Heavy metals in coral reef sediments of Kavaratti Island, India: An integrated quality assessment using GIS and pollution indicators.

The present study aims to document the contamination levels and ecological risks of heavy metals in the sediments of Kavaratti lagoon, India. A total of 15 sediment samples were collected for the analysis of Al, Pb, Cd, Cu, Cr, Mn, Ni and Zn. The decreasing trend of heavy metals was observed in the lagoon sediment as Pb > Zn > Al > Mn > Ni > Cr > Cd > Cu. The Geo-accumulation index (Igeo) results indicate that Cu, Cr, Mn, Ni and Zn were uncontaminated, while Cd was strong to extremely contaminated and Al and Pb were moderately contaminated. The enrichment factors (EF) of Cd and Pb range from moderate to extremely high (EF > 1) indicating that they have anthropogenic origin on Kavaratti Island. The Contamination factor (Cf) indicated that Cd, Pb and Al belong to a high risk of contamination (Cf > 6). The pollution load index (PLI) value near one suggested that a moderate level of pollution occurs in the study area. The modified degree of contamination (mCd) shows that Al, Cd and Pb have an ultra- higher degree of contamination (mCd ≤ 32). The potential ecological risk (RI) index confirmed that Pb and Cd have considerable to the serious thread of ecological risk (RI > 600). Additionally, multivariate statistical analysis and pollution indexes showed that the Kavaratti lagoon is moderate to considerably polluted by heavy metals. Diesel-based power generation, activities related to shipping, untreated sewage, fishing and tourism activities are the main anthropogenic sources of heavy metal pollution on Kavaratti Island.

Grazing behaviour of tropical calanoid copepods and its effect on phytoplankton community structure.

The Netravathi estuary is a micro- to mesotidal, tropical, shallow estuary with an abundant density of phytoplankton. The impact of the zooplankton grazing rate and the selected environmental variables on the phytoplankton community structure was studied seasonally from 2017 to 2019. Microplanktons of centric diatoms such as Skeletonema costatum and Cosinodiscus radiatus dominated during monsoon seasons, whereas dinoflagellates such as Peridinium sp. and Ceratium furca were observed in high numbers at the estuary during non-monsoon seasons. Water temperature showed a strong association with grazing rates of microzooplankton (r = 0.910). Canonical correspondence analysis studies established an intensification in grazing rate during non-monsoon seasons by calanoid copepods which in turn occasioned the reduction of microplanktons belonging to diatoms. Moreover, during monsoon seasons, diminution in grazing rates of calanoid copepods coupled with the presence of micro larvae as a secondary consumer of zooplankton resulted in the proliferation of centric diatoms. The grazing behaviour of microzooplankton affected the phytoplankton species diversity of the estuary in a negative manner (D = 0.29 in 2017 Pre-M, D = 0.76 in 2019 Pre-M). Selective grazing behaviour of calanoid copepods concerning temperature alteration exerted a strong influence in determining the phytoplankton community structure of the estuary to a great extent.

Nickel(II) adsorption onto biomass based activated carbon obtained from sugarcane bagasse pith.

Bioavailability of Nickel in the form of hydrated Nickel(II) attributes to its toxicological effects and hence its removal from aqueous solution is of great concern. Adsorption is used as an efficient technique for the removal of Nickel(II), hereafter Ni(II), from water and wastewaters. Activated carbon obtained from sugarcane bagasse pith (SBP-AC), a waste biomass collected from juice shops in Sarkara Devi Temple, Chirayinkeezhu, Trivandrum, India during annual festival, is used as adsorbent in the study. The process of adsorption is highly dependent on solution pH, and maximum removal occurs in the pH range of 4.0-8.0. Moreover, the amount of Ni(II) adsorbed onto SBP-AC increased with the time increase and reached equilibrium at 4h. Adsorption kinetic and equilibrium data were analyzed for determining the best fit kinetic and isotherm models. The overall study reveals the potential value of steam pyrolysed SBP-AC as a possible commercial adsorbent in wastewater treatment strategies.

Adsorption of Pb(II) and Pb(II)-citric acid on sawdust activated carbon: Kinetic and equilibrium isotherm studies.

The removal of Pb(II) and Pb(II)-citric acid (Pb(II)-CA) from aqueous solutions by sawdust activated carbon (SDAC) was investigated. The higher adsorptive removal of Pb(II) from aqueous solutions containing Pb(II)-CA than Pb(II) only was observed due to the presence of CA in the former system. The mechanism of adsorption process was studied by conducting pH as well as kinetic studies. Batch adsorption experiments were conducted to study the effect of adsorbent dose, initial concentration and temperature for the removal of Pb(II) from Pb(II) only and Pb(II)-CA aqueous systems. The adsorption was maximum for the initial pH in the range of 6.5-8.0 and 2.0-5.0 for Pb(II) and Pb(II)-CA, respectively. The solution pH, zero point charge (pH(zpc)) and species distribution of Pb(II) and Pb(II)-CA were found to play an important role in the adsorption of Pb(II) and Pb(II)-CA onto SDAC from water and wastewaters. SDAC exhibited very high adsorption potential for Pb(II) ions in presence of CA than when Pb(II) ions alone were present. The kinetic and equilibrium adsorption data were well modeled using pseudo-first-order kinetics and Langmuir isotherm model, respectively.

Removal of phosphate from aqueous solutions and sewage using natural and surface modified coir pith.

Iron impregnated coir pith (CP-Fe-I) can be effectively used for the removal of phosphate from aqueous streams and sewage. Iron impregnation on natural coir pith was carried out by drop by drop addition method. The effect of various factors such as pH, initial concentration of phosphate, contact time and adsorbent dose on phosphate adsorption was studied by batch technique. The pH at 3.0 favored the maximum adsorption of phosphate from aqueous solutions. The effect of pH on phosphate adsorption was explained by pH(zpc), phosphate speciation in solution and affinity of anions towards the adsorbent sites. A comparative study of the adsorption of phosphate using CP-Fe-I and CP (coir pith) was made and results show that the former one is five to six times more effective than the latter. Kinetic studies revealed that the adsorption process followed a pseudo-second order kinetic model. Adsorption followed Langmuir isotherm model. Column studies were conducted to examine the utility of the investigated adsorbent for the removal of phosphate from continuously flowing aqueous solutions.

Removal of mercury(II) from aqueous solutions and chlor-alkali industry wastewater using 2-mercaptobenzimidazole-clay.

The 2-mercaptobenzimidazole loaded natural clay was prepared for the removal of Hg(II) from aqueous media. Adsorption of the metal ions from aqueous solution as a function of solution concentration, agitation time, pH, temperature, ionic strength, particle size of the adsorbent and adsorbent dose was studied. The adsorption process follows a pseudo-second-order kinetics. The rate constants as a function of initial concentration and temperature were given. The adsorption of Hg(II) increased with increasing pH and reached a plateau value in the pH range 4.0-8.0. The removal of Hg(II) was found to be >99% at an initial concentration of 50 mg/l. Mercury(II) uptake was found to increase with ionic strength and temperature. Further, the adsorption of Hg(II) increased with increasing adsorbent dose and decrease with adsorbent particle size. Sorption data analysis was carried out using Langmuir and modified Langmuir isotherms for the uptake of metal ion in an initial concentration range of 50-1,000 mg/l. The significance of the two linear relationships obtained by plotting the data according to the conventional Langmuir equation is discussed in terms of the binding energies of the two population sites involved which have a widely differing affinity for Hg(II) ions. Thermodynamic parameters such as changes of free energy, enthalpy, and entropy were calculated to predict the nature of adsorption. It was found that the values of isosteric heat of adsorption were varied with surface loading. The chlor-alkali industry wastewater samples were treated by MBI-clay to demonstrate its efficiency in removing Hg(II) from wastewater.