Reuse of urban wastewater: Implementation of an innovative system

FAO Projet GCP/RAB/013/ITA

Prof. Salvatore Masi

Associate Professor of Sanitary-Environmental Engineering School of Engineering – University of Basilicata, Potenza (Italy)

The scarcity of water resources is a global problem. Even in the south of Italy there are large areas classified as

semi-arid and desertification risk.

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Why reuse of urban wastewater?

Urban wastewater:

is an unconventional and non-competitive with other

uses resource ;

Is often the most available water resource in dry areas

and areas with low availability of fresh water;

provide environmental benefits to receiving water

bodies and reduce CO2 emissions

Wastewater is widely used in an uncontrolled way

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Sanitary risks

The risks associated with the handling of treated wastewater, alone or in combination, are relatively low.

If conducted in a controlled way, treated wastewater reclamation for agricultural reuse is safe from health risks.

In any case, the level of risk depends on the following aspects:

Types of treatment

Irrigated crops

Irrigation techniques

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Health risks associated with crops

RISK LEVEL TYPE OF CROP

High

Vegetables to be eaten raw

Fruit grown near the ground

Gardens and parks

Medium Vegetables to be eaten cooked

Fruits harvested in the irrigation period

Low Forage consumed after drying

Crop seeds (maize, soybean)

Very Low Fiber crops (cotton, hemp)

Energy crops

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Health risks associated with different irrigation systems

RISK LEVEL IRRIGATION SYSTEMS

High SPRINKLING

Medium INFILTRATION

Low DRIP IRRIGATION

Very Low SUB-SOIL IRRIGATION

General aspects of waste water reuse

Currently for wastewater reuse trying to achieve the same quality of natural surface water. This is true in particular for the content of pathogenic microorganisms. In this way, however, are lost almost entirely agronomically useful substances contained in the wastewater organic carbon nitrogen Phosphorus. These substances are subsequently added to the soil for their enrichment and for fertilization.

The innovative idea is to operate a controlled and selective removal of these substances.

Recirculation of sludge

Recirculation of NO3

High Corg

O2 CO2 CO2

High NH4

N2

Corg

NH4

NO3

NO3

NH4

Corg

Low Corg

Low NH4

High Sludge

production

Conventional scheme of treatment: flux of macro compound

discharge

into surface

waters

Recirculation of sludge

Recirculation of NO3

High Corg

O2 CO2 CO2 N2

High NH4

Corg

NH4

NO3

NO3

NH4

Corg

Low Corg

Low NH4

Low NH4

Low NO3

High Corg (stable)

High NH4

Low NO3

NH4

Corg

Innovative scheme of treatment: flux of macro compound

Low Sludge

production

discharge

into surface

waters

Fertiirrigation

application

Recirculation of sludge

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Main compounds Wastewater

Influent

Treated

Wastewater

Effluent

Ammonia High Low

Nitrate Low High

Readily Biodegradable Organic Matter High Low

Slowly Biodegradable Organic Matter High High

Selective remotion schemes for wastewater agricoltural reuse

HYPOTHESIS:

partial, selective and modular removal of the agronomically useful substances

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Pilot plant scheme

1. Dortmund clariflocculation unit

2. Storage tank water to be filtered

3. Filtration pressure on quartz san

4. Disinfection

5. Disinfected water storage tank for backwashing filter

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Pilot plant

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MODULAR REMOTION SCHEMES FOR WASTEWATER AGRICOLTURAL REUSE

100% internal recirculation

0% internal recirculation

HIGH Release

LOW Release

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LOW REMOTION SCHEMES FOR WASTEWATER AGRICOLTURAL

REUSE

100% all internal recirculation

0% internal recirculation

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Experimental field for irrigation of olive trees

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Experimental field for irrigation of olive trees

Irrigated Not irrigated Irrigated Not irrigated

Kg trees-1 t ha-1

average 62.4 27.0 9.7 4.2

Experimentation of olive trees: production (average 2000-2008)

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Irrigated Not irrigated

pruning material cut

and left on the ground

spontaneous

vegetation

Experimentation of olive trees: production (average 2000-2008)

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Treated WW W.W.T.P.

scheme

Average content of

fertilizing

substances (mg/l)

Disinfection

Residual microbial

contamination

(MPN/100 ml)

COD Ntot Ptot Disinfectant mg/l Total

Coliforms Streptococchi

Sheme

n°1

Raw water

Grilling

Grit removal

Flocculation

Filtration

Disinfection

300 50 10

PAA 5-15 100-105 10-102

NaOCl 5-25 100-105 10-102

Scheme

n°2

Output by

anoxic

reactor

Sedimentation

Flocculation

Filtration

Disinfection

250 35 8

PAA 2-10 10-103 0-10

NaOCl 5-10 10-103 1-10

Scheme

n°3

Output by

secondary

settler

Flocculation

Filtration

Disinfection 60 15 2

PAA 0.5-2.5 0-102 0

NaOCl 1-5 0-102 0

Analysis of the microbial content of wastewater reuse

CO2 EMISSIONS FROM Waste Water Treatment Plant (WWTP)

W.W.T.P.

(biological oxidation)

Power

Plant

ENERGY

+ 0,5 kg CO2

SLUDGE

0,4 kg BOD

LANDFILL

Organic

Matter

1 kg BOD

CH4 RECOVERY SYSTEM

50% recovery of CH4

METABOLISM

+ 1,5 kg CO2

CH4 LOST

+ 1,25 kg CO2

CH4 lost

RECOVERY ENERGY

- 0,15 kg CO2

CO2 TOTAL PRODUCTION:

3,1 kg CO2 / kg BOD removed

Carbon Mineralisation

Equivalent Inhabitants E.I. 10.000

Water supplied per capita (m3/d) 0,2

Amount of treated water in a year (m3/year) 700.000

Total costs of conventional treatment (€/year) 250.000

Adoption of Low Remotion System,

ferti-irrigation

Recovering costs (removal of organic matter at

50%) €/year 100.000

Equivalent value of organic matter recovered €/kg 0,030

Equivalent value of nitrogen recovered €/kg 0,5

Equivalent value of phosphorus recovered €/kg 1,2

Commercial value of the recovered substances per

m3 of water €/m3 0,050

Commercial value of the recovered organic

matter for fertilization €/year 30.000

Economic value of substances recoverable by wastewater

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Thanks for your attention