Real-time inline BOD/COD…a step-change in technology to provide load-based control within WWTWs

Rob Stevensrob.stevens@rshydro.co.uk

• Lack of permanent operators & local expertise;• Relatively high energy costs;• Variable influent hydraulic & organic loads – daily, weekly,

seasonal & storm-based variability• Joined up control with influent sewer network• Inflexible & mechanical operating regimes• Increasingly stringent EU legislation• Pollution Incident Prevention• Work more efficiently within discharge consent limits

‘A real need for innovative operation & control solutions for WWTWs’

The Need for Control…

• Ammonia-nitrogen (NH4-N)• Removal responsible for c.50% of WWTw energy consumption;• Challenging due to sensor robustness, accuracy, affordability

• DO – proven to be a poor surrogate for BOD• Over-aeration – higher energy & maintenance costs;• Under-aeration – reduced biological activity and inefficient BOD and NH4-N

removal (Qureshi et al, 2008)

• Turbidity - proven to be a poor surrogate for BOD• Total Phosphorous – very expensive, requires regular maintenance• UV-VIS254 – significant usage but correlation, trust, reliability & accuracy issues• BOD

• BOD5 - 5-day testing – cannot be used for RTC control;• Analysers/Respirometers – very expensive, requires regular maintenance• Almost every WWTW worldwide has a BOD5 permit.

BOD is our ideal parameter BUT innovation is required to provide a ‘go anywhere sensor’ with low maintenance

Which Parameters

Traditional monitoring method

5 day Biochemical

Oxygen Demand Test

(BOD5)

• The scientific literature highlights TLF is strongly correlated with BOD, COD and faecal coliforms for discharges from STWs and CSOs.

TLF for BOD?

Proteus: A robust solution

Fluorescence based sensor platform for real time BOD

TLF (Tryptophan-like fluorescence): Optical signal associated with free amino acid/proteins and amino acids bound in microbial cells.

TLF

Medium sized STW: AST (~80,000 p.e)

Sewage treatment works: raw water application

Proteus BOD (mg L)Proteus performs much better than traditional BOD surrogates (Turbidity / dissolved oxygen)

(Water Research, Carstea 2017)

BOD Removal

A RECENT PROJECTUK WATER COMPANY

Mission1. To understand the dynamics of a WWTW and whether the Proteus could be

used to control or optimise the WWTW process based on real-time load.2. To become Framework Approved for next AMP Cycle

All data is anonymous but has approved for dissemination.

WWTW: settled sewage lane

• 3-month project• 30,000 real-time BOD/COD readings using wireless telemetry• 72 lab BOD/COD readings to prove repeatability and accuracy

Installation Images

• Sensor given no protection to understand how well the self-cleaning sensor maintains itself.

• Without cleaning would expect drift within an hour!

• Protection could be offered by stilling well, flow cell chamber or bio-fouling systems.

Luckily this presentation wasn’t before lunch ;-)

3 Months with no maintenance

Proteus: laboratory BOD (all samples)

Outliers from run of poor analytical quality

Proteus: laboratory BOD

Outliers

• Outliers do not mean the Proteus is not accurate• BOD/COD load varies continuously in time and place. • To obtain exactly the same reading for the Proteus and LAB you

have to take sample• At exactly the same second• At exactly the same location (ie in front of the sensor)• Neither are possible hence small variations.

• The above variability shows the vulnerability of BOD sampling. • By talking to operators of WWTWs – regular spiked BOD

samples…relies on a perfect BOD sampling process.• Best lab in UK can only offer +/-10%; most are +/-15% or worse.

Preparation: Sample collection: Transportation and storage: Laboratory test:

• Cleaning of sample bottles

• Storage of sample bottles

• Contamination of sample

• Collection of representative sample

• Manual grab samples-coarse monitoring resolution and labour intensive

• Automatic sampler -contaminated sample bottles/pump tubing + sample degradation while awaiting collection

• Fluctuations in temperature during transport

• Uncontrollable logistical constrains delaying analysis

• Storage degradation

• Variations in dilution water / contamination

• Variations in microbial seed

• Toxicants in sample inhibit oxygen consumption during assay

• Calibration/accuracy of DO meter

• Accuracy at best ±10-20%

Sources of error & uncertainty in BOD measurement

Cum

ulat

ive

err

or

Stage in the process

BOD5 result uncertainty

Proteus: laboratory COD (all samples)

Outliers from run of poor analytical quality

Proteus: laboratory COD (all samples)

Time series BOD

Time series COD

Real-Time BOD Enablers

• Optimize biodegradable chemical reagents ie methanol to enhance denitrification

• Optimization of waste water treatment processes (aeration lanes – energy saving – variable speed drives)

• Learn how a WWTW operates – nobody has ever done it!• More efficient process (working within permit limits): less

chance of pollution events• Directly match incoming load to WWTW capacity• Joined up control with influent sewer network• Provide 672 to 604,800 BOD readings (15min/1sec) per week;

not just one sample per week 7 days later.• Pollution avoidance

Thank You