Application of Electrocoagulation and Electrolysis on the Precipitation of Heavy Metals and Particulate Solids in Washwater from the Soil Washing

Soil washing, ex situ mechanical technique, is one of the few permanent treatment alternatives to remove metal contaminants from soils by employing physical separation based on mineral processing technologies to remove discrete particles or metal-bearing particles and/or chemical extraction based on leaching or dissolving process to extract the metals from the soils into an aqueous solution. However, washwater remained from soil washing process contains discrete particulate particles along with heavy metals as solution phase to be treated separately, as well as this process can produce large amount of sludge that requires further treatment, slow metal precipitation, poor settling, the aggregation of metal precipitates. Electrical treatments including electrocoagulation and electrolysis can be effective in removing these substances from washwater. This paper reviews the theoretical models in applying electrocoagulation and electrolysis to remove heavy metals and discrete particulate particles in washwater by examining and comparing the status of washwater treatment technologies which have been undertaken, mostly in the US and EU for the period 1990-2012.

A Novel Approach to Reduce the Environmental Footprint of Maritime Shipping

Maritime shipping is a strategic sector with a strong international vocation and management.The need to define regulations valid for many different countries without generating disparities of treatment slowed down the formulation of environmental regulations,especially for atmospheric emissions.In particular,regulations pertaining to the reduction of sulphur compounds allowed two distinct approaches:the use of low-sulphur fuels or exhaust gas cleaning systems,the so-called Scrubbers.The actual implementation of these solutions presents specific concerns either related to the toxicity of atmospheric by-products and to the fuel cost or to the generation of polluting washwaters that may need treatment before discharge.In this paper we analyzed the potential environmental benefit deriving from the use of a distillate fuel,not compliant with current IMO Sulphur Regulations,together with a Scrubber.The pilot-scale experimental results indicated that a limited amount of water and/or scrubber volume is needed to reduce sulphur emissions below regulations on maritime shipping,especially with the addition of NaOH reaching a water-saving between 25%-33%compared to the use of pure seawater.Experiments indicated that scrubber washwater PAHs emissions are within the available water quality standards indicated by EU and USA guidelines.A bottom-up analysis on heavy metals concentration shed light on the prominent role of metal-parts corrosion on the washwater emissions.Taking into account for corrosion phenomena,the actual heavy metals concentration in the washwater deriving from scrubbing was normally below the water quality standards.