Wastewater streams include separation process wastewater, tank bottoms, cooling tower condensate blowdown, source water treatment, and storm water. American Petroleum Institute (API) separators are commonplace in most refineries and separate sludge and hydrocarbon components out of process wastewater. Refineries today have installed dike systems to keep process wastewater from draining into storm sewers.
1.7.4 Illustrative Example 4
Refer to Table 1.5 and calculate the desalination mass capture efficiency of salt in seawater to convert typical seawater to potable water. Assume a basis of 100 g of seawater.
Table 1.5 Seawater and potable water major components.
| H2O, wt% | Salt, wt% | |
|---|---|---|
| Seawater | 96.5 | 3.5 |
| Potable water | ≥99.95 | ≤0.05 |
Solution. For 100 g of seawater,
Salt in seawater = 3.5 g
Salt in potable water = 0.05 g
The required salt capture efficiency, SCE, is therefore:
1.7.5 Illustrative Example 5
Mekonnen and Hoekstra (2011) provide a summary of national water footprints of production and consumption for countries around the world. They provide a guideline for the determination of the representative water footprint of various commodities that may be both produced within a country as well as imported for consumption from elsewhere around the globe. An example that is provided determines the average water footprint for tomatoes consumed in Germany. Using the data presented in Table 1.6, determine what the water footprint for tomato consumption in Germany is assuming the total quantity imported is consumed, using a weighted average of each water footprint for tomatoes imported from other countries.
Solution. Using a weighted average of the water footprint and Germany’s import levels from the countries listed in Table 1.6 yields the following results using Equation 1.1 for the calculations.
where Tomato Consumption = annual T of tomatoes produced or imported and consumed from each country, i; Water Footprint = m3 water/T tomatoes produced from each country, i; and n = total number of countries, including itself, from which Germany imports tomatoes. Substituting values from Table 1.6 into Equation 1.1 yields:
Table 1.6 Water footprint and quantities of German tomato consumption as a function of place of origin.
| Place of origin | Quantity imported or consumed, T/yr | Water footprint, m3/T |
|---|---|---|
| Germany | 47,000 | 36 |
| The Netherlands | 252,000 | 10 |
| Spain | 244,000 | 83 |
| Italy | 72,000 | 109 |
| France | 52,000 | 110 |
| Total | 667,000 |
1.8 Problems
1 In terms of the question “how much water is there?” explain why only approximately 0.3% of the entire water on the Earth is considered usable fresh water.
2 With so much water on the planet explain why there is a water availability and water supply crisis.
3 List and briefly describe the four major aquatic habitats in the United States and indicate concerns regarding contamination of these resources.
4 SIWI (2005) and Hares (2017) have made strong cases for the economic benefit of water infrastructure investments around the world. In the United States, the US Water Alliance (2017) outlined the way forward for ensuring all people have access to clean, affordable water, and all benefits from water infrastructure investments to make water supplies more reliable and resilient in the face of climate change pressures. Review the US Water Alliance (2017) national briefing paper on water equity and summarize the “Three Pillars” of water equity put forth in this document.
5 A comparison of global drinking water supply and sanitation services provided by WHO (2017) suggests that in 2015, North America had some of the highest rates of improved water supplies (96%) and basic sanitation (97%) and safely managed improved sanitation facilities (78%) in the world. The statistics for the United States are even higher at 99% of the population using improved water supplies, while 89% were using improved sanitation facilities. For those in the United States either not having access to improved water supplies or improved sanitation