Very small hydro power - using pump?

Hello. I am trying to extract birch sap from trees on my property, with the intention to make birch syrup. I have bought a reverse osmosis (RO) system to concentrate the sap to save boiling time. The RO system comes with a pump to push the sap through the filters. The pump is electric. I was originally thinking to power the pump directly, that is mechanically without electricity, connecting the shaft of the pump to a small turbine wheel, possibly with some gearing in between. But I was told that it may not be a good idea to open ut the pump in question to access the shaft, because of thermal protection, so it would be easier to use the turbine to make the electricity needed. There is a small creek running through the property where the birches are. I wish to do the concentrating there without having to transport all the sap down to my house. There is no electricity in the birch forest. I have been looking online for various combinations of turbine wheels (pelton), generators, shafts and so on. But I have been thinking that maybe the easiest would be if I could use an electric pump and run it in reverse as a generator (running water through it), so that it produces electricity instead of consuming it. The pump for the RO system runs on 24 volts and I think it is 150 W. My terrain is steep and the head of a hydro power system could be anywhere from 1 to 100 meters. The water flow is not huge, it varies a lot and may for example be 5 - 10 liters per second.
Would anyone here have any advice?

But - I just now saw that the pump runs on DC. And a turbine would make AC, and I would need and inverter. Maybe the easiest would be to carry up a few car batteries? Or check if the pump could be disassembled and be connected directly to a turbine wheel after all. I have not received said pump yet. Anyway, if any of you had suggestions, I would be grateful.

If the pump is an ac motor some lack a  field excitation so it won't create electricity.

This is the sort of thing you want
12/24V 1000W pelton wheel
Manufacturer I think
Manufacturer

Hi Oystein;
Having lived with hydro power over 30 years. Here are a few bits of info.  
First, is that quite a few put out DC voltage. So if you look around you can find one.
Second is it is not cheap setting up a hydro.
A running alternator must ALWAYS stay connected to a battery with a load on it. This is called a diversion load.
Disconnect an alternator while running and it will spike voltage and burn itself out in short order.
Leave it running into a small battery with no load against it and it will boil the water out of your battery.

If fact hydro, really is probably the most expensive way to make power.

For your Idea, I  believe I would choose  Solar.   One battery and one decent size panel should do the job.
If your area is really low on sunlight use two panels or two battery's.  One goes home each night to sit on a trickle charger.
Solar panels can overcharge a battery without a charge control. But they can be disconnected in full sunlight with no ill effects.