BERCEN Training Program on On-site Inspection for the Environmental Enforcement Agencies and

InspectoratesSeptember 9-13, 2003

Ohrid Lake, Republic of Macedonia

The Waste Water Treatment PlantVranista, Struga

LOCATION

- The WWTP Vranista is located in the village of Vranista near Struga. - It works as a part of water waste infrastructure for protection of the water of Ohrid lake. - This system covers the coastal part on the Macedonian site of Ohrid lake. - It consist of: 1.east collector (the west part is being constructed) 2.the main collector 3.pumping stations 4.WWTP

- The east collector beginning from the village of Pestani acceptsall the waste waters from the tourist objects from the town of Ohrid, and the town of Struga, and the small industrial plants.

- On the other hand the part beginning from St. Naum is not constructed at all.

- The waters are directed into the main collector witch is 4 km long to the WWTP-Vranista.

- The west collector is being constructed and it will be 12 km long.

DESCRIPTION OF The WWTP

- The WWTP began working in 1988. It was designed for capacity of waste waters of 120. 000 inhabitants in the region of Ohrid and Struga as well as from the tourist object.

- The waste waters coming from the industry are also collected in this system but previously treated in the very plants.

- The system is under constant additional constructions.

CLEANSING PROCESS

- Biological procedure has been applied for treatment of the active slime based on biological oxidation of organic material with active slime at separate aerobic stabilization of the same.

- For realization of the designed performances the following objects has been built in technological line :

Pumping station

Biological pond

Building with coarse and fine sieve

Sand aero gripper and oil and fat retainer

Pond for stabilization

of the slime

Slime denser

Dehydration of the slime

Secondary sedimentor Chlorine station

Administrative building

1. PUMPING STATIONS WITH A SNAIL-LIKE AGGREGATE

- There are 9 pumping stations along the eastern collector- They are used for the first step i.e. for the bringing up of the waste waters from the sewage system witch is deep under the ground.

2. COARSE AND FINE SIEVE

- After the bringing of the waste waters up through the system they are directed firstly through the coarse and the through the

fine sieve. - In this way solid segments of 40mm to 17mm is automatically retained and then descended from the sieves and by means of a moving belt are disposed in the waste container.

4. SAND AEROGRIPPER AND OIL AND FAT RETAINER

5. BIOLOGICAL POND

- In the next phase the waste waters go into the biological pond.- It is significant to provide the necessary oxygen for a proper performance of the biological process for decomposing of organic material with active slime. - Aeration is performed with surface aerators known as "mammoth rotors". - The active slime consists of microorganisms (bacteria) which mix with the waste waters and the organic material transforms from the dissolved form into colloid and solid form which is eliminated with sedimentation.

6. SECONDARY SEDIMENTOR

- It is used for sedimentation of the active slime and clearing of the treated water waste.

7. PUMPING STATION FOR RECIRCULATION OF THE SLIME

- The slime is recirculated in the biological pond

7. AEROBIC STABILIZATION OF THE SLIME

- The freshly gained slime is additionally aired.

8. SLIME DENSER/THICKENER

- The role of this denser is to lessen the content of water in the slime- The densed slime is directed to a pit from where it is transported into the filter press or into the drying fields.

9. DEHYDRATION OF THE SLIME

- the further processing of the stabilized densed slime can be preformed by a filter press or in the drying fields in a natural way

10. DESINFECTION OF THE EFLUENT

- After the sedimentation and clearing of the treated water waste it gravitationally leaks out into the disinfecting pond and proceeding into the river Crn Drim.- According to the designed performances it has been intended to disinfect the water by chlor in a gas form but it is not performed due to the danger of polluting the river Crn Drim- Currently a procedure is undertaken to replace the above stated performance with disinfection with UV radiation.

AIR POLLUTION

a. Waste gases in untreated water waste

- The sewage waste water consists of liquid and solid materials which have dissolved gases such as: O2, CO2,N2, H2S, CH4, NH3 and VOCs

b. Odors

The rotting of the sewage water produces odors coming from H2S, amines, ammonia, diamins, merkaptans, organic sulphids and scatol.

c. Waste gases and odors from the water waste treatment installations

For the biological treatment the emission of gases is characteristic as they come from the biological treatment of decomposition of organic substances which is more intensity in warmer period of the year.

d. Waste gases and odors at processing and disposal of the same

- The active slime contains a lot of live micro organisms (bacteria and alike) and it absorbs the colloids and the dissolved organic material transforming them into mineralized solid materials - mineralized slime. - The unplanned odor can become even more intense if anaerobic conditions influence the process. That is why it is important to maintain the process in aerobic conditions.- In the process of digestion of the slime which is performed in aerobic conditions CO2 releases as it is aimed.- The mineralized slime is obtained with aerobic digestion. If it is well mineralized it becomes odorless, humus, biologically stable final product.

AIR POLLUTION/CONCLUSION

With this technological procedure applied in the WWTP Vranista it is impossible to get high concentration and emission of harmful material in the air if the process are properly performed.

WATER POLLUTION

- As it has been pointed out the whole infrastructure system with the collectors, the pumping stations and WWTP functions to protect the Ohrid lake from waste waters.

- The Water waste treatment plant Vranista treats:• the waste waters from the town of Ohrid• the waste waters from the town of Struga• the waste waters from the objects (such as the hotels, the hospitals small industrial objects and alike) along the built collector. • atmospheric waters (rain and waters from the melted snow)

- In case of improper functioning of the WWTP (defect or incorrect performance of the technological process, pollution with untreated industrial waste waters and alike) pollution of the river Crn Drim may be expected with:

• organic polluters• mineral polluters• sewage• increased content of suspending articles• increased concentration of nitrites.

MONITORING

- In order to implement the process of the cleansing of waste waters successfully, it is necessary to control the same in the beginning and in the end of the process as well as in certain stages of the technological process.- The controlling is performed by the physic-chemical laboratory of WWTP Vranista with regular analyses every day and when is necessary- The laboratory is obliged to send the results to the SEI and to the Info-centre of the MoE

POLLUTION WITH SOLID, LIQUID AND SEMI-LIQUID WASTE

The processes of cleansing the waste waters in WWTP Vranista are proceeded with appearance of solid, liquid and half-liquid waste.

The waste material and the treatment of the same is given on the following chart:

Part of the process Waste material Quantity Yearly quantity Treatment

Mechanical treatment

Solid waste (coarse substances selected with the coarse and fine sieve)

2.6 m3/d 960 m3/year to taken to disposal site

sand separated with the sand gripper

taken to sand container

Biological treatment

densed slime

195 m3/d 71.175 m3/year

dehydratation with -filter press-in drying fields

GENERAL CONCLUSION

It may be concluded that WWTP Vraniste is in a quite good state.

However, it must be admitted that it works with certain problems as:

- the plant works from 1988 and it needs certain revitalization- it needs solving of the problem with the biological treatment - disinfection for the treated waste water- it needs a permanent solution for the mineralized slime- it needs the complete construction of the eastern collector to St. Naum- it needs complete construction of the western collector from Radezda to Struga- it needs construction of the secondary sewage system in Ohrid and in Struga for separation of the sewage water and atmospheric water

Thank you !