Lead Remediation

The increasing influx of heavy metals into water bodies from industrial, agricultural, and domestic activities is of global concern because of their well documented negative effects on human and ecosystem health. A recent study of streams in Blantyre and Zomba, Malawi revealed lead levels of up 0.118 mg/L, exceeding the World Health Organisation acceptable level of 0.01 mg/L. Our ongoing study on low cost effective heavy metal remediation techniques in developing countries has already demonstrated that Moringa oleifera , the well-known source of natural water clarifiers, is effective in heavy metal detoxification of water. This paper presents the first reported use of a related species, the African moringa, Moringa stenopetala for lead detoxification and preliminary investigation of the interaction of the metal with the polyelectrolytes of M. oleifera and stenopetala . The potential of M. stenopetala for lead removal was tested by means of jar tests. With an initial lead concentration of 7 ppm, M. stenopetala seed powder, at doses of 0.50, 1.00, 1.50, 2.00 and 2.50 g/100ml, reduced the concentration of lead by 20.00 ± 0.00, 46.19 ± 2.06, 71.19 ± 2.06 and 89.43 ± 0.60 and 96.23 ± 0.12 % respectively. M. stenopetala was more effective than M. oleifera in removing lead from water (p=0.001 at 95% confidence level). For oleifera , lead levels decreased exponentially during the first 5 h of the reaction and then equilibrium was established; for stenopetala , a linear decrease was observed. The pH of the mixture rose from 2.30 to a maximum of 2.53 and 2.57 and then fell to an equilibrium value of 2.30 and 2.29 for oleifera and stenopetala respectively. Lead removal was also affected by pH, ionic strength, and water hardness. Our results show that M. stenopetala has potential in lead remediation of contaminated waters. Further studies are being carried out on remediation of other metals and the mechanism of the metal - moringa interaction.

OBJECTIVE To assess householders' satisfaction with the process of residential lead abatement in an urban Australian population. METHOD The study area consisted of suburbs immediately surrounding a lead-related industry on Australia's east coast. Nineteen of 20 remediated households in the study area agreed to participate in the survey. One trained interviewer conducted semi-structured qualitative interviews with one 'key' person from each remediated household. Participants were asked for their personal views as well as general household views about the rationale for, process and results of lead remediation. RESULTS The 19 households varied from three to seven people and contained 1-5 children (16 years or under). The opinions of residents of remediated households were polarised, with the majority being either greatly satisfied or greatly dissatisfied with the process. Level of satisfaction was clearly linked to perceived quality of the remediation works. CONCLUSIONS Satisfaction with household lead remediation could be improved by ensuring effective communication between all parties; providing clear, simple, but detailed information about the remediation works to be undertaken on each household; providing timely support for householders when problems arise; and ensuring that all contractors are skilled, reputable and have acceptable communication skills.

Heavy metal contamination during the rapid urbanization process in recent decades has notably impacted our fragile environments and threatens human health. However, traditional remediation approaches are considered time-consuming and costly, and the effect sometimes does not meet the requirements expected. The present study conducted test tube experiments to reproduce enzyme-induced carbonate precipitation applied to lead remediation under the effects of urease concentration and a calcium source. Furthermore, the speciation and sequence of the carbonate precipitation were simulated using the Visual MINTEQ software package. The results indicated that higher urease concentrations can assure the availability of CO3 2− during the enzyme-induced carbonate precipitation (EICP) process toward benefiting carbonate precipitation. The calcium source determines the speciation of carbonate precipitation and subsequently the Pb remediation efficiency. The use of CaO results in the dissolution of Pb(OH)2 and, therefore, discharges Pb ions, causing some difficulty in forming the multi-layer structure of carbonate precipitation and degrading Pb remediation. The findings of this study are useful in widening the horizon of applications of the enzyme-induced carbonate precipitation technology to heavy metal remediation.