Search

We develop an Israeli version of the Multi-Year Water Allocation System (MYWAS) mathematical programming model to conduct statewide, long-term analyses of three topics associated with agricultural reuse of wastewater. We find that: (1) enabling agricultural irrigation with treated wastewater significantly reduces the optimal capacity levels of seawater and brackish-water desalination over the simulated 3-decade period, and increases Israel's welfare by 3.3 billion USD in terms of present values; (2) a policy requiring desalination of treated wastewater pre-agricultural reuse, as a method to prevent long-run damage to the soil and groundwater, reduces welfare by 2.7 billion USD; hence, such a policy is warranted only if the avoided damages exceed this welfare loss; (3) desalination of treated wastewater in order to increase freshwater availability for agricultural irrigation is not optimal, since the costs overwhelm the generated agricultural benefits. We also find the results associated with these three topics to be sensitive to the natural recharge of Israel's freshwater aquifers, and to the rate at which domestic-water demand evolves due to population and income growth.

Recent studies dealing with the potential of Renewable Energy Sources (RES) for desalination along the Mediterranean Coast and in the Middle East choose to use RES to generate electricity first, and then use this electricity to power desalination. The present work eliminates the phase of electricity generation by using solar thermal energy directly for distillation by evaporation. Saving the thermal to mechanical conversion losses allows the proposed Multi Effect Distillation (MED) process to compete economically with Reverse Osmosis (RO) process of significantly lower energy consumption. The new opportunity to revive direct thermal evaporation, arises from a new collector technology developed by Solel Solar Systems, that is coupled to the familiar MED process modified by IDE Technologies to match the solar steam characteristics. Solel has applied its unique technique of selective coating to demonstrate a very efficient solar radiation collection, achieving high temperatures with relatively low installation costs. While the generated steam is not sufficient for efficient generation of electrical power to be used for RO — its quality far exceeds the minimum necessary for the existing methods of steam powered desalination by evaporation. Our analysis shows that a combination of a large number of effects of evaporation, together with high pressure saturated steam available for recycling, yields a dramatic improvement in the production rate of water desalination, accompanied by relatively modest increase in the desalination installation cost. For the specific case analyzed in detail, replacing the commonly used low temperature MED with the new combination, increases the Economic Ratio (ER) from 7 to 16 — a factor of 2.3, while the installation costs grew by only 60%. This implies that the distillate production costs are significantly lower with the new proposed combination. The cost increase is mainly due to the higher costs for the expansion of the desalination system, with relatively low additional costs for producing the high temperature solar steam. A basic assumption, drawn from economic considerations and technological constraints, is that the desalination system would operate continuously, while the solar system, which is limited to daytime operation, would feed a steam generator combined with a storage tank. Therefore utilization of solar energy requires either large and expensive heat storage capacity or fossil fuel backup — a hybrid plant. The effects of storage and fuel cost are presented. The paper refers to three levels of desalination capacity: 1) A small 1000m3/d plant, typical for plants serving small settlements or industries at rural locations, isolated from fresh water and grid power sources. Applying the present model distillate cost for such a solar powered plant along the Red Sea coast is about $1.2/m3 for solar-only plant with large capacity steam storage, and $1.1/m3 for hybrid plant using $0.18/kg diesel oil when solar-steam is not available. Where brackish water are available for mixing, these costs decline approximately by 30%; 2) The medium size 10,000m3/d plant is of the scale actually required for the town of Eilat. Here the Solar-MED plant would produce distillate at $0.92/m3 and by blending with brackish water available on site, the cost would decline to $0.74/m3; 3) On the other extreme we evaluated a large 100,000m3/d plant, on the scale of a national water supply plant. Here the distillate cost is about $0.69/m3 for hybrid plant (including land cost) at an available site close to the southern end of Israel's Mediterranean shore. These preliminary results suggest a competitive distillate cost as compared to grid-powered RO, when electricity cost is about ¢6.5/kWh. To conclude: Solar-powered desalination is conceivable in Israel at a reasonable cost, and has even broader economic potential along the Red Sea and similar sites.

Anecdotal evidence suggests that defense procurement processes lead to the purchase of weapons of apparently excessive quality. In this paper, we present a model that suggests that this could be the result of the timing and informational structure of procurement decisions.

This paper analyzes the operation of an agricultural multipurpose service cooperative in which family farms are the producer-consumer economic units. The cooperative is aimed at maximizing the utility of its member-patrons. The cooperative provides services and sets prices, taxes, and usage restrictions in conformity with the individual's decision making rules. The cooperative can establish a mode of operation that will induce the individual members to behave in a manner compatible with the requirements for Pareto optimality. The economic stability of the cooperative cannot be guaranteed.

Agricultural production involves a large number of random variables, many of which are physical and biological functions connected with the production process. The knowledge of the biological response function of crop yield to soil salinity is essential in decision-making regarding irrigation with saline water. In this paper we investigate (analytically and empirically) the expected profitability to farmers (the decision makers) of acquiring additional information on this biological function. The true values of the parameters of the response function are usually unknown to the decision maker, and therefore he uses the estimates of the parameters and may become a victim of a suboptimal solution. The deviation from the optimum may be measured by a loss function and the calculation of its expectation. The estimates of the parameters (which are arguments in the loss function) are based on a priori information available to the decision maker. He can acquire additional information that will reduce the variances of these estimates and, hence, will improve his ability to choose a suitable strategy with resulting decrease of the expected loss (or, equivalently, increase of the expected profit). Expected value of sample information (EVSI) is defined as the difference between the reduction of the expected value of the loss function due to the additional information and the cost of its acquisition. The optimal number of observations to be acquired is the one that maximizes EVSI.

Stochastic optimization of inputs in a spatially variable natural resource is studied, with special emphasis placed on the problem faced by a risk-averse decision maker (DM): how to use, in the best possible way, the given body of information, which is embodied in one realization of the relevant measurements. Two approaches, unconditional and conditional, are investigated and compared. The unconditional and the conditional stochastic optimization problems are defined and an illustrative numerical example is given. The principal conclusion drawn is that the conditional analysis has the potential to increase the DM's welfare substantially, as compared with the unconditional one.