It is common knowledge that shipping is deemed as the most reliable, secure and a more sustainable option and thus accounts for an excess of 90 of the worlds trade.[8888]This report evolves around the ballast water management systems (BWMS) adopted in all the various modes of shipping (gas, oil and chemical tankers). Therefore, a short background research is followed in regards to the aspects surrounding ballast water as well as the importance of systems monitoring it.
Figure 1: Stages corresponding to the retention and discharge of ballast waterIn order for a ship to float, the principle followed is that the buoyancy forces are of equal measure and opposite direction to forces due to gravity. The load capacity influences the stability of the ship as the center of gravity shifts. Marine vessels are incorporated with holding tanks which are capable of withholding and discharging vast amounts of sea water. The amount of water charged into these compartments is dictated by the presence or absence of the cargo capacity. As shown in Figure 1, ballast water systems come into effect when there is no or minimal load in contrast to when it's loaded where the opposite occurs. At first, the concept of "floading" these compartments with sea water may seem irrational to some, however it provides stability due to ideal buoyancy conditions as well as monitoring the deadweight tonnage exerted through the submersion of the draft.
The shipping industry is vital to global economy. However, if the IMO (International Maritime Organization) standards are not met with respect to ballast water management, a chain reaction takes place that has negative ecological, economical and welfare impacts. To prevent such disasters, systems are employed to meet IMO's ballast water standards. There is a wide range of technologies that are applicable and are readily available. The specification of each system is dependable on the quality of contaminated ballast water upon discharge as well as a tanker's size and class.
One common methodology is the use of physical separation whereby the larger solid particles can be removed via filtration in combination with chemical disinfection which targets the inactivation of the reactive and re-productive nature of micro-organisms. To be noted that the species involved, the temperature and salinity of seawater are regarded as sensitivity parameters that determine the choice of the system used.(22) In this case, the focal point is revolved around electro-chlorination. (20)
One preferred ballast water management system is BALPURE which is patented by Severn Trent Services. The treatment commences during ballast water intake whereby organisms and particulates of particle size larger than 40 microns are withheld, though can be removed through back-wash, due to the presence of a filter.
From the main ballast water line, 1% of the available volume is re-directed via a side-stream which is forwarded to the electrolytic system for the production of hypochlorite with a concentration of 1% that is used as a powerful oxidizing agent. This is achieved within an electrolytic cell comprising of anodes and cathodes, both electrodes (rod-shaped conductors) connected to a battery and responsible for oxidation and reduction respectively. The anode is positively charged thus attracting anions (negatively charged) and similarly for the negatively charged cathode attracting cations (positively charged).(30) For this redox reaction to take place, the presence of seawater is required that comes into contact with a current of electricity which is provided by the DC power ; thus leading to yielding of sodium hypochlorite (NaOCl) through the main chemical reaction : (18)(60)C:\Documents and Settings\User\Desktop\Dissertation\pic\fig-1-diagram.jpg
NaCl (salt) + H2O + electricity ïƒ NaOCl + H2
To be noted, multiple electrodes can be employed to improve the production of the disinfection solution or the installation of a train of electrolytic cells to accommodate high flow rates . The removal of by-product (hydrogen gas) is achieved through diffusion with air in a degas cyclone separator and released into the atmosphere, whereas the remaining solution is mixed into the main ballast water stream and placed into tanks where disinfection takes place. (40) (5)
Objectives
The aim of this proposal is to take an existing technology such as ballast water treatment which is applied commercially and develop it in an innovative manner to render it as a more efficient, economical and environmental attractive alternative.
Experimental practice ensures the safe and proper operation of a process. Through this, one becomes familiar with the set up of the apparatus and how to operate them as well as the ability to distinguish, measure and assess necessary data. Also, the investigation of how the system is affected through parameter sensitivity checks. More importantly, the impact of the results obtained, have a wider range of significance in operational, biological and environmental terms.
The chlorine comes into effect in the contact chambers within the tanker whereby the retention time is observed, usually adding up to half an hour without taking into consideration the response time of five minutes due to the residual analyzer . As a result, the residual chlorine can only be evaluated with an appropriate analyzer after that time has passed and then assessed whether it has met its set target of 1mg/L. Thus, the delay time for the control system responsible for chlorine dosing is noticeable and ineffectual.[999]The necessity of achieving necessary levels of residual chlorine is vital due to long retention times of ballast water in tanks and the possibility of pathogenic bacteria re-appearing. Similarly, biologically speaking, the density of organisms is not permitted to be above a certain threshold due to operating reasons. Finally, the discharge of contaminated water has a negative impact environmentally as it can cause a possible hazard to both the maritime habitat as well as to the well being of humans.[567]
As a result, the aim of this proposal is to gain approval and funding to utilize, analyze and determine whether the boron doped diamond sensor, a novel electrochemical sensor, will improve the noticeable and precarious lagging effects of residual chlorine measurements.
Approach
It is a fact that applying theory into practice is not straightforward. Thus, once the concept of a process is predefined and initial calculations have been conducted, laboratory testing is followed whereby data is collected, assessed and determines the feasibility of a project via scale up. As Industrial processes operate successfully once properly installed and that is mainly due to prior testing on an experimental scale. This is achieved through laboratory work. Similarly, ballast water management systems are set up with respect to electro-chlorination measurements.
Electro-chlorination takes place in a cell comprising of electrodes operating as conductors. The set up of the cell is a key feature with regards to the analysis and depends on the aggregate, type and configuration of the electrodes which are positively (anode) and negatively (cathode) charged. As a result, it is vital to acquire the proper assembly in order to commence experimental testing. To be noted, according to literature reviews similar testings have taken place with the application of a 3-mode electrode. This set up involves a working, a reference and a counter electrode. Following this structure allows the study of half the cell with accuracy and confidence with the attention given to the reaction taking place at the anode or in other terms the working electrode which is responsible for chlorine production.
Necessary apparatus are provided which include: a high flow rate peristaltic pump (Watson Marlow - 323 Du series), solenoids and a potentiostat (PGSTAT12).
Versatility is acceptable when it comes to experimental procedures, though one viable approach is the following:
Set single or multi channel pump to a constant flow rate between its applicable range of 2μl/min to 2200ml/min.[234]
Apply direct current to electrodes of up to 12V using the potentiostat. [345]
Potentiostat measures potential difference between reference and working electrode, which corresponds to the resistance of the electrolyte as a electricity conductor. Ohms law I=VR
Production of chlorine (Cl2) at anode.
Measure free and total chlorine levels of up to 5mg/L using Palintest Chlorometer Duo.[123]
Adjust D.C.power to meet chlorine residual levels to avoid contamination
Take Temperature and pH levels
Accuracy ± 0.2%
Electrochemical detection thus working and reference electrode undergo voltage leading to the oxidation of molecules at the anode at a predetermined potential resulting in a flow of electrons which are traceable and picked up by the potentiostat (measured and quantified).selective and sensitive process .Going to make step changes to applied potential resulting in the calibration of optimum potential where response reaches steady state at a set flow rate.
Safety Similarly, the is visible in industries ranging from ballast water management in shipping to wastewater disinfection
Boron doped diamond and neutralization
Timescale and Resource Requirements
Beneficiaries
The focal point of process industries is to determine and meet the customer's needs. However, design concepts are faced with external constraints ranging from the availability of resources to the economic feasibility of the project as well as government and environmental regulations. The table below provides the sectors that benefit from the proper application of automated control of chlorine dosing.
Recipients:
Justification:
Ecosystem
Pollution of rivers and sea beds are directly related to the contamination due to improper management of wastewater systems. Through the agglomeration of ballast water, micro-organisms, plants and marine animals are engulfed in these tanks leading to their re-location when released. The invasive nature of marine species tends to endanger the native ones due to the absence of their natural predators as well as the additional competition with respect to the food supply. In other words, marine biodiversity and their natural habitat are maintained. [21]
Shipping, Water and Sewage Treatment Industries
Innovative concepts for ballast water management systems could potentially lead to the reduction of both operating and capital costs as well as the reduction of installation space required upon the vessel. In addition, the appearance of non-domestic species were not accounted for during the set up of underwater infrastructure (i.e. sewage systems), thus compromising their conventional operation and potential loss on investment. The mismanagement of chlorine dosing in terms of over/under-dosing will lead to additional expenditure of chemical agents in regards to the neutralization process and receive fines for not complying with IMO's standards. [21]
Healthcare
Chlorine dosing is responsible for the termination and suppression of pathogenic micro-organisms. As a result, contamination of seawater and aquatic life may potentially lead to cholera and other perilous outbreaks, putting at risk local and wider communities. The same applies to water supply for domestic purposes that do not meet the set residual chlorine targets could possibly put human lives at risk.[21]
Myself
As a future chemical engineer, to take a well established technology and attempt to improve it is both challenging and motivating. To simulate a real-life problem through laboratory work and have actual hands on practice will give me an in-depth insight into how to approach experimental work and relate it to an existing process. Through this experience I hope to improve my research, development and analytical skills. Finally, the aim is to obtain an extensive understanding on how the water treatment industry operates.
Conclusion
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[123] http://www.aquaticlife.ca/Products/ProdPages/ChlorometerDuo.asp
[234] http://www.watson-marlow.de/pdfs-global/b-sciq-gb-05.pdf
[345] http://www.metrohm.de/Produkte/Downloads/Autolab_Brochure_2012.pdf
.
[999] http://www.environmental-expert.com/Files/5306/articles/13870/504.pdf
[8677] http://globallast.imo.org/monograph%205%20symposium.pdf =
[567] http://www.nemw.org/GSI/GSI-LB-F-A-5_NaOCl.pdf
(20) (http://www.lr.org/Images/BWT0210_tcm155-175072.pdf )
(21) http://www.maritimecenter.dk/public/dokumenter/EMUC/Konferencer/2012/Dandu%20Pughiuc.pdf
(22) http://www.lr.org/Images/BWT0210_tcm155-175072.pdf
(23) http://www.vchlorin.com/product.htm (pic anode, cathode)
50) http://power-topics.blogspot.co.uk/2007/09/advances-in-power-supplies-for.html (pic electrolytic cell)
(5)http://www.severntrentservices.com/BALPURE__Ballast_Water_Treatment_System_BALPURE__Process/Ballasting_prod_618.aspx
(18)http://www.severntrentdenora.com/Products-and-Services/Ballast-Water-Treatment-Systems/BALPURE/750-5020.pdf
(30) http://electro-lysis.blogspot.co.uk/2011/01/in-electrolytic-cellvoltameter.html
(60)http://www.severntrentservices.com/BALPURE__Ballast_Water_Treatment_System_BALPURE__Process/Electrolytic_Disinfection_Technology_prod_617.aspx
figure 2 http://www.tutorvista.com/content/physics/physics-i/forces/equilibrium-and-stability.php
[8888]( http://www.maritimecenter.dk/public/dokumenter/EMUC/Konferencer/2012/Dandu%20Pughiuc.pdf )
[7777](http://www.inc.com/encyclopedia/transportation.html )
