When it comes to sludge it can be easy to get confused with what the best dewatering plan is. There are several factors to take into consideration such as sludge components, government regulations, budget, and geographical location. In this article, we will provide a breakdown of what sludge is, how it is processed, and how it can be properly disposed of.
What is Sludge?Sludge is a byproduct of treated wastewater. It is important to dewater sludge to reduce:
- Volume (for more effective hauling and disposal purposes)
- Harmful effects on public and environmental health
- System Upsets
Sludge Processing MethodsThe two main processes that sludge is reduced by is:
- Destruction- is when sludge is oxidized to carbon dioxide to then be reduced to methane. This can be achieved through incineration, anaerobic digestion, pyrolysis, and other methods.
- Consolidation- is when sludge volume is reduced by removing water and dissolved solids from the sludge. This can be achieved by using belt filter presses, screw presses, centrifuges, plate & frame filter presses, and other dewatering or thickening methods.
Consolidation methods can be categorized into two different categories: thickening or dewatering, depending on how much water is removed from sludge. Dewatered sludge is commonly referred to as cake, as it has a higher solids concentration, and it cannot be pumped. Whereas thickened sludge has a more liquid-like consistency, and it can be pumped.
When it comes to the dewatering process there are several types of equipment to use such as:
Belt presses work by removing sludge onto two different dewatering belts where freestanding water molecules are separated from the sludge by gravity and are collected by a trough. Next, the thickened sludge is pressed between two belt filters and squeezed under rollers to force excess water from the sludge. Finally, the sludge is scraped off the belt and collected in a bin while the water content is transferred back into a wastewater system for processing.
The Belt Press is typically used where high-moisture content is acceptable in the filter cake (18-25% solids by weight). The belt process is continuous and effective on high-volume waste streams where maximum production of a lower quality filter cake is acceptable.
A centrifuge employs a high rotational speed to separate components of different densities. The principle of a centrifuge is based via buoyancy. A component with a higher density would fall to the bottom of a mixture, while the less dense component would be suspended above it.
High RPM Centrifuge processing is utilized for certain oily sludge. This process produces 25-40% solids by weight and employs the separation of different specific gravities. Centrifuges are utilized for application where oil recovery is a desire and speed (processing time) is a priority over cake “dryness”.
High Pressure (up to 225psi) Plate & Frame Filter Press
High pressure is achieved with a Piston Diaphragm Pump. This type of processing is generally used on sludge where the solids are disposed of as hazardous waste by high-temperature incineration or secure landfill and the highest volume reduction is desired. It produces a filter cake from 40-70% solid by weight. In addition, high pressure is effective in breaking out bi-products that are entrained in the sludge. For many waste streams, steam enhancement is utilized to change the physical characteristics of the sludge prior to dewatering. Steam enhanced pre-treatment has proven cost-effective for oily sludge where dewatering is difficult under ambient temperatures and would require higher quantities of additives.
Low Pressure (100 psi) Plate & Frame Press
A low-pressure plate and frame press is generally used for processes where sludge characteristics do not require high pressure to achieve a good quality filter cake. And, on non-hazardous waste streams where transportation and disposal/recycling costs are not as high as that of hazardous waste streams. Pressure is achieved by a double diaphragm or self-priming trash pumps. And produces a filter cake from 25-50% solids by weight.
When it comes to choosing the best dewatering process for your project, it is highly dependent on the properties of the sludge. That is why at Handex we always analyze samples taken from project sites, to ensure we are recommending the best dewatering process for our clients.
Disposal of sludge is highly dependent on government regulations, sludge components, budget, and geographical location. But the main methods of disposal are:
- Landfill- As long as sludge will not contaminate groundwater, it can be buried underground in landfills
- Land Application- Depending on sludge components it can be spread on agricultural land to fertilize the soil
- Incineration- this evaporates the moisture and converts the solids into ash
Handex is a provider of Pumping, Dredging, Sludge Dewatering, and Treatment of industrial and process wastes. Our staff includes experienced Project Managers, Engineers, Operators, Technicians, Fabricators, Scientists, Mechanics, and Health and Safety Professionals. Our objective is to meet and exceed client expectations while providing quality, safe and cost-effective services. In some cases, our clients find that the value of the materials returned to the plant pays partially for the cost of the sludge dewatering service.