Ballast Water Treatment Using Hydrodynamic Cavitation

Transcription

1 Indian Journal of Geo-Marine Sciences Vol. 43(11), November 2014, pp Ballast Water Treatment Using Hydrodynamic Cavitation Pratik P. Sangave, Anjan C. Mukherjee* and Aniruddha B. Pandit HyCa Technologies Pvt. Ltd., Mumbai, India *[ Received 07 March 2014; revised 10 October 2014 A novel physicochemical disinfection method based on hydrodynamic cavitation has been identified to disinfect ballast water. The phenomenon of hydrodynamic cavitation which is associated with the formation, growth and the collapse of microbubbles, leads to the generation of very high pressures and temperatures locally, which can cause cellular damage and makes microorganism nonviable. This paper explores the microbiocidal effectiveness of hydrodynamic cavitation coupled with in-situ generated chemicals from sea-water itself for the disinfection of ballast water with respect to the ballast water discharge standards of the International Maritime Organization (IMO). Experiments performed in this study indicate that this method is a potential physicochemical ballast water disinfection technique. This advanced technology is eco-friendly as it does not use harmful external chemicals, UV or ultrasound, does not produce harmful by-products, and is energy efficient, economical, and can be scaled up for disinfection on very large scale. It is an alternative to current technologies and can be easily installed on vessels with minimum foot print area, as filtration and disinfection happen in a single compact unit. [Keywords: Ballast; Disinfection; Hydrodynamic Cavitation; Clean Technology] Introduction Shipping is the backbone of global economy and facilitates transportation of 70% of the commodities. It is estimated that 6 7 billion tons of ballast water is carried around the world each year. Translocation of organisms through ships is considered to be one of the important issues that threaten the naturally evolved biodiversity, the consequences of which are being realized increasingly in the recent years 1. The ballast water quality is of utmost importance today and the need for ballast water treatment has arisen from the requirements of regulation D-2 of the Ballast Water Management Convention to regulate discharges of ballast water and reduce the risk of introducing nonnative species from ships ballast water 2. Several chemical, physical and physicochemical treatment technologies have been developed for the disinfection of ballast water. However, their use is constrained by key factors such as space, cost, disinfection by-products and efficacy 3. Physical separation methods such as filtration and hydrocyclon are first choice of methods for the separation of micro-organisms in the range of μm. The efficiencies of such physical filtration have been >91% 4. UV-irradiation, ultrasonication, deoxygenation, heat treatment etc. have been considered as the simplest methods of ballast water disinfection and have shown their effectiveness up to 95%. In comparison with the capital and operating cost, the effectiveness of these methods are much lower and therefore are not considered as prominent methods of ballast water disinfection at a commercial level 5. In contrast to physical methods, chemical disinfection methods appear to be better choice in terms of capital costs, power requirements and footprint. Two general types of biocides i.e. oxidizing and non-oxidizing are broadly used for the ballast water treatment. The effectiveness of chemicals is attributed to their fundamental actions: alteration of cell permeability/colloidal nature of protoplasm/organism DNA or RNA, cell wall damage and inhibition of enzyme activity 6. The production, storage and use of chemicals raise questions regarding long-term harm to the environment and personnel. Firstly, disinfection byproducts (DBPs) such as trihalomethanes (THMs) could cause environmental and health harm, as in the case of chlorine, chlorine-di-oxide and ozone. Apprehensions about accumulation of mutagenic and carcinogenic chemicals as also effects on the aquatic webs have been expressed in NRC Report 7. Therefore, there should be a method that combines merits of both physical and chemical methods and remove respective disadvantages. A physicochemical method like hydrodynamic cavitation coupled with chemical disinfectant could be the choice of ballast water treatment due to its disinfections efficiency and environmental safety. The phenomenon of hydrodynamic cavitation is associated with the formation, growth and the collapse of micro bubbles/ cavities leading to the

2 2034 INDIAN J. MAR. SCI., VOL 43, NO.11 NOVEMBER 2014 localized generation of very high pressures and temperatures 8. The cavity undergoing rapid volumetric implosions/ oscillations produces high turbulence shear stress in the surrounding liquid. Thus, the cavitation occurring in the system can produce several effects, such as high velocity liquid jet, shock wave and turbulent shear stress, which are responsible for cell disruption 9. There are some 10, 11, 12 developed ballast water treatment systems which use hypochlorite as an active substance (AS) for chemical disinfection. The concentration of the chemical disinfectant used is approximately of 10 mg/l; therefore, there is need for an effective neutralization to avoid any DBPs. The human and aquatic risk associated with THMs in these systems is more due to the utilization of high dose of hypochlorite. Therefore, in the present study, we have developed a physicochemical method (HyCator : BWT Reactor system) based on hydrodynamic cavitation along with optimum sodium hypochlorite dosing (generated in-situ by electrolysis of sea water itself) for disinfection of ballast water with respect to the IMO s ballast discharge standards and D2 regulations. We have designed and developed HyCator : BWT Reactor system which requires minimum dose of sodium hypochlorite and compared its efficacy with IMO approved ballast water disinfection systems on the basis of disinfection rate, acute toxicity, concentration of DBPs generated, risk characterization and assessment with respect to ship s safety, human health and aquatic environment. Materials and methods Sea water (32 PSU) and brackish water (21 PSU) were collected from the sea shore of Dadar Chowpati, Mumbai, Maharashtra, India and fresh water was collected from local source. The biological water quality criterion as per D-2 regulation was matched by using combination of indigenous organisms and cultured surrogate species (>50 µm: Artemia salina, µm: Chlorella marina) supplied by Maharshi Dayanand College (MDC), Parel, Mumbai. A hydrodynamic cavitation based system HyCator : WDE and HyCator : OLM was designed and fabricated by HyCa Technologies Pvt. Ltd., (HyCa) Mumbai for ballast water disinfection and residual chlorine neutralization respectively. An electrochlorination unit for in-situ generation of sodium hypochlorite (NaOCl) using sea-water and back-flush filter was also designed by HyCa. A neutralizing agent, sodium thiosulfate (STS) was prepared using stored solid STS and sea water. Acute toxicity was measured on the crustacean, Artemia salina, the microalga, Chlorella marina and the fish Terapon jarbua supplied by MDC. Nutrient agar and all other chemicals were obtained from HiMedia India Ltd., Mumbai. The HyCator : BWT Reactor system s test and analysis were performed based on G8 Guidelines 13 and in accordance with G9 Procedure 14 under the supervision of the Directorate General of Shipping (DG Shipping), Government of India and Indian Register of Shipping (IRS), Mumbai. Analyses of the physicochemical parameter s of water sample were done in the world renowned Institute of Chemical Technology (ICT), Mumbai and the biological efficacy test, aquatic eco-toxicity test, risk assessment were performed and evaluated at MDC. The schematic process diagram of the HyCator : BWT Reactor system is shown in Fig. 1. The disinfection of ballast water was achieved by passing the water through HyCator : BWT Reactor system only once. The treatment system consists of two stages i.e. ballasting & de-ballasting. In the first stage of ballasting operation, ballasting water was pumped through the automatic back flushing filter unit by which large microorganism and suspended particles having size more than 50 µm were removed. The filter unit was installed directly at the main ballasting line. A side stream of the ballasting water was taken to electrochlorination unit to generate active substance (AS) of 3 mg/l concentration sodium hypochlorite (NaOCl) by electrolysis. The hypochlorite was then injected back to the main ballasting line through the suction valve of HyCator : WDE Reactor system. After injection, sodium hypochlorite was mixed and diluted with the main ballasting water and discharged into ballast tank. The maximum concentration was 3 mg/l Total Residual Oxidant (TRO), which was controlled by using the on-line TRO sensor and by adjusting current supplied to the electrochlorination unit. Electrochlorination unit of HyCator : BWT Reactor system was designed to operate at the seawater salinity of 10 PSU or more. For operation in the low salinity water, HyCator : BWT Reactor system was designed to use the seawater in the existing onboard seawater tank because this system use only small amount of seawater in comparison with the incoming ballast water flow (less than 5% of ballast water flow). If the ship is to trade in river water, a suitable tank filled with sea water can be used to generate hypochlorite. Hydrogen gas, a by-product of

3 SANGAVE et al.:ballast WATER TREATMENT USING HYDRODYNAMIC CAVITATION 2035 electrochlorination unit, hydrogen gas was vented from the system using hydrogen separator. The Fig 1. Schematic process diagram of the HyCator : BWT Reactor system Sample ID ph Temp. ( C) Salinity (PSU) DO a (mg/l) TDS b (gm/l) TOC c (mg/l) TW (Test Water) B-Control (D5) B-Treated (D5) < 0.1 a Dissolved Oxygen (DO) b c Treated water is divided into two types, before neutralization and after neutralization. The analyses were performed according to ISO Table 1: Water quality analysis with HyCator : BWT Reactor system. Cl 2 as TRO (mg/l) generated hydrogen gas was diluted to less than 1% of atmospheric concentration by forced air blowing by two air blowers and was always maintained below its lower explosive limit (LEL) of 4%. A booster pump was used to increase pressure of flowing ballast water which pumps the ballast water at a designed flow rate and pressure to the hydrodynamic cavitation reactor i.e. HyCator : BWT Reactor system. The precision engineered HyCator : BWT Reactor system consists of a HyCator : WDE reactor where the ballast water is subjected to controlled magnitude, random and targeted pressure variations so as to generate precise gas, gas-vapour and vapour filled cavities. The cavities are allowed to grow to a desired size and then made to oscillate or collapse under highly controlled conditions. The collapsing cavities generate spherically diverging shock-waves (symmetric collapse) or surface normal liquid jets (asymmetric collapse) of magnitude high enough to either implode or shear and shatter the invasive marine organisms (by shock wave) or cut open (liquid jets) the same rendering the phytoplankton and zooplankton in the ballast water nonviable. Maximum ballast water is disinfected by HyCator : WDE Rector System itself. Sodium hypochlorite generated onboard was dosed in HyCator : WDE which also disinfects the microbes in synergy with cavitation. Then the treated ballast water was taken into the ballast tank. During voyage/ holding period, the residual hypochlorite (TRO) in ballast water (1 mg/l) was constantly disinfecting the aquatic organisms, which were not disinfected during ballasting and prevent them from re-growth. During de-ballasting process, de-ballasting water was discharged only through the neutralization unit. The neutralizing agent, sodium thiosulfate (STS) was injected into the de-ballasting

4 2036 INDIAN J. MAR. SCI., VOL 43, NO.11 NOVEMBER 2014 line to neutralize the residual TRO (1 mg/l). The injection amount of STS was controlled by monitoring de-ballasting flow rate and residual TRO concentration. To prevent secondary marine environmental pollution at the time of de-ballasting, the AS which was generated from Day 0 Day 1 Day 5 Chemicals DL a (μg/l) Test Control Treated Control Treated Control Treated b Before N After N Anion c Bromate 0.08 ND ND 9.3E-1 ND 9.3E-1 ND 1.0E+0 8.9E-1 Chlorate 0.06 ND ND 7.0E-2 ND 7.0E-2 ND 6.0E-2 6.0E-2 Bromide 0.08 ND ND 8.0E-2 ND 1.0E-1 ND 1.2E-1 1.1E-1 Fluoride 0.07 ND ND 9.0E-1 ND 9.1E-1 ND 1.0E+0 9.2E-1 Trihalomethanes (THMs) d Dibromochloromethane E+0 3.6E+0 3.0E+0 9.4E-1 9.8E+0 ND 5.0E+0 1.0E+0 Dichlorobromomethane 0.02 ND ND 1.0E+0 ND 1.0E+0 ND 1.1E+0 1.0E+0 Tribromomethane E+0 4.6E+0 2.1E+1 3.5E+0 4.5E+1 9.1E-1 5.5E+1 5.1E+1 Trichloromethane E-2 7.0E-2 1.0E+0 5.0E-2 1.7E+0 ND 4.2E+0 3.9E+0 Haloacetic Acids (HAAs) e Monochloroacetic acid E+0 4.6E+0 3.9E+0 2.6E+0 3.5E+0 1.7E+0 1.2E+0 5.7E-1 Dichloroacetic acid E+0 1.3E+0 2.4E+0 2.0E+0 2.7E+0 2.0E+0 5.8E+0 4.9E+0 Trichloroacetic acid E+1 7.3E+0 1.9E+1 4.0E+0 3.7E+1 2.7E+0 4.6E+1 4.3E+1 Monobromoacetic acid E+0 2.0E+0 8.7E+0 1.9E+0 1.5E+1 8.7E-1 2.8E+1 2.4E+1 Dibromoacetic acid E+0 1.1E+0 2.0E+1 8.8E-1 3.9E+1 6.4E-1 5.6E+1 4.9E+1 Tribromoacetic acid E+0 1.5E+0 8.5E+0 1.5E+0 1.9E+1 1.5E+0 2.6E+1 2.3E+1 Bromochloroacetic acid E+1 6.1E+1 8.3E+1 3.7E+1 1.3E+2 1.7E+1 1.7E+2 1.7E+2 Dibromochloroacetic acid E-2 9.0E-2 1.1E-1 9.0E-2 1.2E-1 1.1E-1 2.4E+0 2.1E+0 Dichlorobromoacetic acid E+0 1.2E+0 1.4E+1 1.2E+0 2.6E+1 1.2E+0 3.4E+1 3.1E+1 Haloacetonitriles (HANs) f Chloropicrin E-3 3.0E-3 1.0E-2 ND 1.9E-1 ND ND ND Monobromoacetonitrile E-2 2.4E-2 4.0E-2 2.0E-2 5.0E-2 1.5E-1 9.2E-1 9.1E-1 Dibromoacetonitrile E-1 1.1E-1 1.2E-1 1.1E-1 1.4E-1 1.2E-1 8.7E-1 8.1E-1 Halogenated Phenols g 2,4,6-Tribromophenol 0.04 ND ND 5.0E-2 ND 5.0E-2 ND 8.0E-2 7.0E-2 a DL- detection limit. b Treated water is divided into two types, before neutralization and after neutralization. c The analyses were performed according to ISO d The analyses were performed according to US EPA e The analyses were performed according to US EPA f g The analyses were performed according to US EPA The analyses were performed according to US EPA 8041A. ND- Not detected Table 2. Relevant Chemicals (RCs) and Other Chemicals (OCs) in ballast water treated with HyCator : BWT Reactor system. Sample ID 50 µm> (no/m 3 ) 10~50 µm (no/ml) Heterotro. Bacteria (cells/ml) E. coli (cfu/100 ml) Vibrio cholerae (cfu/100 ml) Entero coccus (cfu/100 ml) TW (Test Water) 1 x x S-Control (D5) x S-Treated (D5) ND ND ND ND ND ND (ND: not detected) Table 3. Biological efficacy of HyCator : BWT Reactor system for seawater.

5 SANGAVE et al.:ballast WATER TREATMENT USING HYDRODYNAMIC CAVITATION 2037 Taxon Crustacean Algae Species Artemia salina Chlorella marina Test Protocol Endpoint Mortality OECD (after 96 hrs) Inhibition OECD (after 96 hrs) Sample ID Day Zero (D0) Results Results (LC 50, (NOEC, %) %) Day Five (D5) Results Results (LC 50, (NOEC, %) %) S-Control > > S-Treated > > S-Control > > S-Treated Mortality Terapon OECD S-Control > > Fish jarbua (after 96 hrs) S-Treated > Table 4. Results of acute toxicity tests using various marine organisms exposed to Control water (S-Control) and Treated water (S- Treated) associated with HyCator : BWT Reactor system for seawater (32 PSU). Classification Chemical BCF (L/kg) Reference Sodium hypochlorite EPI Suite v AS Hypochlorous acid 13.2 EPI Suite v Anions Bromate 31.8 EPI Suite v Tri Halo Methans (THMs) Halo Acetic Acids (HAAs) Halo Acetonitirles (HANs) Other Chemicals Dibromochloromethane 84 HSDB 22 /TOXNET (2011) 23 Dichlorobromomethane 9 HSDB 22 /TOXNET (2011) 23 Bromoform 35 HSDB 22 /TOXNET (2011) 23 Chloroform HSDB 22 /TOXNET (2011) 23 Monochloroacetic acid 31 HSDB 22 /TOXNET (2011) 23 Dichloroacetic acid 75 HSDB 22 /TOXNET (2011) 23 Trichloroacetic acid 130 HSDB 22 /TOXNET (2011) 23 Monobromoacetic acid 1.9 HSDB 22 /TOXNET (2011) 23 Dibromoacetic acid 1.5 HSDB 22 /TOXNET (2011) 23 Tribromoacetic acid 5.3 HSDB 22 /TOXNET (2011) 23 Bromochloroacetic acid 1.9 HSDB 22 /TOXNET (2011) 23 Dibromochloroacetic acid 3.23 EPI Suite v Monobromoacetonitrile 8.3 EPI Suite v Dibromoacetonitrile EPI Suite v Sodium thiosulfate 2.21 EPI Suite v Hydrogen gas - - 2,4,6-Tribromophenol (TBP) 1,186 OECD SIDS (2003) 24 1,2,3-Trichloropropane - - Table 5. BCF values for Active Substance (AS), Relevant Chemicals (RCs) and Other Chemicals (OCs).

6 2038 INDIAN J. MAR. SCI., VOL 43, NO.11 NOVEMBER 2014 Observation Test Parameter Material Control Water Treated Water ± ± 1.04 Stainless steel 316 Visual Assessment No pitting No pitting ± ± 0.60 Copper Visual Assessment No pitting No pitting ± ± 1.11 Brass Visual Assessment No pitting No pitting ± ± 0.12 Fluoroelastomer Visual Assessment No pitting No pitting Epoxy coated steel ± ± 1.25 Visual Assessment 316 No pitting No pitting Table 6. The results of Weight of Variation and Visual assessment of uncoated and epoxy coated metals after six months corrosivity test exposed to 180 days. Control & Treated water from the HyCator : BWT Reactor system. HyCator : Parameter Test Water BlueWorld 10 Smart Ballast 11 SiCURE 12 BWT Reactor Systems TRO as Cl2 used (mg/l) µm> (no/m3) 1 x 10 6 ND ND ND ND 10~50 µm (no/ml) 1100 ND 1 ND ND Heterotrophic Bacteria (cells/ml) 105 x 10 2 ND ND ND ND E. coli (cfu/100 ml) 300 ND ND ND ND Vibrio cholerae (cfu/100 ml) 180 ND ND ND ND Entero coccus (cfu/100 ml) 220 ND ND ND ND Crustacean (Artemia salina) >100% >100% >100% >100% >100% Acute toxicity Algae (Chlorella (LC 50, %) marina) >100% 100% >100% 100% 100% Fish (Terapon jarbua) >100% >100% >100% >100% >100% Crustacean (Artemia salina) 100% 35% - 50% 50% Acute toxicity Algae (Chlorella (NOEC, %) marina) 100% 20% 100% 20% 25% Fish (Terapon jarbua) 100% 50% - 50% 50% Table 7. Comparison of HyCator : BWT Reactor System with IMO approved BWMS. electrochlorination unit should be discharged into the sea at a concentration less than 0.2 mg/l TRO. To comply with this condition, the concentration of STS was set to the stoichiometric ratio of TRO to sodium thiosulfate at 1:2 parts. Stored STS crystals were dissolved in the seawater or fresh water in the STS storage tank. Sodium thiosulfate of concentration 6 mg/l was injected at the suction valve of HyCator : OLM Reactor so that the residual TRO in de-ballasting water was rapidly neutralized by the mixing effect in the cavitation reactor system. Individual TRO sensors were used to measure the residual TRO concentration at two points, before and after the neutralization unit. TRO measurement before the neutralization unit was used to measure the residual TRO concentration and to determine the injection amount of the neutralizing agent into the de-ballasting line. Another TRO measurement installed after the neutralization unit was used to check the residual TRO which was neutralized properly or not. Samples were collected immediate after the treatment (Day zero-d0) and after five days of treatment (D5) to evaluate the disinfection rate, acute toxicity, concentration of DBPs generated, risk characterization and assessment with respect to ship s safety, human health and the aquatic environment. Also, we have evaluated and compared the performance and efficacy of HyCator : BWT Reactor system with other IMO

7 SANGAVE et al.:ballast WATER TREATMENT USING HYDRODYNAMIC CAVITATION 2039 approved ballast water treatment systems. Results Water quality analysis The quality of the treated ballast water (physico-chemical analysis) and the biological efficacy were evaluated as per G8 guidelines and G9 procedure. The quality of the test, control and treated water is summarized in Table 1. The maximum concentration of AS sodium hypochlorite dosed into the HyCator : BWT Reactor system during ballasting was observed to be 3 mg/l and the concentration of same in the treated water after five days and after neutralization during deballasting was observed to be less than 0.1 mg/l. The Relevant Chemicals (RC) and Other Chemicals (OC) are the DBP s and have equal importance as of AS because of their toxicity effects on human health and aquatic environment. The control, treated and neutralized ballast water was tested and analyzed as per IMO and United State Environment Protection Agency (US EPA) regulations and the results are represented in Table 2. The concentration of organisms of the size group bigger than 50 µm in size varied from 1 x 10 5 to 1 x 10 6 nos/m 3, while that of the size group between 10 µm and 50 µm in size varied from 1100 to 1200 nos/ml, in the test water (Table 3). The heterotrophic bacterial population density ranged from 10 x 10 2 to 10.5 x 10 3 cfu/ml in the test water (Table 3). After HyCator : BWT Reactor system treatment no living organisms were detected in deballasts water and the treated water met the D-2 regulation and IMO s ballast water discharge standards. The results showed that the hydrodynamic cavitation treatment system along with only 3 mg/l of sodium hypochlorite as an active substance was sufficient for the disinfection of ballast water and to prevent the regrowth of microorganism during the voyage period of the ship. The deballast water coming out of the ballast water treatment system complied with the Maximum Allowable Discharge Concentration (MADC) standard of TRO as Cl 2 i.e. less than 0.2 mg/l with the number of living organisms under standard of D2 regulation (Table 1). These results indicate that with the use of HyCator : BWT Reactor system along with 3 mg/l sodium hypochlorite we can effectively disinfect the ballast water and meet ballast water disinfection standards. Acute aquatic test Toxicity tests were intended to evaluate the effects of the preparations and their components on the organisms and the environment when released with treated ballast water or accidentally during the process. A comprehensive risk assessment analysis of the performance of the HyCator : BWT Reactor System was carried out in accordance with G9 Procedure. Several disinfection by-products such as trihalomethanes, haloacetic acids, haloacetonitriles, chlorate and bromate were identified as RC s along with STS used as a dechlorination chemical, when required. All these chemicals were investigated for their toxicity and other critical properties, either based on the results of literature search or by direct toxicity testing. The effects of treated water by the HyCator : BWT Reactor systems on various marine organisms were evaluated in various acute tests (OECD 201, 202 & 203) and summarized in Table 4. Acute ecotoxicity tests associated with HyCator : BWT Reactor System s treated ballast water covering multiple test species (a crustacean, an alga, and a fish) indicated no acute toxicity to any test organisms at discharge as compared to control water. Even full strength effluent (100%) did not reveal any significant deleterious effects on any of the test species in acute tests. There was no toxicity found in a trial with neutralization, providing no observed effect concentration (NOEC) of 100% for de-ballast water. Therefore, the de-ballasting water from HyCator : BWT Reactor System is expected to be non-toxic to aquatic organisms as well as to the marine environment in general. Bioavailability/ Biomagnification/ Bioconcentration The Bio Concentration Factor (BCF) is the best property of bioavailability, biomagnification, and bioconcentration. This ecotoxicological property characterizes the accumulation of pollutants through chemical partitioning from the aqueous phase into an organic phase, such as the gill of a fish. Generally, a high potential BCF is greater than 1000, a moderate potential BCF is less than a 1000 but greater than 250, and a low potential BCF is less than 250. Typical BCFs for organic chemicals in fish and most aquatic invertebrates are in the 500-1,000 L/kg range. The BCFs for Active Substance and Relevant Chemicals are all well below 1000 L/kg as presented in Table 5, indicating that they are unlikely to bioconcentrate/bioaccumulate in aquatic organisms. Thus, it is clear that the potential of bioaccumulation/bioconcentration is

8 2040 INDIAN J. MAR. SCI., VOL 43, NO.11 NOVEMBER 2014 negligible for free active chlorine and hypobromous acid/hypobromite ion generated from HyCator : BWT Reactor system. Risk Assessment Safety of ship Two major phenomena are identified as of potential safety concerns to a ship: (1) fire/explosion; and (2) ballast tank corrosion. Fire/explosion can cause immediate damage to a ship. Hydrogen gas generated is the only gas that may cause fire/explosion. Corrosion in ballast tank may damage the tank and eventually the ship. During the electrochlorination process, hydrogen gas (H 2 ) is produced as a by-product. Because hydrogen gas is highly explosive, it should be properly vented from system. The hydrogen gas produced in the electrolyser is immediately separated from side-stream water by means of a hydrogen gas separator (cyclone) before high hypochlorite concentrated water is injected into the main ballasting line. The separated hydrogen gas is diluted to less than 1% hydrogen by forced air blowers (non-sparking blowers) and vented to a safe area outside the ship. The lower explosive limit (LEL) for hydrogen is 4% and the operating limitations of the system therefore provide a fourfold safety factor. Regarding corrosion, both coated and uncoated steel specimens were tested over six months for corrosion in HyCator : BWT Reactor system treated and control ballast water. Based on the result of corrosivity test (Table 6) using the method as Weight of Variation, the little difference on epoxy-coated steel specimens was observed between control (untreated) and treated water. However, the statistical weight data difference of in the corrosive effect on epoxy-coated steel was due to increase the weight of specimen. Thus, the corrosive effect based on this result will not enhance the level of corrosivity of uncoated and epoxy-coated samples compared to those in Control water. Taken as a whole such as the result of corrosivity test and the level of chemicals, the corrosion of ballast tank or pipe etc. as part of ship by the HyCator : BWT Reactor system might not be enhanced when they are exposed to the seawater treated by the HyCator : BWT Reactor system Comparison and discussion In order to assess the performance and efficacy of developed HyCator : BWT Reactor system, it is compared with IMO approved ballast water management systems (BWMS) on the basis of treated water quality and toxicity related to DBP s (Table 7). The IMO approved chemical disinfectant based BWMS BlueWorld (MEPC62/2/3) 10, Smart Ballast (MEPC 62/2/8) 11 and SiCURE (MEPC 62/2/10) 12 utilizes hypochlorite of concentrations of 12 mg/l, 10 mg/l and 6 mg/l respectively whereas HyCator : BWT Reactor system utilizes only 3 mg/l which is around two to three times lesser than comparable systems. When the treated water analysis and toxicity tests of each BWMS are compared and it is observed that the HyCator : BWT Reactor system disinfects the ballast water as effectively as approved by BWMS, without producing acute toxicity related to active substance. The concentrations of the RCs and OCs generated through HyCator : BWT Reactor System is 2 to 3 times less in comparison with the other IMO 15, 16, 17 approved BWMS. Results of earlier studies shows that the by-products generated through approved BWMS are not harmful to aquatic and human life. The result of this study indicate that the physico-chemical ballast water disinfection method based on hydrodynamic cavitation (HyCator : BWT Reactor system) disinfects the ballast water in a way comparable to that by approved BWMS, but with two to three times less concentration of active substance (sodium hypochlorite) and without causing any harmful effects to aquatic and human life. HyCator : BWT Reactor system can be easily scaled up for operation to a very large scale especially as required for ballast water treatment. The device works on the principle of hydrodynamic cavitation creating a specific value of cavitation number which creates cavitation and mixing of the added active ingredient in the flowing liquid. The cavitation number is a dimensionless number and hence it is independent of the scale of operation (flow rate and the operating pressure and is only a function of geometrical similarities) and a unique value of cavitation number, as reproduced in a similar device at any scale of operation, ensures equivalent cavitation and mixing performance during a single pass through the cavitating device used in this trials. Therefore HyCator : BWT Reactor system is scalable to any flow rate of ballast water and can be applicable to all types of vessels. A major concern regarding the use of biocides is the safety of crew members who handle the chemicals. Due to less usage of chemical disinfectant by HyCator : BWT Reactor system, the human risk associated with disinfectants, the cost

9 SANGAVE et al.:ballast WATER TREATMENT USING HYDRODYNAMIC CAVITATION 2041 associated with disinfectants as well as its treatment and neutralization cost go down substantially. Thus the HyCator : BWT Reactor system becomes an environmentally safe and economical ballast water treatment system. Conclusion The newly developed novel hydrodynamic cavitation technique coupled with chemical disinfection is a promising technique for ballast water disinfection. Being a physico-chemical method, it uses very less chemical disinfectants. Maximum disinfection occurs inside the hydrodynamic cavitation system itself and the process does not result in the formation of any toxic byproducts, as is the case with chemical treatments. The data for the chemicals associated with the HyCator : BWT Reactor System indicate that; there is a low potential for bioaccumulation, sediment adsorption, and persistence in the aquatic environment. Also the system is safe to ship and crew members as no apparent risks could be identified. The HyCator Reactor System can be easily installed and have minimum maintenance and operation cost. It requires minimum foot print area as filtration and disinfection happen in single compact unit. In terms of the minimum requirement of disinfectants, environmental safety, capital costs, power requirements and footprint, the hydrodynamic cavitation technique appears better than various physical and chemicals disinfection methods available. References 1. Anil A.C., Venkat K., Sawant S.S., Dileepkumar M., Dhargalkar V.K., Ramaiah N., Harkantra S.N. & Ansari Z.A., Marine bioinvasion: concern for ecology and shipping. Current Science, 83(3) (2002) International Maritime Organization (IMO), 3. Balaji R. & Yaakob O. B., Emerging Ballast Water Treatment Technologies: A Review. Journal of Sustainability Science and Management, 6(1) (2011) Parsons M. G., Considerations in the design of the primary treatment for ballast systems. Marine Technology and SNAME News, New York, 40(1) (2003) M Gregg M., Rigby G. & Hallegraeff G. M., Review of two decades of progress in the development of management options for reducing or eradicating phytoplankton, zooplankton and bacteria in ship s ballast water. Aquatic Invasions, 4(3) (2009) Tsolaki E. & Diamadopoulos E., Technologies for ballast water treatment: a review. Journal of Chemical Technology and Biotechnology, 85 (2009) National Research Council (NRC) Report (1996). 8. Moholkar V.S. & Pandit A.B., Bubble behavior in hydrodynamic cavitation: effect of turbulence, American Institute of Chemical Engineers Journal, 43(6) (1997) Sawant S. S., Anil A. C., Krishnamurthy V., Gaonkar C., Kolwalkar J., Khandeparker L., Desai D., Mahulkar A. V., Ranade V. V. & Pandit A. B., Effect of hydrodynamic cavitation on zooplankton: A tool for disinfection. Biochemical Engineering Journal, (2008) Application for Basic Approval of the BlueWorld Ballast Water Management System. Marine Environment Protection Committee (MEPC) 62 nd session Agenda item 2 (MEPC 62/2/3) (2010). 11. Application for Basic Approval of STX Metal Co., Ltd. Ballast Water Management System (Smart Ballast). Environment Protection Committee (MEPC) 62 nd session Agenda item 2 (MEPC 62/2/8) (2010). 12. Application for Final Approval of the SiCURE Ballast Water Management System Submitted by Germany. Environment Protection Committee (MEPC) 62 nd session Agenda item 2 (MEPC 62/2/10) (2010). 13. G8 Guidelines: Guidelines for approval of ballast water management systems. 14. G9 Procedure: Procedure for approval of ballast water management systems that make use of Active Substances. 15. Hazardous Substances Data Bank (HSDB) (2010). 16. Toxicology Data Network (TOXINET) (2010). 17. Estimation Program Interface (EPI) Suite v Organization for Economic Co-operation and Development (OECD), OECD Guidelines for the Testing Of Chemicals. Freshwater Alga and Cyanobacteria, Growth Inhibition Test 202. OECD Publications, Paris (2006). 19. Organization for Economic Co-operation and Development (OECD), OECD Guidelines for the Testing Of Chemicals. Freshwater Alga and Cyanobacteria, Growth Inhibition Test 201. OECD Publications, Paris (2006). 20. Organization for Economic Co-operation and Development (OECD), OECD Guidelines for the Testing Of Chemicals. Freshwater Alga and Cyanobacteria, Growth Inhibition Test 203. OECD Publications, Paris (2006). 21. Estimation Program Interface (EPI) Suite v Hazardous Substances Data Bank (HSDB) (2011). 23. Toxicology Data Network (TOXINET) (201). 24. Screening Information Data Sets (SIDS) (2003).