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1
Batch reactor design for algal biosorption of mercury-contaminated acidic water in the presence of competing ions

( Rosamond Tshumah-mutingwende ),( Fumitake Takahashi ),( Ewa Cukrowska ),( Julien Lusilao-makiese ) 한국폐기물자원순환학회(구 한국폐기물학회) 2017 한국폐기물자원순환학회 심포지움 Vol.2017 No.1
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The anthropogenic release of mercury, a known mutagenic and teratogenic element, is by far the largest threat to the well-being of ecosystems and human health. The rudimentary and unscrupulous operations of conventional miners and Artisanal and Small scale Gold Miners (ASGM) in Zimbabwe have led to an unprecedented increase in mercury exposure to humans through the contamination of potable water sources. Reports of elevated blood levels of mercury in human blood and hair and the general deterioration of affected rivers are evidence of a rising problem. One such river is Ngwabalozi River in Mzingwane District in Zimbabwe. An area of concern for Ngwabalozi River is the high mercury levels of 0.31 mg L-1 and low pH of 3. The cyanidation technique for gold recovery used at a nearby conventional mine, How Mine, results in the release of other heavy metals such as iron and copper from the gold ore. The discharge of mine waste water rich in heavy metals and sulphates; and the use of nitric acid by artisanal miners for the removal of impurities from the gold-mercuiy amalgam have contributed to the low pH of the water. This has made the water in Ngwabalozi river unsuitable for irrigation and domestic use. Hence, the purpose of this study is to design a 1000 L batch reactor for the adsorption of mercury from acidic waters. Due to the myriad of chemicals used by small scale gold miners and conventional mines, mercury abatement by algal adsorption must consider the presence of potentially competing metal cations. From the foregoing, adsorption kinetics in the presence of Fe2+, Cu2+, Zn2+, Co2+ cations were studied. Single component (Hg only) batch experiment adsorption studies displayed a rapid uptake of mercury. More than 99% of the Hg in solution was removed within the first five minutes of contact and equilibrium was attained after ten minutes. High adsorption capacities (up to 800 mg kg-1 at pH 3) were obtained at the optimum Hg concentration of mg 1-1. The experimental data fitted very well with the pseudo-second order kinetics model. In competitive adsorption studies, a maximum extraction efficiency of 67.2% was obtained after 60 mins of contact at pH 3 and initial metal cation (Hg2+, Fe2+, Cu2+, Zn2+, Co2+) concentration of 1.0 mg L-1. The selectivity of metal cations by Cladophom sp. was in the following order: Hg2+ > Fe2+> Cu2+> Zn2+ > Co2+. The effect of the presence of Cu2+, Zn2+ and Co2+was negligible. The adsorption data was modelled on the multicomponent Freundlich, Langmuir and Sips equilibrium isotherm models. Nonlinear regression and Solver were used to determine the best fit equation. Using the equilibrium mass balance equation, scaling up revealed that the mass of algae required to reduce Hg2+ in presence of Fe2+ to the WHO standard of 0.006mg L-1 ranged from 13.4 kg to 54.7 kg for a minimum and maximum initial Hg2+ and Fe2+ concentration of 0.25 mg L-1 and 1.0mg L-1 respectively; for a contact time of 60mins in a 1000 L batch reactor.
2
Quantitatively scaled negative impression of mercury: A comparison with other hazardous materials and events

( Fumitake Takahashi ),( Rosamond Tshumah-mutingwende ) 한국폐기물자원순환학회(구 한국폐기물학회) 2018 한국폐기물자원순환학회 심포지움 Vol.2018 No.1
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Mercury has been concerned more and more as a persistent toxic substance. In this context, international efforts have been paid to assess mercury risk to human health and the environment. Minamata convention on mercury was agreed in Oct. 2013 and took effect in Aug. 2017 in order to internationally control mercury applications, emission to the environment, and promote final disposal of recovered mercury in environment-safe manners. Environmental risk assessment of mercury landfill disposal is necessary to design appropriate landfill methods. In addition, it is also helpful to build public acceptance of mercury landfill site construction. Because mercury must be immobilized before landfill disposal, treatment facilities for mercury stabilization is also necessary as well as landfill sites. This means that public acceptance to construct mercury treatment facilities is also a necessary process in terms of mercury management. In general, it is easily expected that building public acceptance to construct a mercury treatment facility and a mercury landfill site is difficult owing to potential hazards and high toxicity of mercury. As a first step to evaluate difficulty to build such public acceptance, this study aims to quantify how much negative impression people have to mercury when it is compared to other hazardous materials and events. Negative impression of mercury was compared to those of radioactive wastes, infectious medical wastes, dioxin, cadmium, PM2.5 (particulate matters causing air pollutions), ultraviolet light (UV), noise, and gene-altered foods. Negative impressions of those materials and events were scaled quantitatively by pairwise comparison method with Thurstone’s law of comparative judgement. All pairs of tested subjects were presented to quenstionees one by one. Questionees selected a subject with worse impression for them. Questionnaire survey was conducted online on March 22-23rd, 2018. Selection data was collected from 1030 persons. Gender of respondents were balanced equally. The ages of respondents were from 20’s to 60’s and also balanced equally with 10-year interval. Selection ratio of each tested subject as worse impression were converted correspondingly to Z score based on Thurstone’s law of comparative judgement. Higher Z score means less negative impression. The result of web-questionnaire survey is shown in Figure 1. The subject with the worst negative impression is radioactive wastes. It agrees with our expectation because of severe social conflicts on radioactive wastes management since Fukushima nuclear plant accident in 2011. Mercury has the second worst impression compared to other materials and events. It can be explained by Minamata disease caused by mercury and its social conflicts still have remained in Japan. Although cadmium also caused public hazard, which was kidney failure and following bone softening with severe pains (itai-itai disease), people’s impression to cadmium is better than mercury. When dioxin emissions from combustion facilities like waste incinerators was reported, it gave large impacts on Japanese society (dioxin shock). However, its impression is also better than mercury. This result suggests large difficulty to construct mercury treatment facilities and landfill sites for future mercury management. It also suggests to us that mercury is regarded as severer pollutant than dioxin and other hazardous materials/events in Japan. Gaps between real toxicity and perceptual toxicity of mercury and other pollutants would be further study in terms of environmental education.

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