Why Controlling Wastewater Treatment?

Transcription

1 WW T 2002 Content Why Controlling Wastewater Treatment? Gustaf Olsson IEA Lund University Gustaf.Olsson@iea.lth.se Why control? Incentives Disturbances Control Dissolved oxygen Chemical dosage Instrumentation Control How to operate the plant towards a defined goal, despite disturbances Feedback Characteristics Large flow rates Large disturbances The influent must be accepted and treated Concentrations are small Process depends on microorganisms The product has to be consistently good Gustaf Olsson, IEA, L TH 1

2 WW T 2002 Incentives Energy consumption 1 line (Källby) Effluent quality standards Economy Plant complexity Improved tools Pumping 21% Energy consumption Mixing 4% Aeration 75% Constraints Legislation Education and training Economy Measuring devices Plant constraints Software Disturbances Gustaf Olsson, IEA, L TH 2

3 WW T 2002 Typical Disturbances - Small Plant Typical Disturbances - Large Plant Flow COD tot N tot P tot Rya Plant Sweden The Källby WWTP Lund Sweden Gustaf Olsson, IEA, L TH 3

4 WW T 2002 Typical influent characteristics Influent flow rate (Källby) Flow rate Ammonia Temperature and influent flow rate Temperature A rainy period with sludge escape Rain intensity s iu C els Meausurements (week 50-52) Flow to line Flow rate l/s Meausurements (week 50-52) Susp solids Gustaf Olsson, IEA, L TH 4

5 WW T 2002 Internal disturbance - filter backwash Unexpected COD disturbances Total flow Backwash flow Feedback control Control Implement Process Measure Decision Goal Gustaf Olsson, IEA, L TH 5

6 WW T 2002 Open Loop Control Bio-P removal plant Timer Control Process Influent Bio-P reactor Anoxic reactor Aerobic reactor Effluent No measurement made to verify control actions! Internal recirculation Sludge recirculation Sludge outtake Control Handles Timescales Small costs waste sludge flowrate return sludge flowrate step feed recycle schemes Larger costs chemical additions external carbon sludge conditioning aeration Days - weeks biomass growth Hours to days concentration dynamics nutrient removal Minutes to hours flow dynamics dissolved oxygen Supervisory control Advanced process control Basic control Gustaf Olsson, IEA, L TH 6

7 WW T 2002 Control structures for aeration 3,5 DO concentrations in 3 zones over a 7 day period DO (6 and 7) DO (8) DO (9) (a) Constant aeration rate Com pressor Aerobic reactor (d) D issolved profile control 3 DO sensor in zone 8 2,5 (b) Open loop control based on tim e Timer (e) Dynamic set point control Ammonia sensor DO, mg/l O n/off 2 (c) Closed loop control Communicati Programmabl o n lin e e controller Variable speed drive Dissolved oxygen sensor 1,5 Lines sending set point,qjlogvhq 1 22-okt 23-okt 24-okt 25-okt 26-okt 27-okt 28-okt 29-okt 30-okt 2500 Air flow rates in 3 zones over a 7 day period Airflow (6 and 7) Airflow (8) Airflow (9) Total Phosphorus Precipitation 2000 Precipitation chemicals Flow Normal M3/hour DO sensor in zone 8 Phosphates 1. Dosing of precipitation chemicals 2. Precipitation Flocs/particles sedimentates 500,QJLOGVHQ 0 22-okt 23-okt 24-okt 25-okt 26-okt 27-okt 28-okt 29-okt 30-okt 3. Coagulation 4. Flocculation 5. Sedimentation Gustaf Olsson, IEA, L TH 7

8 WW T 2002 Chemical dosage based on hydraulic load Chemical dosage based on P load Effluent PO 4 -P conc. Ingildsen Effluent PO 4 -P conc. Ingildsen Chemical dosage based on P sensor feedback Effluent PO 4 -P conc. Instrumentation Ingildsen Gustaf Olsson, IEA, L TH 8

9 WW T 2002 Instrumentation in WWT Physical variables (levels, flows, pressure) Primary properties of WW (SS, ph, alk., cond.) DO Organic content (COD, TOC) Nutrient concentrations (NH 4, NO 3, PO 4 ) Bacterial content Respiration rate Traditional nutrient analysers Heated pipes Pump Heated building Traditional analyser Ultra filters All functions in one, EVITA INSITU sensor Nutrient InSitu Sensor Principle of Danfoss In-situ sensor Gustaf Olsson, IEA, L TH 9

10 WW T 2002 Conclusion Disturbances are significant Try to compensate for disturbances Save energy Save chemicals Save on labour costs Consistent operation around the clock Gustaf Olsson, IEA, L TH 10