Study on the Recycling and Reuse of Water Resources for Study on the Recycling and Reuse of Water Resources for the Arid and Water-deficient Area in Western Chinathe Arid and Water-deficient Area in Western China

Key Project of the National Natural Science Foundation of China (NSFC)Key Project of the National Natural Science Foundation of China (NSFC)(Grant No. 50138020)(Grant No. 50138020)

In western China especially the northwestern region, people have been for long suffering from chronic water shortage. This restricts the speed of development and affects peoples’ living quality. There are mainly three reasons for this problem: (1) Dry climate and low rainfall resulting in an absolute deficiency of total water quantity; (2) Water quality pollution due to natural and artificial reasons, resulting in a shortage of qualitatively available water resources; (3) Shortage of financial sources for water resource development or appropriate water treatment.

Study OutputsStudy Outputs

BackgroundBackground

Dynamic analysis and modeling Dynamic analysis and modeling of centralized and decentralized of centralized and decentralized wastewater treatment and reuse wastewater treatment and reuse systemssystems

System dynamic (SD) method was applied for the development of a mathematic model for the analysis of a water supply system which incorporates reclaimed water from centralized or decentralized wastewater treatment as a supplementary water resource, taking into consideration of social, economic and environmental factors.

Consequently many people in this region cannot be supplied with the minimum amount of water for drinking and sanitary purposes, and water shortage becomes more and more serious with the increase of population as well as industrial development. Continuous development of exploitable water resources or long distance water transfer may be one measure to solve the water shortage problem but this needs large-scale investment and often causes new environmental problems. Under such circumstances, water recycling and reuse is thought to be a practical way to meet the needs of sustainable development in western China.

Modeling and optimization of Modeling and optimization of treatment for wastewater reusetreatment for wastewater reuse

A soft package (SimWin) was developed for an optimized selection of unit treatment technology and combination of physical, physiochemical, biological and chemical processes for the treatment of domestic wastewater to meet the requirement of water reuse for certain purposes according to raw wastewater quality, scale of treatment and reuse, and other factors. This leads to a rational design of a treatment plant to achieve water reclamation in China, especially in the dry and water deficient northwestern regions.

Development of applicable Development of applicable treatment technologiestreatment technologies

Enhanced primary treatmentEnhanced primary treatment

Suspended matter takes a large portion of the contaminants in the raw domestic wastewater and enhanced primary treatment was found to be applicable to achieve a substantial removal of COD, BOD etc.

Combination of enhanced primary Combination of enhanced primary treatment with biodegradation – treatment with biodegradation – Fluidized Pellet Bed BioreactorFluidized Pellet Bed Bioreactor

Within a total hydraulic retention time (HRT) of 33 minutes, the FPB bioreactor achieved COD, BOD, SS and TP removals of 90.0%, 93.6%, 95.6% and 94.1%, respectively from raw domestic sewage. About 40% removal of TN and 35% removal of NH3-N were also achieved.

A newly developed biofilm supporterA newly developed biofilm supporter

With its surface well modified with pore size suitable for microorganisms to grow, the newly developed medium is used as biofilm supporter in a turbulent bed or moving bed bioreactor to achieve effective removal of nitrogen and phosphorus.

0.45mSuspendedDissolved

BOD

COD

TPTN SS

←40% 60%→

← 35% 65%→

←50% 50%→←80% 20%→

Classifi-cation

←70

%30%→

←60

% 40%→

←55

%45

%→

←30

% 70%→Org

anic

Inor

gan

ic

Original surfaceOriginal surface Modified surfaceModified surfaceBiomass on theBiomass on the

surfacesurface

Advanced treatment processesAdvanced treatment processes

A series of experimental studies were conducted for advanced wastewater treatment for water reclamation:

• Application of ultrafiltration (UF) for tertiary treatment of the secondary effluent

• Development of a dispersed-ozone floatation (DOF) separator for simultaneous tertiary treatment and disinfection

• Development of a hybrid submerged membrane bioreactor which combines both suspended growth-activated sludge and attached growth-biofilm with MF membrane for wastewater treatment and reuse.

Pilot study of a decentralized Pilot study of a decentralized wastewater treatment and reuse systemwastewater treatment and reuse system

A pilot plant was implemented in a village at the entrance of Xi’an Xiang-yu Forest Park, using a modified SBR and enhanced filtration process. The treated water is used for onsite irrigation.

Risk assessment of water reuseRisk assessment of water reuse

The risk of using treated wastewater for various purposes of wastewater reuse was assessed mainly regarding the pathogenic microorganisms. PCR assay was applied for a fast and accurate identification of microorganisms.

Economic and management aspectsEconomic and management aspects

Several models were developed for economic assessment of water reuse. Life Circle Assessment was used as a tool for a comprehensive analysis of both centralized and decentralized wastewater treatment and reuse systems.

R ational size of reused w ater

C hange of reused w ater price

Wastew ater drainage volum e

Expected volum e of reused w ater treatm ent

+

Wastew ater treatm ent volum e +

Financial dem and of reuse project

Investm ent of reused w ater distributive netw ork

Pipe m aintaining cost

Financial dem and of reused w ater running

+

-

Increasing rate of reused w ater

+

Factors influencing consum ers ’ acceptable degree

-

<w ater price>

+

R eused w ater volum e <district living w ater>

+

Wastew ater drainage coefficient

+ <reused w ater dem and>

+

Expected increasing rate of reused w ater

-

R eused w ater treatm ent size

+

-

+ +

+

+

Legend

1 – raw water tank2 – raw water pump3 – static mixer4 – flow meter5 – FPB column6 – agitating blades7 – sampling tube8 – motor9 – outlet10 – recycling water tank11 – air dissolving pump 12 – pressure tank

10

1

Raw wastewater

1211Effluent9

8

Air

2 3 4

PAM

4

6

5

PAC

7

Recycle