Dewatering involves the separation of water and other materials from waste or sludges. Mechanical dewatering is when the sludge is mechanically removed from the solid matter. There are various types of mechanical dewatering techniques. These include Hyperbaric centrifugation, Hydrothermal carbonization, Cell treatment, and Sand bed.
Water in biomass is bound by capillary sorption and adhesion to chemisorption
Capillary sorption and adhesion to chemisorption are two methods of transferring water from a source to a destination. They are used in various natural, biological, and industrial applications.
Capillary action is an essential mechanism by which plants take advantage of the surface tension of water and air to push liquid water upward through hydrophilic capillaries. Plants do this to provide liquid water to their root systems for growth and development. Alternatively, they can also utilize this phenomenon to move hygroscopic water, or liquid water, from a low-lying surface to an aerial part of a plant.
Adsorption is when a solid adsorbent (a substance that adsorbs molecules) forms a film on the surface. It is widely used in various industrial applications, including cooling water and waste heat recovery. Adsorption is often followed by desorption, which removes a molecule from the solid adsorbent.
Sand beds are the most cost-effective sludge management alternative
Using sand beds as an alternative to mechanical dewatering is an effective, economical, and environmentally friendly solution to sludge management. However, there are important considerations when considering their use.
One of the most critical issues is optimizing the treatment capacity of the STRB. For example, the sludge loading rate and type can affect its dewatering performance. It is also possible to vary the type of materials used in the construction of the sand bed.
Another important factor is the quality of the sludge. For example, sludge from waterworks contains contaminants, such as heavy metals and emerging micropollutants. Consequently, it is advisable to conduct a trial before full-scale operation.
Depending on the type of sludge, the dewatering characteristics of mechanically dewatered sludges can vary significantly. They are often thick and slurry-like. Moreover, they may contain trace elements and pollutants.
Hyperbaric centrifugation can effectively dewater ultrafine (0.04 mm) coals
The hyperbaric centrifuge is a mechanical dewatering device that can effectively dewater ultrafine coal particles. This technology can also help companies to minimize waste generation.
Dewatering of ultrafine coal particles has been a problem. Conventional dewatering systems have been unable to remove moisture from these particles. Hyperbaric centrifugation was developed to solve this problem.
In dewatering fine coal, surfactants can help improve filtration rates. These additives can adsorb onto coal particles, thereby improving wettability and surface tension.
Adding oil to the dewatering process can improve the throughput and filtration rates. Oil agglomeration is an expensive process. It requires oil consumption of at least 30%.
However, this process was not economically feasible. Another limitation of this dewatering method was the use of volatile hydrocarbons.
Hydrothermal carbonisation
Hydrothermal carbonization is a process where sludge is converted into a carbon-rich hydrochar which can be used as a solid fuel or soil conditioner. It is an effective and stable method for dewatering excess sludge.
Several steps are involved in the process. First, the precursor is hydrolyzed into monomers, which are cleaved into individual hydrochars. The hydrochars contain different elements which contribute to the total mass.
The second step involves the production of degradation products such as hydroxymethylfurfural (HMF), furfural, and humic acids. These degradation products partially condense to coal.
The hydrothermal process has received renewed attention in recent years, in part due to the focus on climate protection and resource conservation. Several new processes are in development.
One of these is a combination of thermo-chemical preparation and hydrothermal carbonization. This combination is said to achieve an energy balance, which is beneficial for converting dissolved organic matter and improves the biological absorption of the treated water.
