Innovative solution addresses challenges faced by landfarming of oil sludge

Landfarming is a waste treatment process that ploughs oil-contaminated sludges into the soil, and while this practice is being increasingly abandoned around the world, it is still very popular in the U.S. With the heightened focus on environmental impact, what are the alternatives to the problem of landfarming?

MARK BATT-RAWDEN, Envorem

Petroleum industry activities unavoidably generate a large quantity of sludge, and the production rate has naturally increased, because of the ascending energy demand. This oily sludge has been shown to contain hazardous constituents that may negatively affect the environment and public health. Thus, treatment and disposal of this waste is a global issue. In the United States particularly, the most common method of disposal is landfarming, whereas in Europe, it is not permitted, and in the Middle East, the practice is increasingly being abandoned.

Yet, we can demonstrate why there is a better solution to managing oil sludge than the traditional landfarming method. Landfarming is a waste treatment process that basically ploughs oil-contaminated sludges into the soil. Contaminated soils, sediments or sludges are transported to the landfarming site, mixed into the soil surface, and periodically tilled to aerate the mixture. Although a liner is not a universal requirement for the process, it commonly uses a clay or composite liner to intercept leaching contaminants and prevent groundwater pollution.

However, in this age of increased environmental awareness, the effectiveness of landfarming must be questioned.

WHAT IS LANDFARMING?

Landfarming has been used for years in the managing and disposing of drill cuttings, oily sludge and other petroleum refinery wastes, using equipment that is typical of the kind used in agricultural operations. These landfarming activities cultivate and enhance the microbial degradation of hazardous compounds. As a rule of thumb, the higher the molecular weight, the slower the degradation rate.

During landfarming, the waste materials are typically placed as a layer on the ground surface with variable thickness. The waste is then tilled and amended with nutrients, to enhance biodegradation by naturally occurring bacteria. Reduction in hydrocarbon concentrations can be expected within weeks to months, depending on the initial concentration and composition of hydrocarbons and whether the soil conditions are optimized for biodegradation.

Once cleanup goals have been achieved, the treated material can be reused in construction activities, such as berms, landfill cover, backfill, regrading or agricultural purposes. Alternatively, the material can be disposed of at a landfill or left in place and revegetated, depending on local regulations or site-specific considerations.

There are apparent reasons why landfarming is such a popular solution. It is a low-cost technology, and facilities are simple to construct and easy to operate. Moreover, standard construction and farming equipment can be used to move soils to the land treatment facility, to amend the soils with fertilizer, to apply water to the grounds and to till the soils.

Despite its general acceptance, landfarming comes with its own problems. The primary concern is leaching, when contaminants enter groundwater, thus polluting it. Although there are already questions about the effectiveness of the technology in some situations, there are also doubts about whether the pollutants can be degraded, as many contaminants might be non-biodegradable, which can permanently damage the soil, Fig. 1. The pollution level is also a factor; extensive trials in Kuwait found that the microbes needed to degrade the oil would not survive if contamination exceeded 5%. Sludges generally have much higher levels of contamination. Furthermore, the process depends on nature; the conditions required for biodegradation are hostage to rainfall and temperatures, both of which being uncontrollable factors that can cause the remediation to fail.

ADOPTING A NEW APPROACH

Envorem has developed an innovative new technology that uses a little-known property of water to process production sludges, cleaning the soils and recovering the entrained oil without generating emissions. The ability of water jets to clean soft material from hard surfaces is well-known, and the concept of using high levels of kinetic energy, delivered by water, with various engineered techniques for industrial cleaning, is also well-established.

Cavitation is a phenomenon that creates high-energy and microscopic water jets that impact surfaces with immense force. When the pressure falls below the vaporization point of the water, it vaporizes, forming tiny bubbles. The bubbles rapidly collapse, releasing microjets and shock waves at pressures up to 9.6 MPa. Nearby surfaces are subsequently impacted with water at point forces as high as 500N and temperatures above 3,400^oK.

The Envorem technology combines cavitation and high kinetic energy within water to produce a comprehensive system that cleans oil-contaminated sand, silts and sludges. Within the technology, cavitation generators and the accelerated sand/silt particles cause cavitation bubbles to form within the sludges and on the particle surfaces. These rapidly collapse, impacting with high force, inverting emulsions, and driving contamination from the particle's surface into the water phase.

Cavitation and kinematic stripping are introduced at two separate stages of the process. In one step, some 200 KW of cavitation and kinetic energy, delivered through water, are focussed into a processing area that is roughly the size of a grapefruit. This energy input is equivalent to firing three professional bowling balls—at a speed close to that of an airliner—into that small area every second.

Millions of cavitation bubbles are artificially generated within the target material, and particles accelerate to 550 km/h. Clumps of particles are instantly disassembled, and hydrocarbons are ripped from the target material surfaces, both by the microjet impact and kinematic viscosity, as the particles accelerate. Liberated hydrocarbons and other contaminants are transferred from the particles to the water phase.

The accelerated particles inevitably impact slower-moving or stationary particles, rubbing each other and effectively scraping off molecules adhering to the surfaces. The effect could be likened to sandblasting or drawing a particle across a piece of sandpaper—albeit at speeds close to that of a jet airliner. When subjected to such intense abrasive action, any contamination adhering to the surfaces is rapidly removed.

The solution has already been tested in a highly successful pilot in Oman, for their national oil company (PDO), to treat sludge and oil-contaminated soil, Fig. 2. The pilot proved that the technology generates a fraction of thermal treatment emissions while being cheaper and faster. Ninety-nine percent of the oil was removed from sludge as crude of usable quality—a double benefit reducing the need for extraction and its associated carbon footprint, also saving emissions from disposal by incineration.

The pilot demonstrated that if the value of recovered oil is included, costs are potentially net positive, providing a financial and environmental case for a change in practice. This may finally provide an alternative to the growing problems that are associated with landfarming and therefore, benefit the planet as a whole. WO

MARK BATT-RAWDEN is an entrepreneur, business developer and engineer, having spent the last 12 years researching and developing systems for oil removal from sludge/soil. He is currently a managing director for Envorem, which he founded in 2019 with Mike Levey, who has a long history of treating industrial effluents.