World’s most desired liquid. We can drink it. We can us it.
Whatever purpose, it must be of excellent quality! With water treatment you can reach such goal.
Water treatment is a process to improve the quality of water to make it appropriate for a specific application. Like drinking water, process water or purified wastewater for reuse.
Within all those types of water it’s often about:
- production of drinking water (city water, tap water, potable water)
- production of process water, like:
- reverse osmosis water (RO water)
- demineralised water (demi water)
- ultrapure water (UPW), water for injection (WFI) or other definition for the ‘cleanest possible’ water.
- boiler water treatment (BWT)
- cooling water treatment (CWT)
- sludge/brine treatment
Water treatment removes contaminants and undesirable components. It reduces such till low enough concentrations. Water treatment is crucial to human health and for quality control of any kind of (production) process.
In the definition of such treatment plants we can use different names like:
- water treatment plant (WTP)
- drinking water treatment plant (DWTP) or potable water treatment plant (PWTP)
- process water treatment plant (PWTP)
Below you can find some information about different types of water. A possible treatment solution is described briefly as well.
Water resources
For the production of clean water, almost exclusively fresh water is used. Fresh water containing only a limited amount of dissolved compounds like salts. That distinguished from brackish water and sea water. Desalination of brackish or sea water is only used if fresh water is scarce. While removal of salts will take much more effort, energy and cost.
groundwater
well, dune/river infiltrated, etc.
surface water
river, canal, lake, sea, ocean, etc.
effluent reuse
wastewater treatment effluent.
Drinking water
A good water supply is an essential part of human society. Not only as drinking water, but especially for personal and domestic hygiene, such as bathing and washing. Good personal and domestic hygiene is a primary condition for good public health.
See the simplified and generalised flow diagram for a typical treatment plant on river water. Depending on the source quality less or even more process steps might be needed. Such is of course also applicable if the source often is better (ground water) or ‘worse’ while serious desalination is needed (sea water).
Bottom line over 95% of the incoming fresh water could become available as drinking water.
See below for some processes and it’s purification goal.
- filtration processes. To remove suspended solids:
- rapid gravity filters
- roughing filters
- pressure filters
- slow sand filter
- bank filtration
- aeration. To remove iron, See deironed water.
- chemical coagulation. To particularise colloids and solids.
- activated carbon adsorption. To remove pesticides, organic chemicals, taste/odor/color producing compounds, etc.
- ion exchange. To remove hardness and dissolved ions in general. To remove nitrate, chromate, arsenic, etc.
- membrane processes. To remove suspended solids and much more:
- high-pressure processes. See RO water.
- lower-pressure processes
- disinfection processes, like chlorination or ozonation. To make water bacterial safe.
- other processes:
- precipitation softening. To remove hardness.
- ion exchange softening. To remove hardness. See softened water.
- biological (de)nitrification. To remove ammonia and/or nitrates.
- activated alumina (or other adsorbents). To remove fluoride, arsenic, lead, sulfur, etc.
Deironed water
For several processes deironed ground or well water has the desired quality. In such cases the treatment could be based on removing the iron by oxidation and filtration.
By oxidation, the iron will coagulate/flocculate till iron flocs. Flocs that can be removed by sand filtration. The sand is trapped in a pressure vessel (or open tank), and clean deironed water will flow out.
Over time the filter will hold more and more captured flocs. To prevent a partly flush-trough and minimize head loss it needs to be cleaned (backwashed). That results in a a small waste flow (containing the separated flocs). Such flow can be discharged on the (local) sewer for example.
Bottom line over 95% of the incoming water could become available as deironed (process) water.
Softened water
For several processes softened (drinking) water has the desired quality. In such cases the treatment could be based on removing calcium and magnesium by ion exchange (on a resin).
By exchange (with sodium), the calcium and magnesium will become adsorbed on the resin. The resin is trapped in a pressure vessel, and clean softened water will flow out.
Over time the system needs to be cleaned (regenerated with a sodium chloride brine) and a small waste flow will remain. Such flow can be discharged on the (local) sewer for example.
Bottom line over 95% of the incoming water could become available as softened (process) water.
Alternatively, other technologies can be used to soften water. Like pallet reactors and reverse osmosis systems.
Reverse osmosis water
For several processes reverse osmosis water has the desired quality. In such cases the treatment could be based on removing salinity, ions, viruses, bacteria, algae and suspended solids by membrane filtration. A type of (semipermeable) membrane with very small ‘pores’ is used. Pores often smaller then 1 nm.
By filtration all removed ‘contamination’ will be concentrated on the pressurised side of the membrane, the concentrate. The clean water will go through the membrane (then named permeate), and is available for consumption as ‘RO water’.
Such systems are designed as continuous filtration systems. A defined ratio of concentrate over permeate will be maintained. Depending on the incoming water quality a pre-treatment is needed. For example hardness must be removed from the water or controlled with antiscalants. Hardness will otherwise give scaling of the membranes. Also other contamination can lead to scaling, fouling or clogging of the membrane. All such is controlled by using ‘best possible’ feed water in combination with having more or less concentrate. The concentrate can be discharged on the (local) sewer for example.
Bottom line over 75% of the incoming water could become available as reverse osmosis (process) water.
For more information you can read about the technology membrane filtration.
Demineralised water
For several processes demineralised water has the desired quality. In such cases the treatment could be based on removing (minerals) ions by ion exchange (on a resin).
By exchange (with OH– and H+), the positively vs negatively charged ions will become adsorbed on the resin. The resin is trapped in pressure vessels, and clean demineralised water will flow out.
Over time the system needs to be cleaned (regenerated) and a small waste flow will remain. Such flow can be discharged on the (local) sewer for example.
Bottom line over 95% of the incoming water could become available as demineralised (process) water.
Alternatively, other technologies can be used to demineralise water. Where reverse osmosis already removes most minerals, technologies like electro deionisation (EDI, CEDI) can be used as well to remove remaining minerals.
Ultrapure water
For some processes the cleanest of the cleanest water is needed. Chemically almost exclusively containing H2O. Water purified to the highest standards, by removing all contaminants. Such as:
- organic and inorganic compounds
- dissolved (TDS) and particulate or suspended (TSS) matter
- volatile and non-volatile
- reactive and inert
- hydrophilic and hydrophobic
- dissolved gases
A combination of techniques will be mandatory. Also to know that storage of such water needs special attention. It’s an ‘aggressive’ water, with the ability to ‘attrack’ all kind of gasses and pollutants, to become a ‘balanced’ water again. A possible process setup like reverse osmosis + ion exchange or electro deionisation + degasification.
All those techniques will give brines/concentrates and the aimed ultrapure water.
Bottom line over 95% of the incoming water could become available as ultrapure (process) water.
Boiler water treatment
In the production of steam, boilers are used. Differently from some water boiling at home it’s mandatory in industrial boilers to understand about water quality.
Ideally all supplied water will be transformed into steam. Unfortunately that is not how it works.
Due to boiling, the water quality in the boiler will change significantly. For example the salts (while that will not evaporate) will be concentrated. For each type of boiler quality and safety guidelines are defined to get the best overall performance.
At least hardness must be removed from the incoming water, while it will otherwise deposit on the steel boiler pipes. That will increase the energy consumption significantly. And most probably it will also damage the boiler sooner or later. See softened water.
Better would be to feed with cleanest water possible, to remove salts as well. See reverse osmosis water or demineralised water. It will produce a less ‘aggressive’ steam and it will reduce the amount of (concentrated and hot) boiler water to be drained, to a minimum.
Despite the incoming water quality, more treatment is needed to secure a safe and efficient steam production. Often chemicals are added to ‘remove or control’ the latest traces of oxygen and hardness.
Cooling water treatment
For cooling of water, cooling towers are used. Like with steam production (see boiler water treatment) it’s mandatory in industrial cooling towers to understand about water quality.
The principle behind a cooling tower is to evaporate cooling water to cool down your (process) water, as counter flow.
Ideally all supplied water will evaporate. Unfortunately that is not how it works.
Due to evaporation the water quality in the cooling tower will change significantly. For example the salts (while that will not evaporate) will be concentrated. For each type of cooling tower, quality and safety guidelines are defined to get the best overall performance.
At least hardness must be removed from the incoming water, while it will otherwise deposit on the heat exchangers. That will increase the energy consumption significantly. And most probably it will also damage the exchanger or cooling tower sooner or later. See softened water.
Often it is better to feed with a more clean water, to remove salts as well. See reverse osmosis water or demineralised water. It will reduce the amount of (concentrated) cooling water to be drained, to a minimum.
Despite the incoming water quality, more treatment is needed to secure a safe and efficient cooling process. Often chemicals are added to ‘remove’ the latest traces of hardness. Also to ‘control’ corrosion of metals (equipment and pipes) used in the cooling system.
Bacteriological issues! Another important aspect to be controlled is the fact that bacteria will find a perfect environment to grow in cooling towers. For example Legionella could give health problems if not treated well. To keep the system ‘bacterial safe’ chemicals (biocides) can be added, continuously or shock-wise. More sustainably, ‘non-chemical’ solutions can be used as well.
Sludge/brine treatment
An approach in minimising it’s volume (ideally 100% water in = 100% purified water out) and valorisation and disposal of the ‘by-products’ from water treatment.
Read more in our application sludge treatment.
