Physicochemical wastewater treatment
Physicochemical wastewater treatment techniques
General overview :The treatment method selected depends in the first place on the size of the particles present in the wastewater. Solids, visible to the naked eye, can be removed by filtration, or can be settled by sedimentation, or they can be separated by means of flotation techniques, this in function of the density of the solids. The major problem however comes from fine suspended solids (particle size < 1 µm). These are very stable and they all have an electrostatic laden surface (usualy negative), which means that they repell each other, and will not clot together nor settle. This kind of fine suspended solids can only be removed by means of physicochemical techniques. For this purpose chemicals are added (coagulants or floculants) to accomplish the clotting or coagulation of the suspended solids, allowing to finally settle. Preliminar laboratory tests with wastewater samples (Jar tests), will allow in advance a rather accurate view on the estimated result of the proposed wastewater treatment technique in practice.
Flotation : separation of suspended solids, oils, greases and undissolved particles. This technique can be used as a preliminary treatment method for further purification, but at the same time the wastewater treatment can be limited to the flotation technique only. The most used flotation technique is D.A.F. (Dissolved Air Flotation), by which compressed air is dissolved in the waste water, to be treated. The released air forms tiny bubbles, adhering to the suspended matter (flakes) in the water (to which coagulants and/or flocculants have been added previously – see above), this tiny bubbles and suspended solids flakes can now float to the surface, because of their now reduced density (by the dissolved air). The float layer formed that way is skimmed and collected in a container, installed next to the DAF-unit. The sludge can be further thickened and/or dewatered. This kind of installations can be fully automated and as a result, they are most maintenance friendly.
Neutralisation : too acid or too alkaline wastewater flows are neutralized until a pH value of approx 7 is reached. The main reason to neutralize wastewater is to prepare it for further treatment in a biological wastewater treatment station or to meet the standards for discharge (eg. too acid wastewater can damage the sewer system and wastewater treatment plants). The most important objectives of this technology are the following : part from neutralization, the pH of the wastewater can be altered for several reasons : eg. a better control of the speed of chemical reactions, breaking down emulsions, conditioning, stabilization of raw wastewater, etc. For neutralization techniques, chemicals are added to the wastewater. Some examples of neutralisation units are to be found in the pictures above : neutralization units are compact units, composed of storage- and reaction tanks, completed with the necessary dosing- and mixing equipment. The chemicals added to obtain a higher pH-value are lye (NaOH) or limemilk (Ca(OH)2), to obtain a lower pH-value sulphuric acid (H2SO4), hydrochloric acid (HCl) or carbon dioxide (CO2) are used. Neutralization techniques can be used for a wide range of wastewaters coming from almost any kind of industrial activities. This kind of installation is uncomplicated, can be fully automated and are thus maintenance friendly. The simple construction allows for a reduced investment cost.
Membrane technology-membrane filtration : deferrization, water softening, demineralization by means of membranes, also water recycling and reuse (see the corresponding page for more details).
Stripping: removal of volatile substances with an NH3 stripper (stripping tower) – absorber (see corresponding page for more details).
Sludge treatment : in many cases sludge will be the residue in the final stage of the physicochemical wastewater treatment process. Many companies have opted for removal of this sludge by third parties (waste collection and waste treatment companies), hence the importance of reducing the volume of this sludge as much as possible. Seen the strong reduction of the sludge collecting and treatment cost by investing in sludge volume reduction equipment, the payback time for this part of the physicochemical wastewater treatment process will be rather short. One of the methods to dewater sludge is the chamber filter press. The sludge is dewatered by pumping it into a confined space or chamber under increasing pressure (to 10 – 15 bar). These chambers are formed by pressing opposite square plates against each other, under high pressure. Each filter plate is on both sides covered with filter cloth. The filter cloths retains the sludge, while the water is drained away by the ribbed surface of the filter plates. After the pressing stage, the chambers open and the filter cakes, in normal circumstances, fall off automatically. The filter presses can optionally be equipped with a high pressure spraying system for automatic cleaning of the filter cloths every cycle or after a certain number of cycles. The dewatered sludge residue can now be collected periodically for further treatment.
- electroflotationmembrane technology – membrane filtration
- NH3 stripper-absorberssludge treatment
Physicochemical wastewater treatment plants – Integrated solutions
No matter the installation is brand new or a renovation or optimisation of an existing installation, our objective is always to offer a correct solution, with an optimal price-quality ratio. Our installations are always seamlessly integrated in the existing unique production circumstances. We are striving for durable, maintenance friendly, correctly dimensioned and flawlessly functioning installations. A thorough instruction of the maintenance staff at site should guarantee a smoothly running wastewater treatment plant in the long run. If, despite all these precautions, problems occur, a quick intervention is always guaranteed.
Wastewater treatment in general and physicochemical wastewater treatment in particular : our expertise
Various industries from the waste collection and processing industry up to the food industry, from the automobile industry up to the textile sector, from pet food manufacturers up the pharmaceutical industry, from the metal industry up to chemical/petrochemical industry – are or have been relying on our experience for the realization of wastewater and/or emission treatment installations. For all of these specialisations we can present the corresponding job references.