Treatment of a low-strength bilge water of Caspian Sea ships by HUASB technique

Oily bilge water is one of the major pollutants that threats marine environment due to its direct discharge from ships into sea. The aim of this paper is to investigate the possibility of dilute bilge water treatment by using hybrid up-flow anaerobic sludge blanket (HUASB) bio-reactor. The reactor operated at two hydraulic retention times (HRTs) of 10 h and 8 h. The organic loading rate (OLR) was gradually increased from 0.12 g to 0.6 g chemical oxygen demand (COD)/l day. After the immobilization of sludge on the surface of the support materials and 10 days of batch feeding of the reactor with the waste water as acclimation period (with COD removal of 59%), the continuous operation of the reactor started. At the end of the experiment, with the HRT of 8 h and OLR of 0.6 g COD/l day, the COD removal efficiency reached the amount of 75%. Furthermore, the bio-reactor showed a good performance in removing oil from the waste stream which was significantly lower than the standard value which has been laid down for the discharge of the bilge water from ships by the International Maritime Organization (IMO). The obtained data demonstrated that the HUASB reactor is an appropriate system for the treatment of a low-strength bilge water.