Nitrates removal technology for bore well water

In my project area, we use bore wells as a water source, but recently the water is contaminated by nitrates.

Could you please let me know which low-cost technology can be used to removes nitrates in borehole water in rural areas of a developing country? 

Conventional processes for nitrate removal - ion exchange, reverse osmosis and electro dialysis - are quite expensive and pose a question of subsequent disposal of generated nitrate waste brine. 

By the Zambian Drinking Water Standard (ZDWS), recommended nitrate levels are 10 mg/l NO3-N equaling 44.3 mg/l NO3. 
We would like to reach these levels so any advice is helpful.

A picture of one of our bore wells is attached.