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Vol. 26（2021），59 ～ 64

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Biofouling Assessment in Ocean Thermal Energy Conversion(OTEC) Power Plant Facility - A Case Study Conducted in
UPM-UTM OTEC Centre in Port Dickson, Negri Sembilan
Mohd Zaki Zainal Abidin*, Mohd Amir Hilmi Ibrahim, Fazlena Hamzah and Miradatul Najwa Mohd Rodhi
Biocatalysis & Biobased Material Technology Research Group, School of Chemical Engineering, College of Engineering, Universiti
Teknologi Mara UITM, 40450 Shah Alam, Selangor, MALAYSIA

Abstract
Ocean Thermal Energy Conversion (OTEC) is renewable source of energy that harnesses potential energy ofsea water at difference sea water temperature. In an example of a closed-loop OTEC system, the hot surface sea
water is used to vaporized refrigerant in a separate system, where the vaporized refrigerant is channelled to theturbine for power generation before it is cooled down to liquid form with the cold deep sea water. Apart fromits advantage as a base-load source of renewable energy, OTEC could be exploited for various other industries
which potentially generate various economic activities for surrounding communities. However, operating thissystem that utilises sea water as its main fluid may increase potential biofouling in pipelines and processing
equipment due to unwanted growth and accumulation of microorganisms which may affect the overall
performance in OTEC system by reducing efficiency of heat exchanger, hindering optimum flow insidepipelines or in a worst-case condition causing severe blockage and damage to the processing equipment. There
are numbers of reported biofouling assessment techniqes in OTEC but these methods are time-consuming andadopt destructive method in analysing biofouling sample, thus losing important information especially on
biofouling deposition mechanism. A new biofouling detection system which adopts non-destructive, continuous
and robust in rigorous field application is required for overcoming this problem. Therefore, this research aims
to determine a suitable biofouling detection system particularly under OTEC power plant conditions. By taking
UPM-UTM OTEC Centre as an actual case, the proposed activity starts with field biofouling assessment bycollecting seawater sample from potential site, along with other important parameters. The sample is later used
to mimic biofouling growth and deposition under controlled-environmental laboratory setup, followed bysuitable application of analytical instruments for assessing biofouling growth profile and its deposition under
different substrates and conditions.
Key words : OTEC, marine biofouling, cultivation techniques, non-invasive assessment

1. Introduction
Ocean Thermal Energy Conversion (OTEC) is one of renewable sources of energy that utilises thermal gradientof the sea water at different sea level by pumping warm water supply from sea surface to generate vapour that run aturbine, while concurrently the cold water supply from deep sea water is used to cool down the outlet steam from theturbine for re-condensation (Pelc & Fujita, 2002). Based on this concept, optimum OTEC system could be achieved atminimum sea temperature gradient of 20oC within the sea depth of 1000 m (Syamsuddin et al., 2015).

*

Received Date: 2021.11.30

E-mail of corresponding author: zakizainal@uitm.edu.my

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Mohd Zaki Zainal Abidin, Mohd Amir Hilmi Ibrahim,
Fazlena Hamzah and Miradatul Najwa Mohd Rodhi

Apart from its capability as a continuous and base-load renewable energy generation (Mitigation, 2011), it isestimated that OTEC has capability for producing energy up to 3 TW (Nihous, 2007), where this number is estimatedcould meet twice of electricity demand worldwide. Unlike other sources of renewable energy such as solar and windenergy, the applicability of OTEC could be diversified to other industries such as deep sea water (DSW) and desalinatedwater generation, air conditioning system, aquaculture industries, hydrogen gas production, mineral extraction (i.e.
lithium) from sea water and for cosmetic and high-grade food production (Kobayashi et al., 2001). In an example ofclosed-loop OTEC system, refrigerants such as ammonia and R-134a is used as working fluid in the closed-loop cycle
through cooling and heating stage (Pelc & Fujita, 2002). This is done when warm sea water obtained at the sea water
surface is channelled to an evaporator to vaporize the working fluid, converting it to from liquid to high-pressure vapor
flow where it is later used to run a gas turbine for power generation. The stream coming out from the turbine is then cold
down by a condenser using cold deep-sea water intake, where the condensed working fluid is pumped and circulatedback into the evaporator. The efficiency for about 3-5% could be achieved in an optimum OTEC system (Uehara &Ikegami, 1990). However, this efficiency could reduce for about 1-2% as a result of fouling that could take place inside
the heat exchangers (evaporator or condenser) (Berger & Berger, 1986).
When considering a system that uses water as a main processing fluid, the untreated and raw water usage contains
various physical-chemical properties which directly affects a system that is in contact with water. One of such examples
is on fouling where it could occur as a result of deposition of matters that could disrupt optimum flow of water in aprocessing system. This fouling problems could be contributed by various factors, whether scaling or crystalline fouling,organic fouling due to the deposition of organic matter, particle and colloidal fouling as a result of silt or clay deposition
or microorganism fouling (Al-Juboori & Yusaf, 2012). Over period of time, the deposition of fouling along pipeline walland other parts of exposed surface such as joints, fittings, valves and rotating equipment (rotors, compressors andturbines) may hinder optimum flow of water and reduces functionality of the equipment where eventually if it is notcontrolled, it could lead to major loss of time and function. In relation to biofouling, each biofouling assessment is
explicit with respect to the physio-chemical properties of water source as well as complex and detailed engineering
specifications, which consequently affects the overall process performance (Mitchell & Benson, 1980). For example, thepresence of thin biofilm of 25-50 micrometer could reduce the performance of OTEC by 50% (Berger & Berger, 1986).
Apart from that, large deposition of macrofouling may potentially restricting water pipeline, increasing additional weight
to a floating OTEC facility and in worst condition, might cause serious damage to the processing facilities (Flemming
et al., 2009).
The concern in biofouling study in OTEC is comparative to the interest and advancement of OTEC over periodof years with most of reports on the assessment of biofouling in OTEC facility have been initiated since late 1970s to
mid-1980s (Berger & Berger, 1986; Fetkovich et al., 1977; Mitchell & Benson, 1980). Several biofouling assessment
techniques proposed in this report were based on the nature of biofouling that growth and deposited on a concerned
surface inside OTEC facilities. For example, the direct-contact shell-and-tube heat exchangers used in the study adopted
the heat transfer monitoring (HTM) device for determining the thickness of micro fouling that is appeared as a thin layerof biofilm on the surface of heat exchanger (Berger & Berger, 1986; Mitchell & Benson, 1980). The thickness of biofilm
is estimated by measuring rate of heat transfer, considering heat transfer resistance as a result of thin biofilm on thesurface of heat exchanger. Apart from this physical assessment, few biological and biochemical assessments werereported using extracted sample of biofouling. A set of coupons attached to the surface of heat exchanger were subjectedto accumulated biofouling deposition over period of time. The accumulated sample on the coupons was extracted byscrapping manually by cutting out a section of heat exchanger tube (Berger & Berger, 1986) or using a special tool toscrap any deposit on the surface of heat exchanger (Nebot et al., 2010). The sample was later subjected to either visualinspection or by biochemical assessment. In this case, scanning electron microscopy (SEM) was used to provide
qualitative assessment of biofouling growth on the contact surface with water, providing crucial information on the typeof organisms or materials involved, rough estimation of biofilm thickness and the nature of its growth (Mitchell &Benson, 1980). In addition, several laboratory biochemical assessments were carried out, for example adenosine
triphosphate (ATP), total organic compound (TOC), carbohydrate analyses and chlorophyll contents (Berger & Berger,1986).

Biofouling Assessment in Ocean Thermal Energy Conversion (OTEC) Power Plant Facility- A Case Study Conducted in UPM-UTM OTEC Centre in Port Dickson, Negri Sembilan

61

The establishment of these methods indicates their applicability for assessing biofouling in OTEC system. The
usage of coupon-stripped method in an actual OTEC facility provides realistic evaluation of biofouling, thus providing
effective measures for its preventive approach. For instance, the TOC method is still considered as the most important
method today for analyzing potential biofouling due to the fact that the biodegradable content is proportional to thebiofouling growth (Flemming, 2011). However, these techniques are lack in term of their feasibility aspect whenstrategizing suitable biofouling controlling measures in correspond to the severity of biofouling as they only allows forlong-term biofouling observation assessment, which in reality biofouling deposits may change over period of time withspatial deposition profile on surfaces (Farhat et al., 2015). In addition, the destructive substratum extraction procedures
provide discrepancy particularly for a progressive biofouling deposition over period of time (Nivens et al., 1995),
limiting biofouling controlling measures only for a short-term basis. A flexible and effective biofouling monitoring
method is required for overcoming this limitation, with focus on several qualities of non-invasive and non-destructive
detection technique, with its feasibility to be implemented in field as well as on-line biofouling detection system.
Apart from the biofouling assessment techniques, method for simulating biofouling growth and deposition inlaboratory assessment is another aspect that need to be considered. While field biofouling assessment provides realistic
biofouling growth and profile, this method is tedious and time-consuming, thus setting up simulated environment for isessential for continuous and convenient assessment of biofouling growth and deposition. However, this effort considered
to be challenging, taking into accounts various realistic environment factors to imitate biofouling growth and deposition
such as the presence of nutrient, physical and chemical characteristic of sea water sample, and also presence of otherseawater biological species (either flora or fauna) (Stewart, 2012). Under engineering perspective, numerous studies
have discussed biofouling laboratory setup using a known species that are cultured under controlled environment (Bryers& Characklis, 1981; Videla & Characklis, 1992), but it is almost impossible to culture most marine microbial species(Rinke et al., 2013) under actual microbial growth medium (i.e. seawater). Even with the success of cultivating microbial
species under laboratory setup, the microbial species may not realistically represent overall species as it cover only 1%of overall species. Nonetheless, several improved, in-situ cultivation techniques for marine microbial growth have beenreported such as diffusion chamber technique (Kaeberlein et al., 2002), ichip technique (Nichols et al., 2010), I-tips
technique (Jung et al., 2014) and others, which indicating prospect in conducting this analysis under laboratory setup.

2. Research Objectives and Scope of Study
Potential biofouling deposition might give adverse effect towards OTEC power plant facility as a result of large
usage of seawater intake as its main processing fluid. However, most of reported techniques adopt destructive method in
extracting biofouling sample and require long period of time for each assessment, thus losing important information
especially for the biofouling deposition mechanism. A non-destructive and continuous method which could be adopted
in actual field condition is needed for solving this problem. Therefore, this research activity aims to identify potential
biofouling in OTEC system, specifically at UPM-UTM OTEC Centre, Port Dickson, Negri Sembilan and to
conduct laboratoy assessment for biofouling using suitable analytical instruments. UPM-UTM OTEC Centre is apioneering and the first OTEC facility in the world that serves as a laboratory-scale hybrid OTEC (H-OTEC) system
which has potential for generating up to 3 kW of electricity as well as concurrent desalinated water (DSW) production
using the same facility.
The scope of study for this research activity covers two major parts, the first part is to assess potential biofoulinggrowth and deposition by conducting field assessment evaluation at coastal area near to UPM-UTM OTEC Centre, Negri
Sembilan, Malaysia as well as to simulate biofouling growth under laboratory setup. The information obtained from thisassessment activity allows preliminary evaluation of biological and physical-chemical profiles of potential biofoulingthat may be present on the subjected surface (or substrate). The second part of this study covers on methods for detecting
biofouling, both through direct assessment on the subjected substrates (in-situ assessment) as well as external assessment
from collected biofouling sample (ex-situ assessment). This assessment provides physical and/or quantitative analysis of
biofouling growth which is then compared to the results obtained from the first activity.

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Mohd Zaki Zainal Abidin, Mohd Amir Hilmi Ibrahim,
Fazlena Hamzah and Miradatul Najwa Mohd Rodhi

3. Research Methodology
The overall research activity covers three major activities, covering on biofouling assessment activities on field
as well as in laboratory work and biofouling detection using several laboratory analytical instruments. The summary ofthese proposed activities are presented in a flow chart, presented in Figure 1.

Fig. 1 Flow chart for proposed research activities

The first activity which is the field study allows realistic assessment of potential biofouling particularly in physicochemical parameters which support biofouling growth and deposition. However, for practical and continuous monitoring
setup, it is adequate to represent actual biofouling setup by obtaining sea water sample before the sample is cultivatedunder controlled-environment laboratory setup using the sea water sample. This requires suitable sea water sampling at
near location near to UPM-UTM OTEC Centre, with focus on to the intake and outlet sea water pipeline for the newlydeveloped OTEC facility. In addition, measurement of physico-chemical properties of the seawater sample is needed as
it provides important information for the growth and deposition of biofouling. For example, parameters such as pH,
salinity, gradient seawater temperature at different sea water depth, the availability of nutrients, sea water tide and flow
and other parameters are some of crucial parameters that need to be considered.
After acquiring seawater sample and important parameters, the cultivation of biofouling is conducted underlaboratory scale in UiTM facility. The objective is to grow biofouling, as close as possible, to real environment of thesystem. One of proposed setups is by imitating biofouling growth inside a small seawater tank, presented as in Figure 2.

Biofouling Assessment in Ocean Thermal Energy Conversion (OTEC) Power Plant Facility- A Case Study Conducted in UPM-UTM OTEC Centre in Port Dickson, Negri Sembilan

63This setup serves as a basis for identifying biological as well as physical-chemical profiles of biofouling growth before
a small or medium-scale flow cell is developed. Unlike the setup presented in Figure 2, the flow cell simulates biofoulinggrowth and deposition under continuous flow inside a small channel, which indirectly serves as a setup for biofoulingassessment using suitable laboratory analytical instruments.

Fig. 2 Schematic diagram of biofouling laboratory setup using a small seawater tankConsidering option for non-destructive assessment, analytical instruments such as optical microscope orspectroscopic instruments (i.e. Fourier Transform Infrared or Raman Spectroscopy) could be used by observing
biofouling from collected biofouling samples or direct observation at the biofouling laboratory setup. After identifying
appropriate analytical instruments, other options such as chemical detectors could be used for biofouling detection. The
comparison between previous analytical instruments results and the chemical detector system allows adequate calibration
and additional measurement for conforming the biofouling detection. In addition, appropriate modification to the current
analytical techniques might be considered for suiting up actual measurement condition to the setup of analytical
instruments. After completing this stage, the proposed analytical instrument could be potentially used in field byconducting its applicability and practical implementation under rough environment condition. If it turns to be successful,the biofouling detection system could be then implemented in strategic location near or in seawater intake pipeline
system at UPM-UTM OTEC Centre.

8. Expected results and outcomes
Upon completion of this research activity, a comprehensive report which evaluate any potential biofoulinggrowth and deposition in UPM-UTM OTEC Centre is available as a guideline for the laboratory operator in mitigating
biofouling within their facility. Options which include non-destructive and practical biofouling detection systems or
sensor which have been analysed and tested in this research activity provide a practical and effective technique toanalyse biofouling growth and deposition, either in laboratory setup or in operating OTEC setup.

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