STPs

Question 1

Advantages of an board STP?

Answer 1

1) Reduce the number of ship side openings.
2) Simplify pipe runs.
3) Heads & and bathrooms can be lower in the ship.
4) Heads and bathrooms can be used in dry dock.
5) The ship can operate in anti pollution areas.
6) It is easier to close down in CBRN conditions.

Question 2

Explain Aerobic digestion

Answer 2

Aerobic digestion is the action of digesting the sewage in the STP, with the use of Activated Floc.

Question 3

Explain Anaerobic Digestion

Answer 3

Lack of oxygen to waste matter, which causes activated floc to die off. This in turn stops floc from digesting waste, and a sulphuric smell is released.

Question 4

How would you detect Anaerobic Digestion at low levels?

Answer 4

Notice a rotten egg smell.

Question 5

What would cause Anaerobic Digestion?

Answer 5

Non-authorised items being flushed down a trap.

Question 6

What is the purpose of the coarse screen?

Answer 6

Remove any large foreign objects passing through the macerator.

Question 7

Purpose of primary and secondary air lifts?

Answer 7

Primary:
Uses air to transfer slurry from aeration compartment to settlement hopper.

Secondary:
Called the sludge return line. Undigested sewage at the bottom of the settlement hopper is returned to the aeration tank via this lift tank.

Question 8

Purpose of oxygen Aeration Diffuser?

Answer 8

Passes oxygen through the waste.

Question 9

Fully explain the collect, hold and transfer system.

Answer 9

This is a fully automated, collection system consisting of 2 or 3 tanks and a series of pumps.

Sewage is collected via a vacuum. Pumps draw a vacuum on the initial collection tank, with a capacity of +- 1 day. This tank is connected to WC via pipes also under a vacuum.

Through using level switches, a discharge/transfer pump transfers sewage to one of the larger holding tanks, with a capacity of +-12 days. The waste will remain there until either discharged overboard or to a shore reception facility.

To stop waste from turning Anaerobic, it is circulated between tanks via an ejector, which slightly aerates it.

Question 10

Name the effects of H2S at:
0.03ppm
150-400ppm
1000+ppm

Answer 10

0.03ppm - Detectable by odour.

150-400ppm - Kills sense of smell between 3 & 15 minutes. Irritates eyes, throat and lungs.

1000ppm+ - Immediate unconsciousness and death within seconds.

Question 11

Hazards of Raw Sewage?

Answer 11

Hepatitis. Typhoid. Gastro Enteritis.

Question 12

Hazards of an STP?

Answer 12

Dangerous Chemicals.
Raw Sewage.
Dangerous Gasses.