Kuwait's Ministry of Electricity and Water is planning to supplement the existing electric power generation capacity in the country by constructing new Combined-Cycle Gas-Turbine Stations at Shuaiba North Power Station and Subiya Power Station in order to meet the increasing power demand. The plans also include installation of a Multistage Flash Distillation Plant for seawater desalination at Shuaiba to increase Kuwait's supply of potable water.
Construction of these new facilities will impact the environment, and so therefore needed to be carefully assessed before the planned work could go ahead. Thus, the Kuwait Institute for Scientific Research conducted an environmental impact assessment for these sites, as per the guidelines of Kuwait's Environment Public Authority. The environmental impact assessment was performed in three parts: air, marine, and hydraulics, by separate multidisciplinary teams that conducted field surveys, took measurements, collected and analyzed samples, and in some cases, carried out predictive numerical modeling studies of the potential impact of plant operations on the surrounding environment. These studies took into account the impact of the already existing, as well as the planned, power generation and desalination facilities. This paper summarizes the final results of the marine environmental impact assessment, including the results of the hydraulic surveys and modeling studies.
The population of Kuwait is now around 2.6 million, and it has been increasing at an annual rate of about 3.6% per year for the past five years. This rapid increase in population has created a corresponding increase in the demand for electricity and water. The demand for both power and desalinated water is forecast to increase at approximately 5 to 6% per annum for the next 10 years. The need for more energy-efficient means of production and consumption of electricity and water in Kuwait has been discussed by Darwish et al. (2008). Electrical power generation and water desalination in Kuwait is now done at co-generation power-desalination plants, where steam from turbines is used to desalinate water using a multistage flash distillation (MSF) process. Most of the fuel consumed by these plants consists of heavy oil and crude oil. The use of gas turbines in combined-cycle gas-turbine power and desalination plants could promote a significant increase in energy efficiency; in addition, the use of natural gas in place of crude oil as a fuel source for power generation results in less air pollution and helps to conserve Kuwait's oil resources. Kuwait's Ministry of Electricity and Water (MEW) has accordingly made plans to construct two new large-capacity gas-fueled plants at Shuaiba North and Subiya.
The proposed power plants at both Shuaiba and Subiya will be constructed at sites where there are existing power plants, with intake and outfall structures (Figure 1). In Shuaiba, the proposed site of the new plant is the decommissioned Shuaiba North Thermal and Gas-Turbine Power Station, located within the existing Shuaiba Area Authority Industrial Complex, about 50 km south of Kuwait City. In Subiya, the proposed site of the new combined-cycle gas-turbine power station is within the existing Subiya Power Station (SPS), which is about 100 km north of Kuwait City. At the Shuaiba site, new intake and outfall structures will be constructed at the approximate locations of similar structures that existed prior to the decommissioning of the power station that formerly occupied the site. At the Subiya site, the proposed design of the plant may use existing seawater intake and outfall structures. Therefore, land use at both sites will not change as drastically as it would have if the sites had been previously undeveloped. Shuaiba is a heavily industrial area where the impact of the construction and operation of the new plant will be relatively small compared to ongoing industrial activities.
The major objectives of this study were as follows: to assess the existing baseline conditions of and potential environmental impacts on the local marine environment, with emphasis on water and sediment quality as well as benthic ecology; and to provide recommendations on design specifications and mitigation measures, in order to minimize potential environmental impacts of the proposed power and desalination plant developments.
The specific objectives of this study were as follows: to demonstrate that the proposed development projects meet all local, national, and international regulations and guidelines pertaining to the environment; to ensure that this environmental impact assessment (EIA) and the proposed developments are compliant with the regulations of Kuwait's EPA, so that the MEW can obtain the necessary permits to construct and operate the new power stations in accordance with all existing and proposed regulations, orders, and legislations; to ensure that this EIA and the proposed developments are acceptable to international lending institutions; to enable the MEW to obtain necessary funding for construction and operation of the new power stations in accordance with all existing and proposed international regulations, orders, and legislation; to ensure comprehensive understanding of the coastal biotopes that are likely to be impacted by the new plants’ seawater intakes and effluents (i.e. heat, brine, and pollutant discharges); to recommend mitigation measures to be followed during construction and operation of the new plants; and to ensure that the locations selected for seawater intakes and outfall channels have the least environmental impact. The proposed plants will be constructed in accordance with the findings of this study, which was prepared in accordance with Law 210/2001 regarding Kuwait's EPA and the policies and guidelines of the World Bank and the International Finance Corporation.
The approach followed to obtain the necessary information involved three phases:
Data-gathering, including literature survey, previous studies conducted by the Kuwait Institute for Scientific Research (KISR) and others, documents from Kuwait's MEW, and personal communications; field surveys, including a hydraulic survey of water levels, currents, and other hydrodynamic parameters, and environmental quality surveys of the water, sediment, and marine ecology; and laboratory analyses of water and sediment samples for detailed characterizations of the baseline condition of nutrients, pollutants, and marine ecology.
Numerical hydraulic modeling, using the RMA-10 code (produced by Resource Modeling Associates, Suisun, California, USA) for both project locations, inputting field survey data for calibration and validation; and assessment of a variety of model scenarios for plant intake and outfall discharges, weather conditions, and intake designs.
Data and model result integration, including synthesis of baseline data and assessment of baseline environmental quality at the two project locations; synthesis of numerical modeling results and assessment of likely environmental impacts of the two projects on their respective local marine environments; and documentation of all EIA results in the form of a final environmental impact statement.
Results and Discussion
Impact on water quality
The concentration of dissolved oxygen (DO) in seawater is controlled mainly by temperature, and it decreases with increasing temperature. Therefore, when seawater is heated it loses some of its DO. In MSF plants, the seawater is completely de-aerated, losing all of its oxygen, but the residual seawater is normally mixed with cooling water before discharge. Outfall water from power and distillation plants is thus somewhat depleted of DO, even though the design of the outfalls promotes re-oxygenation by turbulent mixing with air. If oxygen scavengers such as sodium bisulfite (SBS) are added to the intake water to prevent corrosion, then additional oxygen loss may be evident. Measured DO concentrations in the seawater in the Shuaiba and Subiya areas during field surveys of water quality taken in 2008 were all above the EPA water-quality standard of 4 mg l−1
Normal operations of a power-desalination plant should not affect the pH of seawater significantly (Altayaran and Madany, 1992). The only time that pH values may decline to unacceptable values (below Kuwait's EPA recommended range of 6.5 to 8.5) is during acid cleaning of distillers to remove calcium carbonate scale. It is suggested that when such cleaning is performed, it be done in small sections, and the acidic cleaning waste be greatly diluted with cooling water during discharge. The natural buffering capacity of the carbonate system in seawater should be able to neutralize the acidity of the cleaning waste.
Chlorine and other additives
Chlorine (as Cl2 gas or hypochlorite solution) is added continuously to seawater at the intake of power plants to act as a biocide to reduce biofouling. The Kuwait's EPA recommended limit for Cl concentration in discharge water is 0.5 mg l−1. The practice at the existing SPS is to maintain the Cl concentration at 0.2 mg l−1 in the intake water and to monitor its concentration at the outfall. The Cl concentration at the outfall of the existing Subiya Power Station is 0.05 mg l−1 or less. Therefore, if the Cl at the intake does not exceed 0.5 mg l−1, the discharge water of the proposed plants is not likely to exceed the Kuwait's EPA recommended limit.
Although the chlorine concentration is low, the total amount discharged is large (e.g. about 2,000 kg d−1) because of the high volume of seawater used for plant operations. It is important to minimize the usage of chlorine, because chlorine is highly toxic to marine organisms, and because it can react with natural organic matter to form carcinogenic trihalomethanes and with petroleum components to form chloroaromatics such as chlorophenols and chlorobenzenes (Saeed et al., 1999). It is suggested that the experience with chlorine usage by existing plants be reviewed to determine the minimum amounts of Cl that are effective in preventing biofouling, so that the proposed plants can plan to minimize their use of Cl. According to Lattemann and Höpner (2003), intermittent shocking is commonly performed daily, in which much higher concentrations of Cl (up to 8 mg l−1) are used to control regrowth of bacteria. So, there will be occasional pulses of high-Cl discharge. This could be harmful to the local marine ecosystem. The impact of these high-Cl wastewaters can be mitigated by mixing them with low-Cl cooling water before discharge.
Other additives commonly used in power-desalination plants include polymer-based antiscalants and polyethylene glycol as an antifoaming agent. Although polyethylene glycol is readily biodegradable and does not pose a significant hazard, the antiscalants are less biodegradable and have metal-complexing tendencies similar to natural humic substances; therefore, they could influence metal solubility and transport in the marine environment (Lattemann and Höpner, 2003). At this time, no specific information on which antiscaling and antifoaming agents or other additives, if any, will be used in the proposed plants at Shuaiba and Subiya.
Heavy metals (corrosion products)
Heavy metals are added to the discharge water at power-desalination plants through the slow but inevitable corrosion of pipes and heat exchangers. Heat exchangers are typically constructed of Cu-Ni alloys, and some other components of the plants are constructed of stainless steel which can release Fe, Cr, Ni and Mo during corrosion. Higher amounts of heavy metals may be released during antiscaling procedures using acids. Surveys of power-desalination plant discharges, seawater near these plants, marine life, and sediment transects show that the amounts of heavy metal contamination that can be attributed to power-desalination plant operations is apparently minimal (Abdel-Moati and Kureishi, 1997; Bou-Hamad et al., 1997). Most of the heavy metal load associated with industrial sources ends up in the sediment column, where it may have limited bioavailability (Khordagui, 2002).
Impact on sediment quality
Physical and chemical characterizations of bottom sediments from the Shuaiba and Subiya areas were performed as part of this EIA. There were no clear indications in this data set of an impact from the existing power-desalination plants on sediment quality. The distribution of petroleum hydrocarbons and heavy metals appeared to reflect the impact of other industrial and shipping activities in the study areas. The major sediment-related issue pertaining to the power plants is sediment deposition around the intake of the SPS, which requires continuous dredging to maintain an open intake channel. This dredging activity disturbs sediments and increases the turbidity of the water column, as well as interfering with normal sediment transport by tidal currents and wave action. In comparison, little sediment transport occurs at the Shuaiba site because of its protected location adjacent to the Shuaiba harbor.
Impact on marine ecology
The impact of power-desalination plants on the marine ecosystems of the Gulf has been reviewed recently by Khan et al. (2002) and Abuzinada et al. (2008). Even though there is a good amount of information in the literature, understanding of the impacts of pollution on Gulf ecosystems remains incomplete. Specific criteria regarding the impact of impingement and entrainment in seawater intakes, as well as thermal pollution, biocides, and heavy metals in outfalls, on marine life have been developed in a number of studies; these are reviewed here for the most important pollutants known to be associated with power-desalination plants in Kuwait.
Impingement and entrainment in seawater intakes
Seawater is used in large amounts for cooling and steam generation in power-desalination plants. It is practically impossible to prevent fish and macroinvertebrates (e.g. shrimp) from being impinged on the 10-cm screening racks and 1-cm moving screens, and consequently being removed from the ecosystem permanently. Likewise, smaller planktonic organisms entrained into the seawater that circulates through the power-desalination plant will be mostly destroyed by chlorination and thermal shock. These effects will have the overall impact of reducing biomass, productivity, and species populations and diversity in the vicinity of the power-desalination plant. Some of the most abundant fish species in the territorial waters of Kuwait, such as the zobaidy, suboor, maid, and beyah, are found primarily in the northern waters including the waters around Bubiyan and Failaka Islands. The suboor, an anadromous species (Tenualoso ilisha) that moves from saltwater to freshwater to complete its life cycle, travels up the Khor Al-Subiya past the seawater intake for the SPS. It is likely that there will be loss of suboor to this intake, along with shrimp and other species.
Hydrodynamic models, discussed previously, showed that the temperature of seawater in the vicinity of the outfalls of the proposed plants at Shuaiba and Subiya will increase by as much as 10°C or more, depending on operating conditions. The normal temperature of the Gulf waters around Kuwait ranges from about 15 to 35°C (Al-Yamani et al., 2004). According to Shams El-Din et al. (1994), the critical temperature is 39°C, above which a sharp decline in biological activity is observed in Gulf waters. Therefore, during summer operations, there are times when temperatures >39°C are likely to occur in the vicinity of the outfalls at Shuaiba and Subiya. A simple way to mitigate this problem is to increase the intake of water by the plant temporarily when outfall temperatures are likely to exceed 39°C. This will dilute the excess heat with relatively cooler seawater. The same approach can be applied during winter operations, when hydrodynamic models predict outfall temperatures >10°C above ambient for the Shuaiba plant at times.
A comprehensive review of the types and amounts of chemical pollution associated with desalination plants in the Gulf region has been presented by Lattemann and Höpner (2003). These authors identified chlorine and copper as the two pollutants of major concern in terms of their total loads and potential detrimental effects on the marine ecosystems. An example cited in their study is the Doha West Power-Desalination Plant that has an outfall located in the intertidal flat of Sulaibekhat Bay. The Doha West plant has a daily seawater intake of about 10.5 million m3, which is treated with about 26,000 kg of chlorine. About 10% of this chlorine (2,500 kg d−1) remains in the discharge to Sulaibekhat Bay. Even though the residual chlorine is rapidly degraded in the environment by exposure to sunshine (∼90% degradation in 45 min), there is enough residual chlorine to pose substantial danger to marine organisms, especially during incoming tides that increase the residence times of pollutants in the Bay. The seawater intake feedwater at Doha West is treated to maintain a chlorine concentration of about 2.5 mg l−1. Assuming that only 10% of this chlorine remains in the outfall water, then the residual concentration is about 0.25 mg l−1. This is much higher than chlorine levels that are known to be harmful or lethal to some marine organisms. Such chlorine concentrations are likely to result in decreased phytoplankton productivity as well as a shift in species composition. When chlorine concentrations are higher during shock and cleaning treatments, even greater environmental effects are likely. Fish species can sense chlorine and respond by swimming to chlorine-free waters, but small planktonic organisms cannot avoid being exposed to chlorine if they drift into the vicinity of the outfall.
Not only is chlorine directly toxic to marine ecosystems, but it reacts with bromide in seawater to form hypobromous acid, as follows:
The hypobromous acid then reacts to produce halomethanes such as bromoform that, although below acute toxicity levels (Ali and Riley, 1986; Saeed et al., 1999), can be toxic or carcinogenic to marine organisms through chronic exposure. The reproductive tissues and juvenile forms of marine organisms are particularly sensitive to exposure to trihalomethanes. In addition, such compounds can be persistent in seawater and the potential exists for them to become pollutants in the drinking water produced by desalination plants, which could pose a serious threat to public health.
Other than chlorine, the chemical pollutant found to be of greatest concern is copper (Lattemann and Höpner, 2003). Copper is the main component of Cu-Ni alloys used in heat exchangers in desalination plants, and there is a typical corrosion rate of 0.025 mm y−1 which contributes a steady dose of Cu to the seawater discharge. A range of 0.005 to 0.033 mg l−1 Cu is estimated for the discharge concentration (Oldfield and Todd, 1996), which exceeds the US-EPA's water-quality criterion for short term exposure to Cu (0.0048 mg l−1). During cleaning procedures when acid is used for scale removal, Cu concentrations in discharges are likely to be several times higher, perhaps up to 0.1 mg l−1 or more. Such concentrations can be toxic to marine organisms, but the level of toxicity is moderated by natural processes that may change the chemical speciation of Cu, causing it to be present in nonbioavailable complexes or to precipitate as insoluble minerals. In addition, Cu is an essential nutrient at low concentrations. It may accumulate in biological tissues and become bioaccumulated at higher levels of the food chain, thus becoming hazardous for larger organisms. The cumulative effect of a continuous increase in the Cu load on a marine ecosystem is not known. Lattemann and Höpner (2003) estimate that 30 g of Cu is added to the marine ecosystem with every 1,000 m3 of seawater used in a power-desalination plant. Similar quantities of other metals such as Fe, Cr, Ni, Mn, and Mo are also likely to be released to the marine environoment, but little data on the concentrations of these metals in plant discharges is available at present.
This overall marine environmental impact assessment of two new power-desalination stations in Kuwait identified potential negative impacts, especially in terms of biology and ecology, at each of the sites. Recommendations are given here for mitigating and monitoring the most negative potential impacts on the environment. There were positive changes identified in terms of social and cultural impacts; in particular, a highly positive change in the quality of life comes with the more reliable and abundant supplies of energy and potable water that will be created by the new power-desalination plants.