The purpose of a septic tank is to allow solid waste to be broken down in an anaerobic environment and to buffer the amount of liquid being released into the leach system. In the leach system (field, trenches, chambers, sand filter, engineered wetland, etc) additional microbial action digests the remainder of organic waste and converts ammonium into nitrates. Dumping wastewater, including kitchen waste, directly on the ground is a horrible idea.
Before deciding on what type of system to install there are a lot of things to consider. Cost, availability of equipmentand materials and laborers, soil quality, water table depth and proximity to surface water and wells. If septic tanks are uncommon in the area, can you obtain one? You can build one, but there is no point unless its water tight. Can you hire or obtain heavy equipment, i.e. a backhoe? Can you get enough gravel for a common leach field?
A cheap and non-labor intensive option is a pit privy (i.e. outhouse) but I would still recommend a micro septic system for kitchen waste. If you want I can post a link to plans for an engineer approved pit privy design.
