Sludge dewatering reduces the volume and weight for more accessible transport and disposal. It can be achieved by thickening or mechanical machines like sludge dryer beds or centrifuges. Hydrate dissociation has been observed to transform some mechanically bound water into free water. This transformation is irreversible.
Cost-Effectiveness
Mechanical dewatering is one of the most cost-efficient ways to handle sewage sludge. It uses mechanical devices to remove water from the sludge and reduce its volume for transport and disposal. These machines are generally large and expensive, but they can reduce operational costs by up to 50% compared to other systems. The changing trend in the water content of sludge during mechanical dewatering showed that increasing pressure and dewatering time significantly impact the dewatering process. Additionally, the sludge cake thickness significantly influences the dewatering process.
The most common method of dewatering sludge is using a sediment pond, which utilizes Stokes Law to separate sediment from the water column. The pond allows the sludge to slow down and settle before discharging. It makes the sludge more straightforward to handle and less expensive to transport, which helps reduce energy costs. It also reduces the number of vehicles needed for transporting sludge and reduces emissions of pollutants.
Environmentally Friendly
Dewatering reduces sludge volume, making it easier to transport and dispose of. It also allows for more efficient post-processing, such as thermal drying, which can save energy and money. In addition, mechanical dewatering equipment can reduce the need for chemicals and labor costs, resulting in more excellent environmental benefits. This type of equipment uses a mechanical process like filtration, squeezing, centrifugal separation, or compaction to separate water from solids. It is a simple process that uses less energy than chemical flocculants and human workforces.
Using sludge for fertilizer is an environmentally friendly alternative to land disposal. Sludge can also be used for gas production or sold as a soil conditioner. Sludge was dumped in the ocean in the past, but this practice is now illegal in many areas worldwide. However, sludge can be incinerated to convert it into an inert ash. It is a less odor-causing and more energy-efficient solution for the air.
Reliability
Mechanical dewatering separates sludge (residual sludge from wastewater treatment plants or fecal sludge from on-site sanitation such as septic tanks or pit latrines) into its solid and liquid parts. The process uses equipment such as belt filter presses and centrifuges to dewater the sludge. The sludge residue is transported to a landfill or sent for dry land application. However, this method does not treat the sludge and may contain pathogens or pollutants.
The permeability of the substrate media and the hydraulic loading rate of STRBs affect dewatering performance. The latter can cause bed clogging, slowing aerobic mineralization and leading to poor leachate purification performance. A resting period must be provided to allow sufficient liquid loss through draining and evapotranspiration. Moreover, the sludge residue layer must be sufficiently thin to promote oxygen diffusion to achieve aerobic mineralization. It can be achieved by adjusting the sludge feeding rate to ensure an appropriate hydration level of the sludge residue.
Flexibility
Dewatering systems must be adaptive and flexible to reduce sludge volumes. They must also be efficient, requiring fewer resources and producing less waste. In addition, they must be designed for easy maintenance and able to work without electricity. Mechanical dewatering allows for a greater level of flexibility than thermal methods. It separates sludge into a solid and liquid portion. Many equipment or processes exist, including gravity thickening, dissolved air flotation, and centrifugal separation.
Other treatment methods that don’t involve dewatering are composting and adding lime. These methods are often less energy-efficient than digestion and require a large area for storage. In addition, land application can be a costly alternative because it requires sufficient land and adequate permitting. It can also result in a high level of wastewater contamination. As a result, there is a rising demand for substitutes that offer the same level of performance but at a cheaper cost and with less harmful environmental effects.