Liquid waste is generated from all types of processes and operations, and although there are many different technologies and techniques to treat and manage liquid waste, the basic principles are similar, which is to either separate the solids from the liquid or to turn the liquid waste into a solid material by adding an amendment or drying.
“Liquid landfills” do not exist, which means that any liquid waste must be processed and treated. Traditional liquid waste dewatering methods typically involve filters, presses, and centrifuges to separate the solids from the liquid, where the liquid component is discharged or reused, while the solids component is trucked off for disposal.
An alternative treatment approach is solidification, where an amendment or reagent is added directly into the liquid waste which causes the liquid waste to turn into a solid material through the principles of absorption or adsorption.
Although dewatering and solidification are sometimes seen as competitive processes, they should instead be considered as complimentary, as their target waste streams have some significantly different characteristics.
Dewatering methods are typically costlier as they require expensive capital equipment which also have high operating costs; however, they work well on low solids waste streams, such as wastewater, to remove large amounts of free liquid and obtain a higher solids sludge. Solidification methods are typically easier to apply and do not require an expensive capital investment in processing equipment; however, they should really be applied to high solids waste streams, which may be a thick liquid or semi-solids. Solidification can also be used to “polish” off the solids separated from dewatering processes. It is very common for dewatering to produce a semi-solid sludge that will fail slump or paint filter regulatory solids test criteria and may require a small amount of an amendment to meet this requirement.
From the solidification point of view, it is beneficial to remove any free liquid from the waste stream before adding solidification reagents, as this will lower the reagent dosage and result in a drier, crumbly material. Simple dewatering methods, such as gravity settling, may be used to remove free water, and the remaining, higher solids content, sludge may be easily solidified.
From the dewatering point of view, it is often very easy to remove the initial portion of free water, but a significant amount of energy is required to remove “bound” water in the liquid waste stream. Therefore, utilizing solidification methods as a polishing step at the end may prove to be more beneficial and cost effective compared to using dewatering equipment to achieve a dry material.
In summary, liquid waste treatment is an innovative and growing industry. We have an opportunity to pull our resources together and use multiple technologies to achieve the common goal. Dewatering and solidification both excel in different aspects, and we should exploit these methodologies for synergies and utilize them where most appropriate.