Learning objective: to become familiar with

basic functions of various physical, chemical

and biological processes.

Ph

ysical ~

screening and filtration, sedimentation, flotation

Chemical ~ coagultation/flocculation, adsorption, precipitation, UV-radiation

Bio

log

ical

~

mic

robi

al d

ecom

posi

tion,

pre

datio

n, u

ptak

e in

pla

nts

4.6 Physical, biological and chemical treatment processes

What compounds can be removed from wastewater? How can Nature assist or react?

Some wastewater treatment results for small and large

water utilities

More than 2,000 persons

Less than 2,000 persons

J-O Drangert, Linköping University, Sweden

B: Physical processes

Possible combinations of physical processes

Jan-Olof Drangert, Linköping university, Sweden

screening forced micro- filtration

filtrationflotation and sedimentation

Screening of debris and other solid items

Solids trapped by a screen in a city wastewater treatment plant

Organics from kitchen pipe sorted out in a plastic screen

Jan-Olof Drangert, Linköping university, Sweden

Flotation and sedimentation processes

Inlet ofwastewater

Baffels

Outlet of treated water

Inspection hole

Floating grease, particles, organisms

Jan-Olof Drangert, Linköping university, Sweden

Sludge built up

Filtration – mainly by gravity

Saturated flow of wastewaterPartially unsaturated flowJan-Olof Drangert, Linköping university, Sweden

Forced micro-filtration

Manufactured porous material

Direction of filtered water flow

Appliedpressure

Jan-Olof Drangert, Linköping university, Sweden

C: Chemical processes

Adsorption of charged particles

G. Jacks, Royal Institute of Technology, Stockholm

OHH2PO4- + Fe OH

OH H2PO4- + Al OH

Adsorption of phosphateon ferric hydroxide

Adsorption of phosphate on aluminium hydroxide particles

The three important kinds of charged soil particles are:

1. Organic matter

R-COOH < > R-COO- + H+

(a negative pH-dependent charge)R is phenolic ring derived from lignite in residues of plants

2. Clay mineralsClay mineral consist of Al-Si-sheets

with different cations (Na+, K+ etc.)

in between the sheets. There is a

negative charge on sides and edges:

3. Ferric hydroxides

Fe(OH)3 <

> Fe(OH)2-

+ H+

(a pH-dependent positive charge)

R-COO

- Pb

2+

R-COO-

Organic ”overcoat” on a soil mineral

- -

Na+ K

+ Mg

2+ -

- -

Cu 2+

OH

Fe(III) + HAsO4

-

OH

Adsorption of charged particles to soil medium

G Jacks, Royal Institute of Technology, Stockholm

Mineral grain

Adsorption of chemical compounds differ

Copper (Cu) and Zink (Zn) are positively charged, and adsorb easily on organic matter and clays when the pH > 7

Arsenic (As) is negatively charged and adsorbs easily on ferric hydroxides when pH < 7 G Jacks, Royal Institute of Technology, Stockholm

• Precipitation – a chemical reaction between dissolved compounds to form solids

• Flocculation - an aggregation process (or processes) leading to the formation of larger particles from smaller particles

G. Jacks, Royal Institute of Technology, Stockholm

Precipitation and flocculation

+ -

-+

+

-

- +

+

Source: Ubomba-Jaswa et al. 2009

http://www.sodis.ch/Text2002/T-TheMethod.htm

UV-radiation by sunlight

Inactivation of micro-organisms by UVA-radiation and increased temperature

More diffuse stratification

Strong algal stratification

K Tonderski, Linköping University Sweden Courtesy of Duncan Mara, University of Leeds, UK

Vertical view of the pond

Shallow ponds with a dense population of algae

Ozonation and chlorination

D: Biological processes

Karin Tonderski, Linköping university, Sweden

Soil organisms vary tremendously in size and numbers

Modified from Sylvia, D. et al. 2004. Principles and applications of soil microbiology

A teaspoon soil ~ one gram

Microbial group

Example Size (µm)

Numbers (per gram soil)

Biomass (g wet mass per m2 soil)

Bacteria Pseudomonas 0.5 – 1.5 108 - 109 30 – 300

Fungi Mucor 8 (hyphae diameter)

105 – 106 50 - 500

Protozoa Euglena 15 * 50 103 - 105 0.5 – 20

Nematodes Pratylenchus 1000 10 – 102 0.1 – 10

Earthworms Lumbricus 100 000 1 - 100

3

Biological processes - with air

Oxygen is vital for most living organisms, including bacteria. When oxygen is present, organic matter (measured as BOD) is efficiently decomposed by organisms into CO2 + water:

+ oxygenUnsaturated soil profile Aerobic

bacteria

Jan-Olof Drangert, Linköping university, Sweden

organic matter in wastewater

Biological processes - without air

Many microorganisms can survive in environments with no oxygen and they use other compounds for their survival:

+ e.g. nitrate, sulphate or iron ions (Fe 3+ )

Organic matter in wastewater

CO2 + e.g. N2, S2-, Fe2+

Saturated soil profile with little or no oxygen

Anaerobic micro-organisms

Jan-Olof Drangert, Linköping university, Sweden

Microorganisms attached to surfaces are more stable than those suspended in water

Grain particle

Jan-Olof Drangert, Linköping university, Sweden

O2 H2O (oxygenisation)

NO3- N2, N2O (denitrification)

MnO2 Mn2+

Fe(OH)3 Fe2+

SO42- H2S (sulphate-reduction)

CO2 CH4 (methanogenesis)

When microorganisms descend the redox-ladder they first use O2 as an electron acceptor, then nitrate NO3, and further down other compounds as electron acceptors. The blue arrow indicates a reaction with energy-rich organic substances (electron donors) in the wastewater

Gunnar Jacks, Royal Institute of Technology, Stockholm

“Redox-ladder”

Decrease in oxygen

Gunnar Jacks, Royal Institute of Technology, Stockholm

Changes in concentrations of electron acceptors when organic matter (TOC) decomposes

What happens in the root zone?

O 2, sugars, proteins, etc.

Jan-Olof Drangert, Linköping university, Sweden

Water, nutrients, heavy metals, gases (e.g. CO2)

Organic matter, O2, NO3

- , SO4

2-, CO2 etc.

Predation on microorganisms stimulates decomposition

Courtesy of Frida Lögdberg, Linköping university

Organic matter is decomposed most efficiently in the top soil

Million organisms per gram soil

106

106

De

pth

in m

ete

rAnaerobic bacteria Aerobic bacteria

0.5 m

Courtesy of G. Jacks, Royal Institute of Technology, Stockholm

Soil surface

0