Part 1: SYSTEM DESCRIPTIONS
- Given that both recycled water treatment and seawater desalination plants have the same capacity to supply a new 10,000 suburb.
- Primary assumption:
+ There is one pipeline system to distribute fresh water for this suburb with the main purpose of potable water. This kind of water will be mainly used for drinking, preparing and cooking food, bathing and washing.
+ Each person needs an average amount water of 315L/day for above mentioned uses. Therefore, there should be a supply of 3150kL/day to distribute to this population.
According to Australian Government (2006), 285 litres per person per day in household in Australia, whereas other reference suggests Australia's average per person water consumption was 493 litres per day (Green living tips 2010). Therefore, based on (Schulz, M 2010), we assume that Each person needs an average amount water of 350L/person/day for above mentioned uses. As a result, there should be a supply of 3.5ML/day to distribute to the new suburb of 10,000 citizens.
Desalination is the process of extracting seawater, filtering it and distributing the water directly into the water reticulation system.
A desalination project would comprise:
- seawater intake pipelines, taking water from offshore
- pre-treatment facilities, including screening and dual media filtration
- a reverse osmosis facility, to extract salt and other impurities from seawater
- a disinfection and stabilisation plant
- product pumping and transfer to water distribution system
- an outfall to dispose of the concentrated seawater.
Some description about the situation of the ocean: salinity, TDS, TSS,...
The water in the Arabic Gulf is known to be challenging for reverse osmosis (RO) seawater desalination. The water is relatively shallow and the temperatures are high. Many small islands off the coast reduce the water exchange with the open sea. This results in seawater with high salinity, high organic content and microbiological activity posing a very high fouling risk for the RO membranes. Carefully designed pretreatment is absolutely essential to ensure economical plant operation.
After the open intake, hypochlorite and polyaluminiumchloride (PAC) are dosed to the seawater. The PAC is used as a coagulant for the dissolved air flotation (DAF) unit. The main task of the DAF unit is to remove oil and grease, which might clog the membrane surface. Another target, especially in summer when the raw water quality is potentially more difficult, is the reduction of turbidity, organics and suspended matter to improve the feed water quality to the subsequent UF system. The UF system purifies the water of biological, organic and particulate contaminants before it enters the two-pass RO system where 600 m/h of desalinated water with a TDS of approximately 20 ppm are produced. The first-pass concentrate is discharged to the sea; the second-pass concentrate is recirculated to the feed of the first pass.
According to Cerci (2002), the RO desalination plant analyzed is the mission basin desalting facility. The plant is located in Oceanside, California, USA, which is a semi-arid coastal city 145 km south of Los Angeles and 55 km north of San Diego. The construction of the plant started in May 1992 and the entire facility was completed in March 1993. The plant produces 7250 m3/d of fresh water with a salinity less than 500 ppm, employs four people including a manager, and operates 24 h/d and 7 days a week throughout the year. The source of raw water is underground brackish water at a salinity of about 1550 ppm. The potable water produced is directly supplied to the city's water system and the brine is dis-charged to the Pacific Ocean.
Option B: Centralized Desalination Plant
The seawater desalination plant is built on the region 3km away from the intake point and 13km from the first household. In the final step, the treated water is stored in a reservoir before being distributed to end users.
Based on Kruger (2009), Kim et al. (2009) and Prihasto et al. (2009), the treatment processes is illustrated in the following diagram
PART 2: LIFE CYCLE ASSESSMENT
Goal definition and scope
- In this study, there are two targets referring to the comparison in using potable water resulted from two treatment technology systems namely: recycled water treatment and seawater desalination.
- To compare the environmental impacts in term of CO2 emission;
- To assess the health risk associated with waterborne pathogens.
- In addition, the relative sustainability of operations under different planning scenarios enabling consideration of environmental issues in parallel with financial, social, and practical considerations in strategic planning;
- This study is aimed for the internal use in the government bodies, existing residents from the new suburb, future residences and holiday makers.
- Both systems should have the capacity of 3.5ML/day potable water (or 1,3 GL/a) to support the demands of 10,000 people in the new suburb;
- The lifespan of both recycled water treatment and seawater treatment plants is 30 years.
l Functional unit:
- In term of water concept, the applied functional unit is kilolitre of potable water;
- For LCA analysis, there are two kinds of functional units:
(1) To assess environmental impacts resulted from the operation of both systems during the lifespan, 1kg of emitted CO2 is used;
(2) To quantitatively assess the health risk related to microbiological presence in the water.
- LCA for two options is the necessity and demand of different audiences, let say:
+ The water authorities who will make the final decision about selecting the appropriate water supply for this new suburb in term of economic, environmental and health aspects promote and evaluate the results of a LCA report;
+ The public pay most attention to the risk of microbial infection;
+ The proposed project operators use the advantages reported in the LCA to call for the approval of the relevant authorities and community;
+ The environmental activists and scientists look for the friendly environmental goods and processes.
Option B: Centralized Desalination Plant
- The main treatment processes of the seawater desalination plant is simplified and described on the previous figure 2 (part 1.2).
(2) System boundary:
- The simplified boundary of the seawater desalination plant is presented in figure 5.
+ The length of the pipeline to transport water:
v Between the intake point of seawater to the desalination plant: 3km;
v Between the seawater treatment plant and the treated water reservoir: 5km;
v Between the reservoir and the first household: 7km;
+ The diameter of the pipeline system is: 350mm;
+ The excavation is calculated by the equation: 2 x volume of the pipelines;
+ The data for plant construction such as concrete, reinforcing steel, steel pump is referenced from the operating plant (references)
- To simplifying the calculation and comparison between two plants, assuming that both of them have the same magnitudes of the whole plant during the plant construction phase such as concrete, steel reinforcing, steel pump and excavation;
- However, the two plants have different electric uses for the operation phases.
- The data used for Life Cycle Inventory stage for option B is illustrated in the table 2.
- The environmental impacts of the operation of two plants are equivalent to the amount of CO2 emitted from the construction and operation phases which are calculated by using the GaBi program. The results are illustrated in table 3.
- Based on the input data, it is obvious that the energy consumption of the seawater desalination plant is two times than that of the recycled water plant. As a result, the calculation from the use of GaBi software program shows that the amount of CO2 released from the operation of option B is two folds than that emitted from option A.
- In conclusion, in term of environmental impact, the selection of the seawater desalination plant as a potable water supply should not be a sustainable option for the future.
PART 3: QUANTITATIVE MICROBIAL RISK ASSESSMENT
According WHO (2009, p.9):
In stool surveys of patients with gastro-enteritis, the reported prevalence of Cryptosporidium is 1-4% in Europe and North America and 3-20% in Africa, Asia, Australia, South and Central America [Current & Garcia, 1991]. Peaks in the prevalence in developed countries are observed in the late summer [van Asperen et al., 1996] and in spring [Casemore, 1990]. In industrialised countries, the prevalence is high in children under 5 years of age and in young adults. In developing countries, infection is common in infants less than 1 year, but is rarely seen in adults.
Asymptomatic carriage, as determined by stool surveys, generally occurs at very low rates in industrialised countries (<1%) [Current & Garcia, 1991], although in day care centres higher rates have been reported [Lacroix et al., 1987; Crawford & Vermund, 1988; Garcia-Rodriguez et al., 1989]. Routine bile endoscopy suggests a higher asymptomatic prevalence: 13% of non-diarrhoeic patients were shown to carry Cryptosporidium oocysts [Roberts et al., 1989]. High rates of asymptomatic carriage (10-30%) are common in non-industrialised countries [Current & Garcia, 1991]. Seroprevalence rates are generally higher than faecal carriage rates, from 25-35% in industrialised countries up to 68-88% in Russia [Egorov et al., 2004] and 95% in South America [Casemore et al, 1997]. Seroprevalence rates increase with increasing age [Zu et al., 1992; Kuhls et al., 1994; Egorov et al., 2004] and are relatively high in dairy farmers [Lengerich et al., 1993] and day care centre attendants [Kuhls et al., 1994]. Two city studies in the USA showed that people that consumed treated surface water were more likely to show seroconversion during the study period than the people that consumed well-protected groundwater [Frost et al., 2001; 2002; 2003]. During the months of the study, a significant proportion of the population exhibited seroconversion (also in the groundwater cities), indicating that Cryptosporidium infections may be relatively common. Illness rates were not increased in the cities supplied with surface water, so, although infections were more common, illness was not. The more intense serological response in the residents of the surface water cities could indicate an increased level of protection from illness. Human feeding trials also indicated a protective effect of a prior infection to illness after low dose exposure, but not against high dose exposure [Chappell et al., 2004]. Both in the USA and in Russia, consumption of drinking water from shallow wells was correlated to a high seroprevalence [Frost et al., 2003; Egorov et al., 2004].
According to Curtis (2010)
Giardia: Giardiasis refers to a syndrome of diarrhea, excess gas, and abdominal cramping. It is caused by Giardia lamblia, a water-borne parasite that is worldwide in distribution. The symptoms usually occur one to two weeks after exposure to the parasite. Symptoms initially include diarrhea, bloating, nausea, abdominal cramping, and malaise. Weight loss is also a frequent finding. Backcountry travelers usually contract giardiasis by drinking water from untreated or improperly treated sources. Chemical treatment of the water and commercial water filtration systems, used properly, eradicate the parasite. The diagnosis of giardiasis can be confirmed by inspecting a stool sample for the presence of the parasite. Because this test may not always identify the organism even if it is present, a physician may elect to treat you empirically for the infection. The use of an appropriate antibiotic for seven days is usually highly effective in relieving symptoms and curing the disease.
Cryptosporidium: Cryptosporidium is a protozoan that causes a diarrheal illness similar to Giardia. Symptoms include watery diarrhea, headache, abdominal cramps, nausea, vomiting, and low-grade fever that may appear 2 to 10 days after infection. Some infected people will be asymptomatic. Currently, there is no effective treatment for Cryptosporidium. Symptoms usually last 1 to 2 weeks, at which time the body's immune system is able to stop the infection. People with normal immune systems are generally not at risk and improve without taking antibiotics or antiparasitic medications. For people with compromised immune systems this can be a dangerous disease. Please see your physician.
It is supported that protozoa is more resistant to disinfection with chlorine than most other microbial pathogens, hence protection against protozoa should give protection against other pathogenic organisms (Haas & Eisenberg 2001). Moreover, in comparison between Cryptosporidium parvum and Giardia lamblia, NRMMC - EPHC - AHMC (2006, p.88) highlight that Cryptosporidium parvum should be the suitable represent because it is not only reasonably infective but also resistant to chlorination and is one of the most important waterborne human pathogens in developed countries. Despite the fact that Giardia lamblia is typically present in sewage at some 10-100 times the concentration of C. parvum and may be marginally more infective (Rose et al 1996), it is more readily removed by treatment processes and is also more sensitive to most types of disinfection than C. parvum (WHO 2004, NHMRC-NRMMC 2004). In fact, Cryptosporidium is currently the subject of much research concerning its sources and pathways (Pitt 2008). As a result, C. parvum has been chosen for risk assessment, representing waterborne pathogens in stormwater in Western Sydney.
The pathogen is chosen in this study is Giardia lamblia.
(1) Giardia lamblia is a water-borne flagellated protozoan parasite that colonies and reproduces in the small intestine (http://en.wikipedia.org). Giardia causes giardiasis which refers to a syndrome of diarrhea, excess gas, and abdominal cramping. In the past 20 years, it has been realised that Giardia infection is one of the most common illnesses caught from water worldwide (http://www.princeton.edu/).
(2) Giardiasis is most common in toddlers and young children, and also their parents and caregivers. It is also common in people who have travelled overseas especially to developing countries where the water supply is not safe (http://www.cyh.com/HealthTopics/HealthTopicDetails.aspx?p=114&np=303&id=1947);
(3) The symptoms of Giardiasis usually occur one to two weeks after people have been exposure to the parasite. Symptoms initially include diarrhea, bloating, nausea, abdominal cramping, and malaise. Weight loss is also a frequent finding;
(4) Backcountry travelers usually contract giardiasis by drinking water from untreated or improperly treated sources. Chemical treatment of the water and commercial water filtration systems, used properly, eradicate the parasite. The diagnosis of giardiasis can be confirmed by inspecting a stool sample for the presence of the parasite. Because this test may not always identify the organism even if it is present, a physician may elect to treat you empirically for the infection. The use of an appropriate antibiotic for seven days is usually highly effective in relieving symptoms and curing the disease. (http://www.princeton.edu/~oa/safety/giarlyme.shtml);
(5) Giardia affects humans, but is also one of the most common parasites infecting cats, bdogs and birds. Mammalian hosts also include cows, beavers, deer, and sheep. (http://en.wikipedia.org/wiki/Giardia_lamblia#Manifestation_of_infection)
Option B: Seawater desalination plant
In order to calculate the probability of Giardia infection, there is a range of assumptions being made.
- Giardia concentration in seawater: 30 cysts/L (Impact of bathers on levels of Cryptosporidium parvum oocysts and Giardia lamblia cysts in recreational beach, 2007);
- There are six barriers used in this plant.
- Coagulation with a decimal reduction capacity is 1;
- Dual media filter has a decimal reduction is 2.5;
- Cartridge filter has a reduction log is 2
- Reverse osmosis with a reduction log is 6.5;
- Decarbonator has a reduction log is 2.5;
- Reservoir has an inactivation factor is 0.5
The desireable reduction and the effectiveness of each barrier resulted from the application of the Monte Carlo model are presented in table 5.
For the purpose of desalination to supply potable water in Western Sydney, there are 3 main pathways by which people could be infected by the hazardous exposures
- seawater may affect not only inhalation of aerosols or sprays but also involuntary or intentional ingestion of swimmer or bathers (social swimming activities, sporting swimming), children playing in water or body-washing in the rivers, beaches.
- Influences workers in the treatment plant (shown in Figure 1)
- Infection or toxic impacts (shown in Figure 2)
The standard dose-response concentration for Giardia is 10-4.
The information about dose-response is usually achieved from the animal experiments and based on the survey with human heath. Due to the main targets of this study, the performers will not go further with this stage which should be performed with several animal assays and human health survey.
According to the calculation based on the Monte Carlo Model, the results are:
- The concentration of Giardia after being treated at barrier 6: 3.00E-14
- The consumption of Giardia per person: 2.70E-14
- The infection risk probability per day: 0.00E+00
- The annual Risk probability: 0.00E+00
In conclusion, after using 6 barriers to control and prevent the infection of pathogens in general and Giardia in particular, there is no risk in term of the use of this kind of water.
Based on the analysis by risk assessment technology, the annual Risk probability for option A of Centralised Recycling Water Plant: 6.28E-12, option B of Centralized Desalination Plant: 00E+00
Therefore, option B is better than option A.
PART 4 CONCLUSION
Seawater Desalination Reverse Osmosis Plants is a solution to grow demand for fresh water, but the technical processes used could damage the environment, with impacts such as the global warming by the increases use of energy, adverse effects on the marine environment. The consumption of energy and the replacement of renewable resources.
The use of recycled water is receiving increasing favor from the governments, scientists, environmental protectors as well as residents. While it is undoubted about this fact, the environmental authorities need to pay most attention at monitoring the health risk associated with waterborne pathogens presenting in recycled water. Due to the calculation result in this assessment, there is no microbial risk for drinking use related to the application of recycled water from the Western Sydney sewage treatment plant. However, the water quality has been obtained only after being treated at eleven treatment processes which are obviously expensive and management for this kind of facilities require a high degree of technical expertise. In contribution with the disadvantages of using these barriers, the complexity in operating and maintaining the facilities may be obstacles for the purpose of using recycled water.
Consequently, an effective water management should include ongoing monitoring plan in conjunction with the proper implementation of various treatment technology. The preventive measures chosen will be determined by issues such as:
- intended use;
- existing treatment facilities;
- technical expertise;
- availability of land (eg if buffer zones are to be used);
- public access (eg use in tourist areas within capital cities compared with recycling in ruraltowns);
- public perception and requirements.
A multiple barrier approach operating from catchment to tap should be implemented to minimize the risk of contamination by Cryptosporidium. Protection of water catchments from contamination by human and animal wastes should be a priority. Water from unprotected catchments is likely to be subject to contamination by Cryptosporidium and treatment including effective filtration will be required to remove these organisms to ensure a safe supply. The lower the quality of source water, the greater the reliance on water treatment processes.
Sanitary surveys of water catchments for potential contamination sources should be undertaken, together with investigative and event-based testing of source water for Cryptosporidium to assess risk factors for contamination, to provide a basis for catchment management to reduce these risks and to determine the level of water treatment required.The bores of treatment plant need to be well maintained and protected from intrusion of surface and subsurface contamination. Integrity should be monitored using traditional indicators of faecal contamination.
The design and operation of water treatment plants should be carefully examined where Cryptosporidium oocysts are suspected or known to be present in the raw water, to ensure that required performance is achieved and maintained.
The performance of filtration plants should be monitored continuously and treated water of a constant quality should be produced irrespective of the quality of raw water.
Filtration plants should be operated by trained and skilled personnel. Failure of water treatment processes, including failure to meet specified targets for turbidity (or particle counts), should be regarded as representing a potential risk of oocyst contamination of the drinking water supply. The integrity of distribution systems should be maintained. The use of unroofed treated water storages within distribution systems should be avoided as these could allow the entry of contamination from birds and small animals. Backflow prevention policies should be applied and faults and burst mains should be repaired in a manner that will prevent ingress of contamination.
Investigative testing of drinking water may be required if Cryptosporidium contamination is suspected. This could occur in association with a major rainfall event leading to a marked decrease in water quality and a marked increase in the numbers of Cryptosporidium in source water, sub-optimal operation of treatment processes, a breakdown in treatment plant operations or a fault within the distribution system. Monitoring may also be required in response to suspected waterborne cryptosporidiosis.
Potable water production from seawater by the reverse osmosis technique in Libya
Mohamed Aboabboud*, Salaheddin Elmasallati
Case studies on environmental impact of seawater desalination
J. Jaime Sadhwania*, Jose M. Vezaa, Carmelo Santana
Energy and Air Emission Effects of Water Supply
J E N N I F E R R . S T O K E S A N D A R P A D H O R V A T H
Towards indirect potable reuse in South East Queensland
W. H. Traves, E. A. Gardner, B. Dennien and D. Spiller
Water reuse and health risks real vs. perceived
Australian government 2006, Water use in Australia, viewed 10th May 2010, http://www.nwc.gov.au/www/html/236-water-use-in-australia.asp
Green living tips 2010, Consumption statistics, viewed 10th may 2010, http://www.greenlivingtips.com/articles/185/1/Consumption-statistics.html
Schulz, M 2010, Lectures in Sustainability Assessment - CVEN9892, School of Civil and Environmental Engineering, UNSW.
NHMRC-NRMMC 2004, Australian Drinking Water Guidelines, National Health and Medical Research Council and Natural Resource Management Ministerial Council, Canberra, viewed 10th April, 2010, http://www.nhmrc.gov.au/publications/synopses/eh19syn.htm
NRMMC - EPHC - AHMC 2006, Australian guidelines for water recycling: managing health and environmental risks (Phase 1), Natural Resource Ministerial Management Council (NRMMC) - Environment Protection and Heritage Council (EPHC) - Australian Health Ministers' Conference (AHMC), National Water Quality Management Strategy
Haas, C & Eisenberg, JNS 2001, 'Chapter 8: Risk assessment' in L, Fewtrell & J, Bartram (eds), Water Quality- Guidelines, Standards and Health: Assessment of risk and risk management for water-related infectious disease, pp.161-183.
Hunter, PR & Fewtrell, L 2001, 'Chapter 10: Acceptable Risk', in L, Fewtrell & J, Bartram (eds), Water Quality- Guidelines, Standards and Health: Assessment of risk and risk management for water-related infectious disease, pp.207-227.
Kruger, R 2009, Ultrafiltration Pretreatment in a Large Seawater Desalination Plant in the Arabic Gulf, Water World.
Prihasto, N, Liu, QF & Kim, SH 2009, 'Pre-treatment strategies for seawater desalination by reverse osmosis system', Desalination, vol.249, pp.308-316.
Cerci, Y 2002, Exergy analysis of a reverse osmosis desalination plant in California, Desalination, vol.142, pp.257-266.
Kim, YM, Kim, SJ, Kim, YS, Lee, S, Kim, IS, Kim, JH 2009, 'Overview of systems engineering approaches for a large-scaleseawater desalination plant with a reverse osmosis network', Desalination, vol.238, pp.312-332
Curtis, R 2010, Outdoor Action Guide to Giardia, Lyme Disease and other 'post trip' Illnesses, viewed 12th May 2010, http://www.princeton.edu/~oa/safety/giarlyme.shtml
WHO 2009, Risk Assessment of Cryptosporidium in Drinking Water, Public Health and EnvironmentWater, Sanitation, Hygiene & Health, World Health Organization, WHO/HSE/WSH/09.04.
Sydney water, Quarterly Drinking Water Quality Report, from 1 January 2009 to 31 March 2009;