Determination of Wastewater Behavior of Large Passenger Ships Based on Their Main Parameters in the Pre-Design Stage

Volkan Şahin,Nurten Vardar

doi:10.3390/jmse8080546

Abstract

Wastewater formed on ships is divided into blackwater and graywater. While blackwater refers to wastewater from toilets, graywater defines wastewater from sinks, laundry and restaurants. Even though some treatments are applied onboard before discharge, wastewater contains significant amounts of fecal bacteria, heavy metals, etc., in excess of water quality standards. Dilution is a secondary natural treatment in the ship-wake region, which occurs after wastewater discharging. According to the Environmental Protection Agency (EPA), the natural treatment process is quantified by dilution factor, which is strongly dependent on vessel width, draft, speed and wastewater discharge rate. In this study, an Artificial Neural Network (ANN) model linked with the main ship parameters was developed to estimate the dilution factors while the ship is in the preliminary design stage. Gross ton, deadweight ton, passenger number, freeboard, engine power, propeller number and block coefficient values of 1041 large cruise ships were used to estimate the likely dilution factors. The best ANN estimation model was determined by Root Mean Square Error (RMSE) and Mean Absolute Error (MAE) methods. A decision tree was created for the results and the most important parameters affecting the dilution factors were determined. The main ship dimensions are needed for the dilution factor formulation of EPA whereas in the model created in this study only the gross ton or engine power of the ship is sufficient to estimate the dilution. Moreover, this new model is also usable for the estimation of dilution factors even if the main dimensions of the ship are not known.

Highlights

Cruise ships are enormous floating towns which are major sources of marine pollution through the dumping of garbage and untreated sewage at sea, and the release of other shipping-related pollutants
Sewage is considered to be dirty water coming from the toilets of the ship, animal habitats, and the infirmary, and it has high pollutant concentration while graywater is the wastewater from sinks, baths, laundries and the restaurant part of the ship, which have a lower concentration of contaminants than sewage
Ship-based wastewater has pollutant concentrations such as organic matter, nutrients, suspended solids and coliforms, which constitute a high level of pollution in the marine environment

Summary

Introduction

Cruise ships are enormous floating towns which are major sources of marine pollution through the dumping of garbage and untreated sewage at sea, and the release of other shipping-related pollutants. A large cruise ship with 3000 passengers generates over than 100,000 L of human waste a day. Cruise ships are required to have on-board waste treatment systems, the Environmental Protection Agency (EPA) has found that many cruise ships treat sewage with old technology, resulting in discharge that often contains significant amounts of fecal bacteria, heavy metals, and nutrients in excess of federal water quality standards [1]. The ships produce two distinct streams of wastewater named as black and grey water. Black water is sewage while grey water is general cooking and cleaning waste. In most treatment systems used in passenger ships, sewage and graywater are collected in the same tank and treated through the same treatment processes

Objectives

Results

Conclusion