Wastewater treatment in urban areasChristoph Hinrichs, Daniel Schäfer, Nico Kocks

Wastewater sources

History of wastewater treatment•Cholera outbreaks in Europe (e.g. London, Hamburg) around 1850 Construction of sewer systems

•Around 1900: Mechanical treatment

•1960: Biological and chemical treatment

•Until today: Development of tertiary/ advanced treatments

Constituents of concernConstituent Reason for importance

Nutrients N, P & C promote growth eutrophication.

Biodegradable organics

BOD and COD Reduce natural O2resources

Suspended solids (SS)

Anaerobic conditions Photosynthesis is reduced (elevated

turbidity)

Pathogens Fecal-oral cycle needs to be disrupted.

Priority pollutants

carcinogenic, mutagenic, teratogenic, or highly toxic

Wastewater treatmenttechnology

Disinfection with UV

Wastewater flow & quality

Control of the biologicaltreatment:

•F/M ratio

•Sludge Age

³)sin(*³)/()/³(*³)/(

= 5

mPlantBamKgMLVSSdmInfluentmKgBOD

MF

DayedSolidsWastVSS

SludgeAge nkAerationTa

/=

Need for nutrient removal to avoid eutrophication of receiving waters

Biological treatment- Removal of ammonium and nitrate nitrogen - Removal of phosphorus

Biological treatment- Ammonium:Ammonia equillibrium- At neutral pH 99:1- At ~ pH8 shift to 70:30

Nitrogen removal in the biological treatment step

Ammonium

Nitrite

Nitrate

Nitrite

Nitrogen oxide

Dinitrogen oxide

NitrogenA

erobicA

naerobic

Post-anoxic Denitrification- Assembly according the order of removal processes - Organic - Additional carbon source as e-donor required

Pre-anoxic DenitrificationModified Ludzak-Ettinger (MLE) process - Organic carbon from wastewater is used as e-donor- Recirculation of sludge from nitrification tank- Reduction of recirculated Nitrate by oxidation oforganic carbon

- Most cost efficient assembly, although more removalefficient setups are available

Simultaneous Nitrification/Denitrification- Constant alternation of aerobic and anaerobic zones- Stepwise removal of Nitrogen by changingnitrifying and denitrifying conditions

Biological Phosphorus removal- P-accumulating Bacteria - Storage of acetate as carbon source under anaerobicconditions (anoxic selector)

- Utilization of these when entering aerobic zone and accumulation of phosphates as polyphosphates.

European guidelines

In march 1991 the European commision passed the guideline91/271/EWG which deals with the

• collection,• treatment and• discharge

of municipal waste water and specific industrial waste water.

This guideline came with an obligatory time schedule thatshould have been completed in 2005, but the deadline has beenwidely ignored.

A report of the EU commissionreveals that until 2001 110 of 542 bigger cities have poor or notreatment for waste water.Among them are popular citieslike Milan, Lisbon, Liverpool, Paris and Brussels.

Problem:

• These cities create an image of unimportance especially to the countries of the eastern enlargement of the EU.

• Environmental pollution is massive.

Reason:

• Great imprecision of the guideline.• EU commission trusts on self-motivation of member states.

Examples:

• “Until December 2005: All communities with a PE 2.000 and 10.000 that discharge their waste water to delicate regions as well communities with a PE between 2.000 and 15.000 that don’t discharge their waste water in such regions are bound to have a canalization and a treatment system.”

• Only North and Baltic Sea are mentioned to protect, Atlantic Ocean and Adriatic Sea are missing.

• Heavy miscalculation of the costs:– Estimated: 30 billion Euros for whole Europe– Fact: 50 billion spent just by Germany until 2001