Analytical Instrumentation for Wastewater Monitoring

Transcription

1 January 23, 2014 Analytical Instrumentation for Wastewater Monitoring ONLINE MONITORING FOR INDUSTRIAL WWT APPLICATIONS 1

2 Did you see this? It is sooo cold. 2

3 Rob Smith, P.E., BCEE, Ph.D. Applications Engineer - Wastewater 3

4 Outline Intro to online process instrumentation Applications Automotive Chemical Dairy 4

5 Intro to online process instrumentation 5

6 Instrumental methods of analysis Electrical Potentiometric - ISE - Titration Amperometric - Polarographic Optical Absorption - colorimetry - spectrophotometry Scattering - nephelometry Emission - AAS Fluorimetry 6

7 Industrial WW monitoring Type Sample collection Sample measurement Manual Manual (grab) Manual (lab) Offline Automatic (sampler) Manual (lab) Online Automatic Automatic 7

8 Automatic sampling & measurement Cabinet analyzers Wet chemistry miniaturized, automated lab Colorimetry, titration, ISE 8

9 Cabinet analyzers Advantages / Disadvantages Advantages 1) Accurate 2) Always on (w/ incremental cost) 3) Compliance methods 4) Many parameters Disadvantages 1) Cost acquisition and operation 2) Complexity sample transport, processing, measurement 3) Time lag 9

10 Automatic sampling & measurement Immersible sensors Direct measurement Amperometry, ISE, light scattering, spectroscopy 10

11 Sensors Advantages / Disadvantages Advantages 1) Continuous 2) Always on (no incremental cost) 3) Suitable for feedback control 4) Simplicity Disadvantages 1) Acquisition cost 2) Familiarity 3) Limited number of parameters 4) Accuracy 11

12 Instrument characteristics Accuracy vs. Repeatability 12 Using On-Line Analyzers to Meet Stringent Nutrient Discharge Limits, Workshop 105, WEFTEC 2012.

13 Instrument characteristics Linearity y = b + mx b = zero offset m = slope Local linearity 13

14 Instrument characteristics Dynamic characteristics Damping / signal averaging Response time 14 Automation of Wastewater Treatment Facilities, 3 rd Edition, WEF MOP-21, WEF Press, Alexandria, VA, 2007.

15 Applications 15

16 Industrial WW management Reasons to monitor Regulatory (requirement) Local Limits NPDES (Pre-)Treatment optimization (optional / beneficial) Surcharge minimization Energy demand reduction Goodwill / community relations (optional / beneficial) Product loss prevention (economic requirement) 16

17 Automotive accessory manufacturer Objective: compliance with TIN limit Ammonia-N = mg/l (untreated, before modifications) Modifications for N removal (predenitrification configuration) EQ converted to anoxic Recycle pump MicroC Ammonia-N = 15 to 25 mg/l (treated, after modifications) Composited samples 17

18 Ion selective electrode (ISE) measurement system

19 Structure of an ISE 19

20 ISE measuring systems Nernst equation y = b + mx 20

21 Predenitrification Typical online monitoring system 21

22 Nitrification dynamics Online effluent monitoring 22

23 Monday effect Online anoxic zone monitoring Carbon dosing off to save money Aerators, Recycle pumps - on Nitrified influent displaced to anoxic zone 23

24 Solution: Increase C feed or recirculation? Degradable C limiting reaction Feed pump set to lowest setting over weekend Next step: dial-in recirculation rate 24

25 Dairy wastewater applications Indirect discharge monitoring TSS ph Organics Load detection / product retention TSS Conductivity Organics (SAC 254, COD) (Pre)-Treatment optimization DO ORP ph 25

26 Case Study Product retention Monitoring solids product losses TSS sensor in-channel Detection of product loss Sequential sampler Identification of origin 26

27 Dairy wastewater load detection 27

28 UV-Vis spectroscopy What does absorbed light tell you? 28

29 Case study - dairy Improved troubleshooting with UV spectral sensors

30 Wastewater simulation Correlation of measured spectra to reference measurements + Mathematics Analysis models (mathematical Algorithms) 1. Municipal 2. Brewery 3. Dairy

31 Calculation Models stored in instrument Measurement procedure Record spectra Calculate concentrations from model mathematics COD, TOC, BOD, NO 3 -N, TSS mg/l

32 Chemical industries Turbidity to detect hydraulic overload or process upset Sensor fouling almost daily, instrument accessibility a challenge Rapid biofilm formation Lime addition Wipers ineffective 32

33 Measurement of scattered light at an angle Many different designs light Backscatter Thickened sludge Absorbance (traditional) 33 < 90 (MLSS) Nephelometry (effluent)

34 Interferences Solids / Turbidity Biomass Emulsions Grease Bubbles Scale Walls, floor Cleaning options: Mechanical wiper Air or water Ultrasonic Combination Manual 34

35 Dairy wastewater Pre-Treatment optimization Q = 100,000 gpd COD = 7,500 mg/l Anaerobic treatment Aerobic treatment 6 blowers Treated effluent discharged to municipal sewer 35

36 Optical DO sensor Detector Filter Optical insulation Gas selective membrane with fluorescence dye

37 Low DO Concentrations High signal intensity

38 High DO Concentrations Low signal intensity O 2 O 2 O O 2 2 O 2 O 2 O 2 O 2 O 2

39 Automated DO control Saved time, saved money Time spent on manual measurement One-man operation Sampling & measuring Maintenance hassle factor Money saved with online measurement System reacts immediately Blowers start/stop to maintain target DO (0.2 to 0.5 mg/l) continuously Constant information, better job at operations 39

40 Resistance to the use of instrumentation 3 critical factors 1. Types of instruments with unique maintenance requirements 2. Too many instruments 3. Safety / accessibility 40