electro-osmosis

The 2nd China-US Workshop on Ground Improvement Technologies, Shanghai, China, May 27, 2018

electro-osmosis dewatering and electrokinetic geosynthetics

Yan-Feng Zhuang, Maggie L. White, Claire I. Fialips

Abstract
Laboratory experiments have shown that reducing iron in smectites promotes the degradation of various redox sensitive organics, including nitroaromatics and chlorinated compounds. Fe-bearing smectites have however never been used in the design of permeable reactive barriers (PRBs) for groundwater remediation. One basic requirement when designing PRBs is to keep their permeability equal to or higher than that of the surrounding aquifer materials to avoid affecting groundwater flow. Smectite clays are very low permeability materials and, when physically mixed with permeable materials, such as sand, clay particles can migrate and clog up pores, resulting in a progressive loss in permeability. In this study, we are developing a novel Fe-bearing clay-material suitable for permeable water treatment systems, including PRBs. Fe-smectite particles are tightly attached to the surface of sand grains using polyvinyl alcohol (PVA). To identify optimum procedures, we are studying the relationships between the size and texture of the sand grains, the clay/PVA and clay/sand ratio, the quality and extent of clay coverage, the stability of the clay-coated sand to changes in pH and redox conditions, and its hydraulic properties before and after iron reduction. The best clay coatings have been obtained using the most angular sands with rough surfaces and medium grain sizes (0.3-0.6mm). An optimum coating of 61.5 mg clay/g sand was obtained using the nontronite Nau- 2. The clay-coated sand is stable when pH is below 7 (no detachment of the clay particles). For pH higher than 7, a maximum of 14% of the clay-coating is detaching when the sample is not disturbed, and 28% if shaken. XRD analyses of the clay-coated sand also show that the coated smectite retains its swelling properties (d-spacing at 17.1Å after ethylene glycol treatment). The clay-coated sand is also stable to changes in redox conditions, with less than 15% detachment after 4h of treatment with sodium dithionite at 25°C. The coated clay is reducible, with a maximum reduction level of 83% (Fe(II)/Fe total). The hydraulic properties of the clay-coated sand are suitable for use in permeable systems. The effect of the reduced clay-coated sand on the degradation of redox-sensitive organics will be tested using nitrobenzene.

Development Of A New Redox-Active Porous Material For Groundwater Remediation

Yan-feng Zhuang, Zhitao Liu, Zhengxin Li, Hongwei Wang, Tong Yang, Ganglin Li. Upward gradient EKG and electro-osmosis for deep soft ground consolidation. 11th International Conference on Geosynthetics, 16th-21st September, 2018, KGSS, Seoul, Korea. (Flash Disk, paper SS3-01)

ABSTRACT:
Electro-Kinetic Geosynthetics (EKG) presents a new category of geosynthetics. It inspires enthusiasm to apply electro-osmosis (EO) in large scale engineering applications, such as soft ground improvement, sludge dewatering, soil remediation, etc. This paper presents a kind of specially designed EKG and DC power source to carry out electro-osmotic consolidation for soft ground in vertical direction instead of horizontal direction. It is aiming at providing a better consolidation effect without degradation along depth for deep soft ground improvement. In-situ experiment shows that bearing capacity of the hydraulically filled sludge could be increased to 80-90 kPa after upward gradient electro-osmosis treatment and consolidation effect along depth is more homogenous than that of horizontal electro-osmosis using normal E-board. Development of EKG materials and automated DC power source are two key breakthroughs that pushing forward both researches and applications EO technique, which has over 200 years of history already.

Keywords: Electro-osmosis; EKG; consolidation; soft ground improvement

Upward gradient EKG and electro-osmosis for deep soft ground consolidation

Yan-feng Zhuang. Application of Novel EKG and Electro-osmosis in Hydraulically Filled Sludge Dewatering and Consolidation. Proceedings of 61h Asian Regional C onference on Geosynthetics, “Geosynthetics for Infrastructure Development”, 8th-llth Nov. 2016, in New Delhi. India. Central Board oflrrigation & Power
(CBIP), New Delhi. India: KN-55 ~ KN-63. (Keynote)

ABSTRACT

Electro-Kinetic Geosynthetics (EKG) inspires enthusiasms for research on electro-osmosis. Mechanically dewatering of hydraulically filled sludge is difficult due to low hydraulic permeability of sludge, while electro-osmosis provides a promising solution. Two types of EKG, E-board and E-tube, are developed for sludge dewatering. EKG solved the problem of electrode corrosion and new challenges is high electric power requirement. Energy level gradient theory is presented as a fundamental theory to propose design method for sludge dewatering. Key parameters of flow coefficient and time factor are discussed, including their test method, value range and scale effect. Roll polling electro-osmosis scheme is the solution for high power requirement. Estimation of power and design of roll polling electro-osmosis scheme is core of electro-osmotic dewatering design. Novel DC power source is custom built to realize the roll polling scheme. The DC power source of 80V/1000A has roll polling program embedded and it is in charge of 12 independent sections, which can deal with ~2000 square meters of hydraulically filled area.

Application of Novel EKG and Electro-osmosis in Hydraulically Filled Sludge Dewatering and Consolidation

ABSTRACT: A hydraulic reclaimed sludge of 19m long, 15m wide and 5.8m deep was treatedusing electro-osmosis technique. A novel Electrokinetic Geosynthetics (EKG) and automated electric power source was developed for the electro-osmotic consolidation. It took only 36 days to reduce water content from 62% to 36% and it would take 3 years for preloading consolidation to achieve the same effect. After the treatment, bearing capacity of the fluid-like sludge was increased to 70kPa. Besides EKG materials, design of electro-osmosis scheme is the key issue for the success of electro-osmotic consolidation. Issues of energy consumption and cost and challenges in large scale applications are discussed after presenting experience with the EKG.

Keywords: Electro-osmosis; EKG; consolidation; reclamation

Case Study on Hydraulic Reclaimed Sludge Consolidation Using Electrokinetic Geosynthetics