Advanced Wastewater Treatment Processes

Kung-Hui (Bella) Chu, P.E. Ph.D.Assistant Professor

The Zachry Department of Civil Engineering, Texas A&M UniversityTel: 979-845-1403 e-mail: kchu@civil.tamu.edu

March 24, 2009

Topics

• Regulation: Current & Future• Biological Nutrient Removal

– Nitrification/Denitrification– Phosphorus Removal

• Membrane Bioreactor• Emerging Contaminants in Wastewater

US Federal Regulation

Min 2nd Eff. Nat. Std.• BOD5 220 mg/L <30 mg/L• TSS 220 mg/L <30 mg/L• Total Nitrogen 40-50 mg/L

NH4+-N 10-30 mg/L

Organic-N 10-25 mg/L• Total Phosphorous (as P) 8 mg/l• Total coliforms 107- 108/100 ml <200 CFU/100mL

In 2001, US EPA published water quality criteria for 17 ecoregions.

3 mg/L

0.03-0.07 mg/L

Wastewater Characteristics & 2nd Effluent Discharge Criteria

Texas 2nd Effluent Limitations

• BOD5– 20 mg/L (30-day average)– 10 mg/L (30-day average, enhanced with

nitrification)• TSS

– 20 mg/L (30-day average– 15 mg/L (30-day average, enhanced with

nitrification)

• No Numerical criteria

• Residual chorine removed

Status of Nutrient Regulation in Texas

Current: no numerical criteria for nutrients

Future: TCEQ currently considers nutrient controls by

1) applying narrative criteria to address permitted nutrient loadings at sites of concern,

2) developing watershed rules which require nutrient reductions in wastewater discharges in or near specified water bodies, and

3) employing the TCEQ’s antidegradation policy to increases in discharge loads of nutrients.

The TCEQ also screens phosphorus and nitrate nitrogen andchlorophyll a monitoring data as a preliminary indication of areas of possible concern in the Texas Water Quality Inventory under Section 305(b) of the federal Clean Water Act (CWA).”

Source: http://www.tceq.state.tx.us/permitting/water_quality/wq_assessment/standards/WQ_standards_intro.html

wastewater

Screen

Wastewater Treatment Plant Conventional Activated Sludge Process

For optimized operation conditions • BOD Removal : 90%~99.5% • TN Removal : 50%~70% (~ 14-40 mg/L)• TP Removal : 70%~90% (~ 6 mg/L)

⇒ Might not meet future effluent limitations

Biological Nutrient Removal (BNR)

Using certain types of microorganisms to remove nitrogen and phosphorus in

wastewater for us

• Electron Donor (e- donor)– Reduced compounds

Organics: Glucose, oils, grease, etc.Inorganics: Fe 2+

• Electron Acceptor (e- acceptor)– O2– NO3

-

– SO42-

– CO2

Electron Donor and Acceptor

Biological Nitrogen RemovalFor N removal:

• Nitrification (O2 required)NH4

+ NO2- NO3

-

• Denitrification (no O2)NO3

- N2

For P removal: (first no O2 then with O2)

Poly P Pi + PAH (polyhydroxybutyrate)

Pi + PAH Poly P

Nitrification • Two major groups of microorganisms

NH4+ + 1.5 O2 NO2

- + 2H+ +H2O (Nitrosomonas, prefix Nitroso)

NO2- + 0.5 O2 NO3

-

(Nitrobacter, recently Nitrospira)

• Long SRT (~ 15 d) and low decay rate ( b = 0.05 day-1)θx, min, nitrifiers = 2.1 days >> θx, min, heterotrophs = 0.2 days

One-Sludge Nitrification

• One-sludge – nitrifiers and

heterotrophscoexist.

– One reactor and one settler for all types of microorganisms.

Source: Environmental Biotechnology: Principles and Applications, By Rittmann and McCarty McGraw-Hill, 2001

Two-Sludge (Nitrification)

• Two-sludge – Reduce

competition between the nitrifiers and the heterotrophs.

– Two reactors and two settlers.

– Two different microbial communities, one for each sludge.

Source: Environmental Biotechnology: Principles and Applications, By Rittmann and McCarty McGraw-Hill, 2001

One-Sludge vs Two-Sludge

• One-sludge • little control on incoming toxicants and pH• rising sludge problem

• Two-sludge• keep toxicants from 2-stage• 1st settler doesn’t have rising sludge, 2nd settler

might.• Good to keep BOD5/TKN low for nitrification

C/N ratio vs. nitrifier fraction

Denitrification• Many heterotrophic and autotrophic bacteria

are capable of shifting between oxygen respiration and nitrogen respiration.

• All denitrifiers are facultative aerobes.– G – Proteobacteria, such as Pseudomonas,

Alcaligenes, Paracoccus, and Thiobacillus.– G+ : Bacillus– Archaea: Halobacterium

Denitrification• Dissimilatory reduction of NO3

- or NO2- to N2

e- acceptor: NO3- or NO2

-

e- donor: organics or inorganics(H2 and reduced sulfur)

• Possible e- donor sources: sewage organics (effluent)external source

(sugars, methanol, acetate, ethanol)

One-Sludge Denitrification: Biomass Storage and Decay

Source: Environmental Biotechnology: Principles and Applications, By Rittmann and McCarty McGraw-Hill, 2001

One-sludge Denitrification:Predenitrification

Source: Environmental Biotechnology: Principles and Applications, By Rittmann and McCarty McGraw-Hill, 2001

Mechanisms for P Removal

Source: Environmental Biotechnology: Principles and Applications, By Rittmann and McCarty McGraw-Hill, 2001

Process Configurations for P Removal

Source: Stensel, 2001, WEFTEC

BNR: Nutrient Removal Efficiency

What’s New?

Membrane Bioreactors (MBR)

• Developed 40 years ago

• Used commercially in Japan for 30 years

• Needs for high quality water

Membrane & Membrane Bioreactor

Source: Filtration + Separation January/February. 2008. 45(1):32-35

Conventional WWTP vs. MBR

Based on • Membrane Process Mode

– Diffusion– Extraction– Rejection

• Process Configuration– Immersed– Sidestream

• Membrane Configuration– Hollow fibre– Flat Plate– Multitubes

Principle Configurations of MBR Technologies

Can be Airlift or Pumped

Process Configuration

Membrane ConfigurationSource: Trends in Biotechnology 2009. 26(2):109-115

Source: Trends in Biotechnology 2009. 26(2):109-115Source: Trends in Biotechnology 2009. 26(2):109-115

in Biotechnology 2009. 26(2):109-115

• Low space required.• Maintain higher biomass concentration,

volumetric loading rates, and less sludge production.

• Greater control of longer SRT & HRT allow for retention and degradation of slowly biodegradable contaminant.

• Higher rate of nitrification and denitrification.• High quality treated effluent.

Advantage of MBR

• Higher operation and energy cost

• Membrane lifetime and replacement

• Membrane fouling problem

Disadvantage of MBR

Source: Meng et al. Water Research (2009), DOI:10.1016/j.waters.2008.12.044

Source: Meng et al. Water Research (2009), DOI:10.1016/j.waters.2008.12.044

What’s Hot?

Emerging Contaminants

1962 1996

Population decline FeminizationAbnormal reproductive system Reproduction failure

Endocrine Disrupting

Compounds(EDCs)

Endocrine-Disrupting Compounds• Endocrine system regulates important biological functions

• Growth • Development • Reproductioneating/sleeping fetus, puberty reproductive system

• Chemicals (synthetic or natural) mimic or act like hormones

• One of top six research priorities identified by EPA’s Office of Research and Development in 1996.

Estrogens and PPCPs in Environment• Found in sediments, rivers, lakes, drinking water,

treated wastewater, and groundwater.

• Hormones and many other pharmaceuticals were detected in 108 (80% of 139) US rivers surveyed by USGS in 1999-2000 (Koplin et al. 2002. ES &T).

Frequently detected compounds• Caffeine • Insect repellents• Hormones• Fire retardants• Plasticizers

• sample locations

PPCPs• Considered as environmental pollutants recently• More than 80 different classes (Daughton and Ternes, 1999)

Prozac, antidepressant

17β-estradiol

COH

CH

HO

17α-ethynyl estradiol

Diltiziam Verapamil (antiarrhythmic)

OH

HO

Wastewater: A major source of EDCs / PPCPs

Adapted from Ternes (April 2000)

• Individual usage

• Intentional disposal: flushing expired drugs into toilets

Eff (ng/L) Removal (%)17 β –estradiol 0.1-64 76-92Estrone 3-82 19-94Estriol 0.4-18 85-9917α-ethynyl estradiol 0.1-42 83-84

from Lai et al. (2000), Johnson and Sumpter (2001) and Ying et al. (2002).

Estrogen removal varies among WWTPs

Adapted from Ternes (April 2000)

Eco-health impacts

Wastewater Treatment Plant

Water treatmentDrugged drinking water (EHP,2000)

Reclaimed

Improve estrogen removal through biodegradation

• 70-80% of added 14C-17β-estradiol was mineralized into 14CO2 in 24 hours in activated sludge samples (Layton et al. 2000).

• The first 17β-estradiol-degrading culture, Novosphingomonassp. ARI-1, was isolated from activated sludge (Fujii et al. 2002).

=> Biodegradation can be a major removal mechanism

Wastewater TreatmentPlant (WWTP)

• 14 estrogen-degrading isolates were phylogenetically diverse.

• 7 uncultivable estrogen degraders were detected by Q-FAST assay.

• 3 patterns of estrogen degradation were observed.• Application of ARI-1 for estrogen removal is challenging. • Mineralization of estrogen might involve many microbes.

Estrogens can be biodegraded effectively

Our Current Research

Source: Yu et al. 2007. ES &T, 41:486-492

Questions?