The device was delivered in 2015. for the purpose of purification of technological wastewater generated in the process of slaughterhouse and meat processing plant. The capacity of the device is 100 m3/day.
Table 1. shows the input parameters of wastewater on the basis of which the device was designed and the treatment technology was selected.
| No. | PARAMETER | UNIT | VALUE | JEDINICA | PROJECTED VALUE |
| 1 | Daily wastewater quanity | m3/day | – | m3/day | 100 |
| 2 | Average flow | m3/h | – | m3/h | 5 |
| 3 | Peak flow | m3/h | – | m3/h | 10 |
| 4 | COD | mg/l | 5000 – 8000 | kg/day | 800 |
| 5 | BOD5 | mg/l | 2000 – 3500 | kg/day | 350 |
| 6 | Total nitrogen | mg/l | 250 * | kg/day | 25 |
| 7 | NH4-N | mg/l | 200 * | kg/day | 20 |
| 8 | Suspended solids | mg/l | 2650 * | kg/day | 265 |
| 9 | Total phosphorus | mg/l | 40 * | kg/day | 4 |
| 10 | Oil and fats | mg/l | 350 * | kg/day | 35 |
Table 1. Wastewater characteristics
*due to unknown values in wastewater, values were taken according to previous experiences from similar projects
The designed device uses a combination of DAF technology and biological treatment. Wastewater first undergoes a coarse mechanical pretreatment where larger solid particles are removed, then through the pumping shaft the water is pumped to a fine mechanical pretreatment where smaller particles are removed (Figure 1.), and the mechanically treated water goes to an equalization tank equipped with a system for aeration (Figure 2.) and serves to equalize the concentrations of impurities and mitigate hydraulic shocks during the day.
Figure 1. Automatic screw screen
Figure 2. Aeration system in equalization tank
The feed pump takes the wastewater from the equalization tank and sends it directly in the pressure pipe to the pipe flocculator in which the chemical treatment of the wastewater takes place. A tubular flocculator is a long tube with a larger number of elbows and arches, in order to obtain water retention and efficient turbulent mixing (Fig. 3). The tubular flocculator has three dosing points for the introduction of chemicals: iron(III) chloride (FeCl3) or polyaluminium chloride (PAC) is most often used as a coagulant, sodium hydroxide (NaOH) or hydrochloric acid (HCl), is used for pH neutralization, and an aqueous solution of polyelectrolyte (polymer) is used as the flocculant. Each chemical has its own tank and associated dosing pump.
The polyelectrolyte solution is prepared in a tank with a mixer by adding polyelectrolyte powder (Figure 4).
Figure 3. Tube flocculator
Figure 4. Polyelectrolyte prepratation station
In the DAF flotation tank (Figure 5.), by introducing compressed air into the wastewater, the dissolved air expands in the form of micro-bubbles. There is an interaction between the suspended matter and the micro-bubbles, and they float to the surface together. A layer of floating sludge is created on the surface, which is continuously removed with a scraper (Figure 6.).
Figure 5. DAF flotation
Figure 6. Scraper
After the treatment, the wastewater gravitationally goes to the distribution tank. From it one part of the water goes to the biological purifier while the other part is discharged into the sewer.
Biological purification is based on MBBR technology (Moving Bed Biofilm Reactor). The reactor is filled with biomass carriers in the amount of 10 – 15% of the tank volume. Free-floating biomass carriers are used. The correct ratio of macro nutrients (C:N:P) plays an important role in biological wastewater treatment. According to the characteristics of technological wastewater, in some periods it will be necessary to control the dosing of phosphorus sources into wastewater. Mixing and aeration of the tank takes place by means of aeration with medium-sized air bubbles. Air is blown into the tank using a blower located in the engine room.
After biological treatment, the wastewater goes to an equalization tank where it dilutes the raw wastewater.
Excess activated sludge from the biological reactor and flotation device is transferred to the sludge tank. The sludge is then transferred to a press where it is dehydrated and collected in a closed container after which it can be transported in accordance with local laws.
