Innovation in Wastewater Sludge Dewatering
Which Sludge Dewatering Technology Best Fits Your Needs?
Sludge handling/disposal costs are one of the three major O&M costs every wastewater facility faces. The sludge dewatering system has a big impact on these costs. For years sludge dewatering has been dominated by just a few equipment options. Most facilities built in the early 1970s had cumbersome vacuum filter systems which gave way to early generation centrifuges and belt filter presses. Through much of the 1980s and 1990s belt filter presses were the most common dewatering equipment. Over the past few years there have been numerous improvements and innovation in sludge dewatering equipment.
There are now several dewatering alternatives available to treatment facilities. Each option has its advantages and disadvantages and range of optimum applicability. Before upgrading to new equipment you should explore all your options. Highlights of some of the major options available today are summarized below.
Belt Filter Presses
Belt filter presses have been the industry standard for many years and continue to be a suitable alternative for many plants. There are many manufacturers of presses and there have been many improvements with these systems over the years. While these systems are relatively simple to operate and most plant operators are familiar with them, they are more difficult to contain for odor mitigation.
Centrifuges
Centrifuges have been around for a long time and the latest generation of equipment is vastly superior to early generations of centrifuges. There are several reliable manufacturers of centrifuges. While they are a speed dewatering device (typically about 3000 rpm) requiring the need for regularly scheduled maintenance work, these systems are remarkably reliable and operator friendly. Their flexibilty handles changing sludge conditions and they perform well in straight activated sludge applications. Centrifuges often produce the driest sludge cake. They are also self contained, making odor control easier. Wright Pierce has recently designed centrifuge systems for a number of large plants with incinerators and for several smaller and mid-sized plants that do not have primary sludge.
Rotary Disc Press
The rotary disc press technology is a relatively new technology introduced a number of years ago by Fournier Industries, a Canadian manufacturer. The technology has been recently modified and other manufacturers have been introduced to the market. This system involves feeding flocculated sludge between two parallel, rotating screens within each disc assembly which rotate very slowly on a single shaft (typically between 1 and 3 rpm). The dewatering equipment can contain from 1 to 6 discs assemblies per unit. Operators of these systems like the slow rotational speed and the fact that they are self contained. These systems work best with a significant primary sludge fraction.
Inclined Screw Press
The inclined screw press technology was introduced to the treatment plant market in Europe well over a decade ago by Huber Technology, a German manufacturer. This system involves feeding flocculated sludge into an inclined screw rotating
inside a stainless steel wedge wire screen. Like the rotary disc press, the screw press is self contained and operates at a very slow operational speed.
Horizontal Screw Press
The horizontal screw press is very similar to the inclined screw press, except that it is configured in a horizontal arrangement. Generally the horizontal press is considered where there are higher capacity requirements and a need for a custom designed press to match anticipated sludge quantities. FKC, a Japanese manufacturer, had marketed these for years in the pulp and paper industry as well as other industrial sectors, and more recently they have been marketing these to municipal treatment plants. The FKC press can also be configured to stabilize the sludge with quick lime and steam to produce a Class A Biosolids. Huber also makes a horizontal screw press. Wright Pierce is currently designing the first municipal application of a horizontal screw press in New England for Merrimack, NH.
Which technology is right for you?
The best dewatering solution for a facility is a function of many variables such as the sludge quantity and characteristics, the sludge disposal methodology, available space to house the equipment, the dewatering time period, the desire for containment to minimize odors and operator preferences. Often it is desirable to pilot test the various alternatives and then perform a life cycle cost analysis to select the best solution for your facility. You should also visit other plants with the technology you are considering to check out the equipment and gain a first hand understanding of the operational requirements. Upgrading antiquated dewatering equipment can pay big dividends in terms of operational and disposal cost savings, reduced operator attention, and improved odor control. Wright Pierce continues to be at the forefront of sludge dewatering innovations, and we welcome the opportunity to discuss options with you.
Wright-Pierce has extensive experience with the various technologies installed in facilities throughout New England. If you’d like more information, please contact us