Factors Affecting Reuse of Wastewater Effluents in Irrigation: Towards Sustainable Applications.

Transcription

1 Factors Affecting Reuse of Wastewater Effluents in Irrigation: Towards Sustainable Applications. Dr. Saleh Al-Mogrin Ministry of Water and Electricity. Water Affairs; POB Riyadh 11321, Saudi Arabia. fax:int

2 Contents Introduction The six factors affecting reuse Conclusions Recommendations

3 Introduction Advantages of reuse separate system Approximately 60-80% of the organic matter is biodegradable domestic wastewater is 75% graywater and 25% black water Disadvantages of reuse Many compounds are not removed by secondary treatment. Increasing population Increasing quantaties of wastewater

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6 Factors Affecting Wastewater Reuse 1) Quality vs. standards 2) Irrigation method 3) Planning of the reuse project 4) Management of reuse projects 5) Costs and benefits of reuse practices 6) Limitations of wastewater reuse

7 1) Quality vs. standards The effluent quality is usually characterized by: 1. Microbial parameters: virus, bacteria, parasite, including protozoa and higher animals. 2. Agronomical aspect: salinity, sodium absorption ratio (SAR), bicarbonate (HCO 3 ), 3. Organic matter: suspended solids (SS), biochemical oxygen demand (BOD), chemical

8 The most widely used guidelines available and adopted in reuse projects are: 1. Engelberg report 1985, as product of the Meeting of the World Bank and WHO in Engelberg, Switzer-land. 2. Health Guidelines for the Use of Wastewater on Agriculture and Aquaculture, WHO 1989, 3. Wastewater Directives EU Directive (91/271/EEC), 4. California Standards 1987 (most restrictive) 5. US EPA 1992.

9 Standards are based on: Health Risks: based on hazard identification,exposure assessment, dose-response, and risk characterization. Environmental Risks: soil deterioration and groundwater pollution. Methodology of developing human health-related guidelines a- Prevention of Pollutant Accumulation: min.risk very stringent: min. risk b- Maximizing soil capacity: relaxed: acceptable risk (based on maximum permissible loading} exploiting mechanisms such as attenuation, detoxification, and assimilation.

10 2) Irrigation method Mechanized irrigation is advantageous in the production of crops with a high com-mer-cial value. Pumped and mechanized irrigation could reduce human con-tact with water Subsurface or localized irrigation can give the greatest degree of health protection as well as using water efficiently but it is relatively expensive and a high degree of water quality is required to avoid clogging of the orifices drip irrigation is used as subsurface, a lower probability of crop contamina-tion Forrow irrigation, although cheapest, is the worset in term of human contact and water use.

11 3) Planning of the reuse project Planning is not a simple task. It requires deep understanding of unit processes and operations as well as the economical issues involved This is usually left to consultants who lack a throughout knowledge of local conditions and limitations

12 Planning of such projects should be done as early and as deeply as possible. It involves three distinctive stages: - Conceptual planning, - Feasibility investigation, and - Facility planning. The planning criteria of reuse programs in terms of engineering and environmental issues should include the details for constructibility and operability and required coordination in all component parts in order to achieve a cost effective programs.

13 Some of these criteria that to be considered during planning stages are: i Studies to minimize the construction and maintenance costs by : - selecting cost effective construction materials and architectural finishes - grouping buildings & unit processes (e.g shared walls, ii. Investigations to ensure a complete economic analysis before selecting treatment process. The economic analysis should include both capital and operation and maintenance costs.

14 iii. Review the design criteria to be adopted or selected for each unit process. iv. Evaluate the potential for optimizing the number and size of each type of equipment item used in the treatment process in order to attain a lower operation and maintenance costs. v. To consider duplication or combination of similar units around the site and /or other sites (Ideal model).

15 4.Management of reuse projects: involves a complex interaction between many parameters different overlapping fields Major management pitfalls are: 1. Responsibilities which are divided between several centralised institutions leading to inadequate co-ordinations in this field and in an inefficient exploitation of all resources 2. Weak pollution control and other environment-orientated monitoring programs

16 3. Absence of functional regulatory agencies 4. Absence of policies, standards and regulations to govern this issue 5. The adoption of European Standards, which are not adequate for the region. A national policy as a management tool should be established clearly, and legislations must be enacted to promote and control this activity.

17 5. Costs and benefits of reuse of effluents in irrigation in some countries without water shortage, treated wastewater is reused in agriculture irrigation as a cheap and safe disposal method the per capita/year production of nutrients are: 2.75 kg N, 3.2 kg P as P 2 O 5 and 24.2 kg K as K 2 O estimated 55 kg N, 10 kg P and 30 kg K in 1000 m 3 wastewater The utilization of 1.5M m 3 of wastewater/day in KSA will yield about 33% and 5% of the country s requirements of nitrogen and phosphorus

18 Costs of irrigational reuse projects have varied widely depending on the location and distance from source: In Tunis, the acceptable price by farmers was US$ /m³ In Morocco, irrigation reuse was estimated to cost 22% less than the use of fresh water Cost of storage for seasonal variation

19 Table 1. Cost estimates for different kinds of irrigation projects. Treatment Type Cost US $/m 3 Reference Secondary + Chlori-na-tion MOMRA, 1995 Secondary + Coagu-lation 0.56 Arar, 1991 Tertiary treatment, KSA MOMRA, 1995 Tertiary treatment, USA Asano, 1991 Reuse of drainage Smith and Walker, 1994 Groundwater 0.45 Ukayli and Husain, 1988 Desalination Ukayli and Husain, 1988 Drinking water 0.60 Appan & Rahman, 1998 Industrial water 1.0 Appan & Rahman, 1998

20 Processes Relative Construction Costs Trickling Filter Standard High Rate Trickling Filters Activated Sludge Aerated Lagoons Oxidation Ditches Stabilization Ponds Relative maintenance Cost

21 Power Kwh/ mgd. Land Acres Type of Process Annual Cost; SR/m 3 Primary treatment Low rate High rate T.F. n.a Activate Sludge Oxidation ponds Negligible 35 acre in warm climate RBC Chlorination 25 - Filtration n.a m Aerated Lagoon n.a About acres Oxidation ditches n.a About 4-5

22 6. Limitations of reuse of effluents in irrigation A) Public health risks From a public health perspective, the most critical group of pathogenic organisms are helminths and enteric viruses (EVs) due to the possibility of infection from low doses and the lack of rou-tine, cost effective methods of detection and quantification the treatments that are effective for bacterial removal may not be so effective for other organ-isms B) Possible environmental and agricultural impacts The risk of contamination of groundwater through the irrigation depends on the effluent quality, local conditions and the rate of application. impact is possible if industrial wastewater is discharged to publicly-owned wastewater treatment plants The reuse of treated wastewater within recommended quality limits has given higher yields than fresh well water

23 C) Possible effects on soil I ) SAR is recommended to be less than 12 II) Salting: Soil salinization is a common problem in arid regions with the presence of high Cl - D) Effects on plants Treated wastewater was reported to be used in irrigation of different plants without any detrimental effects even with long-term application. However, poorly treated efflents were find to increased concentration of heavy metals (Cu, Zn, Cr, Mn) in soils.

24 Parameter ppm Cu 5-20 Mn Zn Fe Co 10 Ni Pb 13.5 Hg 0.30 As 14 Cd 1.5 B 2

25 Conclusions 1. It seems that wastewater reuse practices in some GCC states are in unsustainable path. Many reuse projects are embarked without careful planning 2. Limited water resources and increased population are threatening problems in our region 3. Wastewater reuse schemes are long-term practices, therefore, their sustainability should be considered for many generations to come. On the level of the legislator, a clear policy should be established containing a clear cut future vision. Legislations are then drawn to be enacted to promote this practice.

26 4. For sustainable reuse projects key factors affecting wastewater reuse practices should be carefully studied by highly qualified teams. These factors include planning for the reuse program, management of the reuse practice, quality of the effluent to be used and standards or guidelines available, irrigation method and crop restriction, costs and benefits of reuse program, and limitations of this practice.

27 Recommendations 1) Statement of future visions that consider scenarios and analysis of their implications for sustainable reuse practice should be adopted. 2) Planning should incorporate total environment concept (i.e. comprehensive regional planning). 3) Policies should be crafted via legislations and updated to incorporate social, economical, health, and environmental aspects.

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