Industry and household polluted water is knows as wastewater. Untreated wastewater discharged directly into the environment pollutes water bodies and groundwater, thus contributing to the overall pollution of nature. A lot of attention is paid globally to eliminate this problem.
Wastewater treatment equipment is used for
- Cities of various sizes (by applying mechanical and biological treatment)
- Industrial companies – dairy, meat, fish, beer, etc. (by applying chemical, flotation and biological treatment);
- Surface – rain wastewater (by applying mechanical treatment);
- Landfills and waste sorting plants (by applying membrane treatment)
- Biogas power plants (by applying membrane treatment)
Types of wastewater treatment equipment
- Mechanical – equipment that mechanically removes suspended pollutants (sand, silt, grease) from water. This treatment method is used for cleaning all types of wastewater.
- Biological – equipment that cleans wastewater polluted with organic and chemical pollutants by using bacteria. Bacteria are able to absorb pollutants that have dissolved in wastewater. Bacteria are continuously removed from the bioreactor and replaced with new ones.
- Chemical – equipment that is able to bind wastewater pollutants into flakes by inserting certain chemical compounds. This method of cleaning is used in industrial companies
- Flotation – equipment that enables to remove suspended substances and grease from wastewater. This method is widely used in industry.
- Membranes – equipment intended for cleaning heavily polluted wastewater. This method is usually used when there is no other way to clean wastewater. Water is filtered through a membrane using high pressure. The membrane allows water molecules to pass through and suspends all pollutants.
Mechanical wastewater treatment plants
Mechanical treatment is a group of devices which treats wastewater mechanically from suspended matter. In practice, it is widely used prior to biological treatment, flotation, membrane, in order to intercept sediments and sand.
Primary pre-treatment plant – it is a complex unit consisting of automatic screens, grit separator, silt press, fat separator. This device is widely used in wastewater treatment facilities as a part of primary treatment chain. Depending on that, they might vary in their size and appearance, as well as the equipment necessary for the composition. The grit separator in the unit could be aerated and no. The sand and silt could be supplied to containers automatically via screw. Thus, silt and sand are dewatered. These devices are quickly and easily installed.
Automatic screens – suspend all the solids contained in the wastewater and remove them automatically by spinning them into the press bunker, where sediments are compressed and washed if needed. Inside the presses there are screws installed that helps to press screenings and push them via pipe towards the container.
The grit separator – the device is intended to remove the sand from the wastewater and dewatering it automatically transported it to the container. The purpose of the grit separator, while separating sand to dewater it as much as possible to minimize moisture and wash off the organic compounds stuck to the sand in order the sand would not decompose and would not give the unpleasant odour.
Tertiary treatment plant – is intended for additional treatment of treated wastewater, where is necessary to significantly reduce the insoluble materials, as well as to reduce the BOD and COD. Micro sieve filter is the important part in tertiary wastewater treatment process. All sewage enters inside of the sieve and is strained a through the sieve drum. The drum is fitted with the sieve with a mesh size of 17 to 80 mic. size. Sieves may have different efficiency, depending on the demand and wastewater contamination of suspended particles.
Biological wastewater treatment plants
The wastewater treatment takes place in biological, multi-precast reactor. Regarding to the wastewater amount, type, concentration the bioreactor is divided by walls into following zones: anaerobic, denitrificative, nitrificative and secondary clarifier. Mechanic, stirring devices and aeration, intensively and continually stirs the wastewater consistency in the bioreactor. Pumps and airlifts direct the wastewater consistency into different zones. This method allows activating the wastewater treatment process. The sludge and the oxygen concentration are different in the bioreactor zones. Accordingly, in the activation zone, the sludge concentration may differ from 4-6 g/l, the oxygen from 2,5 – 3,5 mg/l. The air blowers ensure the air feed to the bioreactor by supplying the suppressed air through bottom, membrane, aeration elements. In the secondary clarifier, the most advanced method applied to the separation of treated wastewater though suspended sludge. This process is rather complex in a hydraulic matter. During this process, the sludge rises to the top, where it forms into compounds, afterwards becomes heavier, and therefore descends to the bottom. The water separation process takes place exactly through this descending layer of sludge. The technological process does not change no matter if the wastewater treatment plant is big or small. Although the components such as sludge treatment, pre-treatment plant, automation level, etc., may vary. We might suggest various sludge treatment methods for the excess sludge, depending on customers’ demands. The excluded excess sludge from the bioreactor falls into the sludge capacity – the thickener, it is thickened by gravitating method to 2% of dry materials, and the excess water is brought back to the beginning of the biological treatment. Additionally, after gravitating thickening, the sludge might be dried with presses up to 20% of dry materials. After additional drying, the excess water is brought back to the beginning of the biological treatment, whereas dried sludge is taken to landfills for utilization or it is used for other purposes.
Flotation (DAF) wastewater treatment
Floation (DAF) cleans the wastewater generated by the industry. After the flotation process reduces wastewater pollution:
- BOD5 & COD from 50 – 80%;
- SS & Fat from 50 – 95%;
- Common P up to 95%.
The wastewater flows into the pumping station, where the manual screenings are installed to stop large sediment. Pumps are fed into a rotary sieve, where the particles larger than 1 mm are separated. Withheld screenings while pressing through automatic screw are fed into the container. Afterwards the effluent flows into a separate yield and concentrations balancing tank. From this capacity, pumps inject the wastewater into the tubular mixer. In the mixing tank, the valves are installed and flocculants, coagulants dosing pipelines are in mounted, they are all connected with the dosing tanks. Such mixing with chemical reagents required to bind pollutants into flakes. The sewage flows through the mixer to the floater. The mixture of the suppressed air with bubbles is fed to the floater as well. Small bubbles entering the wastewater rise up of the pollutants bounded into flakes to the surface where they are mechanically removed from the surface with the raker. The raker scraps away pollutants that are diverted after to the sludge collection tank from which with a special transport are taken for further utilization. In the sludge tank there is a mixer installed, which ensures sludge stirring. Suspended materials descended at the bottom of the floater, that bubbles failed to bring to the surface, are directed to the sludge collection tank through the valve mounted at the bottom. A separate compressor provides the air supply to the floater. The water, required to prepare water and air mixture is taken from the floater, which is fed into the pressurized container. From this tank, the air-water mixture is fed into the floater, in this way air bubbles are formed.
Membranes for Waste Water Treatment
Membranes designed for treatment of heavily polluted industrial waste water are increasingly applied for treatment of domestic waste water. It is the most complex and the most expensive waste water treatment procedure resulting in particularly high treatment indices. Membranes are often used when no other waste water treatment methods (biological, flotation, etc.) could be applied. It is advisable to combine membranes with other treatment systems, planning their application as the last stage of treatment. In this way they provide additional treatment of waste water until the required parameters are achieved.
A membrane is a semi-permeable material with particularly small pores separating water molecules from impurities dissolved in water. Water molecules flow past through the membrane, whereas impurities are caught by it. Different membranes are selected each time: this depends on the type, concentration, and quantity of waste water to be treated.
Membranes are divided into four groups based on pore size: micro-filtration; ultra-filtration, nano-filtration, reverse osmosis. The key difference between them is the size of the retained molecules (impurities). The type of membrane is selected based on the type of the waste water to be treated and the analysis of the impurities prevailing in them.
Several different membrane types may be used within a single system. This is done in order to retain bigger molecules during the first phase and then retain smaller molecules during the second phase. This method enables to reduce the price of the technological equipment and to extend the lifetime of membranes significantly.
Reverse osmosis (RO) ensures the highest level of treatment involving elimination of all trace elements and impurities with clean and pure water as the final result. Special detergents are used for flushing the membranes designed to eliminate any impurities from the surface of the membrane. A flushing system is installed for flushing of the membranes.