Afteruse development of former landfll sites in Hong Kong

Landfll is one of the major methods in disposing of municipal solid waste(MSW) in Hong Kong. There are now 13 closed landfll sites in Hong Kong, and a restoration program has been launched since 1999 to transform the closed landfll sites back into recreational area. The MSW underneath these closed landfll sites will biodegrade slowly and gradually, releasing toxic gases and leachate. As there have only been a few afteruse development ever completed in Hong Kong, this paper describes the consideration in planning and design of two former landfll sites in Hong Kong–Ngau Chi Wan(NCW) and Jordan Valley(JV) landflls, in particular a discussion on the MSW settlement. Various models in predicting the longterm MSW settlement have been available. This paper reviews the applicability of these models to predict MSW settlement. However, as the predicted settlements can be signifcantly in error, they need sitespecifc calibration and validation. This paper therefore presents the settlement monitoring data in these former landfll sites over the last 30 years, and suggests modifying the Bjarngard and Edgers’ method for estimating this long-term settlement as well as the effect of additional surcharge due to afteruse development. Based on the regression of these data, compression indices Cce and C at different stages of the settlement in the modifed method have been calibrated and validated.

A review on the chemical speciation and influencing factors of heavy metals in Municipal Solid Waste landfill humus

Heavy metal pollution in landfill humus can cause serious environmental problems and may endanger soil ecosystems and human health.The biological toxicity of heavy metals is not only related to their total amount but also influenced to a greater extent by the distribution of their chemical speciation.Exploring the different chemical speciation and proportions of heavy metals can provide a more comprehensive and accurate understanding of the pollution characteristics and biological toxic-ity of heavy metals in landfill soil.Based on a review of the relevant literature,this paper systematically summarizes the recent research status of typical heavy metal chemical speciation in landfill humus.This chemical speciation is diverse and complex.For instance,heavy metals in residual states and organically bound states have little impact on organisms,while heavy metals in exchangeable states and Fe-Mn oxide states can easily migrate and transform.The chemical speciation of heavy metals is affected by many factors,among which the soil pH and organic matter content are some of the most important factors.Finally,the existing gaps in the current research on the chemical speciation of heavy metals in landfills are described and future research directions are proposed.This work provides a theoretical reference for researching the restoration of heavy metal-contaminated humus soil and the resource utilization of humus soil.