Treatment Strategies and Improvements at the Blackhawk WWTP Alex Kuzovkov, P.E.

Transcription

1 Treatment Strategies and Improvements at the Blackhawk WWTP Alex Kuzovkov, P.E.

2 Topics Covered Background Challenges and Priorities UV and Filters High Flows Evaluation Aeration Evaluation

3 Aeration Basins 2 and 3 Aeration Basins 4 and 5 Secondary Clarifiers Headworks Solids Treatment Building Filters Aeration Basin 1 Aerobic Digesters Blackhawk UV Disinfection Outfall to Clear Creek Regional WWTP

4 Basic information Originally constructed in 1980, upgraded in 1984,1993 and recently in 2013/2014 Average Daily Flow MGD Permitted Average Flow MGD Actual Peak Flow - 27 MGD Permitted Peak Flow MGD Participants: City of Friendswood, Harris County, MUD 55, City of Houston and Baybrook MUD 1

5 TPDES Permit Effluent Limits Daily Average mg/l 7- Day Average mg/l Daily Max mg/l Single Grab mg/l CBOD TSS Ammonia- Nitrogen Enterococci Bacteria 35 MPN/100 ml N/A 89 N/A

6 Challenges High I/I in the participants collection systems Ratio of Permitted ADF to 2 hour Peak 3.0 Ratio of Actual ADF to 2 hour Peak 5.0 Exceeded permitted effluent limits for Ammonia-Nitrogen, CBOD 5, TSS and Enterococci Filters overflowed during sustained peak rain event High aeration and UV energy use Equipment maintenance issues associated with a lack of efficient preliminary treatment Multiple stakeholders

7 Prioritization of Challenges Top Priority goals Bring effluent parameters into compliance with TCEQ permit Provide efficient and reliable primary treatment Second Priority goals Improve energy efficiency Plan for future upgrade

8 Prioritization of Challenges Top Priority Items Replacement of UV Disinfection System and rehabilitation of Filtration System Replacement of Headworks Second Priority Items Improvement of Aeration System energy efficiency: replacement of diffusers, aerators, and blowers

9 Alternatives Evaluation UV Disinfection and Filters Retrofit existing UV channel versus construction of new channel Existing channel is structurally sound Existing chlorination/dechlorination system in place can be used during construction Rehabilitate existing traveling bridge filters versus retrofit or construction of new filters Life cycle cost analysis based on NPV Sufficient capacity of existing filters

10 Alternatives Evaluation Filters: Retrofit existing traveling bridge filters into Aqua Diamond Filters versus rehabilitation of existing filters Retrofit existing traveling bridge filters Rehabilitation of the existing filters Net Present Value $3,244,000 $3,062,000 Capital Cost $2,862,000 $1,580,000 Annual Power and Maintenance Cost Life span 20 years

11 UV Disinfection and Filters Completed in April 2014 Separate Procurement and Construction Contract Total Construction Cost - $3,137,000

12 Alternatives Evaluation Replacement of Headworks Structure Headworks structure Rehabilitate existing structure Construct new structure Grit removal system Include as part of the Project Postpone installation of grit removal as part of the aeration system replacement

13 Replacement of Headworks Structure Construction Completion April 2015 Construction Contract - $1,922,100

14 Mitigation of High Flows Impact TCEQ Agreed Order Analysis of participant flow contribution during peak flow events Impact of peak flow events on plant hydraulic and process performance

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17 2013 Effluent Daily Flow with CBOD and TSS Effluent Data (24-hr Composite) CBOD Daily Average Limit: 5 mg/l TSS Daily Average Limit: 12 mg/l Flow, MGD Effluent TSS, mg/l Effluent CBOD, mg/l Flow, MGD Concentration, mg/l Jan-13 Feb-13 Apr-13 May-13 Jul-13 Sep-13 Oct-13 Dec-13 0 Month

18 Alternatives Evaluation Mitigation of High Flows Impact Side-stream equalization basin New secondary clarifier Ballasted flocculation/clarification treatment system as a tertiary treatment in lieu of the filters

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22 Alternative 1:Equalization Basin PROS Lower capital cost and life cycle cost in comparison with other alternatives CONS Potential odor problems even with aeration Requires large amount of space, limiting any future plant expansion Requires intensive labor to clean and maintain after each rain event

23 Alternative 2: New Clarifier PROS Reduce loading rate on the existing clarifiers to prevent solids washout during high flow events Provides sufficient redundancy allowing operators to rehabilitate the existing 32 year old clarifiers Saves space on site for future expansion. An additional clarifier is essential equipment critical to any plant expansion. CONS Higher capital cost and life cycle cost than constructing an equalization basin

24 Summary of Construction Cost Description Estimated Cost of Construction Alternative 1: Equalization Basin $2,554,000 Alternative 2: New Clarifier $3,888,000 Alternative 3: Ballasted Clarification $6,491,000

25 Recommended Alternative: New Clarifier and RAS Pump Station Add a new 135-foot clarifier Other equipment includes: two new RAS pumps, new grinder pumps for pumping scum to digesters, new flow splitter box with three weir gates, site work and electrical/control modifications

26 Improvements of Aeration System Efficiency Basins 1, 4 and 5: medium bubble diffusers and multistage centrifugal blowers

27 Improvements of Aeration System Efficiency Basins 2 and 3: mechanical surface aerators

28 Alternatives Evaluation Aeration: Coarse bubble and existing aerators versus fine bubble diffusers Coarse Bubble Diffusers Fine Bubble Diffusers Net Present Value $7,570,000 $6,129,000 Annual Power and Maintenance Cost; Life span 20 years.

29 Alternatives Evaluation Blowers: Rehabilitation and modifications of existing multistage centrifugal blowers versus new turbo blowers Existing Multistage Blowers New Turbo Blowers Net Present Value $7,570,000 $6,129,000 Annual Power and Maintenance Cost; Life span 20 years.

30 Conclusions Prioritization and Phased Approach Beneficial if project involves several participants Useful because of budget constraints Retrofit versus New Construction Structural analysis of existing process units Potential cost savings Life cycle analysis Considerations of Future Upgrade Site limitations Consideration of capital cost for oversizing structures

31 Questions? Alexander Kuzovkov Kenyon Hunt