Technology

General Technological Description of WasteWater Treatment Plants BioTeh

Mechanical pre-treatment

Wastewater flows by gravity from the sewerage system through stainless fine bar rack. Impurities are captured there, otherwise they could damage the equipment. Cached impurities are manually removed and disposed into nearby container.

Biological treatment

In designing of waste water treatment plant it is necessary to choose the appropriate type of technology able to reach satisfactory parameters in reducing organic pollution and removing nitrogen and phosphorus compounds from polluted wastewater.

The D–N (denitrification – nitrification) technology along with chemical phosphorus precipitation, applied in the system under consideration, is the most appropriate one for satisfying the relevant water quality standards. This technology is implemented by design of the wastewater treatment facility introducing two activation zones with different technological conditions. In aerated (nitrification zone), ammonia is oxidised to nitrates by bacteria in presence of dissolved oxygen.

Mixture of activated sludge and nitrates is then returned by recirculation pump back to denitrification compartment, which is situated at the inlet of the treatment facility. There the returned nitrates are reduced to nitrogen gas, which is escaping into the air. It is possible to regulate the efficiency of the whole process easily by regulating the recirculation rate. Nitrification is ensured by specific bacteria.

Because this particular bacteria has longer proliferation period than bacteria eliminating the organic pollution, it is necessary to prolong the sludge age over this value, so that their augmentation will be higher than their decrement through surplus sludge. Each of the activation zones can be operated under different regimes according to the local requirements.

The wastewater treatment plant BioTechnology has the following technological zones:

• Denitrification (anoxic) compartment - for full nitrate removal and partial BOD decrease;
• Nitrification (aerobic) compartment – for full ammonia oxidation to nitrate in aerobic conditions, aerobic oxidation of the remain organic matters and phosphorus removal by chemical precipitation (installed by the decision of the customer). A storage tank for ferric salt and dosing pump are envisaged for the phosphorus removal and for decreasing the required effluent parameters. The ferric salt will be dosed into the nitrification tank;
• Compartment for UV disinfection - installed by the decision of the customer;
• Sludge aerobic digestion and thickening compartment - excess activated sludge is pumped to the digestion zone, where it is thickened by gravity. Sludge holding tank is aerated by fine-bubble aeration elements. It is constructed for 60 days of required storage time. Remaining water is pumped back to the biological processing. Stabilized thicken sludge is removed from the compartment by pump and is further dewatered in a drainage bag.

Outlet parameters

Parameter	Measure	Standard methods	Standard water emissions quality values
рН	-	BSS 17.1.4.27-80	6.5 - 8.8
Total suspended solids at 105°C	mg/l	BSS 3546-77	30
Phosphates	mg/l	BSS 7210-83	1.0
Nitrate	mg/l	BSS 3758-85	10
Nitrite	mg/l	BSS 3762-81	Not allowed
Ammonia	mg/l	BSS 3587-79	Not allowed
Dissolved oxygen	mg/l	BSS 1.4.08-78	6
COD	mg/l	DIN 38409-H41-1(2)	80

Impurities reduction in the relevant technological compartments is as follows:

• At the bar rack – 20% reduction of the coarse materials;
• In the anoxic compartment – 20% reduction of BOD5 and 85% reduction of nitrogen (anaerobic reduction of the nitrates, transferred there from the aerobic compartment);
• In the aerobic compartment – 95% reduction of BOD5, 95% reduction of ammonia, 75% reduction of phosphorus (by chemical precipitation) if required and suspended solids reduction down to 15 mg/l;
• In the disinfection chamber – 99,9 % reduction of the bacterial impurity (in respect to Esherihia Coli).