Possibility of reuse the sewage dischage water

I am a　marine engine engineer who lives in the island and investigating how to reduce the　GHG from ship.
I hope to join your group specially. Because, I understand that the drinking water and　discharge　water　are the most important material at our island　in　future.
In addition, my friend is supporting desertification in some region in Spain.
The drinking water is pumped from the mainland to our island through a long water pipe　line.
Therefore we don’t need to distill from seawater　at　this　stage.
However, we need to keep the green island as it is now.

Under such circumstances, I feel followings.

1. It is seemed　that　ｔhe sewage　treatment system of my home is　good　for　sea　condition.
To keep the good environment　condition, this discharge water is inspected and managed　twice　a　
year.

2.　On the other hand ,I　found that the grass in this open　ditch　for　discharge water is growthvery
fast.
I assume that these phenomenon are caused by a lot of nitrogen and phosphorus elements for the
plant　compared　with　the　rain　and/or　fresh　water　which　we　use　normally.

3. Hard (metal) 　materials might be included in this discharge water.
Therefore, I think it is necessary to clear this point, if I use this discharge water for vegetable plant.

4. If subject　discharge water　is　possible　to　reuse　for the　fuel　grass　plant　and/or　grass　plant　
on　the desertification region、water　circulation　is　more　comfortable.
　　 By application　of　the　sewage　treatment　system　、big　or　small　it　is　not　a　matter、I think　　 we　can　change　our　direction.

Hopefully、I think that sewage　discharge water and　their　effective　material　element　 are automatically possible　to　pump　up　to　the　area　to　be　required　even　if　it　is　faraway area.

I afraid if you can　understand　because　of　my　poor　explanation.
It would be greatly appreciated if the comment of everybody could be gotten.