Abstract
In this study, initial minimum inhibitory concentration (MIC) of Pb(II) ions was analysed to check optimum concentration of Pb(II) ions at which the growth of sulphate-reducing consortium (SRC) was found to be maximum. 80 ppm of Pb(II) ions was investigated as minimum inhibitory concentration for SRC. Influence of electron donors such as lactose, sucrose, glucose and sodium lactate was examined to investigate best carbon source for growth and activity of sulphate-reducing bacteria. Sodium lactate was found to be the prime carbon source for SRC. Later optimization of various parameters was executed using Box–Behnken design model of response surface methodology to explore the effectiveness of three independent operating variables, namely, pH (5.0–9.0), temperature (32–42 °C) and time (5.0–9.0 days), on dependent variables, i.e. protein content, precipitation of Pb(II) ions, and removal of COD by SRC biomass. Maximum removal of COD and Pb(II) was observed to be 91 and 98 %, respectively, at pH 7.0 and temperature 37 °C and incubation time 7 days. According to response surface analysis and analysis of variance, the experimental data were perfectly fitted to the quadratic model, and the interactive influence of pH, temperature and time on Pb(II) and COD removal was highly significant. A high regression coefficient between the variables and response (r2 = 0.9974) corroborate eminent evaluation of experimental data by second-order polynomial regression model. SEM and Fourier transform infrared analysis was performed to investigate morphology of PbS precipitates, sorption mechanism and involved functional groups in metal-free and metal-loaded biomass of SRC for Pb(II) binding.
Highlights
IntroductionIndustrialization and urbanization have resulted in a phenomenal increase in metallic contents in the environment and has emerged as a worldwide environmental problem
Industrialization and urbanization have resulted in a phenomenal increase in metallic contents in the environment and has emerged as a worldwide environmental problem.Heavy metals are innate constituents of the earth’s crust.Some are fundamental micronutrients for life, but at elevated concentrations they induce rigorous poisoning.Heavy metals are recalcitrant and in no way degrade in environment, but are only transformed and transferred (Satyawali et al 2011; Hashim et al 2011; Barka et al.2013)
In this study, initial minimum inhibitory concentration (MIC) of Pb(II) ions was analysed to check optimum concentration of Pb(II) ions at which the growth of sulphate-reducing consortium (SRC) was found to be maximum. 80 ppm of Pb(II) ions was investigated as minimum inhibitory concentration for SRC
Summary
Industrialization and urbanization have resulted in a phenomenal increase in metallic contents in the environment and has emerged as a worldwide environmental problem. Inorganic form of lead is reviewed as a metabolic poison and enzyme inhibitor; still, organic forms of Pb(II) are extremely noxious (Anayurt et al 2009; Javanbakht et al 2011) Several methodologies such as chemical oxidation, electrocoagulation, electrodeposition, filtration, adsorption, chemical precipitation, solvent exchange, photo-degradation and membrane separation technologies have been explored long ago to mitigate recalcitrant heavy metals from adulterated wastewater (Verma et al 2013; Rasool et al 2013; Kumar et al 2014; Zewaila and Yousef 2015). Sulphate-reducing bacteria (SRB) metabolize organic matter in rigorous anaerobic environment using sulphate as an electron acceptor and subsequently results in generation of hydrogen sulphide and bicarbonate This biogenic sulphide quickly reacts with heavy metal ions and transforms them into insoluble metal sulphides (Bratkova et al 2013; Hao et al 2014). The presence of black precipitates and foul odour of hydrogen sulphide was examined which indicates the presence of sulphate-reducing microbial consortia proficient in precipitating metal ions
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