Abstract

The occurrence of hypoxic muddy sediments on shallow beaches and other sheltered areas is a well-known environmental problem, which negatively affects coastal areas, tourism potential, the public use of beaches and sediment biodiversity. The usual solution is limited to dredging and removal of sludge to a landfill site. In this study, a laboratory-scale experiment was performed to determine the effectiveness of two technologies: a modification of air sparging and a new approach based on injecting oxygen-saturated seawater in hypoxic muddy sediments (oxygen-saturated seawater injections method), for remediating sludge in coastal sediments, minimizing environmental impact respect to dredging. Our results showed that both technologies significantly increased dissolved oxygen content in pore water, facilitating the oxidation of more than 90% of the organic matter, and other reduced inorganic compounds such as sulphide, with the consequent increase in sulphate concentration from 0.3 to 3.0 g·L⁻¹. Moreover, a rise of redox potential from − 258 mV to above 200 mV, and a dramatic drop in chemical oxygen demand were also indicators that oxic conditions had been restored. After 65 days, soft, black, muddy and hypoxic sediment with high organic matter content and a characteristic foul odour was transformed into well-oxygenated sediment, which had a low organic matter content and had lost its initial shiny black colour and odour. The main difference between both technologies was the depth influenced by sediment remediation; oxygen-saturated seawater injections affected deeper areas than clean pressurized air injections.

Graphical Abstract

中文翻译：

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氧饱和海水注入和空气喷射技术在修复沿海海洋淤泥沉积物中的有效性

摘要

浅滩和其他庇护区出现缺氧泥质沉积物是一个众所周知的环境问题，它对沿海地区、旅游潜力、海滩的公共利用和沉积物生物多样性产生负面影响。通常的解决方案仅限于将污泥疏浚和清除到垃圾填埋场。在这项研究中，进行了一项实验室规模的实验，以确定两种技术的有效性：空气喷射的改进和基于在缺氧泥质沉积物中注入氧饱和海水的新方法（氧饱和海水注入法），用于修复沿海沉积物中的污泥，最大限度地减少疏浚对环境的影响。我们的结果表明，这两种技术都显着增加了孔隙水中的溶解氧含量，^-1。此外，氧化还原电位从 - 258 mV 上升到 200 mV 以上，以及化学需氧量的急剧下降也表明有氧条件已经恢复。65 天后，软质、黑色、泥质、缺氧、有机质含量高且具有特征性恶臭的沉积物转变为含氧良好的沉积物，有机质含量低，失去了最初闪亮的黑色和气味。两种技术的主要区别在于受沉积物修复影响的深度；与清洁加压空气注入相比，氧饱和海水注入影响更深的区域。

图形概要