I'm with Claudio. Biological ...

I'm with Claudio. Biological treatment is probably the way to go, according to Your waste "strength" and composition. Nowadays we are designing anaerobic systems to improve the treatability of some industrial wastes by means of combined anaerobic-aerobic sequential steps.

For small decentralised and isolated areas, said systems could be easily implemented with low investment and no operation costs. Hereto attached - just for Your reference - the idea. It's about a biological filter derived from old-fashioned septic tanks and ABRs, modified for industrial purposes. System becomes way simpler for civil wastewater.
HTH

Tiziano