration," causing the "cotton bolls" to shrink and await food.

The wastewater then enters the settling tank, where, because there is no aeration, the activated sludge continuously settles. The sludge sediment is automatically and periodically "airlifted" and returned to the primary aeration tank for recycling.

The supernatant from the settling tank flows into the membrane tank, creating favorable operating conditions for the membrane modules. The membrane tank contains submerged membrane modules and also participates in the biochemical reactions through aeration, hence it is also called a membrane bioreactor (MBR). The membrane is made of hollow fiber ultrafiltration material. A self-priming pump draws the water that has permeated through the membrane, which is then disinfected with ultraviolet light to meet discharge standards and discharged overboard or into the ship's clean water tank.