Fabrication and characterization of bio-nanocomposite films using κ-Carrageenan and Kappaphycus alvarezii seaweed for multiple industrial applications.

In the present study, the whole seaweed from Kappaphycus alvarezii (containing carrageenan) was used for preparation of bio-nanocomposite films by blending with metal oxide nanoparticles such as zinc oxide (ZnONPs), cupric oxide (CuONPs) and silicon dioxide (SiO2NPs) for multiple applications, and their properties were compared with standard refined κ-Carrageenan (commercial grade). Simultaneously, the antibacterial activity and biodegradation profile of the prepared bio-nanocomposite film were also studied. The incorporation of nanoparticles into the bioplastic film matrices altered the surface morphology, increased the roughness and significantly (p < 0.05) reduced the UV transmittance, water uptake ratio (WUR), moisture content and solubility in both standard carrageenan-based bio-nanocomposite films (CBF) and Kappaphycus- based bio-nanocomposite films (KBF) compared to control. The average roughness (Ra) of KBF increased compared to CBF; however, CBF showed better tensile strength compared to KBF. Both KBF and CBF loaded with nanoparticles exhibited strong antibacterial activity against Staphylococcus aureus and Escherichia coli. However, KBF performed better compared to CBF. Antimicrobial effect of nanoparticles delayed the degradation of the bio-nanocomposite films. The present study proposes that the whole seaweed (Kappaphycus alvarezii) can be used directly for multiple industrial applications.

Response of green mussels (Perna viridis) subjected to chlorination: investigations by valve movement monitoring.

Perna viridis Linnaeus (1758) is a major foulant in the cooling water systems of electric power stations located on the East coast of India. Though chlorination is considered an effective fouling control measure, the strategy may fail in the case of bivalve mussels, due to the ability of the mussels to close their shells and still survive for extended periods of time. In a given power station, continuous low dose (exomotive) chlorination (0.2 ± 0.1 mg l-1) is practiced to control biofouling. Laboratory experiments were carried out to assess the mortality and valve movement response of Perna viridis exposed to chlorine, using a Mosselmonitor®. All size groups tested showed progressive reduction in valve opening upon chlorination. However, continuous dosing of chlorine concentration as high as 1.0 mg l-1 was required for sustained and complete valve closure response in this mussel. At lower concentration (0.7 mg l-1), the mussels were able to open their shells and feed. Sustained valve closure resulted in physiological stress to the mussels due to reduced feeding, subsequently leading to death. Time to 100% mortality was dependent on the size of the mussels. At 1.0 mg l-1 chlorine residual, smaller size group (30-50 mm) mussels showed 100% mortality in 79.3 h, while larger groups (50-70 mm and 70-90 mm) took 152 h and 243 h, respectively. Frequency of valve opening was high in smaller size group mussels (30-50 mm), compared with larger groups (70-90 mm). Even though the time taken for killing was size-dependent, frequency of valve opening and time period between successive openings were found to be characteristic of individual mussels. The observations provide new insight into the response of bivalve mussels to continuous chlorination in the context of biofouling control and point to the need to adopt pragmatic strategies to prevent mussel spat settlement rather than killing of adult mussels, thereby reducing environmental burden due to chlorine residuals. Usage of target-specific biocidal strategies (intermittent/pulse dosing) or alternative biocides (chlorine dioxide) may help mitigate green mussel fouling in tropical cooling water systems.

Chlorine dioxide as an alternative antifouling biocide for cooling water systems: Toxicity to larval barnacle Amphibalanus reticulatus (Utinomi).

Chlorine dioxide (ClO2) is seen as an effective alternative to chlorine, which is widely used as an antifouling biocide. However, data on its efficacy against marine macrofoulants is scanty. In this study, acute toxicity of ClO2 to larval forms of the fouling barnacle Amphibalanus reticulatus was investigated. ClO2 treatment at 0.1mg/L for 20min elicited 45-63% reduction in naupliar metamorphosis, 70% inhibition of cyprid settlement and 80% inhibition of metamorphosis to juveniles. Increase in concentration to 0.2mg/L did not result in any significant difference in the settlement inhibition or metamorphosis. Treatment with 0.2mg/L of ClO2 elicited substantial reduction in the settlement of barnacle larvae compared to control. The study indicates the possibility of using ClO2 as an alternative antifouling biocide in power plant cooling water systems. However, more work needs to be done on the environmental effects of such switchover, which we are currently undertaking.

Chlorination induced damage and recovery in marine diatoms: Assay by SYTOX® Green staining.

Phytoplankton entrained into cooling water systems of coastal power stations are subjected to acute chemical stress due to biocides (chlorine) used for biofouling control. They are subsequently released into the environment, where they may survive/recover or succumb. Experiments were conducted to evaluate the susceptibility of a centric (Chaetoceros lorenzianus) and pennate (Navicula sp.) diatom to in-plant administered concentrations of chlorine (0.2-0.5mg/L, TRO). Viability of cells exposed to chlorine was assessed by SYTOX® Green fluorimetry and was compared with other conventional end points like total cell counts, chlorophyll a content and cellular autofluorescence. Results showed a concentration-dependant reduction in viability, chlorophyll a and autofluorescence. C. lorenzianus cells were more susceptible to chlorine compared to Navicula sp. SYTOX® Green staining appears to be a sensitive method to assess chlorine-induced damages. The data show that in-use levels of chlorination can potentially impact entrained organisms; however, they can recover when returned to coastal waters.