Sludge Problem? What Sludge Problem?

By David Martin, P.E.
January 1999

The Author, a civil-sanitary engineer with over 40 years of experience, is responsible for engineering analysis and design of municipal and industrial wastewater treatment systems at LAS International Ltd in Bismarck, USA

Wastewater sludge. What to do with it. Dewatering, conditioning, storage, hauling and final disposal – it all adds up to significant manpower, capital costs and operating expenses including a good deal of equipment, supplies and chemicals. Even more troublesome, where do you put it? Landfills are costly and limited in capacity. Incineration has its own staggering costs and complexities. Land application is running into resistance and regulatory issues. Everywhere you look things are becoming more and more difficult, complex and expensive when it comes to wastewater sludge.

What if someone were to tell you that there are hundreds upon hundreds of towns, cities and industries processing wastewater each and every day without producing any sludge for removal or disposal? What if they told you that these towns, cities and industries have been treating their wastewater for the past 30 to 40 years with systems that simply "self-digest" the sludge at no cost and with no operator attention? Might sound too good to be true given the huge expenditures suggested to address current and proposed curtailments of certain sludge disposal methods.

In fact, it is true. A wastewater treatment process little known or understood in the UK has been used for large cities, small villages, towns, and industries of every type for over 40 years. The process, known as the facultative biological process, is used throughout the world and is by far the most prevalent method of wastewater treatment of any kind throughout North America from the far reaches of Northern Canada to the many different climates of the U.S. The process, which has been the fundamental method nature employs for the breakdown of wastewater since the beginning of time, was first discovered as a controllable process almost 50 years ago in the U.S. state of North Dakota. Since that time it has spread throughout North America and the world – that is, other than the UK.

Twenty-three years ago, LAS International, whose global headquarters is located in North Dakota (with offices in the UK), pioneered the use of this fundamental biological process in advanced, high-rate systems that eliminated many of the perceived compromises or shortcomings of the essential process itself. Wastewater treatment plants (generally using no pre-screening of any type, by the way) that have been in operation for years produce no excess sludge requiring any handling, conditioning, removal or disposal. This includes treatment works for beef packing facilities, chicken and poultry plants, food processors, and everyday municipal sewage.

In the facultative process all heavy solids entering the system are allowed to settle out in the primary stage of treatment. The soluble components are treated with aerobic bacteria in the upper strata, while the sludge component settles out into a "capped" and non-disturbed anaerobic digestive zone at the bottom of the cell. The adaptive bacteria begin the conversion/digestion of the entire sludge blanket into primarily gasses – methane, hydrogen sulphide, carbon dioxide and ammonia, which in turn are used as a partial food source by the aerobic bacteria. The sludge blanket grows to only a few centimetres initially where, if conditions are right, it will go into a steady-state condition where the materials are digested as fast as they enter the system.

While this process is not as fast as activated sludge, it is effective. Long term studies show that facilities that have been in operation since the mid 1950s or early 1960s have accumulated only centimetres of total sludge (inerts and all) without any effort or cost on the part of the operators. A ten-year study by the U.S. state of Kentucky's regulatory agency on a municipal/industrial facility that had been converted from a conventional plant to a facultative-based system documented that the total sludge blanket at the bottom of the cells remained virtually unchanged in volume over that 10-year period. The effluent continually met a <10/15 BOD/TSS during that same period.

Does this mean that all facultative-based systems can operate without eventually requiring sludge removal? Not necessarily. The design must be correct and the overall biological conditions must be maintained. This is where LAS International has spent nearly a quarter of a century perfecting the use of the process as a basis for its proprietary systems, the Aero-Fac® and Accel-o-Fac© treatment systems. As an example, the small community of Charlo, Montana located in the scenic Rocky Mountains had a conventional lagoon-based facultative system treating the population's wastewater for many years. However, the cells had developed an accumulation of sludge and it was growing. Effluent quality was also erratic with some occasional odour problems. Three years ago, the community elected to convert the system to the improved LAS Accel-o-Fac© system utilising free wind power as its primary energy source. The sludge blanket prior to installation of the zero-to-low-energy-cost system measured 75-90 cm. After only three years of operation, the Accel-o-Fac© system reduced the sludge blanket to less than 35 cm. This was accomplished with minimal operating costs over and above the previous system. Charlo now has a completely self-digesting wastewater treatment facility that requires no significant operator attention or cost to enjoy the benefits of ignoring sludge altogether, both now and into the future.

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