Answer:
Wastewater treatment
Explanation:
The major aim of wastewater treatment is to remove as much of the suspended solids as possible before the remaining water, called effluent, is discharged back to the environment. As solid material decays, it uses up oxygen, which is needed by the plants and animals living in the water. 
 
        
             
        
        
        
Answer:
I am not entirely sure about this one. But I believe that the "Emancipation Manifesto" signed by Czar Alexander II gave serfs land, or at least gave them the freedom to do what they wanted, like buying that said land.
No freedom of religion, or elections was yet to be had in Russia.
Explanation:
 
        
             
        
        
        
In recent years, Russia has advanced its military capabilities in the Arctic, reopening old military bases that had been abandoned following the collapse of the Soviet Union in 1991, and bolstering the Russian Navy's prestigious Northern Fleet that oversees operations and defense in the region.
        
             
        
        
        
<h2>
The End of Trans-Saharan Trade Routes:</h2>
Explanation:
The factors that led to the end of trans-Saharan trade routes are:
- Civil unrest due to collapse of the Songhay Empire, the Timbuktu, by the Morracans in 1591
 - The extreme desert conditions like extreme climates, excessive heat, lack of water and food etc made the travel logistics very tough. This made people opt for other transport systems
 - Huge advancements made in maritime travel  
 - Exploration of West African trade routes
 - Economic, political and social changes which led to the end of trans-Saharan trade routes