1. EPAL - Empresa Portuguesa das Águas Livres S.A. www.epal.pt
Efficient Biological Treatment at Beirolas WWTP - critic oxygen
determination
METHODS
RESULTS
DISCUSSION
M. Pinheiro*, C.Carneiro**; E.Cardoso***; J. Martins***; M.J. Benoliel***;A. P. Teixeira***
*Tecnilab, marcia.pinheiro@tecnilab.pt
**Escola Superior de Tecnologia de Setúbal, carla.carneiro@estsetubal.ips.pt
***EPAL,e.cardoso@adp.pt;j.martins@adp.pt;mjbenoliel@adp.pt;ana.p.teixeira@adp.pt
The sampling period took place from July to September 2011.The analytical work was performed by Márcia Pinheiro
during her Master degree at EPAL WW Analyses Laboratory Department located at Beirolas WWTP.
The samples were collected 2 times a day, at 8h30 and 16h00. Two sampling points were controlled in each sampling
period: RBA e RBB, a total of 46 samples were analysed.
The StrathoxTM is a closed cell respirometer, developed by Strathkelvin Instruments, to performed rapid tests in order
to determine the activity of bacteria in activated sludge. This equipment measures the consumption of dissolved
oxygen,determiningtheoxygenuptakerate(OUR),andthespecificoxygenuptakerate(SOUR)fromaspecificmicrobial
population, providing relevant information for the biomass characterization.
ThetestsperformedwithStrathoxTMwerecarbonaceousandnitrifyingsludgehealth,respirationinhibition,nitrification
inhibition, short-term BDO, and optimization process test.
Each trial is carried on with 8 ml of activated sludge, 2 ml synthetic
compound and 10ml of deionized water. It is also performed at controlled
temperature and takes from 10 to 15 minutes or until complete oxygen
depletion, in the case of optimization process tests.
The nitrification inhibition test is performed by previously adding ATU
(allythiourea) to the sludge. Trials for determine MLSS from each sample
of mixed liquor were carried on.
CriticaloxygenconcentrationsforthebiologicalpopulationfromBeirolas
WWTP, were obtained from the performed protocol tests described.
Along with the sampling period the secondary effluent quality was
monitored by standardized accredited methods for BOD, COD, TSS and
pH weekly, and monthly for NO3, NH4 and NTK. Dissolved oxygen in the
aeration tank was monitored by on-line sensors during the sampling
period.
At that time we had implemented some energy-efficiency measures to improve performance of biological treatment,
namely reducing internal recirculation rate, aeration during peak energy consumption and precipitation events. The
implementation of those measures was progressive and weekly validated by secondary effluent characteristics like
BDO, COD and suspended solids.
The biological reactors also have monitoring probes for dissolved oxygen, redox potential and suspended solids.
Over a period of three months, from July to September, 46 trials were analysed by StrathoxTM, to determine bacteria
activity and oxygen consumption rates in the biological sludge.
The biological treatment at Beirolas WWTP has been designed as a
Bardenpho three-stage process, promoting the integrated removal
of nitrogen and carbon, with the possibility to promote biological
phosphorus removal. The process consists of three distinct zones:
anaerobic, anoxic and aerobic one. In the aerobic tank, it has four
theoretical“cells”inseries(Table1)wheretheoxidationoftheremaining
COD and ammonia occurs. The aeration system was dimensioned
on the basis of usage rates obtained from the application of the
mathematical model BioWIN.
Table 1 – Theoretical oxygen demands
Theoretical oxygen demand
Units Cell 1 Cell 2 Cell 3 Cell 4
g/m3
/h 58 51 50 49
KgO2
/d 3637 3198 1818 2349
mg/L 1 1 1 1
KgO2
/d 9534 7545 3900 4618
Nm3
/h 4983 4146 2175 2625
At the time this project was developed the main driving forces were
to achieve a good quality level of treated wastewater. This will allow
to discharge on Tagus estuary
References: Pinheiro, M. StrathoxTM, Energetic optimization and toxicity, IPS/ESTSetúbal; Steven A. Bolles Modeling watewater aeration systems to discover energy savings opportunities, Process Energy Services, LLC
Diamond, Ken, Mason, G, Daldowie SWT, Energy Optimization Programme Report.
Acknowledgement: Diamond, Ken, Strathkelvin Instruments; Póvoa, Pedro, AdP, The authors would like to thank EPAL the opportunity to participate in WWCongress IWA2016.
Beirolas WWTP is located in Lisbon in the right side of Tagus estuary. It began operating in 1989. In the late nineties it was up-graded. The plant capacity is 215.000 inhabitants which corresponds to a daily flow of 54.500m3. The plant design includes a secondary
treatment by activated sludge, a mesophilic anaerobic digestion of sludge and biogas utilization which provides thermic and electrical energy. The discharge permit allows for treated wastewater reuse.
The plant design was developed to achieve a good quality of treated wastewater and the possibility to reuse it for irrigation. The plant energy-efficiency was not a driver.
Activated sludge processes may be responsible for more than 50% of the energy consumption in a wastewater treatment plant.
The performance of the biological treatment may be compromised by several factors namely wastewater characteristics, industrial discharges, dissolved oxygen, etc. However the most limiting factor is the amount of available oxygen to bacteria growth. Activated
sludge respiration rate is the key to efficient process control. It indicates the BOD removal rate and the aeration requirements.
The treatment process and operational routines were already consolidated. At that time we were facing an adverse economic environment with lack of resources. The challenge was to adopt measures that would result in a more energy-efficient process.
As part of a Master’s thesis, a closed cell respirometer, StrathoxTM, was used to perform rapid tests in order to determine the microbial activity in the activated sludge of BeirolasWWTP.Those tests indicate the critical oxygen, i.e. the oxygen diffusion capacity in the bacterial
cell wall.Then we were able to adjust the aeration system to supply the necessary amount of oxygen to the bacterial growth, reducing de energy consumption in the biological process and simultaneously validating the energy-efficiency measures implemented.
INTRODUCTION
CONCLUSIONS
without any environmental damage and to consider
the possibility of reusing wastewater after treatment.
Energy-efficiency was not an issue. Latter cost’s issues
and operational optimizations became more and
more important. The operation process was under
control. The final effluent had very good quality and
the challenge was to optimise energy consumption
in the biological treatment without compromising
thequalityoffinaleffluent.Wegraduallyadoptedand
implemented several measures in order to achieve
those goals.
The StrathoxTM was the tool we used to a better
understanding of bacteria activity and its oxygen
needs. The tests are quick and simple. Performed in
10 to 15 minutes, with a friendly software, we can
validatedtheenergy-efficientmeasuresimplemented
on the biological process and aerated in function of
the critical oxygen point instead of a recommend
bibliography oxygen dissolved set point.
• We can operate the biological reator under 1mgO2
/L
• Ensure the quality of the final effluent
• Reduce energy consumption (<0,2Kwh/m3
)
• Methodology easy to implement to another WWTP
• One more step to wastewater resource recovery facility
Figure 1. Critical oxygen determination from July to September 2011 Figure 2. Critical oxygen concentration
Figure 4. Energy distribution by unit operation before implementing the
energy-efficient measures
Figure 5. Energy distribution by unit operation after implementing the
energy-efficient measures
Figure 6. Secondary clarifier
Figure 7. Alfaiates (Recurvirostra avoseta) nearby Beirolas WWTP discharge point