Learning chapter

Sewage Treatment Plant

10 lessons

Sewage at sea: what sewage is, aerobic versus anaerobic breakdown, MARPOL Annex IV discharge distances, the biological treatment plant, retention and zero-discharge systems, effluent quality, sludge disposal, troubleshooting, maintenance and safety.

This chapter collects 10 illustrated lessons on Sewage Treatment Plant as part of Auxiliary Machinery & Shipboard Systems, ordered as they are best studied. It opens with What Sewage Is — the Definition, the Daily Volumes, and Why It Must Be Treated, Aerobic and Anaerobic Breakdown — Why the Colony Dies and How Long Recovery Takes, Where Sewage May Be Discharged — the 3 Mile and 12 Mile Rules, The Sewage Treatment Plant — Aeration, Settling and Chlorination, Retention, Holding and Zero-Discharge Systems — Holding Tanks, Vacuum Toilets and Elsan, Effluent Quality — BOD, Suspended Solids and Coliform Count and 4 more. Each lesson is written for MEO oral and written preparation: definitions first, then how the system behaves, then the checks and figures used in practice.

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01 What Sewage Is — the Definition, the Daily Volumes, and Why It Must Be TreatedWhat counts as sewage under MARPOL: the three limbs of the definition, why it must be treated, and how many litres per person per day a ship produces.3 sections 02 Aerobic and Anaerobic Breakdown — Why the Colony Dies and How Long Recovery TakesAerobic versus anaerobic sewage breakdown: why ships use aerobic treatment, what kills the bacteria, and why a dead colony takes 5 to 14 days to recover.4 sections 03 Where Sewage May Be Discharged — the 3 Mile and 12 Mile RulesWhere sewage may be discharged: the 3 and 12 nautical mile lines, treated versus untreated, holding tank rules, and the American Type I, II and III standards.3 sections 04 The Sewage Treatment Plant — Aeration, Settling and ChlorinationHow the sewage treatment plant works: aeration, settling and chlorination chambers, the sludge return, 0.5-0.8 bar blowers and three-monthly desludging.8 sections 05 Retention, Holding and Zero-Discharge Systems — Holding Tanks, Vacuum Toilets and ElsanRetention and zero-discharge sewage systems: holding tank construction, vacuum toilets, the comminutor and chlorine contact tank, and the Elsan arrangement.4 sections 06 Effluent Quality — BOD, Suspended Solids and Coliform CountHow sewage effluent quality is measured, including the MEPC.227(64) type-approval standards for BOD5, suspended solids, COD, pH and coliforms.4 sections 07 Sludge Disposal — Overboard at Sea, Sullage Tank, or IncineratorSewage sludge disposal: pumping overboard at sea clear of restricted areas, the sullage tank route in port, and burning sludge in the ship's incinerator.3 sections 08 Troubleshooting the Sewage Plant — Ten Faults, Cause by CauseSewage plant troubleshooting: black effluent and odour from anaerobic conditions, dead bacteria colonies, grease ingress and float switch faults.2 sections 09 Maintenance of the Sewage Plant — Desludging, Aeration and the Daily ChecksSewage treatment plant maintenance: three-monthly desludging of three quarters of the aeration tank, keeping the air supply clean, and testing float switches.3 sections 10 Safety on the Sewage Plant — Gas Hazards and Enclosed Space EntrySewage plant safety: hydrogen sulphide, methane and ammonia, why an air failure is a gas hazard, enclosed space entry, and chlorine handling precautions.6 sections