Description of Proposed Pollution Mitigation Measures

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7. Description of Proposed Pollution Mitigation Measures

 

Given that a full feasibility study has been developed for KVK’s entire system (water treatment and distribution as well as wastewater collection and treatment), the assessment is largely summarizing the findings of the feasibility study in the context of the UNIDO project.  The results of the site assessment will be discussed in the following section.  Much of the discussions with facility personnel were based upon the results of the Feasibility Study but updated the situation, stressed the projects within the overall situation, identified priorities and, in some cases, provided further details.

 

The Danish Feasibility Study developed a list of projects for the entire water supply and treatment system of which the following relate to BWTP:

 

Table 7.1 : Summary of Prioritized Mitigation Measures

 

 

Note 1:  The rank number was designated based on 40 prioritized subprojects of the proposed immediate investment program (IIP).  Reference 1, Page 11. 

 

In addition to the above, there are 23 other, non-priority projects proposed by the COWI study.  These are summarized in Table 7.1 (Reference No. 3, Appendix 6.3). 

 

It should be noted that most of the proposed projects address repairs of the facilities of Line 1, the oldest treatment line at KVK.  Treatment Lines 2 and 3, which are identical in design, are also very similar to those of Line 1.  As a rough estimate, the cost for rehabilitating the facilities of Lines 2 and 3 would be of a similar order of magnitude as those of Line 1.   Relatively speaking, the facilities of Line 2 and 3 are in better condition than those of Line 1 due to their later construction, however, they still require attention in the near future.  If the Kyiv Design Institute’s Rehabilitation Plan for Line 1 is implemented, this report could serve as a starting point for the scope and magnitude of the rehabilitation of Lines 2 and 3. 

 

 

WWT-14  Monitoring Equipment

The BWTP has little automation or monitoring equipment.  Monitoring/measurement was limited to the Venturi flumes for each treatment line which  is used for estimation of the total accumulated inlet flow.  All other monitoring and measurement is not instantaneous and largely limited to daily or weekly laboratory analysis of process parameters, primarily oxygen content and sludge content in the activated sludge tanks.  Analysis is conducted at the on-site laboratory as portable monitoring devices are not available.  For example, dissolved oxygen measurements in the aeration tanks are based on the Winkler method.  According to the COWI Study, this method may give substantially misleading results because oxygen may be transferred to the water during the sampling (Reference 4, page 7-22).  In addition, the current methods for sampling and analysis used at the on-site laboratory are time and labour intensive.  Portable on-line measurements of dissolved oxygen would improve the control process and may improve treatment performance.  

 

The following monitoring devices are recommended for installation:

 

- Portable oxygen metres;

- Stationary oxygen metre stations;

- Portable suspended solid metres;

- On-line ammonia metres;

- Flow metres; and,

- Level metres.

 

Training for staff in the operation and maintenance of these devices is also recommended.  Further investigation is required to identify exactly which pieces of equipment are needed, how many and where they should be installed. 

 

Monitoring and control equipment will provide better awareness regarding the actual process conditions and performance which can be used to better treatment efficiency and process optimization.  Another possible benefit is the reduction of aeration in the process tank and hence a reduction in power consumption.  It is also expected that portable equipment will reduce labour consumption in the laboratory.

 

 

WWT-19  Grit Chambers (Line 2 & 3)

The grit chambers of the first treatment line at the BWTP are constructed as horizontal grit chambers, while the second and third treatment lines are constructed as aerated grit chambers.  Line 2 and 3 grit chambers achieve a sand removal rate of 84 to 88%.  Their design removal rate is 93 to 95%.  The relatively high sand content in the wastewater after the grit chambers adversely impacts the performance of succeeding treatment facilities (primary clarifiers, aeration tanks and sludge digesters), which must be compensated by various methods (i.e. increased aeration rates resulting in higher energy costs).  The presence of sand increases the wear on equipment, thus increasing maintenance and replacement needs. 

 

Sand deposits in the digesters is particularly detrimental, reducing the active volume resulting in a less stabilized sludge and reduced gas production.  There is no removal system for sand in the digesters so removal is done manually, a time-consuming, hazardous and difficult task.  At the time of the site reconnaissance, the build up of solids was being removed from one of the digesters.

 

Reconstruction of the grit chambers would result in a more reliable and efficient treatment of wastewater at the facility.  Significant savings on repairs and maintenance would result, particularly with respect to cleaning the digesters and aeration tanks.

 

Lines 1 and 2 each have four aerated grit chambers, each with a volume of 467m³.  The project comprises complete construction of the grit chambers as well as the replacement of sand removal systems, including aeration systems, scrapers, grit pumps and associated equipment. 

 

 

WWT-1A  Replacement of Screens (Line 1)

The existing screens for Line 1 have been in operation since 1965 and are in poor condition.  The screens are a coarse with 16 mm bar spacing allowing relatively large amount of solid materials to pass through the screens.  These solid materials that pass through the screens adversely effects the performance of the downstream treatment processes (primary clarifiers, aeration tanks and sludge digesters).  The presence of solid materials also increases the wear on down-stream.

 

Replacement of the screens with a new system with smaller bar spacing for improved removal of solid materials would increase the performance of down-stream treatment processes and decrease the wear on down-stream equipment.  Furthermore the installation of fine screens will improve the quality of sludge generated.  If the new system comprised mechanically cleaned bar racks with a conveyer system for the removal of screenings, worker hazard would be minimized.

 

The project proposed by COWI in their feasibility study comprised replacing two of the existing five screens at the at the first treatment line, based on projected loadings on BWTP over the next ten years.  The existing coarse screens would be replaced with mechanical fine screens.  Conveyers (closed screw) and compactors for screens would also be installed.  Water-level monitors would automatically control the activation of the rakes.  An air treatment and exhaust system would also be installed.

 

 

WWT-13  Sludge Digesters No 1-4

Primary sludge from all three treatment lines at the BWTP is pumped to sludge digesters for anaerobic digestion.  BWTP has eight digesters divided into two groups, Nos. 1 to 4 which were constructed in 1965 and Nos. 5 to 8, which were constructed in 1975.  The former are in operation but in poor condition.  The latter were constructed poorly and are not operational.  This COWI project proposes the extensive reconstruction and installation of new mechanical and electrical equipment for Digesters 1 to 4. 

 

Because the digesters are in poor condition, with resulting poor performance, or are not operational, BWTP cannot anaerobically treat all of the primary sludge generated at the plant.  The treated sludge is not adequately stabilized and unhygienic (pathogens remain).

 

Because of low retention times and inadequate mixing, the methane gas  production rates are relatively low (50 to 60% of potential generation rate).  Thus, BWTP must purchase natural gas to supplement the gas production from the digesters for the Heating Plant operation.  The present consumption of natural gas (approximately 8200 m³/day) could be reduced considerably if digesters No.1-4 are reconstructed and equipped with new mechanical and electrical equipment.

 

The project proposed by COWI involves the following:

 

- Repair of structures associated with the four digesters;

- Replacement of pipelines, pumps, gas pipelines and other equipment associated with the sludge digester;

- Installation of mechanical mixers, control equipment and gas meters; and

- Installation of heat exchangers and modernization of the existing process of sludge heating.

 

If the project were implemented, the digesters would have more reliable operations, lower repair and maintenance costs and increased production of biological gas (reducing the cost of purchasing natural gas needed for heating).  The resulting sludge would be more effectively stabilized, reducing the health risks associated with handling the sludge now produced.

 

 

WWT – 18  Sludge Dewatering

Digested primary sludge and surplus activated sludge from BWTP is stored in reservoirs and then pumped to sludge lagoons for subsequent natural drying.  Rejected sludge water from the sludge lagoons is pumped back to the beginning of the treatment facility for subsequent treatment.  The total amount of pumped sludge is approximately 9,000 m³/day which 3,000 m³/day is rejected.  The rejected sludge water contains suspended solids up to 1.5 g/L, which has substantial negative influence on the wastewater treatment performance at the plant.

 

There is no reserve sludge lagoons and the concentrations of heavy metals in the sludge is too high for disposal on agricultural land.  The sludge lagoons are only emptied and restored gradually according to need and sludge is disposed on nearby agricultural land (despite metal content).  It was reported by COWI that the pipes between the wastewater treatment plant and the sludge lagoons are in very poor condition and need extensive repair/replacement before future use.

 

To reduce the amount of sludge to be disposed of at the sludge lagoons it is necessary to install mechanical dewatering equipment.  New sludge dewatering centrifuges have already been installed for dewatering digested primary sludge.  When all of the centrifuges are in operation, there is sufficient capacity for all the primary sludge generated. 

 

COWI recommended that new sludge dewatering equipment for surplus activated sludge should be installed in order to reduce the volume of sludge to be disposed, eliminate the reject sludge water from the sludge lagoons (due improved treatment performance).   Eliminating the requirement for reject sludge water treatment will reduce operation costs, including electrical usage, as well as repair and maintenance of the pump equipment and pipelines associated with the reject sludge water and decrease the risk of spills that this system represents.

 

The sludge dewatering system recommended by COWI should comprise either centrifuges or belt filter presses to be determined by project tendering.  A complete sludge dewatering system will include the following units and works:

 

- 3 sludge dewatering units: centrifuges or belt filters presses, with a capacity of approximately 130 m³/h each (3-5%DS);

- Sludge feeding pumps, 3 units of approximately 130 m³/h;

- Complete polymer dozing pumps, 3 units;

- Control panels, 3 units;

- Conveyers for transport of dewatered sludge to containers, 3 units;

- Container for dewatered sludge, 3 units;

- Flushing pumps, 3 units;

- Water supply and electrical works; and

- Pipe works from sludge thickeners to sludge dewatering building.

 

Operation of the dewatering equipment will in itself lead to an increase in energy consumption.  On the other hand the reduced pumping of the sludge to the sludge lagoons will reduce power consumption.  In total a reduction in energy consumption can be expected.

 

Surplus activated sludge production is approximately  200 tonnes of dry solids per day.  The polymer consumption for dewatering of sludge is approximately 4kg of polymers per tonne of dry solids.  Assuming western prices, the cost of the polymers could be as much as 1.5 million USD/year, a significant cost to KVK. 

 

 

WWT-26B  Sludge Disposal, Phase 1

Anaerobic stabilized primary sludge from the digesters and aerobic stabilized biological sludge from the BWTP is pumped to the sludge lagoons.  Mechanically dewatered sludge is transported by truck to the sludge lagoon areas, where it is disposed of in separate cells.  At present, approximately 9000 m³ of sludge is pumped into the lagoons each day.

 

Presently the sludge lagoons are almost at capacity which degrades their performance with respect to solids settling and results in reject water having a high content of suspended solids.  The sludge lagoons are only emptied and restored as the demand for additional storing capacity occurs.  When this occurs, sludge is disposed of on nearby agricultural land.  Unfortunately, the concentrations of chromium, cadmium, nickel and mercury are relatively high and hence the sludge is not suitable for disposal on agricultural land.  In addition, when a sludge lagoon is prepared for re-use, the cost of the disposal of the settled sludge as well as the repair of sludge lagoon’s foundations and drainage systems can be significant. 

 

To resolve these issues, the COWI feasibility study recommended that some existing lagoons require rehabilitation and new sludge lagoons need to be constructed.  Due to the size and complexity of the work, COWI divided the project into two phases. 

 

Phase I of the proposed project includes the reconstruction of the existing sludge lagoons, rehabilitation of the drainage system and design and construction of new sludge lagoons for disposal of dewatered sludge.  In total, new or reconstructed lagoons should be able to contain approximately 1 million m³ of sludge over the next five years of sludge production.

 

 

WWT-21  Return Sludge Pumps (Line 1)

Line 1 has six pumps to transfer return sludge from the secondary clarifiers to the aeration tanks.  These pumps have been in operation since 1965 and are in poor condition and need to be replaced.  The pumps require frequent and expensive repair and their lack of reliability contributes to the poor performance of the biological treatment Line 1.  The pumps require heavy energy use (approximately 55-75kW each), significantly more so than modern equivalents. 

 

The COWI Feasibility Study recommended that new sludge pumps (three of existing six based on projected loadings on BWTP) should be installed directly into the lower sludge channel.  Corresponding piping, valves, electrical installations and other ancillary services should also be replaced.  It is also recommended that the pump sump and the lower sludge be repaired.

 

If the project is implemented, it is anticipated that more efficient operation of the aeration tanks of Line 1 would be more efficient, improving the operational efficiency of the entire line.  The energy consumption, repairs and maintenance cost would be reduced and the number of breakdowns and emergency situations decreased.

 

 

WWT-4A  Primary Clarifiers (Line 1)

The primary clarifiers of the 1^st treatment line (14 units) at BWTP have been in operation since 1965.  They are in poor condition with only 50% fully operational.  They are no longer inefficient at removing suspended solids and floating materials.  The inspection performed by COWI as part of the feasibility study noted that mechanical equipment such as bridges, scrapers, overflow weirs and grease removal systems were corroded and require replacement. 

 

The COWI feasibility study recommended that only seven of the existing fourteen primary clarifiers by rehabilitated based on demand-projections.  Such a project will improve the efficiency of primary sludge removal, reduce the load to the aeration tanks and secondary clarifiers (improving overall treatment efficiency) and reduce the number of equipment breakdowns, operational and maintenance costs.  As part of the rehabilitation, control panels should be replaced and modern control and monitoring equipment installed.

 

 

WWT-11A  Secondary Clarifiers (Line 1)

The secondary clarifiers of Line 1 (14 units) at BWTP have been in operation since 1965 and are in poor condition which adversely effects the overall biological treatment performance of the line. The inspection performed by COWI as part of the feasibility study noted that mechanical equipment such as bridges, scrapers, overflow weirs and grease removal systems are corroded and require replacement. 

 

The COWI feasibility study recommended that only seven of the existing fourteen secondary clarifiers by rehabilitated based on demand-projections.  Such a project will improve the hydraulic functions of the secondary clarifiers increase their efficiency (reduce suspended solids in the effluent, increased sludge concentration in the aeration tanks and generally improve the overall efficiency of biological treatment) and reduce the number of equipment breakdowns, operational and maintenance costs.  As part of the rehabilitation, control panels should be replaced and modern control and monitoring equipment installed.

 

 

WWT-20  Sludge Thickeners

The sludge thickeners at Line 1 (14 units) have been in operation since 1965 and are not in operational condition.  They were originally designed for thickening of the surplus activated sludge before the material was pumped to the sludge digesters or aerated sludge stabilization tanks.  When the sludge is not sufficiently thickened the quantity of material requiring digestion/stabilization increases as does the energy required for pumping.  Odour problems may also arise if the sludge starts to digest in the sludge thickeners.

 

The COWI feasibility study recommended that the existing thickeners be replaced by mechanical sludge thickeners, which can increase the sludge content to approximately 5-6% DS (i.e. centrifuges. Gravity belt thickeners, rotary drum thickeners, etc.).  It has been noted that if the sludge thickeners are replaced with new “traditional” sludge thickeners the sludge content will only increase by 3-4% DS for surplus activated sludge.

 

In order to implement the project two new mechanical thickeners will need to be installed that can be used for both primary sludge and surplus activated sludge.  The project would comprise the installation of the following:

 

- Two new mechanical sludge thickeners

- Two feeding pumps

- Complete polymer station

- Two control panels

- Two flushing pumps

- Pipe works, valves etc.; and

- Water supply and electrical works.

 

Implementation of this project would decrease operation costs by reducing energy consumption for sludge pumping, improve efficiency of the digester system which will result in an increase of gas production and decrease the quantity of sludge generated thus reducing the load on the sludge lagoons which would result in an improvement of the quality (suspended solids) of the reject water from the lagoons. 

 

The polymer consumption will depend on the actual choice of equipment and the type of sludge that is to be thickened, however, the costs can be significant, as much as $500,000 USD per year.  As KVK has already found the purchase of polymers for treatment to be difficult to maintain, this may be a significant constraint.

 

 

WWT-7A  Aeration Tanks (Line 1)

The aeration tanks of Line 1 have been in operation since 1965 and are in poor condition.  The COWI feasibility study team observed that the air pipes and valves that regulate the air supply to different corridors are in poor condition.  The aeration system is based on filter plates that are inefficient in terms of air distribution during the aeration process.  The existing air blowers are operated by energy-inefficient motors.  The aeration tanks have no control or monitoring equipment for the measurement of operational parameters (i.e. oxygen, air consumption etc.).  The structural integrity of the tanks is in poor condition. 

 

The COWI study proposed that the aeration tanks and the corresponding aeration system require significant repairs or replacement.  The project developed by COWI proposed that only three of the existing six aeration tanks for the first treatment line be repaired.  The project comprises the following major elements:

- Replacement of three of the seven existing blowers with new blowers equipped with adjustable air flows;

- Replacement of automatic valves for air flow control on the three replaced units;

- Installation of monitoring and control equipment;

- Replacement of filter plates on the tree replace aeration tanks with new fine bobble diffusers;

- Replacement of pipes and valves; and

- Reconstruction of structures.

 

If the project were implemented, the benefits would include reduced costs associated with energy consumption, repair and maintenance.  Overall treatment performance would be improved including achieving stable nitrification.  The new diffusers would also result in an improvement of biological treatment by increasing the efficiency of oxygen transfer in the aeration tanks.

 

 

WWT-3A  Grit Chambers (Line 1)

Line 1 has five horizontal grit chambers, each with a volume of 190 m³.  They have been in operation since 1965 and are in poor condition. Due to the condition of the grit chambers, their performance is inadequate resulting in significant quantities of sand passing through the chambers and degrading the performance of subsequent treatment processes (primary clarifiers, aeration tanks, sludge digesters).  Sand accumulates in downstream facilities causing blockages and breakdowns. Sand deposits in the digesters reduce the active volume, degrading performance, resulting in reduced gas production and inadequately stabilized sludge.  At present time there is no efficient method of removing sand from the digesters. 

 

Structural repairs are needed including the replacement of scraper systems, grit pumps, pipelines, valves and other ancillary equipment.  The project proposed in the COWI feasibility study comprises complete reconstruction of three of the grit chambers as well as the replacement of the ancillary equipment mentioned above.  Replacement and repairs should ensure the optimal rate for sand removal resulting in improved performance of downstream systems. 

 

 

WWT-25  Gas Storage

Gas Storage Tank No.1 has been in operation since 1965 and is in relatively poor condition.  Metal parts of the gas storage tank are corroded, inlet gas pipes are partially blocked and the gas storage tank does not fulfil the necessary technological functions for adequate use of digester gas storage for the boiler house.  Additionally, some digester gas is being emitted to the air through faulty equipment. 

 

Replacement of the gas storage tank is required for efficient operation of both the digesters and the gas utilization facilities. The project will include:

 

- Replacement of metal parts associated with the gas storage tank;

- Replacement of inlet and outlet gas pipelines;

- Installation of equipment for biological gas treatment; and

- Installation of control and monitoring equipment (i.e. gas meters, gas-analysers).

 

The objectives of this project are to:

 

- Provide optimal use of biological gas at the boiler plant in order to reduce the amount of natural gas used;

- Reduce the number of breakdowns; and

- Reduce or eliminate emission of biological gas to the air.

 

If the gas storage tank is rehabilitated, digester gas utilization would be more reliable and efficient in the boilers.  This would reduce the need for supplementing the digestor gas with purchased natural gas as well as a reduction biological gas emissions released to the environment.