PRoACC. WASTEWATER REUSE TOWARD ADAPTATION TO CLIMATE CHANGE IN THE MEKONG DELTA VIETNAM (WWa-ACC) TRINH THI LONG

Transcription

1 PRoACC WASTEWATER REUSE TOWARD ADAPTATION TO CLIMATE CHANGE IN THE MEKONG DELTA VIETNAM (WWa-ACC) TRINH THI LONG MENTORS: Prof. Piet Lens & Dr. Van Der Steen 1

2 THE USE OF THIS EDUCATION MATERIAL This education material can be used for postgraduated short course training as well as MSc students. Entrance level of the participants: Bachelor degree on water resources management, environment or agricultural water management. Depending on the knowledge level of the participants, the lecture including exercise can takes 1 to 2 days. 2

3 Study of Urban group This lecture is DROUGHT 3

4 LEARNING OBJECTIVES The students able to: Drought study Characterize the impacts of CC in the MD Calculation of the potential of wastewater reuse in CC adaptation measures Describe how wastewater can be reused in the MD Develope set of indicators to assess wastewater reuse options 4

5 CC IMPACT ON THE MEKONG DELTA Why wastewater should be reused in Can Tho City CONTENT REUSE WASTEWATER AS A CLIMATE CHANGE ADAPTATION MEASURE Climate change adaptation indicators to assess options for wastewater management and reuse 5

6 Climate change impacts on The Mekong Delta 6

7 MEKONG DELTA Mekong Delta, extends over 13 provinces with a land area of about 39,712 km2 (about 12.1% of the national area) is located in the centre of a dynamic and development area, connecting the Southern Focal Economic Zone, and neighboring Southeast countries, which are considered as markets and important investment partners. is the most important agricultural area of Vietnam, which contributes more than 50% foodstuff output, more than 55% aqua-cultural and fruit products; more than 61% of aqua product export of the country. The water resources contribute substantially to such achievements and therefore it is considered as a leading factor, which should be utilized carefully to sustain the environment, to ensure the high growth rate of agriculture, aquaculture, and industry. Recently, the very important constraint for socio-economic development in the Mekong Delta, especially in climate change condition, is poor wastewater management, both in 7 urban and rural areas.

8 Charasteristic of the Mekong delta Rainfalls 1,200 2,400mm/year Discharge at Tan Chau and Chau Doc Stations Flood season: 28,000 30,000 m 3 /s; high: 40,000m 3 /s Dry season: 2,600 4,000 m 3 /s; low: 2,000 2,400 m 3 /s Tides East Sea Semi dual (2 cycles/day); Amplitude: 3.2 m at Vung Tau; 1.6 m Ca Mau Thailand Gulf Combined (1cycle/day) Amplitude: 1.2m at Rach Gia, < 1m at Ha Tien 8

9 Months Problems Flood Salinity Intrusion Acid Water Drought Water-related Problems in Mekong Delta Bank Erosion Estuaries sedimentation Environmental pollution Sea Water level 9

10 Y # % Salinity distribution #% Y Y # Y # Y # Svay Rieng Takeo Cao Lanh Y # Y # Ho Chi Minh City Chau Doc Long Xuyen Y # Vinh Long % Y% # My Tho Y # Y # Kampot Y # Y # Ha Tien Y # Y # Y # Y # Kien Luong Can Tho Y # Legend Y # Y # Y # Rach Gia Tra Vinh Kb0_msal_98 VALUE Y # Khong man µ 0-1g/L Soc Trang 1-2g/L Y # 2-3g/L 3-4g/L Y # Bac Lieu 4-6g/L 6-10g/L millions ha have been affected by salinity intrusion Ca Mau 10-15v 15-30g/L 30-40g/L Kilometers

11 Droughts in the Mekong Delta 11

12 The acid sulfate soil covers 1,600,263ha, accounting for 41.10% of the total area ACID SULPHATE SOILS Shrinkage of ASS in the dry season 12

13 Flood in the Mekong Delta School 13

14 Why wastewater should be reused in Can Tho city 14

15 Area: 1,401 km2 Located at the heart of the Mekong River Delta, Can Tho City is bordered by the Hau River to the north-east, Kien Giang province to the west, Hau Giang province to the south and An Giang province to the north-west 15

16 Population of 1,171 million is the biggest city in the Mekong Delta The population density is 812 people/km², this is distributed unevenly. the population density of the Vinh Thanh, Co Do and Phong Dien districts is only 383 to 440 people/km² Source: WISDOM project in the remaining districts it is as high as 1,032 to 7,241 people/km². Especially, it is up to 7,241 people/ km² in the Ninh Kieu district. 16

17 158 rivers and canals 779 km of main (primary) canals 2000 km of secondary canals tertiary canals in each rural district 60 km Discharge water in Bassac river: about 200 billion m3/year. Rainy season: about 81% of the annual discharge Dry season: about 19% In exhausted months from March to May: only about 4%. About 84 % of the area in Can Tho is used for agriculture, more than 90 % of it for rice production. Rice is harvested up to three times per year. With a demand of 1,000 million cubic meters per year for irrigation 17

18 3h 9h 15h 21h 3h 9h 15h 21h 3h 9h 15h 21h 3h 9h 15h 21h 3h 9h 15h 21h 3h 9h 15h 21h 3h 9h 15h 21h Water level (cm) Variation of water level in Can Tho City Can Tho river Tham Tuong canal Cai Khe canal Time (7-13/9/2010) 18

19 Rain water with total average calculation for 10 year ( ) is about 2.3 billion m3/year. If making use of this source, it s nearly enough for domestic use in 3 months in the dry season. However, it s not possible to havest 100% of the rainwater. WATER RESOURCES SURFACE WATER? GROUND WATER Over-extraction, saltwater intrusion, and pollution Designed capacity: 163,558 m3/day Actual extraction: 101,061 m3/day Depression of groundwater level in Tra Noc Industrial zone Well 5 m3/day: 32,000; 50 m3/day: 400; m3/day: 30; 200 GWP in

20 BOD (mg/l) DO (mg/l) 6,0 Water quality 5,0 4,0 3,0 2,0 1,0 0,0 60,0 N18 N20 N1 N3 N6 N8 N12 N14 N11 N25 N23 N36 N38 N33 N27 N29 N31 50,0 DO in Can Tho TCVN 6773:2000 QCVN -B1 QCVN-A2 40,0 30,0 20,0 10,0 0,0 N18 N20 N1 N3 N6 N8 N12 N14 N11 N25 N23 N36 N38 N33 N27 N29 N31 20 BOD QCVN-A1 QCVN-A2 QCVN-B1

21 Total Coliform (MPN/100ml) Pathogenic organisms N18 N20 N1 N3 N6 N8 N12 N14 N11 N25 N23 N36 N38 N33 N27 N29 N31 Coliform QCVN-A1 QCVN-A2 QCVN-B1 21

22 3h 9h 15h 21h 3h 9h 15h 21h 3h 9h 15h 21h 3h 9h 15h 21h 3h 9h 15h 21h 3h 9h 15h 21h 3h 9h 15h 21h WL (inch); COD (mg/l); T-N (mg/l) Variation of COD and TN in Tham Tuong canal water Water level COD-canal Total N-canal COD-river Total N-river QCVN A1 = 10 mg/l A2 = 15 mg/l B1 = 30 mg/l MRC value TN = 1.7 mg/l 22

23 WL (inch); COD (mg/l); Total N (mg/l) Variation of COD and Total N in Cai Khe canal water h -10 9h 15h 21h 3h 9h 15h 21h 3h 9h 15h 21h 3h 9h 15h 21h 3h 9h 15h 21h 3h 9h 15h 21h 3h 9h 15h 21h -20 Water level COD-canal TN-canal COD-river TN-river QCVN A1 = 10 mg/l A2 = 15 mg/l B1 = 30 mg/l MRC value TN = 1.7 mg/l 23

24 T-N (mg/l) T-N (mg/l) COD (mg/l) COD (mg/l) Water quality Organic pollution in river/canal system of Can Tho City 30,0 25,0 20,0 15,0 10,0 5, Year VN standard Cantho river Cai Khe canal Tranoc Canal O Mon canal Thot Not canal Cai San canal Hau river 80,00 70,00 60,00 50,00 40,00 30,00 20,00 10,00 0,00 COD in canal system (9/2010) Sampling station Thoi Lai O MOn Ninh Kieu-TT Ninh Kieu-CK Vinh Thanh Thot Not Cai Rang Binh Thuy VN Standard Total N in canal system (9/2010) 35,000 30,000 25,000 20,000 15,000 10,000 5,000 0, Thoi Lai O Mon Ninh Kieu-TT Sampling station Ninh Kieu-CK Vinh Thanh Thot Not Cai Rang Binh Thuy MRC Value 4,000 3,500 3,000 2,500 2,000 1,500 1,000 0,500 0,000 Total P in canal system (9/2010) Thoi Lai O MOn Ninh Kieu-TT Ninh Kieu-CK Vinh Thanh Thot Not Cai Rang Binh Thuy MRC value Samling station 24

25 Pollution level of organic and pathogens in River/canals system in Can Tho City Level A1: for domestic water supply and other purposes as A2, B1 and B2 Level A2: for domestic water supply with appropriate treatment technology and other purposes as B1 & B2 Level B1: for irrigation and B2 Level B2: Navigation and other purposes required low quality 25

26 -The results of the water quality monitoring in the rainy season 2010 and dry season 2011 show that water in the river and canal systems in Can Tho city is contaminated with organic matter, nutrients and pathogens -According to the water quality standards of the Institute of Biology of Inland waters Academy of Sciences USSR and Principles of aquatic chemistry - The Soviet Union Academy - The water resource in the project area is classified as Meso saprobe to polisaprobe (from contaminated to heavily contaminated). Pollution sources??? 26

27 WATER POLLUTION DUE TO DOMESTIC WASTEWATER According to WHO people in the city have discharged household waste at an average of 0.87kg/day/person If this amount of pollution is diluted with rainwater in the year, it will cause rainwater polluted. in 1999 every person in Can Tho city polluted rainwater with 12mgCOD/l; in 2008 it is up to 16 mg COD/l It exceeds the Vietnamese standard level A1 with water source for water supply for domestic use (QCVN 08: 2008/BTNMT). Moreover, the idea of diluting wastewater to achieve standards is nowadays not acceptable anymore 27

28 WATER POLLUTION DUE TO WASTEWATER OF FISH POND 12,216 fishponds: average of a 2m depth (varies from 1.5 4m) upon renewing the pond water discharge amounts of up to 70 million m3/day = 27 billion m3/year The content of COD in fishponds can be up to 80mg/l. If this wastewater is diffused with the flow of the Hau River in the best conditions, the river water will carry 10mg/l of COD (exceeds QCVN 08: 2008/BTNMT) For pond Tra fish breeding in Thot Not District: 25.9% of the farmers discharged pond effluents into the Hau River, 34.3% into the canals, 5.6% into settling ponds, and 34.3% into paddy fields. Most of respondents (60.2%) reported that they dumped wastewater into public water sources, while 39.8% dumped it onto private land. 28

29 WATER POLLUTION DUE TO AQUATIC PRODUCT PROCESSING INDUSTRY WASTEWATER Aquatic product processing wastewater daily: m3 Average COD: 1,500mg/l. Rivers and canals in Can Tho City receive 22,500 tons of COD every day. At this moment, most of the industrial estates in Can Tho City do not possess a concentrated wastewater treatment system. Presumably, two-thirds of the COD concentration is disposed of, leaving just one-third of the unprocessed COD to be diffused with Hau River water. However, the concentration of COD after dilution is up to 13.6 mg/l, Exceeds the Standard QCVN 08: 2008/BTNMT 29

30 So, only one of those sources can make water quality in river/canal system of Can Tho city exceeds the permissible limitation of the current National Standard QCVN 08: 2008/BTNMT. Meanwhile, Can Tho has all those 3 sources. This is the reason that concentration of COD in surface water is increasing every year even with high flow of Hau river and pollution water if wash out to the sea everyday. 30

31 Sewage system in Can Tho city WWTP Total amount of 18,7million Euros Vietnam approximately 52% KfW and 48% Capacity 22,550m3/d, Maximum hydraulic flow of 0,726 m3/sec Mechanical treatment and biological reduction of BOD and COD TCVN B LEVEL TCVN BOD: 50 mg/l COC: 80 mg/l WWTP 31

32 REUSE WASTEWATER AS A CLIMATE CHANGE ADAPTATION MEASURE 32

33 INCREASING POPULATION URBANISATION INDUSTRIALISATION CLIMATE CHANGE DROUGHT SALINITY INTRUSION ACID WATER SPREADING INCREASING WATER DEMAND POOR W.W MANAGEMENT POOR RUNOFF WM? WATER SCARCITY 33

34 Temperature increases from C to C Rainfall decreases about 10 20% The dry seasons are predicted to lengthen and intensify Change in monthly rainfall in the Total annual rainfall in An Giang, Can Tho Mekong and Soc Delta Trang (mm) will decrease about 20%, and rainy season will start 2 weeks later. With the use of Global Circulation Models (GCMs) combined with the downscaling regional climate model PRECIS and series of data from , University Chulalongkorn - Thailand and Climate Change Research Institute Can Tho University (Vietnam) have done the forecasting for the year that many areas in the Mekong Delta will get serious impacts due to climate change 34

35 Radiation (hour/year) Temperature (ToC) Humidity (%) Rainfall (mm) Radiation average humidity Average humidity ( ) Radiation ( ) Power (average humidity) year humidity has a trend of decreasing 5% Power (Radiation) air-temperature increasing C Year ,3 27,2 27, ,9 26,8 26,7 26,6 Average Annual Rainfall ( ) Average Rainfall Pow er (Average Rainfall) Rainfall decreasing 200mm/year Average Tem perature ( ) Average Temperature ( ) Pow er (Average Temperature ( )) sun radiation increasing 200 hours/year From 2000 to 2007 in Hau river at Tan Chau, water level is decreased 0.8m, meanwhile the max water level in Can Tho is increased 0.3m with decreasing precipitation in the area facilitate salinity to intrude deeply into the land In the dry season of the year 2006, 2007 and 2008 water discharge of Hau river was only 800 m3/s instate of 1250 m3/s in about 30 years ago 35 Year Year

36 Advantages of reuse of wastewater in agriculture Conserves water (by recycling and groundwater recharge); Is a low-cost method for sanitary disposal of municipal wastewater; Reduces pollution of rivers and other surface water; Conserves nutrients, thereby reducing the need for artificial fertilizer; Increases crop yields; and Provides a reliable water supply to farmers Use for pushing seawater purposes 36

37 Guidelines for Water Reuse Type of Reuse AGRICULTURAL Food crops commercially processed Orchards and Vinerds AGRICULTURAL Food crops commercially processed Treatment Required Secondary Disinfection Secondary Filtration Disinfection Reclaimed Water Quality Recommended Monitoring Setback Distances ph = 6-9 ph weekly 300 ft from BOD 30 mg/l BOD weekly potable water supply wells SS = 30 mg/l SS daily FC 200/100 ml FC daily 100 ft from areas accessible to Cl2 residual = 1 Cl2 residual public mg/l min. continuous BOD 30 mg/l SS 30 mg/l BOD weekly SS daily FC 200/100 ml FC daily 100 ft from areas accessible to the Cl2 residual = 1 Cl2 residual public mg/l min. continuous ph = 6-9 ph weekly 50 ft from potable BOD 30 mg/l BOD weekly water supply wells Turbidity 1 NTU FC = 0/100 ml Cl2 residual = 1 mg/l min. Turbidity daily FC daily Cl2 residual continuous Source: USEPA, Process Design Manual: Guidelines for Water Reuse, Cincinnati, Ohio,

38 Potential of wastewater reuse as climate change adaptation measure 38

39 Getting bigger Wastewater is not a waste AGRICULTURE. CITY Waste water INDUSTRY Waste water HAU RIVER CANAL SYSTEM Waste water Waste water HOUSE AQUACULTRUE reuse Salinity intrusion Wastewater treatment plant reuse reuse Volume demand for water Demand SEA REUSE OPTION Wastewater reuse Renewable supplies Renewable supplies due to impacts Time 39

40 40

41 Vinh Thanh Thot Not Cropping calendar, monthly rainfall and water demands in Can Tho Co Do effluent effluent 41

42 METHODOLOGY A comprehensive assessment of the potential for reuse of wastewater in Can Tho city is a rather difficult problem. There are no previous studies on the issue and wastewater reuse has not been addressed in the: overall planning of the city, environmental protection strategy, development plans for the future water supply, or in the water resources management of the city. 42

43 METHODOLOGY The asessment of the potential of wastewater reuse for Can Tho City is based on the following investigations: Investigation of the water resources in Can Tho City (quantification, system level mapping). Baseline water quality determinations in the river/canal system in Can Tho City in rainy and dry season. Analysis of pollution sources in the city and the availability/stability of secondary treatment of centralized wastewater treatment plants in the region. Analyzing water and nutrients requirements of paddy rice crops and the demand that treated wastewater can meet. City planning of water supply and wastewater treatment. Meetings and interviews with local authorities and farmers 43

44 Amount of treated wastewater from domestic and industries available for rice irrigation by 2020 Demand and ability to provide water Winter Spring Summer Autumn Autumn Winter Total / 3 crops Water demand by crop (m 3 /crop) 1,319,346, ,230, ,109,750 2,546,687,125 Amount of Water need to be supplied (m 3 /crop) 1,257,832, ,555, ,368,674 1,952,757,085 Average amount of water need to be supplied (m 3 /day) 15,722,908 7,069,447 1,617,108 24,409,463 Treated wastewater from domestic and industries can be able to provide by 2020 (m 3 /day) 283, , , ,000 The area that treated wastewater can be irrigated (ha) 1,011 1,416 1,861 4,288 Area that treated wastewater can be irrigated (%)

45 Amount of treated wastewater from catfish farming available for rice irrigation crop by 2020 Winter Spring Summer Autumn Autumn Winter Total / 3 crops Fish production up to 2020 (tons) 240, , , ,000 Wastewater emissions from catfish farming (m 3 /day) 3,287,671-4,602,740 3,287,671-4,602,740 3,287,671-4,602,740 9,863,013-13,808,220 Potential amount of treated wastewater can be irrigated for rice (37% of the area) m3 1,216,438-1,703,014 1,216,438-1,703,014 1,216,438-1,703,014 3,649,314-5,109,042 Potential rice area that treated wastewater from catfish breeding can be irrigated (ha) 4,344 6,086 8,001 18,431 Area that treated wastewater from catfish farming can be irrigated (%)

46 Amount of nutrients as fertilizer from wastewater by 2020 Winter Spring Summer Autumn Autumn Winter Total / 3 crops Rice cultivated area (ha) 58,893 56,295 26, ,082 Nitrogen Requirement of Nitrogen (tons N/crop) 4,123 5,889 3,941-5,630 1,883-2,689 9,947-14,208 Providing capacity of N from domestic, industrial and catfish farming wastewater (tons/crop) , ,714.4 Rate of providing capacity and requirement (%) Phosphorous Requirement of phosphate (tons P/crop) 1,042-1, , Providing capacity of P from domestic, industrial and catfish farming wastewater (tons/crop) ,514-3, Rate of providing capacity and requirement (%)

47 Wastewater was found to be a highly available potential water source for rice irrigation and therefore is really not a waste. The effluent can be used to irrigate up to 22,719 ha paddy rice/year with 3 crop harvests, corresponding to 16% of the rice cultivated area. The fertilizing properties of the water eliminate part of the demand for synthetic fertilizers, providing a maximum of 22% N and 14% P of the requirement of the winter spring crop. On a yearly basis, recovery of wastewater can reduce the emission up to 15-27% for N and 8-17% for P, contributing to a decrease in the level of pollution in the river/canal systems, thus eliminating the need for expensive tertiary treatment. 47

48 Climate change adaptation indicators to assess wastewater reuse options 48

49 CLIMATE CHANGE ADAPTATION INDICATORS A major contemporary issue for policy and decisionmakers is to understand and respond to the impacts of climate change on environmental, social, and economic systems Adaptation is best measured by the indicators in the context of planned adaptation to climate change impacts because they show whether adaptation policies and measures are implemented and whether vulnerability is reduced through effective actions. Climate change adaptation indicators have played a critical role in increased understanding of climate change and its effects 49

50 Climate change adaptation indicators of wastewater management and reuse Indicator 1: Rice production from wastewater during the winter-spring crop Indicator 2: % of demand for irrigation water satisfied by treated wastewater Indicator 3: % remaining flow downstream of Can Tho in Hau River Indicator 4: % of nutrient demand satisfied by treated wastewater Indicator 5: Environmental benefits Indicator 6: Total cost investment for wastewater treatment 50

51 Evaluation of strengths and weaknesses of indicators Indicators Strengths Weaknesses Rice production from wastewater during the winter-spring crop M, C, L, CS, S, U, R % of demand for irrigation water satisfied by treated wastewater % of nutrient demand satisfied by treated wastewater % remaining flow downstream of Can Tho in Hau River M, C, L, CS, S, U, R M, C, L, CS, U, R S M, C, L, CS, S, U, R Environmental benefits C, L, CS, S, U, R M, C, V Total cost investment for wastewater treatment C, L, CS, S, U, R M, C, S 51

52 DEVELOPMENT SCENARIOS Factors Scenario 1 The best case: assumed that everything as is in the year 2020 Hau River flow Salinity intrusion Precipitation during the dry season Area of cultivated rice Minimum values of flow for the Hau River in the driest month, winter-spring crop from : 900 m 3 /s No problem, no sea water intrusion in Can Tho Scenario 2 The medium case: assumed that everything may happen as predicted by 2050 Hau River flow in the driest month of the winter-spring crop: 500 m 3 /s 2 g/l at the inlet of canal system Scenario 3 The disaster case: assumed that by 2050 climate has changed as much as predicted by 2100 Hau River flow in the driest months of the winter-spring crop: 300 m 3 /s 3.5 g/l at the inlet of the canal system as in 2010 reduce by 10% reduced by 20% as in 2020: 58,893 ha (Trinh et al., 2011) assumed that rice area increasing 15% to compensate the reduction of rice production due to climate change assumed that rice area increased by 30% to compensate for the reduction of rice production due to climate change Temperature Increase of 0.4 ºC Increase of 1ºC increase of 2.7 ºC Sea level rise increase of 11 cm increase of 33 cm increase of 100 cm 52

53 Wastewater management and reuse options Option 1: Reuse of effluent from centralized WWTPs with the capacity of 283,000 m3/day. Option 2: Reuse of effluent from centralized and decentralized WWTPs with a total estimated capacity of 500,000 m3/day. Option 3: Extensive reuse of aquaculture wastewater for rice irrigation, especially wastewater from catfish farming. Option 4 (combined option): reuse wastewater from domestic, industry and aquaculture Option 4a: Combined option 1 and option 3 Option 4b: Combined option 2 and option 3 53

54 Rating the utility value of the indicators for wastewater management and reuse assessmen Indicator Alternative Rate Indicator 1: Rice production from wastewater during the winter-spring crop (tons/crop) Indicator 2: % of demand for irrigation water satisfied by treated wastewater Indicator 3: % remaining flow downstream of Can Tho in Hau River Indicator 4: % of nutrient demand satisfied by treated wastewater 150, , N P Indicator 5: Environmental benefits (million /crop) Indicator 6: total investment cost for wastewater treatment ( ) , < 80,000, ,331,

55 Weights of indicators Indicator Weight Indicator Weight Indicator 1: Rice production from wastewater during the winter-spring crop (tons/crop) Indicator 2: % of demand for irrigation water satisfied by treated wastewater Indicator 3: % remaining flow downstream of Can Tho in Hau River 8 Indicator 4: % of nutrient demand satisfied by treated wastewater 10 Indicator 5: Environmental benefits (million /crop) 7 Indicator 6: total investment cost for wastewater treatment ( )

56 Total score of different options of wastewater reuse toward climate change adaptation Item Scenario 1 Scenario 2 Scenario 3 Item Scenario 1 Scenario 2 Scenario 3 Option 1: Reuse of effluent from centralized WWTPs with the capacity of 283,000 m3/day Option 4a: reuse wastewater from domestic, industry and aquaculture - Combination of option 1 and option 3 Total Total Option 2: Reuse of effluent from centralized and decentralized WWTPs with estimated capacity of 500,000 m3/day Option 4b: reuse wastewater from domestic, industry and aquaculture - Combination of option 2 and option 3 Total Total Option 3: Reuse aquaculture wastewater for rice irrigation, especially wastewater from catfish farming Total Reuse wastewater from catfish farming is the very important option for wastewater management, reuse and also for the environment. 56

57 6 sound climate change adaptation indicators: (1) Rice production from wastewater during winter-spring crop; (2) % of demand satisfied by treated wastewater; (3) % of nutrient demand satisfied by treated wastewater; (4) % remaining flow downstream of Can Tho in Hau River; (5) Environmental benefits; and (6) total cost investment for wastewater treatment, have been selected to assess various options/strategies for wastewater management and reuse in Can Tho City Mekong Delta, Vietnam. With the total scores of the strategy of Reuse aquaculture wastewater for rice irrigation, especially wastewater from catfish farming is the very important option for wastewater management, reuse and also for the environment. It shows the necessary for the City to set up plan and strategy to treat and reuse wastewater from catfish farming as priority among three scenarios with different climate change impact factors. It also indicates that adaptation is best measured by the indicators in the context of planned adaptation to climate change impacts because of its defining whether adaptation policies and measures are implemented and whether vulnerability is reduced through effective actions. 57

58 Take home messages 58

59 Wastewater reuse is an adaptation measure of water scarcity Wastewater should not be considered as a waste. It can be reused for agriculture Wastewater reuse in the agricultural sector can be used as climate change adaptation measure that addresses water scarcity and salinity intrusion from sea level rise. Besides being a water source, treated wastewater can be an important source of nutrients, including nitrogen and phosphorous. Reuse in agriculture can reduce wastewater treatment cost and improving the water quality of a receiving river/canal system. As such, environmental impacts can be reduced 59

60 THE END 60