Please check this link for a ...
Published by Anthony Reid Harvey
Please check this link for a Technology of River Water Treatment, on the supposition that the issue is one of pathogen contamination: https://drive.google.com/file/d/0B3E-qEW1tsGmM2pXcmlLMVFoNXJacktzYm9qbDhMdmpSX0Y4/view?usp=sharing
Please note that this approach to treatment is simply by gravity on the presumption that the plant to which you refer would require electricity and chemicals.