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WASTEWATER FROM SHIPYARDS

NARCIZA TOPOR

Abstract. Oil lost and discharged represents a direct and significant pollution threat for

marine life as well as industries, which depend on clean water and shore, notably tourism, fishingand aquaculture.

Oil is used by the population at large and enters the marine and coastal environment notonly direct, as in shipping, oil drilling etc. but also as final sink from a large variety of hinterland uses.

The wastewater from shipyard operations like vessel cleaning, operations, solventcleaning and degreasing operations including fugitive emissions will generate significantquantities thus making it imperative on part of environmental managers to minimize the resulting

water pollution. For better management of wastewater, it is important to know the characteristicsof wastewater

Keywords: wastewater, wastewater stream, wastewater concentrations, specific pollutants,

effluent quality, influent characteristics, treatment capacity, treatment efficiency.

1. Introduction

The impact of the pollutant depends on type of oil, sensitivity of the area

(e.g. salt marsh damage may be almost irreversible, while a rocky shore may be

hosed down with relatively quick and satisfactory recovery), weather and how

the pollution is tackled. This variability makes oil as state indicator prone to

argument and highlights the need for controlling the handling of oil and

avoiding loss or illegitimate disposal.

The shipyard industry generates significant quantities of wastewater from

various operations. Some of the major operations that generate wastewater are

vessel cleaning operations, water used for cleaning the equipment, and waterused in the processes. Efficient management of shipyard wastewater requires

understanding of specific pollutants present and their concentrations.

Integration of environmental plans minimizes duplication and encourages

coordination between safety and health, emergency response, and environmental disciplines.

Most of the management techniques like source reduction, waste minimization,

control, treatment etc. can be effectively utilized once the composition of the

Department of Physics, The Ovidius University of Constana, Constana, 900, Romania.

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waste stream is known. This paper is the compilation of the knowledge acquired

through the shipyard interaction.

2. International conventions and agreements

Worldwide the MARPOL 73/78 Annex 1 Regulation for the Prevention

of Pollution by Oil applies. This is concerned with vessels and harbours only.

Other conventions and agreements cover specific areas and include land-based

sources e.g.

OSPARCOM for the North-East Atlantic, the Mediterranean Blue Plan,Odessa Declaration, Black Sea Action Plan. EU law: tries to control oil pollution in

three ways: 1. by limiting the pollutant discharge such as Dangerous Substances

Directive 76/464/EEC, Barcelona Convention concluded on behalf of the EU by

Council Decision 77/585/EEC and approval of the oil pollution control protocol of

1/420/EEC; 2. by setting receiving water standards (eg. bathing water 76/160/EEC,

shellfish water 79/923/EEC) and 3. Management, practise include emergency and

information such as Directive 93/75/EEC on minimum requirements for vessels

bound for or leaving EU ports and carrying dangerous or polluting goods, the North

Sea decision 84/358/EEC approving the Bonn Agreement to ensure active

cooperation between riparian states in case of pollution incidents and its equivalent

for other seas. Decision 86/85/EEC sets up an information system on oil spills.

A EU Directive on oil reception facilities is being prepared.

3. Wastewater characterization based on process knowledge and

wastewater analysis

Characterization forms basis for managing the shipyard wastewater and to

improve the existing practices.

In order to design onsite wastewater treatment systems, we must consider the

nature of the wastewater because the effluent quality depends upon the influent

characteristics. The treatment capacity and treatment efficiency of systems are

calculated based upon the influent concentrations and the effluent requirements.

Efficiency = [(C in Cout )/Cin ] 100

Where: Cin = Influent concentration (typically mg/l)

Cout = Effluent concentration (typically mg/l)

And Efficiency is expressed as a percentage (%)

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WASTEWATER FROM SHIPYARDS 33

Also, the treatment capacity over time for biochemical processes is

usually modelled as a first-order equation such that

Ct/C0 = e kt

Where: Ct = Concentration at time, t (typically in mg/l)

C0 = Initial concentration at time = 0 (typically in mg/l)

k = reaction rate constant (typically in days1)

t = time (typically in days)

By exercising the characterization process, the constituents of the wastewater

stream and their concentrations are known. Wastewater characterization can be

done by looking into the processes and also, by sampling. Process knowledge helps

in estimating roughly various pollutants by analysis of the raw materials going into

the process. Also, the evaluation of various operations can help in understanding the

possible pollutants that are coming out of the operations. Sampling is done to know

the exact composition of the wastewater stream and the concentrations. The various

processes and/or operations that contribute to the wastewater have been given in the

following sections.

3.1. Vessel Cleaning Operations

The vessel cleaning operations cover many different areas and include

those operations as tank washing operations, pipeline cleaning operations,

mucking operations, chemical cleaning, chemical spot washing, engine room

cleaning, and others. The wastes associated with the vessel cleaning are actually

generated when the ship is in use. The most common wastes from the vessel

cleaning operations are the bilge wastes, which are a mixture of oil and fuel

with water. Therefore, the pollutants/parameters include oil & grease, COD

(Chemical Oxygen Demand), phenols, purgeable halocarbons and TSS (Total

Suspended Solids).

3.2. Pipeshop Operations

The department of pipeshop in the shipyard is concerned with the

testing of the pipes for leakages, cleaning of the pipes after installation and

other related activities. The shop uses different types of solutions for

cleaning the pipes which include some rust inhibitors. Some of the

solutions include sodium hydroxide, sodium nitrite, sodium silicate, dry

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chlorine (granular), morpholine, hydrazine, potassium hydroxide, and

others. The cleaning of the pipes is done to remove the rust and the scales

formed inside the pipes. The rust and the scales contribute to the TSS

component of the stream. Some of the cleaning solutions like sodium

hydroxide, potassium hydroxide also affect the pH of the wastewater

coming out of the operation.

3.3. Operators Department

Other major source of wastewater from the shipyard is the operatorsdepartment. The job of the operators is to run trial tests of the ship before

handing over to the customer. The testing includes main engine testing,

boiler testing, testing of cranes, refrigerators, automated controls etc. In the

process of testing the ship, the department generates wastes like spent

engine oil, cleansing solutions, spent lubricating oils and wash water. The

pollutants/parameters include oil & grease, COD, phenols, purgeable

halocarbons, and TSS. Solvent Cleaning and Degreasing Operations

Degreasing operations also contribute to the wastewater generation in the

shipyard. These operations are again sub-divided into other operations like

wipe cleaning, soak cleaning, ultrasonic cleaning, diphase cleaning, steam

gun stripping, vapor phase cleaning, mechanical cleaning, and others. The

pollutants/parameters from these operations include oil & grease, COD,and purgeable halocarbons. Other contributors to the wastewater are processes

like wet blasting (TSS being the pollutant), chemical stripping, and hydro

blasting.

There are other main streams of wastewater from the shipyard. They are

sanitary wastewater and stormwater. The characteristics of sanitary wastewater

are well known and need not be discussed in detail here. However, the

stormwater characteristics may vary depending on the shops or operations

located within the area of concern. The concentrations of pollutants from

stormwater outfalls of a typical shipyard are given in Table 1.

The above sections enumerate the different types of pollutants from the

processes and/or operations in the shipyard. Sometimes, the wastewater streams

include heavy metals as pollutants. Some processes generate liquid wastes,

which require handling as either solid or hazardous waste. Great care has to be

taken when heavy metals are present owing to their toxicity. Table 2 gives

results of the analysis of pipe shop effluent. Though the concentrations may

vary, Table 2 includes all the pollutants/parameters that may be encountered in

the shipyard operations.

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Table 1

Stormwater characteristics of a typical shipyard

CONCENTRATION, mg/lPARAMETER

Outfall 1 Outfall 2 Outfall 3 Outfall 4

Oil & Grease (O&G) 3.0 7.0 2 1

Chemical OxygenDemand (COD)

31.0 74.0 30 19

Total Organic Carbon(TOC)

8.4 14.3 7.7 7.3

Cadmium 0.02 0.04 0.06 0.09

Chromium (MQL= 0.10) 7.0 0.0 1 7

Copper (MQL= 0.10) BQL BQL BQL BQL

Lead (MQL= 0.005) 0.05 0.16 0.06 BQL

Tin (MQL= 0.02) 0.0 1.0 0 BQL

Zinc 0.02 0.04 0.02 BQL

MQL = Minimum Quantification Level - USEPA Region VI NPDES; BQL = Below MQL

Table 2

Wastewater characteristics of a typical pipe shop

Parameter Concentration, mg/l

Biochemical oxygen demand 1358

Total suspended solids 660

Chemical oxygen demand 3720Total organic carbon 1240

Cadmium 0.004

Chromium 0.015

Copper 6.3

Lead 0.187

Mercury

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issued by various agencies specify the discharge limits for various pollutants.

Therefore, the control options and the treatment technologies adopted are in

proportion to comply with the discharge limits outlined in the permits.

4. Treatment

The treatment of the wastewater is generally carried out on-site owing to

substantial quantities generated. Treatment of wastewater involves preliminary

treatment, primary treatment followed by secondary treatment. The secondary

treatment can be chosen from two alternatives: biological treatment andphysico-chemical treatment. These treatment options have been discussed in the

following sections.

4.1. Biological Treatment

Biological water treatment methods for the removal of heavy metals and

other inorganic contaminants have grown in popularity during the last decade.

Low costs and minimal sludge generation have convinced many environmental

managers in the shipyard industry to experiment with biological systems. The

key to successful implementation of biological water treatment is process

control: specifically biological process control.Suspended solids in a shipyard wastewater can be of two types: settleable

and non settleable. The non settleable particles can be colloidal and dissolved

particles, both organic and inorganic.

The organic biodegradable fraction can be removed using conventional

biological treatment processes, while the inorganic colloidal solids need some

form of flocculation to become settleable.

A biological treatment plant is using biomass to convert pollution into

water. Biological treatment is primarily aimed to reduce dissolved materials.

Based on the wastewater characteristics of a typical shipyard, the

following treatment processes are deemed necessary to obtain concentrations

below discharge limits: preliminary treatment, primary treatment, secondary

biological process, secondary settling, effluent filtration, adsorption of non

biodegradable organics, final effluent disinfection and sludge treatment.

4.1.1. Preliminary Treatment

The objective of preliminary treatment is the removal of coarse solids and

other large materials often found in raw wastewater. Removal of these materials

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is necessary to enhance the operation and maintenance of subsequent treatment

units. Preliminary treatment operations typically, in a shipyard wastewater

treatment plant, include coarse screening, grit removal. In shipyards grit would

be composed of sand, metal chips, or other heavy discrete particles generated in

metal surface preparation. In grit chambers, the velocity of the water through

the chamber is maintained sufficiently high, or air is used, so as to prevent the

settling of most organic solids. Grit removal is not included as a preliminary

treatment step in most small wastewater treatment plants. Flow measurement

devices, often standing-wave flumes, are always included at the preliminary

treatment stage.

4.1.2. Primary Treatment

The objective of primary treatment is the removal of settleable organic

and inorganic solids by sedimentation, and the removal of materials that will

float (scum) by skimming. Approximately 25 to 50% of the incoming

biochemical oxygen demand (BOD5), 50 to 70% of the total suspended solids

(SS), and 65% of the oil and grease are removed during primary treatment.

Some organic nitrogen, organic phosphorus, and heavy metals associated with

solids are also removed during primary sedimentation but colloidal and

dissolved constituents are not affected. The effluent from primary sedimentation

units is referred to as primary effluent.Wastewater from barge cleaning, bilge wastes, process waters and

sanitary wastewater have concentrations of oil and grease typically between 100

and 150 mg/L. The general discharge limit for oil and grease is 15 mg/L. Hence,

an oil-water separator is usually employed to separate out the oil from the

wastewater. This separated oil can be sold to outside customers for use as fuel.

4.1.3. Secondary Treatment

The objective of secondary treatment is the further treatment of the

effluent from primary treatment to remove the residual organics and suspended

solids. In most cases, secondary treatment follows primary treatment and

involves the removal of biodegradable dissolved and colloidal organic matter

using aerobic biological treatment processes. Aerobic biological treatment is

performed in the presence of oxygen by aerobic microorganisms (principally

bacteria) that metabolize the organic matter in the wastewater, thereby

producing more microorganisms and inorganic end-products (principally CO2,

NH3, and H2O). Several aerobic biological processes are used for secondary

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treatment differing primarily in the manner in which oxygen is supplied to the

microorganisms and in the rate at which organisms metabolize the organic matter.

Biodegradable organics contained in shipyard wastewater can be easily

removed using any of the conventional biological treatment processes or their

combination. Several of the available alternatives, namely, suspended growth

processes (conventional activated sludge, extended aeration) and fixed-film

processes (trickling filters, rotating biological contactors, aerobic fluidized

beds) could be selected.

High-rate biological processes are characterized by relatively small

reactor volumes and high concentrations of microorganisms compared with low

rate processes. Consequently, the growth rate of new organisms is much greaterin high-rate systems because of the well controlled environment. The

microorganisms must be separated from the treated wastewater by

sedimentation to produce clarified secondary effluent. The sedimentation tanks

used in secondary treatment, often referred to as secondary clarifiers, operate in

the same basic manner as the primary clarifiers described previously. The

biological solids removed during secondary sedimentation, called secondary or

biological sludge, are normally combined with primary sludge for sludge

processing.

Common high-rate processes include the activated sludge processes,

trickling filters or biofilters, oxidation ditches, and rotating biological contactors

(RBC). A combination of two of these processes in series (e.g., biofilter

followed by activated sludge) is sometimes used to treat municipal wastewatercontaining a high concentration of organic material from industrial sources.

i The Activated Sludge Process

In the activated sludge process, the dispersed-growth reactor is an

aeration tank or basin containing a suspension of the wastewater and

microorganisms, the mixed liquor. The contents of the aeration tank are mixed

vigorously by aeration devices which also supply oxygen to the biological

suspension. Aeration devices commonly used include submerged diffusers that

release compressed air and mechanical surface aerators that introduce air by

agitating the liquid surface. Hydraulic retention time in the aeration tanks

usually ranges from 3 to 8 hours but can be higher with high BOD 5

wastewaters. Following the aeration step, the microorganisms are separated

from the liquid by sedimentation and the clarified liquid is secondary effluent.

A portion of the biological sludge is recycled to the aeration basin to maintain a

high mixed-liquor suspended solids (MLSS) level. The remainder is removed

from the process and sent to sludge processing to maintain a relatively constant

concentration of microorganisms in the system. Several variations of the basic

activated sludge process, such as extended aeration and oxidation ditches, are in

common use, but the principles are similar.

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The activated sludge process can be easily employed for treating shipyard

wastewater as it does not occupy much space. The treatment process can be carried

out in floating tanks placed on a barge. The complete mix system may require heating

to enable proper temperature conditions for the microbes to work effectively.

ii Trickling Filters

A trickling filter or biofilter consists of a basin or tower filled with

support media such as stones, plastic shapes, or wooden slats. Wastewater is

applied intermittently, or sometimes continuously, over the media.

Microorganisms become attached to the media and form a biological layer or

fixed film. Organic matter in the wastewater diffuses into the film, where it ismetabolized. Oxygen is normally supplied to the film by the natural flow of air

either up or down through the media, depending on the relative temperatures of

the wastewater and ambient air. Forced air can also be supplied by blowers but

this is rarely necessary. The thickness of the biofilm increases as new organisms

grow. Periodically, portions of the film 'slough off the media. The sloughed

material is separated from the liquid in a secondary clarifier and discharged to

sludge processing. Clarified liquid from the secondary clarifier is the secondary

effluent and a portion is often recycled to the biofilter to improve hydraulic

distribution of the wastewater over the filter.

The TF process efficiently treats industrial wastes having a high

percentage of soluble, small molecule organic material, and readily removes

suspended and colloidal organics by the combined process of flocculation,adsorption, and enzyme complexing (WEF, 1991). The versatility of trickling

filters towards variations in the wastewater characteristics makes them useful

for treating shipyard wastewater as the wastewater from various operations

varies with factors like different types of vessels being cleaned, different kinds

of processes being employed at times owing to their intermittent nature, and

others. Also, the ability of TFs to treat low-strength streams can be utilized for

treating shipyard wastewater.

iii Rotating Biological Contactors

Rotating biological contactors (RBCs) are fixed-film reactors similar to

biofilters in that organisms are attached to support media. In the case of the

RBC, the support media are slowly rotating discs that are partially submerged in

flowing wastewater in the reactor. Oxygen is supplied to the attached biofilm

from the air when the film is out of the water and from the liquid when

submerged, since oxygen is transferred to the wastewater by surface turbulence

created by the discs' rotation. Sloughed pieces of biofilm are removed in the

same manner described for biofilters.

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4.1.4. Tertiary Treatment

Tertiary and/or advanced wastewater treatment is employed when specific

wastewater constituents which cannot be removed by secondary treatment must

be removed. Individual treatment processes are necessary to remove nitrogen,

phosphorus, additional suspended solids, refractory organics, heavy metals and

dissolved solids. Because advanced treatment usually follows high-rate secondary

treatment, it is sometimes referred to as tertiary treatment. However, advanced treatment

processes are sometimes combined with primary or secondary treatment (e.g., chemical

addition to primary clarifiers or aeration basins to remove phosphorus) or used

in place of secondary treatment (e.g., overland flow treatment of primary effluent).As part of tertiary treatment, the treatment plant could have filtration to further

remove suspended solids, and adsorption, to remove non biodegradable organic

compounds that may be toxic to aquatic life. The filtration of effluents from

wastewater treatment processes is a relatively recent practice (Metcalf & Eddy, 1991),

used for achieving supplemental suspended solids removal from biological or

chemical treatment processes. Carbon adsorption is an advanced wastewater

treatment method used for the removal of refractory organic compounds as well as

residual amounts of inorganic compounds such as nitrogen, sulfides, and heavy

metals (Metcalf & Eddy, 1991). Filtration of effluents through granular activated

carbon beds must be preceded by sand filtration to protect the carbon particles against

significant pressure loss, channeling or blockages. If powdered activated carbon

(PAC) is used, it is usually added to the activated sludge aeration basin, so thatbiological oxidation and physical adsorption occur simultaneously.

4.2. Physico-chemical Treatment

The main difference between the biological treatment plant and physico-

chemical treatment is that the latter does not rely on bacteria to remove organic

matter from wastewater. To remove colloidal particles, both organic and

inorganic, chemical addition is required. Coagulants added to the wastewater

stream will destabilize the colloidal suspensions and floc formation will take

places in a flocculator. Dissolved organic substances must be removed by

adsorption in activated carbon filters. Thus, the sequence of treatment units in a

typical physico-chemical shipyard treatment plant would be the following:

preliminary treatment, chemical addition, flocculation, dissolved air flotation,

effluent filtration, adsorption of organics, final effluent disinfection and sludge

treatment. This section will only describe the new units needed in physico-

chemical treatment, namely, flocculation and dissolved air flotation.

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4.2.1. Flocculation

Flocculation is the agglomeration of destabilized particles into microfloc

and after into bulky floccules which can be settled called floc. The addition of

another reagent called flocculant or a flocculant aid may promote the formation

of the floc.

The factors, which can promote the coagulation-flocculation, are the

velocity gradient, the time, and the pH. The time and the velocity gradient are

important to increase the probability of the particles to come together. Moreover

the pH is a prominent factor in the removal of colloids.

The purpose of flocculation is to form settleable particles from thedestabilized colloidal particles. The flocculator is a separate reactor, with a

holding time of around 30 minutes, where the wastewater is agitated gently with

paddles rotating at a velocity between 1.3 and 3.3 ft/s. This gentle agitation will

promote particle growth so that the larger floc particles will be easily separated

by gravity or by flotation.

4.2.2. Dissolved Air Floatation

The addition of chemical coagulants (alum, polymers) will also

destabilize emulsified oil particles and promote the formation of oil droplets;

these larger particles can be easily dragged to the surface by the small airbubbles generated in the flotation unit.

Dissolved Air Flotation (DAF) is a solids-liquid separation process that

transfer solids to the liquid surface through attachment of fine air bubbles to

solid particles. The phenomenon of DAF consists of three processes:

bubble generation;

attachment of solids to the bubbles,

and solids separation.

The DAF process involves holding recycled effluent for 0.3 to 3 minutes

in a retention tank and introducing air at high pressure (60-90 psi). When the

pressure is released as the recycle mixes with the feed stream in the flotation

chamber it forms microbubbles (4-50 micors), removing a large number of

small floc particles by adhesion of air bubbles on the floc surface, entrapment

under the floc and absorption into the floc. The attraction between the air

bubbles and particles is primarily a result of the particle surface charge and

bubble size distribution.

There are three modes of injecting air bubbles into the waste stream:

recycling, total pressurization, and partial pressurization. Total pressurization is

used in small installations, whereas in larger units, recycle or partial

pressurization is usually selected (EPA 1973a, 1973b). With wastewater

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containing emulsified oil or grease, chemical conditioning is necessary to break

the emulsion and form a floc to absorb the oil or grease.

The particle growth preceding floatation contributes to the effectiveness

of the floatation process. Therefore, when chemical addition is used to break up

the emulsion, a flocculation chamber is generally used preceding the floatation

process. In the case of shipyard wastewater, excluding storm water runoff,

treatability studies should be conducted to determine not only the design

parameters for the DAF unit, but also to determine whether chemical treatment

and flocculation are needed to improve the DAF unit efficiency.

5. Conclusions

Various shipyard operations like vessel cleaning, solvent cleaning and

degreasing and others generate huge quantities of wastewater. The quantities

from the process/washwaters in a typical shipyard can be as high as million tons

in a year. Such high quantities invariably draw the attention of the shipyard

environmental managers to reduce the waste streams.

The first step towards reducing the pollution is the characterization which

is done to differentiate various pollutants in the waste stream and their

respective concentrations. Process-wise delineation of pollutants will help in

better management of wastewater. Waste minimization methods with stress on

source reduction can be employed to reduce the pollution. Various methods likeprocess changes, replacement of solvent strippers, alternative cleaning

solutions, cleaner abrasive media, efficient rinse systems, effective reuse and

recycling options including evaporation, reverse osmosis, electrolysis, and

others are viable source reduction methods.

The biological treatment can employ either the activated sludge process

or the trickling filter concept in the secondary treatment. On the other hand,

physico-chemical treatment does not involve treatment by microorganisms but

will require additional physical processes like flocculation and dissolved air

floatation.

REFERENCES

KURA, B., TADIMALLA, R., SAHA, S., Wastewater from Shipyards Characterization, Minimization,and Treatment.

ECKENFELDER, W. W., 1980, Principles of Water Quality Management, CBI PublishingCompany, Inc., Boston, Massachusetts.

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Environmental Protection Agency, 1973a,Pretreatment of Poultry Processing Wastes, UpgradingExisting Poultry-Processing Facilities to Reduce Pollution, EPA Technology Transfer

Publication.Environmental Protection Agency, 1973b, In-Plant Modifications and Pretreatment, Upgrading

Meat Packing Facilities to Reduce Pollution, EPA Technology Transfer Publication.Environmental Protection Agency, 1994a, Guide to Cleaner Technologies Alternatives to

Chlorinated Solvents for Cleaning and Degreasing, EPA/625/R-93/016.Environmental Protection Agency, 1994b, Guide to Cleaner Technologies Metal Surface

Treatment and Plating Operations, EPA/625/R-94/007.

Environmental Protection Agency, 1994c, Guide to Cleaner Technologies Organic CoatingRemoval, EPA/625/R-93/015.

KIELY, G., 1997,Environmental Engineering, McGraw Hill, London, England.

KURA, B., 1996a, Integrated Environmental Management Plan First Year Interim Report,Gulf Coast Region Maritime Technology Center Project No. AMTC95-008A.

CHANG, E. L., CALVERT, J. M., KOLOSKI, T., PRICE, R., RATNA, B, 1997, Separation ofOil from Bilge Water. I. Bilge Water Characteristics and the Interaction of Bilge Waterwith Chemically Modified Surfaces,Naval Research Lab Washington DC.

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