No-Holds-Barred Match: RBC vs. MBR

Transcription

1 No-Holds-Barred Match: RBC vs. MBR Northeast Onsite Wastewater Short Course & Exhibition April 6 th, 2016 Erin K. Moore, PE Services provided in NY as T&B Engineering, PC

2 Overview Evaluation target Historic use of technology Technology differentiators Case studies Design considerations

3 The Battlefield

4 The Battlefield

5 RBCs vs. MBRs Rotating Biological Contactors (RBC) Invented in Europe in 1960 Used in US late 1970 s to present Paired with clarification for secondary treatment Additional reactors for denitrification Membrane Bioreactor (MBR) Invented in mid 1960 s Used in US mid-1990 s to present Capable of secondary & tertiary treatment

6 RBC Principals of Operation Rotating media aerates waste Attached growth on media removes BOD & nitrogen Excess growth falls off RBC and is settled

7 MBR Principals of Operation Same principal as activated sludge process Membrane filters replace clarifiers

8 RBC vs. MBR Similarities Both technologies proven performers Both widely used throughout NE Differences Site Constraints Effluent Quality Energy Usage Sludge Production Operational Complexity High Flow Management

9 Annual Excedances per Facility Process Reliability 3.0 Facility Exceedance Comparison BOD TSS TN RBC MBR Note: 1. Analysis based on MassDEP DMR records analysis of 100 RBC and 7 MBR facilities over one calendar year out of 18 TN exceedances for MBR treatment were observed at one facility.

10 Process Reliability RBCs had period of lower quality components resulting in early failure and less confidence in performance - Not current concern, but stigma is still present MBR membranes are susceptible to fouling with high FOG and fibers - Need appropriate pretreatment

11 Site Constraints MBRs will have smaller footprint than RBCs for the same average flow rate Design Factor RBC MBR Large Site Small Site

12 Sample Design Comparison Required Process Volumes for 100,000 gpd System System Component RBC MBR Preliminary Treatment N/A 6,000 gal Primary Treatment 28,000 gal N/A Flow Equalization N/A 32,000 gal Anoxic Tank N/A 20,300 gal Aeration Tank N/A 21,400 gal RBC or Membrane Tank 42,000 gal 15,400 gal Secondary Clarifiers 46,000 gal N/A Sludge Storage 40,000 gal 16,300 gal Tertiary Treatment 24,000 gal N/A Total: 180,000 gal 111,400 gal Note: Plants designed to achieve a discharge permit of 30/30/10 for BOD/TSS/TN.

13 Effluent Quality Nitrogen & Phosphorus Removal Required? Lower Lifecycle cost with MBRs Lifecycle Cost Capital Electricity Sludge Production Chemical Usage Equipment Replacement Design Factor RBC MBR Nutrient Removal or Effluent Reuse BOD/TSS/ Ammonia Limits

14 Lifecycle Cost Factors MBRs have higher energy consumption MBRs have higher maintenance costs RBCs produce more sludge Design Factor RBC MBR Less Electricity Permeate pumps and blowers drive MBR energy consumption Lower Maintenance Cost Less Sludge

15 Effluent Quality MBR Higher Quality Effluent = Greater Protection of Disposal Area Design Factor RBC MBR Subsurface Disposal Protection

16 Operational Complexity MBRs More Complicated, But Highly Automated RBCs More Operator Labor Less Maintenance Labor RBCs May Have Lower Grade Operator Requirement Design Factor RBC MBR Higher Complexity & Automation Less Maintenance Lower Grade Operator

17 Highly Variable Flows RBCs better suited to handle highly variable flows Highly Variable Flows = High MBR Equalization Cost Design Factor RBC MBR Highly Variable Flows Low Peaks or I&I Impacts

18 Case Study 1 Hyde Park, NY RBC Plant built in 1980 s Permitted Flow: 132,000 gpd Average Flow: 70,000 gpd

19 Case Study 1 Hyde Park, NY Site Constraints: Large Parcel

20 Case Study 1 Hyde Park, NY Effluent Quality BOD: <5 mg/l TSS: <10 mg/l Ammonia: < 2 mg/l No Nitrogen or Phosphorus Limits Surface Discharge Operations Some Operator Grade Requirement Concerns High I/I Flow Impacts Daily Average Flows >400,000 gpd

21 Case Study 1 Hyde Park, NY Design Factor RBC MBR Large Site Effluent Quality Operations Concerns Highly Variable Flows Plant rehabilitation with continued use of RBCs was recommended for this facility

22 RBC Design Considerations Consider Load Cells Determined weight of contactor to determine thickness of biomass Baffles Can existing tank support baffles to create additional treatment stages Enclosures Easy media observation vs. humidity and HVAC concerns Maintenance needs Site Topography Can layout be adjusted to avoid pumping? Process pumping lessens cost effectiveness.

23 Case Study 2 Wayland, MA WWTP built in 1960 s Permitted Flow: 52,000 gpd

24 Case Study 2 Wayland, MA Site Constraints: ¾ acre parcel with close neighbors

25 Case Study 2 Wayland, MA Effluent Quality BOD: <5 mg/l TSS: <10 mg/l Nitrogen: < 10 mg/l Phosphorus: <0.1 mg/l Surface Discharge to wetland Operations No staffing concerns Low flow variability Low pressure collection system

26 Case Study 2 Wayland, MA Design Factor RBC MBR Small Site Effluent Quality No Operational Concerns Low Flow Variation New MBR Plant was recommended for this location

27 Case Study 2 Wayland, MA MBR Features Minimal aesthetic impact to adjacent development Entire system in building for odor/noise control 2 mm fine screens Kubota flat plate membranes» Reduced fouling» Stacked plates reduce cleaning air Anoxic Zone & RAS Pumps Pre-aeration Tank MBR Tank

28 Case Study 2 Wayland, MA Influent BOD Loads Design = 320 mg/l Observed 600 to 1,500 mg/l Typical effluent <5 mg/l Noise Blower turn down during startup created resonance Piping changes resolved problems Program changes increased loads Overnight blower turndown noise issue

29 MBR Design Considerations Influent Screening 2-3 mm perforated plate recommended Flow Equalization EQ is often less expensive than more membranes to handle peaks Surface Wasting Near surface sludge wasting allows solids & FOG removal Cleaning & Process Aeration Cleaning & process air systems vary between vendors and are not all equal in terms of energy/efficiency

30 Questions?? Thank You! Erin Moore, P.E., Project Manager, Tighe & Bond, Inc.